Chemosphere 87 (2012) 137–143

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Chemosphere

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Dissipation pathways of organic pollutants during the composting of organic wastes

Gwenaëlle Lashermes a,1, Enrique Barriuso a, Sabine Houot a,⇑a INRA, UMR1091, Environnement et Grandes Cultures, INRA-AgroParisTech, F-78850 Thiverval-Grignon, France

a r t i c l e i n f o a b s t r a c t

Article history:Received 25 July 2011Received in revised form 30 November 2011Accepted 1 December 2011Available online 30 December 2011

Keywords:CompostingFluorantheneLinear alkylbenzene sulfonates (LAS)Nonylphenol (NP)GlyphosateNon-extractable residues

0045-6535/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.chemosphere.2011.12.004

⇑ Corresponding author. Tel.: +33 130815401; fax:E-mail addresses: gwenaelle.lashermes@reims.inr

barriuso@grignon.inra.fr (E. Barriuso), sabine.houot@g1 INRA, UMR614, Fractionnement des AgroResso

Esplanade Roland Garros, BP 224, F-51686 REIMS cede

The organic pollutants (OPs) present in compostable organic residues can be recovered in the final com-posts leading to environmental impacts related to their use in agriculture. However, the composting pro-cess may contribute to their partial dissipation that is classically evaluated through the concentrationdecrease in extractable OPs, without identification of the responsible mechanisms as mineralization orstabilization of OP as non-extractable residues (NER) or bound residues. The dissipation of four 14C-labeled OPs (fluoranthene; 4-n-nonylphenol, NP; sodium linear dodecylbenzene sulfonate, LAS; glyphos-ate) was assessed during composting of sewage sludge and green waste. The dissipation of LAS largelyresulted from its mineralization (51% of initial LAS), whereas mineralization was intermediate for NP(29%) and glyphosate (24%), and negligible for fluoranthene. The NER pathway mostly concerned NPand glyphosate, with 45% and 37% of the recovered 14C being found as NER at the end of composting,respectively. In the final composts, the proportions of water soluble residues of OPs considered as readilyavailable were <11% of recovered 14C-OPs. However, most fluoranthene remained solvent extractable(72%) and potentially available, whereas only 18% of glyphosate and less than 7% of both NP and LASremained solvent extractable in the final compost.

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1. Introduction

Compost can be contaminated with organic pollutants (OPs) ini-tially present in organic feedstock materials. A broad range of OPscan be found including pesticide residues on green waste(Büyüksönmez et al., 2000) or many other chemicals in wastewatersludge (Harrison et al., 2006) or in biowastes (Brändli et al., 2005).

Composting has been recognized to largely decrease OP concen-trations in the final composts applied on soil (Amir et al., 2005;Pakou et al., 2009). In several countries, thresholds of maximumconcentrations into the compost have been defined for some ofOPs such as polycyclic aromatic hydrocarbons (PAHs), polychlori-nated biphenyls (PCBs) or polychlorinated dibenzo-p-dioxins/fur-ans (PCCDs/Fs) (Hogg et al., 2002). New regulations includinglimitation for other emergent OPs such as linear alkylbenzenesulfonates (LAS) or nonylphenol (NP) are under discussion(European Commission, 2000, 2001).

During composting, OPs can be incompletely degraded bymicroorganisms into metabolites or mineralized as CO2, lixiviatedor establish sorption interactions with the composted organic mat-ter (Michel et al., 1995; Lashermes et al., 2010) culminating with

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the formation of non-extractable residues (NER) that remain inthe compost after classical analytical extraction procedures(Barriuso et al., 2008). However, the OP dissipation during com-posting is classically evaluated through the concentration decreaseof solvent extractable OP, without consideration of involved mech-anisms: mineralization or stabilization as NER.

Mineralization is the only true mechanism of OP eliminationwhile the stabilization as NER reducing their mobility and poten-tial ecotoxicological effect (Kästner et al., 1999) limits contamina-tion risks on the short term. However, NER are susceptible to laterremobilization (Gevao et al., 2000) and have to be taken intoaccount in risk assessment over medium and long terms.

