Is humanity killing itself off? In a study published last week, a team of epidemiologists found that sperm counts among men in the United States, Europe and Australia have declined by more than 50 percent between 1973 and 2011. Alongside the deleterious effects of cigarette smoke, especially during critical stages of prenatal development, the authors of the study point out that exposure to certain synthetic chemicals has been associated with decreased fertility.

“Men residing in Western countries over the last decades were exposed to new manmade chemicals during their life course, and there is more and more evidence that these chemicals hurt their reproductive function,” one of the study’s authors said in an interview. The authors insist that their findings should drive further research aimed at determining ways to stem the decline, including regulating the chemicals that are contributing to it.

Sounds reasonable. But synthetic chemicals have long been subjects of research and attempted regulation. Beginning in the 1960s, thanks to the efforts of scientists, activists and regulators, chemical products from the pesticide DDT to the all-purpose industrial materials PCBs to the plastics additive BPA, previously understood as unalloyed technological boons, were identified as hazards and partially or fully phased out of use.

Yet even in the rare instances where chemicals are banned outright, they are often replaced by alternatives subsequently found to be just as worrisome. Meantime, more and more synthetic chemicals continue to hit the market. They may draw the most attention when they show up in places like children’s pajamas or macaroni and cheese, but in reality, they are everywhere. Laws such as the recently revised Toxic Substances Control Act in the U.S. give regulators tools to grapple with these substances, but they also highlight the tens of thousands of chemicals that still await assessment.