ASSESSING AND REDUCING TOXIC METAL TRANSFER FROM SOILS INTO CROPS

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1003735
• Project Start Date: Oct 1, 2014
• Project End Date: Sep 30, 2017
• Program Code: [(N/A)]- (N/A)

Recipient Organization
CORNELL UNIVERSITY
(N/A)
ITHACA,NY 14853

Performing Department
Crop & Soil Sciences

Non Technical Summary
Toxic metals in food and water are now known to pose a greater hazard to human health than previously believed. Contaminated soils are an important source of human exposure to these toxins, particularly in urban and previously industrial areas. This project will define the conditions under which arsenic and lead transfer from soils into crops can be minimized, identify crops prone to uptake of these toxic metals, and test methods of amending or remediating soils to remove or stabilize the metals in less soluble forms. The experimental approach will utilize field and greenhouse studies of crops with known tendencies to bioaccumulate these metals, and measure the transfer of toxic metals from contaminated soils into the edible plant tissues. The goal of this project is to reduce exposure of gardeners and consumers to toxic metals in vegetables, fruits and other food crops through science-based management of soils to reduce toxic metal uptake into crops, and through selection of crops which tend to exclude these toxic metals.

Animal Health Component

50%

Research Effort Categories

Basic

30%

Applied

50%

Developmental

20%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
711	1499	1060	40%
133	0110	1150	20%
723	1430	2000	40%

Knowledge Area
711 - Ensure Food Products Free of Harmful Chemicals, Including Residues from Agricultural and Other Sources; 133 - Pollution Prevention and Mitigation; 723 - Hazards to Human Health and Safety;

Subject Of Investigation
1499 - Vegetables, general/other; 0110 - Soil; 1430 - Greens and leafy vegetables;

Field Of Science
1060 - Biology (whole systems); 2000 - Chemistry; 1150 - Toxicology;

Keywords

food safety

vegetable crops

soil contamination

toxic metals

lead

arsenic

metal uptake

Goals / Objectives
The type of food crop grown on contaminated soils strongly affects the risk of human exposure to toxic metals. Plant species, crop type, and even cultivar have profound effects on soil-to-crop transfer of metals. For this reason, a more detailed assay of metal transfer coefficients for common crops is needed, as broad generalizations presently used (e.g., "there is negligible transfer of As from soils into fruit crops") may not adequately assess risk to the food chain. Soil tests, historically designed to test for essential plant macro- and micro-nutrients need to be redesigned and recalibrated to estimate risk of human and ecosystem exposure to toxic metals, particularly arsenic, lead and cadmium, through the consumption of food crops and plants. These soil tests ideally need to be sensitive to soil properties such as pH, because toxic metal bioavailability and plant uptake are strongly influenced by differences in soil properties. Some commonly used soil extractants for toxic metals, such as Mehlich 3, are quite insensitive to these soil properties.The specific objectives of the present project are to:1. Measure the potential for As, Pb and Cd transfer into different vegetable and fruit crops when grown in contaminated soils.2. Assess the role of soil properties, particularly pH, organic matter content, texture and soil redox potential in affecting phytoavailability of the metals.3. Assess the effectiveness of soil remediation techniques, including stabilization (by soil amendments) and phytoextraction (by hyperaccumulator plants).Develop web-based educational materials and conduct outreach to ag. advisors, testing labs, farms and gardening communities, elucidating the behavior of toxic metals in soil, their potential for crop uptake and the pros and cons of different methods of soil testing for toxic metals and remediation of contaminated soils.. We will provide interpretation of the potential health impacts of these tests and describe inherent limitations or uncertainties in the tests. Soil remediation approaches with proven effectiveness will be described and explained.

