Theme: 7. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7h2. PFAS Fate and Transport in Surface Water

Formatted Title:

Cloudy with a Chance of PFAS: Influence of Precipitation Formation Mechanisms and Demographics on PFAS

Background/Objectives:

PFAS are commonly detected in surface water, groundwater, and soil at concentrations exceeding drinking water or other regulatory criteria, at locations far from known sources. This implicates atmospheric transport; however, little is known regarding the impact of cloud and precipitation formation dynamics nor the range of variability in PFAS concentrations within a closely distributed regional monitoring network. We collected precipitation samples from a network of closely spaced sampling locations to evaluate regional variability and the influence of precipitation mechanisms on PFAS concentrations. We compiled our results with published data from across the U.S. to evaluate relationships of PFAS in precipitation with demographic factors such as population density. Our objectives were to assess influencing factors and the range of variability in PFAS concentrations in precipitation at a regional scale, and to determine if cloud and precipitation formation dynamics (e.g., stratiform and convective storm systems) influenced PFAS concentrations in precipitation.

Approach/Activities:

Precipitation samples were collected from a network of 25 sampling locations in the Commonwealth of Massachusetts during 50 discrete sampling events over a six-week period to evaluate regional variability and the influence of storm formation mechanisms. Each precipitation event was classified as either a convective or stratiform event based upon meteorological data, with an objective to sample one convective event and one stratiform event at each station. Samples were analyzed for a suite of 36 PFAS compounds using an LC-MS/MS method with isotope dilution. We also compiled published precipitation PFAS data from United States locations, excluding sample stations directly adjacent to major PFAS manufacturing facilities. Each sample station was identified as urban, suburban, or rural based upon county-level population data from the U.S. Census and incorporated into U.S. Department of Health and Human Services county classification schemes for evaluating urban and rural health differences. An additional industrial descriptor was also applied based upon the county-level classification data.

Results/Lessons Learned:

In our Massachusetts study, PFAS were detected in 11 of the 50 discrete precipitation sampling events. Of the 11 events from which PFAS were detected, 10 of the events were convective in nature. PFAS were detected during only one stratiform event at one station. This suggests that local and regional atmospheric PFAS sources entrained by convective events control regional atmospheric PFAS flux. The PFAS detected were primarily perfluorocarboxylic acids, with relatively higher detection frequency for shorter-chained compounds. Published precipitation PFAS data are primarily from the eastern United States. Compilation of the precipitation PFAS data from our study and published results aggregated into urban, suburban, and rural areas, including those in industrial areas, indicates population density is a poor predictor of precipitation PFAS concentrations. While the total PFAS concentration in precipitation in some areas exceeds 100 ng/L, the median concentrations across urban, suburban, and rural areas, including industrial areas, are generally less than about 10 ng/L. This study strongly suggests further assessment of convective mechanisms as an important factor for PFAS atmospheric distribution is warranted.

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James Occhialini