Progress 10/01/11 to 09/30/14
Target Audience: We have made an effort to publish our findings in peer-review journals particularly in the last year of the project. The audience for these publications includes agricultural scientists who are engaged in the study of contaminants in urban gardens. Also, NGOs (such as Greenthumb in New York City) are a key audience for our published research findings, as they work directly with individual gardeners and farmers to foster the growth of food production in urban areas while encouraging practices that minimize risk from soil contaminants. Changes/Problems:
What opportunities for training and professional development has the project provided? The project provided the opportunity for one Fulbright Fellow from Slovenia and two visiting soil scientists from the South China Botanical Garden, Zhuang Ping and Yi Ping, to each spend a year in our laboratory, conducting research on chemical testing and bioavailability of toxic metals in soils. In addition, several undergraduate students have worked on specific experiments within the project over the summer months. How have the results been disseminated to communities of interest? In addition to peer-review publications, we have disseminated our results to community stakeholders through numerous gardening events and discussion forums in NYC (e.g, GrowTogether), urban farming workshops in Buffalo, and by responding to many information requests by email and phone. Fact sheets, workshops and powerpoint presentations to address the topic of soil contamination and interpretation of soil test results have been created and presented over the time of this project to augment existing resources available at our CWMI website. What do you plan to do during the next reporting period to accomplish the goals?
What was accomplished under these goals?
Research in this project focused on methods of testing contaminated soils for toxic metals (particularly arsenic and lead) in urban and other contaminated environments, measuring food crop uptake of these metals, and reducing bioavailability by soil amendment and remediation. Regarding testing methods, we have found that soil tests can in some cases be simplified and made less costly without compromising accuracy significantly. For lead, this has important practical implications, as a simple 1.0 M nitric acid extraction estimates total soil Pb quite reliably, whereas a commonly used screening test for Pb using Morgan’s solution is not very reliable for estimating total Pb in soils with different sources of Pb contamination. The extreme heterogeneity of Pb distribution in urban soils has also been proven by our work, with important implications for soil sampling protocols needed to characterize contaminated sites. Field and greenhouse assays of Pb and As uptake into various vegetable crops showed that transfer from soil to leafy green vegetables was more efficient for As than for Pb. Some leafy greens had inherently higher tendency to bioaccumulate. As than others, with arugula taking up As more readily than collards or lettuce. Our studies also demonstrated, using aluminum (Al) as a marker element for soil particle contamination of plant tissues that most Pb contamination of leafy green vegetables was due to particulate deposition from wind or rain splash. In contrast to leafy greens, vegetable fruits (e.g., bean, tomato) were much less prone to accumulating Pb or As from the soils. Our conclusions are that vegetable fruit crops (beans, tomato) can be safely grown on orchard soils moderately contaminated by historical lead arsenate use. However, leafy greens and root crops are the most prone to contamination by Pb and As. Attempts to remediate the Pb and As-contaminated soils showed that high levels of added organic matter (compost) reduced bioavailability of Pb to both soil invertebrates and to crops, as indicated by soil testing and bioassays. However, organic matter amendments did not reduce As bioavailability as indicated by soil tests and bioassays. Other soil amendments, such as Fe oxides and phosphates, were unsuccessful in remediation as indicated by their failure to reduce Pb and As in soil solution, in soil extracts and in leafy green vegetables. Phosphate amendment had the additional undesirable side-effect of increasing As solubility in the soil; recommendations presently being given to amend severely Pb-contaminated soils with phosphates are not supported by our work.
McBride, MB, HA Shayler, HM Spliethoff et al. Concentrations of lead, cadmium and barium in urban garden-grown vegetables: the impact of soil variables. Environmental Pollution 194, 254-261.
Mitchell, RG, Spliethoff, HM , Ribaudo, LN, Lopp, DM, Shayler, HA, Marquez-Bravo, LG, Lambert, VT, Ferenz, GS, Russell-Anelli, JM, Stone, EB, McBride MB.
Lead (Pb) and other metals in New York City community garden soils: Factors influencing contaminant distributions. Environ Pollution, 187, 162-169.
