Effect of some pesticides on reproduction of rotifer Brachionus plicatilis Muller

Pesticides have been major contributors to environmental pollution and they are now widely distributed in aquatic environments. Zooplankters are frequently used as test animals to detect aquatic contaminants because of their sensitivity and ecological importance. We investigated the effect of a 7-day exposure to four commonly used pesticides (diazinon, fenitrothion, methoprene and isoprothiolane) on reproduction of the rotifer Brachionus plicatilis. Pesticide concentrations of 3-7 times lower than the 24-h 50% lethal concentration (24-h LC50) were tested to determine the 'no observed effect' concentration (NOEC), 'lowest observed effect' concentration (LOEC), and the '50% effective' concentration (EC50) on specific growth rate (r), sexual reproduction, fertilization, resting egg production, and hatchability of resting eggs. Results showed that the lowest EC50 value of r, mixis, fertilization, and resting egg production of 1.4 mu M for diazinon was 63 times lower than its 24-h LC50 of 88.4 mu M, while for fenitrothion it was 66 times (3.5 and 229.8 mu M, respectively). For isoprothiolane, the lowest EC50 value of r, mixis, fertilization.. and resting egg production of 8.9 mu M was 25 times lower than its 24-h LC50 of 220.7 mu M, while for methoprene was 37 times (2.7 and 100.8 mu M, respectively). In all pesticides, hatching rate of resting eggs consistently gave the lowest EC50 values which is about 2-40 times lower than the lowest EC50 of r, mixis, fertilization, and resting egg production. Hatchability of resting eggs therefore is the most sensitive parameter in detecting effects of pesticides exposure in rotifer B. plicatilis.