Organochlorines and mercury in eggs of coastal terns and herons in California, USA

In San Franciso Bay, California, USA, concentrations of DDE and mercury in eggs differed among Caspian Tern, Forster's Tern, Black-crowned Night-Heron, and Snowy Egret in 1982. Geometric mean DDE concentrations were higher (P < 0.05) in Caspian Tern eggs (6.93 ppm, wet weight) than in eggs of other species (1.92-2.84 ppm). Mean mercury concentrations were significantly greater in Caspian Tern (1.25 ppm) and forster's Tern (0.90 ppm) eggs than in night-herons (0.41 ppm), but night-heron eggs contained higher concentrations of mercury than did the eggs of Snowy Egrets (0.21 ppm). There were no significant differences among species for mean concentrations of trans-nonachlor or PCBs; other organochlorines occurred in fewer than half of the samples, so means were not compared. Caspian Tern eggs from San Francisco Bay had higher PCB concentrations (4.85 ppm) than did eggs of this species from San Diego Bay, California (1.70 ppm) or Elkhorn Slough, California (1.83 ppm), but we detected no significant differences in mean concentrations of other organochlorines. DDE concentrations in 5 of 47 (10.6%) night-heron eggs from San Francisco Bay exceeded 8 ppm, a level associated with impaired reproduction in this species. DDE concentrations were negatively correlated with eggshell thickness in night-herons and egrets.