PCBs damage fish immune systems.

A common Arctic fish can suffer subtle immunological impairments from polychlorinated biphenyls (PCBs) at concentrations found in some remote polarwaters, new research indicates.

Alec G. Maule of the U.S. Geological Survey in Cook, Wash., and his colleagues fed various doses of PCBs to Arctic char (Salvelinus alpinus) living in laboratory tanks. Then, for 4 months, the researchers fed some fish and starved others. The latter regimen replicates the fast that char endure each year during a fresh water phase of their life cycle. At the end of the period, the scientists measured the activity of disease-fighting proteins and enzymes in the fish.

The differences between the groups offish indicate that PCB exposure triggers several adverse immunological changes, the scientists report in the January Environmental Toxicology Chemistry. Among fish deprived of food, for instance, those that received PCBs had a less-active form of the protein called lectin in their blood than did fish whose diets were free of PCBs. Lectin binds to many germs and other foreign materials in animals' bloodstreams. For fully fed fish, the protein remained active, regardless of whether the fish received PCBs. On the other hand, PCBs significantly lowered the activity of germ-killing enzymes called lysozymes in fed fish but not in fasting fish.

When the researchers exposed the starved char to infectious bacteria, half of the PCB-exposed fish died, yet only 30 percent of their PCB-free peers did. There was no survival effect from PCBs among the fish that had been given food.

Says Maule, "PCBs definitely affected the fish% ability to resist disease."--J.R.