Effects of environmentally realistic daily temperature variation on pesticide toxicity to aquatic invertebrates.

The toxicity of several agricultural chemicals to aquatic invertebrates has been shown to be temperature-dependent, but the role of daily temperature variation has rarely been examined. The authors simulated a natural daily temperature pattern (a fluctuating cycle of 21 °C to 31 °C over a 24-h period) based on field-collected data from Southern High Plains wetlands (TX, USA) and conducted a series of experiments comparing responses from this exposure scenario to a constant exposure at 24 ± 1 °C. Results indicate alterations in pesticide toxicity under the fluctuating temperature regime compared with that of the constant temperature exposure. There was a significant interaction of temperature regime and bifenthrin on Chironomus dilutus survival, and C. dilutus ash-free dry mass was lower in the fluctuating temperature treatment. The 10-d median lethal concentration (LC50) for Hyalella azteca exposed to chlorothalonil was lower under the fluctuating temperature regime compared with the constant temperature regime. For Daphnia magna exposed to malathion, the main effects of temperature regime and malathion were observed on cholinesterase activity. The present study demonstrates how environmentally relevant daily temperature variation influences contaminant effects on aquatic invertebrates.