Occurrence of per- and polyfluoroalkyl substances and unidentified organofluorine in leachate from waste-to-energy stockpile - A case study

Highlights

• Short-chain PFASs were dominant in leachate from a Waste-to-Energy stockpile.

• Most (88%) extractable organofluorine came from unidentified substances.

• Temporary waste storage is a non-negligible source of PFASs.

Abstract

Per- and polyfluoroalkyl substances (PFASs) are a diverse group of chemicals used in consumer products, which will inevitably end up in waste streams. Landfills are widely recognized secondary point sources of PFASs, but other types of waste management sites have received less attention. Therefore, in a case study presented here we investigated releases of PFASs from temporarily stored waste by determining quantities of 34 PFASs in leachate from a Waste-to-Energy stockpile (45 000 ± 2000 tonnes) during five months in 2019. We also measured extractable organofluorine (EOF) to account for PFASs not included in the target list. The mean total concentration of the 34 PFAS (Σ₃₄PFAS) was 211 ± 31 ng/L, and short-chain (C4–C7) perfluorocarboxylic acids (PFCAs) accounted for 56–60% of the total. Moreover, we found that Σ₃₄PFAS only accounted for 12% ± 4% of EOF detected in the leachate. Our results demonstrate that waste stockpiles are previously unexplored sources of PFASs in the environment, and the dominance of short-chain PFCAs is consistent with observed profiles of contaminants in landfill leachates.

Introduction

Per- and polyfluoroalkyl substances (PFASs) comprise a diverse group of compounds with fluorinated alkyl chains that make them excellent surfactants and strong C–F bonds that make them highly resistant to chemical and physical degradation (Kissa, 2001). Due to these properties, PFASs have been utilized as industrial chemicals and in consumer products as surfactants and surface protectors since the 1970s (Kissa, 2001; Olsen et al., 2005). They are used, inter alia, for water- and dirt-repellent surface treatment of textiles and leather products, paper and food contact materials, firefighting foams, paints, lacquers and non-stick products (KEMI, 2015; Kissa, 2001; Zushi et al., 2012). They are also present in construction materials such as wood, wood fibre insulation and oriented strand board (Bečanová et al., 2016). However, PFASs are substances of increasing environmental concern due to their persistence, high mobility in water, bioaccumulation potential and toxicity (Kissa, 2001; Knutsen et al., 2019; Lindstrom et al., 2011; Zushi et al., 2012). They have been found in ecosystems all over the globe (Giesy and Kannan, 2001; Yamashita et al., 2005) and human plasma (Olsen et al., 2005). In addition, according to recent estimates there are more than 4700 PFASs on the global market in various products, and new fluorinated chemicals are continuously being introduced (OECD, 2018). (Fig. 4).

Given the persistence of linear economies, consumer products containing PFASs will inevitably end up in waste streams. Landfilling is still the most common method of waste disposal globally (Kaza et al., 2018) and numerous studies have shown that PFASs can leach from landfilled waste (Huset et al., 2011; Fuertes et al., 2017; Benskin et al., 2012; Björnsdotter et al., 2019). Other waste management sites, such as Waste-to-Energy facilities, are also potential secondary point sources of PFASs, but estimates of amounts emitted from them are very scarce (Swedish EPA, 2016). Only one previous study has provided data on potential short-term (>1 year) emissions of PFASs from intermittently stored waste (Wang et al., 2020). This is a cause of concern as Waste-to-Energy is a common waste management method throughout large parts of Western Europe, and the amount of waste incinerated in EU member states increased by 285% between 1995 and 2018 (Eurostat, 2020). Thus, there is a clear need to investigate potential environmental releases of PFASs during Waste-to-Energy treatment processes, including intermittent storage of waste fuel prior to incineration. To date, up to 70 PFASs have been reported in a study (e.g. Kärrman et al., 2019), but this is a tiny fraction of the number (4700) in OECD registers. Furthermore, these 4700 do not include intermediate degradation products, which might form during storage, so there is also a clear need for much more comprehensive evaluation of potential emissions.

The purpose of this study was to explore the importance of a Waste-to-Energy fuel stockpile as a source of PFASs, through a case study of a Waste-to-Energy plant. The target list included a suite or 34 PFASs, but to assess the total release of PFASs from the stockpile we also measured the extractable organofluorine (EOF) contents. Aims of the investigation were to assess: i) the occurrence and speciation of PFASs in leachate from a waste stockpile, ii) the relative amounts of short- and long-chain PFASs, iii) the utility of EOF for assessing total PFAS contamination, and amounts of unidentified organofluorines in the leachate.