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This study was conducted to investigate the change of some biochemical parameters in the aquatic invertebrate Daphnia magna following exposure to the fungicide tebuconazole and to determine the most sensitive biomarker among the ones tested in this species. Four biochemical biomarkers (protein, glycogen, lipids and caloric content) were correlated with feeding behaviour studies of D. magna after fungicide exposure. Juveniles of D. magna were exposed to four sublethal concentrations of tebuconazole (0.41, 0.52, 0.71 and 1.14 mg L−1) for 5 d. Daphnid samples were taken from each test and control group at 24, 48, 72, 96 and 120 h after the start of the experiment. Tebuconazole EC50 values were calculated on D. magna in our laboratory as 56.83 and 40.10 mg L−1 at 24 and 48 h, respectively. Results showed that daphnid energy content decreased as tebuconazole concentration increased, especially after 96–120 h of exposure to 0.52 mg L−1 and higher fungicide concentrations. The data suggest that tebuconazole is moderately toxic to D. magna but also that it seriously impairs the metabolic functions, resulting in alterations in biochemical constituents. In the D. magna feeding study, algae feeding rates were inhibited after fungicide exposure. Such findings indicate the importance of feeding studies in laboratory toxicity test as well as their relationship with others studies. The results emphasize the importance of considering different kind of biomarkers to identify and evaluate the biological effect of a fungicide in the aquatic environment. Although the biochemical biomarkers used resultated good indicators of tebuconazole toxicity, feeding rates in D. magna decreased after only 5 h exposure to the fungicide resulting in the most sensitive parameter of daphnid fungicide exposure.

Acute and chronic toxicity tests with propanil were conducted on Daphnia magna. The 24 and 48 h LC50 were 43.74 and 5.01 mg/l respectively. Chronic toxicity tests were carried out using sublethal propanil concentrations (0.07, 0.10, 0.21 and 0.55 mg/l) during 21 days. The effect of propanil on survival, reproduction and growth of D. magna organisms was monitored. The parameters used to evaluate herbicide effect on reproduction were: mean total young ones per female, mean brood size, time to first reproduction, mean number broods per female and intrinsic rate of natural increase (r). Survival and growth (body length) were also determined after 21 days of exposure to the herbicide. Reproduction was significantly reduced when propanil concentration increased in the medium. The intrinsic rate of natural increase (r) decreased with increasing concentrations of propanil especially in those animals exposed to 0.55 mg/l. However, growth as well as survival of the exposed organisms only decreased in daphnids exposed to the highest propanil concentration tested. The maximum acceptable toxicant concentration (MATC) was calculated for D. magna exposed to the herbicide using as parameter of evaluation the intrinsic rate of natural increase (r). The interpolation of these results gave MATC values of 0.08 mg/l herbicide. We have derived the EC50 values for some selected parameters on D. magna exposed to propanil. EC50 values indicated that reproductive parameters were very sensitive of the effect of propanil on daphnids. Finally, the daphnids were exposed to the same sublethal herbicide concentrations as in the chronic study and the effect of the toxicant on filtration and ingestion rates was determined. Feeding rates of D. magna declined with increasing propanil concentrations. The effective propanil concentrations at which feeding rates were reduced to 50% of that in controls (EC50) were also calculated.