Bay Nature magazineFall 2011

The Bay

Trawling for Plastic in SF Bay

October 1, 2011

Normally, when scientists lower trawls into the Bay, they’re sampling and inspecting things like anchovies, gobies, and bat rays. But last winter, researchers from Baykeeper and San Francisco Estuary Institute were looking for something else. The net they tossed in the water was designed to measure micro-plastic, bits of plastic smaller than 5 millimeters. It isn’t known how much micro-plastic is in the Bay, so these organizations wanted to find out. They hope to go out again this winter.

During their one-day study, they trawled for plastic in six locations. Baykeeper’s Ian Wren says concentrations were lower than expected, probably due to runoff from a recent storm. Near the Berkeley Marina, they got their lowest reading–just 0.145 micrograms of plastic per liter of water. In comparison, University of Washington researchers found 7.5 micrograms per liter in urban runoff areas of Puget Sound.

San Francisco Bay is a well-flushed estuary, which might have something to do with the low concentrations, says Wren. That’s what worries Lorraine Palmer, founder of Sea Scavenger Conservancy. “If a person drops a piece of plastic in the Bay, its destination is the North Pacific Gyre,” she says. The goal of her organization is to help rid the oceans of plastic by ensuring that no plastic goes out the Golden Gate.

The volunteer group meets the second Saturday of every month to clean public areas on the San Francisco shoreline, between AT&T Park and Candlestick, where a two-hour scour can yield two truckloads of garbage, predominantly plastic. The worst culprit is film plastic (such as potato chip bags), which can’t be recycled. Volunteers fill bags with the stuff.

Palmer says shoreline cleanup is just one way to help. Making smart buying choices is another: Avoid single-use plastic whenever possible, and sequester any plastic you do use. “Think of plastic as a precious resource that needs to be kept in a closed stream,” she says. Learn more about Sea Scavenger Conservancy at

About the Author

Writer Aleta George trained as a Jepson Prairie docent in 2009. In addition to writing Bay Nature's Ear to the Ground column, she has written for Smithsonian, High Country News, and the Los Angeles Times.

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