S2O8/UV-C and H2O2/UV-C TREATMENT OF AQUEOUS BISPHENOL A RESULTS IN DIFFERENT ACUTE TOXICITY PATTERNS

Bisphenol A (2,2-bis(4-hydroxyphenyl)propane), a chemical compound used in the manufacture of polycarbonate, epoxy and polysulfonate resins, can alter the endocrine system, causing adverse effects in the reproductive systems of humans and animals. More recently, the application of advanced oxidation processes (AOPs) has been recommended to treat toxic and/or biorefractory compounds including BPA. AOPs involve the fast and non-selective degradation of organic pollutants by highly reactive free radicals such as HO and SO4 to more biodegradable oxidation intermediates or nontoxic end products. However, it should be considered that owing to the non-selective and difficult-to-control nature of AOPs, the toxicity of degradation products should be measured during their application. Toxicity assessment is of crucial importance in order to decide whether the treatability of industrial pollutants via AOPs is ecotoxicologically and technically feasible. In the present work, the performance of UV-C treatment and two photochemical AOPs, namely S2O8/UV-C and H2O2/UV-C treatments, was investigated for the degradation and detoxification of 20 mgL (88M) aqueous BPA solutions. The acute toxicity of BPA and its degradation intermediates was examined by employing V. fischeri and P. subcapitata test protocols. Based on preliminary experiments, optimum reaction conditions were set as 2.5 mM oxidant concentration and an initial pH of 6.5. Experimental results indicated that as compared to HO and SO4-radical based treatment, direct UV-C photolysis appeared to be inefficient for the removal of BPA (52%) and TOC (3%) after 60 min irradiation. In parallel to these results, only a minor decrease in the acute toxicity towards the investigated test organisms was observed at the end of 60 min irradiation. On the other hand, BPA removal was complete within 3 min when being subjected to S2O8/UV-C oxidation, accompanied by a rapid mineralization that resulted in 84% TOC removal after 60 min treatment. During the application of H2O2/UVC oxidation, complete BPA removal could be achieved after only 4 min; whereas 93% TOC was removed after 50 min treatment. Noteworthy were the acute toxicity profiles observed for V. fischeri during H2O2/UV-C treatment; a prompt reduction from 73% (relative inhibition caused by 20 mgL BPA) to only 14% after 5 min was followed by an abrupt re-increase to 85% after 20 min oxidation, thereafter decreasing to 3-5%, speaking for the formation and subsequent degradation of relatively toxic oxidation products by H2O2/UV-C treatment. During S2O8/UV-C oxidation of BPA solution, however, a continuous decrease in the acute toxicity towards V. fischeri and P. subcapitata was observed; the relative inhibition decreased to insignificant values after 10 min treatment and did not change thereafter. The above results revealed that although treatment efficiencies were found similar for S2O8/UV-C and H2O2/UV-C processes, differences in acute toxicity responses suggest variations in reaction pathways and products.