From 1977-1978 to 1990, concentrations of polychlorinated biphenyls (PCBs) and most organochlorine pesticides declined in eggs of red-breasted mergansers (M ergus serrator) nesting on islands in northwestern Lake Michigan. Total PCBs decreased 60% (from 21 ppm in 1977-1978 to 8.5 ppm in 1990) and p, p'-DDE decreased 66% (from 6.5 to 2.2 ppm). Dieldrin decreased only 16% (from 0.82 to 0.69 ppm). In 1990, 79.1 % of incubated eggs hatched, which was not significantly different from the 83.5% that hatched in 1977-1978.
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Declines in organochlorines in eggs of red-breasted mergansers from Lake Michigan, 1977-78 versus 1990