In-vitro Oral, Inhalation, and Dermal Bioaccessibility and Bioavailability of Metal(loid)s from Polluted Soils and Mine Tailings

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Children are particularly sensitive to contaminant exposure due to their physiological and developmental properties. They are regularly exposed to toxic substances such as metal(loid)s via incidental or deliberate soil ingestion, inhalation of particulate matter (PM) and dermal contact with polluted soil. Finer fractions of contaminated soils and mine tailings, suspended following wind erosion or anthropogenic activity, contain high levels of metal(loid)s. Ingestion of contaminated soil and inhalation of dust and PM may cause the release of contaminants following contact with gastro-intestinal or lung fluids depending on the exposure pathway. Additionally, dermal contact with contaminated soil may cause solubilization of soil-bound metal(loid)s in sweat and the permeation of these elements through the skin. After exposure, not the total amount, but only a portion of soil-bound metal(loid)s will become bioaccessible i.e., solubilized in body fluids and only a portion of the bioaccessible fraction will then reach the systemic circulation and be actually bioavailable. The use of synthetic gastro-intestinal, lung, and skin surface fluids can help environmental engineers and risk assessors to obtain more accurate risk estimates. An in vitro approach entails, at the same time, a reduction in the use of animal testing which involves strong ethical, technical, and financial issues.  In spite of recent progress on in vitro oral bioaccessibility determination, there is a huge knowledge gap regarding the in vitro assessment of bioaccessibility and bioavailability through inhalation and dermal contact for metal(loid)s bound to geological materials. The objective of this research program is to develop novel and improved in vitro assays for bioaccessibility and bioavailability assessment (ingestion, inhalation, dermal) of metal(loid)s in contaminated soils and mine tailings with an emphasis on in vitro bioavailability assessment. These tests will incorporate in vitro exposure to cultured intestinal and lung cells for oral and inhalation pathways and permeation tests through synthetic skin for dermal pathway. The research will determine the influence of bioaccessible metal(loid)s chemical forms on intestinal (Caco-2) and lung alveolar cells (A549) metal(loid) uptake and the potential toxic effects. This program will enable the training of 12 highly qualified environmental engineers (3 PhD, 3 MSc, and 6 undergraduates). This innovative research program is conducted with the clear intent of providing a basis for standardization of inhalation and dermal bioaccessibility assays and incorporation into new regulations in Canada. The widespread use of these advanced in vitro bioaccessibility and bioavailability methods by environmental engineers and risk-assessors should improve site-specific risk characterization studies, while replacing animal testing.This will allow for reduced clean-up costs and the use of more sustainable remediation approaches.