An increasing number of references have reported the dissipa-tion of OPs during composting. In most cases the dissipation ofPAHs has been observed, with median decrease of OP concentra-tions varying from 10% for chrysene to 81% for acenaphtene(Lazzari et al., 2000; Amir et al., 2005; Oleszczuk 2006, 2007;Brändli et al., 2007). A dissipation higher than 77% of LAS has beenrecorded (Pakou et al., 2009), 87% of NP (Gibson et al., 2007) and50% for pesticides (Kupper et al., 2008). However, only very fewstudies differentiated the dissipation pathways, which requiresthe use of 14C-labeled OPs. Less than 25% of initial 14C-PAH formedNER during composting (Racke and Frink, 1989; Hartlieb et al.,2003). The formation of NER has been reported as very variablefor pesticides, from 20% of initial 14C-2,4-D to 86% for 14C-carbarylwith low mineralization in most cases (Racke and Frink, 1989;Michel et al., 1995; Hartlieb et al., 2003).

138 G. Lashermes et al. / Chemosphere 87 (2012) 137–143

The objectives of this study were to assess the dissipation path-ways of OPs with contrasted characteristics during composting andtheir availability in the final compost. A mixture of aerobically di-gested sewage sludge with green waste including branches, grassclipping, hedge trimming and leaves was spiked with 14C-OPsand composted over 83 d in triplicate, using small-scale instru-mented reactors. Four 14C-labeled OPs were studied: a PAH (fluo-ranthene), two surfactants (NP and LAS) and a widely-usedherbicide (glyphosate) whose behavior during composting hasbeen poorly investigated (Büyüksönmez et al., 2000). The mineral-ization, volatilization and lixiviation of the OPs during compostingwere determined. The speciation of OP was also followed duringcomposting: (1) water extraction was used to estimate an easilyavailable fraction for degrading microorganisms, plant assimilationor transfer to ground water; (2) solvent extraction allowed toassess potentially available fraction; and (3) the NER was consid-ered as non directly available fraction (Benoit and Barriuso, 1997).

2. Materials and methods

2.1. Organic pollutants

The [3C-ring-14C] fluoranthene (specific activity:1665 MBq mmol�1, 98.3% radiopurity) and the [methyl-14C] N-(phosphonomethyl)glycine (glyphosate) (specific activity: 81.4MBq mmol�1, 93.8% radiopurity) were purchased from SigmaChemicals (St. Louis, USA), the [U-ring-14C] 4-n-nonylphenol (spe-cific activity: 1924 MBq mmol�1, 99% radiopurity) from ARC-900(St. Louis, USA), and the [U-ring-14C] sodium linear dodecylbenzenesulfonate (specific activity: 230.9 MBq mmol�1, 92.7% radiopurity)from Izotop (Budapest, Hungary). Non-labeled fluoranthene (99%purity), NP (99.5% purity), and LAS (79.9% purity, containing theC10–C13 homologous) were obtained from Sigma Chemicals (St.Louis, USA), Interchim (Montluçon, France), and Sasol (Marl, Ger-many), respectively. The water solubilities (Sw) were 25 � 104,1 � 104, 7 and 0.26 mg L�1 for LAS, glyphosate, NP and fluoranthene,respectively. The octanol–water partition coefficients (Kow) were5.16, 1.23,�2.73,�3.4 (as log Kow) for NP, fluoranthene, LAS, and gly-phosate, respectively (PHYSPROP database).

Solutions of 14C-labeled OPs were prepared in methanol for flu-oranthene and NP, in MilliQ water (Millipore, Molsheim, France)for LAS and glyphosate. Isotopic dilution with non-labeled OPwas used to reach the final concentrations of 44, 28919, 29 and700 mg L�1 and 53407, 47816, 84233 and 51071 MBq L�1 for gly-phosate, LAS, fluoranthene, and NP, respectively.

2.2. Composting set-up

The waste mixture and composting reactors have beendescribed in Lashermes et al. (2012). Briefly, the waste mixturewas roughly ground and contained (% of DM): aerobic digestedsewage sludge (20%), branches (25%), grass clippings (15%), hedgetrimmings (20%), and leaves (20%). The composting system com-prised 4-L glass reactors supplied with warm humidified air andsurrounded by an external jacket through which water circulatedfrom a thermostatic bath. Composting was performed in triplicatefor each OP introducing into each reactor 750 g wet weight of theinitial waste mixture which corresponded to different equivalentdry weight in the two sets of composting experiments becausethe DM of organic waste evolved during storage, 250 g DM in gly-phosate and LAS experiments and 400 g DM in fluoranthene andNP. The initial waste mixture was spiked with the OP solution dropby drop and under continuous mixing (either 20 mL of the fluo-ranthene, NP and glyphosate solutions, or 25 mL of the LAS solu-tion) to reach the following initial OP concentrations (mg kg�1

DM): 3, 2860, 1.5 and 34, for glyphosate, LAS, fluoranthene andNP, respectively. Finally, the waste mixtures were humidified with59 mL Milli-Q water for fluoranthene, NP and glyphosate and54 mL for LAS experiment.

