Document N2Q5qwy3xmjzLmLy1Y94LXkEp

V. Zeisberger, HLNUG: Are PFAS mobilized in soil by biological processes? A one-year laboratory experiment provides clues Are PFAS mobilized in soil by biological processes? A one-year laboratory experiment provides clues Volker Zeisberger Hessian Agency for Nature Conservation, Environment and Geology Dezernat G3 ,,Boden and Altlasten" Contact: @hlnug.hessen.de Preliminary remark The following article is a translation, the original can be found here, see page 25: https://www.hlnug.de/fileadmin/dokumente/altlasten/Boeden Altlasten Newsletter 2022 web fin al.pdf General A group of fluorinated organic substances is referred to as PFC or PFAS, these substances are contained in numerous industrial and household products. In addition to the well-known applications as repellents and surfactants (e.g. in greaseproof food packaging, sunshades, awnings, special papers, stone floor care products) and as a component of special fire-extinguishing foams (AFFF foams), there are many other areas of application: latex and facade paints, heat transfer fluids, ski wax, dental floss, etc. [1]. The abbreviation PFC stands for per- and polyfluorinated chemicals. The term PFAS (per- and polyfluoroalkyl substances) has established itself in the scientific literature. Both terms can usually be used synonymously. The term PFAS is used below. PFAS have both positives and negatives. PFAS have very attractive material properties, above all a very high resistance to environmental influences, so that PFAS products are very durable and the desired positive product properties last for a long time. The very stable Fluorine-Carbon bonds cause this persistence. The advantages mentioned turns out to be disadvantages when PFAS finds their way into the environment: with waste, in wastewater, as trace substances in water and soil, in drinking water and in food. They are extremely stable and accumulate in environmental media. Therefore, some of the PFAS are now banned (PFOS, PFOA). There are current publications that deal with the areas of application, analysis and evaluation of PFAS [2, 3]. The following is of particular relevance for the laboratory test "Degradation/mobilization of PFAS in soils" for: Instead of the previously used perfluorinated PFAS, polyfluorinated PFAS are now almost exclusively produced and used. There are several thousand polyfluorinated PFAS on the market. -1- V. Zeisberger, HLNUG: Are PFAS mobilized in soil by biological processes? A oneyear laboratory experiment provides clues Currently the socalled fluorocarbon resins, which are a type of polyfluorinated PFAS, have a wide range of applications (see below). Although the analysis of perfluorinated PFAS is now established, many of the polyfluorinated PFAS can either not be detected or only with special analysis (TOP, AOF). The above fluorocarbon resins are not mobile. They cannot be detected with standard analysis. It is unclear whether fluorocarbon resins can be detected using specialized analysis methods such as the TOP method (see below). Concerning the persistence of the substances: perfluorinated chemicals are not degradable; although polyfluorinated chemicals are partially degradable, perfluorinated substances are formed as the final degradation product. Presumably, with the above referenced degradation, biological degradation processes are of particular importance. This can be caused by microorganisms in soil and water. The laboratory tests are intended to provide information as to whether the following scenario is plausible: polyfluorinated chemicals such as fluorocarbon resins are currently used and at least some of them end up in the environment. The polyfluorinated chemicals are neither mobile nor analyzable, so these substances remain undetected in the environment. However, degradation processes take place over time, converting the polyfluorinated chemicals into perfluorinated chemicals. These are usually both mobile and analyzable and can therefore be detected in soil, water and food. Fluorocarbon Resins Fluorocarbon resins are commonly used polyfluorinated chemicals. They are fluorinecontaining macromolecules based on polyacrylates, polymethacrylates or polyurethanes, which have fluorine containing side chains. Figure 1 shows an example of a fluorocarbon resin based on polyacrylate. The polyacrylate polymer forms a long carbon chain (main chain) shown as a horizontal zigzag line in the figure. The polymer chain has functional groups: Crosslinkers cause the polymer chain to crosslink with the material to be protected, such as paper or textiles. Ester bonds make the connections between the main chain and the side chains. The side chains are partly fluorinated (red line) and partly nonfluorinated (light blue line). The chemical properties of the fluorocarbon resins can be influenced by varying the chain lengths of the main and side chains, as can the ratio of fluorinated to nonfluorinated side chains. In the laboratory test, fluorocarbon resins were examined which, according to the manufacturer's information, have fluorinated side chains with a length of six carbon atoms. Further details about the chemicals used are not known. 