Progress 10/01/12 to 09/30/13
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 in Buffalo, responding to information requests by email and phone). These interactions 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:
What opportunities for training and professional development has the project provided? The project provided the opportunity for two visiting soil scientists from the South China Botanical Garden, Zhuang Ping and Yi Ping, to spend a year in our laboratory, learning new research methods and conducting research on chemical testing and bioavailability of toxic metals in soils. How have the results been disseminated to communities of interest? We have disseminated our research results and interpretations to community stakeholders (gardeners, farmers, extension agents) through gardening events and discussion forums in New York City, urban farming workshops in Buffalo, and by responding to information requests by email and phone calls. Additional fact sheets and workshops to address these topics continue 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? We will continue the field and greenhouse studies of Pb and As uptake into vegetable crops grown in soils variably contaminated with these toxic metals. Since both the type of crop being grown and the level of soil contamination determine risk and must be factored into recommendations to stakeholders, additional research will be designed to study important crops not investigated to this point. We also intend to further investigate soil remediation approaches, ranging from phytoremediation to chemical stabilization of soil toxic metals. We believe that the only way to counter unsubstantiated and misleading claims that still persist about the effectiveness of phytoremediation (especially for lead) and several other soil remediation schemes is to present the facts objectively, preferably based on field experiments.
What was accomplished under these goals?
Research in this project focuses on testing contaminated soils for toxic metals (arsenic, lead, and cadmium) in urban and other disturbed environments, measuring plant uptake of these metals, and reducing bioavailability by soil remediation. Our specific objectives in the past year were to assess the potential for soil amendments to limit Pb and As solubility and bioavailability to leafy green vegetables from contaminated orchard and urban soils. To do this, we measured soluble and extractable Pb and As in two contaminated soils pre-amended with soluble phosphate, gypsum, Fe oxide and peat. In addition, greenhouse assays of Pb and As uptake into a lettuce-mustard mixed crop and into other common garden crops (carrots, beans, tomatoes) from amended and unamended soils were conducted by measuring leafy tissue metal concentrations using ICP-MS. Attempts to reduce Pb and As bioavailability were unsuccessful for all amendments as indicated by their failure to reduce Pb and As in soil solution, in soil extracts and in the leafy greens. Phosphate amendment did, however, increase As solubility. Transfer from the soil to the edible greens was more efficient for As than for Pb. Generally, beans and tomato were much less prone to accumulating Pb or As from the soils than carrots or lettuce. Several indicators suggested that Pb in the greens derived largely from soil particle contamination. In summary, vegetable fruit crops (beans, tomato) could be safely grown on orchard soils moderately contaminated by historical lead arsenate use. However, none of the soil amendments tested showed promise in reducing the phytoavailability of Pb or As when applied at rates feasible for field-scale remediation.
McBride MB. 2013. Arsenic and lead uptake by vegetable crops grown on historically contaminated orchard soils. Applied and Environmental Soil Science. Vol 2013 ID 283742, 8 pp.
Tai Y, MB McBride and Z Li. 2013. Evaluating specificity of sequential extraction for chemical forms of lead in artificially-contaminated and field-contaminated soils. Talanta 107, 183-188.
Fleming M, Y Tai, P Zhuang and MB McBride. 2013. Extractability and bioavailability of Pb and As in historically contaminated orchard soil : effects of compost amendments. Environmental Pollution
Wharton, SE, HA Shayler, HM Spliethoff. LG Marquez-Bravo, L Ribaudo and
MB McBride. 2012. A comparison of screening tests for soil Pb. Soil Science 177, 650-654.
McBride MB, T Simon, G Tam and S Wharton 2012. Lead and arsenic uptake by leafy vegetables grown on contaminated soils: Effects of mineral and organic amendments. Water Air and Soil Pollution 224, 1378.
