No. U 6235 January 2020
Analysis of PFAS, phthalates, alternative plasticizers and organophosphate esters in sludge
Commissioned by Naturvårdsverket
Georgios Giovanoulis, Jenny Aasa, Jon Benskin, Merle Plassmann, Minh Nguyen, Raed Awad and Robin Vestergren
Author: Georgios Giovanoulis, Jenny Aasa, Minh Nguyen, and Robin Vestergren Commissioned byNaturvårdsverket
Project Participants: Naturvårdsverket Report number: U 6235
© IVL Swedish Environmental Research Institute 2020 IVL Swedish Environmental Research Institute Ltd., P.O Box 210 60, S-100 31 Stockholm, Sweden Phone +46-(0)10-788 65 00 // www.ivl.se
This report has been reviewed and approved in accordance with IVL's audited and approved management system.
Table of contents
Summary ... 4
Sammanfattning ... 5
1 Introduction ... 6
2 Materials & Methods ... 8
2.1 Sampling ... 8
2.2 Extraction and analysis of phthalates, alternative plasticizers and organophosphate esters ... 8
2.3 Extraction and analysis of PFAS ... 9
2.3.1 Quantitative/target analysis ... 9
2.3.2 TOP analysis ... 10
2.3.3 EOF analysis ... 11
2.3.4 Suspect screening ... 11
3 Results & discussion ... 12
3.1 Phthalates and alternative plasticizers ... 12
3.2 Organophosphate esters ... 13
3.3 PFAS ... 14
3.3.1 Quantitative/target analysis ... 14
3.3.2 TOP analysis ... 17
3.3.3 EOF analysis ... 18
3.3.4 Suspect screening ... 20
4 Conclusions... 21
5 References ... 22
Appendix A. Phthalate and alternative plasticizer levels (mg/kg dry weight) ... 24
Appendix B. Organophosphate ester levels (mg/kg dry weight) ... 25
Appendix C. PFAS levels (ng/g dry weight) ... 26
Appendix D. PFAS levels after TOP (ng/g dry weight) ... 28
Summary
Wastewater treatment plants (WWTPs) can be considered a water pollution point source as all potential pollutants from household as well as from certain industry production passes the WWTPs.
Therefore, sludge from WWTPs may be enriched with pollutants and is a relevant matrix for screening for both known and hitherto unknown potential hazardous chemicals. If the sludge from municipal WWTPs is to be used as a source of nutrient or other purposes, then it could be necessary to employ methods for removal of micropollutants in the sludge. The present study constitutes an addition to a large-scale experiment focusing on the reduction of pharmaceuticals, antibiotics and hormones in sewage sludge stored over a period of a year.
The objective of the present study was to analyse the presence of per- and polyfluoroalkyl substances (PFAS), organophosphate esters, phthalates and alternative plasticizers and their potential degradation/reduction in mesophilic anaerobic digested sludge in different treatments. This study is part of a larger on-going project on reduction of pharmaceuticals and organic pollutants in sludge.
Extracts of sludge samples were analysed using three instrumental methods: liquid chromatography coupled to both tandem mass spectrometry (LC-MS/MS) and high-resolution mass spectrometry (LC-HRMS) and gas chromatography coupled to tandem mass spectrometry (GC-MS/MS). Target analysis of several compounds (PFASs, organophosphate esters, phthalates and alternative plasticizers), analysis of total oxidizable precursors of PFASs and a suspect-screening of more than 1000 PFAS were performed at IVL. Extractable organic fluorine (EOF) was also performed on combustion ion chromatography at Stockholm University for quantification of potential unknown fluorinated compounds in the sludge.
Decreasing trends for concentrations of organophosphate esters, phthalates, alternative plasticizers and PFAS could be observed in composted sludge over the storage time while the non-composted showed variable time trends for different substance classes. For PFAS, the sum concentrations of target analytes increased by almost an order of magnitude during 12 months of storage in the non- composted sludge. Furthermore, the results from TOP and EOF furthermore suggested that the sludge from both treatment experiments contained a significant fraction PFAS that could not be quantified by the targeted analysis.
Sammanfattning
Avloppsreningsverk kan betraktas som en viktig punktkälla för föroreningar i vatten. Slam från avloppsreningsverk kan anrika föroreningar som har en huvudsaklig fördelning till slammet, och är således en relevant matris för screening för både kända och potentiella farliga kemikalier. Om slammet från kommunala avloppsreningsverk skall användas som en källa för näringsämnen eller andra syften kan det vara nödvändigt att avlägsna eller bryta ned potentiellt farliga mikroföroreningar i slammet. Denna studie utgör ett tillägg till ett storskaligt experiment som fokuserar på minskning av läkemedel, antibiotika och hormoner i avloppsslam som lagrats ett år. Kompakt eller poröst slam som rötats antingen termofilt eller mesofilt har i ovan nämnda experimentet lagrats under flera olika betingelser: täckt eller öppet, med och utan tillsats av urea, samt med och utan kompostering. I denna studie har endast poröst mesofilt rötat slam, som antingen har lagrats öppet eller med kompostering, studerats.
Syftet med den här studien var att studera om per- och polyfluoralkylsubstanser (PFAS), organofosfatestrar samt ftalater och alternativa mjukgörare bryts ned under lagring. Extrakt av slamprover har analyserats med tre instrumentella metoder: vätskekromatografi kopplad till både tandemsmasspektrometri (LC-MS / MS) och högupplösta masspektrometri (LC-HRMS) samt gaskromatografi kopplad till tandemsmasspektrometri (GC-MS / MS). Förutom riktad kvantitativ analys av flera föreningar har analys av totala oxiderbara prekursorer av PFAS-ämnen och en sk suspect screening av mer än 1000 PFAS genomförts. Andelen extraherbart organiskt bunden fluor (EOF), dvs den totala fluormängden bundet till organiska ämnen, har också bestämts av Stockholms Universitet med förbränningsjonkromatografi för att kvantifiera andelen av potentiellt okända PFAS.
