New research shows that trace elements in a fish’s ear bones can be used to identify and track coal ash contamination in the waters where it lived.

“Calcified structures—or otoliths—found in a fish’s inner ear are known to store a lot of life history information, including chemical and physical records of the fish’s age, natal habitat and migration patterns,” said Jessica Brandt, lead author of the paper and a 2018 PhD graduate of the Nicholas School. “We’ve shown that otoliths also capture the signatures of contaminants that have affected the fish’s ecosystems.”

Brandt and her team found that strontium isotope ratios in the otoliths of fish from two North Carolina lakes, both of which had received effluents from coal ash ponds at nearby power plants, matched the strontium isotope ratios in samples collected from sediment at the bottom of the lakes.

Strontium is a naturally occurring trace element in coal that retains unique isotopic ratios even after the coal is burned and coal ash comes into contact with an aquatic environment.

“While strontium behaves differently than the toxic elements in coal ash effluents, it helps us connect high levels of those elements back to the contamination source,” said Brandt, who is now a postdoctoral researcher with the U.S. Geological Survey.

Past studies have used strontium isotope ratios to track coal ash’s impacts on water quality, “but this is the first time we’ve been able to prove they can also be used to track coal ash’s impacts in living organisms,” said Avner Vengosh, professor of geochemistry and water quality.

“This represents an emerging and important new direction in environmental toxicology and water-quality research,” Brandt said.

The Duke team which included Richard DiGiulio, Sally Kleberg Professor of Environmental Toxicology, published its peer-reviewed findings in the journal Environmental Science & Technology Letters (DOI: 10.1021/acs.estlett.8b00477).