Effects of sunscreens on plants: Impact of TiO2 nanoparticles on the phytoremediation of oxybenzone

Increasing levels of sunscreens have been found in surface waters, and in waste water. In most cases mixtures of organic and inorganic sunscreen compounds can be detected. Wetland plants, and vegetation along shores have been used as biological filters for this kind of pollution along beaches, and in phytoremediation. The situation is complicated since organic sunscreens like Oxybenzone (OBZ) can be present in the environment as emerging contaminant together with inorganic nanoparticulate TiO2 as typical for the composition of many sunscreens. Hence, potential effects caused by TiO2 must be considered when investigating the performance of aquatic plants with regard to fate and potential remediation of OBZ. When toxic effects of both, OBZ and TiO2 on plant development were evaluated, OBZ significantly inhibited germination rate of tomato (Lycopersicum esculentum) seeds, while no effect was observed for germination of barley (Hordeum vulgare). Interestingly, co-exposure with TiO2 lowered the toxicity of OBZ on the tomato seedlings as there were no differences on germination rate and root length between co-exposure and control treatments. Moreover, growth inhibition tests with Lemna minor showed that addition of TiO2 even enhanced growth of the plantlets, by increasing the frond area. Furthermore, influence of TiO2 at concentrations of 3 mg/L on the uptake and removal of OBZ (5 µM) by plants was exemplarily examined with respect to the variations in uptake and metabolism of OBZ in a hairy root culture system of horseradish (Amoracia rusticana). Co-exposure with TiO2 led to an increased accumulation of OBZ in the plant tissues, while transient decreases of the transformation rate to OBZ metabolites was recognized when TiO2 had been added to the media. It might hence be concluded that Ti nanoparticles deriving from sunscreens may generally reduce the phytotoxicity of the co-occurring OBZ and increase the uptake of this compound in plants. Further studies must consider the interaction of these PPCP molecules with the transformation capacity of plants when planning to apply phytoremediation for UV-filter contaminated water.