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PHYSIOLOGICALLY BASED EXTRACTION PROCEDURE: COMPARISON OF FIVE FLUIDS
Citation:
Acheson*, C M., V. S. Magar, S. J. Naber, L. Wang, R. D. Lizotte, AND V. S. Steed. PHYSIOLOGICALLY BASED EXTRACTION PROCEDURE: COMPARISON OF FIVE FLUIDS. Presented at In situ and On-site Bioremedation Symposium, San Diego, CA, 6/6/2001.
Description:
Traditionally, the performance of soil remediation technologies has been evaluated based on the total amount of extractable contaminants. However, some have argued that remedial treatments may alter the bioavailability as well as the mass of contaminants. For example, it has been suggested that remedial soil treatment changes contaminant bioavailability by reducing the contaminant desorption from soil or the contaminant adsorption by target organisms. These theorized changes in bioavailability are possible but must be proven to contribute to risk assessment decisions. For cases where ingestion is the primarily exposure route, one might prove altered bioavailability by conducting an animal feeding study. However, these studies are expensive and difficult to generalize. An alternative effort is underway to quantify changes by developing an in vitro extraction method that mimics the human gastrointestinal tract. This physiologically based extraction procedure (PBEP) is being developed sequentially beginning with the stomach and has focused on desorption of polycyclic aromatic hydrocarbons (PAHs) from soil. Since the stomach is a complex environment, many variables could affect contaminant desorption from soil. A preliminary scoping experiment identified simulated stomach fluid composition and pH as important variables in liquid PAH concentrations. Batch to batch variability in liquid PAH concentrations was also observed in scoping experiment. A study was conducted to evaluate five stomach fluid compositions, obtained from the literature, over the range of physiological pHs. Most fluids contained pepsin and hydrochloric acid, but the concentrations and other components varied. The fluids were evaluated using a land treated soil from the Calhoun Park Superfund site, a former manufactured gas facility in Charleston, SC, with a concentration of 1g total PAH/kg dry soil. Triplicate soil samples were incubated with each fluid for 2.3 hrs, and the liquid and solid phase concentrations of 16 PAHs were measured. Statistical analysis considered variation due to fluid type, pH, and incubation/analytical batch. Despite analytical difficulties due to emulsions, 89% of the PAh mass measured in unincubated soil samples was recovered in BPEP treated samples. The 5 fluids differed in the liquid concentrations with values ranging from 438-939ug total PAHs/L. On average, about 5% of the total PAHs were found in the water phase following incubation. The fluids displayed marked differences in reproduciblity and sensitivity to pH. In addition, batch effects were statistically significant, and thus, the liquid concentrations may be sensitive to small changes in fluid composition or analytical variation. Assuming linear response with ingested study soil, the benzo(a)pyrene dose for adults and children would be 9 and 275%, respectively, of the allowed drinking water dose of 0.4 and 0.1 mg/day. Based on this experiment, stomach fluids may extract physiologically significant quantities of PAHs from contaminated soils. This situation will be explored further in future studies using two fluids evaluated in this study.