Freshwater shellfish serve as recording devices for fracking wastewater contamination.
In Pennsylvania, contaminated water created from recovery of oil and gas by hydraulic fracturing, or fracking, in the Marcellus formation was allowed to be discharged to publicly-owned wastewater treatment facilities under National Pollutant Discharge Elimination System (NPDES) permits. After treatment, the waters were discharged to the Alleghany River.
This practice continued from 2008 to 2011, when evidence came to light that fracking-related chemical contamination was on the rise in spite of the treatment. Authorities quickly prohibited any further fracking discharge to the treatment facilities after which the industry began recycling most of its wastewater.Researchers at Penn State have now shown that freshwater mussels can be used to read the history of contamination from that period. They collected Elliptio dilatata and Elliptio complanata mussels, upstream and downstream of a NPDES-permitted facility as well as from rivers with no known fracking discharges. Nathaniel Warner, assistant professor of environmental engineering at Penn State explains what they were looking for:
"Freshwater mussels filter water and when they grow a hard shell, the shell material records some of the water quality with time. Like tree rings, you can count back the seasons and the years in their shell and get a good idea of the quality and chemical composition of the water during specific periods of time."
Sure enough, when they analyzed the shell composition layer by layer, they found that the downstream mussels showed significantly elevated levels of strontium, an element brought to the surface with the fracking waters. Not only that, the scientists could recognize the distinctive signature of the wastewater from the Marcellus shales in the characteristic values of strontium isotopes found (an isotope is a variation of a chemical element that has a different number of neutrons).
Surprisingly, the levels did not drop off as expected when the discharges stopped. This indicates that the contamination remains in the river sediments and can continue to affect the aquatic life for a long time. Warner emphasizes that, "the wells are getting bigger, and they're using more water, and they're producing more wastewater, and that water has got to go somewhere. Making the proper choices about how to manage that water is going to be pretty vital."
This work on the pollution record left behind in the shells of mussels could be of use for tracking spills and accidental releases from fracking operations as well. Next, the team wants to research the contaminants in the soft tissues, which could affect the fish and muskrats that dine on the mussels.
The study, Accumulation of Marcellus Formation Oil and Gas Wastewater Metals in Freshwater Mussel Shells was published in Environmental Science & Technology. DOI: 10.1021/acs.est.8b02727