Minskande trender för koncentrationer av organofosfatestrar, ftalater och alternativa mjukgörare samt PFAS kunde observeras i slam med kompostbehandlingen medan slammet som lagrats öppet inte visade någon tydlig trend för de ämnen som mättes i denna studie. För PFAS ökade summan av analyserade ämnen med nästan en tiopotens under 12 månaders lagring i det icke-komposterade slammet. Resultaten från TOP och EOF visade även på en betydande andel (91-97%) av hittills oidentifierade PFAS i slam från båda försöken.
1 Introduction
During the purification process in wastewater treatment plants nutrients from the waste water are enriched in the sludge. For recycling purposes these nutrients should ideally be returned to the fields.
However, chemicals that are toxic to the environment and to human health may also become enriched in the sludge, making the sludge unsuitable for use as fertilizer or land fill. A large-scale experiment has been performed during 2018 and 2019 to evaluate the degradation of micropollutants in sludge that is stored over a period of a year and where different conditions are kept in order to see the influence of different storage parameters. The overall hypothesis tested in the experiment was that the presence of oxygen (or air) would enhance the degradation of the compounds studied. Sludge from municipal WWTPs having different characteristics concerning digestion methods and porosity was transported to the waste-processing facility at Hovgården close to Uppsala and placed in separated piles on an asphalt surface. The piles were 15 m in length, 3 m across and with a height of roughly 1.5 m. The following experimental conditions were studied:
1. The sludge had been subjected to either thermofilic or mesophilic digestion at the WWTPs 2. The sludge was either porous or compact in nature
3. The sludge was stored either under plastic covers or open to the air
4. To further reduce the presence of oxygen 1.5% urea was mixed into one of the piles of mesophilic digested compact sludge
5. To increase the biological activity, one pile was mixed with biomass (wood chips and other biomass from garden waste) for composting and the pile was mixed after 6 months of storage.
The number of sludge piles were 6 in total representing a scale of expected oxygen content in the piles. An additional experiment aimed at highlighting the effect of the presence of oxygen was a depth-sampling performed at different distances from the surface of the sludge piles, which was performed after 6- and 12-months storage.
The sampling was performed after removal of a specific length of the pile, 3 m, 6 m or 12 m using a wheel loader, thus creating a fresh face of the sludge. Samples were created by mixing sludge taken from 7 positions on the face surface and mixing these to form homogeneous samples. Sampling was further performed in triplicate at each sampling occasion. Samples were also taken at much shorter intervals during the initial weeks of the compost experiment, after only 4 and 13 weeks.
Several physical and chemical parameters were measured at each sampling occasion, for instance ammonia, nitrate, phosphate, TOC, etc. The temperature in each storage condition was monitored continuously using sensors buried into the sludge piles. For the compost pile, the sensor could not measure the high temperature (<60ºC) produced during periods when the biological activity was most active. As this study constitutes an addition of analysis performed on the sludge sampled over the course of the experiment only a subset of the samples was analyzed, but for a greater number of parameters.
The objective of the present study was to analyse the presence of per- and polyfluoroalkyl substances (PFAS), organophosphate esters, phthalates and alternative plasticizers in mesophilic anaerobic digested sludge that has been stored open to the air or using composting to accelerate the degradation of organic compounds. Samples were taken at three timepoints during the course of the experiment, at 0 days, 179 days (6 months) and 361 days (12 months).
Per- and polyfluoroalkyl substances (PFASs) have been used extensively for several decades in a wide range of industrial applications, consumer products and in fire-fighting foams (Berger et al.
2004) and as a result PFASs are ubiquitously distributed in the environment Hekster et al. 2003, Schultz et al. 2003, Giesy et al. 2001, Kannan et al. 2002, Martin et al. 2004, Kallenborn et al. 2004).
PFASs were of concern due to their extreme persistence and potential toxicity and bioaccumulation potential (DeWitt et al. 2015). As a result of regulations and voluntary phase-out of perfluorooctane sulfonic acid (PFOS) and perfluorooctanecarboxylic acid (PFOA), usage of PFAS replacements such as perfluorether compounds, short chain perfluorocarboxylic acids (PFCAs) and perfluoroalkanesufonic acids (PFSAs) in industrial productions have increased. However, monitoring and hazard data are missing for a large fraction of these PFAS replacements. Due to the numerous uses of PFASs in modern society wastewater treatment plants have been considered as a point source with PFASs partitioning into the sludge and a potential source for their release into the biosphere (Eriksson et al. 2015). It is well established that various fluorotelomer and perfluoroalkyl sulphonamide compounds could degrade into more stable and potential toxic end products (primarily PFCAs and PFSAs) in activated sludge (Eriksson et al. 2015; Lee et al. 2010; Wang et al. 2011).
Thus, the fate of PFASs during different treatment conditions is of particular interest.
Understanding the transformation of PFAS in sludge is a quite complicated task since screening of all PFASs that may be present in environmental samples is not possible using a single mass spectrometry-based approach. Perfluoroalkyl acids, including PFCAs and PFSAs, require analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS), while neutral, semi-volatile monomeric PFAS-precursors (e.g. fluorotelomer alcohols and perfluorooctane sulfonamido alcohols) are more amenable to analysis by gas chromatography mass spectrometry (GC-MS). In addition, the availability of native standards presents limitations for development of quantitative compound specific analysis of some emerging PFASs. To address the difficulties of analyzing all relevant PFASs by traditional quantitative mass spectrometry some alternative approaches have been developed. In the total oxidizable precursor assay (TOP) a strong oxidation reagent is added to the sample in order to convert the majority of fluorotelomer and perfluoroalkyl sulphonamide compounds present in the sample to PFCAs and PFSAs which can subsequently be quantified by LC-MS/MS. In measurements of extractable organic fluorine (EOF), all molecules containing organic fluorine are converted to fluoride by combustion, which is subsequently measured by ion chromatography. By combining data from TOP and EOF with targeted (LC-MS/MS) analysis, fractions of as-of-yet unidentified precursors or fluorine-containing substances in the sample can be quantified.
