Forensic tracers of exposure to produced water in freshwater mussels: a preliminary assessment of Ba, Sr, and cyclic hydrocarbons

Abstract

Hydraulic fracturing is often criticized due in part to the potential degradation of ground and surface water quality by high-salinity produced water generated during well stimulation and production. This preliminary study evaluated the response of the freshwater mussel, Elliptio complanata, after exposure to produced water. A limited number of adult mussels were grown over an 8-week period in tanks dosed with produced water collected from a hydraulically fractured well. The fatty tissue and carbonate shells were assessed for accumulation of both inorganic and organic pollutants. Ba, Sr, and cyclic hydrocarbons indicated the potential to accumulate in the soft tissue of freshwater mussels following exposure to diluted oil and gas produced water. Exposed mussels showed accumulation of Ba in the soft tissue several hundred times above background water concentrations and increased concentrations of Sr. Cyclic hydrocarbons were detected in dosed mussels and principle component analysis of gas chromatograph time-of-flight mass spectrometer results could be a novel tool to help identify areas where aquatic organisms are impacted by oil and gas produced water, but larger studies with greater replication are necessary to confirm these results.

Figure 1

The GC × GC-TOFMS total ion chromatograms for fatty tissue of mussels exposed to produced water from hydraulic fracturing operations (A) control group, (B) low-dose, (C) high-dose (D) the produced water used for the dosing. The mussels exposed to produced water (panel B and C) show an increase in cyclic hydrocarbons as observed in the produced water panel (D) as highlighted in the white ovals. The produced water (D) is dominated by saturated hydrocarbons, including n-alkanes, branched alkanes, and cyclic saturated hydrocarbons.

Figure 2

The principle component analysis score plot of aligned GC × GC-TOFMS peak lists from produced water (pink circles) and fatty tissue of mussels exposed to both high (green circles) and low doses (blue circles) of the same produced water from hydraulic fracturing operations. Fatty tissue from mussels that were not exposed are shown in red circles, and method blanks are in light blue circles. Note that the exposed fatty tissue samples score separately than both the unexposed control tissue samples and method blanks. Over 70% of the score difference between the control and the exposed mussels is attributable to cyclic hydrocarbons. Analytes detected by GC × GC-TOFMS were subjected to Kruskal–Wallis ANOVA and p < 0.05 was required for PCA modeling; shading represents the 95% confidence interval.

Figure 3

Metal (Sr, Ba, Mg, Mn, Ca) to calcium ratios and metal concentrations (mg/kg) in the soft tissue of freshwater mussels compared to the values in the water for control (red circle) and samples in the high dose (squares) and low dose (triangles) tanks collected both early (~ 4 weeks [green square and blue triangle) and late (~ 8 weeks following a second dose [yellow square and green triangle]). The color represents the dose of produced water with the highest dose (1:20) represented by yellow, the moderate dose 1:40 (green), and the low dose (1:80) by blue. Metal/Ca ratios in the soft tissue of mussels collected from dosed tanks generally increased relative to the control tanks for both Sr, and Ba (A, C). However, other metal/Ca ratios such as Mg or Mn (E, G) did not show a clear relationship. For example, Mn/Ca ratios in the soft tissue were highest in the control tank mussels. Mn/Ca_tissue displayed a slight negative trend with dose and exposure time. Mg concentrations in the soft tissue appear to be related to concentration in the water without apparent influence from ratios with calcium, but similar to both Sr and Ba, the relationship may not be as strong at the extreme concentrations observed in the highest dose of produced water.