U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 2 of 3--Contamination of Hydrologic Systems and Related Ecosystems, Water-Resources Investigation Report 99-4018B

Methylmercury in Aquatic Food Webs: Consequences and Management Challenges

By James G. Wiener and David P. Krabbenhoft

ABSTRACT

In the past decade, mercury contamination has prompted steadily increasing numbers of fish-consumption advisories in 40 states, now accounting for more than three-fourths of all such advisories in the Nation. Nearly all of the mercury in fish is methylmercury (MeHg), a highly neurotoxic form that readily crosses biological membranes, can accumulate rapidly in exposed organisms, and can biomagnify to high concentrations in aquatic food webs. Consumption of fish is the primary route of MeHg exposure in humans and in many species of wildlife. Scientific attention to the national mercury problem has been motivated largely by concerns regarding effects on human health, yet wildlife near the top of aquatic food webs are particularly vulnerable to MeHg. Recent work indicates that some fish-eating species, such as the common loon (Gavia immer), are being adversely affected in mercury-sensitive ecosystems, in which seemingly small inventories or inputs of total mercury can seriously contaminate aquatic food webs with MeHg. All ecosystems are contaminated to some extent with inorganic mercury from anthropogenic emissions, and actions taken to manage ecosystems can decrease or substantially increase both the net microbial production of MeHg and the subsequent exposure of biota to MeHg. The goal of decreasing biological exposure to MeHg presents major challenges to environmental managers and scientists alike.