As a result of its 1998 assessment of water bodies in the Bay Area, the
Regional Board listed San Francisco Bay as impaired due to the following
pollutants: diazinon, mercury, polychlorinated biphenyls (PCBs), copper,
nickel, chlordane, DDT, dieldrin, and selenium. The U.S. EPA subsequently
added dioxin-like compounds as one of the bay’s impairing pollutants; listed
several creeks in Alameda County as impaired by Diazinon.
Pollutants of Concern:
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 "bio-accumulate" 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.
Diazinon is a widely used insecticide. It has been found in streams and storm
drains throughout the Bay Area and California, often in concentrations toxic
to aquatic life. It is also highly toxic to birds and other wildlife. 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 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 such as roofs, and roads
where copper is released from the brake pads of cars.