Persulfate anion (S2O2 8 ), a widely used in situ chemical oxidation agent, is increasingly applied for environmentalremediation. However, limited information on environmental and toxicological effects isavailable for the evaluation of the environmental risk of exposure to S2O2 8 , particularly after its application.In this study, the acute toxic effects on the common carp (Cyprinus carpio) were employed as amodel to investigate S2O2 8 , sulfate ion (decomposition product of S2O2 8 ), hydrogen/hydroxide ions andalso the mixtures of these ion species. Acute toxicity test results showed 96 h median lethal concentrations(LC50) of 540 ± 23 mg L 1 for S2O2 8 and 4100 ± 110 mg L 1 for SO2 4 . S2O2 8 was considerably moretoxic than its decomposition product SO2 4 . Additionally, solution pH was also an important factor influencingtoxicity, and S2O2 8 posed reduced acute toxicity when pH was in the range of 6–10. Water conductivityup to approximately 8000 lS cm 1 did not appear to significantly increase fish mortality. Inthe mixture toxicity test (i.e., S2O2 8 /OH ), LC50 values of 130 ± 10 mg L 1 for S2O2 8 and 23 ± 2 mg L 1for OH were lower than those obtained from the individual toxicity tests and therefore exhibited highertoxicity to fish. However, upon complete decomposition of S2O2 8 in the mixture, a reduction in acute toxicitymay be expected. The results of this study revealed that it may be necessary and/or desirable to controlthe residual S2O2 8 and pH after S2O2 8 addition when potential exposure to an aquatic system is aconcern
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