Humans, fish, birds, rodents, and reptiles: Climate shifts and endocrine-disrupting chemicals may have compounding impacts on fertility across species

The effects of climate change and toxic chemicals are likely weaving together — not acting alone — to impact fecundity and fertility across species and even multiple generations of species, according to a paper published in npj Emerging Contaminants last month.

In a scientific review of 177 studies, researchers found that exposure to toxins and climate shifts "such as warming temperatures and associated decreases in oxygen levels" may be combining to contribute to reproductive harms among not only humans but also invertebrates, fish, birds, reptiles, rodents, marine mammals, and more.

Simply put, when it comes to the difficult conditions of bringing forth new life on planet Earth: 

"Pollution and climate shifts make the regular stressors more extreme and add new stressors," Jamie DeWitt, a study co-author and Director of the Pacific Northwest Center for Translational Environmental Health Research at Oregon State University, told CG in an email. 

That reproductive impacts may be associated with exposure to the endocrine-disrupting chemicals often found in plastics and, separately, with exposure to rising temperatures is fairly well-established. However, as the Guardian reported, there has been "little research on what happens when living organisms are subjected to both."

Lead author Susanne Brander, who now directs a safer chemicals project at The Pew Charitable Trusts, told the news outlet that the "additive" effect of the combination of the two was "alarming."

The researchers' review included reproductive impacts such as hormonal changes, egg production, preterm birth, sperm shape, and sperm count — with some of the same toxic chemicals linked to some of the same effects across species. For example, as the Guardian noted, phthalates — used as a plasticizer in countless household products — have been linked to sperm shape changes in invertebrates as well as reduced sperm counts in humans.

This last item has been one area of focus for co-author Shanna Swan, an environmental and reproductive epidemiologist who was recently featured in the Netflix documentary The Plastic Detox and who was also involved in a 2017 study that found sperm counts among people in Western countries had decreased by more than 50% in the span of about 40 years. She was also involved in a similar study published in 2022.

It's work that has been cited by, among others, the controversial U.S. Secretary of Health and Human Services Robert F. Kennedy, Jr. But while a number of scientists have disputed Kennedy's concern that lower sperm counts and lower fertility in general may constitute an "existential crisis," as he said at a White House event this week, the impacts of climate and chemicals on reproductive health may still be worth exploring. 

That is, while the much-discussed and often-politicized decline in birth rate may be more largely driven by social and economic factors, individuals may still wish to learn more about the potential effects of climate and chemicals on their own personal health — and what might be done to meaningfully address them. 

This would almost certainly eschew programs like those promising individuals financial incentives for giving birth and instead focus on systemic solutions, such as divestment from fossil fuels, caps on plastic production, cleanups of "forever chemicals," and corporate accountability. In their paper, the researchers underscored the urgency of globally coordinated regulatory action. 

But taking action would also require an understanding of what exactly we are up against.

In addition to rising temperatures, DeWitt said the co-authors also considered how climate changes can impact resource access, redistribute pollutants, shift infectious diseases, and change pest populations. (It's worth noting that biodiversity loss resulting from declines in wildlife fecundity and fertility may also affect human health, well-being, and maybe even family size through downstream effects such as disease spread and poor agricultural production.)

"These probably didn't resonate as deeply as temperature as a stressor within our article, but we appreciate that other aspects of climate shifts also are stressors," DeWitt said. "We did have page limits to adhere to, so we had to be selective about some specifics," she noted — perhaps pointing to the need for more research, more publications, more pages altogether.

"Appropriate funding to study the health effects of synthetic chemicals and climate shifts is imperative!" DeWitt emphasized, encouraged that some new energy to tackle microplastics in particular may prove fruitful.

Kirsten Krueger contributed to the editing of this article.