Chronic toxicity of fenitrothion to an algae (Nannochloris oculata), a rotifer (Brachionus calyciflorus), and the cladoceran (Daphnia magna).

Chronic toxicity studies were conducted with an algae (Nannochloris oculata), a rotifer (Brachionus calyciflorus), and a cladoceran (Daphnia magna) to determine their relative sensitivities to the organophosphorus insecticide fenitrothion. The cladoceran D. magna was the most sensitive of the three species. The no observed effect concentrations (NOECs) for the study with the algae (1.0 mg/liter) and for the rotifer (1.0 mg/liter) were higher than the NOEC (0.009 microgram/liter) and the LC50 of 24 hr (0.067 microgram/liter) for D. magna. Most of the algal populations were not initially affected by exposure to fenitrothion. Pesticide concentrations higher than 1.0 mg/liter significantly reduced algal densities after 72 hr exposure. The effects of chronic exposure of the rotifer B. calyciflorus to fenitrothion were evaluated using some demographic parameters: intrinsic rate of natural increase (r), generation time, net reproductive rate, and life expectancy. All the parameters studied decreased with increasing toxicant concentrations. The parameters used to determine the effect of the pesticide on D. magna reproduction were mean total young per female, mean brood size, mean time to first reproduction, and r. The r and the rest of the studied parameters were affected at 0.011-microgram/liter and higher fenitrothion concentrations. Growth, as measured by body length, was only depressed significantly at 0.011 microgram/liter pesticide.