Progress 10/01/15 to 09/30/16
Outputs
Progress Report Objectives (from AD-416): Objective 1: Characterize the influence of zinc and iron concentrations in edible crop tissues and crop species on the bioavailability of crop cadmium to animals (C1; PS 1.F). Objective 2: Characterize the potential transfer of soil lead, arsenic, and other trace elements by vegetable crops grown on element enriched urban and orchard soils and develop methods to prevent this transfer. (C1; PS 1.F). Objective 3: Characterize genetic resources and inheritance of grain Cd to reduce cadmium in durum wheat, flax and soybean. (C1; PS 1.F). Objective 4: Evaluate information about the risk from Cd in foods to support public decisions for foods of both plant and animal origin. (C1; PS 1.F). The ultimate goals of this Project Plan are to improve the science about risk of heavy metals in soils and crops in order to obtain improved regulatory limits for Cd in crops under Codex, and the information needed to provide improved advice about the risk of Pb in urban garden soils and crops. Essentially all human Cd disease from soil Cd has resulted from paddy rice grown on fields contaminated by mining or smelter emissions. Garden vegetables and other grains have not been found to induce Cd disease in highly exposed populations who grow crops on highly Cd+Zn contaminated soils. Some Europeans want to set crop Cd limits based on �attainable� levels rather than on the basis of potential risk to consumers. Such non-risk based standards will harm U.S. growers of durum wheat, sunflower kernels, flax, soybean, and some other crops. If crops must contain lower levels of Cd to win importation by other nations, both soil treatments, selection of soil series which produce lower Cd crops, and improved cultivars which accumulate lower amounts of Cd will contribute to growers needs. Providing a clear technical basis for the bioavailability of Cd in different crops appears to be the central issue which could change the demand for lower limits for crop Cd, and protect growers from unnecessary costs to produce lower Cd crops which may have no benefit. Only animal feeding tests can provide valid information about the bioavailability of crop Cd to animals, and the concentrations fed must represent levels in foods rather than toxic levels fed in most previous research. Because Zn is usually greatly increased in crops (except rice) when Cd is increased, the presence of Zn may substantially reduce the bioavailability of crop Cd, alleviating presumed risk of crop Cd. Because commercial carrots were found with higher than normal Pb concentrations when grown on historic orchard soils, U.S.-FDA requested that ARS examine the basis for carrot Pb accumulation and to learn if agricultural amendments can reduce carrot Pb when they are grown on high Pb soils. Certain root crops have xylem elements growing through the edible storage root, so if Pb is trapped within the xylem during normal growth of the crop, it will be in the edible root. But such Pb might have much lower bioavailability than the Pb-acetate used to establish diet Pb risk; 2-10% of food Pb is absorbed, while 60-80% of soluble Pb in water is absorbed by human volunteers. Approach (from AD-416): Characterize the influence of zinc and iron concentrations in edible crop tissues and crop species on the bioavailability of crop cadmium to animals. Zinc incorporated in lettuce reduces weanling rat absorption of lettuce Cd. Using controlled chelator-buffered nutrient solutions (similar to Kukier and Chaney, 2002), Romaine lettuce will be grown to contain basal and sub-phytotoxic concentrations of foliar Zn (25 and 450 mg kg-1 DW), and the Codex Cd limit (4 mg Cd kg-1 DW); the high Zn represents maximum Zn levels normally present if lettuce is grown in acidic soils with geogenic Cd+Zn contamination at the beginning of yield reduction due to Zn phytotoxicity. Fe concentration in lettuce is tightly controlled genetically, but lettuce can supply higher bioavailable Fe than the marginal AIN diet, and thus plant Fe can reduce Cd bioavailability. The lettuce will be fed to weanling rats following the protocol of Reeves and Chaney (2004) in which American Institute of Nutrition (AIN) purified diets with marginal or adequate Fe-Zn-Ca were fed. The basal and high Zn lettuce will be mixed with both the marginal and adequate diets and fed for 28 days without radioisotope labeling used previously. At autopsy, the liver, kidney and duodenum will be removed for analysis. Tissues and blood will be tested to establish Fe status of the test animals. The tissues will be digested in HNO3, and Cd, Zn and Fe levels measured by ICP-Atomic Emission Spectrometry or ICP-Mass Spectrometry. Eight replicate rats will be fed each diet to accommodate the natural variation in such feeding tests (Reeves and Chaney, 2001). If the lettuce experiment shows a strong effect of crop Zn on crop Cd bioavailability, other crops may be studied using a similar approach (durum wheat; soybean). Effect of plant species and Zn co-contamination on bioavailability of Cd in leafy vegetables: After a successful preliminary feed acceptance test to determine if weanling pigs would consume diets containing lettuce and spinach at 20% of the diet weight, a complete feeding test was completed. Treatments included Control pig feed (about 0.05 mg Cd/kg), feed with 20% lettuce or with 20% spinach with added Cd and Zn to supply 0.8 mg Cd/kg diet or with 0.8 mg Cd and 80 mg Zn/kg diet to test the effect of leafy vegetables and normal Zn in high Cd crops on bioavailability of ingested Cd. Tissues are in the process of preparation for analysis of Cd and other important elements. Nutritional composition of Brassica microgreens: Brassica vegetables (such as broccoli, cabbage, and radish) are valued for containing significant amounts of cancer-fighting glucosinolates. ARS scientists in Beltsville, Maryland, analyzed 30 of the most common commercial varieties of Brassica microgreens for nutrients and metals composition. The results showed that microgreens are good sources of both macroelements (calcium, phosphorus and potassium) and microelements (iron and zinc). Heavy metals such as cadmium and lead were below detection limits of the instrument. Consumption of microgreens could be a health-promoting strategy to meet dietary reference intake requirements for essential elements beneficial to human health. This information can be used by commercial growers, health professional and consumers. Methods to reduce Cd accumulation by crops from Cd-mineralized soils of California: Field tests of Zn fertilizer to reduce Cd accumulation by spinach in 2013 to 2014 were inadequately effective due to minimal mixing of Zn sulfate fertilizer into soils, and failure to include limestone shown to be needed based on earlier greenhouse testing. Field tests in 2015 attempted to incorporate the Zn more thoroughly and were more effective but still limited by inadequate incorporation of applied Zn into rooting zone of spinach and lettuce and lack of limestone application. A greenhouse pot test with Lockwood soil was conducted to compare the effectiveness of Zn without and with limestone, biosolids compost, or Zn or Mn fertilizer. Spinach on the control and Mn fertilizer treatments had extremely high (>50 mg/kg DW) Cd levels, while single treatments of Zn, limestone or biosolids compost substantially reduced spinach Cd. Combining limestone treatment with Zn or biosolids compost or both of these allowed production of spinach within the CODEX limit of 4 mg/kg DW. In this pot study, roots were restricted to the amended soils and it is not certain if thorough incorporation of the combined amendments within the usual tillage depth will be adequate, or whether deeper incorporation of the amendment combinations is required to achieve lower Cd in spinach on these soils. Additional cropping with another spinach cultivar and a commercial Romaine lettuce have been conducted to further characterize the ability of these combined amendments to achieve production of leafy vegetables meeting market Cd limits but await analysis. Effect of Zn and Mn supply on uptake and translocation of Cd by spinach and rice: Interactions between Cd and other elements in food crops are complex. As noted last year, it was shown that Cd was absorbed into roots on a Mn transporter rather than a Zn transporter believed to transport Cd in all other plant species. Because levels of Cd in rice and spinach are important food safety issues around the globe, working with visiting scientist Dr. Meie Wang, we tested the interactions between Zn and Mn with Cd uptake using chelator buffered nutrient solutions. Initially we tested chelators which could be used to supply controlled Cd with adequate or even excessive Zn and Mn to both crops. Only use of the chelator ethyleneglycol-diamine-tetra acetate (EGTA) supplied adequate and high levels of Zn or Mn while providing constant low Cd uptake from nutrient solutions while suppling adequate Fe for both species. As expected, increasing Mn supply strongly inhibited both uptake and translocation to shoots of Cd by rice, while Zn strongly reduced root Cd concentration while having little effect on shoot Cd. For spinach, increasing Mn had no effect on tissue Cd, but increasing Zn reduced