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PHYSICOCHEMICAL FACTORS AFFECTING TOXICITY IN FRESHWATER: HARDNESS, PH, AND TEMPERATURE
Citation:
Mayer, Jr., F., L. Marking, T. Bills, AND G. Howe. PHYSICOCHEMICAL FACTORS AFFECTING TOXICITY IN FRESHWATER: HARDNESS, PH, AND TEMPERATURE. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/A-94/199 (NTIS PB95122990).
Description:
A search of the literature for effects of hardness, pH, or temperature on the toxicity of chemicals to freshwater organisms suggested that the amount of reliable and useful data is limited. uch of the disparity among results reported in the literature was caused by improperly designed tests. hus, effects of modifying factors on toxicity should be interpreted within experiments and not between them. ardness does not appear to affect the toxicity of organic chemicals, but metals are generally more toxic in waters of low hardness. f the chemical characteristics of water, pH caused the greatest change in toxicity. ndisassociated organic molecules penetrate cell membranes more readily than dissociated ones. he toxicity of ionizable organic chemicals (weak acids and bases) is greatly affected by pH; decreases in pH increase the toxicity of acids but lowers the toxicity of bases. ncreased temperature is known to stimulate metabolism -- and thus the uptake of chemicals -- in invertebrates and fish. orrespondingly, most reports in the literature suggested that for many chemicals, acute toxicity increased as test temperature increased. owever, chronic no-observed-effect concentrations are not affected by temperature; only the rate of intoxication is altered. hysicochemical factors do not appear to affect toxicity per se, but do affect bioavailability and exposure.