Per- and polyfluoroalkyl substances (PFASs) is the term for a large group of chemicals present in a wide range of products on the global market. Although PFASs have many commercially useful properties including high thermal stability and surface tension lowering potential, many PFASs fulfill regulatory criteria for persistent, bioaccumulative and toxic contaminants. Due to the concerns for adverse environmental and human health effects of PFASs several regulatory actions and substitution initiatives have been implemented to reduce the primary sources to the environment of these chemicals. Considering the long production history and widespread uses of PFASs in a myriad of products there may, however, be continuous emissions from the use and disposal of such products for a considerable time to come.
At the end of their use phase, PFAS-containing products enter the waste stream where they are primarily subject to incineration which is the dominating treatment in Sweden for solid waste. Although municipal waste incineration often leads to complete mineralization of organic contaminants there is little knowledge on the destruction efficiency of PFASs which are known to be extremely persistent. Among the studies that have investigated the thermal stability of PFASs, different conclusions are reached regarding the temperature needed to achieve complete mineralization of PFASs, and it is not known to what extent small-scale experiments mimic the conditions of incineration facilities. Field data on combusted solids (slag and ash), flue gases and flue gas condensate are also very limited and may be associated with analytical problems related to matrix effects. Clearly, there is a need for further studies to determine if PFASs are emitted from municipal waste incineration facilities in significant quantities.
The objectives of this study were to (i) develop and validate analytical methods for 11 PFASs of regulatory concern in slag and flue gas condensate and (ii) apply the improved analytical methods to a small set of samples collected from two different waste incineration facilities in Sweden.
After optimization of the extraction conditions, the majority of PFASs could be measured with acceptable accuracy (70-130% of the nominal value) and precision (<20% relative standard deviation), down to 1 ng/g and 1 ng/L respectively in slag and condensate, using routine instrumentation based on tandem mass spectrometry (MS/MS). However, for perfluorobutanoic acid (PFBA) acceptable accuracy and precision were only achieved when using high-resolution MS due to co-eluting matrix components which otherwise give rise to a positive bias of concentrations in both slag and condensate. None of the tested slag samples contained detectable concentrations of PFASs while three samples of condensate water contained detectable concentrations of perfluoropentanoic acid (PFPeA) and perfluorohexanoic acid (PFHxA) in the range 2.4-3.6 ng/L and 1.2-2.1 ng/L. As these concentrations are comparable to or lower than measurement data from background lakes in Sweden the condensate effluents would not be a source of PFASs to the environment. However, it should be noted that the samples analysed here were a limited number of grab samples which may not be representative of yearly averages or reflect the emissions of all incineration plants in Sweden. It is therefore recommended that additional samples from different incineration plants at multiple time points are analysed to support the observations of this study. Additional recommendations for future studies include innovative methods for sampling flue gases and analysis of a wider suite of potential PFAS transformation products.