Investigating the Effect of Polystyrene Nanoplastics on Female Reproductive System

Abstract

Introduction The degradation of plastic waste into smaller micro- and nanoplastic (MNPs) molecules has led to widespread distribution of these particles and accumulation in the environment, making human exposure inevitable. This can result in, or exacerbate, pathological conditions leading to immune dysfunction, neurodegenerative diseases, and infertility. Yet few studies have examined the effects of nanoplastics (NPs) on human health, especially the reproductive system. Reproductive toxicity of plastic particles has been mostly studied in males with most studies investigating microplastics. Therefore, the present study aims to assess the reproductive health consequences of NPs exposure in females by quantifying serum estradiol and progesterone, examining estrous cyclicity, and assessing ovarian reserve (number and quality of follicles) which is a key indicator of female fertility.

Materials & Methods The present study was carried out in female mice (C57BL/6) exposed orally to water (control) or one of two solutions containing different concentrations of Polystyrene nanoplastics (PS-NPs; 100 µg/l or 1000 µg/l in water. Exposure occurred daily for 29 days, and vaginal lavage samples were collected for the last 15 days of the exposure phase to check for change in estrous cyclicity. Mice were euthanized at the end of the study and their blood samples and reproductive tissues were collected. Ovaries were fixed in 10% formalin, embedded in paraffin wax, serially sectioned at 5 µm thickness, and stained with hematoxylin and eosin (H&E) for microscopy and follicle analysis. ELISA was also performed to quantify the progesterone and estradiol serum levels.

Results There was a significant increase in the estrous cycle length in the high dose (1000 µg/l) PS-NPs exposure group compared to control (5.53±.25 days vs 4.7±0.23 days, P=0.02). Moreover, there was a significant decrease in serum progesterone levels in the high-dose exposure group compared to control (mean difference=1.64 pg/ml, standard error of difference (SED)=0.64, P=0.03). Additionally, it was shown that PS-NPs exposure significantly reduced antral follicles’ diameter in both the low dose (238.61±19.01 µm vs 167.35±19.01 µm, P=0.03) and high dose exposure groups compared to the control group with the higher dose showing a more pronounced reduction in antral follicle' size (238.61±19.01 µm vs 131.95±19.01 µm, P=0.001).

Conclusion Oral PS-NPs exposure in female mice appears to induce toxicity by reducing antral follicles size, increasing the estrous cycle length, and decreasing progesterone levels which may result in anovulation and different reproductive issues, such as infertility and polycystic ovary syndrome (PCOS). The effect of PS-NPs on infertility along with NPs’ mechanism of action in female reproductive system should be investigated in future studies.