Emerging Contaminants and Male Reproductive Health: Mechanistic Insights, Clinical Evidence, and Research Priorities.

Male infertility contributes to around 40-50% of the infertility cases worldwide. Emerging environmental pollutants (microplastics, engineered nanoparticles, radiofrequency electromagnetic radiation (RF-EMR), pharmaceuticals and personal care products (PPCPs)) have received significant attention because of their environmental persistence and potential adverse effects on male reproductive health. This review critically synthesizes evidences from experimental, epidemiological and systematic studies, with emphasis on mechanistic pathways. Micro- and nanoplastics are now detected in human blood, testes and semen, act as carriers that alter the transport and bio-availability of co-contaminants.Results from animal studies reported that emerging pollutants impair male reproductive function via interconnected mechanisms namely, oxidative stress, enhanced reactive oxygen species, mitochondrial dysfunction, DNA damage, chronic inflammation, endocrine disruption, blood-testis barrier impairment and apoptosis. Chronic RF-EMR exposure perturbs testicular homeostasis via oxidative injury, calcium channel modulation, hormonal imbalance, and disruption of the blood-testis barrier. Engineered nanoparticles readily cross biological barriers and accumulate in reproductive tissues. PPCPs particularly endocrine-disrupting contaminants cause impairment of steroidogenesis and hormonal homeostasis, resulting in impaired male fertility. Collectively, these pollutants converge on interconnected mechanism that affect sperm count, motility, morphology, viability and fertilization capacity. While animal studies provide evidence of reproductive toxicity, longitudinal human studies with biomonitoring, semen analysis, hormonal profiling and molecular endpoints are required to propose safe exposure thresholds, establish casual relationship and determine the effects of mixture pollutants. These emerging pollutants thus represent a major yet potentially preventable risk for male infertility.