What Science Says About Reproductive Health and Pollution

For the past several decades, fertility rates have been in decline. In 1950, the global total fertility rate was around 4.8, meaning that the average woman could expect to have 4–⁠5 children during her lifetime. By 2021, this fertility rate had more than halved to 2.3—just narrowly above the 2.1 figure needed for population size to remain stable.

There are many potential reasons for this large shift in fertility rate over the past 70 years. Changes in lifestyle, economic conditions, improved access to contraception, and progress in women’s rights and autonomy are all important social factors.

But scientists have also noticed a rise in male and female infertility in recent years. The increasing prevalence and incidence of other reproductive disorders, such as endometriosis and reduced sperm count, are also a concern.

Again, multiple factors could be at play here. General awareness of reproductive health conditions is considerably higher now than it was many decades ago, and medical diagnostic technology has also improved. However, a growing body of evidence suggests that exposure to environmental toxins is also a key contributor to this rise in reproductive health issues.

The health burden of environmental pollution

Environmental pollutants have already been linked to a wide array of chronic and acute health conditions. Air pollution from automobile emissions, burning waste, and volcanic eruptions can disrupt the respiratory system, cardiovascular system, and has been linked to an increased risk of cancers. Long-term exposure to lead—a common environmental contaminant due to its long use as a component in old paints and pipes—can lead to chronic kidney disease and neurological issues.

Now, research is beginning to shed light on the associations between environmental exposure to common pollutants and negative impacts on reproductive health and fertility.

“Comprehensive reviews connect environmental exposures to early puberty, endometriosis, polycystic ovary syndrome (PCOS), early menopause, longer time-to-pregnancy (when actively trying to conceive), higher odds of being infertile (not able to conceive within 12 months), irregular cycles, lower quality of eggs and embryos, lower ovarian response to hormone stimulations during IVF treatments, and higher risk of miscarriage,” Prof. Pauliina Damdimopoulou, a professor of reproductive biology at the Karolinska Institutet, told Technology Networks.

PFAS and POPs: A long-lasting threat

Per- and polyfluoroalkyl substances (PFAS) are a family of thousands of highly fluorinated chemicals. PFAS found widespread use in the mid-20^th century as a component in commercial grease- and waterproof coatings, and as an agent in industrial firefighting foams. While their extreme chemical stability made them useful for these purposes, the stability of PFAS also presents a stark environmental challenge; their relative inability to degrade naturally in the environment means that they easily move through soils and water, where they can contaminate drinking water sources and fishing grounds.

Select PFAS—such as PFOS, PFOA, PFHxS—have been phased out of use, in recognition of their potential harms. However, thousands of other PFAS compounds remain with no restrictions on their production or use. Legacy PFAS and emerging PFAS alternatives also continue to pose risks to the environment, aquatic life, and human health.

In terms of the risk these compounds may pose to reproductive health, studies have linked both long-chain and short-chain PFAS to female reproductive health problems, including PCOS, premature ovarian failure, endometriosis, reproductive system tumors, and pregnancy complications.

Under the Stockholm Convention, PFAS are classified as persistent organic pollutants (POPs). Like PFAS, many other POPs have been linked to reproductive health issues.

“Persistent organic pollutants like DDT [dichlorodiphenyltrichloroethane, an insecticide] and PCBs [polychlorinated biphenyls] are still around despite international regulations two decades ago,” said Damdimopoulou. “They are detected in women of reproductive age and correlate with reduced fertility.”

“Persistent chemicals are particularly concerning as their half-lives are so long in our bodies. If we stop all use today (there are no signs that this will happen), they will still remain in our bodies, pass on to our fetuses, and contaminate our food chain for decades to come,” Damdimopoulou said.

“The longer we allow toxic persistent chemicals on the market, the longer down the generations the problems are passed.”

Endocrine-disrupting chemicals (EDCs) and female fertility

PFAS and many other POPs also belong to another much larger class of chemicals, known as endocrine-disrupting chemicals (EDCs).

EDCs can impact the body through a number of different mechanisms. Some EDCs are “hormone mimics” that trick the body into reacting to them, while others actively block the body’s naturally produced hormones. Other EDCs make their effects felt by affecting how hormones are made, broken down, or stored in the body, which in turn can dramatically affect the levels of hormones circulating in the bloodstream.

