Browsing by Author "Xiao, Feng"

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    Perfluoroalkyl substances in the Upper Mississippi River Basin: occurrence, source discrimination and treatment.
    (2012-07) Xiao, Feng
    Perfluoroalkyl substances (PFASs) are manufactured for use in non-stick cookware, fast-food containers, fire-fighting foams and many other products. These substances, including perfluorooctane sulfonate (PFOS) and perfluorooctane (PFOA), have recently been classified as emerging persistent organic pollutants that are of high concern in the Upper Mississippi River Basin. Several urban lakes in the State of Minnesota (USA) and a 53-km segment of the Upper Mississippi River (Pool 2) have been listed as impaired because of PFOS contamination in fish for human consumption. This dissertation thus examines: (1) the occurrence of PFASs in the Upper Mississippi River Basin; (2) basin-scale source discrimination of PFASs by exploratory data analysis; (3) PFAS (ad)sorption by clay and polar/non-polar resins; and (4) PFAS removal by coagulation. PFASs were observed in stormwater runoff from seven separate rain events (2009-2011) at various outfall locations corresponding to different watershed land uses. Elevated levels of PFOS were found on the particulate matter (PM) in runoff collected from both industrial and commercial areas. PFAS adsorption by kaolinite clay was then investigated and modeled, and the solid-water partition coefficient of PFOS was insufficient to explain PFOS associated with runoff PM. PFOS on the PM suggest that it may have originated from industrial/commercial products, entering the waste stream as PFOS containing particulates/substances. Then the current sources of PFASs were studied, confirming that ongoing industrial/commercial activities as a significant determinant of PFAS pollution in the Upper Mississippi River Basin. This was done after an exploratory data analysis of PFAS concentrations in the influent of 37 wastewater treatment plants (WWTPs) serving more than 40 cities by using a new methodology developed in this dissertation. Both runoff and WWTP discharge can be significant pathways for PFASs into the Mississippi River. Because the drinking water in many cities within this basin comes from the Mississippi River surface water, the mechanisms for removal of PFASs by sorption and coagulation were investigated. PFOS/PFOA removal was minimal under current water treatment operations. The moderately polar XAD-7HP resin, on the other hand, was found to have an excellent potential ability for removing PFASs, including shorter-chained PFASs, from water.
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    Transport of Perfluorochemicals to Surface and Subsurface Soils
    (Center for Transportation Studies, University of Minnesota, 2013-03) Xiao, Feng; Gulliver, John S.; Simcik, Matt
    Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA), as persistent organic pollutants, are ubiquitously present in the environment, and have been detected in human blood and breast milk at concentrations of concern to health and environmental regulators. This project aims to identify the PFOS/PFOA contamination sources, contaminant release mechanisms, and migration pathways from contaminated soils. Soil samples at different depths along and perpendicular to a U.S. highway were collected, and both compounds were regularly quantified in all of our surface soils samples (0.2–125.7 ng/g dry soil weight). The results of the surveying and sampling program and subsequently geo-statistical modeling with the aid of a Geographic Information System (GIS) identified two hot spots, and supported wind as the primary transport carrier causing the mitigation of contaminated soils from the hot spots to off-site soils. The observations indicate that PFOS and PFOA contamination is not contained to a few hot spots, but is migrating with wind and traffic to other locations. This proposed soil-to-soil migration pathway appears to be an important and heretofore overlooked migration mechanism of PFOS and PFOA from contaminated spots. We also studied their occurrence and fate in subsurface soil samples, and found a general increase in concentrations with the depth at which soil samples were collected, indicating that the contamination is also migrating toward the groundwater table.
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    Transport of Perfluorochemicals to Surface and Subsurface Soils
    (2013-03) Xiao, Feng; Gulliver, John S.; Simcik, Matt
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    Transport of Perfluorochemicals to Surface and Subsurface Soils
    (St. Anthony Falls Laboratory, 2013-03) Xiao, Feng; Gulliver, John S.; Simcik, Matt
    Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA), as persistent organic pollutants, are ubiquitously present in the environment, and have been detected in human blood and breast milk at concentrations of concern to health and environmental regulators. This project aims to identify the PFOS/PFOA contamination sources, contaminant release mechanisms, and migration pathways from contaminated soils. Soil samples at different depths along and perpendicular to a U.S. highway were collected, and both compounds were regularly quantified in all of our surface soils samples (0.2–125.7 ng/g dry soil weight). The results of the surveying and sampling program and subsequently geo-statistical modeling with the aid of a Geographic Information System (GIS) identified two hot spots, and supported wind as the primary transport carrier causing the mitigation of contaminated soils from the hot spots to off-site soils. The observations indicate that PFOS and PFOA contamination is not contained to a few hot spots, but is migrating with wind and traffic to other locations. This proposed soil-to-soil migration pathway appears to be an important and heretofore overlooked migration mechanism of PFOS and PFOA from contaminated spots. We also studied their occurrence and fate in subsurface soil samples, and found a general increase in concentrations with the depth at which soil samples were collected, indicating that the contamination is also migrating toward the groundwater table.