Organochlorine chemical residues in white pelicans and western grebes from the Klamath Basin, California

Samples were analyzed for 12 organochlorine chemicals. Concentrations of DDT + DDD and dieldrin in American white pelican(Pelecanus erythrorhynchos) eggs collected at the Klamath Basin National Wildlife Refuges decreased from 1969 to 1981; DDE and polychlorobiphenyl (PCB) residues did not significantly change. Differences between PCB residues in eggs collected from Lower Klamath and Clear Lake colonies in 1969 suggest different migration routes or wintering areas between populations nesting at these two locations. White pelican and western grebe(Aechmophorus occidentalis) PCB/DDE ratios were 0.13 and 1.58, respectively, suggesting different exposure patterns. White pelican eggshell thickness increased between 1969 and 1981, but remained significantly less than pre-1947 values. Western grebe shell thickness was not significantly different from pre-1947 values. Endrin caused some of the pelican mortalities in the Klamath Basin from 1975 to 1981. Pelicans may have acquired endrin in California, but possibly from areas outside of the Klamath Basin.