During the first 6 d, the temperature increased by self-heating;then the temperature was modulated to mimic a typical compost-ing temperature profile. After 41 d, composts were moved to 21-Lglass cells for maturation and placed in a thermostatic room at28 ± 1 �C for additional 42 d. The composting mixtures were sam-pled three times after homogenization: at the end of the thermo-philic phase (day 13), at the end of the cooling phase (day 41)and at the end of the maturation phase (day 83). At each samplingdate, water was sprayed on the compost to maintain the moisturecontent at 50–70% of wet weight. The composting mixture wascharacterized during another set of six composting experiments,with the same initial waste mixture and composting procedurebut without addition of 14C-OPs (Lashermes et al., 2012). The evo-lution of the chemical and biochemical characteristics attested of asatisfactory composting process with a decrease of C:N ratio from15.7 to 12.2 and the increase of the ratio of lignin to holocellulosefrom 0.4 to 0.9.

2.3. Organic pollutant mineralization, volatilization, lixiviation andspeciation during composting

During the first 41 d of composting, the exhaust air of each reac-tor was passed through a 400-mL methanol plug to trap volatile or-ganic compounds (VOCs) and through two successive CO2 traps,each containing 750 mL 3 M NaOH. The traps of methanol andNaOH were replaced respectively 14 and 18 times and analyzedfor 14C-VOC and 14C-CO2 concentrations by liquid scintillationcounting (LSC) with a Tri-Carb 2100 TR counter (Perkin ElmerIns., Courtabeuf, France) using Ultima Gold XR (Packard) as scintil-lation cocktail. Lixiviates were recovered at the bottom of eachreactor and were pumped out after 13 and 41 d of composting.The collected volumes were measured and their 14C content wasdetermined by LSC. During maturation (days 41–83), a vial con-taining 100 mL 3 M NaOH was placed in each maturation cell totrap the 14CO2 produced. These vials were replaced 14 times andthe 14C-CO2 was measured by LSC.

Sequential extraction was carried out in triplicate on fresh sam-ples of the initial waste mixture and composts. An average weightof 4.8 ± 1.0 g DM of organic sample was placed in a glass centrifugetube. The first extraction was performed with 75 mL of MilliQwater. After 24 h of shaking, water extracts were recovered by cen-trifugation at 2400 g for 20 min. Three successive extractions werethen performed following the same procedure but with 75 mL ofmethanol for fluoranthene, NP and LAS, or 75 mL of 0.54 M ammo-nium hydroxide solution for glyphosate. The 14C-OP concentrationin all extracts was measured by LSC. After extraction, the compostresidues were dried at 40 �C, ground at 200 lm and the remainingnon-extracted radioactivity (corresponding to the NER) was deter-mined by scintillation counting of the 14C-CO2 evolved after com-bustion of the solid (Sample Oxidizer 307, Packard, Meriden, CT,USA). All 14C-fractions were expressed in percentage of total recov-ered 14C (sum of the 14C-activity recovered in all the fractions min-eralized, volatilized, leached, extractable and NER) at a specificsampling date. The dissipation of OPs during composting was cal-culated (1) as the difference between the initial and final concen-trations (in mg kg�1 DM) of total extractable residues (additionof water and solvent extractable 14C-fractions) as usually measuredin composts produced on composting plants and (2) as the differ-ence between the initial and final amount (mg) of total extractableresidues per reactor in order to assess the dissipation of OP takinginto account the compost mass reduction during the process.

G. Lashermes et al. / Chemosphere 87 (2012) 137–143 139

2.4. Data analyses

Microsoft Excel Solver was used to adjust the cumulative 14C-CO2 mineralization kinetics to distinct Gompertz sigmoid equa-tions for the thermophilic and maturation phases:

PðtÞ ¼ Ai � exp � explmi � e

Aiðki � tÞ þ 1

� �� �ð1Þ

where P(t) is the total mineralized 14C-CO2 at time t, expressed as apercentage of initial 14C; Ai, the asymptote representing the maxi-mum mineralization attained; lmi, the maximum specific growthrate; ki, the lag time (Zwietering et al., 1990), and i index equaled1 or 2 for the active (thermophilic + cooling phases, 0–41 d) andmaturation phases(41–83 d), respectively.