root Zn and first increased and then at higher levels strongly reduced Cd levels in spinach leaves. Lastly, tests are being conducted of the effect of deficient supply of Zn to spinach and deficient supply of Mn to rice on the rate of Cd uptake and translocation to shoots. If low soil Zn promotes upregulation of Zn transporters, it might also increase Cd uptake, helping to explain the very strong effect of added Zn on Cd uptake by spinach. And similarly for rice, upregulation of the Mn transporter may occur in aerobic soils after drainage of irrigation waters and oxidation of manganous formed during flooded growth, thereby promoting Cd accumulation during grain filling. Improved method for inexpensive analysis of inorganic arsenic in rice grain: Because CODEX has established limits on inorganic As in rice for international trade, and US-FDA has proposed limiting inorganic As in infant cereals to 100 ug/kg, improved methods to measure inorganic As are needed. FDA has used a method which requires ion chromatography separation of the chemical forms of As in rice, followed by analysis using inductively coupled plasma-mass spectrometry. Analysis of one rice sample costs between $150-250. However, only the inorganic As comprises significant potential for risk and thus requires measurement to meet all considered regulations. A new simple and rapid method was evaluated which used Hydride Generation to measure the inorganic As and much less expensive analytical instruments and staff. Some rice contains high levels of dimethylarsinic acid (DMA), an organic form of As, which is much less potentially toxic and which is not regulated. So As analysis methods were modified to prevent DMA contribution to measurement of inorganic As by variation of the pH of the solution used in Hydride Generation to measure inorganic As in rice. The modification was very successful and can be conducted at far lower cost and even with lower variability because of the simplicity of the method. An inter-laboratory evaluation of the method was initiated with 15 national and international laboratories which commonly measure rice As. Effect of irrigation and genotype on rice accumulation of As: In cooperation with scientists at the ARS National Rice Research Center in Stuttgart, AR, we evaluated the genetic variation of rice to flood vs. aerobic irrigation management, and historic As contamination of soil. Newly developed inorganic As analysis methods developed this FY were used to analyze over 1200 samples. Soil enrichment with As had little effect on grain inorganic As, but aerobic irrigation management substantially reduced inorganic As in all genotypes. Significant genetic variation was found, but this variation was much smaller than the effect of irrigation management. Separate cooperative studies of the effect of irrigation management on rice accumulation of As and Cd, and emission of greenhouse gases, were completed and reported. Although previous studies with more aerobic treatments caused significantly reduced rice grain yields, the results of this test achieved full yield of flood irrigation while strongly reducing grain inorganic As and simultaneously alleviating nearly all greenhouse gas emissions of rice production. Synthesis of literature on risks from As and Cd in rice and other foods: During the FY, ARS scientists in Beltsville, Maryland were asked to review the U.S. Food and Drug Administration draft Risk Assessment for inorganic As in rice and rice products, and a proposed rule on inorganic As in infant cereals. Documents required extensive review and comment preparation and advising USDA management. The important role of irrigation management in rice grain accumulation of inorganic As was a critical part of the risk assessment, as was genetic variation. In locations where inorganic As has caused adverse health effects to farm families, both irrigation of rice with As rich well waters, and cooking with contaminated water contributed to human exposure. Cooking can be a more significant source of inorganic As exposure than the rice being cooked using traditional Asian methods. This could have caused higher As exposure than used in toxicologists� risk assessments, which are the basis for limiting dietary inorganic As. Although more aerobic irrigation management can produce rice with much lower grain inorganic As levels, such irrigation is difficult to manage on leveled fields. Fortunately, growers have shown they can produce all the low inorganic As rice needed for manufacture of US infant rice cereals to meet the FDA guidance using Alternate Wetting and Drying irrigation management to maintain a more aerobic soil environment. Accomplishments 01 Simple, inexpensive method to measure inorganic arsenic in rice was developed. Because the FDA-developed method to measure inorganic arsenic in rice costs about $200 per sample, and because CODEX and US- FDA have set limits for inorganic arsenic in rice, simpler and much less costly methods for analysis are needed. A validated method was developed and shown to obtain correct results with diverse rice types and samples, and costs less than 20% of the FDA method. Method availability benefits both rice growers, the rice industry, infant cereal manufacturers and consumers. 02 Alternative rice production methods needed to reduce grain inorganic As were demonstrated. Excessive inorganic arsenic in rice grain will limit marketing of rice. ARS researchers in Beltsville, Maryland, in cooperation with rice agronomists in Arizona and California, tested more aerobic �Alternate Wetting and Drying� irrigation management methods. During the fiscal year, a method was demonstrated to strongly reduce grain inorganic As and maintain high yield of flood grown rice. Such methods will benefit rice growers, consumers, and the environment including climate change because more aerobic management reduces greenhouse gas production in addition to lowering grain arsenic. 03 Methods to reduce cadmium in spinach from Salinas Valley were demonstrated. National and international limits on cadmium in leafy vegetables limit marketing of spinach and romaine lettuce if cadmium exceeds 0.20 ug/g fresh weight. Soil series developed from marine shale in Salinas Valley have caused spinach cadmium to greatly exceed the standard; US-FDA required a recall of high cadmium spinach. ARS researchers in Beltsville, Maryland, confirmed that several combinations of soil amendments, if well mixed with topsoil, strongly reduced cadmium levels in spinach; both Zn fertilizer + limestone, and biosolids compost + limestone, or Zn fertilizer + biosolids compost + limestone reduced spinach Cd from over 2.5 to below 0.2 ug Cd/g fresh weight. Method tested in the field was less successful because of poor mixing with topsoil by growers. Both growers, marketers and consumers will benefit from production of leafy vegetables with meet CODEX cadmium limits. 04 More complete understanding of cadmium accumulation by rice and spinach will help in development of production methods to reduce crop cadmium. Marketing of rice and spinach with cadmium in excess of limits is prohibited by CODEX and US limits. Fuller understanding of element competitions with cadmium accumulation by these crops would help in development of management methods to meet limits. Methods to grow both rice and spinach using chelator-buffered nutrient solutions were developed to attain plant Mn and Zn levels (chemical activities similar to soil solution) from deficient to phytotoxic while providing controlled cadmium and adequate iron. Growing rice with varied Zn had no effect on leaf Cd but did reduce root Cd, while increasing Mn increasingly reduced leaf Cd in rice shoots. And while growing spinach with increasing Zn activity strongly reduced Cd in leaves, increasing Mn had little effect on spinach uptake or translocation of Cd. Results will assist in developing production methods or genetic improvement to limit cadmium in these crops. Both growers and consumers will benefit from limiting cadmium in diets. 05 Brassica microgreen vegetables are increasingly popular, but their composition had not been reported. Brassica microgreens were grown under controlled conditions and were analyzed for macro and micro elements and toxic elements. The greens were rich sources of macro and micro nutrients, and contained very low levels of cadmium and lead. Both growers and consumers will benefit from nutritionally valuable leafy vegetables.
Impacts
(N/A)
Publications
- Xiao, Z., Codling, E.E., Luo, Y., Nou, X., Lester, G.E., Wang, Q. 2016. Microgreens of brassicaceae: mineral composition and content of 30 varieties. Journal of Food Composition and Analysis. 49:87-93.
- Codling, E.E., Chaney, R.L., Green, C.E. 2016. Accumulation of lead and arsenic by potato grown on lead-arsenate contaminated orchard soils. Communications in Soil Science and Plant Analysis. 47:799-807. doi.org/10. 1080/00103624.2016.1146754.
- Brown, S.L., Chaney, R.L., Hettiarachchi, G. 2016. Lead in urban soils - A real or perceived concern for urban agriculture. Journal of Environmental Quality. 45:26-36. doi:10.2134/JEQ2015.07.0376.
- Chaney, R.L., Kim, W., Kunhikrishnan, A., Yang, Y.E., Ok, Y.S. 2016. Integrated management strategies for Arsenic and Cadmium in rice paddy environments. Geoderma. 270: 1-2.
