Source: CORNELL UNIVERSITY submitted to
REDUCING TOXIC METAL TRANSFER TO FOOD CROPS FROM CONTAMINATED SOILS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
REVISED
Funding Source
Reporting Frequency
Annual
Accession No.
1013734
Grant No.
(N/A)
Project No.
NYC-125449
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Oct 1, 2017
Project End Date
Sep 30, 2021
Grant Year
(N/A)
Project Director
Mcbride, MU.
Recipient Organization
CORNELL UNIVERSITY
(N/A)
ITHACA,NY 14853
Performing Department
Crop & Soil Sciences
Non Technical Summary
Historically polluted soils are an important source of human exposure to toxic metals such as lead, cadmium and arsenic, particularly in urban areas. Human exposure can occur by inhalation of dust, by direct ingestion of soil (particularly the case for young children), and by consumption of vegetables and fruitscontaminated by physical processes (soil particles attached to plants) or by plant uptake via roots.This project will investigate the processes by which food crops become contaminated, identify which crops are most prone to contamination, test methods of remediating soils to reduce toxic metal uptake by crops, and share findings with gardeners.
Animal Health Component
0%
Research Effort Categories
Basic
30%
Applied
50%
Developmental
20%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
71101101150100%
Goals / Objectives
Present guidelines for urban gardens are based solely on soil total concentrations of toxic metals. These are clearly inadequate, as our recent work in urban gardens shows only a weak dependency of vegetable lead content on the soil concentration of lead. This indicates that a more in-depth understanding is needed of the processes by which food crops are contaminated.To this end, the specific research objectives of the present project are to:Determine the exact mechanisms by which toxic elements, especially lead and arsenic, contaminate food crops, and identify sources of the contaminants.Explain the large differences observed in toxic metal accumulation by different crop types.Assess the effectiveness of soil remediation techniques, particularly stabilization by soil amendments such as composts, in reducing toxic metal transfer into vegetables.
Project Methods
Toxic metals can contaminate food crops by three distinct processes; each may be influenced by site-specific environmental, soil, and crop factors:(a) uptake from soil solution into roots and transport from roots to the harvested part of the crop;(b) crop contamination by soil particles from dust or splash originating below the plants;(c) crop contamination by aerosol particles originating from more remote locations.To identify mechanisms of crop contamination (Objective 1), we will measure toxic metals in vegetable crops grown in both urban (NYC garden) and more rural (Cornell field) sites. We will transport soils from urban sites to create metal-contaminated garden beds in rural sites. Conversely, we will create uncontaminated (initially) garden beds in urban sites by transporting "clean soils" from uncontaminated sites. By growing and analyzing vegetable crops in both contaminated and uncontaminated soils at rural and urban sites, we will determine the extent of crop contamination by the processes listed above. Our earlier research established that crop analysis for insoluble elements (aluminum, titanium) allows us to estimate the extent to which crop contamination is due to the physical contamination of plant surfaces. Greenhouse studies will complement field studies; crop contamination by the two physical contamination mechanisms are generally much lower under greenhouse growing conditions. This combination of experiments will isolate those mechanisms largely responsible for crop contamination, and point to management most effective in minimizing toxic metal concentrations in the harvested crop.Lead and arsenic transfer from contaminated soils into vegetables will be measured in the greenhouse (Objective 2). Our past research has shown little transfer of toxic metals into most fruit crops, so we will focus on several leafy vegetables and root crops with high potential for contamination. To date we have tested several leafy vegetables but few root crops for lead uptake, basing recommendations for gardeners on limited data showing a potential for lead uptake by carrots. We need a more solid basis for root crop recommendations.To assess the effectiveness of soil remediation techniques (Objective 3), we will measure lead and arsenic transfer into contamination-prone vegetables (leafy crops) from compost-amended orchard soils containing high levels of lead and arsenic, as well as from compost-amended urban soils containing high levels of lead. Beneficial effects of the compost could include a chemical stabilization of metals such as lead (by complexation), improvement of soil structure to reduce particle mobility (in dust or rain splash), and improvement of crop growth causing "dilution" of toxic metals in the plant. This research will complement an ongoing CWMI study of compost quality across NYS.Research findings will inform Extension activities as we respond more comprehensively to stakeholders impacted by soil contamination concerns.