Phthalates are widely used in the manufacture and processing of plastic products as plasticizers.
Some phthalates are endocrine-disrupting chemicals that may cause adverse health effects in wildlife and humans. Due to domestic and global regulations of phthalates in commercial products, alternative plasticizers have been introduced into markets. Diethyl phthalate (DEP), di-n-butyl phthalate (DnBP), and di(2-ethylhexyl) phthalate (DEHP) have been repeatedly detected in sludge and compost (Net et al. 2015). Composting can reduce the concentrations of phthalates initially present in sewage sludge with removal rates of up to 77–100% (Cai et al. 2012; Cheng et al. 2008).
In sludge, the removal rates of low molecular weight phthalates are higher compare to high molecular weight phthalates, since short alkyl chains are more easily biodegraded and mineralized. However, during the composting, long alkyl chain length compounds could be transformed to compounds with shorter alkyl chain length compounds (Net et al. 2015).
2 Materials & Methods
2.1 Sampling
Sludge samples (mesophilic anaerobic digested) were transported from the Henriksdal wastewater treatment plant in Stockholm to the waste-processing facility at Hovgården close to Uppsala. The sludge was stored on an asphalt surface with or without composting and sampling was performed at different times (Table 1). Triplicate samples were taken from each experimental condition at each sampling occasion, giving in total 21 samples. Each replicate contained a mix (homogenized) of seven subsamples collected at random spots of a freshly opened surface a few meters in from the end of the sludge windrow, or for the composted sludge from the freshly mixed compost. The samples were stored at – 20 °C until freeze drying and extractions.
Table 1. Storing conditions of sludge from the Henriksdal wastewater treatment plant and sampling times.
Sludge Details Sampling timesa
MesPKom The sludge was composted with garden waste, mainly woodchips.
Day 0
4 weeks13 weeks 6 months
MesPÖpp The sludge was stored without cover.
Day 0 6 months 12 months
a Calculated according to Haug (1993), b Triplicate samples at each sampling time.
2.2 Extraction and analysis of phthalates, alternative plasticizers and
organophosphate esters
Freeze-dried sludge (0.2-0.25 g) was weighed in 25 mL glass tubes (pyrolyzed at 400 ºC overnight).
An internal standard mix (200 ng), consisting of dimethyl phthalate-3,4,5,6-d4, di-n-butyl phthalate- 3,4,5,6-d4, bis(2-ethylhexyl)phthalate-3,4,5,6-d4, triamyl phosphate and triphenyl phosphate-d15 (Sigma Aldrich), was added to each sample and let to stand for 1-2 h. The samples were then extracted twice during 15 min of ultrasonication, using 6 mL acetone: n-hexane (3:1, v/v) and 6 mL acetone: n-hexane (1:1, v/v), respectively. The pooled extracts were centrifuged (2000 rpm) and transferred to new glass tubes and evaporated under a gentle stream of nitrogen to a final volume of 1 mL of n-hexane. The sample extracts were then loaded to pre-cleaned (3 mL acetone) and conditioned (3 mL n-hexane) Florisil SPE cartridges (Isolute FL 500 mg/3 mL) with 500 mg PSA
on top (Biotage, Uppsala, Sweden). The samples were washed with 6 mL n-hexane and eluted with 1) 2×3 mL acetone: n-hexane (3:1, v/v) and 2) 2×3 mL acetone: n-hexane (1:1, v/v). The samples were evaporated under a gentle stream of nitrogen to a final volume of 1 mL of n-hexane followed by addition of biphenyl (100 ng) as a volumetric pre-injection standard. The analyses were performed by GC/MS/MS (Agilent 7000; Agilent Technologies, Inc., Santa Clara, CA, USA) in electron impact (EI) ionization with a DB-5 column of 30 m, 0.25 mm inner diameter and 0.25 μm phase thickness.
The specific analysed compounds are presented in Table 2.
Table 2. List of phthalates, alternative plasticizers and organophosphate esters.
