Even though the use of polychlorinated biphenyls (PCBs) has been restricted for 20 years, measurable toxic effects from the chemicals still exist at the top of the San Francisco Bay food web. Specifically, researchers at UC Davis studying double-crested cormorants to detect effects of PCBs on developing embryos, have found reduced egg mass and reduced spleen size associated with high PCB concentrations in egg yolks. UC Davis researchers Jay Davis and D. Michael Fry and others collected cormorant eggs in 1994, artificially incubated them, and examined the hatchlings for effects related to PCB exposure. The data from the study, presented last month at the Society of Environmental Toxicology and Chemistry, suggest that high concentrations of PCBs may have a negative effect on the immune systems of double-crested cormorants. The findings "raise concern for possible detrimental effects on chick survival and immune competence," says Davis. But because the population of the birds in the San Francisco Bay has increased in recent years, the apparent effects of the PCBs have not been severe enough to limit the population, say the study's authors. The study was supported by the U.S. Environmental Protection Agency's UC Davis-based Center for Ecological Health Research.