Acute toxicity of the chloroacetanilide herbicide butachlor and its effects on the behavior of the freshwater fish Tilapia zillii

Abstract

Acute toxicity of butachlor, a chloroacetanilide herbicide (2-chloro-N-[2, 6-diethylphenyl] acetamide) to Tilapia zillii, was studied in a semi static bioassay. The 24, 48, 72 and 96 h LC₅₀ values (with 95% confidence limits) estimated by probit analysis were 3.13 (2.88 to 4.61), 1.93 (0.63 to 4.41), 1.27 (0.59 to 1.92) and 1.25 (0.60 to1.85) mgl^-1, respectively. There were significant differences (p<0.05) in the LC₅₀ values obtained at different exposure times and the safe levels estimated by different methods varied from 1.25×10^-1 to 1.25×10^-5 mgl^-1. There were dose and time dependent increase in mortality rate due to exposure to the herbicide. Stress signs in form of hyperactivity, erratic swimming, skin discoloration, vigorous jerks of the body followed by exhaustion and death were observed. The 96 h LC₅₀ of 1.25 mgl^-1 obtained indicate that the herbicide was toxic to T. zillii. Agricultural use of butachlor in the environment, especially, near water bodies, must be restricted to avoid the severe risk associated with the use of the pesticide.

Keywords: Tilapia zillii, butachlor, toxicity, mortality, behavioral changes, safe level

African Journal of Biotechnology Vol. 12(5), pp. 499-503