Pollutants of Concern

Pollutants of Concern: Storm drains can carry a variety of pollutants to creeks and the Bay. Some of these can harm wildlife and humans--a few which cause particular concern, are listed below.


Much of the mercury that runs into the Bay is a remnant of the historic use of mercury in gold mining operations. Bacterial and chemical processes in the Bay cause Mercury concentrations to increase or "bioaccumulate" in the bodies of animals high in the food web. As a result, fish consumption advisories suggest that humans, particularly children and pregnant women, limit consumption of fish from San Francisco Bay to avoid harm to developing nervous systems.

Polychlorinated Biphenyls or PCBs

PCBs were used in the past in a number of industrial and commercial applications, most importantly as coolants, lubricants, and insulators in electrical equipment. Although new uses are banned, PCBs continue to pose a serious risk due to their persistence in the environment. PCBs are listed by US EPA as a potential carcinogen, and are suspected of having negative effects on the human immune, reproductive, nervous, endocrine, and digestive systems. As with Mercury, PCBs pose human health risks because they accumulate in fish tissue.


Pesticides have been found in streams and storm drains throughout the Bay Area and California, often in concentrations toxic to aquatic life. Although a very small percentage of the amount that is applied finds its way into urban runoff, this is still enough to raise concerns about impacts to aquatic health.


At low concentrations, copper is beneficial to aquatic life, but at higher concentrations can be extremely toxic to aquatic life; this toxicity can occur at levels that are not harmful to humans. This metal finds its way down storm drains through runoff from building materials and roads where copper is released from the brake pads of cars.