EFFECTS OF WATER TEMPERATURE AND PH ON TOXICITY OF TERBUFOS, TRICHLORFON, 4-NITROPHENOL AND 2,4-DINITROPHENOL TO THE AMPHIPOD GAMMARUS-PSEUDOLIMNAEUS AND RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

Acute toxicity tests were conducted to determine (a) the individual an d interactive effects of water temperature (7, 12, 17-degrees-C), pH ( 6.5, 7.5, 8.5, 9.5), and time on the toxicity of terbufos, trichlorfon , 4-nitrophenol, and 2,4-dinitrophenol to rainbow trout (Oncorhynchus mykiss) and the amphipod Gammarus pseudolimnaeus, and (b) the individu al and interactive effects of water temperature and pH on chemical bio concentration during acute tests with rainbow trout and Gammarus expos ed to terbufos, 4-nitrophenol, and 2,4-dinitrophenol. The toxicity of all four chemicals was significantly affected by pH in all tests, exce pt for Gammarus exposed to terbufos. The toxicity of terbufos to rainb ow trout and Gammarus was less at pH 7.5 than at higher or lower pH. T he toxicity of both nitrophenols decreased as pH increased, whereas th e toxicity of trichlorfon increased with pH. The effect of pH on trich lorfon toxicity decreased with temperature. Temperature significantly affected the toxicity of all four chemicals to both species. Toxicity increased with temperature in all tests, except for rainbow trout expo sed to nitrophenols; toxicity decreased as temperature increased for r ainbow trout. Chemical bioconcentration was also significantly affecte d by temperature and pH and was directly related to toxicity in most t ests. Significant interactive effects between toxicity-modifying facto rs were also frequently observed. Temperature and pH effects on chemic al toxicity need to be considered in chemical hazard assessment to ens ure adequate protection of aquatic organisms.