Phthalates and alternative plasticizers Organophosphate esters
Name CAS Name CAS
Dimethyl phthalate DMP 131-11-3 Triethyl phosphate TEP 78-40-0
Diethyl phthalate DEP 84-66-2 Triisobutyl phosphate TiBP 126-71-6
Di-n-butylphthalate DnBP 84-74-2 Tri-n-butyl phosphate TnBP 126-73-8
Diisobutyl phthalate DiBP 84-69-5 Tris(2-chloroethyl) phosphate TCEP 115-96-8 Benzyl butyl phthalate BzBP 85-68-7 Tris(2-chloropropyl) phosphate TCPP 13674-84-5
Bis(2-ethylhexyl)phthalate DEHP 117-81-7 1,3-Dichloro-2-propanol phosphate TDCPP 13674-87-8 Diisononyl phthalate DiNP 28553-12-0 Tris(2-butoxyethyl) phosphate TBEP 78-51-3
Diisodecyl phthalate DiDP 26761-40-0 Triphenyl phosphate TPhP 115-86-6
Bis(2-propylheptyl)phthalate DPHP 53306-54-0 2-Ethylhexyl diphenyl phosphate EHDPP 1241-94-7 1,2-Cyclohexane dicarboxylic
acid diisononyl ester
DINCH 166412-78-8 Tris(2-ethylhexyl) phosphate TEHP 78-42-2
Acetyltributylcitrate ATBC 77-90-7 Tri-o-cresyl phosphate ToCrP 78-30-8
Bis(2-ethylhexyl)terephthalate DEHT 6422-86-2 Tricresyl phosphate (technical mixture)
TCrP (mix) 1330-78-5
2.3 Extraction and analysis of PFAS
2.3.1 Compound-specific target analysis
Target analyses of PFASs were performed by weighing freeze-dried sludge (~0.5 g) in 15 mL plastic tubes. Stable isotope internal standards (18O2, 13C or 2H) of selected PFASs were spiked in all sludge samples and equilibrated for 1-2 h prior to extraction. The samples were then extracted thrice with 30 min of ultrasonication, using 2x5 mL MeOH and 5 mL EtOAc. The MeOH extracts were then combined into a new plastic tube for further treatment for LC-MS/MS measurement while the EtOAc extracts were stored in freezer for later treatment for GC-MS/MS analyses. The pooled MeOH extracts were evaporated under a gentle stream of nitrogen to a final volume of 1 mL followed by filtering through 0.45 µm polypropylene filter. Prior to instrumental analyses, 50 ng of 3,5-
bis(trifluoromethyl)phenylacetic acid was added as a volumetric pre-injection standard. The analyses were performed by LC-ESI-MS/MS (AB SCIEX API 4000) with a reversed phase column (Thermo Scientific HyPURITY C8, 5 µm, 50x3 mm) using MeOH and H2O with 2 mM ammonium acetate buffer as mobile phases. After the analysis the MeOH extracts were combined with the respective EtOAc extracts. The combined extracts were evaporated under a gentle stream of nitrogen until a final volume of about 0.5 mL followed by an addition of 10 mL of EtOAc (solvent exchange). The volatile PFAS were analyzed using GC-MS/MS (Agilent 7000; Agilent Technologies, Inc., Santa Clara, CA, USA) in electron impact (EI) ionization with DB-5 30 m, 0.25 mm, 0.25 μm column. All groups of quantifiable PFAS are included in Table 3. Fel! Hittar inte referenskälla.. List of groups of PFAS.
Substance group Number of
perfluorinated carbons
Instrumental method
PFCA Perfluoroalkyl carboxylic acids C4-C14 LC-MS/MS PFSA Perfluoroalkyl sulfonic acids C4, C6, C8 and C10 LC-MS/MS HFPO-DA Hexafluoropropylene oxide oligomers C6 LC-MS/MS Cl-PFESA Chlorinated polyfluoroalkyl ether
sulfonic acids
C10 and C12 LC-MS/MS
PFECHS Cyclic perfluoroalkyl sulfonic acids C8 LC-MS/MS
mono-PAP Monosubstituted polyfluoroalkyl phosphoric acid esters
C6, C8 LC-MS/MS
di-PAP di-Substituted polyfluoroalkyl phosphoric acid esters
C6:C6 and C8:C8 LC-MS/MS
PFOSA Perfluorooctanesulfonamide C8 LC-MS/MS
N-Me-FOSAA N-Methyl perfluorooctane sulfomamidoaccetic acid
C8 LC-MS/MS
N-Et-FOSAA N-Ethyl perfluorooctane sulfonamidoacetic acid
C6 andC8 LC-MS/MS
FTCA Fluorotelomer carboxylic acids C6 and C8 LC-MS/MS FTSA Fluorotelomer sulfonic acids C6 and C8 LC-MS/MS FTOH Fluorotelomer alcohols C6, C8 and C10 GC-MS/MS
FTAc Fluorotelomer acrylates C6 and C8 GC-MS/MS
FTMAc Fluorotelomer methacrylates C6 and C8 GC-MS/MS
2.3.2 TOP analysis
Total Oxidizable Precursors (TOP) analyses of PFASs were carried out with two different approaches, direct and indirect oxidation. The first approach (direct oxidation) was performed by mixing approximately 0.1 g of freeze-dried sample (pre-spiked with 13C8-PFOSA) with 60 mM potassium persulfate and 150 mM NaOH at 85°C for 6 h. The pH was adjusted with concentrated HCl followed by addition of the internal standards 13C4-PFOS, 13C4-PFOA prior to extractions using 2×5 mL MeOH twice. The samples were evaporated under a stream of nitrogen until a final volume of 1 mL. For the second approach (indirect oxidation), 0.5 g freeze-dried sample pre-spiked with the internal standards 13C4-PFOS, 13C4-PFOA and 13C8-PFOSA were extracted twice with 2×5 mL
MeOH. Oxidation of the extracts was performed using a similar mixture as the direct oxidation method, i.e. 60 mM potassium persulfate and 150 mM NaOH at 85°C for 6 h followed by pH adjustment with HCl. The extracts were then evaporated to a final volume of 1 mL. The extracts from both approaches were filtered through 0.45 µm PP filters before analysis with LC-ESI-MS/MS.
2.3.3 EOF analysis
For the extractable organic fluorine (EOF), approximately 1 g of freeze-dried homogenized sample was extracted twice using 2×5 mL MeOH. The combined extracts were centrifuged at 3000rpm for collecting the supernatants into new plastic tubes. The extracts were concentrated using a gentle stream of nitrogen to a final volume of 1 mL, followed by cleaning up using Envi-carb with glacial acetic acid. The extract from each sample was stored at -20 °C until analysis on combustion ion chromatography system at the Department of Environmental Science and Analytical Chemistry (ACES) at Stockholm University. The extracts were subsequently combusted slowly in a combustion furnace (HF-210, Mitsubishi) at 1100 °C under a flow of oxygen (400 l min−1) and argon mixed with water vapor (200 l min−1) for approximately 5 minutes. Combustion gases were absorbed in MilliQ water during the entire length of the combustion process using a gas absorber unit (GA-210, Mitsubishi). An aliquot of the absorption solution (200 μl,) was injected onto an ion chromatograph (Dionex Integrion HPIC, Thermo Fisher Scientific) equipped with an anion exchange column (Dionex IonPac AS19 2 × 50 mm guard column and 2 × 250 mm analytical column, 7.5 μm particle size) operated at 30 °C. Chromatographic separation was achieved by running a gradient of aqueous hydroxide mobile phase ramping from 8 mM to 60 mM at a flow rate of 0.25 ml min−1. Fluoride was detected using a conductivity detector.
