A study by Duke University shows that trace elements in the fish's ear bones can be used to identify and monitor carbon contamination in the waters where it lives.
"Calcified structures – or otoliths – found in the inner ear of fish are known to store many life information, including chemical and physical data on the age of the fish, birthplace and migration schemes," said Jessica Brandt, chief author of Labor and a doctorate from the Nicholas School of Environmental Sciences in 2018. "We have demonstrated that otoliths also capture the signatures of pollutants that have affected ecosystems of fish."
Brant and her team found that the ratio of strontium isotopes in fish baskets from two North Carolina lakes – both of which received effluents from charred ash ponds in nearby power plants – compared isotopic views in samples collected from sludge at the bottom of the lakes.
"This shows that otoliths can be used as biogenic trackers to assess the potential for environmental impacts of coal waste streams in the affected waters," said Brandt, now a postdoctoral researcher in US geological exploration. "While strontium behaves differently from toxic elements in coal ash, it helps us to link the high level of those elements back to the source of contamination."
Strontium is a naturally occurring element in coal that retains the unique isotope rates even after the charcoal burns, and the ash of the coal comes in contact with the aquatic environment.
In previous studies, the ratio of strontium isotopes to use carbon impacts on water quality was used, but this is the first time we can prove that they can also be used as fingerprints to monitor the impacts of carbon in living organisms "says Avner Vengosh, professor of geochemistry and water quality at the school, Nikolai Duke, who coauthored the study.
"This definitely shows the strontium in the fish must be contaminated with coal," Wengosh said.
Duke's team published their peer-reviewed findings of November 21 in the magazine Letter of Science and Technology for the Environment.
The researchers collected samples of water on surface water and on the basis of sediments from two North Carolina lakes – Mayo and Lake Sutton – which historically were reserved to supply cooling water to nearby power plants and obtain their effluents. Sathon Lake was the site of a large coal leak in the nearby Cape Strau River after Hurricane Florence caused flooding this fall.
The researchers also collected samples of surface and pores of water from two locations located upstream of the lakes, as well as from two other lakes – Lake Tilleri and Lake Wakkam – which are not related to coal waste streams. The samples were then analyzed in the laboratory, along with the otoliths of the great bass from each of the lakes.
"The strontium isotopes in strontium isotopes in large basalite otoliths overlap with the proportion in the corresponding sedimentary waterways of all lakes and reservoirs, which is convincing proof that otoliths can serve as biogenic trash traps of coal," says Richard Di Giulio, professor Sali Kleber Environmental Toxicology at Duke, co-author of the study.
Strontium isotope coefficients in surface water samples from lakes do not always coincide with those in otolithic fish and water samples on water, Di Giulio explained, but this may be because the ratio of surface water is more volatile over time.
"The results of this study show that otolithium studies can contribute to our existing research efforts," Brandt said. "Materials for water-based strontium isotope provide only information on the impact of carbon at a specific time, but since otoliths are continuously growing over the life of fish, we can use time series analysis of the otoliths to determine the time of discharge of waste or spill return for several years. This is a new and important new direction in environmental toxicology and water quality research. "