Progress 10/01/19 to 09/30/20

Outputs
Target Audience:Our research has the goal of improved understanding of the bioavailability of toxic metals, particularly lead (Pb), in soils, and possible methods of remediation of urban lead-contaminated soils to reduce human exposure to this toxic metal. Since regulators at present use total rather than bioavailable quantity of toxic metals in soils to set rules and guidelines, our results are directed at these agencies in order to provide a more scientific basis for such rules. In addition, our interactions with landowners and other community stakeholders (e.g., through gardening events and discussion forums in New York City (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. All of these topics are informed by our past and ongoing research on the behavior of metal contaminants in urban garden soils. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project has provided the opportunity in 2019 and 2020 for two PhD-level graduate students from China, Yuting Zhou from Zhejiang University, and Xinxin Li from Shandong University, to each spend a year in our laboratory, learning new research methods and conducting research on chemical testing of soils and 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. In addition we have provided interpretations of our results on soil remediation to reduce exposure to lead in less technical form to community stakeholders (gardeners, farmers, extension agents) through gardening events and discussion forums in New York City, Buffalo, Pittsburgh and other urban centers via urban farming workshops, and by responding to numerous information requests by email and phone calls. Fact sheets and workshops to address these topics continue to be developed to augment existing resources and are available at our newly developed Healthy Soils website: blogs.cornell.edu/healthysoils/ What do you plan to do during the next reporting period to accomplish the goals?We have conducted a series of Pb adsorption experiments on organic polymers, including tannic acid, humic acid, and carboxymethylcellulose, in an effort to determine the types of functional groups in natural soil organic matter that are involved in Pb2+ bonding. The Pb ion-selective electrode was used in these studies to measure the free Pb2+ ions in solution at equilibrium with the organic solids. The resulting data will be analyzed in the coming year to calculate partitioning coefficients of Pb on organic polymers, and provide better understanding of the critical role that soil organic matter has in immobilizing and reducing bioavailability of Pb in soils. Experiments have also been completed in determining the importance that biological activity in soils can have in controlling Pb solubility and bioavailability. We have measured the "rhizosphere effect", that is, the impact that plant roots have on Pb solubility in the soil and potential for plant uptake. This involved extracting the soil water from Pb-contaminated soils that either do or do not have established plant populations. The results have been summarized in a manuscript that is now under review in the high-impact journal Environmental Pollution.

Impacts
What was accomplished under these goals? Our overall goal with this project is to improve our understanding of the mechanisms by which solubility and bioavailability of toxic metals in soils contaminated by past uses are controlled and influenced by soil physical, chemical and biological properties. Toxic heavy metals such as Pb and Cd are retained in soils by one or more processes depending upon soil properties. These processes include chemical adsorption on mineral surfaces, precipitation as carbonates, sulfates and phophates, and complexation by natural organic polymers (humic materials) in the soil. In this particular funded period, our research focused on thechemical adsorption and precipitation reactions of Cd and Pb. Adsorption isotherms of both Pb and Cd over a very wide concentration range were curvilinear and were better modeled using the linearized Freundlich compared to the linearized Langmuir isotherm. Pb adsorbed more strongly than Cd on all soils, but soil pH, soil organic matter content, CEC and total Mn were positively correlated with the Pb and Cd bonding constants of the soils. Experiments were completed on the precipitation reactions of Pb with carbonate, sulfate and phosphate with mineral precipitates identified based upon Fourier Transform IR and X-ray diffraction methods. Finally, studies of the bonding of Pb ions by natural and synthetic organic polymers were conducted to determine the effects of functional group type, pH and metal loading on the bonding affinity for these polymers. We are in the process of finalizing manuscripts on the latter two studies for publication in peer-review journals.

Publications

  • Type: Journal Articles Status: Published Year Published: 2020 Citation: Zhou, Y , S Sherpa, MB McBride. 2020. Pb and Cd chemisorption by acid mineral soils with variable Mn and organic matter contents. Geoderma Vol. ? 368,Article No. 114274