2 V. Zeisberger, HLNUG: Are PFAS mobilized in soil by biological processes? A oneyear laboratory experiment provides clues Figure 1: Chemical structure of a fluorocarbon resin (red line: fluorinated side chain) Analytical Procedure PFAS with short and medium chain lengths (max. six fluorinated carbon atoms) are relatively easily soluble in water. Since the PFAS determination limits are significantly higher in solids analysis than in aqueous media, it makes sense to elute PFAScontaining soil samples with water and measure the PFAS in the eluate. An elution process with a watersolid ratio of 2 to 1 was used in the laboratory tests (DIN 19529). A portion of each eluate sample was analyzed directly (native sample) and a portion after pretreatment using the TOP method (TOP sample). In the TOP method (total oxidizable precursor), the sample is first subjected to strong oxidation, during which the polyfluorinated compounds (which cannot be analyzed using standard analysis) are converted into (analyzable) perfluorinated compounds. The analysis is then carried out analogously to the native sample according to DIN 3840742. Then the results of the TOP sample and the native sample are compared. If the TOP sample contains significantly more PFAS than the native sample, this is evidence that the analyzed soil sample contains polyfluorinated PFAS. Conception of the laboratory test "Degradation/mobilization of PFAS in soil" The test setup was developed jointly by the DVGW Water Technology Center (TZW) and HLNUG. The laboratory tests were carried out at the TZW in Karlsruhe. The questions were: To what extent do biological degradation processes cause the release/mobilization of analytically detectable PFAS? Are fluorocarbon resins considered a relevant source of PFAS in soil, water and food? Mixtures of sandy soil and 5% compost were mixed with PFAScontaining materials: Impregnation agent (fluorocarbon resin with fluorinated side chains of 6 carbon atoms) Textile, treated with the above mentioned impregnating agent Paper, treated with an impregnating agent similar to that mentioned above. 3 V. Zeisberger, HLNUG: Are PFAS mobilized in soil by biological processes? A oneyear laboratory experiment provides clues The soilcompost mixtures were moistened for almost a year to promote aerobic biodegradation processes. Subsamples were taken at the start of the tests and after 2.5, 4.5 and 11 months and analyzed as described above. Results The investigations of the three materials (impregnating agent, impregnated textile, impregnated paper) showed a similar release behavior. The results of the impregnating agent are shown as an example. Since the individual PFAS have different fluorine contents, it makes sense to state the molar fluorine concentration [mol/l] in addition to the PFAS concentration. In the native samples as well as in the TOP samples, three PFAS occur in particularly high concentrations (Fig. 2): PFBA perfluorobutanoic acid (perfluorinated triple chain) PFPeA perfluoropentanoic acid (perfluorinated 4chain) PFHxA perfluorohexanoic acid (perfluorinated 5chain) This shows that the "fluorocarbon resin with fluorinated 6side chains" does not contain any long chain (and comparatively humantoxic) PFAS, i.e. no chain lengths of 7 or more. The perfluorinated carboxylic acids with the chain lengths 4 to 6 dominate. On the other hand, perfluorinated sulfonic acids only occur to a lesser extent. It is known from the literature that the chains in the TOP process are shortened as a result of oxidation (here: from a chain length of 6 to 5 or 4). Chain shortening also seems to play a role in biological processes. Soil+Compost+Impregnating Agent percentage after 11 months 100% 80% 60% 40% 20% 0% nativ t11 PFBA PFBS PFPeA PFPeS PFHxA PFHxS TOP t11 PFHpA PFHpS PFOA PFOS Figure 2: Percentages of individual PFAS in the "soil+compost+impregnating agent" samples after a test period of 11 months In the case of the native samples, an almost linear increase in the PFAS concentrations can be seen as the duration of the test increases. After 11 months the concentrations increased by a factor of 6 (Fig. 3). 