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Progress 10/01/14 to 09/30/15
Outputs
Progress Report Objectives (from AD-416): Objective 1: Characterize the influence of zinc and iron concentrations in edible crop tissues and crop species on the bioavailability of crop cadmium to animals (C1; PS 1.F). Objective 2: Characterize the potential transfer of soil lead, arsenic, and other trace elements by vegetable crops grown on element enriched urban and orchard soils and develop methods to prevent this transfer. (C1; PS 1.F). Objective 3: Characterize genetic resources and inheritance of grain Cd to reduce cadmium in durum wheat, flax and soybean. (C1; PS 1.F). Objective 4: Evaluate information about the risk from Cd in foods to support public decisions for foods of both plant and animal origin. (C1; PS 1.F). The ultimate goals of this Project Plan are to improve the science about risk of heavy metals in soils and crops in order to obtain improved regulatory limits for Cd in crops under Codex, and the information needed to provide improved advice about the risk of Pb in urban garden soils and crops. Essentially all human Cd disease from soil Cd has resulted from paddy rice grown on fields contaminated by mining or smelter emissions. Garden vegetables and other grains have not been found to induce Cd disease in highly exposed populations who grow crops on highly Cd+Zn contaminated soils. Some Europeans want to set crop Cd limits based on �attainable� levels rather than on the basis of potential risk to consumers. Such non-risk based standards will harm U.S. growers of durum wheat, sunflower kernels, flax, soybean, and some other crops. If crops must contain lower levels of Cd to win importation by other nations, both soil treatments, selection of soil series which produce lower Cd crops, and improved cultivars which accumulate lower amounts of Cd will contribute to growers needs. Providing a clear technical basis for the bioavailability of Cd in different crops appears to be the central issue which could change the demand for lower limits for crop Cd, and protect growers from unnecessary costs to produce lower Cd crops which may have no benefit. Only animal feeding tests can provide valid information about the bioavailability of crop Cd to animals, and the concentrations fed must represent levels in foods rather than toxic levels fed in most previous research. Because Zn is usually greatly increased in crops (except rice) when Cd is increased, the presence of Zn may substantially reduce the bioavailability of crop Cd, alleviating presumed risk of crop Cd. Because commercial carrots were found with higher than normal Pb concentrations when grown on historic orchard soils, U.S.-FDA requested that ARS examine the basis for carrot Pb accumulation and to learn if agricultural amendments can reduce carrot Pb when they are grown on high Pb soils. Certain root crops have xylem elements growing through the edible storage root, so if Pb is trapped within the xylem during normal growth of the crop, it will be in the edible root. But such Pb might have much lower bioavailability than the Pb-acetate used to establish diet Pb risk; 2-10% of food Pb is absorbed, while 60-80% of soluble Pb in water is absorbed by human volunteers. Approach (from AD-416): Characterize the influence of zinc and iron concentrations in edible crop tissues and crop species on the bioavailability of crop cadmium to animals. Zinc incorporated in lettuce reduces weanling rat absorption of lettuce Cd. Using controlled chelator-buffered nutrient solutions (similar to Kukier and Chaney, 2002), Romaine lettuce will be grown to contain basal and sub-phytotoxic concentrations of foliar Zn (25 and 450 mg kg-1 DW), and the Codex Cd limit (4 mg Cd kg-1 DW); the high Zn represents maximum Zn levels normally present if lettuce is grown in acidic soils with geogenic Cd+Zn contamination at the beginning of yield reduction due to Zn phytotoxicity. Fe concentration in lettuce is tightly controlled genetically, but lettuce can supply higher bioavailable Fe than the marginal AIN diet, and thus plant Fe can reduce Cd bioavailability. The lettuce will be fed to weanling rats following the protocol of Reeves and Chaney (2004) in which American Institute of Nutrition (AIN) purified diets with marginal or adequate Fe-Zn-Ca were fed. The basal and high Zn lettuce will be mixed with both the marginal and adequate diets and fed for 28 days without radioisotope labeling used previously. At autopsy, the liver, kidney and duodenum will be removed for analysis. Tissues and blood will be tested to establish Fe status of the test animals. The tissues will be digested in HNO3, and Cd, Zn and Fe levels measured by ICP-Atomic Emission Spectrometry or ICP-Mass Spectrometry. Eight replicate rats will be fed each diet to accommodate the natural variation in such feeding tests (Reeves and Chaney, 2001). If the lettuce experiment shows a strong effect of crop Zn on crop Cd bioavailability, other crops may be studied using a similar approach (durum wheat; soybean). Role of leafy vegetable species and Zn level on bioavailability of crop Cd to weanling pigs: High levels of cadmium in crops threatens marketing of some U.S. crops. Present Cd limits in crops have ignored the bioavailability of Cd in different crops and the possible inhibition of Cd bioavailability by Zn present in the crop. Methods to use Zn fertilizer plus limestone to limit maximum levels of Cd in spinach grown on Cd-mineralized soils in California were identified but markets are still threatened because the low bioavailability of Cd from spinach, and the ability of crop Zn to inhibit crop Cd risk are ignored by some food scientists. In order to clarify these issues, a pig feeding study was designed with CODEX maximum Cd levels along with basal Zn or Zn at 100- fold the Cd level. Extensive work was conducted to develop feed mixtures for pigs which contain appropriate nutrients and added lettuce or spinach, and with added Cd and Zn salts such that the Cd and Zn were evenly mixed throughout the feed batch. After testing many published methods to obtain even mixtures of metal salts into feeds, we found that mixing the metal salts with enriched wheat flour, and then mixing that with lettuce or spinach yielded the desired Cd and Zn levels with small variance. We then mixed these crops plus Cd and Zn �pre-mixes� at 20% of the feed with the weanling pig feeds ordinarily used at BARC. A test feeding of the mixtures to pigs showed that they will voluntarily consume diets including lettuce and spinach. Over 1500 pounds of the vegetables were washed, dried and ground to a fine powder to prepare feeds for the planned test. We await the pigs for the approved feeding test. The role of irrigation management in rice accumulation of Cd and As: Excessive As or Cd in rice interferes with international marketing of rice and U.S./FDA is considering national limits on inorganic As (iAs) in rice. A previous study analyzed rice grain from a field experiment in Arkansas in which irrigation management was varied. These tests used Alternative Wetting and Drying (AWD) compared with flood irrigation; because the soil is less anaerobic, AWD produced rice with substantially lower grain levels of inorganic As, but also increased grain Cd. At the same time greenhouse gas evolution was substantially reduced by AWD, and water use efficiency was significantly improved. For the least irrigated treatment, grain As was very low but yield was significantly reduced but the extent of yield reduction was less than in previous tests. Alternate Wetting and Drying is a promising method to significantly reduce inorganic As in rice grain but additional testing is required to identify how to obtain both low iAs and normal yields. In a second field test conducted in California, irrigation was managed to be slightly less dry than previous tests; full grain yields were obtained with strong reduction in grain arsenic and only small increase in grain cadmium indicating that yields can be maintained while reducing arsenic. Reliable rapid methods for analysis of inorganic As (iAs) in rice are needed: Methods developed by the U.S. Food and Drug Administration to measure all species of As in rice gain are slow and very expensive such that iAs analysis limits research progress. Research clarified that the individual species concentrations are not needed for food safety decisions, only the iAs. By diligent searching and testing, we ruled out several published methods for iAs as irreproducible, slow, requiring expensive new equipment, etc. Research by others showed that using a higher concentration of hydrochloric acid in hydride generation of arsine gas could alleviate errors from dimethylarsinic acid (DMA), such that inorganic As can be measured reliably. Valid results were confirmed by measuring the certified levels of inorganic As in multiple rice Standard Reference Materials. This method is less than 10% of the cost of the complex FDA method (which requires very expensive and difficult to maintain HPLC-ICP-MS-MS equipment). Using hydride generation can remarkably lower costs of, and time required for appropriate agronomic research to reduce the concentration of iAs in rice products. Improved understanding of why rice accumulation of Cd is different from wheat and lettuce: Excessive ingestion of Cd in foods can cause human disease so agriculture must develop methods to limit Cd accumulation from both normal and contaminated soils. Since human Cd disease was discovered in a subsistence rice farming community in Japan where their soils were contaminated with Cd and Zn from mining wastes, and human Cd disease has repeatedly been observed at similar locations in several nations, we have worked to understand why these rice farmers were harmed by soil Cd; but other populations have not been harmed by wheat or vegetables grown on soils contaminated by mine or smelter wastes even at higher contamination soil levels than the locations where rice caused disease. Recent Japanese research showed that Cd was absorbed by rice on a Mn transporter, not the Zn transporter found to transport Cd in wheat and vegetables. In rice, high Mn in soil solution of flooded soils inhibits Cd uptake, but Zn does not. Using chelator-buffered nutrient solution we showed that Cd uptake by rice from Cd concentrations relevant to soil solutions was not inhibited by Zn, while a separate study showed that increased Mn clearly reduced Cd uptake to grain. This improved understanding will help scientists understand how the normal high Zn which accompanies Cd in nearly all Cd contaminated soils and crops (except rice) is able to prevent risk to consumers. The protection occurs because of Zn inhibiting Cd uptake and translocation to shoots and grain, and by the Zn reaching the shoots and grain inhibiting absorption of Cd by animals consuming the crops. These findings now integrate an understanding of why rice but not other crops have caused human Cd disease and should reduce concern about Cd risk form other crops. Excessive Cd accumulation in spinach grown on Cd-mineralized CA soils limit crop sales. Certain soils developed from marine shale rocks in CA contain high levels of Cd with little Zn enrichment compared to normal U. S. soils. These soils cause high accumulation of Cd in spinach and lettuce and threaten markets for crops grown on these soils. Cooperative field tests in CA fields tested Zn fertilizer or Zn fertilizer plus limestone (which had been shown in greenhouse pot studies to alleviate high Cd accumulation by romaine lettuce). Analysis of soils and plants indicated that inadequate mixing of Zn fertilizer limited inhibition of Cd uptake, while the combination of Zn and limestone and better mixing was able to reduce Cd uptake into spinach. Cd in these soils is throughout the soil profile rather than only in the tillage depth and it is not yet clear whether deeper incorporation of Zn fertilizer is required to achieve the effectiveness found in pot studies. Effect of irrigation on rice accumulation of As from contaminated orchard soil: Previous research has demonstrated that total arsenic concentration was lower in rice grown on non-flooded lead-arsenate contaminated soil compared to flooded soil. A greenhouse experiment was conducted in Beltsville, MD in which rice was grown on three lead-arsenate contaminated soils amended with vegetable compost under flooded and non- flooded conditions. Total arsenic concentration was lower under the non- flooded condition. Composted manure incorporation in the orchard soil caused increased rice yield but did not significantly influence the total and inorganic arsenic concentrations in the rice. Effect of phosphate or compost on plant uptake of Pb from orchard soils: Previous research has shown that phosphorus was effective in reducing Pb plant availability in old orchard soils contaminated with lead-arsenate pesticide but increased arsenic concentrations in soil solutions and even induced arsenic phytotoxicity. Uptake of lead and As by three plant species, Black Nightshade (Solanum dulcamara), Sorrel (Hibiscus sabdifere) , and Callaloo (Amaranthus cruentus) were grown in lead-arsenate contaminated soils amended with superphosphate. Plants were harvested, analyzed, and data are being analyzed for manuscript preparation. Accomplishments 01 Accumulation of lead and arsenic by carrots grown on lead-arsenate soils evaluated. Lead-arsenate was used as a pesticide in apple orchards from the 1900's to 1960's. Residual lead and arsenic remain in these soils. Some of these lands are being converted to vegetable crop production. Because of food safety concerns about lead in carrots, the Food and Drug Administration (FDA) asked the USDA-ARS to investigate the nature of the lead. A greenhouse experiment was conducted in which three cultivars of carrots were grown on four lead-arsenate contaminated soils to determine lead and arsenic uptake. Lead was significantly higher in the peeled carrots compared to the peel, while arsenic was highest in the carrot peel compared to the peeled carrot. These findings will provide valuable information to the FDA and farmers on the safety of alternative use of old orchard soils.
