Biological impact of environmental polycyclic aromatic hydrocarbons (ePAHs) as endocrine disruptors

Polycyclic aromatic hydrocarbons (PAHs) are often detected in the environment and are regarded as endocrine disruptors. We here designated mixtures of PAHs in the environment as environmental PAHs (ePAHs) to discuss their effects collectively, which could be different from the sum of the constituent PAHs. We first summarized the biological impact of environmental PAHs (ePAHs) found in the atmosphere, sediments, soils, and water as a result of human activities, accidents, or natural phenomena. ePAHs are characterized by their sources and forms, followed by their biological effects and social impact, and bioassays that are used to investigate their biological effects. The findings of the bioassays have demonstrated that ePAHs have the ability to affect the endocrine systems of humans and animals. The pathways that mediate cell signaling for the endocrine disruptions induced by ePAHs and PAHs have also been summarized in order to obtain a clearer understanding of the mechanisms responsible for these effects without animal tests; they include specific signaling pathways (MAPK and other signaling pathways), regulatory mechanisms (chromatin/epigenetic regulation, cell cycle/DNA damage control, and cytoskeletal/adhesion regulation), and cell functions (apoptosis, autophagy, immune responses/inflammation, neurological responses, and development/differentiation) induced by specific PAHs, such as benz[a]anthracene, benzo[a]pyrene, benz[l]aceanthrylene, cyclopenta[c,d]pyrene, 7,12-dimethylbenz[a]anthracene, fluoranthene, fluorene, 3-methylcholanthrene, perylene, phenanthrene, and pyrene as well as their derivatives. Estrogen signaling is one of the most studied pathways associated with the endocrine-disrupting activities of PAHs, and involves estrogen receptors and aryl hydrocarbon receptors. However, some of the actions of PAHs are contradictory, complex, and unexplainable. Although several possibilities have been suggested, such as direct interactions between PAHs and receptors and the suppression of their activities through other pathways, the mechanisms underlying the activities of PAHs remain unclear. Thus, standardized assay protocols for pathway-based assessments are considered to be important to overcome these issues.