2.3.4 Suspect screening
Suspect screening of PFASs was performed by using pooled freeze-dried samples from 3 replicates of each sampling occasion. The samples were spiked with 13C4-PFOS and 13C4-PFOA before extraction using 2x5 mL MeOH. The combined extracts were then evaporated to a final volume of 1 mL before filtering through 0.45 µm PP filter. The analyses were performed using an HPLC-Orbitrap MS (Thermo Fisher Scientific Inc., Waltham, MA) operating in both negative electrospray ionization (ESI-) and positive electrospray ionization (ESI+) modes. A reversed phase column (Waters Atlantis 5µm, C18-A, 150x2.0 mm) was used with MeOH and H2O with 2mM ammonium acetate buffer as mobile phases. Data were acquired in both full scan mode (100-1200 m/z, resolution 70 000) and dd- MS2 for high detected peaks. Tracer Finder 4.1 (Thermo Fisher Scientific) was used to screen for suspect PFASs which included in Norman Suspect List Exchange database.
3 Results & discussion
3.1 Phthalates and alternative plasticizers
In general, lower levels of phthalates were detected in the composted sludge compared to the non- composted. The highest detected levels of phthalates were corresponding to diisononyl phthalate (DINP) in both the non-composted and composted sludge. Reduction of DINP over time was only observed in the composted sludge (i.e. 69% decrease of DINP after 6 months). Other phthalates that occurred at relatively high levels in all sludge samples were DEHP, diisodecyl phthalate (DIDP) and 1,2-cyclohexane dicarboxylic acid diisononyl ester (DINCH). Some reduction of these phthalates was observed in the composted sludge (e.g. 37%, 34 and decrease of DEHP and DIDP after 6 months, respectively) but not in the non-composted. Overall, in the composted sludge, the phthalate and alternative plasticizers were reduced by 52%. The median levels of phthalates in sludge from triplicate samples are illustrated in Figure 1. The determined levels in all replicates are included in Appendix A.
Figure 1. Median levels of phthalates (mg/kg dry weight) from triplicates samples of sludge treated through mesophilic anaerobic digestion with or without composting, MesPKom and MesPÖpp, respectively. See Table 2 for nomenclature.
Concentrations of individual phthalatesfrom the non-composted at day 0 sample in this study (2019) were similar or lower than the results from previous analyses performed in sludge at the same Henriksdal waste water treatment plant as a part of the Swedish national monitoring program (2015- 2017) (Table 4). There has been a downward trend for DEHP and DINP over the last years. However,
at the same time, the alternative phthalate and non-phthalate plasticizers such as DPHP, DINCH and DEHT have been determined at considerable concentrations.
Table 4. Comparison of selected phthalates in sludge (mg/kg dry weight) at Henriksdal in year 2015-2017 and this study.
Name; Year 2015 2016 2017 2019 (This study) DMP <0.02 <0.01 <0.01 <0.04
DEP 0.01 <0.01 <0.05 <0.03 DiBP 0.02 N/A N/A 0.11 DnBP N/A 0.03 <0.1 0.32 BzBP 0.09 0.04 <0.05 0.07
DEHP 56 25 19 14
DINP 56 44 50 23
DIDP 13 12 14 1.3
DPHP N/A N/A N/A 3.6 ATBC N/A N/A N/A 0.06 DEHT N/A N/A N/A 1.1 DINCH N/A N/A N/A 9.4 N/A: not available
3.2 Organophosphate esters
All of the analysed organophosphates except for ToCrP were detected in the sludge samples. In general, the levels were low in all samples. The highest levels were corresponding to tris(2-chloro- 1-methylethyl) phosphate (TCPP) in the non-composted sludge. Slightly lower levels of TCPP were detected in composted sludge. Some reduction of TCPP was observed over time in both sample groups (47% decrease in composted after 6 months, and 29% decrease in the non-composted but only after 12 months). The levels of the replicates of the organophosphates are included in Appendix B.
Figure 2. Median levels of organophosphates (µg/kg dry weight) from triplicates samples of sludge treated through mesophilic anaerobic digestion with or without composting, MesPKom and MesPÖpp, respectively. See Table 2 for nomenclature.
Organophosphate ester levelsfrom the non-composted at day 0 sample in this study (2019) were similar (i.e. EHDPP, TBEP, TPhP) or in some cases increased (i.e. TCEP, TCPP, TDCPP) compared to results from previous analyses performed in sludge at the same Henriksdal waste water treatment plant by the Swedish EPA (2015-2017) (Table 5).
Table 5. Comparison of selected organophosphate esters in sludge (µg/kg dry weight) at Henriksdal in year 2015-2017 and this study. For 2019, this study, the values presented are the measurements made on the non-compost sample at the day 0 sampling occation.
Name; Year 2015 2016 2017 2019 (This study)
TEP N/A N/A N/A 69
TiBP N/A N/A N/A 5.5
TnBP 580 1000 1500 261
TCEP 6.2 4.5 7.1 21
TCPP 1700 650 520 1804
TDCPP 110 90 60 437
TBEP 400 180 170 494
TPhP 130 77 44 74
EHDPP 1600 1300 1000 1145
TEHP N/A N/A N/A 1841
ToCrP N/A N/A N/A <3.9
TCrP 210 260 250 958
N/A: not available
3.3 PFAS
3.3.1 Compound-specific target analysis
The median levels of the detected groups of PFAS from triplicate samples are illustrated in Figure 3.
