Evaluation of the effect of cypermethrin and fipronil on Paracheirodon innesi ‘Neon Tetra’ using short-term bioassays and ecological risk assessment

The increasing use of agrochemicals in developing countries raises concerns about water and soil contamination, leading to significant environmental and social risks. This study evaluates the toxic effects of cypermethrin and fipronil on Paracheirodon innesi (Neon Tetra) through short-term bioassays, focusing on LC₅₀, EC₅₀, NOEC, and LOEC values using the Ecological Risk Assessment (ERA) approach. Fish acclimatisation and definitive bioassays established concentration ranges: cypermethrin (6.5–104 µg/L) and fipronil (8.5–136 µg/L), along with controls. Cypermethrin exposure caused mortality rates of 27.5% at 6.5 µg/L and 100% at 104 µg/L after 96 hours, with an LC₅₀ of 10.08 µg/L, indicating high toxicity. Behaviour effects increased with concentration and exposure time, reaching 90% at 52 µg/L. Fipronil exposure resulted in 100% mortality at 136 µg/L across all time points, while no mortality occurred in controls. PEC values for both chemicals exceeded PNEC values (RC > 1), highlighting substantial ecological risks to aquatic ecosystems. The findings demonstrate the acute toxicity of cypermethrin and fipronil to aquatic organisms, with decreasing safety margins as exposure time increases.