Project Methods
Our research objectives will be met using greenhouse and field trials with selected crops. We have established small-scale field plots on the Dilmun Hill student farm, an area that is contaminated with Pb and As. Contaminated orchard soils will be collected from other areas as well as from old mining/smelting areas. These soils will represent a range of soil properties that can be correlated to soluble and plant-available Pb and As in the soils. Plant availability of Pb and As for all soils will be measured using greenhouse trials with indicator crops. Pb and As concentrations in the edible portions of the crops will be measured by ICP-MS. The strength of correlation between measures of metal extractability in the soils and uptake by the crops will be used as an indicator of the value of a particular method of soil testing for predicting crop contamination by these toxic metals.Soil remediation research will include the testing of soil amendments which have shown promise in previous research. Contaminated orchard soils will be amended with compost and ferric hydroxide. Effectiveness of remediation will be evaluated by measuring soluble As and Pb in the soil, and by greenhouse trials using metal-accumulator species such as Eruca sativa. To assess potential for As phytoremediation, greenhouse and field assays will screen several brassica species for their potential to extract As from soils. Success with these approaches will be evaluated based on measured reductions in metal solubility in the soil and reduced uptake into plants.Outreach objectives, to develop web-based educational materials, will draw upon the research component of this project to categorize risk to human health based on soil toxic metal concentration, bioavailability, crop species and remediation strategies. Dissemination of guidelines for the toxic metals (Pb, As, Cd) will be posted on the website of the Cornell Waste Management Institute.

Progress 10/01/14 to 09/30/17

Outputs
Target Audience:Our interactions with landowners and other community stakeholders (e.g., through gardening events and discussion forums in NYC, urban farming workshops in Buffalo, responding to information requests by email and phone) have indicated a need for comprehensive educational programs addressing diverse topics, including: 1) Training on site assessment for contaminants and soil sampling and testing protocols; 2) Information about and access to reliable, affordable, certified soil testing labs; 3) Simple guidelines for interpretation of soil test results that allow for site-specific considerations; 4) Assessment of contaminants in municipal compost and available soil/fill, and access to these materials; and 5) Possible liability issues or closure or avoidance of gardens if soil tests reveal contamination. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project has provided the opportunity in 2016-2017for one PhD-level graduate student (Xiaoyan Tang), and one research scientist( Cai Meifang)fromSouth China Botanical Garden,to spend a year in our laboratory, learning new research methods and conducting research on chemical testing of soilsand measuring bioavailability of toxic metals in soils. How have the results been disseminated to communities of interest?We have disseminated our research results in peer-reviewed publications, andin additionprovide yearlyinterpretations of ourresults in less technical formtoto community stakeholders (gardeners, farmers, extensionagents) through gardening events and discussion forums in New York City and Buffalo viaurban farming workshops, and byresponding to numerous information requests by email and phone calls. Fact sheets and workshops to address these topicscontinue to be developed to augment existing resources available at our old CWMI website under the heading "Soil Quality", and in a newly developed website devoted to urban gardening and soil health. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Thisresearch projectattemptedto correlate thechemical extractability and bioavailability of toxic lead, arsenic and other metals in urban garden and old orchard soils to measured uptake of these elements in vegetable crops grown in the field and greenhouse. We found that total or bioavailablelead in the soil did not usually predict the uptake of lead by many crops because soil particle adherence to leafy vegetables and root crops in particular circumvented the physiological barrier to uptake via roots. Consequently, although high soil lead concentrations presented a potential hazard for food crops, the severity of contamination of vegetables depended more strongly on a number of uncontrolled and unpredictable environmental factors such as rainfall, soil splash, and wind-blown dust. Such risk factors were effectively diminished by mulching the soil surface of garden beds. Soils with the highest lead (Pb) contents also had the most easily extracted and potentially plant-availaPb, but higher organic matter in the soils reduced the extractability and the bioaccessibility measured using a physiologically based extraction test (PBET) designed to mimic the gastric stomach. In the urban soils, the finest particles had the highest heavy metal (including Pb) concentrations but the bioaccessible fraction of Pbwas lowest in these finer particles. Despite evidence from electron microprobe work that Pb in urban garden soils tended to be highly heterogeneous and associated spatially with phosphorus in micron-sized particles, extraction tests failed to show that the phosphorus status of the soil had any consistent beneficial effect in reducing the bioavailability of the lead. Thus, the commonly recommended remediation scheme of amending urban Pb-contaminated soils with high doses of soluble phosphate may prove to be ineffective in reducing bioavailability of soil Pb to individuals exposed to these contaminated soils. Other means of reducing Pb bioavailability in urban soils, particularly amendment with composts, were shown to be relatively effective in reducing extractable Pb and may be a practical means of reducing vegetable crop contamination.