Progress 10/01/11 to 09/30/12
OUTPUTS: Research in this project continues to focus on the challenges presented by testing of soils for heavy metals in the urban environment, with most of the emphasis being on the potentially toxic metals lead (Pb), cadmium (Cd), zinc (Zn) and arsenic (As). We have evaluated simple and inexpensive screening tests for estimating total Pb, As, Cd and Zn concentrations in contaminated urban garden soils. We have found that 1M HNO3 extraction compares favorably with other commonly used "screening test" for Pb in urban soils, and total soil Cd and Zn can also be estimated reliably by the same test. In fact, we have demonstrated that our estimate of soil Cd by this screening method, using flame atomic absorption to measure Cd in the acid extracts, provides a more reliable measure of total soil Cd than the widely used microwave acid digestion of soil (EPA Method 3050/3051) with ICP-emission analysis of the digests. Recently, the EPA has recognized that "false positive" or "biased" results for analysis of heavy metals in soils by ICP-emission is a severe problem (particularly for arsenic and thallium), indicating that alternative testing methods may be needed for some toxic metals in soils. Our recent extensive surveys of soils in urban areas, particularly private yards and community gardens, show that Pb is the toxic metal most frequently at levels of concern for human exposure. Unfortunately, for many gardeners, the cost of having soil testing done for toxic metals by standard methods (e.g., 3050 EPA) is an impediment to the adequate assessment of soil contamination because Pb is typically very heterogeneously distributed in gardens and private yards, requiring intensive sampling and testing in order to establish its spatial distribution. Consequently, our simple and inexpensive screening test using 1 M nitric acid to estimate total metal concentrations, particularly Pb, in contaminated urban garden soils, will provide gardeners with a practical and affordable alternative to standard soil testing. The results for the Pb screening test have been summarized in two manuscripts, one already published and the other recently accepted for publication. A third manuscript evaluating the screening test for Cd and Zn is in preparation. We are presently working on evaluating the 1 M HNO3 screening test for soil arsenic (As), a metalloid of increasing concern for human health. Soil Pb presents a serious challenge for remediation because phytoremediation is not feasible ( there are no known strong Pb hyperaccumulator plants), and attempts to stabilize Pb in soils and thereby reduce its bioavailability have not been widely successful. However,The removal of Pb from soils using chelating agents to solubilize the metal has been demonstrated by other researchers , and we are beginning experiments to determine whether Pb in urban garden soils is readily susceptible to dissolution and removal. There are numerous obstacles and disadvantages to this chemical remediation approach, however, and we intend to evaluate these potential pitfalls. PARTICIPANTS: Dr. Metka Udovic spent 6 months in my laboratory in 2010-2011, conducting research on correlating soil test methods for Pb and As with bioavailability assays in soil invertebrates. In addition, two visiting scientists from the South China Botanical Garden have been involved in soil toxic metals research in my laboratory since early 2012. One of them (Yi Ping) is a Ph.D. candidate, and the research she has completed here will become part of her graduate thesis when she returns to China. TARGET AUDIENCES: Our interactions with community stakeholders (e.g., through gardening events and discussion forums in NYC and Ithaca, 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. Additional fact sheets, workshops, etc. to address these topics continue to be developed to augment existing resources available at our CWMI website under the heading "Soil Quality". PROJECT MODIFICATIONS: Not relevant to this project.
The results from the soil lead (Pb), cadmium (Cd) and zinc (Zn) test comparisons have produced a highly useful observation in practice - extraction of a wide range of soil types with 1 M nitric acid provides a very good approximation of total lead, cadmium and zinc in the soil without the added effort and expense of measuring total metals using an acid soil digestion process. Furthermore, the Pb, Cd and Zn in the acid extracts are easily measured by either standard flame atomic absorption or by ICP emission with equivalent results. Because many laboratories, particularly in underdeveloped countries, have greater access to atomic absorption equipment than to ICP because of lower cost, these simpler "screening" tests may be adopted by many laboratories for practical reasons. We have used the screening test for Pb to advantage in assisting urban gardeners to get rapid spatial mapping of soil Pb concentrations for their gardens, allowing them to best site locations for vegetable-growing areas. This screening test is also now offered as a less expensive soil test for lead by the Cornell Nutrient Analysis Laboratory. Our observation of extreme Pb spatial heterogeneity in urban soils has informed our recommendations on the minimum number of discrete soil samples needed to characterize gardens and yards, and the methods best used to combine and homogenize these samples prior to analysis. Our results indicate that it is inadvisable to base management of contaminated yards and gardens on the results from one or two composited soil tests. In addition, thorough grinding of urban soils has the effect of reducing Pb soil test variability. Our understanding of heterogeneity in Pb concentrations found at several spatial scales in urban soils is helping to guide future sampling designs in New York City community gardens, and is also influencing our recommendations to homeowners who wish to test their own yards for Pb and other toxins.
- Udovic, M and MB McBride. 2012. Influence of compost addition on lead and arsenic bioavailability in reclaimed orchard soil assessed using Porcellio scaber bioaccumulation test. Journal of Hazardous Materials, 205-206, 144-149.
- McBride, MB. 2011. A comparison of reliability of soil cadmium determination by standard spectrometric methods. Journal of Environmental Quality 40, 1863-1869