Grantee Research Project Results
2004 Progress Report: Biogeochemistry of Arsenic in Contaminated Soils of Superfund Sites
EPA Grant Number: R830842Title: Biogeochemistry of Arsenic in Contaminated Soils of Superfund Sites
Investigators: Sarkar, Dibyendu , Datta, Rupali
Institution: The University of Texas at San Antonio
EPA Project Officer: Hahn, Intaek
Project Period: August 1, 2003 through July 31, 2005 (Extended to July 31, 2007)
Project Period Covered by this Report: August 1, 2003 through July 31, 2004
Project Amount: $391,473
RFA: Superfund Minority Institutions Program: Hazardous Substance Research (2002) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Safer Chemicals , Land and Waste Management
Objective:
The overall objective of this research project is to explore the central hypothesis that more focused and cost-effective remedial methods can be designed if arsenic (As) species with higher solubility and greater bioavailability are identified as a function of soil biogeochemical properties. The specific objectives of this research project are to: (1) examine the relationship between geochemical speciation and As bioavailability as a function of soil properties; (2) evaluate the use of low-cost chemical amendments, such as water treatment residuals (WTRs), in decreasing soil-As availability; and (3) identify the physiological and genetic mechanisms behind uptake and detoxification of As in a hyperaccumulating plant. Collectively, this new knowledge is expected to have a positive impact in our reevaluation of the current human health risk assessment practices from exposure to As-contaminated soils by understanding how soil biogeochemical properties influence As uptake and bioavailability.
Progress Summary:
In Phase I of this study, we selected four types of soils based on certain physicochemical properties that are most likely to influence As retention. These are: (1) Immokalee series (Florida), an acid soil with 93 percent sand and low oxalate-extractable Fe+Al (hence, likely to have minimum As adsorption capacity); (2) Millhopper series (Florida), an acid sandy loam with high extractable Fe+Al (hence, likely to have high As adsorption capacity); (3) Pahokee Muck series (Florida), high in organic matter in addition to high Fe/Al and Ca/Mg content (high potential for As retention); and (4) Orelia series (Texas), a clay soil with high levels of Ca/Mg and Fe/Al and high pH. The uncontaminated surface soil (0-6") samples were air dried and passed through a 2 mm sieve prior to characterization.
We characterized the soils for pH, electrical conductivity, particle size, and water content following standard protocols. Organic matter content was determined using the loss-on-ignition method. Exchangeable cations were extracted in 1 M ammonium acetate (pH 7.0) and cation exchange capacity was determined by removal of ammonium ions. Plant-available Ca, Mg, and P were extracted by Mehlich III solution. Oxalate-extractable Fe and Al were obtained using Tamm’s reagent. Total recoverable Ca, Mg, Fe, Al, P, and As were obtained by soil digestion according to U.S. Environmental Protection Agency (EPA) Method 3050B. As was analyzed using graphite furnace atomic absorption spectrometry (GFAAS).
In mid June 2004, we started the greenhouse experiments. We spiked the soils with two arsenical pesticides, sodium arsenate and dimethylarsenic acid (DMA), at two rates representative of Superfund soil As concentrations (675 and 1,500 mg kg-1). Pesticide-amended soils were packed in the top 6" of PVC columns (13" tall x 6" id), with a reservoir compartment to hold the excess leachate and a hole fitted with nalgene tubing to collect the leachate; the bottom 6" of the columns were filled with bleached white sand with no As retention capacity. Rice was used as the test crop. For each pesticide treatment, there are a total of 48 columns: 4 soils x 2 pesticides x 2 rates x 3 replicates, plus controls. The first leaching was induced after 2 weeks of pesticide spiking to promote regermination and growth of rice, which experienced less than 10 percent germination because of the toxic effects of high-pesticide concentrations; the second leaching event took place in September. Rice will be grown for a period of 6 months. We already have sampled the soils twice: immediately after spiking (“time 0”) and 3 months after spiking (“time intermediate”). We will sample the soils again at the end of the 6-month period (“time final”). The soils collected at time 0 and time intermediate were extracted by a sequential extraction technique. Soils also were assessed for bioavailable As using an in vitro gastrointestinal method and total As using EPA Method 3050B. The leachates collected were analyzed for As. The difference in soil As concentrations at the various time periods reflect a combined effect of adsorption, leaching, uptake, and soil aging. Some of the plant tissues were harvested at time intermediate, weighed, dried, acid digested, and analyzed for As using GFAAS with spikes, internal standards, and replicates as quality assurance checks. Analysis of certain samples was repeated at fixed intervals to confirm the reproducibility of values; replicate data that deviated by more than 5 percent were discarded and samples were reanalyzed.
We started the second set of column experiments in late June 2004 to examine the impact of WTRs on the speciation and bioavailability of As in a dynamic soil-water-pesticide-plant system. This study involved two soils (Immokalee and Orelia), the same two pesticides added at the rate of 1,500 mg kg-1, and two WTRs (Al-WTR and Fe-WTR) applied at two rates (5% and 10%) with two replicates for each treatment. Rice was used as the test crop; however, leaching was not induced until late September because of the unhindered germination and growth of rice. Apparently, the WTRs were capable of converting soluble As to forms not available for plant uptake within a very short period of time following pesticide spiking. Similar to the prior study, columns were maintained at 70-80 percent of their optimal water holding capacity. The same speciation and bioavailability experiments were performed at time 0 and time intermediate, and the leachates were analyzed for As. Plant tissues were harvested in late September and analyzed for As concentration. The same quality assurance/quality control measures were followed.