Impacts
(N/A)
Publications
- Codling, E.E., Chaney, R.L., Green, C.E. 2015. Accumulation of lead and arsenic by carrots grown on four lead-arsenate contaminated orchard soils. Journal of Plant Nutrition. 38(4):509-525. DOI: 10.1080/01904167.2014. 934477.
- Chaney, R.L. 2015. How does contamination of rice soils with Cd and Zn cause high incidence of human Cd disease in subsistence rice farmers? Current Pollution Reports. DOI: 10.1007/S40726-015-0002-4.
- Codling, E.E. 2014. Accumulation of lead and arsenic by lettuce grown on lead-arsenate contaminated orchard soils. Open Agriculture Journal. 8:35- 40.
- Linquist, B., Anders, M.A., Adviento-Borbe, M., Chaney, R.L., Nally, L., Da Rosa, E., Van Kessek, C. 2015. Reducing greenhouse gas emissions, water use and grain arsenic levels in rice systems. Global Change Biology. DOI: 10.1111/GCB.12701.
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Progress 10/01/13 to 09/30/14
Outputs
Progress Report Objectives (from AD-416): Objective 1: Characterize the influence of zinc and iron concentrations in edible crop tissues and crop species on the bioavailability of crop cadmium to animals (C1; PS 1.F). Objective 2: Characterize the potential transfer of soil lead, arsenic, and other trace elements by vegetable crops grown on element enriched urban and orchard soils and develop methods to prevent this transfer. (C1; PS 1.F). Objective 3: Characterize genetic resources and inheritance of grain Cd to reduce cadmium in durum wheat, flax and soybean. (C1; PS 1.F). Objective 4: Evaluate information about the risk from Cd in foods to support public decisions for foods of both plant and animal origin. (C1; PS 1.F). The ultimate goals of this Project Plan are to improve the science about risk of heavy metals in soils and crops in order to obtain improved regulatory limits for Cd in crops under Codex, and the information needed to provide improved advice about the risk of Pb in urban garden soils and crops. Essentially all human Cd disease from soil Cd has resulted from paddy rice grown on fields contaminated by mining or smelter emissions. Garden vegetables and other grains have not been found to induce Cd disease in highly exposed populations who grow crops on highly Cd+Zn contaminated soils. Some Europeans want to set crop Cd limits based on �attainable� levels rather than on the basis of potential risk to consumers. Such non-risk based standards will harm U.S. growers of durum wheat, sunflower kernels, flax, soybean, and some other crops. If crops must contain lower levels of Cd to win importation by other nations, both soil treatments, selection of soil series which produce lower Cd crops, and improved cultivars which accumulate lower amounts of Cd will contribute to growers needs. Providing a clear technical basis for the bioavailability of Cd in different crops appears to be the central issue which could change the demand for lower limits for crop Cd, and protect growers from unnecessary costs to produce lower Cd crops which may have no benefit. Only animal feeding tests can provide valid information about the bioavailability of crop Cd to animals, and the concentrations fed must represent levels in foods rather than toxic levels fed in most previous research. Because Zn is usually greatly increased in crops (except rice) when Cd is increased, the presence of Zn may substantially reduce the bioavailability of crop Cd, alleviating presumed risk of crop Cd. Because commercial carrots were found with higher than normal Pb concentrations when grown on historic orchard soils, U.S.-FDA requested that ARS examine the basis for carrot Pb accumulation and to learn if agricultural amendments can reduce carrot Pb when they are grown on high Pb soils. Certain root crops have xylem elements growing through the edible storage root, so if Pb is trapped within the xylem during normal growth of the crop, it will be in the edible root. But such Pb might have much lower bioavailability than the Pb-acetate used to establish diet Pb risk; 2-10% of food Pb is absorbed, while 60-80% of soluble Pb in water is absorbed by human volunteers. Approach (from AD-416): Characterize the influence of zinc and iron concentrations in edible crop tissues and crop species on the bioavailability of crop cadmium to animals. Zinc incorporated in lettuce reduces weanling rat absorption of lettuce Cd. Using controlled chelator-buffered nutrient solutions (similar to Kukier and Chaney, 2002), Romaine lettuce will be grown to contain basal and sub-phytotoxic concentrations of foliar Zn (25 and 450 mg kg-1 DW), and the Codex Cd limit (4 mg Cd kg-1 DW); the high Zn represents maximum Zn levels normally present if lettuce is grown in acidic soils with geogenic Cd+Zn contamination at the beginning of yield reduction due to Zn phytotoxicity. Fe concentration in lettuce is tightly controlled genetically, but lettuce can supply higher bioavailable Fe than the marginal AIN diet, and thus plant Fe can reduce Cd bioavailability. The lettuce will be fed to weanling rats following the protocol of Reeves and Chaney (2004) in which American Institute of Nutrition (AIN) purified diets with marginal or adequate Fe-Zn-Ca were fed. The basal and high Zn lettuce will be mixed with both the marginal and adequate diets and fed for 28 days without radioisotope labeling used previously. At autopsy, the liver, kidney and duodenum will be removed for analysis. Tissues and blood will be tested to establish Fe status of the test animals. The tissues will be digested in HNO3, and Cd, Zn and Fe levels measured by ICP-Atomic Emission Spectrometry or ICP-Mass Spectrometry. Eight replicate rats will be fed each diet to accommodate the natural variation in such feeding tests (Reeves and Chaney, 2001). If the lettuce experiment shows a strong effect of crop Zn on crop Cd bioavailability, other crops may be studied using a similar approach (durum wheat; soybean). The project objectives fall under National Program 108 Action Plan, Component 1B Foodborne Contaminants, Problem Statement 1.F Chemical and Biological Contaminants, covering improving understanding and reducing risks from trace elements in agricultural products. Under Objective 1, Vegetables (lettuce and spinach) are being processed for a cadium (Cd) bioavailability feeding trial using pigs. Previous studies by the lab have shown that Cd in spinach has significantly lower bioavailability than Cd in other foods, and that Zn in spinach and lettuce significantly reduced the bioavailability of Cd to mammals and birds. However, CODEX regulations continue to ignore crop variation or the presence of Zn in setting limits for Cd in foods. Thus additional feeding tests are needed to more fully inform decisions about limits for Cd in vegetables. Working with the Beltsville Human Nutrition Research Center, an experiment was designed and initiated to feed weanling pigs 20% of their diet as leafy vegetable dry weight. The control treatment is basal corn-soy diet with usual supplements; the Cd reference would include the same Cd concentration in total diet as fed in the leafy vegetables, and represent 100% bioavailable Cd. Spinach and lettuce were amended with Cd or Cd and Zn so that the crop would contain 4 mg Cd/kg dry weight with both basal Zn level (15-25 mg Zn/kg dry weight), or high Zn level near 400 mg/kg dry weight. Large amounts of lettuce and spinach were purchased, prepared for the study, dried and ground. Extrinsic Cd and Zn addition is being used as has been shown valid for Cd bioavailability assessment. A preliminary experiment to learn how best to encourage the test pigs to consume the powdered vegetables with their pelletted or un-pelletted diets was conducted to check Cd accumulation in tissues after one week to assure that the full experiment would allow useful measurements. The full test will follow. Under Objective 2, research to assist rice researchers and managers to better understand the joint potential for accumulation of inorganic arsenic (iAs) and cadmium (Cd) in rice grain with variation of irrigation or soil management to reduce accumulation of As in rice continues. Also advised other ARS researchers and rice industry on many aspects of rice accumulation of As and Cd. By analysis of samples from existing field trials in Arkansas and Missouri, showed that growing rice under more aerobic conditions could substantially reduce grain accumulation of As although strong reductions required strong aerobic soil management to obtain. Similarly, growing rice under more aerobic conditions caused significant increase in grain Cd with any increase in aerobic status causing increase in grain Cd. Analyzed rice grain samples from other experiments in cooperation with ARS Rice Research Lab scientists to evaluate production methods effect on grain As, Cd, and other elements. Effect of flood management of old orchard soils contaminated by lead arsenate pesticides on accumulation of arsenic (As) and lead (Pb) in rice. Previous research in this lab has demonstrated that rice grown on lead- arsenate contaminated soil under flooded management accumulated considerably more arsenic compared to aerobic soil management. Research is being conducted to evaluate the effects of organic matter (low phosphate compost)-amended lead-arsenate contaminated soils on arsenic accumulation by rice under aerobic and anaerobic conditions. Some publications indicate that although added organic matter usually increases rice As, higher levels may cause formation of sulfide which can precipitate As in soil and reduce uptake by rice. Findings should be applicable to grower soils where arsenate has accumulated from pesticide applications for several crops. Analysis of soybean and durum wheat samples to support breeders continued during FY14. Under Objective 3, data from carrot Pb localization tests was evaluated and dissected samples were also analyzed to confirm X-Ray localization conducted earlier. Under Objective 4, advised USDA-FAS and FDA about As and Cd accumulation in rice grain to support their discussions with the CODEX Cereal Crops commission, and the Rice Arsenic Code of Practice Electronic Workgroup. Traditional use of chemical fertilizers was compared to rice produced using organic production methods. Use of organic matter fertilizers adds energy to soil microbes; this causes more rapid and more extensive reduction of the soil, producing higher levels of dissolved arsenite in the soil solution and thus uptake by rice. In collaboration with other ARS scientists, As was measured in rice grown with organic methods compared to traditional production. Results showed somewhat higher As in grain from most organic production samples compared to traditional chemical fertilizer production samples. Accomplishments 01 Effect of alternate wetting and drying (AWD) irrigation management on arsenic (As) and cadium (Cd) accumulation in rice grain. Public concern about levels of As in rice grain has increased the need for improved understanding of agricultural and food management practices which may influence concentrations of these elements in rice. Earlier research showed that more aerobic soil management (compared to traditional continuous flood) caused a decrease in grain total As, but an increase in grain Cd. In the previous study, yield reduction from longer drying periods was appreciable compared to more recent tests, and the reduction in grain total As was significant, allowing the concentration to fall below proposed limits. Apparently because As test soils remain low in soil Cd, even with more aerobic management, grain Cd remained well below recommended limits. 02 Risk assessment for Cd and As in foods, and advice to Agency staff. With the increased interest in dietary As from rice, the FDA and FAS have worked with CODEX international projects to develop a �Code of Practice� to lower rice grain As. After extensive information seeking, discussion with both ARS and other scientists concerned about levels of As and Cd in rice, provided comments to FDA regarding several drafts of the CODEX draft Code of Practice to lower As and Cd in rice. Similarly, advised FDA and rice industry scientists about the scientific findings relevant to these questions. Because U.S. rice soils are largely free of Cd contamination, growing rice with Alternate Wetting and Drying can significantly reduce grain As without raising grain Cd to levels of concern, in strong contrast with Japan and China where soil Cd contamination threatens large increase in grain Cd if soils are more aerobic. It is, however, possible that AWD production in the U.S. will require higher soil pH management than usual rice production practices.
