Mercury at Oak Ridge: outcomes from risk evaluations can differ depending upon objectives and methodologies

Risk evaluations play an important role in environmental management, remediation and restoration. Yet when different agencies and groups evaluate risk, the objectives and methods may differ, leading to different conclusions, which can confuse managers, policy-makers and the public. In this paper, we examine two evaluations of the potential risk from mercury contamination deriving from the Y-12 facility at the Department of Energy's Oak Ridge Reservation (Tennessee, USA). The US Agency for Toxic Substances and Disease Registry (ATSDR) examined the past and present risks from mercury to humans, using data provided in government reports and publications. The Consortium for Risk Evaluation with Stakeholder Participation (CRESP) used a risk-informed prioritization model, developed for managers to evaluate different remediation projects. The CRESP prioritization model considered both human and ecological receptors, as well as future potential risks. Risk was an important component of both evaluations, and both evaluations found that there was a completed pathway of mercury from the source on the Oak Ridge Reservation to offsite human receptors, although the evaluations differed in their final conclusions. CRESP evaluated the risk as 'high', while the ATSDR noted that the risk was 'moderate' for people consuming fish from East Fork Poplar Creek. In both cases, the pathway to off-site human exposure was through fish consumption. The two evaluations are compared with respect to purpose, specific goals, target audience, receptors, assumptions, time frames, evaluation criteria and conclusions. When these aspects are considered, the risk evaluations are congruent, although the risk communication messages differ. We conclude that there are many different possible risk evaluations, and the aforementioned variables must be carefully considered when making management decisions, determining remediation goals, and communicating with regulators, managers, public policy-makers and the public.