Methylmercury exposure and health effects in humans

Abstract

Environmental Context. Dietary intake of fish and other seafood products is the dominant source of human exposure to methylmercury, a toxicant that can have serious adverse effects on the developing nervous system and may promote heart diseases. The existing evidence of human toxicity should inspire prudent choices in maintaining fish intakes to secure an ample supply of essential nutrients, while at the same time choosing species that are low in mercury concentrations. The combination of essential nutrients and avoidance of this toxic contaminant will benefit brain development and human health in general. In addition, current contamination levels suggest that intensified efforts are needed to reduce and eliminate mercury release to the environment. Abstract. Methylmercury (MeHg) is a worldwide contaminant found in seafood and freshwater fish, which constitute the dominant source of human exposure to this substance. The developing human brain is particularly susceptible to injury caused by MeHg, which easily passes the placental barrier. Epidemiological studies in fishing populations have found subtle though lasting adverse effects on brain functions of children who were exposed prenatally to MeHg from seafood diets. This contaminant also seems capable of promoting the development of heart disease. Fish and seafood also contain important nutrients, such as omega-3 fatty acids that may provide beneficial effects, thereby possibly counteracting or obscuring the adverse effects of MeHg. This article reviews the existing evidence on MeHg developmental neurotoxicity and the emerging evidence that MeHg may promote the development of heart diseases. MeHg risks may have been underestimated in the past, in part because of the confounding effects of nutrients from seafood and fish. Improved control of mercury release to the environment is indicated. In addition, regulatory agencies should provide better guidance to consumers in maintaining a balanced diet that includes seafood as low as possible in mercury.