Small mammals as biosentinels of health effects from exposure to oil and gas related contaminants. An integrated experimental and field based approach

Abstract

Canada’s oil sands activities, marked by ongoing controversy about environmental impacts, produce complex mixtures of pollutants including polycyclic aromatic hydrocarbons (PAHs) and metals such as lead (Pb), cadmium (Cd) and mercury (Hg) which are potentially deposited onto soil, water and vegetation posing a risk for surrounding ecosystems and wildlife. Recent studies encompassing the Athabasca Oil Sands Region report increased deposition of total PAHs (mainly alkyl-PAHs) and metals in melted snow within 50 km of upgrading facilities, compared to more distant, undisturbed areas, suggesting that these compounds are a consequence of oil sands activities. Here we present results of an integrated experimental and field-based research approach designed to evaluate how PAHs and metals affect the health of local wildlife in northern Alberta, using herbivorous small mammals as sentinel species. Firstly, an experimental study using lab mice (as a surrogate for wild small mammals) was developed to simulate the subchronic exposure to environmentally relevant concentrations of pollutants. Mice were exposed to a mixture of alkyl-PAHs (food), and/or to a mixture of challenge metals (water) during 28 days. Several biomarkers of exposure and/or effect were evaluated in these groups, and compared with those from control mice. Biomarkers included the antibody response to a challenge antigen, thyroid (T3, T4) and reproductive (T and E2) hormones in plasma, and biomarkers of oxidative stress in liver including glutathione (GSH) redox status, malondialdehyde (MDA), and levels of vitamins A (retinyl esters and all-trans retinols) and E (α-tocopherol). The hepatic biotransformation enzyme, 7-ethoxyresorufin-O-deethylase (EROD), a well-studied indicator of contaminant exposure, was also analyzed in liver. Absorbed PAHs and metals were respectively determined in muscle, fat and kidneys to determine bioavailability and measure tissue residues. Based on findings from the experiment study, the most sensitive biomarkers were selected for subsequent field studies to evaluate exposure and health effects in wild small mammals on the oil sands-affected areas in northern Alberta. Two industrial sites (one in the early reclamation stage, and other in mature reclamation) and a reference site were selected for the study on wild small mammals. Highlights from this integrated research approach will be presented.