Assessing acute toxicity potential of persulfate ISCO treated water

Persulfate anion (S2O8(2-)), a widely used in situ chemical oxidation agent, is increasingly applied for environmental remediation. However, limited information on environmental and toxicological effects is available for the evaluation of the environmental risk of exposure to S2O8(2-), particularly after its application. In this study, the acute toxic effects on the common carp (Cyprinus carpio) were employed as a model to investigate S2O8(2-), sulfate ion (decomposition product of S2O8(2-)), hydrogen/hydroxide ions and also the mixtures of these ion species. Acute toxicity test results showed 96h median lethal concentrations (LC50) of 540±23mgL(-1) for S2O8(2-) and 4100±110mgL(-1) for SO4(2-). S2O8(2-) was considerably more toxic than its decomposition product SO4(2-). Additionally, solution pH was also an important factor influencing toxicity, and S2O8(2-) posed reduced acute toxicity when pH was in the range of 6-10. Water conductivity up to approximately 8000μScm(-1) did not appear to significantly increase fish mortality. In the mixture toxicity test (i.e., S2O8(2-)/OH(-)), LC50 values of 130±10mgL(-1) for S2O8(2-) and 23±2mgL(-1) for OH(-) were lower than those obtained from the individual toxicity tests and therefore exhibited higher toxicity to fish. However, upon complete decomposition of S2O8(2-) in the mixture, a reduction in acute toxicity may be expected. The results of this study revealed that it may be necessary and/or desirable to control the residual S2O8(2-)and pH after S2O8(2-) addition when potential exposure to an aquatic system is a concern.