Among 43 analysed PFASs, 13 PFASs were detected in all samples from (MesPKom) and non- composted (MesPÖpp) groups. The highest detected levels were corresponding to the fluorotelomer alcohols (6:2/8:2/10:2-FTOH) in the non-composted sludge. In the composted sludge only 10:2- FTOH was detected at all sampling times, with no difference between the time points. Some reduction over time in the MesPKom samples was only observed for a few PFAS groups, namely PFDS, 6:2 diPAP and 8:2 FTUA. Reduction over time was observed for seven PFAS groups in the MesPÖpp group (PFUnDA, 6:2-diPAP, FHUEA-2-6:2FTUA, 8:2 FTUA, 6:2 FTMAC, N-Et- FOSAA). The levels of the replicates of the quantified PFAS are included in Appendix C.
Figure 3. Median levels of PFAS (ng/g dry weight) from triplicate samples of sludge treated through mesophilic anaerobic digestion with or without composting, MesPKom and MesPÖpp, respectively.
Concentrations of individual PFASfrom the non-compost sludge at day 0 sample were compared in this study with previous study that was performed in sludge at the same Henriksdal wastewater treatment plant by Naturvårdsverket (2015-2017) (Table 6). It could be seen that most of detected PFAS in this study were in similar range with the previous study. The fluorotelomer alcohols and other volatile PFASs that were dominant in the present study were not included in the study by Naturvårdsverket (2015-2017) and therefore cannot be compared. The sum concentrations of PFAS in composted sludge at day 0 were approximately three times lower than those in the non-compost sludge. Analogously, with phthalates and organophosphate esters the difference in start
concentrations can partly be explained by the addition of wood chips and garden waste to the composted sludge which would dilute the concentrations of PFAS by approximately 25% on a mass basis. The difference in initial concentrations may also be due transformation and/or evaporative losses in the compost samples prior to the start of the experiment. It is worth noting that the largest difference in concentrations between composted and non-composted sludge at day 0 was observed for FTOHs which are known to be semi-volatile and degradable to other PFAS (Buck et al. 2011).
FTOHs of different chain-lengths dominated the concentrations found in both the compost and non- compost samples. However, the sum concentrations as well as the composition of PFAS displayed very different temporal trends over the course of the experiment. For the non-compost samples sum PFAS concentrations increased by one order of magnitude over 12 months of storage due to the drastic increase of 6:2, 8:2 and 10:2 FTOHs. Contrastingly, the sum concentrations of PFAS displayed a slight decrease over 6 months in the compost samples. Although the reasons for the diverging trends are not completely understood, these observations can probably be explained by higher evaporative losses in the compost experiments in combination with different transformation rates of PFAS for the two different experiments. In the non-compost samples the drastic increase of FTOHs, is a clear indication that these substances are formed from other telomer-based PFAS which were not measured here. For example, fluorinated side-chain polymers present in the sludge could be a source of FTOHs and other intermediate products. Although similar transformation processes probably occur in the compost samples the higher temperature would lead to more efficient off- gassing of FTOHs from the sludge during the compost storage. The temperature of the non-compost sludge was around 30ºC at the start of the experiment and decreased over time to even out between 0 and 10 degrees after 180 days. The temperature in the compost experiment was more than 60ºC for the first 120 days (the sensors used could only register up to 60ºC) after which the temperature decreased to approximately 30ºC at 180 days (the time of the last sampling analysed for these compounds in the composted sludge). Combined with the higher porosity of composted sludge (64.3% compared to 34.4%) and the fact that composted sludge was completely mixed 8 times during the experiment it seems plausible that more efficient volatilization of FTOHs can explain the diverging time trends.
Table 6. Comparison of selected PFASs in sludge at Henriksdal in year 2015-2017 and this study.
Name; Year 2015 2016 2017 2019
(This study) Name; Year 2015 2016 2017 2019 (This study)
PFBA N/A <64 N/A <0.7 lin-MeFOSAA N/A 2.06 N/A
2.22*
PFPeA N/A <2.00 N/A <0.1 br-MeFOSAA N/A 0.83 N/A
PFHxA 2.24 1.4 0.94 <0.7 lin-EtFOSAA N/A 10.6 N/A
2.65*
PFHpA 0.489 <0.20 0.11 <0.1 br-EtFOSAA N/A 0.23 N/A
PFOA 1.58 0.97 0.56 <0.1 4:2 FTS N/A <0.25 N/A N/A
PFNA 0.652 0.48 0.47 <0.1 6:2 FTS N/A 0.53 N/A <0.1
PFDA 3.36 3.35 2.23 1.70 8:2 FTS N/A 0.91 N/A N/A
PFUnDA 1.61 1.81 1.22 0.78 6:2 PAP N/A N/A N/A <0.1
PFDoDA 2.48 2.45 1.5 0.96 8:2 PAP N/A N/A N/A <0.5
PFTrDA 0.623 0.46 <1.0 <0.1 4:2 diPAP N/A <7.00 N/A N/A
PFTeDA 1.00 0.43 <1.6 <0.1 6:2 diPAP N/A 3.9 N/A 7.25
PFPeDA 0.221 <0.50 <1.0 N/A 8:2 diPAP N/A 1.28 N/A 2.48
PFHxDA N/A N/A N/A <0.1 10:2 diPAP N/A <1.00 N/A N/A
PFOcDA N/A N/A N/A <0.1 HFPO-DA N/A N/A N/A <0.1
FPrPA N/A <2.00 N/A N/A DONA N/A N/A N/A <0.1
FPePA N/A 4.26 N/A N/A 9Cl-PF3ONS N/A N/A N/A <0.1
FHpPA N/A 1.12 N/A N/A PFECHS N/A N/A N/A <0.1
PFBS 1.23 <0.25 <0.11 <0.1 8:2 Cl-PFESA N/A N/A N/A <0.1
lin-PFHxS
<0.76* <0.25 0.16
<0.1* 10:2 Cl-PFESA N/A N/A N/A 0.12
br-PFHxS <0.10 <0.15 6:2FTUA N/A N/A N/A <54
lin-PFHpS N/A <0.25 N/A
N/A 8:2 FTUA N/A N/A N/A 2.03
br-PFHpS N/A <0.10 N/A 10:2FTUA N/A N/A N/A <0.1
lin-PFOS 11.1 6.52 7.6
6.91* 6:2 FTAc N/A N/A N/A <0.1
br-PFOS 1.59 1.18 1.39 6:2 FTMAC N/A N/A N/A 39
lin-PFNS N/A <0.10 N/A
N/A
8:2 FTAc N/A N/A N/A 16
br-PFNS N/A <0.10 N/A 8:2 FTMAC N/A N/A N/A 1.17
lin-PFDS 1.82 0.61 <0.6
1.53*
10:2 FTAc N/A N/A N/A 8.19
br-PFDS 0.59 0.5 <0.6 10:2 FTMAc N/A N/A N/A <2
lin-PFUnDS N/A <0.10 N/A
N/A
6:2 FTOH N/A N/A N/A 5.88
br-PFUnDS N/A <0.10 N/A 8:2 FTOH N/A N/A N/A 241
lin-FOSA 0.575 <0.90 0.43
0.70*
10:2 FTOH N/A N/A N/A 115
br-FOSA 0.182 <0.25 <0.22 Unit: µg/kg or ng/g d.w
lin-FOSAA N/A 1.35 N/A
N/A * sum of linear and branched compound
br-FOSAA N/A <0.25 N/A N/A not applicable
3.3.2 TOP analysis
Method testing for two different sludge samples analysed in triplicate displayed no significant difference in concentrations between direct and indirect oxidation. Thus, for consistency with previous studies indirect oxidation was applied to all samples for TOP analysis. Overall, the average sum concentrations of PFAS increased between 14 and 54 times for TOP analysis compared with the compound specific analysis excluding the semi-volatile compounds which were extracted in EtOAc.
