Temperature-dependent effects of the pesticides thiacloprid and diazinon on the embryonic development of zebrafish (Danio rerio)

The present study examined combined effects of the insecticides thiacloprid and diazinon and a physical stressor, elevated temperature (28, 30 and 33.5 °C, control at 26 °C), on embryonic development of zebrafish (Danio rerio). Early life stages were exposed to five different concentrations (thiacloprid: 1, 5, 10, 15 and 20 mg/L; diazinon: 100, 500, 1000, 2000 and 3000 μg/L) for 72 or 96 h, respectively, depending on the temperature. Thiacloprid was shown to have no effects on early life stage parameters, except on the heart rate. This effect was probably due to an increased metabolism upon exposure to the pollutant. Exposure to diazinon resulted in mortality which strongly increased with elevated temperature. Within the tested temperature range, increased mortality occured particularly at concentrations of 2000 and 3000 μg/L diazinon. Observed sublethal effects were a decrease of the heart rate with increasing substance concentration, yolk sac edema, heart sac edema and spine deformations, particularly at concentrations of 2000 and 3000 μg/L diazinon. The hatching date was shown to be preponed with increasing temperature, most strikingly in combination with 2000 or 3000 μg/L diazinon. Mixtures of temperature and substance concentration as independent variables were shown to act synergistically in a dose-level-dependent manner on hatching rate, whereas the magnitude of synergism depended on effect levels.