Organohalogen levels in harbor seal (Phoca vitulina) pups increase with duration of nursing.

Maternal transfer of persistent marine contaminants to offspring via milk has been documented in marine mammals, but temporal dynamics of this phenomenon throughout the lactation period are poorly understood. Exposures to organohalogens were investigated in harbor seal pups admitted to a rehabilitation center in north central California during the lactation periods of 2001 and 2002. Ten congeners of PCBs, three congeners of PBDEs, and p,p'-DDE were quantified in whole blood samples. Levels of contaminants increased with admit date, assumed to correlate positively with pup age. This trend was significant when latitude of stranding site, body condition, and body length were included as variables in the model. Contaminant-admit date relationships appeared nonlinear (i.e., threshold or exponential), with greatest increases in contaminant concentrations during late lactation.