On 13 December 1995, the
California Environmental Protection Agency announced a ban on the sale
and use of two pesticides which have proved harmful to the San
Francisco Bay and its estuaries. The emergency regulations affect
copper sulphate products that are poured into sewers and drains to
kill plant and tree roots, and TBT pesticides used in cooling towers
in air conditioning systems to control microbes (such as bacteria,
algae and fungi) that can cause fouling.
For several years, copper and TBT levels have
exceeded acceptable levels in the Bay and its estuaries, prompting the
Regional Water Board to mandate that water treatment plants reduce the
two chemicals in their discharges to acceptable levels by 1996 or face
penalties up to $25,000 a day and possible suspension of their
operating permits.
Although the copper and TBT products are used in
relatively small amounts, their application either directly or
indirectly into sewers, has a disproportionate impact on water
treatment plants and the water discharged. Low-level contamination can
affect marine life such as crabs, clams and micro-aquatic organisms at
the bottom of food chains. In 1992, the Regional Water Board set a
limit for TBT of 0.005 parts per billion (ppb) and 4.9 ppb for copper
in water discharged from treatment plants.
CalEPA has determined that there are many sources
of copper which are not easy to control. They include abandoned mines,
drinking water pipes, brake linings, human wastes, food wastes and
laundry grey water. CalEPA cites a 1994 study of metals in wastewater
which found copper should be given a high priority for control, with
the focus being on reducing use of copper-containing root control
compounds.
Potential sources of TBT are all pesticidal,
including some cooling water system additives, antifouling paints used
on boats, timber treatment products, commercial toilet cleaners, and
disinfectant carpet cleaners. Another study, carried out in the Palo
Alto area found that TBT contamination was primarily as a result of
discharges from cooling systems.
CalEPA, press release, 13/12/95.
[This article first appeared in Pesticides News No. 31,March 1996, page 21]