ECOTOXICOLOGICAL RISK EVALUATION OF HERBICIDES ON NON-TARGET ENVIRONMENTAL RECEPTORS

Globally, with the application of over 4 billion tons of herbicides yearly to suppress or kill weeds, the uncontrollable / unregulated use and disposal of these sometimes-recalcitrant chemicals could result in deleterious effects on non-target ecological receptors. This evaluation recorded varying degree of toxic effects on the environmental receptors (onions – Allium cepa L) and (snails – Archachatina marginata). The highest effective concentration (EC50) for onions was recorded in Dragon® (0.042 ± 0.008 mg L-1) while the lowest effective concentration was in Uproot® (2.185 ± 0.52 mg L-1). Similarly, the highest EC50 in the snail test was obtained in Cotrazine® (0.41 ± 0.012 mg kg-1) and the lowest in Striker® (9.51 ± 0.94 mg kg-1). The risk level estimated using the Ecotoxicological Risk Assessment Matrix (ERAM) revealed that the least toxic herbicide were rated E 3 (P;A;E;C) or 15 (P;A;E;C) while the most toxic herbicides were rated E 5 (P;A;E;C) or 25 (P;A;E;C), which was considered medium to high risk to plants (P), animal (A), the environment (E) and community (C). The use, handling and disposal of these lethal herbicides should be prudently managed so as to safe guide non-target species in the environment of application.