Screening developmental (neuro)toxicity of biocides in zebrafish embryos identifies synergistic and antagonistic neurotoxic effects of biocide mixtures

Exposure to various biocides is a major concern due to their adverse effects on humans and other organisms. However, information on the developmental (neuro)toxicity effects of biocides, particularly that of biocide mixtures, remains elusive. In this study, we evaluated the developmental (neuro)toxicity of 74 individual biocides and 30 mixtures derived from them using a zebrafish embryonic model. Neurobehavioral analyses were conducted at sublethal concentrations, and behavioral disorders were classified into seven categories. The mixture effect was assessed by determining the concentration inducing behavioral disorders and applying the concentration addition (CA) model. Toxicity testing showed that 73 individual biocides (98 %) caused embryonic mortality with a median lethal concentration ranging from 0.73 to 58.82 mM. Of these, 50 (67 %), 15 (20 %), and 8 (11 %) biocides exhibited high, moderate, and low toxicity. Developmental malformations were observed in embryos exposed to 27 biocides. Neurotoxicity, evidenced by altered larval behavior, was detected for 58 (78 %) individual biocides and 28 mixtures (93 %). The CA model identified 6 synergistic, 22 additive, 1 antagonistic, and 1 complex interaction. Synergistic effects were predominantly observed in mixtures containing carbendazim and diuron. This study enhances our understanding of the developmental (neuro)toxicity potentials of individual biocides and the synergistic effect of their mixtures. It also highlights the importance of mixture- or product-based toxicity assessments in regulatory frameworks to ensure the safety of biocides.