One-Hour Temperature-Based Toxicity Test with Daphnia magna

Abstract

A 1-hour temperature-based toxicity test using Daphnia magna was developed and then compared with a 24-hour standard acute toxicity test. The 1-hour toxicity test was based on the observation that daphnids in high temperatures become weak and more susceptible to toxicants than daphnids at room temperature. Theorizing that this relationship could be utilized to produce a short-term toxicity test, we analyzed the experimental data and identified 36.5°C as the ideal temperature for a 1-hour temperature-based toxicity test. After the test was formulated, it was used to screen 15 toxicants. Eight heavy metals, 4 pesticides, 2 anions, phenol, and 2 industrial wastewaters were screened, using the 1-hour toxicity test and the 24-hour standard acute toxicity test. For the 1-hour toxicity test, vials containing 5 daphnids (<24 h), medium, and toxicant, all at room temperature, were prepared and placed in a water bath set at 36.5°C for 1 hour. After 1 hour, the numbers of live (no toxic effect) daphnids and immobilized (toxic effect) daphnids were counted, and the median effective concentrations (EC50) were determined. A comparison of the EC50 values of the 1-hour temperature-based toxicity test and those of the 24-hour standard acute toxicity test produced a correlation of 0.9999. When individual toxicants were compared, the 24-hour standard acute toxicity test was better at detecting lower test concentrations than the 1-hour temperature-based toxicity test. When both tests were used to screen industrial wastewater and their results were compared, the 1-hour toxicity test showed some promise. However, further testing will need to be done, because only 2 of the 10 samples collected initially contained significant amounts of toxicants for EC50 calculation. Finally, while the 1-hour toxicity test was effective in screening 15 tested toxicants and has the potential to be useful in screening industrial wastewater, this conclusion is limited to those 15 tested toxicants and 2 industrial wastewaters. Additional experiments will be needed for other toxicants. The 1-hour toxicity test presented in this study is the first temperature-based toxicity test developed for D. magna, and it will be an attractive short-term assay for its convenience, cost-efficiency, and replicability.