ACUTE TOXICITIES OF NINE CHLORINATED ORGANIC COMPOUNDS TO SELECTED FRESHWATER ORANISMS
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Acute flow-through toxicity tests were conducted with 1 nin e chlorinated organic compounds and four species of freshwater organisms. Eight compounds (1 ,2-dichlorobenzene, 1 ,4-dichlorobenzene, 1,2,4-tirchlorobenzene,hexa chlorobenzene, 1 ,3-hexachlorobutadiene, hexachloroethane, tetrachloroethylene, and pentachlorophenol) were selected from a list of priority pollutants identified by the U.S. Environmental Protection Agency for which water quality criteria would be written. Pentacblorobenzene was also tested. Test organisms included rainbow trout (Salmo gairdneri), bluegills (Lepomis macrochirus), midge larvae (_Par-atanytarsus parthenogeneticus), and gammarids (Gammarus pseudolimna eus). Lc50 values were determined for all compounds except hexachlorobenzene, which did not produce sufficient mortalities at the highest exposure levels. LC50 values (96 h) for trout exposed to 1,2-dichlorobenzene, 1,4-dichlorobenzene, 1,2,4-trichlorobenzene and hexachloroethane were 1.58, 1.12, 1.53, and 0.94 mg/L, respectively. Pentachlorobenzene did not produce 50 percent mortality in trout after 96 h of exposure; however, two 144 h LC50 values of 0.25 and 0.25 mg/L were obtained in separate tests. 1,3-Hexachlorobutadiene tests were conducted with bluegills and rainbow trout and yielded identical 96 h LC50 values of 0.32 mg/L. One gammarid exposure was conducted with pentachlorophenol and yielded a 0.28 mg/L 96 h LC50. Midge larvae were less sensitive than rainbow trout or gammarids when tested with. the same compounds. LC50 values (48 h) of 12.0, 13.b, 46.0, 5.85 and 30.8 mg/L were obtained for 1,2-dichlorobenzene, 1,4-dichlorobenzene, penta chloroph.enol, hexachloroethane, and tetrachloroethylene, respectively, with midge larvae. EC50 values were also calculated.