Progress 10/01/18 to 09/30/19

Outputs
Target Audience:Our research is undertaken to better understand the bioavailability of toxic metals, particularly lead, in soils. Since regulators at present use total rather than bioavailable quantity of toxic metals in soils to set rules and guidelines, our results are directed at these agencies in order to provide a more scientific basis for such rules. In addition, our interactions with landowners and other community stakeholders (e.g., through gardening events and discussion forums in New York City, 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. All of these topics are informed by our past and ongoing research on the behavior of metal contaminants in urban garden soils. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project has provided the opportunity in 2018-2019 for two PhD-level graduate students from China, Yuting Zhou from Zhejiang University, and Xinxin Li from Shandong University, to each spend a year in our laboratory, learning new research methods and conducting research on chemical testing of soils and measuring bioavailability of toxic metals in soils. In addition, one Cornell undergraduate student was employed over the summer of 2019 to conduct experiments on the adsorption of Pb ions by natural organic polymers. How have the results been disseminated to communities of interest?We have disseminated our research results in peer-reviewed publications. In addition we have provided interpretations of our results in less technical form to community stakeholders (gardeners, farmers, extension agents) through gardening events and discussion forums in New York City, Buffalo, Pittsburgh and other urban centers via urban farming workshops, and by responding to numerous information requests by email and phone calls. Fact sheets and workshops to address these topics continue to be developed to augment existing resources and are available at our newly developed Healthy Soils website : blogs.cornell.edu/healthysoils/ What do you plan to do during the next reporting period to accomplish the goals?We are in the process of conducting a series of Pb adsorption experiments on organic polymers, including tannic acid, humic acid, and carboxymethylcellulose, in an effort to determine the types of functional groups in natural soil organic matter that are involved in Pb2+bonding. The Pb ion-selective electrode is being used in these studies to measure the free Pb2+ions in solution at equilibrium with the organic solids. The resulting data will be used to calculate partitioning coefficients of Pb on organic polymers, and provide better understanding of the critical role that soil organic matter has in immobilizing and reducing bioavailability of Pb in soils. Experiments are also underway in determining the importance of biological activity in soils in controlling Pb solubility and bioavailability. Specifically, we are measuring the "rhizosphere effect", that is, the impact that plant roots have on Pb solubility in the soil and potential for plant uptake. This involves extracting the soil water from Pb-contaminated soils that either do or do not have established plant populations.

Impacts
What was accomplished under these goals? The overall goal is to better understand the mechanisms by which the solubility and bioavailability of toxic metals in soils contaminated by past uses are controlled and influenced by soil physical, chemical and biological properties. Research was completed on the specific adsorption of Pb and Cd by acid soils common in the Northeastern states.Adsorption isotherms of both Pb and Cd over a very wide concentration range were curvilinear and were better modeled using the linearized Freundlich compared to the linearized Langmuir isotherm. Pb adsorbed more strongly than Cd on all soils, but soil pH, soil organic matter content, CEC and total Mn were positively correlated with the Pb and Cd bonding constants of the soils. Work conducted in our laboratory had earlier shown that solid-phase Pb oxalate is sufficiently stable relative to Pb phosphates that it can limit Pb solubility in low pH (<5.5) environments, but also that oxalate complexes strongly enough with Pb ions to partially dissolve Pb phosphate and raise the solubility of Pb. We have now further investigated whether Pb solubility in soils and water could be limited by co-precipitation of Pb oxalate with Ca oxalate. Ca oxalate is a relatively insoluble and very commonly occurring biomineral in plants and soils. We found that sequestration of Pb into Ca-oxalate to form a solid solution substantially lowered Pb solubility relative to that of pure Pb oxalate to an extent inversely proportional to the Pb mole fraction for Pb mole fractions less than 0.1. Characterization of the Pb-Ca oxalate co-precipitates by X-ray diffraction, optical microscopy, and Fourier transform infrared spectroscopy revealed that the whewellite (Ca-oxalate monohydrate) structure was destabilized by substitution of small amounts of Pb into the lattice, and thus the formation of the Ca-oxalate dihydrate (weddellite) was favored over the monohydrate. At Pb mole fractions above 0.20, discrete crystallites of Pb-oxalatewere identified. These new findings imply that Pb-Ca oxalate co-precipitates in the presence of Ca could reduce the solubility of Pb in Pb-contaminated acid soils.

Publications

  • Type: Journal Articles Status: Published Year Published: 2019 Citation: M.B. McBride, S. Kelch, M. Schmidt, Y. Zhou, L. Aristilde and C.E. Martinez. 2019. Lead solubility and mineral structures of co-precipitated lead-calcium oxalates. Environmental Science and Technology. M.B. McBride and Y. Zhou. 2019. Cadmium and zinc bioaccumulation by Phytolacca americana from hydroponic media and contaminated soils. International Journal of Phytoremediation, 21, 1215-1224. X.Y. Tang, R. Li, Y. Zheng and M.B. McBride. 2019. Health assessment of nickel-contaminated soils linked to chemical and biological characteristics. Soil Science Society of America Journal, 83, 614-623. M.B. McBride, S.E. Kelch, M.P. Schmidt, S. Sherpa, C.E. Martinez and L. Aristilde. 2019. Oxlate-enhanced solubility of lead (Pb) in the presence of phosphate: pH control on mineral precipitation. Environmental Science- Processes and Impacts, 21, 738-747.


