Chronic toxicity of diazinon todaphnia magna:Effects on survival, reproduction and growth

The sublethal effect of 0.15, 0.18, 0.22, 0.25 and 0.30 μg/L diazinon on the survival, reproduction and growth of D. magna was monitored for 21 days. Neonates (≤ 24 h) were obtained from the stock cultures and raised individually in 50 mL glass beakers. All daphnids were transfered every other day to a new beaker containing fresh medium, food and the appropriate pesticide concentration. The animals were maintained in an environmental chamber at 22±1°C on a 12L: 12D photoperiod and were fed daily on 5 x 105 cell/mL of the green algae Nannochloris oculata. The parameters used to determine the effect of the pesticide on reproduction were: mean total young per female, mean brood size, mean number of broods, mean time to first reproduction and intrinsic rate of natural increase “r”. Growth of surviving adults was determinated after 21 days of exposure. The maximun acceptable toxicant concentration (MATC) was also calculated. Survival was affected with 0.18, 0.25 and 0.30 μg/L diazinon. All concentrations caused a decreased in mean total young per female, mean brood size and intrinsic rate of natural increase compared to control. Only the two highest concentrations used (0.25 and 0.30 μg/L) caused a delay in the time to first reproduction. Growth was depressed at all diazinon concentrations tested.