Impacts
(N/A)
Publications
- Codling, E.E. 2009. Effect of flooding lead-arsenate contaminated orchard soil on growth, arsenic and lead accumulation in rice. Communications in Soil Science and Plant Analysis. 40:2800-2815.
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Progress 10/01/12 to 09/30/13
Outputs
Progress Report Objectives (from AD-416): Objective 1: Characterize the influence of zinc and iron concentrations in edible crop tissues and crop species on the bioavailability of crop cadmium to animals (C1; PS 1.F). Objective 2: Characterize the potential transfer of soil lead, arsenic, and other trace elements by vegetable crops grown on element enriched urban and orchard soils and develop methods to prevent this transfer. (C1; PS 1.F). Objective 3: Characterize genetic resources and inheritance of grain Cd to reduce cadmium in durum wheat, flax and soybean. (C1; PS 1.F). Objective 4: Evaluate information about the risk from Cd in foods to support public decisions for foods of both plant and animal origin. (C1; PS 1.F). The ultimate goals of this Project Plan are to improve the science about risk of heavy metals in soils and crops in order to obtain improved regulatory limits for Cd in crops under Codex, and the information needed to provide improved advice about the risk of Pb in urban garden soils and crops. Essentially all human Cd disease from soil Cd has resulted from paddy rice grown on fields contaminated by mining or smelter emissions. Garden vegetables and other grains have not been found to induce Cd disease in highly exposed populations who grow crops on highly Cd+Zn contaminated soils. Some Europeans want to set crop Cd limits based on �attainable� levels rather than on the basis of potential risk to consumers. Such non-risk based standards will harm U.S. growers of durum wheat, sunflower kernels, flax, soybean, and some other crops. If crops must contain lower levels of Cd to win importation by other nations, both soil treatments, selection of soil series which produce lower Cd crops, and improved cultivars which accumulate lower amounts of Cd will contribute to growers needs. Providing a clear technical basis for the bioavailability of Cd in different crops appears to be the central issue which could change the demand for lower limits for crop Cd, and protect growers from unnecessary costs to produce lower Cd crops which may have no benefit. Only animal feeding tests can provide valid information about the bioavailability of crop Cd to animals, and the concentrations fed must represent levels in foods rather than toxic levels fed in most previous research. Because Zn is usually greatly increased in crops (except rice) when Cd is increased, the presence of Zn may substantially reduce the bioavailability of crop Cd, alleviating presumed risk of crop Cd. Because commercial carrots were found with higher than normal Pb concentrations when grown on historic orchard soils, U.S.-FDA requested that ARS examine the basis for carrot Pb accumulation and to learn if agricultural amendments can reduce carrot Pb when they are grown on high Pb soils. Certain root crops have xylem elements growing through the edible storage root, so if Pb is trapped within the xylem during normal growth of the crop, it will be in the edible root. But such Pb might have much lower bioavailability than the Pb-acetate used to establish diet Pb risk; 2-10% of food Pb is absorbed, while 60-80% of soluble Pb in water is absorbed by human volunteers. Approach (from AD-416): Characterize the influence of zinc and iron concentrations in edible crop tissues and crop species on the bioavailability of crop cadmium to animals. Zinc incorporated in lettuce reduces weanling rat absorption of lettuce Cd. Using controlled chelator-buffered nutrient solutions (similar to Kukier and Chaney, 2002), Romaine lettuce will be grown to contain basal and sub-phytotoxic concentrations of foliar Zn (25 and 450 mg kg-1 DW), and the Codex Cd limit (4 mg Cd kg-1 DW); the high Zn represents maximum Zn levels normally present if lettuce is grown in acidic soils with geogenic Cd+Zn contamination at the beginning of yield reduction due to Zn phytotoxicity. Fe concentration in lettuce is tightly controlled genetically, but lettuce can supply higher bioavailable Fe than the marginal AIN diet, and thus plant Fe can reduce Cd bioavailability. The lettuce will be fed to weanling rats following the protocol of Reeves and Chaney (2004) in which American Institute of Nutrition (AIN) purified diets with marginal or adequate Fe-Zn-Ca were fed. The basal and high Zn lettuce will be mixed with both the marginal and adequate diets and fed for 28 days without radioisotope labeling used previously. At autopsy, the liver, kidney and duodenum will be removed for analysis. Tissues and blood will be tested to establish Fe status of the test animals. The tissues will be digested in HNO3, and Cd, Zn and Fe levels measured by ICP-Atomic Emission Spectrometry or ICP-Mass Spectrometry. Eight replicate rats will be fed each diet to accommodate the natural variation in such feeding tests (Reeves and Chaney, 2001). If the lettuce experiment shows a strong effect of crop Zn on crop Cd bioavailability, other crops may be studied using a similar approach (durum wheat; soybean). The project objectives fall under National Program 108 Action Plan, Component 1B Foodborne Contaminants, Problem Statement 1.F Chemical and Biological Contaminants, covering improving understanding and reducing risks from trace elements in agricultural products. Under Objective 1, feeding tests were discussed but no schedule yet prepared for conducting the tests. Under Objective 2, research was conducted to assist rice researchers and managers to better understand the joint potential for accumulation of inorganic arsenic (iAs) and cadmium (Cd) in rice grain with variation of irrigation or soil management to reduce accumulation of As in rice. Also advised other ARS researchers and rice industry on many aspects of rice accumulation of As and Cd. By analysis of samples from existing field trials in Arizona, showed that growing rice under more aerobic conditions could substantially reduce grain accumulation of As although strong reductions required strong aerobic soil management to obtain. Similarly, growing rice under more aerobic conditions caused significant increase in grain Cd with any increase in aerobic status causing increase in grain Cd. Analyzed rice grain samples from other experiments in cooperation with ARS Rice Research Lab scientists to evaluate production methods effect on grain As, Cd, and other elements. Analysis of soybean and durum wheat samples to support breeders continued during FY. Under Objective 3, data from carrot Pb localization tests was evaluated and dissected samples were also analyzed to confirm X-Ray localization conducted earlier. Under Objective 4, advised USDA-FAS about Cd accumulation in various grains to support their discussions with the EU Commission regarding possible lowering of grain Cd limits in the EU. Strong U.S. technical points helped prevent unnecessary lowering of grain Cd limits and maintain US export programs. Accomplishments 01 Irrigation management strongly affects arsenic and cadmium accumulation in rice grain. Changing concepts of dietary arsenic (As) risk to humans threatens marketing of U.S. rice, the only grain which accumulates substantial levels of As. Flooding rice soils causes arsenite to be generated from soil arsenate; soil arsenite can be accumulated by rice, as can dimethylarsinic acid, a less toxic organic form of As generated by soil microbes. Cooperated with researcher from the University of Arizona and a researcher from the ARS Rice Research Laboratory to measure levels of As and Cd in grain from experiments conducted over the last several years with six levels of varied irrigation management. Rice grown with traditional flooding contained highest As and lowest Cd levels. Any soil oxidation promoted Cd accumulation, while making the soil nearly fully aerobic was required to reach minimal As concentrations in grain. Three tested cultivars varied in As accumulation but had similar change with irrigation management. Results show that growing rice aerobically rather than with traditional flood culture can substantially lower grain As and yield substantially, and increases grain Cd. Results aid researchers in designing tests of methods to reduce grain As and Cd, and provide growers with information which may be needed to meet market As limits.
Impacts
(N/A)
Publications
- Duke, S.O., Lydon, J., Koskinen, W.C., Moorman, T.B., Chaney, R.L., Hanmerschmidt, R. 2012. Glyphosate effects on plant mineral nutrition, crop rhizosphere microbiota, and plant disease in glyphosate-resistant crops. Journal of Agricultural and Food Chemistry. 60:10375-10397.
