| Over the past two decades, bioaccessibility research has been conducted in an effort to adjust the level of risk determined through the human health risk assessment (HHRA) process. This process is necessary as a result of the high rate of incidental ingestion of contaminated soil by humans. Bioaccessibility is measured using a laboratory in vitro extraction method that simulates the human GI tract. In an attempt to "validate" the in vitro methods, research has also been carried out in conjunction with bioavailability studies. These are in vivo experiments using mice, swine or primates to measure how much of a contaminant passes from an ingested dose into the bloodstream and tissues. This thesis carried out both in vitro and in vivo research on seven contaminated soils, as well as contaminated biochar (a gardening amendment made from wood), which contain one or a combination of the heavily studied contaminants, arsenic and lead, as well as others less commonly evaluated: copper, nickel, chromium, zinc, cadmium and mercury. The three in vitro bioaccessibility evaluation methods used were the Physiologically Based Extraction Test (PBET), the Unified BARGE Method (UBM) and the glycine method. A mouse model was used for the in vivo research. It was determined that the three bioaccessibility methods produce similar results (between methods) for all contaminants. In addition, a meta-data analysis was carried out on all available in vitro research, and this thesis produced results that are consistent with those found in that analysis. The in vivo results from the mouse study indicated a dose-response iv relationship for at least one contaminant in each of the sample materials. Liver and kidneys were the most suitable organs for determining bioavailability of less commonly studied contaminants, whereas blood was also beneficial for evaluation of arsenic and lead. With a larger number of study materials (e.g., soils), comparison using traditional linear regression methods would be likely to indicate a predictive relationship. The mouse model appeared to be an appropriate surrogate for the human gastro-intestinal tract and should be considered for use in this field instead of the more expensive and ethically challenging swine and primate models.;Keywords: arsenic, bioaccessibility, bioavailability, cadmium, chromium, copper, lead, in vitro, in vivo, mercury, nickel, risk assessment, soil ingestion, zinc. |
