A federal study of toxic pollution and environmental changes turned up what investigators said are worrisome signs of serious chemical contamination at one sampling point in San Diego Bay. The study of coastal pollution near eight West Coast urban areas found the highest levels of aromatic hydrocarbons, polychlorinated biphenyls (PCBs) and copper in sediments collected off the 28th Street Pier in San Diego Bay. The same site also yielded high levels of chromium in sediments and a high incidence of a condition called "fin erosion" in barred sand bass, a bottom-dwelling fish caught at the 28th Street location. Donald Malins of the National Fisheries Service said the implication of the findings on human health are not known at this time. The 28th Street location was chosen because it seemed to represent "a reasonable example of an urban site in San Diego Bay," Malins said.