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Progress 10/01/11 to 09/30/12
Outputs
Progress Report Objectives (from AD-416): Objective 1: Characterize the influence of zinc and iron concentrations in edible crop tissues and crop species on the bioavailability of crop cadmium to animals (C1; PS 1.F). Objective 2: Characterize the potential transfer of soil lead, arsenic, and other trace elements by vegetable crops grown on element enriched urban and orchard soils and develop methods to prevent this transfer. (C1; PS 1.F). Objective 3: Characterize genetic resources and inheritance of grain Cd to reduce cadmium in durum wheat, flax and soybean. (C1; PS 1.F). Objective 4: Evaluate information about the risk from Cd in foods to support public decisions for foods of both plant and animal origin. (C1; PS 1.F). The ultimate goals of this Project Plan are to improve the science about risk of heavy metals in soils and crops in order to obtain improved regulatory limits for Cd in crops under Codex, and the information needed to provide improved advice about the risk of Pb in urban garden soils and crops. Essentially all human Cd disease from soil Cd has resulted from paddy rice grown on fields contaminated by mining or smelter emissions. Garden vegetables and other grains have not been found to induce Cd disease in highly exposed populations who grow crops on highly Cd+Zn contaminated soils. Some Europeans want to set crop Cd limits based on �attainable� levels rather than on the basis of potential risk to consumers. Such non-risk based standards will harm U.S. growers of durum wheat, sunflower kernels, flax, soybean, and some other crops. If crops must contain lower levels of Cd to win importation by other nations, both soil treatments, selection of soil series which produce lower Cd crops, and improved cultivars which accumulate lower amounts of Cd will contribute to growers needs. Providing a clear technical basis for the bioavailability of Cd in different crops appears to be the central issue which could change the demand for lower limits for crop Cd, and protect growers from unnecessary costs to produce lower Cd crops which may have no benefit. Only animal feeding tests can provide valid information about the bioavailability of crop Cd to animals, and the concentrations fed must represent levels in foods rather than toxic levels fed in most previous research. Because Zn is usually greatly increased in crops (except rice) when Cd is increased, the presence of Zn may substantially reduce the bioavailability of crop Cd, alleviating presumed risk of crop Cd. Because commercial carrots were found with higher than normal Pb concentrations when grown on historic orchard soils, U.S.-FDA requested that ARS examine the basis for carrot Pb accumulation and to learn if agricultural amendments can reduce carrot Pb when they are grown on high Pb soils. Certain root crops have xylem elements growing through the edible storage root, so if Pb is trapped within the xylem during normal growth of the crop, it will be in the edible root. But such Pb might have much lower bioavailability than the Pb-acetate used to establish diet Pb risk; 2-10% of food Pb is absorbed, while 60-80% of soluble Pb in water is absorbed by human volunteers. Approach (from AD-416): Characterize the influence of zinc and iron concentrations in edible crop tissues and crop species on the bioavailability of crop cadmium to animals. Zinc incorporated in lettuce reduces weanling rat absorption of lettuce Cd. Using controlled chelator-buffered nutrient solutions (similar to Kukier and Chaney, 2002), Romaine lettuce will be grown to contain basal and sub-phytotoxic concentrations of foliar Zn (25 and 450 mg kg-1 DW), and the Codex Cd limit (4 mg Cd kg-1 DW); the high Zn represents maximum Zn levels normally present if lettuce is grown in acidic soils with geogenic Cd+Zn contamination at the beginning of yield reduction due to Zn phytotoxicity. Fe concentration in lettuce is tightly controlled genetically, but lettuce can supply higher bioavailable Fe than the marginal AIN diet, and thus plant Fe can reduce Cd bioavailability. The lettuce will be fed to weanling rats following the protocol of Reeves and Chaney (2004) in which American Institute of Nutrition (AIN) purified diets with marginal or adequate Fe-Zn-Ca were fed. The basal and high Zn lettuce will be mixed with both the marginal and adequate diets and fed for 28 days without radioisotope labeling used previously. At autopsy, the liver, kidney and duodenum will be removed for analysis. Tissues and blood will be tested to establish Fe status of the test animals. The tissues will be digested in HNO3, and Cd, Zn and Fe levels measured by ICP-Atomic Emission Spectrometry or ICP-Mass Spectrometry. Eight replicate rats will be fed each diet to accommodate the natural variation in such feeding tests (Reeves and Chaney, 2001). If the lettuce experiment shows a strong effect of crop Zn on crop Cd bioavailability, other crops may be studied using a similar approach (durum wheat; soybean). The project objectives fall under National Program 108 Action Plan, Component 1�Foodborne Contaminants, Problem Statement 1.F Chemical and Biological Contaminants, covering improving understanding and reducing risks from trace elements in agricultural products. Progress was made in each of the four objectives. Under Objective 1, a feeding test to evaluate the effect of zinc in lettuce on the bioavailability of cadmium in lettuce was designed and lettuce grown to prepare the test feeds. A new collaborator was required after changes in programs at Grand Forks, ND. Under Objective 2, cooperators in five states conducting cultivar field evaluations for agronomic performance, provided samples of mature grain of durum wheat or soybean cultivars grown on several soil series so that genotype-by-environment interaction could be assessed. Under Objective 3, the localization of lead in carrot xylem was identified as the mechanism whereby peeled carrots accumulate significant amounts of lead from contaminated soils in contrast with most other garden crops. In addition, a chemical extraction (or bioaccessibility) test was developed to correlate well with the outcome of human soil feeding tests to measure the bioavailability of soil lead from a field test using phosphate to remediate soil lead in Joplin, MO. Compared to earlier tests for soil lead bioaccessibility, the new method is better related to the bioavailability of soil lead to humans, less expensive to conduct, and reflects the influence of soil amendments which reduce soil lead bioavailability based on feeding tests. Under Objective 4, continuing evaluation of the literature and new evidence about dietary cadmium risk to humans was reviewed in order to provide advice to potentially impacted commodity groups and Foreign Agricultural Service staff who represent the U.S. in international food safety discussions. An attempt to sharply reduce allowable intake of cadmium in the European Union must be challenged to protect U.S. producers of durum wheat, soybean, sunflower, flax and other crops. Evidence from long exposures of farm families to excessive cadmium intake in Asia provides clear evidence that internationally accepted cadmium intake limits remain fully protective of humans. Accomplishments 01 A simple and inexpensive test for bioaccessible garden soil lead. With t large increase in interest in gardening and agriculture in urban areas, the high levels of lead from historic paint and automotive exhaust emissions may comprise risk to children who could ingest garden soils either at the garden or when soil is carried to the home on tools and clothes of gardeners. And some crops may accumulate enough Pb to compris risk (lettuce, carrot, etc.). Because common garden soil amendments can induce the formation of chemical forms of lead which have low bioavailability to humans who ingest soil, it is important that advice about urban gardens be based on bioavailable/bioaccessible lead rather than total lead. The soil test presently approved by U.S.-Environmental Protection Agency to estimate soil bioaccessible lead has been shown to over-estimate lead bioavailability in soils treated with phosphate or compost, and is prohibitively expensive for most gardeners. Thus a simplified test calibrated using soil samples from the Joplin field test of using amendments to reduce soil lead bioavailability. The phosphate treated soil had 69% reduction in soil lead bioavailability to humans fe the test soils. The U.S. Environmental Protection Agency (US-EPA) test with 0.4 M glycine-hydrochoride was modified for ease of operations and calibrated against the Joplin soils. Additional evaluation of the method was conducted during the FY, showing that the rate of shaking was a more critical factor than initially believed. The new method, conducted at pH 5 rather than the EPA method at pH 1.5, has nearly the same reduction in Pb bioaccessibility as observed in the human feeding test so estimated bioavailability can be measured from the correlation of bioavailability and bioaccessibility from the Joplin soils. 02 Working with U.S. producers to protect sales of grains with normal level of cadmium. During the last year, an European Union panel recommended lowering of the Potentially Tolerable Weekly Intake of cadmium be lowere from 7.0 to 2.5 micrograms per kg body weight peer week, and then propos lower levels of cadmium for important U.S. export crops. The Codex Alimentarius (World Health Organization) program did not support lowerin the cadmium intake recommendation (previously 7 micrograms cadmium per k body weight per week), and slightly lowered it in changing to a monthly intake recommendation in order to stress the long term nature of dietary cadmium risk to humans (Potentially Tolerable Monthly Intake to be 25 micrograms per kg body weight per month). Our previous research showed that the low iron, zinc and calcium levels of rice grain promote cadmium absorption by animals compared to animals fed adequate levels of these nutrients, but the EU committee did not take these important findings in account. Research findings such as these were brought to the attention o Foreign Agricultural Service and commodity group scientists who participate in international negotiations regarding food cadmium limits they could use available scientific information to support the U.S. farm community. The EU Commission group dealing with the proposed lower limit for Cd in grains has decided not to adopt such regulations at this time, but have not formally rejected the proposal. Additional feeding trials would help settle these questions. 03 Cultivar variation of cadmium accumulation in U.S. soybean and durum whe Because grain cadmium can be a limit for marketing of crops, studies we begun or continued to assess cultivar variation in cadmium accumulation grain of durum wheat and soybean. Breeding lower cadmium accumulating cultivars is one approach to protect markets for U.S. crops, but this requires knowledge of genetic variation and genotype-by-environment variation in crop cadmium. Cooperative studies were undertaken with plan breeders in Montana, Arizona and California to assess durum wheat geneti variation, and in Iowa and North Dakota to assess both genetic variation and soil series effects on cadmium accumulation in soybean. Crops grown during FY11 were analyzed, and the crops grown again during FY12 and wil be analyzed. Both genotype and location affected grain Cd in soybean. 04 Flooding rice soils causes transformation of the chemical species of zin and cadmium present. Previous studies reported on the chemical forms of present in contaminated paddy soils at varied redox status. Additional studies examined the effect of soil redox on the forms of Zn, and the extractability of soil Zn in the highly contaminated paddy soil from Mae Sot, Thailand. The soils were alkaline because the farmers had added limestone to reduce yield reduction due to the massive Zn and Cd contamination of the soil. Extended X-Ray Absorption Fine Structure Spectrometry was conducted to characterize the forms of zinc present and changes during flooding and drainage. Flooding this soil caused no apparent change in the forms of Zn present, nor did draining the flooded soil to allow it to become aerobic. Interestingly, the two major forms o Zn present, the zinc-aluminum layered double hydroxide (hydrotalcite lik and Zn phyllosilicate are capable of holding Zn in forms which have litt phytoavailability. The previous work showed that Cd and Zn were in different positions on solid surfaces in the flooded soil helping to explain how Zn and Cd in rice soils have such different phytoavailabilit 05 Testing use of zinc fertilizer and ground rubber to reduce cadmium in durum wheat in Arizona. Durum wheat grain produced on Arizona soils rich in chloride may contain cadmium at levels which might affect marketing i the European Union. High soil chloride has been shown to interact with l soil zinc (Zn) availability to promote cadmium accumulation, such that application of zinc fertilizers may reduce grain cadmium to protect markets. A field test was designed in cooperation with scientists at Arizona State University to evaluate the effect of zinc sulfate and grou rubber application on cadmium in leaves and grain of two durum wheat cultivars with different cadmium accumulation potential. The plots were established in advance of planting to allow reactions of the amendments the soils. All soils, plant tissues and irrigation waters were analyzed for trace elements and nutritional status. Wheat yield was not affected these soils which were thus not zinc-deficient. The analyses showed that there was no reduction in grain Cd in response to the added Zn, in contrast with some soils which had true Zn deficiency without the high chloride in irrigation water. Other treatments such as foliar Zn spray during grain filling will be examined.
