Temperature-dependent toxicities of chlorothalonil and copper pyrithione to the marine copepod Tigriopus japonicus and dinoflagellate Pyrocystis lunula

Abstract

The anticipated anthropogenically-driven climate change may ultimately result in increased incidents of temperature extremes that will have profound implications on the toxicity of chemical contaminants and hence their ecological risks to marine organisms in the tropics and subtropics. We hypothesised that chemical toxicity generally increases with increasing temperature over the thermal tolerance range (TTR) of a species, and is further exacerbated at extreme temperatures (i.e. lower or higher than the TTR). To test this hypothesis, we investigated the acute toxicity of two commonly used antifouling biocides, chlorothalonil and copper pyrithione (CuPT), to the marine copepod Tigriopus japonicus and dinoflagellate Pyrocystis lunula over a wide range of water temperatures. Our results verified that toxicities of the two biocides, in terms of 96-h LC50 (for T. japonicus) and 24-h EC50 (for P. lunula), were highly temperature-dependent, although the profile of temperature-dependency varied between the two chemicals. The LC50 values of T. japonicus exposed to CuPT decreased with increasing temperature between 15–31°C (i.e. assumed TTR), whereas the LC50 values at 4 and 35°C were significantly lower than those at 10 and 25°C, respectively. The toxicity of chlorothalonil to the copepod followed the same pattern of CuPT between 25 and 35°C but the LC50 values between 4 and 25°C were somehow indifferent. In P. lunula, a similar temperature-dependent toxicity was also observed for CuPT but not for chlorothalonil. Such dissimilar temperature-dependent toxicity profiles between the two biocides may be partially attributable to the differences in temperature-mediated modifications of their physicochemical properties, bioavailability, toxicokinetics, and thus resultant toxicity to the test organism.