Daphnia magna reveals contrasting effects of copper hydroxide nanopesticides and copper chloride in mixtures with commercial pesticide formulations

The use of nanopesticides is expected to increase in the future. Accordingly, the likelihood of agrochemicals occurring in mixture with nanopesticides will increase. Pesticides are typically applied in a variety of mixture formulations, potentially contaminating surface water bodies. Possible interactions in mixtures containing nanopesticides are poorly understood, especially when combined with pesticide formulations instead of their active ingredients. We investigated the mixture toxicity of formulations containing acetamiprid (ACE), glyphosate (GLY) or prochloraz (PRO) in binary mixtures with the copper hydroxide-based nanopesticide Funguran progress (FP) or a copper chloride ion control using a miniaturized version of the Daphnia magna acute toxicity test. We measured recovery rates of active ingredients and dissolution of copper hydroxide nanoparticles (Cu(OH) 2 NPs) in FP, modeled speciation using PHREEQC and characterized Cu(OH) 2 NPs with TEM, ELS and DLS. All mixtures with the nanopesticide behaved differently than expected based on toxicity values calculated via concentration addition. Antagonistic effects of FP and GLY were caused by chelation of dissolved copper by GLY. Synergistic toxicity for FP and ACE was likely caused by copper ions released from Cu(OH) 2 NPs and increased Cu(OH) 2 NP bioavailability. For FP and PRO, the synergistic effect was possibly mediated by stabilized small Cu(OH) 2 NPs. In contrast, all organic pesticide mixtures with CuCl 2 displayed antagonistic effects. In conclusion, chemical innovations like nanopesticides applied to the environment potentially cause synergistic mixture toxicity effects. Our results further warrant restructuring of chemical risk assessment to prevent overlooking any synergisms. Potential mixture component interactions should be considered. • Miniaturized acute daphnia toxicity test combined with ELS and DLS measurements • Mixture toxicity tests of pesticide formulations and copper hydroxide nanoparticles • Synergistic toxicity of acetamiprid and prochloraz with Cu(OH) 2 NPs via ions or NPs • Glyphosate with Cu(OH) 2 NPs causes antagonistic toxicity due to chelation • Cu(OH) 2 NP-mediated synergisms with pesticide formulations are difficult to predict