AMONG THE MOST ENDURING SOUNDS OF SUMMER in North America’s northern forest is the singular call of the common loon. Plaintive yet serene, it conjures images of quiet lakes, glowing sunsets and the iconic black and white birds. Despite the loon’s emblematic status, however, populations have been fluctuating for decades. Extensive research has documented some of the human activities likely responsible, from the use of lead-based fishing tackle to lakeshore development, climate change and pesticides.

In New Hampshire, scientists are investigating whether there may be another culprit: PFAS.

PFAS, or per- and polyfluoroalkyl substances, are a class of at least 15,000 synthetic compounds valued for their incredible durability. Among the most widely used and studied is perfluorooctanoic acid, or PFOA, essential to nuclear weapons production during World War II and famously used to make Teflon. Over time, manufacturers found uses for PFAS in almost everything: food packaging, clothing, furniture, cosmetics and more. A number of PFAS compounds, commonly referred to as “forever chemicals,” are now banned from production in the United States. But given their ability to resist degradation, they remain in our environment—and us—indefinitely.