4 V. Zeisberger, HLNUG: Are PFAS mobilized in soil by biological processes? A oneyear laboratory experiment provides clues Soil+Compost+Impregnating Agent (native) [mol/l] 0,20 0,15 0,10 0,05 nativ t0 nativ t2,5 nativ t4,5 nativ t11 PFBA PFBS PFPeA PFPeS PFHxA PFHxS PFHpA PFHpS PFOA PFOS Figure 3: PFAS concentrations over the course of the experiment (11 months) in native samples In contrast, no relevant increase in the PFAS concentrations can be seen in the TOP samples (Fig. 4). The TOP concentrations are about 4 times higher than in the native samples after an 11month test period. Soil+Compost+Impregnating Agent [mol/l] 1,4 1,2 1,0 0,8 0,6 0,4 0,2 nativ TOP t0 nativ TOP nativ TOP nativ TOP t0 t2,5 t2,5 t4,5 t4,5 t11 t11 PFBA PFBS PFPeA PFPeS PFHxA PFHxS PFHpA PFHpS PFOA PFOS Figure 4: PFAS concentrations over the course of the experiment (11 months) in both native as well as TOP samples The amount of fluorine contained in the impregnating agent that was released and mobilized during the course of the test was balanced. It was shown that less than 0.5% of the fluorine present can be detected with the TOP method; in the case of the native samples, the proportion was only around 0.1%. Results for the impregnated paper and textile were comparable. Interpretation and open questions The laboratory tests "Degradation/mobilization of PFAS in soil" allow the following interpretations: If fluorocarbon resins get into soil or water, a release of perfluorinated PFAS can be assumed. 5 V. Zeisberger, HLNUG: Are PFAS mobilized in soil by biological processes? A oneyear laboratory experiment provides clues After almost a year, the concentrations measured in the native samples were 6 times higher than at the beginning of the experiment. The increase in concentrations over the course of the experiment was almost linear. If the experiment lasts longer, it can be assumed that the concentrations will continue to rise. It is plausible that biological degradation processes are the main reason for the increase. Significantly higher concentrations were found in the TOP samples than in the native samples (approx. factor 4, after 11 months). Since no relevant increase in PFAS concentrations was evident during the course of the experiment, biological degradation processes appear to have only a minor influence on the TOP method. It is to be expected that the concentrations in the native samples and in the TOP samples will equalize over a longer period of time (several years). Therefore, with the TOP method, a "glimpse of the future" is possible. Even with the TOP method, approximately only 0.5% of the applied PFAS (fluorocarbon resins) can be detected. This indicates that over 99% of the PFAS (fluorocarbon resins) are still present in the soil, bound either to the original material (textile or paper) or to the soil grains. Therefore, two scenarios are possible: I. Nonmobile PFAS (here: fluorocarbon resins) are so stable that release of mobile PFAS into the environment occurs extremely slowly. Above all, product impurities are mobilized; these are fluorinated chains that are not attached to the main chain. Due to the very slow release, there is only a low risk for the soilgroundwater path. No statements can be made about other pathways (e.g. soilcrophuman). II. Although nonmobile PFAS (here: fluorocarbon resins) are stable, relevant quantities of mobile PFAS will be released into the environment for the foreseeable future. Even if only low PFAS concentrations are found in the soil or soil eluate, nonmobile PFAS (here: fluorocarbon resins) can remain undetected and represent a significant source of longterm PFAS release/mobilization. The potential for release is therefore greatly underestimated. Whether the optimistic scenario I. or the pessimistic scenario II. is correct should be clarified with further experiments. Until then, for environmental and precautionary reasons, it makes sense to assume scenario II. The ubiquitous pervasiveness of PFAS in the environment (blood, mother's milk, wild boar liver, etc.) shows that the concentrations of mobile PFAS are already too high. Literature [1] Hessisches Landesamt fr Naturschutz, Umwelt und Geologie: PFC - Tausendundeine Verwendungsmglichkeiten https://www.hlnug.de/fileadmin/dokumente/altlasten/PFC/Boeden_Altlasten_Newsletter_20 21_PFC_210831_web.pdf [2] Umweltbundesamt: UBATexte 137/2020 Sanierungsmanagement fr lokale und flchenhafte PFASKontaminationen https://www.umweltbundesamt.de/publikationen/sanierungsmanagementfuerlokale flaechenhaftepfas [3] Bundesministerium fr Umwelt, Naturschutz, nukleare Sicherheit und Verbraucherschutz: Leitfaden zur PFASBewertung Empfehlungen fr die bundeseinheitliche Bewertung von Boden und Gewsserverunreinigungen sowie fr die Entsorgung PFAShaltigen Bodenmaterials https://www.bmuv.de/download/leitfadenzurpfasbewertung 6