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002531 4.3.1 EPA Water Quality Standards , given by e(o..S4Sl_",)]'lA6S) more than' once every three years on the average and if the 1-hour average concentration (in j-IgIl) does not exceed the numerical value given by e(O.9422[In(lwdn"')}1.464) more than once every three years on the average. At a hardness of 50 mgll the acute toxicity for Ptychochei Ius was found to be 16.74 Jl-gIl (EPA 1986). Iron - The EPA criterion for iron is 1.0 mgll. Lead - The acute toxicity of lead in several species has been shown to decrease as water hardness increases. The EP A states that, except where a locally important species is very sensitive, freshwater aquatic organisms should not be affected unacceptably if the 4-day average concentration of lead (in j-Ig/I.) does not exceed the numerical value given by e(l.273[In(lwdn~)}4.70S) more than once every three years on the average and if the 1-hour average concentration (in Jl-gIl) does not exceed the numerical value given by e(1.273[1n(lwdn",])-1.460) more than once every three years on the average. Mercury - TheEPA states that the acute toxicity of mercury (II) for fishes ranges from 30 Jl-gIl for guppies to 1,000 Jl-gIl for Tilapia spp. The chronic toxicity level of mercury (II) in fathead minnow has been shown to be 0.26 j-IgIl. According to the EP A, freshwater organisms should not be affected unacceptably if the 4-day average concentration of mercury (II) does not exceed 0.012 Jl-gIl more than once every three years and if the 1-hour average concentration does not exceed 2.4 Jl-gIl more than once every three years on average. Methylmercury is the most chronically toxic, with values ofless than 0.07 Jl-gIl. Radionuc1ides - No EP A criteria exist for radionuclides (uranium, thorium, radium-226). Selenium -In 1987 the EP A lowered the permissible level of waterborne selenium from 35 Jl-gIl to 5 Jl-gIl as a 24-hour average. Lemly (in press) recommends that waterborne selenium concentrations of 2 j-IgIl or greater be considered highly hazardous to the health and long-term survival of fish and wildlife. The EP A's acute criterion for selenium is 20 Jl-g/I. (U.S. Enviromnental Protection Agency 1993). The EP A acute criterion for selenite is 260 Jl-gIl. Acute toxicity of inorganic selenate can occur as low as 760 Jl-gIl and may be lower for more sensitive fish (U.S. Enviromnental Protection Agency 1986). Silver - The EP A criterion for total silver is based on water hardness. The EP A states that the concentration of total recoverable silver (in Jl-gIl) should not exceed the numerical value given by e(l.72[ln(lwdn",)j.6.S2) at any time. Chronic toxicity to freshwater aquatic life may occur at concentrations as low as 0.12 j-IgIl. Zinc - The EP A criterion for zinc is based on water hardness. The EP A states that for total recoverable zinc, the concentration (in Jl-gIl) should not exceed the numerical value given by e(o,"lln(hm'dnou)]+1.9S) at any time. The chronic criterion is given by e(O.S473[In(lwdn"')]+'604). Hydrocarbons - The EP A has not set any acute or chronic criteria for P AHs as a group. It states that acute and chronic toxicity of naphthalene occurs at concentrations as low as 2,300 j-IgIl and 620 j-IgIl, respectively, and could occur at lower concentrations among sensitive species. The EP A also states that acute toxicity ofbeDZene and toluene to freshwater life occurs at concentrations as low as 5,300 Jl-gIl and 17,500 Jl-gIl, respectively; there are no chronic toxicity standards for either compound. The above standards are only for surface water quality. The EP A has not issued standards for trace elements or organics in soils, sediment, food items, or fish tissue. (The Food and Drug Administration regulates trace elements and organics in fish, but these standards are based on concerns for human rather than fish health.) Data collected for these components are normally compared with data or 21