PFCAs of various chain-lengths and particularly PFBA, PFPeA and PFHpA showed higher concentrations in TOP analysis compared to compound-specific analysis. The higher concentrations for multiple odd and even chain PFCAs in TOP compared to compounds-specific analysis indicate the presence of telomer-based precursors which typically undergo unzipping of the perfluoralkyl chain in the presence of strong oxidants. Interestingly, the most pronounced difference was observed for 6:2 FTS which was more than 8900 times (median value) higher in TOP analysis compared to compound-specific analysis. This finding suggests the presence of fluorotelomer-based precursors which have CnF2n+1CH2CH2S–R or CnF2n+1CH2CH2SO2–R moiety (where R is a functional group which has hydrophilic property) (Buck et al. 2011). Unfortunately, a large inter-sample variability was observed for the TOP analysis (relative standard deviation between 9 and 89%) which did not allow a comparison of the time trends of compost and non-compost samples respectively.
3.3.3 EOF analysis
The mean concentrations of EOF in non-compost sludge ranged from 602 ± 92 ng F/g (Day 0) to 682
± 118 ng F/g (month 12), see Figure 4. These concentrations were significantly higher than in compost sludge, which ranged from 418 ± 63 ng F/g (Day 0) to 266 ± 79 ng F/g (6 months). The observations of higher EOF in non-compost sludge and opposite time trends for the different storage experiments were consistent with the results of the compound-specific PFAS analysis. A comparison of sum PFAS concentrations extracted in methanol (converted to F-equivalents) to EOF revealed a large quantity of unidentified EOF in all samples from both experiments, ranging from 94-97% in non-composted sludge and 91-96% in composted sludge (Figure 5). For compost samples a statistically significant increase in the quantity of known PFAS was observed with time of storage (p=0.03; one-way ANOVA). This trend could potentially be explained by transformation of hitherto unknown precursors which are transformed into PFCAs over the course of the experiment. For non- compost samples the quantity of known PFAS increased between day 0 and 6 months but decreased between 6 months and 12 months (p=0.02; one-way ANOVA). Analogously, with the observations for compound-specific analysis the differences between compost and non-compost samples for EOF would be affected by different rates of volatilization and microbial transformation. Although the identity of the EOF remains unclear it should be noted that the analysis may include small quantities of residual FTOHs that were extracted in the methanol phase. Given the very high concentrations of FTOHs observed in the targeted analysis (of the EtOAc phase), a small fraction of these substances extracted in the methanol extraction step could contribute to the measured EOF signal in addition to hitherto unidentified organofluorine substances.
Figure 4. EOF (orange) and fraction accounted for by target PFAS (blue bars; not including
EtOAc-extracted targets).
Figure 5. Percentage of EOF accounted for by known PFAS.
3.3.4 Suspect screening
Over 1000 PFASs were scanned on 7 pooled samples but no hits were found for any PFASs in the Norman Suspect List Exchange database using Trace Finder 4.1. The result “no hits” should not be interpreted as no other PFASs which can be presented in the sample. The matrix of this type of sample is quite complex therefore it decreased the ionization of the instrument which then affected the compounds detectability. In addition, there might be other PFASs which exist in the samples that was not included in the employed suspect list.
Furthermore, the non-target screening of those 7 pooled samples were performed using Compound Discoverer 3.1 (ThermoFisher Scientific). Spectral data from full-scan experiments on the sludge sample were used to predict the elemental composition and searches for corresponding masses were made on different databases (ChemSpider, online m/z cloud and Thermo Scientific’s mzVault libraries) in an attempt to make a tentative identification of the unknown compounds. Two potential organofluorine compounds were suggested by the software. These were 1,1,1,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14-Octacosafluoro-14-iodo-2-
(trifluoromethyl)tetradecane (C15F31I) and 1,1,1,2,2,3,3,4,4,5,5,6,6-Tridecafluoroicosane (C20H29F13). These tentatively detected compounds would fall into level 5 on the Schymanski scale which means that their identity is highly uncertain (Schymanski et al. 2014). Further investigation should be done to increase the level of confidence of the structures for these compounds.
