Acute Pesticide Toxicity on <i>Oreochromis Niloticus</i>, with Particular Reference to Insecticides

Abstract

Pyriforce 600 EC and Cyperplant 100 EC are insecticides used in large quantities in agricultural practices in Cameroon. Residues due to intensive agriculture combined with surface runoff and surface drainage, a few weeks after application are deposited in water courses like ponds, rivers and lakes. This has negative effects on fish and other aquatic organisms which are of great concern to the wider public. To assess the risks of toxicity and their negative influence on aquatic biodiversity, acute toxicity bioassays on individuals of <i>Oreochromis niloticus</i> were carried out using Pyriforce 600 EC and Cyperplant 100 EC (toxicants) separately with nine concentrations in static media in aquariums for 24 hours. The test solution (P) representing the farmer’s dose was prepared using each toxicant. For Pyriforce 600 EC, P was of 3.125 ml/l while for Cyperplant 100 EC P was 1.33 ml/l. From this test solution (P), different concentrations were calculated and introduced into various aquaria to which <i>Oreochromis niloticus</i> fingerlings were exposed. The nominal test concentrations for Pyriforce were: 0.0 µl/l, 2.60 µl/l, 3.125 µl/l, 3.9 µl/l, 5, 2 µl/l, 7.8 µl/l, 15.6 µl/l, 31.25 µl/l, 39 µl/l and Cyperplant were: 0.0 µl/l, 1.10 µl/l, 1.33 µl/l, 1.66 µ/l, 2.22 µl/l, 3.33 µl/l, 6.66 µl/l, 13.33 µl/l, 16.60 µl/l respectively. The experimental setup constituted of ten specimens, (3,5 ± 0,5) cm standard length and mean weight (2,75 ± 0.5) g placed in each 75 × 45 cm glass aquarium located indoors, each containing 10 L of combined water from the pond from which test specimens were harvested and the test solution. Physicochemical parameters were measured throughout the test period following the recommendations of Rodier et al. Minimum (30±0.00%) and maximum (100 ± 0.00%) mortalities were recorded. Correlations were positive and strong between mortality rates and concentrations. Physicochemical parameters did not vary greatly during the test period. The 50% lethal concentration for 24 hours of exposure (LC50-24 h) was relatively high with Cyperplant 100 EC (P/800) and low with Pyriforce 600 EC (P/1200) which turns out to be the most toxic pesticide. The results showed that they may cause serious long term effects in our ecosystem such as the killing of <i>Oreochromis nioticus</i> fingerlings even at very low doses which may lead to gross drop in their population in the ecosystem and even the extinction of the species if the situation is not controlled.