Reproduction in mallards exposed to dietary concentrations of methylmercury

Abstract

The purpose of this experiment was to use mallards (Anas platyrhynchos) tested under controlled conditions to determine how much harm to reproduction resulted from various concentrations of mercury in eggs. Breeding pairs of mallards were fed a control diet or diets containing 1, 2, 4, or 8 microg/g mercury, as methylmercury chloride. Mean concentrations of mercury in eggs laid by parents fed 0, 1, 2, 4, or 8 microg/g mercury were 0.0, 1.6, 3.7, 5.9, and 14 microg/g mercury on a wet-weight basis. There were no signs of mercury poisoning in the adults, and fertility and hatching success of eggs were not affected by mercury. Survival of ducklings and the number of ducklings produced per female were reduced by the 4 and 8-microg/g dietary mercury treatments (that resulted in 5.9 and 14 microg/g mercury in their eggs, respectively). Ducklings from parents fed the various mercury diets were just as heavy as controls at hatching, but by 6 days of age ducklings whose parents had been fed 4 or 8 microg/g mercury weighed less than controls. Because we do not know if absorption of mercury from our diets would be the same as absorption from natural foods, the mercury concentrations we report in eggs may be more useful in extrapolating to possible harmful effects in nature than are the dietary levels we fed. We conclude that mallard reproduction does not appear to be particularly sensitive to methylmercury.

Mercury Reduces Avian Reproductive Success and Imposes Selection: An Experimental Study with Adult- or Lifetime-Exposure in Zebra Finch

“…birds) will react similarly to a contaminant, but this may often not be the case. In previous dosing studies, reproductive impairment began at 0.5 ppm dietary mercury in mallards [26] and 0.7 ppm dietary mercury in kestrels [27], suggesting that zebra finches may be somewhat more sensitive to mercury than waterfowl or raptors. White ibis showed a 35% decrease in reproductive success at 0.3 ppm dietary mercury [4].…”

“…A series of dosing studies on captive mallards ( Anas platyrhynchos ), combined with direct injection of mercury into the eggs of numerous avian species, has established that there is considerable inter- and intra-specific variation in sensitivity of reproduction to mercury [22]. Mallards are one of the least sensitive species known, with minimum dietary doses of 0.5 – 4 ppm required to depress offspring viability in different studies of this species [26]. A captive dosing study has also found reproductive effects of methylmercury in American kestrels ( Falco sparverius ) at a dietary dose of 0.7 ppm [27].…”

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

“…The results of these studies suggest that the mallard is not the most sensitive avian species to the effects of MeHg (Heinz et al 2009(Heinz et al , 2010a , and thus may not be representative or protective of other species. Therefore, it was deemed desirable to update the TRV values to re fl ect the effects of MeHg on birds that consume aquatic biota.…”

“…Heinz ( 1974Heinz ( , 1975Heinz ( , 1976aHeinz ( , b, 1979 The corresponding concentrations of MeHg in tissues such as liver, kidney, breast muscle, brain, ovary, and primary feathers, and in eggs are given (geometric mean for three generations) for mallards (Heinz 1979 ; Table 2 ). Reproductive effects of MeHg on mallards were investigated by exposing adults to one of four doses of MeHg (1, 2, 4, or 8 m g MeHg/g (dwt)) (Heinz et al 2010a ) . No adverse effects were observed in adults, or on egg fertility or the rate of hatching success.…”

“…1 ). Thus, it was concluded that reproduction of the mallard is relatively insensitive to the effects of MeHg (Heinz et al 2010a ) . This conclusion was con fi rmed by using a study in which the eggs of 26 bird species were injected with MeHg (Heinz et al 2009 ) .…”