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Water quality and nonpoint sources
in urban watersheds
Key findings from the first decade of NAWQA studies
Water resources in U.S. urban areas are impaired. ("Urban"
refers primarily to residential and commercial development
since World War II.) Many of the impairments are attributable
to nonpoint sources, such as vehicle emissions and applications
of pesticides and fertilizers around homes and in public areas.
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Contaminants are widespread in urban streams, and biological
communities are stressed
- Concentrations of total phosphorus exceeded the desired
goal of the U.S. Environmental Protection Agency (USEPA)
to control nuisance plant growth in more than 70 percent
of urban streams. Excessive plant growth can lead to low
levels of dissolved oxygen (hypoxia). Hypoxic conditions
can be harmful to fish and other aquatic life.
- Insecticides are widespread and usually at higher concentrations
than in agricultural areas. Two popular insecticides--diazinon
and chlorpyrifos--are often found mixed together. Herbicides
are in 99 percent of urban streams sampled; simazine and
prometon commonly are found together.
Pesticide concentrations rarely exceeded USEPA drinking-water
standards, but every stream sampled exceeded at least one
guideline for protecting aquatic life. Moreover, standards
do not exist for many pesticides or for mixtures of pesticides
- Fecal coliform bacteria commonly exceeded recommended
standards for water recreation.
- Biological communities are dominated by algae and aquatic
invertebrates that can tolerate pollution, such as worms
and midges, and omnivorous fish, such as catfish and largescale
suckers.
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Volatile organic compounds (VOCs) are widespread in shallow
ground water in urban areas
- Most frequently detected are the solvents trichloroethene
(TCE), tetrachloroethene (PCE), and methylene chloride;
the gasoline additive methyl tert-butyl ether (MTBE); and
chloroform, the solvent and disinfection by-product of water
treatment.
Sediment and fish tissue in urban areas reflect past chemical
use as well as current trends
- Banned insecticides such as DDT, chlordane, and dieldrin
still persist in sediment and fish tissue. Concentrations
exceeded guidelines to protect wildlife at more than 10
percent of urban sites. High concentrations of polychlorinated
biphenyls (PCBs), which were used in insulation and as a
lubricant but have not been sold since 1979, were also found
in most fish tissue; guidelines were exceeded at nearly
70 percent of urban sites. Some states have issued fish-consumption
advisories.
- Lead, mercury, cadmium, and zinc are elevated above background
levels in sediment, most likely caused by emissions from
industrial activities and motor vehicles. Lead concentrations
have been decreasing, however, since being removed from
gasoline in the 1970s.
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