Bioaccessibility Research Canada
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Background

BARC (Bioaccessibility Research Canada) was established in 2005 to develop collaboration and funding opportunities for advancing understanding of the factors influencing soil inorganic and organic contaminant bioaccessibility and its correct measurement. This is important because the correct estimation of bioaccessibility has the potential to significantly impact risk assessments and cleanup goals at contaminated sites.  

 

For most contaminants, toxicity depends on how much of the contaminant is absorbed into the body. When the exposure route is ingestion of soil borne contaminants toxicity depends upon absorption from the gut. Hence, information on the bioavailability of a contaminant (how well a contaminant is absorbed from the gut) is important to determining how much of a contaminant humans can be exposed to without posing a health risk.  

 

Bioaccessibility is a measure of the physiological solubility of a metal in the gut. Because solubility is usually required for absorption across membranes bioaccessibility may be a predictor of bioavailability when solubility is the major determinant of absorption across the gut epithelium

 

The exposure media (i.e. soil versus food or water) can influence the absorbance of a contaminant and therefore accounting for potential differences in absorption between different exposure media can be important to site risk assessment. It is now widely accepted that contaminants in soil may be absorbed to a lesser extent than contaminants in food or water. Hence, if the exposure media used to derive a TRV is water or food, risks from ingestion of the contaminant in soil might be overestimated. For sites where large volumes of soil need to be remediated even a relatively small bioavailability adjustment can have significant impacts on estimated risks and cleanup goals.

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To advance the meaningful incorporation of bioaccessibility in HHRA risk assessment BARC activities are focused on achieving the following research goals:

 

· The development of reliable and rapid bioaccessibility tests that have been validated with in vivo studies ;

 

· The development of two or more Canadian reference materials with in vivo data for ensuring the reliability and consistency of bioaccessibility test results; and

 

The development of standardized in vitro and in vivo protocols for ensuring the correct application of bioaccessibility data in HHRA.

Absolute bioavailability

is defined as the proportion of the mass of a soil-borne contaminant reaching the GIT that is systemically absorbed (in vivo assay), or that is deemed to be available for systemic absorption (in vitro bioaccessibility assay).

 

Relative  bioavailability

is  defined  as the absolute bioavailability (or bioaccessibility)  from  the  site-specific  soil  samples  divided  by the absolute bioavailability of the same substance under the conditions used to derive the toxicological reference value (TRV)

 

(Paustenbach et al., 1997).