Unravelling the potential mechanisms of nano- and microplastic toxicity to the male reproductive system: A systematic review
Paloma da Cunha de Medeiros, A. G. Silva, Ana Beatriz Silva Angelo, Maria Joana Nogueira de Moura, Unnikrishnan Kannan, Mary Gregory, Julie Dufresne, Cibele dos Santos Borges, Daniel G. Cyr
Abstract
The ever-increasing presence of microplastic and nanoplastic (MPs/NPs) particles in the natural environment, organisms, and a wide variety of health products, cosmetics, pharmaceuticals, and foods consumed by humans is a global concern. In recent years, research efforts have shifted towards identifying human exposure and risks associated with MPs/NPs, as well as unravelling the mechanisms underlying their toxicity. This systematic review examined the literature regarding the effects of MPs/NPs on the male reproductive system, focusing on the testis, epididymis, and their associated barriers. Research, conducted primarily on rodents, demonstrated that MPs/NPs of various chemical compositions can bioaccumulate in the testis and epididymis, identifying these organs as key targets of plastic particle toxicity. Several studies using rodent models reported alterations in the blood-testis barrier, a crucial structure necessary for proper spermatogenesis. Additionally, multiple studies observed increased apoptosis of germ cells, malformations of spermatozoa, and decreased sperm motility, which is typically acquired during epididymal transit. Exposure to MPs/NPs disrupted Sertoli and Leydig cell function, leading to hormone imbalance. This is likely due to a combination of oxidative stress, inflammation, and disruption of the blood-testis barrier. These effects appear to be influenced by a combination of particle characteristics, including size, shape, chemical composition, surface properties, and exposure route. Larger MPs often cause greater structural damage, while smaller NPs more readily penetrate tissues and trigger molecular disruptions. Understanding how these particles alter male reproductive functions is essential for evaluating their full impact on fertility.