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Emerging Toxic Compounds in Stormwater Runoff
September 2011 (volume 6 - issue 8)
Background. Perfluorinated chemicals (PFCs) or perfluoroalkyl acids (PFAAs) are persistent and toxic organic pollutants in the environment and have been reported to have nonpoint sources. PFCs (see Table 1) have been produced for both industrial and residential applications such as aqueous fire-fighting foam (AFFF), insecticides and as polymers to repel water and stains on paper and textiles including fabric and carpeting (Martin et al., 2003). They have recently become the target of investigation due to their persistence and toxicity and their ubiquitous presence in the environment (Emmett et al., 2006; Giesy and Kannan 2001; Kim and Kannan, 2007). Because of the strong carbon-fluorine bonds, they are not easily degraded by physical or chemical mechanisms in the environment. PFCs also have relatively high solubility (because of their hydrophilic head groups), low adsorption potentials, and very low volatility (Tang et al., 2010). PFCs such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) have been found in fish, birds and mammals from mid-latitudes to the poles (Giesy and Kannan 2001; Suja et al., 2008 and the references therein) and in human blood at concentrations of several to tens of μg/L (Calafat et al., 2007). PFCs in blood serum can disrupt human hormone activity and their developmental toxicity to mammals has been reported (Suja et al., 2008). More recently, PFC in human blood have been linked to the attention deficit/hyperactivity disorders in children (Hoffman et al., 2010), hyperuricemia (Steenland et al., 2010), and thyroid disease (Melzer et al., 2010). In 2007, “high” concentrations of PFOS and PFOA (>1 μg/L) were found in Minnesota drinking water, and the households in the contaminated areas have been provided with bottled water, carbon filtration, or municipal water hookups (MPCA, 2008).
Table 1: PFCs commonly detected in the environment.
|Chemical||CAS Number||Molecular Formula||Molecular Weight (g/mol)||Chemical Structure|
|Perfluoroheptanoic acid (PFHpA)||375-85-9||C7F13HO2||363|
|Perfluorooctanoic acid (PFOA)||335-67-1||C8F15HO2||413|
|Perfluorononanoic acid (PFNA)||375-95-1||C9F17HO2||463|
|Perfluorooctane sulfonate (PFOS)||2795-39-3||C8F17O3S||499|
|Perfluorodecanoic acid (PFDA)||335-76-2||C10F19HO2||513|
|Perfluoroundecanoic acid (PFUnDA)||2058-94-8||C11F21HO2||563|
Recently, several metropolitan lakes in the Twin Cities of Minneapolis and St. Paul, Minnesota (U.S.) have been labeled impaired for contamination with a suite of PFCs, though primarily PFOS in fish (MPCA, 2008). While Minnesota is home to some well-known industrial manufacturers that have produced and disposed of many of these chemicals, many of the lakes listed as impaired have no connection to these companies. In addition, none of these lakes receives direct wastewater discharge. We hypothesize that a significant source of PFCs to surface waters is urban runoff (nonpoint source), which receives PFCs from commercial, industrial and residential sources within its watershed.
From 2009 to 2011, stormwater runoff samples were collected from various outfall locations corresponding to different watershed land uses: three residential sites, one transportation site, and multiple sites near an industrial area of suspected PFC contamination (Fig. 1). Six PFCs with different chain lengths were monitored in stormwater runoff from seven storm events.
Figure 1 (a): Samples were collected at urban areas of Twin Cities metropolitan areas.
Figure 1 (b): Samples were collected at five locations near an industrial site suspected to be a source of PFCs in runoff.