In addition to the column studies, where we spiked the previously uncontaminated soils, we also experimented with As-containated soils with varying physicochemical properties from 12 former cattle and sheep dipping-vat sites in Florida and Australia and evaluated As speciation and bioavailability in these soils as a function of soil properties. Although we can draw only preliminary conclusions at this time, we can tentatively state that in all of these studies, soil chemistry dictated As speciation in soils and hence its bioavailability. Therefore, the “one size fits all” approach that EPA currently recommends during health risk assessments (usage of an input value of 100% bioavailability irrespective of soil types) may need to be reevaluated. Our preliminary results also indicate that DMA, an organo-arsenical pesticide, considered to be relatively less toxic and still allowed for usage by EPA, may undergo chemical transformation to potentially carcinogenic inorganic forms in mineral soils . Results obtained so far from the WTR study suggest that significantly higher levels of the added As were transformed into bound forms, thus decreasing bioavailability in Fe-WTR- and Al-WTR-amended soils. We expect that the outcome of the study will aid in the development of a suitable in situ chemical method for cleanup of As-contaminated soils.
Future Activities:
We will continue the ongoing greenhouse experiments to collect time-final data (scheduled in November 2004) on plant uptake; total, extractable, and bioavailable soil As as a function of soil properties; and equilibration time. Phase II column studies using Chinese brake fern, an As hyperaccumulator, will start in March 2005 and will attempt to decipher the molecular mechanisms behind uptake and detoxification of As in these plants.
Journal Articles on this Report : 9 Displayed | Download in RIS Format
| Other project views: | All 47 publications | 11 publications in selected types | All 9 journal articles |
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Datta R, Sarkar D. Human health risk from exposure to soil arsenic: Does one size fit all? Geological Society of America Abstracts With Program 2004;36(5):332. |
R830842 (2004) |
not available |
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Khairom A, Sarkar D, Datta R. Bioavailability of arsenic and phosphorus in a sandy soil amended with water treatment residuals. Geological Society of America Abstracts With Program 2004;36(5):334. |
R830842 (2004) |
not available |
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Quazi S, Sarkar D, Datta R, Sharma S. Greenhouse study on arsenic speciation and bioavailability in two pesticide-contaminated soils of Florida: preliminary results. Geological Society of America Abstracts With Program 2004;36(5):399. |
R830842 (2004) |
not available |
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Sarkar D, Parra-Noonan M, Datta R. Bioavailability of arsenic in cattle dipping vat site soils as a function of soil chemistry. Geological Society of America Abstracts With Program 2004;36(5):506. |
R830842 (2004) |
not available |
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Therapong C, Datta R, Sarkar D. Arsenic stress response in rice: comparison between organic and inorganic pesticides. Geological Society of America Abstracts With Program 2004;36(5):398. |
R830842 (2004) |
not available |
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Vandanapu V, Sarkar D, Datta R, Sharma S. Arsenic adsorption and desorption by water treatment residuals: preliminary results. Geological Society of America Abstracts With Program 2004;36(5):334. |
R830842 (2004) |
not available |
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Datta R, Sarkar D. Consideration of soil properties in assessment of human health risk from exposure to arsenic-enriched soils. Integrated Environmental Assessment and Management 2005;1(1):55-59. |
R830842 (2004) R830842 (2005) R830842 (2006) |
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Sarkar D, Parra-Noonan M, Datta R. Distribution of arsenic in chemically variant dipping vat site soils. Bulletin of Environmental Contamination and Toxicology 2004;73(5):838-845. |
R830842 (2004) R830842 (2005) R830842 (2006) |
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Sarkar D, Datta R, Sharma S. Fate and bioavailability of arsenic in organo-arsenical pesticide-applied soils. Part-I: incubation study. Chemosphere 2005;60(2):188-195. |
R830842 (2004) R830842 (2005) R830842 (2006) |
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Supplemental Keywords:
soil, arsenic, As, pesticides, in vitro, bioavailability, speciation, leachate, adsorption, exposure, risk assessment, water treatment residuals, WTRs, chemical remediation, hyperaccumulator fern, phytoremediation, environmental chemistry, plant genetics, molecular biology, health, international cooperation, pollutants/toxics, waste, water, contaminated sediments, geochemistry, hazardous, hazardous waste, health risk assessment, risk assessments, water pollutants, arsenic exposure, arsenic mobility, assessment methods, bioaccumulation, biogeochemistry, contaminant transport, contaminated sediment, contaminated soil, ecology assessment models, reservoir sediments, risk management, sediment quality survey, sediment transport, Superfund site, water quality,, Health, RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, Water, POLLUTANTS/TOXICS, Hazardous, Risk Assessments, Contaminated Sediments, Hazardous Waste, Geochemistry, Arsenic, Environmental Monitoring, Water Pollutants, arsenic mobility, contaminant transport, assessment methods, contaminated sediment, sediment quality survey, water quality, biogeochemistry, contaminated soil, bioaccumulation, sediment transport, water treatment, ecology assessment models, superfund site, reservoir sediments, risk management, arsenic exposureProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.