Accumulation and Hazard Assessment of Mercury to Waterbirds at Lake Chapala, Mexico

Lake Chapala is the largest tropical lake in Mexico. The objectives of this study were to determine bioaccumulation of Hg in fish and to evaluate the potential impacts of Hg in the diet of aquatic birds, particularly the American white pelican (AWPE), in Lake Chapala. Hg concentrations in three fish species ranged from 0.021 to 0.568 mu g/g wet weight. Mercury in fish was positively and significantly correlated with total fish length (R-2 = 0.44, P < 0.05). The delta N-15 values in fish were significantly correlated with Hg concentrations in Chapala and the San Antonio Reservoir (R-2 = 0.69, P < 0.001 and R-2 = 0.40, P < 0.001, respectively). However, Hg concentrations in bird feathers were not significantly different between years, among locations, or among species. Hg concentrations in fish from Lake Chapala were within values reported in many parts of the world. The Hg (mean range of 2.75 to 4.54 mu g/g dw) and delta D (mean range of -62 parts per thousand to -11 parts per thousand) values in bird feathers suggested a wide pattern of exposure for highly migratory AWPE and egrets, although birds with lower delta D values in feathers appeared to have greater concentrations of Hg than those with higher delta D values. Contaminant exposure in aquatic birds in Chapala during the breeding season should be monitored next to better determine the potential effects of Hg on resident aquatic birds.