A new study published in Environmental Chemistry and Ecotoxicology reveals that two mirror-image forms of a persistent pesticide metabolite behave differently when moving from mother fish to their offspring, demonstrating significant environmental risks that current assessment methods may overlook. The research focused on o,p'-DDD, a metabolite of the pesticide DDT, examining how its two enantiomers—molecules that are mirror images of each other like left and right hands—affect zebrafish across generations.
Lead author Lili Niu explained the motivation behind the research: Many pesticides exist in two mirror-image forms, but environmental assessments usually treat them as if they're the same. The team wanted to test whether that assumption is actually safe, especially across multiple generations. To investigate this, researchers fed adult zebrafish diets containing each form of o,p'-DDD for four weeks, then measured chemical accumulation in adults and transfer to developing embryos while tracking hatching success, deformities, survival, and thyroid hormone changes.
The findings revealed striking differences between the two forms. The S-enantiomer accumulated 134-176% more in adult fish and over 100% more in their larvae compared to the R-enantiomer. This preferential accumulation led to more severe outcomes in the next generation, including increased mortality, malformations, and reduced hatching success in the S-DDD exposed groups. Offspring consistently carried even higher chemical levels than their parents, showing that maternal transfer was highly efficient for the S-form.
To understand the mechanism behind these differences, the team used computer-based molecular docking simulations to examine how each form interacts with key proteins involved in producing and regulating thyroid hormones. These simulations showed that S-DDD binds more strongly to several thyroid-related proteins, providing a mechanistic explanation for its greater biological impact. The research demonstrated that a small structural difference in the molecule led to very large differences in accumulation, hormone system effects, and offspring development.
The study, available at https://doi.org/10.1016/j.enceco.2025.10.021, emphasizes that understanding enantiomer-specific effects will help improve ecological risk predictions for long-lasting pollutants and support more accurate environmental standards. Niu noted that if we ignore these differences, we risk underestimating long-term harm to wildlife, as even very low exposure in parents can create meaningful risks for the next generation. The findings suggest that evaluating only racemic mixtures may underestimate real-world hazards of chiral pesticide metabolites in environmental systems.
