Perfluorooctane sulfonate in the environment: chapter 7
Wastewater and Landfill Monitoring
The wastewater treatment component of the CMP monitoring and surveillance program provides information on the significance of wastewater effluent discharges and land application of treated biosolids as sources of PFOS to the environment and on changes in PFOS levels from these sources over time. In 2009-2010, 20 municipal wastewater systems representing typical wastewater treatment processes in Canada were sampled in summer and winter. Raw influent PFOS concentrations across all wastewater systems ranged from below the method reporting limit (1.49 to 7.92 ng/L) to 1140 ng/L, with a median value of 4.93 ng/L and a detection frequency of 60%. PFOS concentrations in final effluent ranged from below the method reporting limit (1.92 to 6.27 ng/L) to 1260 ng/L, with a median value of 5.73 ng/L and a detection frequency of 81%. Preliminary analysis indicates that PFOSconcentrations in final effluent increased in the systems monitored by the program. This increase may be due to PFOS being produced through precursor breakdown during the wastewater treatment processes. Results from wastewater solids analysis showed median PFOSconcentrations of 13.6 ng/g dry weight in primary sludge (n=111, detection frequency of 31%), 36.8 ng/g dry weight in waste biological sludge (n=78, detection frequency of 90%), and 13.7 ng/g dry weight in treated biosolids (n=107, detection frequency of 91%). These preliminary results indicate that PFOS is consistently present in wastewater solids as well as effluents. Levels in these treated biosolids (ppb) are three orders of magnitude higher than levels in effluents (ppt).
In order to monitor the potential release of PFOS from a segment of the solid waste sector, landfill leachate was collected from 10 Canadian municipal solid-waste landfill sites in 2009 and 2010. The landfills all receive municipal waste, and some also receive construction waste, industrial waste and sewage sludge. Samples were collected prior to on-site treatment at all 10 landfill sites. Treated leachate samples were obtained from 3 of the 10 landfills. Concentrations of PFOS in raw leachate samples ranged from below the method reporting limit (9.5 to 44 ng/L) to 744 ng/L, with a median of 22 ng/L and a detection frequency of 48%. Concentrations in the treated leachate samples ranged from below the method reporting limit (9.8 to 20 ng/L) to 2070 ng/L, with a median value of 20 ng/L and a detection frequency of 40%. In some cases, PFOS concentrations increased following treatment, which is likely a result of precursor compound breakdown, similar to the WWTP monitoring described above. Approximately 87% of the leachate generated in Canada is treated by wastewater treatment plants.
The wastewater and landfill monitoring programs for PFOS have focused on emissions to the aquatic environment and biosolids. In contrast, there is little information on the potential for the WWTPs and landfills to emit PFOS to the atmosphere. To fulfill this need, the air at one Ontario WWTP and two landfill sites were monitored for PFOS and volatile PFOS precursor compounds between June and September 2009, using passive and active air samplers.13,14 For the WWTP, concentrations of PFOS and the PFOS precursor compounds were seven and four times higher, respectively, compared with upwind and downwind background locations. Similarly, for the landfills, the concentrations of PFOS and PFOS precursor compounds were approximately three and two times greater, respectively, than the upwind sites.
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