PFCs in the Twin Cities metropolitan area. The PFC concentrations measured in the Twin Cities metropolitan area are presented in a box plot (Fig. 2). The median concentration of PFOA (9.3 ng/L) is not significantly different from the median concentration of PFOS (10.6 ng/L). However, their median concentrations are significantly higher than other PFCs. The results also show that the median concentrations of PFHpA (0.63 ng/L), PFNA (3.65 ng/L), and PFDA (1.07 ng/L) are not significantly different from each other. The overall median PFC concentration is 25.8 ng/L. PFOS and PFOA were detected in all samples from residential areas. Chi-square test results indicate that the frequencies of detection of PFOS and PFOA are much higher than the other four PFCs at a significance level of 0.05. Overall, PFOS, PFOA, and PFNA are the major species, accounting for 38.3 ± 3.7% (mean ± standard error of the mean), 37.0 ± 2.3%, and 11.2 ± 2.6%, respectively, of the total PFCs in the monitored residential stormwater runoff.
Figure 2: PFC concentrations in stormwater runoff. The concentrations of PFCs smaller than the limit of quantification (LOQ) were assigned as half of LOQ, and the concentrations of PFCs that were not detected were assigned as zero.
The levels of four PFCs (PFHpA, PFNA, PFDA, and PFUnDA) in stormwater collected from these areas were then compared to the median concentrations in rainfall and no significant differences were found. The results suggest that these PFCs in surface runoff mainly come from rainfall. On the other hand, the median concentrations of PFOS and PFOA in stormwater runoff at Chateau (a heavy-transportation area) were significantly higher than the median concentrations of PFOS and PFOA in rain (two-tailed p = 0.004 for PFOS and two-tailed p = 0.01 for PFOA), suggesting that non-atmospheric sources may be important for these compounds at this location. Furthermore, the PFC profiles in rainfall were similar to the profiles in runoff from three residential areas (CSCC, CTC, and Mayo) but distinctly different from the profiles in runoff from the heavy-transportation area (Chateau) (Fig. 3). Both statistical analysis and Fig. 3 indicate that pollution sources around the Chateau monitoring location contribute PFOS and PFOA to surface runoff. Chateau is a busy district containing several city blocks occupied by various small businesses, restaurants, food courts, bars, and apartment buildings. Perhaps the vehicular traffic around Chateau is an important source for PFCs in runoff. In addition, around Chateau there was construction of a new apartment building that was replacing an old apartment building during the sampling period. The dust released from the construction workplace may be another source for PFOA and PFOS in runoff at this site.
The contribution of PFCs from stormwater runoff (nonpoint source) in the Twin Cities (Minneapolis and St. Paul, MN) metropolitan area is estimated to be 7.86 kg/year. The estimated contribution of PFOS (3.23 kg/year) in urban runoff is one fourth of the total PFOS load at the confluence of Minnesota and upper Mississippi river (14.6 kg/year, Nakayama et al., 2010), indicating urban runoff is an important source of PFCs to urban waters.
Figure 3: PFC profiles in stormwater runoff at residential area and heavy-transportation area and in rainfall at three heavy rain events (Event 2: August 20 2010; Event 4: Sep 15 2010; Event 6: Oct 26 2010).
Relatively high concentrations of PFOS (median concentration = 55.4 ng/L) were detected in the runoff collected from multiple sites near an industrial area of suspected PFC contamination, without any other PFCs detected (see Table 2). The median PFOS concentration in stormwater runoff around the industrial area is significantly higher (two-sided p = 0.015) than the median PFOS concentration in stormwater runoff at the residential/heavy-transportation areas and the median PFOS concentration in rainfall. Because of their relatively high solubility, PFCs may be washed out from the products within the industrial source by rain and enter into surface runoff.
