Aqueous phenanthrene toxicity after high-frequency ultrasound degradation

Given that polycyclic aromatic hydrocarbons (PAHs), such as phenanthrene (PH), possess a potent risk for aquatic biota, a great attempt to develop and apply advanced oxidation processes, such as ultrasound (US), is of great concern nowadays. However, because US PAH-derived toxic intermediates are difficult to detect, the present study investigates aqueous PH toxicity before and after high-frequency US degradation, in hemocytes of mussel Mytilus galloprovincialis. Specifically, cell viability (with the use of neutral red uptake/NRU method), and oxidative-stress indices in terms of superoxide anions, (O2(-)), nitric oxides (NO, in terms of nitrites), lipid peroxidation products (in terms of malondialdehyde/MDA content) and DNA damage (with the use of Comet assay method) were investigated in mussel hemocytes exposed to environmentally relevant concentrations of PH (0.01, 0.1, 1 and 10 μg L(-1)), before and after US treatment for 120 min (at a frequency of 582 kHz). According to the results, the NRU method showed a significant attenuation of PH-induced mortality in US PH-treated hemocytes in all cases. Moreover, the increased levels of O2(-) and NO generation, as well as MDA content measured in PH-treated hemocytes, were drastically decreased after US degradation in any case. Similarly, the disturbance of DNA integrity (in terms of % DNA in tail, OM and TM), was negligible in case of US PH-treated hemocytes. Although further in vitro and in vivo studies are needed, the present study showed for the first time that high frequency US could be applied as a highly efficient and "environmentally friendly" process for degrading low molecular weight PAH, such as PH.