4 Conclusions
In general, the sum of the levels of all chemicals within respective class (PFAS, organophosphate esters, phthalate and alternative plasticizers) was lower at all sampling times in the composted sludge compared to in the non-composted. The overall concentration profiles for the sum of organophosphate esters, phthalates and alternative plasticizers, as well as perfluorinated compounds determined by EOF, are similar with an increase or no reduction for the non-compost treatment and a reduction in the compost treatment. The largest reductions of the sum of phthalate and alternative plasticizers, and the sum of organophosphates were found for the composted sludge (52% and 34%
decrease after 6 months, respectively) and a measurement of the 12-month sample for the compost treatment may have given further insight into the effect on composting on the reduction of specific micropollutants.
For PFAS there was no consistent reduction of the levels during storage of sludge. Although a slight decrease was observed for the sum PFAS from compound-specific analysis and EOF in the compost samples, the non-compost samples displayed a drastic increase in FTOHs and EOF. As discussed in more detail above the diverging trends between the experiments can probably be explained by a higher volatilization during compost storage and differences in transformation rates of precursors.
Thus, the apparent reduction of PFAS in compost samples should not be interpreted as an efficient degradation of PFAS. The compound-specific, TOP and EOF measurements collectively suggest that a suite of both known and unknown precursors are formed during sludge storage and partly converted to stable end-products such as PFCAs. However, additional experiments would be needed to better understand the complex interaction between transformation and removal mechanisms. Further investigation focused on reduction of selected precursors of PFASs would be necessary in order to improve understanding on the process of PFAS-precursors degradation in composted sludge as the identities of formed PFASs found using the suspect target screening were difficult to assess. The TOP analyses also showed the probable formation of 6:2-FTS and an increase of PFCAs but further studies are needed in order to identify the sources of these compounds.
The phthalates that were most common in both groups of sludge (i.e. DINP, DEHP, DIDP) in the present study were detected at lower levels compared to the earlier studies of sludge from the Henriksdal wastewater treatment plant (Naturvårdsverket, 2019). The organophosphate levels were detected at slightly higher levels compared to the previous study by Naturvårdsverket (2017).
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Appendix A. Phthalate and alternative plasticizer levels (mg/kg dry weight)
mg/kg dw IVL-id DMP DEP DiBP DnBP BzBP DEHP DINP DIDP DPHP ATBC DEHT DINCH MesPÖpp 0day-01 7793 <0.043 <0.335 0.106 0.323 0.040 14.3 19.8 2.49 3.61 0.018 1.73 12.5
MesPÖpp 0day-02 7794 0.047 0.466 0.137 0.355 0.099 14.4 23.2 0.801 3.61 0.056 1.09 9.35
MesPÖpp 0day-03 7795 <0.043 <0.335 0.072 0.187 0.069 14.0 23.3 1.27 3.32 0.069 0.312 4.82 MesPÖpp 6months-01 8408 <0.043 <0.335 0.143 0.447 0.012 12.3 25.1 17.5 4.10 0.045 0.097 5.47 MesPÖpp 6months-02 8409 <0.043 <0.335 0.086 0.297 0.041 12.4 25.4 19.8 5.58 0.086 0.564 17.8 MesPÖpp 6months-03 8410 0.048 0.446 0.149 0.332 0.159 13.5 22.6 15.6 4.06 0.218 0.914 10.0 MesPÖpp 12months-01 9196 <0.043 <0.335 0.121 0.663 0.020 21.3 20.3 14.7 6.21 0.022 0.481 14.8 MesPÖpp 12months-02 9197 <0.043 <0.335 0.133 0.830 0.026 19.1 20.1 14.4 5.30 0.007 0.422 13.8 MesPÖpp 12months-03 9198 <0.043 <0.335 <0.064 0.270 0.012 14.9 23.5 16.7 5.51 <0.005 0.654 14.9
MesPKom 0day-01 7808 0.054 0.375 0.073 0.210 0.078 11.7 17.6 0.492 2.93 0.028 0.689 7.43
MesPKom 0day-02 7809 <0.043 <0.335 0.077 0.250 0.044 11.3 19.0 14.0 3.86 0.060 1.34 11.5 MesPKom 0day-03 7810 0.085 0.592 <0.064 0.172 0.107 9.7 13.7 8.97 2.32 0.076 0.617 5.55 MesPKom 4weeks-01 7811 <0.043 <0.335 <0.064 0.072 <0.004 11.6 17.7 13.1 4.35 0.040 0.788 13.6 MesPKom 4weeks-02 7812 0.046 0.361 0.087 0.247 <0.004 14.8 19.5 14.0 3.51 0.058 0.621 8.85 MesPKom 4weeks-03 7813 <0.043 <0.335 <0.064 0.081 0.015 10.6 16.7 12.7 4.11 0.034 0.803 12.1 MesPKom 13weeks-01 7814 <0.043 <0.335 <0.064 <0.068 0.015 11.8 17.5 14.8 5.10 0.012 0.813 13.4 MesPKom 13weeks-02 7815 <0.043 <0.335 <0.064 <0.068 0.065 8.48 9.16 8.74 2.27 0.007 0.038 4.22 MesPKom 13weeks-03 7816 <0.043 <0.335 <0.064 <0.068 0.051 10.2 14.6 13.0 4.13 0.023 0.058 7.78 MesPKom 6months-01 8423 <0.043 <0.335 <0.064 <0.068 0.021 7.09 5.46 5.88 2.36 0.017 0.004 2.84 MesPKom 6months-02 8424 <0.043 <0.335 <0.064 0.106 0.018 7.01 6.26 7.77 2.97 0.006 7.07 7.49 MesPKom 6months-03 8425 <0.043 <0.335 <0.064 <0.068 0.038 8.79 4.62 5.25 1.80 0.029 0.013 2.84 LOD 0.043 0.335 0.064 0.068 0.004 0.130 0.039 0.039 0.004 0.005 0.004 0.019
DF% 25 25 50 75 90 100 100 100 100 95 100 100
