Abstract

Microplastics are minute plastic particles less than 5mm in size, which have permeated the environment and human biological systems. Their presence in air, water, and food raises significant concerns about human health, especially reproductive health. Evidence suggests that microplastics disrupt fertility by affecting ovarian and testicular function, sperm motility, and hormonal balance. This article explores the pathways through which microplastics infiltrate the human body, their effects on male and female fertility, and the implications for future generations. Insights from animal studies and emerging human research are synthesized to provide a clear understanding of this pressing issue. More studies are essential to determine the precise impact of microplastics on fertility and inform public health strategies.

Keywords: effects of microplastics on female fertility; effects of microplastics on male fertility; how do microplastics enter the body; implications for pregnancy and offspring; mechanisms of reproductive harm by microplastics; the current knowledge gaps; the role of animal studies in understanding human risk

Introduction

Plastic pollution has become a global environmental crisis, with microplastics emerging as one of its most insidious threats. These particles are found in air, water, soil, and food, and they are now being detected in human tissues. As the use of plastics increases, so does the risk of microplastics infiltrating critical biological systems. Fertility rates are declining globally, and while lifestyle and genetic factors have long been studied, microplastics present a novel environmental threat to reproductive health. By exploring how microplastics influence both male and female fertility, this article aims to provide an accessible yet comprehensive analysis of the evidence available to date.

How Do Microplastics Enter the Body?

Microplastics enter the human body through ingestion, inhalation, and dermal exposure. They are present in drinking water, seafood, fruits, vegetables, and even table salt. Inhalation of airborne microplastics is another major route, especially in urban areas with high plastic pollution. Once inside, microplastics can penetrate tissues, enter the bloodstream, and accumulate in vital organs. Research suggests that microplastics can cross the placenta, raising concerns about their impact on fetal development.

Effects of Microplastics on Female Fertility

Emerging research points to the significant impact of microplastics on female fertility. Studies on animal models have demonstrated that microplastics reduce ovarian reserve and affect follicle development. Exposure to microplastics triggers oxidative stress and inflammation, leading to apoptosis of granulosa cells, which play a key role in egg development. Research indicates that microplastics disrupt the hypothalamic-pituitary-ovarian (HPO) axis, resulting in hormonal imbalances that impair ovulation (1). They also report that microplastics accumulate in placental tissues, potentially affecting fetal health and increasing the risk of preterm birth (1). Further studies have detected microplastics in human ovarian follicular fluid, providing the first direct evidence of microplastics' presence in human reproductive tissues. The concentration of microplastics in this fluid was linked to altered levels of follicle-stimulating hormone (FSH), hinting at a potential role in reduced fertility (2).

Effects of Microplastics on Male Fertility

Male fertility has also come under threat from microplastics. Animal studies have shown that microplastics disrupt the blood-testis barrier and interfere with the production and function of sperm. Research has detected microplastics in bull epididymal sperm and demonstrated how polystyrene microparticles impaired sperm motility and reduced blastocyst formation (3). The study underscores that microplastics can alter sperm physiology, potentially leading to subfertility. By penetrating the blood-testis barrier, these particles expose sperm cells to oxidative stress and apoptosis, affecting sperm viability. Human studies have not yet fully quantified the impact of microplastics on sperm function, but the detection of these particles in human tissues raises significant concerns.

Mechanisms of Reproductive Harm

Microplastics impair fertility through multiple mechanisms. First, they induce oxidative stress, which damages cellular components like DNA, lipids, and proteins. This damage is particularly harmful to germ cells, which are crucial for reproduction. Second, microplastics cause inflammation, triggering immune responses that harm ovarian and testicular tissues. Third, they interfere with the body's endocrine system, disrupting the production and regulation of reproductive hormones. Disruption of the hypothalamic-pituitary-gonadal (HPG) axis alters hormone secretion, leading to reduced fertility in both males and females (4). The presence of endocrine-disrupting chemicals (EDCs) in microplastics, such as bisphenol A (BPA), further exacerbates these effects.

Implications for Pregnancy and Offspring

One of the most alarming findings in microplastic research is the evidence of these particles in human placental tissue. Studies have shown that microplastics may cross the placenta, affecting fetal development (1). Animal studies have also demonstrated adverse effects on embryonic development, including lower birth weight, delayed growth, and metabolic alterations in offspring. The accumulation of microplastics in the placenta raises the risk of complications during pregnancy, such as preterm birth and reduced fetal growth (1). While human studies are still limited, the findings are concerning and call for further research.

The Role of Animal Studies in Understanding Human Risk

Much of the evidence on microplastics and fertility comes from animal studies. These studies provide crucial insights into the biological effects of microplastics on reproduction. Research on rodents, cattle, and aquatic species has shown that microplastics reduce ovarian follicle counts, impair spermatogenesis, and alter hormone production. While animal studies are essential for understanding biological pathways, differences between species mean that human relevance must be confirmed through human-based research.

The Current Knowledge Gaps

Despite growing evidence, knowledge gaps persist. Most human studies are limited to the detection of microplastics in biological fluids such as follicular fluid, blood, and breast milk (2). There is a lack of longitudinal studies examining the impact of microplastics on human fertility outcomes, such as miscarriage, time-to-pregnancy, or live birth rates. Research on the effects of different types of microplastics, such as polystyrene, polyethylene, and polypropylene, on fertility is also limited. Another critical gap is the lack of standardized methods for detecting microplastics in human tissues (2).

Conclusion

Microplastics pose a serious threat to human fertility. They disrupt the hypothalamic-pituitary-gonadal axis, impair sperm function, reduce ovarian reserve, and interfere with placental function. Evidence from animal and human studies underscores the need for urgent action to mitigate exposure to microplastics. While studies reveal important insights, further research is needed to establish causal links and quantify the long-term effects of microplastics on fertility. Comprehensive human studies are essential to determine the full scope of this environmental threat to reproductive health.

References

1. Balali H, Morabbi A, Karimian M. Concerning influences of micro/nano plastics on female reproductive health: focusing on cellular and molecular pathways from animal models to human studies. Reprod Biol Endocrinol. 2024; https://doi.org/10.1186/s12958-024-01314-7
2. Montano L, Raimondo S, Piscopo M, Ricciardi MM, Guglielmino A, Chamayou S, et al. First evidence of microplastics in human ovarian follicular fluid: an emerging threat to female fertility. medRxiv. 2024; https://doi.org/10.1101/2024.04.04.24305264
3. Grechi N, Ferronato GA, Devkota S, Ferraz MM. Microplastics are detected in bull epididymal sperm and polystyrene microparticles impair sperm fertilization. Biol Reprod. 2024; https://doi.org/10.1101/2023.12.15.571802
4. Wang M, Wu Y, Li G, Xiong Y, Zhang Y, Zhang M. The hidden threat: Unraveling the impact of microplastics on reproductive health. Sci Total Environ. 2024; https://doi.org/10.1016/j.scitotenv.2024.173177

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