Publications

• Type: Journal Articles Status: Published Year Published: 2017 Citation: Lim, M, MB McBride and A Kessler. 2017. Arsenic bioaccumulation by Eruca sativa is unaffected by intercropping or plant density. Water Air and Soil Pollution 228, 364.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Cai, M, MB McBride, K Li and Z Li. 2017. Bioaccessibility of As and Pb in orchard and urban soils amended with phosphate, Fe oxide and organic matter. Chemosphere 173, 153-159.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Tai, YP, ZA Li and MB McBride. 2017. Dry cultivation enhances cadmium solubility in contaminated soils but minimizes cadmium accumulation in a leafy vegetable. Journal of Soils and Sediments 17, 2822-2830.

Progress 10/01/15 to 09/30/16

Outputs
Target Audience:We interact with urban gardeners, farmers, landowners and other community stakeholders (e.g., through gardening events and discussion forums in NYC, urban farming workshops, responding to information requests by email and phone). These interactions have indicated a need for comprehensive educational programs addressing diverse topics, including: (a)Training on site assessment for contaminants and soil sampling and testing protocols; (b)Information about and access toreliable, affordable, certified soil testing labs; (c)Simple guidelines for interpretation of soil test results that allow for site-specificconsiderations; (d)Assessment of contaminants in municipal compost and available soil/fill, and access to thesematerials; and (e)Possible liability issues or closure or avoidance of gardens if soil tests reveal contamination. We also publish our results in peer-review journals so that other research groups involved with urban soils contaminated by lead and other toxins can learn from our observations and experience. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project has provided the opportunity in the past year for one PhD-level graduate student (Xiaoyan Tang), and one research scientist( Cai Meifang)fromSouth China Botanical,to spend a year in our laboratory, learning new research methods and conducting research on chemical testing of soilsand measuring bioavailability of toxic metals in soils. How have the results been disseminated to communities of interest?We have disseminated our research results in peer-reviewed publications, but in addition have providedinterpretations of these results in less technical formtoto community stakeholders (gardeners, farmers, extensionagents) through gardening events and discussion forums in New York City, urban farming workshops, and byresponding to numerous information requests by email and phone calls. Fact sheets and workshops to address these topicscontinue to be developed to augment existing resources available at our CWMI website under the heading "Soil Quality". What do you plan to do during the next reporting period to accomplish the goals?Weintend to focus more of our research effort ontesting the effectiveness of commonly recommendedsoil remediation approaches, ranging fromphytoremediation to mulching to chemical stabilization of soil toxic metals using organic matter and phosphate fertilizers. There are numerous unsubstantiated andmisleading claims about the effectiveness of phytoremediation or phosphate stabilizationfor Pb or the potential for soil recontamination in urban settings that require an objective science-based re-evaluation to prevent urban farmers and gardeners fromwastingeffort and resources on ineffective practices. Field and greenhouse experiments to test these proposed practices for minimizing human exposure to toxic metals are underway.

Impacts
What was accomplished under these goals? The research effort continued to be mainly focused on the chemical extractability and bioavailability of toxic lead, arsenic and other metals in urban garden and old orchard soils using laboratory methods as well as field and greenhouse tests with vegetable crops. We learned that soils with the highest lead (Pb) contents also had the most easily extracted Pb, but higher organic matter in the soils reduced the extractability and the bioaccessibility measured using a physiologically based extraction test (PBET) designed to mimic the gastric stomach. In the urban soils, the finest particles had the highest heavy metal (including Pb) concentrations but the bioaccessible fraction of Pb and Ba was lowest in these finer particles. Despite evidence from electron microprobe work that Pb in urban garden soils tended to be highly heterogeneous and associated spatially with phosphorus in micron-sized particles, extraction tests failed to show that the phosphorus status of the soil had any consistent beneficial effect in reducing the availability of the lead to dissolution by a pH 4.8 buffer solution. Thus, the commonly recommended remediation scheme of amending urban Pb-contaminated soils with high doses of soluble phosphate may prove to be ineffective in reducing bioavailability of soil Pb to individuals exposed to these contaminated soils. Other means of reducing Pb bioavailability in urban soils, particularly amendment with composts, are now being evaluated more thoroughly.

