Total Organic Fluorine Concentration Along the Little Bighorn River

Abstract

Per- and polyfluoroalkyl substances (PFAS), also known as forever chemicals, are increasingly problematic to humans and environmental health because of their toxicity and persistence in the environment due to the strong carbon-fluorine bond that is not easily broken. Although there are several thousand known individual PFAS compounds, many are not detected with typical targeted liquid chromatography tandem mass spectrometry (LC-MS/MS). Casting a wider net with non-targeted PFAS analysis via combustion ion chromatography to determine total organic fluorine (TOF) can better characterize the total PFAS at a given site, while also potentially including non-PFAS organic-fluorine-containing molecules. Threats of PFAS contamination in the Little Bighorn River, a 138-mile river that begins south of the Montana-Wyoming state line and flows northward through the Crow Indian Reservation, are being investigated because of the tribe’s reliance on the river for diverse uses. Grab samples were collected weekly over a 15-month period at two United States Geological Survey (USGS) flow monitoring locations along the Little Bighorn River to assess the overall water quality in relation to the hydrologic discharge at both locations. The first USGS site is at the headwaters near the Montana-Wyoming state line and the second is at the Black Lodge Hall near Hardin, MT. TOF concentrations were found to increase with increasing discharge at both sites, with TOF concentrations ranging from 0.07-2.97 micrograms per liter (μg L-1). These TOF concentrations were compared with EPA Method 533, a standard analytical method targeting 25 PFAS compounds, to gain a better understanding of the total PFAS in the Little Bighorn River, and the fraction of PFAS that are untargeted by LC-MS/MS methods.