Microplastic exposure is associated with epigenomic effects in the model organism <i>Pimephales promelas</i> (fathead minnow)

Microplastics have evolutionary and ecological impacts across species, affecting organisms' development, reproduction, and behavior along with contributing to genotoxicity and stress. As plastic pollution is increasing and ubiquitous, gaining a better understanding of organismal responses to microplastics is necessary. Epigenetic processes such as DNA methylation are heritable forms of molecular regulation influenced by environmental conditions. Therefore, determining such epigenetic responses to microplastics will reveal potential chronic consequences of this environmental pollutant. We performed an experiment across two generations of fathead minnows (Pimephales promelas) to elucidate the transgenerational epigenetic effects of microplastic exposure. We exposed the first generation of fish to four different treatments of microplastics: two concentrations of each of pre-consumer polyethylene (PE) and PE collected from Lake Ontario. We then raised the first filial generation with no microplastic exposure. We used enzymatic methylation sequencing on adult liver tissue and homogenized larvae to evaluate DNA methylation differences among treatments, sexes, and generations. Our findings show the origin of the plastic had a larger effect in female minnows whereas the effect of concentration was stronger in the males. We also observed transgenerational effects, highlighting a mechanism in which parents can pass on the effects of microplastic exposure to their offspring. Many of the genes found within differentially methylated regions in our analyses are known to interact with estrogenic chemicals associated with plastic and are related to metabolism. This study highlights the persistent and potentially serious impacts of microplastic pollution on gene regulation in freshwater systems.