SAN FRANCISCO (AP) – A new study shows urban runoff is dumping heavy loads of mercury, PCBs and other toxic chemicals into San Francisco Bay.

The annual report card of the San Francisco Estuary Institute concluded that storm water from areas around the nine-county region contribute more toxic pollution to San Francisco, San Pablo and Suisun bays than large rivers that carry agricultural runoff from the Central Valley.

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Institute scientist Jay Davis told the San Francisco Chronicle that tests of striped bass from the bay last year found they contained mercury levels averaging .4 parts per million—twice the level considered safe for moderate consumption.

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The runoff also carries more visible forms of pollution: trash such as plastic bags.

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