They’re called sentinel species — animals that provide early detection for environmental hazards. The most famous example of which would be the canary in the coal mine, used to tip off miners to the threat of carbon monoxide, but there are a host of others. Throughout the 1900s, the widespread death of horses in California served as an indicator of industrial lead contamination. In the 1950s, cats feeding on fish from the Minamata Bay in Japan began to display abnormal behavior, indicating mercury pollution in the water. And now, in Charleston, bottlenose dolphins serve as our sentinels for a little-understood group of chemicals known as PFASs (per- and polyfluoroalkyl substances) — some of the highest national levels of which are found in dolphins that populate our waters.

To provide a bit of background, PFASs (also known as PFCs) are a group of chemicals that have been used in a slew of products ranging from firefighting foams to cookware. These are the chemicals that help prevent food from sticking to frying pans and make stain-resistant fabrics. After more than 60 years of production, this family of chemicals is now present throughout our environment as well as our bodies in low levels. One study detected PFASs in more than 98 percent of samples taken from U.S. citizens. In the early 2000s, 3M announced that it would voluntarily phase out the production of the most extensively produced and studied of these chemicals (PFOA and PFOS) following negotiations with the Environmental Protection Agency. According to the EPA, these two chemicals are no longer manufactured in the U.S., but they are still produced in other parts of the world and may continue to be imported into America in consumer goods.

During an ongoing series of studies focusing on the local bottlenose dolphin population, it was discovered that some of the highest levels of PFASs in marine mammals throughout the world are found here. According to one study from 2008, higher concentrations of these chemicals were found among dolphins populating Charleston Harbor, as well as the Ashley, Cooper, and Wando rivers. A more recent study examined the sediment found in these waterways pointed out potential hot spots for PFASs concentrations. Researchers from the National Oceanic and Atmospheric Administration found the highest concentration of these chemicals along the Lower Cooper River at what was labeled “Site 16.”

“Site 16 is the location of the Charleston Navy Base, which operated from 1901 until its closure in 1996, and currently the Navy Nuclear Power Training Unit is approximately one mile upstream,” researchers wrote. “These higher levels may be related with pre-2002 use of aqueous film-forming foams, which are still used at military bases and airports throughout North America.”

They go on to conclude, “The high PFAS level found in dolphins in Charleston served as an alert for potential environmental concern and warrant further investigations to clarify whether environmental PFAS concentrations are sufficient to cause adverse effects to wildlife, especially sensitive species in the Charleston estuarine system.”

So researchers know that these chemicals are present in higher levels in Charleston’s marine life, but what does this mean for humans? Well, no one is completely certain. The U.S. Department of Health and Human Services say scientists are not sure about the possible health effects of human exposure, but studies have found that some PFAS compounds have demonstrated effects on the liver in rats, mice, monkeys, and humans. Another study conducted by researchers at the Hollings Marine Laboratory founds high levels of PFAS chemicals in the plasma of loggerhead sea turtles along the coast, and blood tests conducted on the contaminated population also showed signs of damage to liver cells and suppressed immune systems.

As for the dolphins that populate Charleston’s waterways, a 2013 report states that their “chronic exposure to these contaminants appear to be producing immune perturbations and tissue toxicity,” providing the first line of evidence that PFASs may be involved with altering immune functions in wild dolphins demonstrating high levels of contaminants.

While the true impact of these chemicals is still not completely understood, some local researchers have already begun trying to understand what possible effects PFASs might have on humans. One MUSC study examined mice with levels of PFAS compounds similar to those found in humans. It was discovered that the immune systems of these mice were compromised as a result of these levels of exposure.

So with the inhabitants of Charleston’s coastal waterways demonstrating higher than average levels of these chemicals, what does this mean for those whose diets consist largely of local seafood? Researchers examining the levels of PFAS compounds in members of South Carolina’s Gullah community found a decline in chemical exposure between 2003-2013.

A series of legal battles related to the manufacturing and disposal of PFASs have continued long past the production of these chemicals in the U.S. In 2010, Minnesota’s Attorney General Lori Swanson filed a lawsuit against 3M on behalf of the people of the state. Citing allegations of polluted groundwater, the suit claimed that the manufacturer should have been aware of the potential harm associated with disposing these chemicals. Attorneys for 3M say that the company followed all state requirements in place at the time. But whether it be in the courtroom or the laboratory, the final word on these chemicals is yet to be written.

All that we can be sure of is that in some form or another, PFAS compounds are found in our waterways, in our marine life, and in our blood. Less than 100 years ago, these chemicals didn’t exist, but now they are ever-present in our environment. As researchers continue to mine the data, they say it’s important to keep a close eye on the creatures that share our coast — because while these sentinel species serve as a helpful early warning system for dangers, it won’t be long before the effects reach the shore.