A study by Duke University shows that trace elements in fish's auricles can be used to detect and track contamination with coal ash in the waters where it lived.
“Calcined structures — or otoliths — found in fish’s inner ear are known to store a lot of life history information, including chemical and physical data about fish age, natural habitat, and migration patterns,” said Jessica Brandt, lead author of the article. and graduate student Nikolai Herzog environmental studies in 2018. "We showed that the otoliths also capture signs of pollutants that have affected fish ecosystems."
Brunt and her team found that the ratios of strontium isotopes in the otoliths of fish from two lakes in North Carolina, which received effluent from coal ash ponds at nearby power plants, corresponded to the ratios of strontium isotopes in samples collected from bottom sediments at the bottom of the lake.
“This shows that otoliths can be used as biogenic indicators to assess the potential environmental impact of coal ash waste streams in affected waters,” said Brandt, who currently works in doctoral studies at the US Geological Survey. "Although strontium does not behave like toxic elements in coal ash drains, it helps us connect high levels of these elements back to the source of contamination."
Strontium is a naturally occurring trace element in coal, which retains unique isotopic ratios even after coal has burned and coal ash comes into contact with the aquatic environment.
In past studies, the ratio of strontium isotopes was used to track the effects of coal ash on water quality, "but for the first time we were able to prove that they could also be used as fingerprints to track the effects of coal ash on living organisms," said Avner Vengosh. Professor of Geochemistry and Water Quality at the Duke’s Nikolaev school, co-author of the study.
“This definitely shows that strontium in fish must be contaminated with coal ash,” said Vengosh.
The Duke’s team published their peer-reviewed results on November 21 in the journal Letters on environmental science and technology,
The researchers collected samples of pore water based on surface water and sediments from two lakes in North Carolina – Lake Mayo and Lake Sutton – which were historically removed to supply cooling water to nearby power plants and to get their drains. Sutton Lake was the site of a large coal ash spill into the neighboring Cape Fir River after Hurricane Florence caused flooding this fall.
Researchers also collected surface and pore water samples from two sites located upstream of the lakes and from two other lakes – Lake Tiller and Lake Vacamo – which are not associated with coal ash waste streams. The samples were then analyzed in the laboratory along with the otoliths of a large perch mouth from each of the lakes.
“The ratios of strontium isotopes in large bass otolith mouths, overlapping with the ratios in the corresponding pore waters of all lakes and reservoirs, which is convincing evidence that otoliths can serve as biogenic indicators of coal ash emissions,” said Sally Kleberg, Environmental Toxicology the duke, who co-authored the study.
Di Giulio explained that the ratios of strontium isotopes in surface water samples from lakes do not always coincide with fish otolith and pore water samples, but this may be due to the fact that the surface water ratios are more variable over time.
“The results of this study demonstrate that otolithic research can add to our existing research efforts,” said Brandt. “Water-based strontium isotope indicators give us information only about the impact of coal ash at a certain point in time, but since otoliths are continuously growing throughout the life of the fish, we could use otolith time-series analysis to determine when the waste stream is dumped or spills return to some years ago. This is a new and important new direction in the field of environmental toxicology and water quality research. ”