Temperature-dependent toxicities of nano-zinc oxides on three marine organisms

Abstract

Nano zinc oxide (nZnO) is increasingly used in sunscreen products, with high potential of being released directly into marine environments. Our laboratory has previously demonstrated that toxicity of nZnO on marine organisms can be attributed to the release of metal ions and aggregate sizes (Analytical Bioanalytical Chemistry 396: 609-618; 2010). Other recent studies have further showed that different temperatures can alter the agglomerate sizes (Journal of Applied Toxicology, 30:276-285; 2010) and ion release rates (Environmental Science & Technology 44: 2169-2175; 2010) of nanomaterials in water. In this study we, therefore, hypothesize that the toxicities of nanomaterials on marine organisms are augmented with increasing temperature within their thermal tolerance ranges. Acute toxicity tests were conducted using the marine diatom Thalassiosia pseudonana, the amphipod Elasmopus rapax, and the fish Oryzias melastigma exposed to nZnO under various temperatures (i.e., 10°C, 15°C, 25°C, 30°C and 35°C). Our results showed that toxicity of nZnO generally increases with increasing temperature. For example, the LC50 values of nZnO on the amphipod decreased from 8.33 mg L-1 at 15°C to 0.10 mg L-1 at 30°C. To further elucidate the mechanism, we are currently investigating the interacting effect of temperature and nZnO on the expression of stress proteins such as heat shock proteins in the fish while we will examine the chlorophyll content and photosynthetic activity of the diatom. The results will be discussed with reference to the temperature-dependent physicochemical properties of nZnO.