The elliptio complanate freshwater mussel, one of the two species used in the experiment. Source: Westcott PhillipThe elliptio complanate freshwater mussel, one of the two species used in the experiment. Source: Westcott PhillipChemicals from fracking wastewater disposal sites are in the shells of freshwater mussels, according to researchers from Penn State and Union College. Concentrations of strontium, an element found in oil and gas wastewater, show up to a great enough degree that the shells can be used as a record of contamination.

"Freshwater mussels filter water and when they grow a hard shell, the shell material records some of the water quality with time," said Nathaniel Warner, assistant professor of environmental engineering at Penn State. "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."

A 2011 discovery revealed the downstream water and sediment from Pennsylvania disposal sites contained fracking chemicals and had become radioactive, despite treatment. The chemicals contaminated drinking water and aquatic creatures, including freshwater mussels, were dying. After that, the industry began recycling its wastewater, but the effects of disposal, mainly from a boom period between 2008 to 2011, will continue to impact the area for years to come.

Now the research team is using the freshwater shells to document this pollution retroactively and monitor health risks to streams, the ecology and ultimately to humans, said David Gillikin, professor of geology at Union College and co-author on the study.

The researchers collected freshwater mussels from the Alleghany River, 100 m upstream and 1 km to 2 km downstream of a wastewater disposal facility in Warren, Pennsylvania, and from two other rivers with no history of oil and gas discharge. They dissected and drilled the shells, collected the powder in layers and searched the powder for isotopes of two elements: oxygen (to determine the year and season) and strontium (to determine the rock formation where they were produced). The shells collected downstream of the facility contained high concentrations of strontium and showed variation over time.

The study is important because, according to the U.S. Department of Energy, a significant number of new wells (up to 95%) are hydraulically fractured. This accounts for two-thirds of natural gas production marketed in the U.S. and about half of U.S. crude oil production.

High levels of strontium, sodium, chloride and other contaminants are present with both conventional and unconventional oil and gas development, Warner said.

"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."

The researchers want to expand their study to include the freshwater mussels' soft tissue, since mussels are a food source for muskrats and fish, as well as to other pollutants. They also believe the mussels can be used to investigate leaks from fracking facilities.

The study was published in Environmental Science and Technology.