The use of pesticides for the prevention and eradication of a variety of pests has been on the increase, hence the need for investigations on their impact on the environment and non-target organisms. Fractions of the 24 h LC50 of dichlorvos in the form of 12 (LC50), 14 (LC50), 18 (LC50) and 116 (LC50) were determined to achieve varying concentrations for this study, and ten Anodonta marginata were placed in each aquarium for the definitive test, with each treatment concentration set up in triplicates. The setup was monitored daily for four days (96 h) for changes in behavioural and biochemical responses. Behavioural responses such as opening of the shell, extension of the foot, complete shell closure, and activity of enzymes such as AChE and GSH were determined as endpoint biomarkers in A. marginata tissue. An analysis of variance was used to determine significant variations in behavioural responses, survival, GSH and AChE content in bivalves across varying concentrations of dichlorvos. The exposure of A. marginata to varying concentrations (0, 10, 20, 40 and 70 mg/L) of dichlorvos for 96 h led to an LC50 value of 4.79 mg/L when compared to exposure concentrations. There was a significant (p < 0.05) variation in biochemical responses and opening of the shell as a behavioural response in A. marginata across varying concentrations of dichlorvos with time, with the highest percentage shell opening and GSH activity recorded at the highest concentration (70 mg/L) of dichlorvos and time (96 h). In contrast, AChE activity and percentage survival of A. marginata were lowest at the highest concentration of dichlorvos, confirming dichlorvos as an AChE inhibitory organophosphate pesticide. There is a need for proper monitoring and management of pesticide contamination in order to protect freshwater ecosystems.