Ninety-five percent confidence intervals were calculated con-sidering the three replicates of composting for mineralizationand speciation results.

3. Results and discussion

3.1. Overall balance of the OP behavior during composting

The evolution of the 14C distribution for each OP and compost-ing experiment among the different analyzed fractions is shown inFig. 1. Each OP presented different behavior with a good replicationbetween the three replicated composting experiments and withconfidence intervals for all fractions generally lower than 10% ofrecovered 14C. The average 14C-OP recovery considering all sam-pling dates was (in % of initially applied 14C): 96, 95, 85, and 83for fluoranthene, glyphosate, LAS and NP, respectively.

The 14C-fluoranthene behavior showed little changes duringcomposting maintaining a high solvent extractable fraction. Inthe case of glyphosate, the proportion of NER increased but a largepart remained extractable with an equal distribution between thewater and solvent extracts. LAS behavior was characterized by a ra-pid mineralization whereas the NP mineralization was balanced bya rapid formation of NER which remained at high level during theentire composting process.

The volumes of leachates recovered were on average 450 mL,820 mL, 620 mL and 520 mL for fluoranthene, glyphosate, LAS andNP experiments, respectively. The highest 14C-lixiviated fractionsrecovered were found for the glyphosate and LAS, representing5 ± 3% of recovered 14C for both OPs after 41 d of composting. The14C lixiviation was negligible for fluoranthene and NP. Volatilizationwas only detected once for LAS and accounted for 5% of recovered14C. This was unexpected since LAS is not a volatile surfactant.

3.2. OP dissipation through mineralization during the compostingprocess

Composting can reduce OP contamination of an initial wastemixture through its complete mineralization as observed for PAHsand pesticides (Michel et al., 1995; Hartlieb et al., 2003). In thepresent experiment, the OP mineralization at the end of compost-ing reached (in % of applied 14C): 0.3 ± 0.2 (95% confidence interval)for fluoranthene, 24 ± 8 for glyphosate, 29 ± 2 for NP and 51 ± 4 forLAS (Fig. 1). The mineralization of glyphosate, LAS and NP mostlyoccurred during the most biologically active composting period(days 0–41) (Ai, Table 1). During maturation (days 41–83) muchless mineralization occurred (on average, 3%, 6% and 1% of initial14C for glyphosate, LAS and NP, respectively).

A lag phase was observed in the mineralization of LAS, glyphos-ate and NP at the beginning of composting, corresponding to thetime required for the degrading microorganisms to reach an effi-cient level (Dörfler et al., 1996). The mineralization kinetics were

well described by the Gompertz equation (R2 > 0.98) (Table 1). Thefirst lag phase (k1) was on average 3, 5, 8 d for glyphosate, NP, andLAS, respectively, corresponding to the self-heating period duringthe thermophilic step. Then mineralization rate of these OPsreached the highest values when the temperature increased until60 �C on days 8–11. During the maturation phase, after homogeni-zation and rewetting, a second lag phase (k2) was on average 7and 8 d for LAS and glyphosate, respectively; while the mineraliza-tion of NP remained very low and nearly linear. The lag phase for NPmineralization was significantly and negatively correlated with themaximum temperature observed during composting (P > 0.001).The microorganisms responsible for NP mineralization may indeedbe less efficient at thermophilic than at mesophilic temperatures(Moeller and Reeh, 2003a).

The variability observed in glyphosate mineralization kineticscould be explained by temperature and moisture limitations whichoccasionally occurred because of aeration and high temperaturesin some reactors. Indeed, the asymptotes of mineralization kinetics(A1 of Gompertz equation, Table 1) were negatively correlated withthe moisture content of the compost sampled after 13 d (P > 0.001)and 41 d (P > 0.01) and positively correlated with the mean tem-perature during the first 6 d (P > 0.001).

