In news that will surprise no one who has ever glanced at a chemistry textbook while sweating, a new peer-reviewed study has found that being simultaneously poisoned by toxic chemicals and cooked by climate change is probably not great for making babies.
The review of 177 scientific papers examined how endocrine-disrupting chemicals - the charming little guests found in plastic - team up with climate change effects like heat stress to wreak havoc on fertility across species, from humans to invertebrates. While the reproductive harms of each villain in isolation are well-documented, the combined assault has been largely ignored, which the authors describe as “alarming.”
“You’re not just getting exposed to one - but two - stressors at the same time that both may affect your fertility, and in turn the overall impact is going to be a bit worse,” said Susanne Brander, a study lead author and courtesy faculty at Oregon State University, with the understated calm of someone who has seen the data.
The paper includes contributions from Shanna Swan, who co-authored a groundbreaking 2017 study showing sperm levels in Western men had dropped by more than 50% over four decades. Human fertility has been declining at a similar rate, and the University of Washington’s Institute for Health Metrics and Evaluation previously predicted a “low-fertility future,” with over three-quarters of countries below replacement rate by 2050.
The authors focused on the effects of endocrine-disrupting chemicals like microplastics, bisphenol, phthalates, and PFAS - substances so ubiquitous that you’re likely reading this while marinating in them. These chemicals are linked to hormone disruption, altered sperm shape in invertebrates, spermatogenesis issues in rodents, and reduced sperm counts in humans. Because why should one species have all the reproductive misery?
Meanwhile, climate change adds heat stress to the mix, which messes with human hormones and, in fish, reptiles, and amphibians, can override the temperature-based sex determination system that evolution spent millions of years perfecting. “Push it too far in one direction or the other,” Brander noted, “which overrides that evolutionary benefit.”
The study broke down overlapping effects across taxonomic groups. Birds, for instance, face abnormal sperm, increased fledgling mortality, and population decline from temperature increases, PFAS, organochlorines, and pyrethroids individually. The big question: what happens when they get the full buffet? “There has been little exploration of that question,” Brander said, before noting the obvious: if two things each cause the same bad outcome, combining them probably doesn’t cancel out.
Katie Pelch, a senior scientist with the Natural Resources Defense Council who was not involved in the study, called the science high-quality and agreed that multiple stressors likely have at least an additive effect. “Even if they have different mechanisms of harm,” she added.
The solution, the authors suggest, involves the radical notion of reining in climate change and reducing toxic chemical use. They point to the global reduction of DDT and PCBs under the Stockholm Convention as a proof of concept, but acknowledge that much more is needed. “There is enough evidence in both areas to act to reduce our impact on the planet,” Brander said, presumably while gesturing at the entire modern world.