Robust chemicals once used in everything from cosmetics to waterproofing to food containers to firefighting foam could have a significant impact on the fertility of women worldwide.

A new study led by researchers from the Icahn School of Medicine at Mount Sinai in the US uncovered evidence in a sample of women in Singapore linking plasma concentrations of perfluoroalkyl substances (PFAS) with an increase in the difficulty of becoming pregnant.

Though the nature of this connection isn't clear, the results add to growing concerns that concentrations of so-called 'forever chemicals' across Earth's surface are silently putting our health at risk and could do for some time to come.

Per- and poly-fluoroalkyl substances such as PFAS are synthetic compounds that have found a wide range of applications in different consumer products since the mid-20th century. Useful as a barrier against water or oily substances, they're commonly encountered as non-stick and stain-resistant coatings.

One of their perks is the strength of the carbon-fluoride bond, which resists degradation. Unfortunately, this also happens to be one of their liabilities, allowing them to persist for years in the environment in ever-increasing concentrations.

Given that these materials are so widespread and encompass a vast catalog of thousands of variants, the chances of potential toxins hiding out in their midst have become too great to ignore.

"PFAS can disrupt our reproductive hormones and have been linked with delayed puberty onset and increased risks for endometriosis and polycystic ovary syndrome in few previous studies," says the new study's senior author, environmental epidemiologist Damaskini Valvi from Mount Sinai.

"What our study adds is that PFAS may also decrease fertility in women who are generally healthy and are naturally trying to conceive."

Valvi and her team recruited more than 1,000 volunteers through the Singapore Preconception Study of Long-Term Maternal and Child Outcomes study, which collected information on women who expressed a desire to conceive.

Each participant attended three preconception sessions over several months before receiving a series of follow-up phone calls over the following year to track their state of pregnancy.

A sub-study then measured levels of different kinds of PFAS in blood plasma collected from 382 of the participants, comparing them with time-to-pregnancy measures and the likelihood of pregnancy, as well as the probability of a live birth.

The team found a drop in fertility of around 5 to 10 percent between the lowest 25 percent of PFAS exposure and the next 25 percent, and so forth into the top quartile.

Ultimately, this amounted to a roughly 30–40 percent reduction on average in the likelihood of becoming pregnant or giving birth within a year of follow-up, in women exposed to a mixture of different PFAS chemicals.

Just why this is the case is still a matter of speculation, though it's a good bet PFAS might interrupt the typical functioning of reproductive hormones in some way.

The fact that recruits were volunteers and had to recall and self-report details of their pregnancies might also have biased results.

Nonetheless, broadly speaking, the results still add up to quite a significant difference when assumed to reflect a larger population, adding to the conception woes of anxious couples.

"Our study strongly implies that women who are planning pregnancy should be aware of the harmful effects of PFAS and take precautions to avoid exposure to this class of chemicals, especially when they are trying to conceive," says lead author Nathan Cohen, an environmental medical researcher from Mount Sinai.

With so much of the world experiencing a sharp decline in fertility – one that could see population growth reverse in decades to come – it's helpful having an avenue of research for potential causes. That's not to say PFAS are solely behind the decline, though it might be at least one factor we can do something about.

Researchers are currently seeking ways to increase the rate of breakdown of these durable substances. Together with measures to restrict their use, we just might be able to see an end to these 'forever' chemicals and the litany of health problems they just might pose.

This research was published in Science of the Total Environment.