Toxicity of glyphosate-based isopropylamine salt and polyethoxylated tallow amine formulations on juvenile Clarias gariepinus

Abstract

The formulation of glyphosate composed of Isopropylamine salt and Polyethoxylated tallow Amine (Clearweed) is widely used as herbicide to control weeds both in the terrestrial and aquatic environments. A static bioassay was conducted to examine toxicity of this formulation on juvenile African catfish (Clarias gariepinus). Catfish juvenile (mean weight 27.97±0.03g) were exposed to glyphosate at concentrations of 0.00mg/l (control), 5.00, 7.50, 10.00, 12.50 and 15.00mg/l. Each concentration was treated in triplicate and the exposure period lasted for 96 hrs. Mortality rates and physico-chemical parameters of water were monitored. Results revealed that fish mortality increased with increasing concentration of glyphosate and time of exposure. The median lethal concentration (96-hr LC50) value was 8.88mg/l with the upper and lower limits of 9.10mg/l and 7.75mg/l respectively. Behavioural changes observed the treated fish included: erratic swimming, jerky movement, increased opercula and tail movements, gulping of air, lost of balance and consciousness, cessation of opercula and tail movement signifying eventual death. Water quality parameters increased significantly (p<0.05) with extract concentration except dissolve oxygen levels which reduced (p<0.05). However, all values reported were within the permissible limits of the Federal Ministry of Environment (FMEnv) for water samples. The results of this study indicated that glyphosate formulation has toxic effects on catfish. Thus, the herbicide should be cautiously used to avoid ecotoxicological hazards particularly on non-target organisms.