Impacts
(N/A)
Publications
- Khaokaew, S., Chaney, R.L., Landrot, G., Pandya, K., Sparks, D.L. 2012. Speciation and release kinetics of zinc in contaminated paddy soils. Environmental Science and Technology. 46:3957-3963.
- Chaney, R.L. 2012. Food Safety Issues: Mineral fertilizers and soil amendments. In: Sparks, D.L., editor. Advances in Agronomy. New York, NY: Elsevier Press. p. 41-106.
- Siebielec, G., Chaney, R.L. 2012. Testing amendments for remediation of military range contaminated soil. Journal of Environmental Management. 108:8-13.
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Progress 10/01/10 to 09/30/11
Outputs
Progress Report Objectives (from AD-416) Objective 1: Characterize the influence of zinc and iron concentrations in edible crop tissues and crop species on the bioavailability of crop cadmium to animals (C1; PS 1.F). Objective 2: Characterize the potential transfer of soil lead, arsenic, and other trace elements by vegetable crops grown on element enriched urban and orchard soils and develop methods to prevent this transfer. (C1; PS 1.F). Objective 3: Characterize genetic resources and inheritance of grain Cd to reduce cadmium in durum wheat, flax and soybean. (C1; PS 1.F). Objective 4: Evaluate information about the risk from Cd in foods to support public decisions for foods of both plant and animal origin. (C1; PS 1.F). The ultimate goals of this Project Plan are to improve the science about risk of heavy metals in soils and crops in order to obtain improved regulatory limits for Cd in crops under Codex, and the information needed to provide improved advice about the risk of Pb in urban garden soils and crops. Essentially all human Cd disease from soil Cd has resulted from paddy rice grown on fields contaminated by mining or smelter emissions. Garden vegetables and other grains have not been found to induce Cd disease in highly exposed populations who grow crops on highly Cd+Zn contaminated soils. Some Europeans want to set crop Cd limits based on �attainable� levels rather than on the basis of potential risk to consumers. Such non-risk based standards will harm U.S. growers of durum wheat, sunflower kernels, flax, soybean, and some other crops. If crops must contain lower levels of Cd to win importation by other nations, both soil treatments, selection of soil series which produce lower Cd crops, and improved cultivars which accumulate lower amounts of Cd will contribute to growers needs. Providing a clear technical basis for the bioavailability of Cd in different crops appears to be the central issue which could change the demand for lower limits for crop Cd, and protect growers from unnecessary costs to produce lower Cd crops which may have no benefit. Only animal feeding tests can provide valid information about the bioavailability of crop Cd to animals, and the concentrations fed must represent levels in foods rather than toxic levels fed in most previous research. Because Zn is usually greatly increased in crops (except rice) when Cd is increased, the presence of Zn may substantially reduce the bioavailability of crop Cd, alleviating presumed risk of crop Cd. Because commercial carrots were found with higher than normal Pb concentrations when grown on historic orchard soils, U.S.-FDA requested that ARS examine the basis for carrot Pb accumulation and to learn if agricultural amendments can reduce carrot Pb when they are grown on high Pb soils. Certain root crops have xylem elements growing through the edible storage root, so if Pb is trapped within the xylem during normal growth of the crop, it will be in the edible root. But such Pb might have much lower bioavailability than the Pb-acetate used to establish diet Pb risk; 2-10% of food Pb is absorbed, while 60-80% of soluble Pb in water is absorbed by human volunteers. Approach (from AD-416) Characterize the influence of zinc and iron concentrations in edible crop tissues and crop species on the bioavailability of crop cadmium to animals. Zinc incorporated in lettuce reduces weanling rat absorption of lettuce Cd. Using controlled chelator-buffered nutrient solutions (similar to Kukier and Chaney, 2002), Romaine lettuce will be grown to contain basal and sub-phytotoxic concentrations of foliar Zn (25 and 450 mg kg-1 DW), and the Codex Cd limit (4 mg Cd kg-1 DW); the high Zn represents maximum Zn levels normally present if lettuce is grown in acidic soils with geogenic Cd+Zn contamination at the beginning of yield reduction due to Zn phytotoxicity. Fe concentration in lettuce is tightly controlled genetically, but lettuce can supply higher bioavailable Fe than the marginal AIN diet, and thus plant Fe can reduce Cd bioavailability. The lettuce will be fed to weanling rats following the protocol of Reeves and Chaney (2004) in which American Institute of Nutrition (AIN) purified diets with marginal or adequate Fe-Zn-Ca were fed. The basal and high Zn lettuce will be mixed with both the marginal and adequate diets and fed for 28 days without radioisotope labeling used previously. At autopsy, the liver, kidney and duodenum will be removed for analysis. Tissues and blood will be tested to establish Fe status of the test animals. The tissues will be digested in HNO3, and Cd, Zn and Fe levels measured by ICP-Atomic Emission Spectrometry or ICP-Mass Spectrometry. Eight replicate rats will be fed each diet to accommodate the natural variation in such feeding tests (Reeves and Chaney, 2001). If the lettuce experiment shows a strong effect of crop Zn on crop Cd bioavailability, other crops may be studied using a similar approach (durum wheat; soybean). Progress was made in each of the four objectives. Under Objective 1, a feeding test to evaluate the effect of zinc (Zn) in lettuce on the bioavailability of cadmium (Cd) in lettuce was designed and lettuce was grown to prepare the test feeds. A new collaborator was required after changes in programs at Grand Forks, ND. Under Objective 2, cooperators in five states conducting cultivar field evaluations for agronomic performance, provided samples of mature grain of durum wheat or soybean cultivars grown on several soil series so that genotype-by-environmental interaction could be assessed. Under Objective 3, the localization of lead (Pb) in carrot xylem was identified as the mechanism whereby peeled carrots accumulate significant amounts of Pb from contaminated soils in contrast with most other garden crops. In addition, a chemical extraction (or bioaccessibility) test was developed to correlate well with the outcome of human soil feeding tests to measure the bioavailability of soil Pb from a field test using phosphate to remediate soil Pb in Joplin, MO. Compared to earlier tests for soil Pb bioaccessibility, the new method is better related to the bioavailability of soil Pb to humans, less expensive to conduct, and reflects the influence of soil amendments which reduce soil Pb bioavailability based on feeding tests. Under Objective 4, continuing evaluation of the literature and new evidence about dietary Cd risk to humans was reviewed in order to provide advice to potentially impacted commodity groups and Foreign Agricultural Service staff who represent the U.S. in international food safety discussions. An attempt to sharply reduce allowable intake of Cd in the European Union must be challenged to protect U.S. producers of durum wheat, soybean, sunflower, flax and other crops. Evidence from long exposures of farm families to excessive Cd intake in Asia provide clear evidence that internationally accepted Cd intake limits remain fully protective of humans. Accomplishments 01 Effect of zinc and iron in Romaine lettuce on bioavailability of lettuce cadmium. Previous research showed that marginal zinc and iron in diets rats strongly promoted cadmium absorption by rats compared to adequate levels. These earlier studies were conducted with sunflower kernels and rice grain, crops for which soil zinc supply has little effect on crop zinc levels, while soil iron supply has little effect on iron concentration in any crop. Lettuce represents the class of vegetable foods which can accumulate high levels of cadmium and zinc depending on soil supply, so an experiment was designed to grow Romaine lettuce to contain minimally adequate zinc and near excessive zinc, with fixed cadmium at the Codex Alimentarium (World Health Organization) limit for vegetable crops. Because the animal scientist cooperator in previous bioavailability testing is no longer available to conduct feeding tests, new collaboration was established with an experienced animal nutritionis at Beltsville as part of the new project. Lettuce has been grown to contain the goal levels of cadmium and zinc and the feeding test is scheduled to occur during FY12. 02 Effect of zinc fertilization of high cadmium soils on cadmium accumulati in Romaine lettuce in the field. Previous study showed that certain sha derived soils in Salinas Valley, CA, are naturally mineralized with cadmium but little zinc such that lettuce, spinach and some other crops grown on these soils contain levels of cadmium which do not comply with Codex Alimentarius limits. Further, greenhouse testing showed that application of a combination of limestone and zinc fertilizer could allo production of normal yields of Romaine lettuce and spinach with Codex compliant levels of cadmium. During FY11, a collaboration was initiated with a lettuce breeder at the USDA-ARS Lettuce research laboratory in Salinas, CA. During the FY, soils across the experiment station were evaluated and found to contain only normal levels of cadmium. Field tes of Romaine lettuce cultivars were sampled to test for genetic variation lettuce cadmium to support selection of cultivars for the planned field test of zinc fertilizer and limestone to reduce cadmium uptake. Present results indicate that farmer�s fields in southwestern Salinas Valley wil have to be sought for cooperating field tests. 