Assessing the toxicity of thiamethoxam, in natural LUFA 2.2 soil, through three generations of Folsomia candida

In the field, long-term exposure is a rule rather than an exception. As a consequence, the relatively short-term standard toxicity tests may not be adequate for assessing long-term effects of pesticide exposure. This study determined the toxicity of the neonicotinoid thiamethoxam, both pure and in the formulation Actara® (25% active substance), to the springtail Folsomia candida, over three generations (P, F1 and F2). For the parental generation (P), the toxicity of pure thiamethoxam and Actara® did not differ significantly, with LC₅₀s and EC₅₀s of 0.32–0.35 and 0.23–0.25 mg a.s./kg dry soil, respectively. For the F1 and F2 generations, LC₅₀s were >0.37 mg a.s./kg dry soil for both compounds. Actara was more toxic towards reproduction in the F1 generation (EC₅₀ 0.16 mg a.s./kg dry soil) than pure thiamethoxam (EC₅₀ 0.23 mg a.s./kg dry soil). For generation F2, there was no significant difference in the toxicity of the compounds towards reproduction, with EC₅₀s of >0.37 and 0.30 mg a.s./kg dry soil for Actara® and pure thiamethoxam respectively. These results suggest a slight decrease in the toxicity of the compounds throughout the generations tested. The similarity in the toxicity of pure and formulated thiamethoxam indicates that the ingredients in the formulation Actara® do not enhance toxicity.