The CWA regulates many toxic pollutants through NPDES permits. Table 4.5.6 lists priority pollutants that the EPA has designated as toxic. Effluent standards have been promulgated for some of these pollutants, listed in Table 4.5.7.
The water environment can be monitored for toxic pollutants in the following three ways:
By a bioassay in which organisms are placed in water samples and their reaction is compared with control. This method is receiving attention for monitoring toxic discharges.
By plants and animals that are reactive to types and degrees of pollution. The absence of organisms known to be intolerant of pollution also serves as an indication of pollution; the presence and expansion of pollutiontolerant organisms is a related index of pollution.
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