1. Bioaccessibility of Arsenic in Mine Tailings from Eastern Canada Brian Laird M.Sc. Candidate Toxicology Graduate Program University of Saskatchewan International Society of Exposure Analysis Paris, France September 2-6, 2006

2. Rationale & Purpose Risk assessors typically assume the bioaccessibility of the ingested compound is at least equal to that used to derive the Toxicological Reference Value. The accuracy of this practice is unknown. Sources of variability of arsenic bioaccessibility were examined to resolve uncertainty currently present in risk assessment

3. Hypotheses Arsenic bioaccessibility in mine tailings depend upon: 1.Arsenic concentration 2.Mine tailing particle size 3.The action of GIT microbes

4. In Vitro GI Model: The SHIME Recent research has demonstrated that colon microbes may be involved in the formation of genotoxic arsenic metabolites. The Simulator the Human Intestinal Microbial Ecosystem (SHIME) incorporates the function of the colon microbial community.

5. Nova Scotia Mine Tailings Arsenic bioaccessibility in the small intestine and colon stages of the SHIME were evaluated for: Two size fractions of mine tailings from 3 residential communities