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Pollutants are carried into the Estuary in runoff from both urban and agricultural areas and discharged by storm drains and wastewater treatment plant and industrial outfalls. Other pollution in the Estuary comes from polluted air, discharges from boats, underground seepage, streams and rivers, and dredged sediments.
Another more visible type of pollution—trash—has become an epidemic in the Estuary and its watersheds. Some pollutants, carried into the Estuary by industrial dischargers and even wastewater treatment plants, are less obvious than trash but may be even more deadly to aquatic life. An estimated five to 40 thousand metric tons of toxic pollutants end up in the Estuary each year, including trace elements such as copper, nickel, silver, and zinc, and synthetic organic compounds. Mercury (from the gold mining that took place over a century ago) is still a problem in the Estuary; one of its forms, methylmercury, can build up ("bioaccumulate") in the food web, as can selenium, discharged into the Estuary by refineries and in runoff from certain agricultural lands. Selenium can cause birth defects in birds.
And while we have phased out the use of certain toxic pesticides, newer replacement pesticides such as pyrethroids, have been found to be toxic to aquatic life even in small amounts (for more about pyrethroids, click here to read an article from ESTUARY NEWS from December 2008). Emerging" pollutants—such as flame retardants and a myriad of personal care products and pharmaceuticals—are also ending up in the Estuary. (To read more about some emerging contaminants, click here.) Harbor seals, fish, Forster's terns, and mussels in the Estuary are now contaminated with PBDEs from flame retardants used in furniture, computers, and other products.
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