Table 2: PFCs in stormwater runoff (ng/L) around an industrial site (Sep 25 2009). LOQ: limit of quantification, LOD: limit of detection, ND: not detected.
|36th Street and Brunswick Ave.||ND||ND||<LOQ||50||ND||ND|
|36th Street and Alabama Ave.||ND||ND||ND||8.7||ND||ND|
|36th Street and Yosemite Ave.||ND||ND||ND||55.4||<LOD||ND|
|36th Street and Kenwood Ave.||ND||ND||ND||150||ND||ND|
|35 ½ Street||ND||ND||ND||59.6||ND||ND|
PFC removal by stormwater management practices (SMPs). In view of their ubiquitous presence in the environment and their persistence, PFCs in stormwater/surface runoff may pose a long-term threat to the quality of urban waters. To date, no information is available on the ability of SMPs to remove PFCs. Many stormwater SMPs are being implemented in metropolitan areas to remove suspended solids and particle-associated pollutants from stormwater runoff. PFCs, however, have relatively high solubility and low adsorption potential. Therefore, conventional SMPs, such as settling/filtration/hydrodynamic separators, may not efficiently remove PFCs, unless they are present on industrial polymeric material or road dust. Thus, PFCs may be an important emerging pollutant which occurs near industrial and high-transportation areas.
- Calafat, A.M., Wong, L., Kuklenyik, Z., Reidy, J.A., Needham, L.L., 2007. Polyfluoroalkyl chemicals in the U.S. population: Data from the National Health and Nutrition Examination Survey (NHANES) 2003-2004 and comparisons with NHANES 1999-2000. Environmental Health Perspective 115(11), 1596-1602.
- Emmett, E.A., Shofer, F.S., Zhang, H., Freeman, D., Desal, C., Shaw, L.W., 2006. Community exposure to perfluorooctanoate: Relationships between serum concentrations and exposure sources. Journal of Occupational and Environmental Medicine 48(8), 759-770.
- Giesy, J.P., Kannan, K., 2001. Global distribution of perfluorooctane sulfonate in wildlife. Environmental Science & Technology 35(7), 1339-1342.
- Hoffman, K., Webster, T.F., Weisskopf, M.G., Weinberg, J., Vieira, V.M., 2010. Exposure to polyfluoroalkyl chemicals and attention deficit/hyperactivity disorder in U.S. children 12-15 years of age. Environmental Health Perspective 118(12), 1762-1767.
- Kim, S., Kannan, K., 2007. Perfluorinated acids in air, rain, snow, surface runoff, and lakes: Relative importance of pathways to contamination of urban lakes. Environmental Science & Technology 41(24), 8328-8334.
- Martin, J.W., Mabury, S.A., Solomon, K.R., Muir, D.C.G., 2003. Bioconcentration and tissue distribution of perfluorinated acids in rainbow trout (Oncorhynchus Mykiss). Environmental Toxicology and Chemistry 22(1), 196-204.
- Melzer, D., Rice, N., Depledge, M.H., Henley, W.E., Galloway, T.S., 2010. Association between serum perfluorooctanoic acid (PFOA) and thyroid disease in the U.S. National Health and Nutrition Examination Survey. Environmental Health Perspective 118(5), 686-692.
- MPCA, PFCs in Minnesota’s ambient environment: 2008 progress report, Minnesota Pollution Control Agency, 2008.
- Tang, C.Y., Fu, Q.S., Gao, D., Criddle, C.S., Leckie, J.O., 2010. Effect of solution chemistry on the adsorption of perfluorooctane sulfonate onto mineral surfaces. Water Research 44(8), 2654-2662.
- Steenland, K., Tinker, S., Shankar, A., Ducatman, A., 2010. Association of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) with uric acid among adults with elevated community exposure to PFOA. Environmental Health Perspective 118(2), 229-233.
- Suja, F., Pramanik, B.K., Zain, S.M. Contamination, bioaccumulation and toxic effects of perfluorinated chemicals (PFCs) in the water environment: a review paper. Water Science & Technology 60(6), 1533-1544.
We want to hear from you!!!
Let us know your thoughts, experiences, and questions by posting a comment. To get you thinking, here are a few questions:
- Despite the restriction on the production/use of some perfluorinated chemicals (PFCs), do on-going emissions from industrial sources continue discharging significant mass flows of PFCs to the environment?