ISEE/ISEA 2006 Conference Abstracts Supplement: Symposium Abstracts: Abstracts
The ingestion of arsenic, mercury, and lead-contaminated soils is a potential risk to human health. This is especially true for members of residential communities that live in close proximity to the tailings of abandoned mines due to the high metal concentrations observed in these sites. Current practice in risk assessment is to assume that the bioaccessibility of ingested compounds are close to 100% or at least equal to the material used to derive the toxicological reference value. However, the validity of this practice has been questioned because recent work has demonstrated that there are large differences in percent bioaccessibility between soils.
Tailing samples containing arsenic (385–105,300 ppm), mercury (6–5024 ppb), and lead (18–462 ppm), which were collected from 3 sites near abandoned mines in Eastern Canada, were digested in an in vitro gastrointestinal model, the Simulator of the Human Intestinal Microbial Ecosystem (SHIME). The SHIME is unique among in vitro models because it features a stage with a microbial community representative of that found in the human colon. The percent bioaccessibilities were measured for arsenic, mercury, and lead in the small intestine and colon stage of the SHIME after treatment with 2 size fractions (Bulk and <38 μm) of the tailings from each location. The effects of metal concentration and particle size on metal bioaccessibility were examined for each of the 3 analytes. Additionally, the effect of the colon microbe community on metal bioaccessibility was evaluated. Preliminary results suggest that metal bioaccessibility in the colon is lower than that of the small intestine due to the activity of sulfate-reducing bacteria. A precipitate was formed in the colon stage of the SHIME, thereby causing the SHIME solution to become black in color. This precipitate was not formed when sterilized (autoclaved) SHIME was added instead.
Results indicate there may be a difference in bioaccessibility between the 2 size fractions examined, which may have been caused by the large differences in metal concentration between the 2 size fractions.