Organochlorine concentrations and eggshell thickness in failed eggs of the California Clapper rail from south San Francisco Bay

In 1992 we collected 22 failed California Clapper Rail (Rallus longirostris obsoletus) eggs from four tidal marshes of south San Francisco Bay for organochlorine analysis and determination of eggshell thickness. Mean eggshell thickness of these eggs (262 microns) was not statistically distinguishable from that of pre-1932 museum eggs (271 microns). Total PCB concentrations in eggs ranged from 0.65 to 5.01 μg g⁻¹ on an adjusted fresh wet weight basis, with a geometric mean concentration of 1.30 μg g⁻¹. DDE concentrations were extremely low at a geometric mean of 0.11 μg g⁻¹. Geometric mean concentrations of all other organochlorines detected were below 0.10 μg g⁻¹. The concentrations of all organochlorines except PCBs appear to have declined in California Clapper Rails since the mid 1980s. PCBs may still be high enough in some rail eggs to produce embryotoxic effects but additional work to quantify the more toxic PCB congeners in rail eggs is needed.