Eggshell Thinning and Organochlorine Contaminants in Western Washington Waterbirds

Within the Puget Sound, Washington, marine environment there are urban-industrial areas with a known variety of pollutants present, including PCB’s and DDT/DDE. In 1984 we studied five species of waterbirds for effects of pollutants at urban-industrial sites and in more remote areas of western Washington. No significant thinning was observed in the eggs of Double-crested and Pelagic Cormorants (Phalacrocorax auritus and P. pelagicus), all taken in remote areas. The same was true of Pigeon Guillemot (Cepphus columba) eggs taken in Puget Sound. Significant average eggshell thinning (to 13%) was observed in eggs of Great Blue Herons (Ardea herodias) from heronries near agricultural areas. Samples from near urban-industrial areas showed less average thinning (5-7%). The generally low average concentrations of total DDT (0.35-2.22 μg/g, wet weight) in heron eggs probably reflect local contamination from agricultural areas and wind drift from elsewhere. Highest average concentrations of PCBs in heron eggs were in those from Seattle (15.58 μg/g) and Tacoma (5.46 μg/g), the most industrially developed parts of Puget Sound. The largest average amounts of thinning (7-9%) in Glaucous-winged Gull (Larus glaucescens) eggs were for colonies in or near the urban-industrial areas of Puget Sound. Average shell thinning in eggs from the remote area colony was less (2%). Concentrations of total DDT in eggs (0.49-1.19 μg/g) do not account for the amount of thinning observed. The levels of the contaminants and the degree of eggshell thinning observed in the study species are all currently below levels associated with reproductive impairment in other studies. There is no current or historical evidence of significant pollution related impairment of reproduction in the study species in western Washington.


Speich. S.M., J. Calambokidis, D.W. Shea, J. Peard, M. Whitter, and D.M. Fry. 1992. Eggshell Thinning and Organochlorine Contaminants in Western Washington Waterbirds. Colonial Waterbirds 15(1): 103-112. doi: 10.2307/1521359