Ratio of Perfluorochemical Concentrations as a Tracer of Atmospheric Deposition to Surface Waters

A major question regarding the global distribution of perfluorochemicals (PFCs) is one of transport. It has been suggested that atmospheric transport of volatile precursor compounds to remote areas and subsequent degradation to the nonvolatile PFCs is responsible for contamination of biota. This paper presents surface water PFC concentrations aimed at identifying tracers of atmospheric sources. Concentrations of PFCs including perfluorocarboxylates from C₆ to C₁₀ and perfluorooctane sulfonate (PFOS) are presented here from urban surface waters with presumably both atmospheric and nonatmospheric sources of PFCs, remote waters with only atmospheric sources of PFCs, and Lake Michigan. Perfluoroheptanoic acid (PFHpA) and perfluorooctanoic acid (PFOA) were detected in all surface water samples, and PFOS was detected in all but two samples. PFOS concentrations ranged from nondetect to 1.2 ng/L and from 2.4 to 47 ng/L in remote and urban surface waters, respectively. PFOA concentrations ranged from 0.14 to 0.66 ng/L and from 0.45 to 19 ng/L in remote and urban surface waters, respectively. The ratio of PFHpA to PFOA increased with increasing distance from nonatmospheric sources suggesting that it can be used as a tracer of atmospheric deposition of PFCs to surface waters. The ratio ranged from 0.5 to 0.9 in urban areas and from 6 to 16 in remote areas. Applying this tracer to measurements from Lake Michigan indicates that the primary source of PFCs to Lake Michigan is nonatmospheric, most likely inputs from wastewater treatment effluent.