“Chemicals that disrupt the hormonal system are no good. They can interfere with the development of the ovaries and eggs in the uterus, which translate to reproductive health consequences later in life, and they can affect the functioning of the ovary in adulthood (hormone production, egg production),” Damdimopoulou explained.

Damdimopoulou’s research focuses on understanding how different mixtures of EDCs impact women’s fertility, with a special emphasis on how these chemicals affect the ovary.

“My studies have found complex mixtures of POPs, phthalates, parabens, and air pollution particles in serum and/or ovarian follicular fluid of reproductive age women living in Sweden. Further, we have seen that these chemicals pass the placenta and can be detected in vital organs of fetuses,” Damdimopoulou said.

“We have seen significant associations between the mixture exposures in women and the size of her ovarian reserve (how many eggs the woman has left), how the follicles that house the eggs grow to ovulation, the quality of the embryos that the eggs become, the time it takes for her to get pregnant, and her risk of being diagnosed with infertility.”

Using cell and tissue culture models, Damdimopoulou’s research group can closely study the effects of environmental pollutants on human endometrial cells and reproductive system tissue, and in turn, learn more about how these pollutants exert their effects.

“When we study some of these chemicals further in the laboratory, using donated small pieces of ovarian tissue in culture, we can confirm that phthalates and POPs disrupt energy balance in the tissue, leading to increased death of the follicles,” Damdimopoulou said.

“Furthermore, the exposures appear to disrupt the structure of the cells as well as lipid metabolism. We have learned that chemicals act in multiple different ways; EDCs can also disrupt energy and cell structures, not only hormone signaling.”

The rise of microplastics

Microplastics can be found in almost every corner of the planet—from the depths of the Mariana Trench to the peaks of remote mountain ranges. Despite their large footprint, the tiny size of microplastics has meant that the damage these particles cause to local ecosystems and to public health has only now started to become clear.

“Despite the several technical limitations in methods to quantify micro- and nanoplastics precisely, these particles are found everywhere, including our reproductive tissues,” said Damdimopoulou.

Human exposure to nano- and microplastics can happen through many routes, including inhaling airborne particles, eating contaminated fish or other foods, and through contact with contaminated materials, such as soil. The accumulation of plastic particles in the placenta has been linked to inflammation, oxidative stress, diminished microbiome diversity, reduced birthweights, and worse fetal growth and development.

In addition to the physical accumulation of microplastics in the body, these plastics also present a chemical toxicity risk. As they move through the environment, microplastics can act as a vehicle for other chemical contaminants, which may carry their own health risks. Recent studies also suggest that some chemical additives used in plastics production can leach out of microplastics and enter the body via dermal contact.

“As plastics are inseparably connected to chemicals (no registries exist, but estimates suggest that ca. 16,000 chemicals are used in the production of plastics, out of which 4,200 are of concern due to being persistent, bioaccumulative, mobile, and/or toxic), microplastics also carry chemical additives and contaminants with them,” said Damdimopoulou. “No one knows what this combination of tiny particles and problematic chemicals does to us—or the environment.”

“Experimental studies across multiple types of animals from fish and waterfleas to rodents suggest negative health effects, including reduced fertility in males and females,” Damdimopoulou added.

How can research help to safeguard reproductive health?

Experimental evidence has shown clear links between exposure to EDCs and the development of reproductive disorders. Early results with microplastics show similar effects, with the plastic particles either acting as a “Trojan Horse” for EDCs or through their physical accumulation in tissues. Exposure to these environmental pollutants is considered a contributing factor to the broader rise in the prevalence of reproductive disorders.

To safeguard public health, researchers stress the need for tighter regulations on chemical testing, with more consideration given to potential reproductive health risks.

“The solution is to introduce legislation that requires chemicals to be thoroughly tested before they are allowed on the market. Sadly, this is currently not the case. An additional solution is to introduce clear rules for chemicals that already are on the market; if they are found to be endocrine-disruptive or toxic to reproduction, they should be phased out across all pieces of legislation,” Damdimopoulou suggested. “Finally, when chemicals are tested, the methods should be appropriate; sensitive and human-relevant, and measuring the right things.”

“Due to limited access to samples (and perhaps limited interest), we are only now mapping the key female reproductive organs, like the ovaries and endometrium, to understand what cells they are made of, how they respond to hormones, and what goes wrong in diseases like endometriosis and PCOS,” Damdimopoulou continued. “In order to protect women, we need detailed knowledge on these key organs so that we can develop human-relevant and sensitive test methods for assessment of reproductive toxicity in women.”