Estimation of pesticide mixture interaction in Nile tilapia (<i>Oreochromis niloticus</i>) using survival analysis

Abstract

The acute toxicity of the pesticides atrazine, mancozeb, chlorpyrifos and lambda-cyhalothrin, acting singly and jointly, was assessed on Nile tilapia (Oreochromis niloticus) fingerlings. Median lethal concentration (LC₅₀), median lethal time (LT₅₀), and mixture interaction were estimated, whereas survival analysis was used to model time-todeath. The most toxic single and joint mixture was lambda-cyhalothrin and chlorpyrifos-lambda cyhalothrin, respectively. The risk of death (RoD) of fingerlings exposed to 9.22 mg l⁻¹ atrazine-mancozeb mixture was 1.76 times higher than fingerlings exposed to 9.0 mg l⁻¹ atrazine (p > 0.05). However, RoD of fingerlings exposed to 9.95 mg l⁻¹ atrazine-chlorpyrifos was 5.59 times higher than fingerlings exposed to 9.0 mg l⁻¹ atrazine (p < 0.01). The risk of death of fingerlings exposed to 20.8 mg l⁻¹ atrazine-lambda cyhalothrin was 2.81 times higher than 21.0 mg l⁻¹ atrazine. The toxicity of 2.3 mg l⁻¹ mancozeb-chlorpyrifos was 254.25 higher than 2.2 mg l⁻¹ mancozeb (p < 0.01). Fingerlings exposed to 4.33 mg l⁻¹ mancozeb-lambda cyhalothrin and 0.177 mg l⁻¹ chlorpyrifos-lambda cyhalothrin mixture were 0.02 and 0.14 times less likely to die than those exposed to 4.8 mg l⁻¹ mancozeb and 0.17 mg l⁻¹ chlorpyrifos, respectively (p < 0.01). Atrazine-mancozeb, atrazine-chlorpyrifos, atrazine-lambda cyhalothrin, and mancozeb-chlorpyrifos interaction were synergistic, and their relative risk was >1. Both mancozeb-lambda cyhalothrin and lambda-cyhalothrin-chlorpyrifos mixtures were antagonistic, and their relative risk was less than 1. Survival analysis can show interaction in complex pesticide mixtures.