Aquatic toxicity and loss of linear alkylbenzenesulfonates alone and in a neonicotinoid insecticide formulation in surface water.

Substance losses of linear alkylbenzene sulfonates (LASs) in a neat surfactant mixture, in an insecticide formulation Mospilan 20 SG, and in solutions with different neonicotinoid active ingredients (AIs) was studied in distilled water and in surface water samples originated from River Danube. Analytical measurements were performed both by HPLC-UV and commercial ELISA methods. Loss rates of LASs were found different in these aqueous matrices, with decomposition rates higher for the neat surfactant mixture than for Mospilan 20 SG (nearly 2- and 9-fold in distilled water and in surface water from River Danube, respectively). Half-lives determined in surface water from River Danube were shown to be affected by the presence of neonicotinoid AIs thiacloprid > imidacloprid > acetamiprid (ACE), while clothianidin and thiamethoxam did not affect LAS decomposition. Aquatic toxicity of Mospilan 20 SG, along with that of its AI ACE and co-formulant LAS, as well as the mixture of ACE and LAS was also investigated in the 48-h acute immobilisation assay on the water flea (Daphnia magna) aquatic indicator organism. LAS appeared to be significantly (8-fold) more toxic in the D. magna test than ACE, and the toxicity of the formulated insecticide was found to be 1.3 and 19.6 times higher than explained by its AI and LAS content, respectively, indicating synergistic toxicity. The strongest synergy between ACE and LASs was observed, when the neat forms of the two substances were applied in combination at concentrations equivalent to those in Mospilan 20 SG.