The Study of PFAS mobility and retention in unsaturated soils using column tests with x-ray attenuation and liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS)
Abstract
Poly- and Perfluoroalkyl Substances (PFASs) are emerging contaminants of concern. Their environmental recalcitrance, high mobility, and toxicity make these compounds a threat to groundwater sources. There has been progress in the detection and treatment of PFASs in surface water and groundwater systems, however many of their transport properties are still poorly understood. Specifically, PFASs are known surfactants, and therefore have significant interactions with the air-water interface under unsaturated flow conditions. Air-water interfacial sorption is a retardation mechanism for PFASs and turns the vadose zone into a long-term source for PFAS contamination.
Preliminary work has been done that confirmed PFASs are highly retarded and retained at the air water interface. However, when PFAS-based aqueous film forming foams (AFFFs) are used, the mixture of PFASs introduced to the environment is significantly more complex: AFFF formulations can contain hundreds of PFASs in varying concentrations. Quantifying air-water interfacial sorption of these compounds one at a time would be ineffective. Furthermore, precise information on the degree of saturation is required to make an accurate assessment of the air-water interfacial interactions of the groundwater system. These problems are overcome through a combination of advanced analytical chemistry techniques and a motorized x-ray absorbance detection system that non-destructively measures the soil-water content. A set of column experiments were designed to track a pulse of PFAS contaminated water. As the PFAS act as surfactants, the expectation is that water mobility as reflected in the measured soil-water content will change, thus affecting mass flux. High purity silica sand was used as a test medium in the columns to minimize interactions other than the air-water interfacial interactions. After addition of AFFF-derived PFASs to the top of the column, the effluent of the column was analyzed by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) at regular intervals for the entire run of the experiment, while the motorized x-ray absorbance system measured the degree of saturation in the column. The data was processed through an inverse model to evaluate the air-water interfacial retention of each PFAS in the AFFF mixture.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGH11B1039S
- Keywords:
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- 0345 Pollution: urban and regional;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0486 Soils/pedology;
- BIOGEOSCIENCES;
- 0496 Water quality;
- BIOGEOSCIENCES;
- 0240 Public health;
- GEOHEALTH