Storms over factories, warehouses and truck terminals wash old industrial poisons into ditches and sad ponds dug beside the levee. When the rain is heavy, workers turn on big pumps and flush the water, chemicals and all, into the river.

During years of rain, pump and flush, the poison has settled bit by bit onto the river's bottom. Creatures that live in the depths take it in as they feed and breathe, and some of them in turn become food for bigger creatures. Through a cruel mathematics of altered nature, the poison builds up in each successive predator.

In time, the biggest fish in the river held so much poison that it became dangerous for people to eat them. So people stayed away, and over time, it no longer mattered which came first _ the toxic fish or the abandoned river.

The poison has lingered across generations of fish and people and has become a part of the river's routine, the way an old tire snagged on a submerged tree eventually forms a hump of mud and new grass.

Experts have measured the amounts of poison in the soil, water and fish. They have marked the results on maps. They have written reports. They have identified, chronicled and documented the poisoning of the river as if to record the dispassionate data of a slow disease. They detailed every important thing.

Except one: They have said little about what people might do to clean up the poison, make the fish healthy and speed up the healing of the Trinity River. They have left that out because they don't know.

Polychlorinated biphenyls were a miracle of 20th-century science. One chemist was said to have proclaimed them perfect.

Put PCBs in electrical equipment, and they will absorb the heat and keep them from catching fire. Put them in paint, and they'll make it pliant and flexible. Put them in caulk, and the seal will keep out water and wind.

Industries did all those and more. Chemists first described the compounds in 1881. Within a few years, PCBs were in hundreds of products.

Problems appeared almost as quickly. By the late 1920s, doctors knew that PCBs caused the skin disfigurement chloracne. Industrial workers' cases and animal studies found liver damage. Lab animals got cancer of the liver and thyroid.

The U.S. Department of Health and Human Services says PCBs can reasonably be anticipated to cause cancer in people. The Environmental Protection Agency and the International Agency for Research in Cancer go a bit further, saying PCBs probably do so. The EPA adds that the types of PCBs that bind to sediment and build up in fish are also the most carcinogenic.