Grantee Research Project Results
2005 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, 2004 through July 31, 2005
Project Amount: $391,473
RFA: Superfund Minority Institutions Program: Hazardous Substance Research (2002) RFA Text | Recipients Lists
Research Category: Land and Waste Management , Safer Chemicals , Hazardous Waste/Remediation
Objective:
The central hypothesis of this research project is that focused and cost-effective remedial strategies for arsenic (As)-contaminated soils can be designed if 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 major impact on 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 Year 2 of the project, we completed Phase II greenhouse experiments. This study started in the first week of May 2005, where brake fern (Pteris vittata) was grown on As-contaminated soils. Two soils, Immokalee (acidic, with 93% sand and low oxalate-extractable Fe+Al and therefore minimum As adsorption capacity) and Millhopper (acid sandy loam with high extractable Fe+Al and therefore high As adsorption capacity) were selected for this study. The soils were spiked with two pesticides (sodium arsenate and dimethylarsenic acid [DMA] at two rates (225 and 500 mg kg-1). Six inches of pesticide-amended soil was packed in polyvinyl chloride (PVC) columns (13" tall x 6' i.d.), with a reservoir compartment to hold excess leachate and a hole fitted with nalgene tubing to collect the leachate. The bottom 6 inches of the column were filled with bleached white sand with no As retention capacity. For each pesticide treatment, there were a total of 12 columns in addition to controls: 2 soils x 1 pesticide x 2 rates x 3 replicates. Brake fern was grown for a period of 6 months (May–October) in the greenhouse. All of the pots were maintained at 70-80 percent water holding capacity. Soil samples were collected three times, immediately after spiking the soils with pesticide (“time-0”), at the time of harvesting (“time-intermediate”) and at the end of the growing session (“time-final”). Leaching was not induced in these experiments because growth of brake fern was unaffected by the pesticide amendments. Soils collected were extracted for total As using U.S. Environmental Protection Agency (EPA) Method 3050B. Bioavailable As was estimated following the in vitro gastrointestinal method developed by Sarkar and Datta (2003). The difference in soil As concentrations between the various time periods reflects a combined effect of adsorption, uptake, and soil aging. Identification and quantification of bioavailable/transformed As species using high performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) is in progress. Plant tissue was harvested at time-intermediate (after 3 months) and time-final (after 6 months), dried, weighed, acid digested, and analyzed for As using graphite furnace atomic absorption spectrometry (GFAAS). Spikes, internal standards, and replicates were used as quality assurance checks. Analysis of certain check samples were 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.
The Phase I greenhouse study (started in Year 1 of this research project) using rice as a test crop was completed in Year 2. The soils were collected at a predetermined interval of time (i.e., after 1 year of soil pesticide incubation) from the Phase I pots (both with and without WTR-amended soils). Collected soil samples were extracted for soil As forms by a sequential extraction technique. Soils also were accessed for bioavailable As using the in vitro gastrointestinal method (Sarkar and Datta, 2003) and total As using EPA Method 3050B. The time-final rice plant tissues were collected in November 2004 (Year 2). In all these studies, soil chemistry dictated As speciation in soils and, therefore, its bioavailability. 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 results also indicate that DMA, an organo-arsenical pesticide, considered to be less toxic and still allowed for usage by EPA, may undergo chemical transformation to potentially carcinogenic inorganic forms in mineral soils.
Batch experiments were conducted at three initial As concentrations of 225, 2,250, and 7,500 mg kg-1 to determine the optimal conditions for As adsorption onto Al- and Fe-WTRs. The optimum solid:solution ratio was determined to be 1:5, and the most suitable equilibration time for the adsorption was 48 hours. Both Langmuir and Freundlich isotherm models fit the As adsorption data. Desorption experiments using Phosphate (P) (7500 mg kg-1) demonstrated minimal As release and for the most part, were unaffected by the P added, suggesting nonequilibrium hysteretic As sorption by both Al- and Fe-WTRs. Amending the soils with the WTRs increased their specific As sorption capacities. The static incubation study using Immokalee soil spiked with 90 mg/Kg of As and amended with Al- and Fe-WTRs (0-5%) indicated that As bioavailability decreased both as a function of WTR rate and incubation time from 100 percent at time-0 to 20 percent after 12 months. 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.
In Year 2 of the project, we also initiated comprehensive analysis of plant tissues (both rice and brake fern) to identify the role of the phytochelatins in the As detoxification in Pteris vittata (brake fern). Plant samples collected from Phase I and II greenhouse studies were extracted for phytochelatins (PCs) and were identified using reversed-phase high performance liquid chromatography (RP-HPLC) coupled with post-column derivatization. We also analyzed plant samples to determine if low molecular weight thiols can be induced in plants (both rice and brake fern) upon exposure to As and, if so, to what extent. We also investigated the effect of As on the activities of antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), in fern and rice tissues. The results showed increased activity of CAT, POD, and SOD in shoot and root tissues in plants treated with both sodium arsenate and DMA. Currently, cloning and expression studies of phosphate transporter genes, as well as glutamylcysteine synthetase (GCS) and phytochelatin synthase (PCS) genes, are in progress in rice and brake fern.
Future Activities:
We will initiate the second set of greenhouse experiments in spring of 2006, with higher pesticide amendment rates (675 and 1,500 mg kg-1) to determine As speciation and bioavailability as a function of both rate and time. Soil aging studies were extended more than 3 years through a no-cost extension. We expect to study the effects of higher amendment on phytochelatin induction and gene expression in brake fern. We will analyze As speciation using HPLC-ICP-MS; plant tissues will be analyzed for the induction of PC using RP-HPLC; and activities of GCS and PCS enzymes will be analyzed in shoot and root. Cloning and gene expression studies of GCS, PCS, and phosphate transporter genes will be completed.
Journal Articles on this Report : 5 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. 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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Makris KC, Sarkar D, Datta R. Evaluating a drinking-water waste by-product as a novel sorbent for arsenic. Chemosphere 2006;64(5):730-741. |
R830842 (2005) R830842 (2006) |
Exit Exit |
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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. Human health risks from arsenic in soils: does one model fit all? Archives of Environmental & Occupational Health: An International Journal 2004;59(7):337-341. |
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) |
Exit Exit Exit |
Supplemental Keywords:
arsenic, soil, pesticides, in-vitro bioavailability, speciation, risk assessment, water treatment residuals, chemical remediation, phytoremediation, molecular biology, hyperaccumulator fern,, RFA, Health, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, Water, POLLUTANTS/TOXICS, Contaminated Sediments, Geochemistry, Arsenic, Risk Assessments, Hazardous Waste, Environmental Monitoring, Water Pollutants, Hazardous, reservoir sediments, contaminant transport, Superfund sites, contaminated sediment, sediment transport, risk management, contaminated soil, sediment quality survey, superfund site, arsenic mobility, assessment methods, water quality, ecology assessment models, biogeochemistry, water treatment, 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.