The proportions of 14C-OP mineralized at the end of compostingin the present study decreased in the same order as found duringincubation with composts sampled at different composting stages(Lashermes et al., 2010): LAS > NP > glyphosate > fluroanthene.However, the extent of 14C-OP mineralization was lower duringcomposting than compost incubations. In particular, NP and fluo-ranthene showed respectively a high potential of mineralizationduring incubation with compost sampled during the cooling phase(56% of initial 14C) and with mature compost (21% of initial 14C).For fluoranthene, the differences may be explained by a durationof composting (83 d) not long enough to allow the compost coloni-zation by microorganisms capable of degrading aromatic struc-tures, such as white-rot fungi (Hammel, 1995) or prokaryotes(Haderlein et al., 2006) which could have developed during theadditional incubation time (92 d). Moreover, the mineralizationof NP could have been limited by the high temperature duringthe thermophilic phase while the mineralization of NP in incuba-tion took place at a lower temperature (28 �C) probably closer tothe optimal conditions for NP degradation.

In soils, the potentials of mineralization also decrease in thesame order among the four OPs. However, the extent of minerali-zation during composting was always lower than found in soils:for LAS (Dörfler et al., 1996), NP (Gejlsbjerg et al., 2003) or glyphos-ate (Mamy et al., 2005), while the mineralization of 14C-fluoranth-ene can reach 25% of initial 14C in agricultural soil (Vessigaud et al.,2007). The presence of specific microflora, in particular for fluo-ranthene, and differences in sorption on soil and compost matrixlimiting the fraction available for degradation can explain thedifference.

3.3. OP stabilization as non extractable residues during composting

The NER formation participates in the OP apparent dissipationestimated through classical OP extraction. The NER were detectedas soon as NP was applied (35% of 14C recovered at the beginning ofthe composting process), whereas the NER proportions at thebeginning of composting reached only 7%, 4% and 3% for fluoranth-ene, LAS and glyphosate, respectively (Fig. 1). The NER formationmainly occurred during the early phases of composting, as previ-ously observed for pyrene by Hartlieb et al. (2003). The NER fromNP tended to slightly decrease during maturation, with a decreaseof 4% of recovered 14C. At the end of composting, NER proportionsrepresented (in % of recovered 14C): 45 ± 2 for NP, 37 ± 3 for gly-phosate, 24 ± 7 for fluoranthene, and 14 ± 3 for LAS (Fig. 1).

Fig. 1. Variation during composting of the distribution (as a % of recovered 14C) of mineralized, volatilized, leached, water-extractable, solvent-extractable and non-extractable residues, from 14C-labeled glyphosate, LAS, fluoranthene and NP applied at the beginning of the three replicated composting experiments GLY-1 to GLY-3, LAS-1 toLAS-3, FLT-1 to FLT-3 and NP-1 to NP-3, respectively. The percentage of recovered 14C corresponded to the 14C-activity in a given fraction compared with the sum of the 14C-activity recovered in all the fractions at a specific sampling date. Bar errors represent the confidence intervals of analytical replicates (n = 3).

140 G. Lashermes et al. / Chemosphere 87 (2012) 137–143

The NER formation during composting has been less studiedthan in soil but the mechanisms described for NER formation insoils are likely to be transposable. The NER can be formed throughphysical entrapment in the nanoporosity of the humic compounds

or through chemical stabilization with the establishment of cross-linking reactions with compounds in the organic matrix (Kästneret al., 1999; Barriuso et al., 2008). Non humified organic mattermay display great affinity to form NER with some OPs (Barriuso

Table 1Values of Ai, lmi and ki parameters obtained by fitting the 14C-CO2 evolution kineticsto the Gompertz equation on the 0–41 (i = 1) and 41–83 (i = 2) day periods forglyphosate, LAS and NP composting experiments.

OP 0–41 d period

A1 lm1 k1 R2

% of initial 14C d�1 dGLY 21 ± 8a 1.4 ± 0.7a 3.1 ± 0.4a 0.998 ± 0.001b

LAS 45 ± 10 5.8 ± 1.4 8.0 ± 3.0 0.997 ± 0.001NP 28 ± 2 4.3 ± 1.7 4.7 ± 2.7 0.998 ± 0.003

41–83 d periodA2 lm2 k2 R2

% of initial 14C d�1 dGLY 3 ± 1 0.1 ± 0.0 8.2 ± 2.1 0.996 ± 0.004LAS 6 ± 5 0.3 ± 0.3 7.4 ± 4.1 0.999 ± 0.001NP 1 ± 0 0.1 ± 0.0 0.0 ± 0 0.983 ± 0.005

a Mean ± 95% confidence intervals of three composting replicates.b Coefficient of determination of linear regression.

