Puzzling out the red drum: Fish population surveys contradict each other (copy)

A red drum is returned to the water after being tagged for research. The fish is one of several species in a recent study of the Charleston Harbor that were found to contain toxic substances, like PCBs. Photo provided

A new study by the Medical University of South Carolina found elevated levels of pollutants in fish caught in Charleston Harbor and the Ashley and Cooper rivers. 

In particular, all species tested exceeded the Environmental Protection Agency's limits for PCBs, a class of human-made compounds that were common in consumer products and industrial applications before being banned in 1979. 

Patricia Fair, a researcher at MUSC, said it made sense to study fish caught in the harbor for PCBs and other pollutants because they do not dissipate in the natural environment.

The study could trigger future consumption advisories. The S.C. Department of Health and Environmental Control currently says fish caught in the harbor can been eaten without restriction on the amount or frequency. 

"I don’t think we were surprised to see (the contaminants), but the fact that there was little data out there to look at these chemicals in fish," Fair said. 

Tommy Crosby, a spokesman for DHEC, said the state agency is reviewing the findings. 

PCBs have been identified by the EPA as probable carcinogens. They are a particularly pernicious type of toxin because they build up over time in the fats of humans and other animals, slowly disrupting the function of several organs and the reproductive system.

It's not clear where the toxins came from. The study also measured lower levels of emerging chemicals that have the potential to impact health but have not yet been regulated, such as some flame retardants.

Finding the sources of chemical contamination in local waterways has proved a frustrating challenge in recent years, said Andrew Wunderley, of Charleston Waterkeeper. 

"Unfortunately, (the study) wasn't a surprise," Wunderley said. "When you start doing water quality work, you really quickly realize there's a lot of contamination issues."

The MUSC study follows other scientific work tracking pollutants in the harbor and the two main rivers that feed it, showing these waters and their marine life contain all kinds of pollutants, including pharmaceuticals, microscopic pieces of plastic, antibiotics, fabric fibers and other compounds.

Pollutants were found in higher concentrations in the specimens caught in the Cooper and Ashley rivers, both of which flow by old industrial sites that the EPA Superfund program has targeted for cleanup in the past.

Fair helped lead a previous study showing that pollutants like PCBs were present in dolphins in the harbor. Dolphins are a canary in the coal mine for public health issues because they're apex predators, accumulating toxins at the top of the food chain, and because their population around the harbor doesn't migrate far, making it likely they're picking up the pollutants nearby.

In the most recent paper, researchers studied spot fish, striped mullet, croaker, flounder, red drum and spotted sea trout. John Vena, another researcher in the study who chairs MUSC's Department of Public Health Sciences, said those samples were chosen because they are eaten by both people and dolphins, with the exception of flounder. He said an estimated 15 to 20 percent of fishing license holders eat those species once a week.

Further research is warranted on how frequently the fish in the study are actually eaten, Vena and Fair said.

They said while fish are a nutritious food that's a good source of protein and Omega-3 fatty acids, it's worth investigating where the fish were swimming before they end up on a dinner plate.

"I guess the message is, be aware of the source of the fish you eat," Vena said. 

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Reach Chloe Johnson at 843-735-9985. Follow her on Twitter @_ChloeAJ.

Chloe Johnson covers the coastal environment and climate change for the Post and Courier. She's always looking for a good excuse to hop on a boat.

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