Researchers at Duke University have found that trace elements in fish ear bones can be used to track down coal ash contamination in the waters where the fish 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 study lead author Jessica Brandt, who is currently a postdoctoral researcher with the U.S. Geological Survey. “We’ve shown that otoliths also capture the signatures of contaminants that have affected the fish’s ecosystems.”
The team discovered that strontium isotope ratios in the otoliths of fish from two North Carolina lakes matched the strontium isotope ratios in sediment samples from the lake bed. Both of the lakes had received waste water from coal ash ponds at nearby power plants.
“This shows otoliths can be used as biogenic tracers to assess the potential for ecological impacts of coal ash waste streams in affected waters,” said Brandt. “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.”
Even after coal is burned and the ash comes into contact with water, the naturally occurring trace element strontium retains its isotopic ratios. According to study co-author Professor Avner Vengosh, this is the first time that strontium isotope ratios have been used to measure the impacts of coal ash on living organisms.
“This definitely shows the strontium in the fish must be from coal ash contamination,” said Professor Vengosh.
Study co-author Richard Di Giulio is the Sally Kleberg Professor of Environmental Toxicology at Duke. He explained that while strontium isotope ratios in surface water samples from the lakes did not always match those in the fish otoliths, this could be because surface water ratios are more variable over time.
“This study’s finding demonstrates that otolith studies can add to our existing research efforts,” said Brandt. “Water-based strontium isotope tracers only give us information about coal ash impacts at a particular point in time, but because otoliths continuously grow over a fish’s lifetime, we could use time-series analyses of otoliths to determine the timing of waste stream discharges or spills going back several years. This represents an emerging and important new direction in environmental toxicology and water-quality research.”