Biological and Ecotoxicological Responses of Daphnia pulex to 2,4-D and Malathion Contaminated Laboratory Microcosm

Abstract

The enormous growth of industrialisation, urbanisation, and agricultural practices has drastically increased the accumulation of contaminants in the environment, often hampering the activity of non-target aquatic species. Cladoceran species are considered valuable biomarkers for ecotoxicity studies because they are easy to culture, have transparent bodies, and are highly sensitive to chemical pollution. The study aimed to determine the acute and chronic toxicity of sublethal concentrations of selected pesticides, i.e., Malathion 50 EC (a.i. Malathion) and 2,4-D ethyl ester 38% EC (a.i. 2,4-D), on the biological characteristics of Daphnia pulex. The 24h and 48h LC₅₀ values for 2,4-D and Malathion were (3.5 mg/L and 1.8 mg/L) and (0.76 µg/L and 0.25 µg/L), respectively. Malathion caused a decrease in clutch size (4±0.8), heart rate (bpm) (98 ± 8.6), population size (ind. L^-1) (134 ± 9.1), and body length (0.368±0.028) of D. pulex, whereas in the case of 2,4-D, a significant reduction in heart rate (bpm) (124±8.1) and clutch size (12±1.2) was observed as compared to the control group. However, the body length and population size of D. pulex were not so affected at lower concentrations of 2,4-D in chronic exposures. Approximately 20% of the Daphnia in the exposure groups switched to producing ephippia, resulting in reduced newborn Daphnia. The study suggests that D. pulex is a reliable marker for toxicity caused by sublethal doses of Malathion and 2,4-D. However, they exhibit varying sensitivity levels throughout the 21-day exposure period at different intervals. The findings indicate that the tested pesticides have noticeable impacts on the evaluated parameters.