Brain Lesions in Mallard Ducklings from Parents Fed Methylmercury

Abstract

Methylmercury dicyandiamide was fed to mallard ducks at 3 ppm mercury. Mercury accumulated in the eggs to an average of 7.18 and 5.46 ppm on a wet-weight basis in 2 successive years. Mercury in the eggs is believed to have caused brain lesions in the hatched ducklings. Lesions included demyelination, neuron shrink-age, necrosis, and hemorrhage in the meninges overlying the cerebellum. Brains of dead ducklings contained an average of 6.17 and 5.19 ppm mercury on a wet-weight basis in 2 successive years.

Toxicity Reference Values and Tissue Residue Criteria for Protecting Avian Wildlife Exposed to Methylmercury in China

“…Corresponding values for LOAEL and NOAEL were calculated to be 0.171 and 0.029 m g MeHg/g (bm)/day. The LOAEL and NOAEL values, expressed as concentrations of MeHg in egg, were, respectively, 0.79 and 5.64 m g MeHg/g (wwt) (Heinz and Locke 1976 ) . Based on multigenerational effects on reproduction, when converted from the dietary values by the use of rates of consumption of food of 0.156 kg food (wwt)/kg (bm)/day (US EPA 1995b ) , the dietary LOAEL value was 0.078 m g MeHg/g (bm)/day.…”

“…As stated in the GLWQI Criteria Documents (US EPA 1995b ) , the dietary LOAEL and NOAEL values for mortality and for neurological effects on the mallard were 3.0 and 0.5 m g MeHg/g feed (dry weight, dwt), respectively (Heinz and Locke 1976 ) . Using the average body mass of 1 kg for a mallard (Delnicki and Reinecke 1986 ) , a rate of food ingestion of 0.051 kg dried feed/kg fresh (bm)/day was derived from Nagy's (Nagy 2001 ) allometric equation for omnivorous birds, rather than the equation (Nagy 1987 ) that was used in the GLWQI Criteria Documents for Protection of Wildlife.…”

Potential for Increased Mercury Accumulation in the Estuary Food Web

“…Almost all of the mercury in bird eggs is methylmercury (Wolfe and others 1998). Toxic effects of mercury in bird eggs have been documented by many investigators in both laboratory and field studies (Barr 1986;Birge and others 1976;Fimreite 1971Fimreite , 1974Heinz 1974Heinz , 1979Heinz and Locke 1975;Hoffman and Moore 1979;Finley and Stendell 1978;Tejning 1967). Egg concentrations in the range of 0.5 to 1.0 µg g -1 (all concentrations given are wet weight, unless stated otherwise) have been associated with toxic effects on embryos.…”

“…Mercury was accumulated in the eggs to an average of 7.2 and 5.5 µg g -1 in two successive years. Lesions included demyelination, neuron shrinkage, necrosis and hemorrhage in the meninges overlying the cerebellum (Heinz 1975). Fish reproduction can be quite sensitive to methylmercury (Wiener and Spry 1996), but data on exposures and sensitivities specific to the Bay-Delta are not available.…”

A Downstream Voyage with Mercury

“…eggs, had caused lesions in the brains of the ducklings (Heinz and Locke 1976). The following year, I fed the same female mallards the diets they had received the year before.…”