Reproductive Effects of Phthalates and Microplastics on Marine Mussels Based on Adverse Outcome Pathway

Microplastic pollution has emerged as a global environmental concern. As filter-feeding organisms, marine mussels are particularly vulnerable to microplastics. Moreover, phthalic acid esters (PAEs) are known to leach from microplastics under various environmental conditions. Among PAEs, bis(2-ethylhexyl) phthalate (DEHP) is a common endocrine disruptor. We investigated the effects of microplastics and plasticizers on the reproductive function of the female mussel Mytilus coruscus. The results revealed that environmental exposure to DEHP and high-density polyethylene (HDPE) triggered molecular changes by allowing DEHP to act as an antiestrogen by binding with estrogen receptors (ER), thereby constituting the molecular initiating event. Key events were the suppression of ER, cytochrome P450-3 (CYP3), and 17β-hydroxysteroid dehydrogenase (17β-HSD) gene expressions, which reduced estradiol and progesterone levels in ovarian tissues. Ultimately adverse outcomes occurred: antioxidant capacity in ovarian tissue was impaired, hindering ovarian development and reducing reproductive function. This study introduces a novel adverse outcome pathway (AOP) framework focusing on reproductive impairment in shellfish. By integrating experimental findings with the AOP concept, the research provides essential data for understanding the toxicological effects of microplastic pollutants on mussels. This framework offers valuable insights for risk assessment, contributing to a better understanding of how microplastics and plasticizers threaten marine life.