The city of San Diego recently cleared a major legal hurdle in its effort to force chemical giant Monsanto to pay tens of millions to clean up local waterways polluted with a class of cancer-linked chemicals, known as polychlorinated biphenyls, or PCBs. Federal and state regulators have in recent years tightened standards for cleaning up PCBs in bays, rivers and creeks. As a result, municipalities, such as San Diego, have shelled out millions to contain or get rid of the toxins. The lawsuit alleges that the St. Louis-based corporation should bear at least part of that cost. Lawyers for the city contend that Monsanto knew for decades before the federal government banned PCBs in 1979 that the chemicals would result in widespread contamination and negative impacts to human and environmental health.