San Jose, Oakland and Berkeley are suing Monsanto for poisoning San Francisco Bay with PCBs, chlorine-based chemicals that can cause cancer and other diseases. The groundbreaking litigation could set a precedent for communities’ right to hold manufacturers liable for pollution from their products, even when the companies didn’t directly spill or dump the toxins.

But the lawsuits could be thwarted by legislation pending in Congress. A little-noticed provision in an industry-friendly chemical regulation bill could let Monsanto off the hook for production of PCBs, or polychlorinated biphenyls, banned in the U.S. since 1979.

The Monsanto bailout clause is in a House bill to rewrite the Toxic Substances Control Act, or TSCA. It could prevent states from passing their own laws on PCBs and block local governments, states and citizens from suing for damage or disease from the chemicals.

At stake is a staggering legacy of human and environmental devastation — and lots of money. Cities are required by state law to treat runoff before it enters the bay, and Oakland’s city attorney says the cost could be $1 billion in Alameda County alone.

PCBs have spread worldwide, polluting the bodies of polar bears, whales and almost everyone on Earth. They are listed as human carcinogens by the state of California and also linked to liver damage and reproductive disorders. Pollution from PCBs and mercury are why the state warns anglers to strictly limit eating fish from the San Francisco Bay.

From 1935 to 1977, Monsanto was the only maker of PCBs, which are fire-resistant agents used in electrical equipment and other products. Monsanto knew early on that PCBs were hazardous but hid what it knew from regulators and the public. The cover-up was revealed through documents unearthed in a lawsuit by residents of Anniston, Alabama, where Monsanto made PCBs. In 2003, the company settled the lawsuit for $700 million.

Monsanto and two spinoffs have been sued by hundreds of people sickened by PCBs, and last year, six Western cities sued to recover costs of treating PCB-contaminated runoff into waterways. They charge that though the pollution comes from other companies using PCBs, Monsanto, as the sole manufacturer, is at fault because it knew there was no way to keep PCBs from leaking.

Early drafts of the House TSCA bill said nothing about PCBs. But when the bill was introduced in May, days after another lawsuit was filed, a paragraph had been inserted that could exempt PCB makers — read: Monsanto — from liability.

If it becomes law, it could powerfully strengthen the company’s argument that federal chemical regulations pre-empt lawsuits by state and local governments and citizens.

The bailout clause is one of many problems with both the House and Senate bills to revise TSCA — a law already so toothless the Environmental Protection Agency has only regulated five chemicals since 1976. Both versions don’t go far enough to give EPA the authority to ensure chemicals are safe before they’re allowed in the market.

The Senate TSCA bill has a similar clause, but a committee report said it is not meant to bar lawsuits. The two versions must be reconciled before the bill becomes law. If the bailout clause stays in, it could leave PCB victims without recourse and stick cash-strapped local governments with the bill for Monsanto’s mess.

Congress should reject the bailout, hold Monsanto responsible and enact real chemical reform to protect public health, not polluters’ profits.

Ken Cook is president of the Environmental Working Group, with offices in Oakland and Washington, D.C. He wrote this for this newspaper.