Further declines in organochlorines in eggs of red-breasted mergansers from Lake Michigan, 1977-1978 versus 1990 versus 2002

From 1977-1978 to 1990, concentrations of polychlorinated biphenyls (PCBs) and most organochlorine pesticides declined in eggs of red- breasted mergansers (Mergus serrator) nesting on islands in northwestern Lake Michigan. Further declines took place between 1990 and 2002. Be- tween 1977-1978 and 1990 total PCBs decreased 60% (from 21 to 8.5 μg/g, wet weight). An addi- tional decline of 46% took place between 1990 and 2002 (8.5 to 4.6 μg/g). Between 1977-1978 and 1990 p,p � -DDE decreased 66% (from 6.5 to 2.2 μg/g), and from 1990 to 2002 an additional decline of 36% took place (from 2.2 to 1.4 μg/g). Between 1977-1978 and 1990 dieldrin decreased only 16% (from 0.82 to 0.69 μg/g), but from 1990 to 2002 a 96% decrease occurred (from 0.69 to 0.03 μg/g).