Publications

• Type: Journal Articles Status: Published Year Published: 2015 Citation: McBride, MB. 2016. Extractability of Pb in urban gardens and orchards linked to soil properties. European Journal of Soil Science, 67, 686-694. Spliethoff, HM, RG Mitchell, H Shayler, LG Marquez-Bravo, J Russell-Anelli, G Ferenz, M McBride. 2016. Estimated lead (Pb) exposures for a population of urban community gardeners. Environmental Geochemistry and Health 38, 955-971. Cai, M , McBride, MB and Li, K. 2016. Bioaccessibility of Ba,Cu,Pb and Zn in urban garden and orchard soils. Environmental Pollution, 208, 145-152. Marquez-Bravo, L.G., D. Briggs, H. Shayler, M. McBride, D. Lopp, E. Stone, G. Ferenz, K.G. Bogdan, R.G. Mitchell, H.M. Spliethoff. 2016. Concentrations of polycyclic aromatic hydrocarbons in New York City community garden soils: potential sources and influential factors. Environmental Toxicology and Chemistry , 35, 357-367.

Progress 10/01/14 to 09/30/15

Outputs
Target Audience:The target audienceincludes different sectors responsible for testing soils, advising gardeners on best practices, and using recommendations. They have been involved in discussions on needs for the testing of soils for Pb, As and other toxic metals, on the project design. They include Cornellextension educators involved in urban gardening and farming projects being developed in urban centers of New York State. They have direct experience with the difficulties of getting urban sites adequately tested for Pb and other contaminants, and will be consulted on gardener and extension educator interests in having more interpretable soil tests for metals. Direct contact with gardeners and farmers also occurs through telecommunications,meetings and workshops. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project in the past year engaged one graduate student (M Lim) and one undergraduate student in conducting field and greenhouse trials of arsenic and lead uptake by a number of different vegetable crops. How have the results been disseminated to communities of interest?In March 2015, We conducted aworkshop presentation to urban gardener groups at Greenthumb's GrowTogether in New York City, titled "What Can We Learn from Soil and Vegetable Test Results ?". In addition, lectures have been presentedto urban gardeners on soil chemistry and soil testing principles. In direct meetings with urban gardeners in Buffalo,soil and vegetable testing results and their implications have been explained. What do you plan to do during the next reporting period to accomplish the goals?The year 2 activities will investigatethe effectiveness of soil amendments such as iron oxide and organic matter (compost) in reducing the solubility and bioavailability of As and Pb in orchard and urban soils. Promising soil remediation approaches, both chemical and biological (phytoremediation), will be further evaluated in the field. The importanceof cultivar selection in limiting toxic metal transfer into vegetables will be further investigated.

Impacts
What was accomplished under these goals? Arugula (Eruca sativa) and collards (Brassica oleracea var. acephala), were grown at a former orchard where soils had been variably contaminated by lead arsenate pesticides. To test for the effect of compost on As and Pb transfer into plants, compost was added (0, 5, and 10% DW) to five plots representing a wide range of soil Pb and As. Arugula accumulated about 5 times higher As concentrations in above-ground tissues than collards, with high variability in individual plant concentrations. Soil to arugula transfer (uptake) coefficients were higher for As than for Pb, and increased with soil As. Arugula contamination by Pb was significantly correlated to soil total Pb, but collard contamination was not. Evidence was found using Al and Ti asindicators of soil particle contamination of plant tissues that Pb in arugula was primarily due to soil particle deposition on foliar surfaces. Compost amendments reduced 0.01 M CaCl2 -extractable Pb but increased extractable As in the orchard soils. However, compost had the beneficial effect of reducing both As and Pb concentrations in harvested arugula grown on most of the plots. Subsequent studies showed that, in 16 different cultivars of arugula, a nearly 3-fold range in arsenic bioaccumulation was observed when these plants were grown at the orchard site. The results revealarugula to be an excellent bioindicator of soil arsenic contamination, as it concentrates but does not hyperaccumulate arsenic.

Publications

• Type: Journal Articles Status: Published Year Published: 2015 Citation: McBride, MB, HA Shayler, JM Russell-Anelli, HM Spliethoff, LG Marquez-Bravo. 2015. Arsenic and lead uptake by vegetable crops grown on an old orchard site amended with compost. Water Air and Soil Pollution, 226, 265-
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Lim, MP, MB McBride. 2015. Arsenic and lead uptake by brassicas grown on an old orchard site. Journal of Hazardous Materials 299, 656-663.