03 Zinc from ground rubber tires can increase wheat yield and reduce wheat grain cadmium. Waste tires are a significant environmental problem; som tires are used to produce energy and others to produce ground rubber to mix with soil to reduce physical compaction in high traffic areas. Because tire rubber contains about 1.5% of highly purified zinc (very lo in cadmium and lead) from use in the vulcanization of rubber, we tested use of ground rubber as a zinc fertilizer which could be used to inexpensively reduce cadmium accumulation by crops. One study tested th kinetics of release of zinc from ground rubber compared to standard zinc fertilizers; rubber served as a slow release source of zinc which kept plant zinc higher than did zinc sulfate. Zinc salts added to soils can rapidly transformed to unavailable zinc minerals, while the slow release of the inexpensive recycled ground rubber as zinc fertilizer can correct zinc deficiency for many years. A field test using ash from burning ground rubber showed effective zinc fertilizer response in zinc-deficien bread wheat which caused a significant reduction in cadmium in wheat gra 04 Testing use of zinc fertilizer and ground rubber to reduce cadmium in durum wheat in Arizona. Durum wheat grain produced on Arizona soils ric in chloride may contain cadmium at levels which might affect marketing i the European Union. High soil chloride has been shown to interact with low soil zinc availability to promote cadmium accumulation, such that application of zinc fertilizers may reduce grain cadmium to protect markets. A field test was designed in cooperation with scientists at Arizona State University to evaluate the effect of zinc sulfate and grou rubber application on cadmium in leaves and grain of two durum wheat cultivars with different cadmium accumulation potentials. The plots wer established in advance of planting to allow reactions of the amendments the soils. All soils, plant tissues and irrigation waters are being analyzed for trace elements and nutritional status. Wheat yield was not affected in these soils which were not zinc-deficient. The 2011 crop wa harvested and is undergoing analysis. 05 Cultivar variation of cadmium (Cd) accumulation in U.S. soybean and duru wheat. Because grain cadmium can be a limit for marketing of crops, studies were begun or continued to assess cultivar variation in cadmium accumulation in grain of durum wheat and soybean. Breeding lower cadmiu accumulating cultivars is one approach to protecting markets for U.S. crops, but this requires knowledge of genetic variation and genotype-by- environment variation in crop cadmium. Cooperative studies were undertaken with plant breeders in Montana, Arizona and California to assess durum wheat genetic variation, and in Iowa and North Dakota to assess both genetic variation and soil series effects on cadmium accumulation in soybean. Crops have been grown during FY11 and will be analyzed in due course. 06 Flooding rice soils causes the transformation of the chemical species of zinc (Zn) and cadmium (Cd). Ingestion of home-grown rice grain with hig levels of cadmium due to mine waste or smelter contamination has caused disease (renal tubular dysfunction) in several Asian countries. Cadmium concentration in rice plants remains low as long as the soil is flooded. But upon drainage, transformation of soil chemical species causes cadmiu uptake to greatly increase from contaminated soils. Studies were undertaken to characterize the mineral species of cadmium and zinc prese in highly contaminated Thai rice soil subjected to aerobic or flooded incubation. Extended X-Ray Absorption Fine Structure Spectrometry was conducted to characterize the forms of zinc and cadmium present, and mic X-Ray Fluorescence was used to examine whether cadmium was co-localized with zinc as has been reported for contaminated aerobic soils. Because the soil was highly contaminated with zinc and cadmium, it had been lime to alkaline phosphorus (pH). Flooding this soil caused partial formatio of cadmium sulfide (a highly insoluble and non-phytoavailable form of Cd along with cadmium carbonate in the soil. But draining the anaerobic so caused the cadmium sulfide to be transformed again to free cadmium bound to soil particles. One of the most significant findings was that rather than cadmium being co-localized with zinc in soil binding sites, cadmium and zinc were bound to different solid phases in the soil. Taken togethe these findings help explain how rice can rapidly absorb soil cadmium whe contaminated soils are drained to maximize rice yield, while grain zinc not increased which promotes absorption of grain cadmium by consumers. 07 A simple and inexpensive test for bioaccessible garden soil lead (Pb). Many urban gardens contain high levels of lead from historic paint and automotive exhaust emissions and may comprise risk to children who could ingest garden soils either at the garden or when soil is carried to the home on tools and clothes of gardeners. Because common garden soil amendments can induce the formation of chemical forms of lead which have low bioavailability to humans who ingest soil, it is important that advi about urban gardens be based on bioavailable/bioaccessible lead rather than total lead. The soil test presently approved by U.S.-Environmental Protection Agency to estimate soil bioaccessible lead has been shown to over-estimate lead bioavailability in soils treated with phosphate or compost, and is prohibitively expensive for most gardeners. Thus a simplified test calibration using soil samples from the Joplin field tes was used to measure the reduction in soil lead bioavailability. The phosphate treated soil had 69% reduction in soil lead bioavailability to humans fed the test soils. Using this test calibrated on the Joplin soi it was shown that most garden and orchard soils had only 5-10% absolute soil lead bioaccessibility rather than the 30% assumed by the U.S.- Environmental Protection Agency in developing of guidance for lead contaminated soils. A house-side non-garden soil had much higher fractional bioaccessibility than did garden soils. The test uses 0.4 molar glycine at pH 2.5, with 50 mL of extractant per 5 g of soil (screened < 2 mm rather than <0.25 mm), conducted at 20C for 2 hr. Commo garden soil amendments which might reduce soil lead bioaccessibility are being evaluated. 08 Working with U.S. producers to protect sales of grains with normal level of cadmium (Cd). During the last year, a European Union panel recommend lowering of the Potentially Tolerable Weekly Intake of cadmium, and then proposed lower levels of cadmium for important U.S. export crops. The Codex Alimentarius (World Health Organization) program did not support lowering the cadmium intake recommendation (previously 7 micrograms Cd p kg body weight per week), and slightly lowered it in changing to a month intake recommendation in order to stress the long term nature of dietary cadmium risk to humans (Potentially Tolerable Monthly Intake to be 25 micrograms per kg body weight per month). In reviewing available information on human dietary cadmium risks, the most reliable data came from a study of Japanese farm families who ingested rice, drinking water and other foods grown on soils contaminated by mining wastes. In contra with crops grown on aerobic soils, rice is commonly grown on flooded soi until flowering, and fields drained to improve yields and ease of harves But rice grown on mine waste contaminated soils can reach 7 mg cadmium per kg compared to the Codex Alimentarius limit of 0.4 mg cadmium per kg rice. Our previous research showed that the low iron, zinc and calcium levels of rice grain promote cadmium absorption by animals compared to animals fed adequate levels of these nutrients. Rice is the principle human food with the ability to promote cadmium movement to edible grain and increased bioavailability due to low levels of iron, zinc and calciu Research findings such as these were brought to the attention of Foreig Agricultural Service and commodity group scientists who participate in international negotiations regarding food cadmium limits so they could u available scientific information to support the U.S. farm community.
Impacts
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Publications
- Khaokaew, S., Chaney, R.L., Landrot, G., Ginder-Voget, M., Sparks, D.L. 2011. Speciation and release kinetics of cadmium in an alkaline paddy soil under various flooding periods and draining conditions. Journal of Environmental Science and Technology. 45:4249-4255.
- Gu, H., Qui, H., Tian, T., Zhan, S., Deng, T., Chaney, R.L., Wang, S., Tang, Y., Morel, J., Qiu, R. 2011. Mitigation effects of silicon rich amendments on heavy metal accumulation in rice (Oryza sativa L.) planted on multi-metal contaminated acidic soil. Chemosphere. 83:1234-1240.
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