New bioindicators for mercury toxicological assessment: Recommendations from the first international bioindicators roundtable

The Mercury Roundtable at the second meeting of the new International Society of Environmental Bioindicators gathered human health, wildlife, and molecularly focused researchers to evaluate the current status of mercury bioindicators. Our goal was to identify a set of indicators, possibly in a tiered approach, suitable for both developed and developing countries, across species (humans, wildlife, rodents) using consistent methods so that the results are comparable over a period of time. The most commonly used indicator of Hg exposure in both humans and wildlife is Hg tissue concentrations. Few bioindicators of effect have been validated for use in both human and wildlife populations, but endpoints that focus on brain development and brain and reproductive function are used in both humans and wildlife, and in both individual and population level evaluations. Endpoints that may be most publicly and politically persuasive include impotence, autism, and cerebral palsy with mental retardation. We recommend additional indicators be used in common across human and wildlife populations. Co-contaminant residues need to be evaluated in tissues, especially selenium, as toxicity is related to the Hg:Se ratio. Further, more species need to be evaluated for the genetic polymorphism (in CPOX4) that leads to a unique Hg-associated peak (iso-keto-porphyrin) in porphyrin profiles in humans and a few non-human species.