A Chinese study has identified novel fluorinated chemicals in sewage sludge. The chemicals are thought to be impurities in mist suppressants permitted for use by China’s metal-plating industry.
Mist suppressants are used to protect workers from exposure to chromium VI spray during the electrolysis process. A lack of cost-effective alternatives means that PFOS and its derivatives are still permitted in closed-loop systems in China.
Newer, shorter-chain perfluorinated chemicals have been tested by the metal plating industry, but indications are that they may be less efficient than PFOS, say the researchers from the Chinese Academy of Sciences’ Research Center for Eco-environmental Sciences
China has been using polyfluoroalkyl ether sulfonates (PFAESs) as mist suppressants since the 1970s, and is the only country to have a documented use of the chemicals. For many years, the most widely used PFAES has been 6:2 Cl-PFAES, known commercially as F-53B.
Despite their decades of use, very few studies have been done on the PFAES emissions and their potential environmental impacts.
The team used high-resolution mass spectrometry to screen for per- and polyfluorinated chemicals in sewage sludge samples collected from 20 provinces and municipalities in China.
They identified a wide range of perfluorinated chemicals, including 6:2 Cl-PFAES, perfluorobutane, perfluorohexane, perfluorooctane, and perfluorodecane sulfonates. They also found two novel chemicals: 8:2 and 10:2 Cl-PFAESs, with eight and ten fluorinated carbons respectively.
“We recognised the existence of the PFAES homologues when we analysed samples of F-53B commercial product by high resolution mass spectrometry,” says lead author Ting Ruan.
The researchers have also been able to use analytical separation techniques to obtain a pure sample of 8:2 Cl-PFAES from F-53B. “We believe that 8:2 and 10:2 Cl-PFAESs are impurities in the chemical synthesis procedure,” says Dr Ruan.
“Biological uptake and accumulation of 6:2 and 8:2 Cl-PFAESs are highly possible,” write the researchers in Environmental Science and Technology. The team is now evaluating the potential of the Cl-PFAES chemicals to bioaccumulate in marine food chains, and is conducting in vitro tests to assess the possible toxicity of the chemicals, focusing on 8:2 Cl-PFAES.
Per- and polyfluorinated chemicals tend to be highly persistent in the environment, often travelling long distances, and so the findings could also affect other regions. Dr Ruan knows of research groups in Norway and Sweden following his Cl-PFAES findings and carrying out their own environmental fate studies.
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Abstract in Environmental Science & Technology 2015, 49 (11), pp 6519–6527
A 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFAES) with the trade name F-53B, is an alternative to perfluorooctanesulfonate (PFOS) in electroplating industry that is uniquely used in China. It was developed as a mist suppressant initially in the 1970s, but the environmental behaviors and potential adverse effects of the 6:2 Cl-PFAES have only recently been investigated. In this work, the occurrence and distribution of perfluoroalkyl sulfonate (PFSA), fluorotelomer sulfonate (FTSA), and PFAES analogues were investigated in municipal sewage sludge samples collected around China. Perfluorobutane, perfluorohexane, perfluorooctane, and perfluorodecanesulfonates, 6:2 and 8:2 FTSAs, and the emerging 6:2 Cl-PFAES were detected. Moreover, 8:2 and 10:2 Cl-PFAESs were identified for the first time as new polyfluorinated contaminants using high resolution mass spectrometry. These fluorinated analytes were further quantified with the aid of commercial and laboratory-purified standards. PFOS was the predominant contaminant with a geometric mean (GM) value of 3.19 ng/g dry weight (d.w.), which was subsequently followed by 6:2 Cl-PFAES and 8:2 Cl-PFAES (GM: 2.15 and 0.50 ng/g d.w., respectively). Both 6:2 and 8:2 Cl-PFAES were positively detected as the major components in the F-53B commercial product, and discrete 6:2 Cl-PFAES/8:2 Cl-PFAES ratios in the product and sludge samples might suggest 8:2 Cl-PFAES had enhanced sorption behavior in the sludge due to the increase in hydrophobicity.