Grantee Research Project Results
1998 Progress Report: Development of Chemical Methods to Assess the Bioavailability of Arsenic in Contaminated Media
EPA Grant Number: R825410Title: Development of Chemical Methods to Assess the Bioavailability of Arsenic in Contaminated Media
Investigators: Basta, Nicholas T. , Rodriguez, Robin R. , Casteel, Stan W.
Institution: Oklahoma State University , University of Missouri - Columbia
EPA Project Officer: Hahn, Intaek
Project Period: November 1, 1996 through October 31, 1999 (Extended to October 31, 2000)
Project Period Covered by this Report: November 1, 1997 through October 31, 1998
Project Amount: $431,677
RFA: Environmental Fate and Treatment of Toxics and Hazardous Wastes (1996) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management , Safer Chemicals
Objective:
Soil ingestion from incidental hand-to-mouth activity by children is an important issue in assessing public health risks associated with exposure to As-contaminated soils and media. Risk from enteric bioavailability of As is difficult to assess because As exists in many geochemical forms (e.g. oxides, sulfides) and physical forms (flue dust, slag, tailings, waste ore) at hazardous waste sites contaminated by mining or smelting of ore. The purpose of this research project is to determine the ability of chemical methods (chemical speciation, in-vitro gastrointestinal) to provide a reasonable estimate of As bioavailability in contaminated media and provide rapid and inexpensive information to characterize risk at Superfund sites. In this project, As measured by chemical methods (soil chemical extractation/fractionation and in-vitro gastrointestinal methods) is compared with As uptake by immature pigs for contaminated media (soil and slag) collected from a mining, milling, and smelter sites. The objectives of the work are:- To determine the degree of correlation between chemical speciation and in-vitro methods with in-vivo methods and the ability of chemical methods to provide accurate assessments of the bioavailability of As in contaminated media.
- To determine if in-vitro methods that mimic gastrointestinal absorption are more accurate than current in-vitro methods that do not address gastrointestinal absorption to assess the bioavailability of As in contaminated media.
- To determine if the bioavailability of As in contaminated media is a function of As concentration (As loading rate).
Accomplishments and Research Results:
Objective 1. | To determine the degree of correlation between chemical speciation and in-vitro methods with in-vivo methods and the ability of chemical methods to provide accurate assessments of the bioavailability of As in contaminated media. |
A method was developed to simulate the human gastrointestinal environment and to estimate bioavailability of arsenic in contaminated soil and solid media. In this in-vitro gastrointestinal (IVG) method, arsenic is sequentially extracted from contaminated soil with simulated gastric and intestinal solutions. Fifteen contaminated soils collected from mining/smelter sites ranging from 401 to 17,460 mg As kg-1 were analyzed. In-vitro results were compared with in-vivo relative bioavailable arsenic (RBA) determined from dosing trials using immature swine which ranged from 2.7 to 42.8% RBA. Both IVG stomach and intestinal methods extracted similar amounts of arsenic as in-vivo methods and provided estimates of bioavailable As across all contaminated media. The IVG methods were not accurate for calcine materials. There was excellent agreement between arsenic bioavailability measured by IVG and in-vivo methods for non-calcine media. Arsenic extracted by the IVG stomach and intestinal phases was linearly correlated (r = 0.83 and 0.82, respectively) with in-vivo arsenic (P <0.01). The IVG method may aid in the design and cost-effectiveness of remedial strategies of arsenic- contaminated sites.
The ability of soil chemical fractionation methods that extract different pools of soil arsenic to measure bioavailable arsenic was studied. Five chemical extractants, ranging from deionized water to very aggressive reagents that dissolve occluded arsenic, were used to fractionate soil arsenic. Results showed poor agreement between the amounts of arsenic measured by soil chemical fractionation methods and bioavailable (in-vivo) arsenic. The fraction of bioavailable arsenic in contaminated soils includes desorbable non-occluded forms and some arsenic associated with iron, manganese, and aluminum oxides.
Objective 2. | To determine if in-vitro methods that mimic gastrointestinal absorption are more accurate than current in-vitro methods that do not address gastrointestinal absorption to assess the bioavailability of As in contaminated media. |
Dissolved metal contaminants are continuously removed from the GI tract by active and passive absorption mechanisms, so equilibrium conditions in the GI tract may never be achieved. An in-vitro method that accounts for absorption that mimics in-vivo GI absorption may be necessary when absorption is the rate-limiting process (k2 < k1).
A modified IVG-AB method, where iron hydroxide gel is used as an arsenic sink to simulate the gastrointestinal absorption of arsenic, was evaluated. Arsenic extracted by the IVG (no gel) and IVG-AB (with gel) methods was not statistically different than RBA arsenic measured by the in-vivo method. Therefore, a method that simulated the gastrointestinal absorption (IVG-AB, with gel) was not more accurate than an in-vitro method that does not address gastrointestinal absorption (IVG, no gel) to assess the bioavailability of As in contaminated media. Dissolution of arsenic under simulated GI conditions was dependent on dissolution of the contaminant matrix (k1) more than adsorption by iron hydroxide gel.
Objective 3. | To determine if the bioavailability of As in contaminated media is a function of As concentration (As loading rate). |
The same weight of two contaminated media (slag or calcine) that range in As concentrations were fed to immature pigs to determine the effect of As loading rate on bioavailability. The ability of chemical speciation and in-vitro gastrointestinal methods to reflect the concentration dependence of contaminants on relative bioavailabity of As was also conducted and is currently under evaluation.
Future Activities:
Laboratory work will be completed by March, 1999. Results from our work will be presented at three international meetings: the annual meeting of the Society of Environmental Toxiciology and Chemistry in November 1999 in Philadelphia, PA, the annual meeting of the Soil Science Society of America in October 1999 in Salt Lake City, UT, and the 5th International Conference on the Biogeochemistry on Trace Elements, July, 11-15, 1999 in Vienna, Austria.Research publications will be prepared and submitted to scientific journals including the Journal of Environmental Quality.
Journal Articles:
No journal articles submitted with this report: View all 20 publications for this projectSupplemental Keywords:
Risk assessment, cleanup levels, remediation endpoints, site-specific bioavailability, oral bioavailability., RFA, Health, Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Contaminated Sediments, Environmental Chemistry, Chemistry, Epidemiology, Arsenic, Risk Assessments, Fate & Transport, Susceptibility/Sensitive Population/Genetic Susceptibility, Children's Health, genetic susceptability, fate and transport, health effects, risk assessment, fate, contaminated mines, ingestion, soil ingestion, Superfund sites, contaminant transport, risk characterization, soil sediment, human health effects, contaminated sediment, dermal contact, sediment transport, transport contaminants, chemical speciation, adverse human health affects, chemical contaminants, kinetic studies, soils, hazardous waste, children, toxicity, human exposure, superfund site, chronic health effects, environmental toxicant, mobility, arsenic mobility, animal research, ecology assessment models, arsenic exposure, hazardous waste sites, exposure assessmentProgress 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.