Progress 10/01/17 to 09/30/18

Outputs
Target Audience:The need for affordable, locally-produced food continues to fuel interest in urban gardening and agriculture, as well as gardening efforts in a variety of residential and community spaces from backyards to schools to old farmlands across NYS. These activities help provide food security, economic savings, green space, opportunities for recreation and community building, reductions in environmental impacts of long-distance food transport and diverse benefits for public health. However, gardens and farms are often located on vacant lots and abandoned properties with a history of contamination, and can contain a number of soil chemicals that may contaminate fruits and vegetables and pose risks to human health. Our research and Extension project will address this challenge by providing science-based resources to help gardeners, farmers, and others maximize the many benefits of gardening and farming while minimizing risks from exposures to toxic metals in soils and vegetables. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project has provided the opportunity in 2017-2018 for one PhD-level graduate student (Yuting Zhou) from Zhejiang University, and one research scientist( Hou Meifang) from the Shanghai Institute of Technology, to spend a year in our laboratory, learning new research methods and conducting research on chemical testing of soils and measuring adsorption behavior of toxic metals such as lead and cadmium in soils. How have the results been disseminated to communities of interest?We have disseminated our research results in peer-reviewed publications. In addition we have provided interpretations of our results in less technical form to community stakeholders (gardeners, farmers, extension agents) through gardening events and discussion forums in New York City, Buffalo, Pittsburgh and other urban centers via urban farming workshops, and by responding to numerous information requests by email and phone calls. Fact sheets and workshops to address these topics continue to be developed to augment existing resources and are available at a newly developed Healthy Soils website : blogs.cornell.edu/healthysoils/ What do you plan to do during the next reporting period to accomplish the goals?We are in the process of conducting a series of laboratory experiments to explore in detail the processes by which the toxic heavy metals, lead (Pb) and cadmium (Cd), are adsorbed and made unavailable to plant or microbial uptake by soils. Strong adsorption in soils is attributable to the mineral (silicate clays, Fe and Mn oxides) and organic components of the soils. We will measure the chemical adsorption of the Pb2+ and Cd2+ ions on several soils of New York and Vermont containing very different levels of Fe, Mn and organic matter. Adsorption isotherms will be fit to the most appropriate mathematical function that describes the relationship between amount of metal adsorbed and the equilibrium concentration of metal in solution. The coefficients determined from these isotherms will allow us to determine which soil properties most strongly influence the affinity of these soils for Cd and Pb. We also will carry out a series of Pb adsorption experiments on organic polymers, including tannic acid, humic acid, and carboxymethylcellulose, in an effort to determine the types of functional groups in natural soil organic matter that are involved in Pb2+ bonding. The Pb ion-selective electrode will be used in these studies to measure the free Pb2+ ions in solution at equilibrium with the organic solids. The resulting data will be used to calculate partitioning coefficients of Pb on organic polymers, and provide better understanding of the critical role that soil organic matter has in immobilizing and reducing bioavailability of Pb in soils.

Impacts
What was accomplished under these goals? Based on our field research in urban and non-urban environments, we were able to establish that the contamination of leafy vegetables by lead was almost exclusively due to soil particle attachment to the plant surfaces, a process that was greatly diminished by mulch or cover of soils. In addition, we found that thorough washing of these vegetables with water could remove a large fraction of this contamination, but the use of surfactants or vinegar solutions provided no additional benefit. Research on soil processes affecting bioavailability of Pbshowed that Pb phosphates were most effective in immobilizing Pb at soil pH above 6. At lower pH, low molecular weight organic acids are able to compete with phosphate for reaction with Pb, elevating Pb solubility. Thus, biological processes in soils are likely toalter the solubility of Pb phosphates, reducing the effectiveness of phosphate amendments to soils as a means to reduce plant availability. Although we continue to explore possibilities for phytoremediation of metal-contaminated soils, our most recent studies using pokeweed as a hyperaccumulator plant have shown far greater potential for Zn and Cd than for Pb phytoextraction from soils. The reason for this is largely the much lower solubility of Pb compared to Zn and Cd in soil solution. Even when the contaminated soils were acidified using oxalic acid, little Pb transfer into the pokeweed shoots occurred. We conclude that reports of significant phytoextraction of Pb from contaminated soils are exaggerated or simply based on faulty data.

Publications

  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Li F, Z Li, P Mao, YW Li, YX Li, MB McBride, JT Wu, P Zhuang. 2018. Heavy metal availability, bioaccessibility and leachability in contaminated soil: effects of pig manure and earthworms. Environmental Science and Pollution Research International. DOI:10.1007/s11356-018-2080-5.
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Zhang, S, J Song, Y Cheng and MB McBride. 2018. Derivation of regional risk screening values for cadmium-contaminated agricultural land in the Guizhou Plateau. Land Degrad Dev., 29, 2366-2377.
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Tang, X , MP Lim and MB McBride. 2018. Arsenic uptake by arugula (Eruca vesicaria, L.) cultivars as affected by phosphate availability. Chemosphere 195, 559-566.
  • 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.
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Tang, X and MB McBride. 2018. Phytotoxicity and microbial respiration of Ni-spiked soils after field aging for 12 years. Environmental Toxicology and Chemistry 9999, 1-7.