Methylmercury hazards and risks-what is the question?

Risk assessment (RA) of methylmercury (MeHg) must explicitly address the public health question being asked by decision makers (e.g., elected or appointed officials) or the public at large. Safety assessment (negligible or zero risk assessment) is useful for identifying contaminant exposures which are insignificant public health concerns. Many MeHg exposures can be inherently described as "unsafe". Quantitative risk assessment (QRA) should then be used to express MeHg risk as a matter of degree. QRA can then be integrated with exposure avoidability, nutritional benefits/risks and competing dietary risks. A principle issue in QRA is uncertainty. In providing a quantitative measure of uncertainty it becomes an explicit part of the risk management process. Uncertainties in MeHg QRA involve every step of the process, including exposure, metabolism/toxicokinetics, hazard identification, mechanisms of cellular toxicity and dose-response. QRA of MeHg must provide the decision maker (e.g., individual citizen and public health official) with; (1) degree of expected harm; (2) variability of the adverse response in a population (e.g., sensitive subpopulations); and (3) degree of uncertainty associated with risk estimates. Measuring uncertainty provides a means of evaluating the utility of additional research and fosters confidence that decisions are based on a transparent analysis of science.