Chlorpyrifos is a common organophosphorus insecticide, and agricultural runoff containing this agrochemical pollutes adjacent water bodies. Static bioassays were carried out in the laboratory to evaluate if the presence of aquatic vegetation and water turbidity could reduce acute toxicity of the emulsified concentrate (EC) of chlorpyrifos (20% EC) to Nile tilapia Oreochromis niloticus. The 72 h-LC50 of chlorpyrifos alone on Nile tilapia was determined as 52 µg·L-1, whereas the LC50 value of chlorpyrifos was 80 µg·L-1 in the presence of the floating aquatic weed (AW) Azolla pinnata (150 g·10 L-1). The LC50 value of the formulation of chlorpyrifos with aquatic weed (CPF+AW) was about 1.45 to 1.7 times higher than that of chlorpyrifos (CPF) alone in clean water. The toxicity of chlorpyrifos decreased over time, but remained unchanged after 72 h in the presence of A. pinnata (150 g·10 L-1) in water. Chlorpyrifos toxicity to fish was also reduced when the turbidity of water was increased, both through the addition of organic compost and clay materials. In conclusion, the biological and physicochemical parameters of the receiving aqueous medium influence the toxicity of chlorpyrifos to fish.
Keywords
Aquatic Ecosystem, Azolla, LC50, Nile tilapia, Organophosphate, Toxicity