Tisserand_2026_Chemosphere_410_145022

Although many organophosphate pesticides are now banned in European countries, they continue to be used in various parts of the world and can still be detected as pollutants of surface waters. Organophosphates are well characterized for their acute neurotoxic effects, while the long-term effects of sub-lethal concentrations, closer to the levels that can be found in the environment, remain poorly understood. In this study, we examined the intergenerational epigenetic effects of diazinon exposure in the freshwater keystone species Daphnia magna. Using chronic exposure to an environmentally relevant concentration (30 ng/L), combined with genome-wide DNA methylation profiling at nucleotide resolution, we found that diazinon induces distinct and context-dependent changes in DNA methylation, without significantly affecting global methylation levels. Methylation patterns varied across generations and exposure windows, with the strongest effects observed following indirect embryonic exposure. Despite such exposure-specific epigenetic signature, we identified a core set of twelve genes whose methylation levels were consistently altered in exposed parents (F0) and their direct offspring (F1). These genes are involved in key biological processes, including reproduction, regulation of gene expression and development, in line with previously reported phenotypic effects of diazinon. Further supporting the impact of diazinon on developmental programs, we found a significant reduction in body size in both F0 and F1. Together, our results show that low-dose diazinon exposure reshapes the epigenetic landscape of D. magna in a developmental stage-dependent manner and suggest that DNA methylation changes may contribute to the response associated with diazinon exposure accross multiple generations.