Assessing Human Health Risks from Arsenic Exposure using a Weight-of-Evidence Approach

The importance of considering a weight-of-evidence approach when evaluating the human health effects of arsenic at contaminated sites became clear during several recent projects involving potential impacts from mining operations. Elevated levels of arsenic were encountered in several Ontario communities, including one near a former gold mine, and one near a sintering plant. Risk assessments, involving multi-pathway exposure assessment (i.e., air, water, soil, backyard produce, fish and market basket foods) and use of U.S. EPA slope factors revealed cancer risk levels in the 1-in-1,000 range. The Ontario Ministry of Environment (MOE) acceptable risk level is 1-in-1,000,000, and as a result these elevated risk estimates raised community concerns. Answers were needed to ensure public safety and satisfy community and regulatory concerns. Further investigation into the risk assessment revealed that: (i) market basket foods were the main contributor to arsenic-related risks; (ii) generic arsenic criteria in Ontario (i.e., 25 ppm) result in elevated risk levels (i.e., greater than 1-in-100,000); (iii) the contribution of soil to overall arsenic-related risks was small; all other pathways were less significant; (iv) health-based intervention levels, as determined by the risk assessment, proved to be economically and technologicall