G. Lashermes et al. / Chemosphere 87 (2012) 137–143 141

et al., 2008). Initial waste mixtures have been found to have high-er sorption capacities than mature compost (Lashermes et al.,2010). The organic matter may be more reactive at the beginningof composting than in mature compost possibly because of higherlevels of aliphatic components. Moreover, the formation of NERduring the early stages of composting might also be related to in-tense microbial activity (Benoit and Barriuso, 1997; Vessigaudet al., 2007), thus the OPs and metabolites may be incorporatedinto growing biomass (Barriuso et al., 2008) or linked to organicmatter after oxidation reactions catalyzed by extracellular en-zymes (Gevao et al., 2000). The high level of NER formation fromNP throughout composting was probably related to its highlyreactive phenolic structure (Gevao et al., 2000; Dec et al., 2003).Nevertheless, the immediate formation of NER after NP applica-tion could also be partly attributed to a lack of efficiency in thesequential water/methanol extraction technique employed, evenif methanol has previously been shown to be an efficient extrac-tive of NP from compost material, reaching 90% recoveries (Pakouet al., 2009). The proportion of NER with glyphosate was also highand could be explained by the chemical reactivity of functionalgroups such as carboxylic, amino and phosphate groups in itschemical structure (Kästner et al., 1999). The level of NER forma-tion during composting with fluoranthene was relatively low andsimilar to that found for pyrene (Hartlieb et al., 2003). The fusedaromatic ring structure of fluoranthene (without any reactivefunctional groups) has a low potential for coupling with organicmatter. And finally, the low NER with LAS revealed the weak reac-tivity of the molecule to binding with organic matter. The forma-tion of NER leads to a decrease in the toxicity and bioavailabilityof OPs (Barriuso et al., 2008). However, the formed NER can besubsequently released through microbial degradation, being thenpotentially available. The environmental impact of NER and theirecological significance thus depends on the reversibility of theirstabilization (Gevao et al., 2000).

3.4. OP availability and estimation of dissipation parameters for riskassessment

The OP fraction easily available for the degrading microflora orfor leaching is usually assessed by water extraction (Benoit andBarriuso, 1997), whereas the use of other solvents can estimatethe overall potentially available residues. The water extractablefractions were related to the water solubility of the different OPs(glyphosate > LAS > NP > fluoranthene). This fraction for all OPsdecreased during the more active thermophilic step of composting,remaining at relatively constant levels thereafter. The 14C-fluo-

ranthene was characterized by a high solvent extractable fractioncorresponding to 72 ± 8% of recovered 14C at the end of compost-ing; thus, fluoranthene could be potentially available in soil aftercompost application. For glyphosate, 47% and 50% of recovered14C were in the water and solvent extractable fractions at thebeginning of composting, respectively, and only 11 ± 5 and18 ± 5% at the end of composting. The proportion of 14C-LAS and14C-NP in the water extracts were low throughout compostingwith 9 ± 1% of recovered 14C for LAS, and 5 ± 1% for NP at the endof composting (Fig. 1). The solvent extractable fractions of LASand NP were very high at the beginning of composting (respec-tively 89% and 60% of recovered 14C) and decreased quickly to6 ± 2% and 7 ± 1% at the end of composting. Concerning fluoranth-ene, due to its low solubility and high hydrophobicity, its waterextractable fraction remained very low during composting thatcould explain its poor availability for degrading microorganisms(Katayama et al., 2010).

At the end of composting, the proportion of water soluble resi-dues considered to be directly available was generally small, sug-gesting a low risk linked to direct OP assimilation by plants ortransfer to soil water (Benoit and Barriuso, 1997). For glyphosate,the water extractable fraction was higher during composting thanin soil (Mamy et al., 2005). Thus, glyphosate mineralization duringcomposting was probably not limited by sorption on compost or-ganic matter, but rather related to a less active glyphosate degrad-ing microflora in compost than in soil. On the contrary, althoughLAS and NP are soluble compounds, the small quantities of waterextractable residues may have limited the extent of theirmineralization.

The dissipation of an OP is classically calculated from the de-crease in its concentration analyzed after extraction between twosampling dates. We used here the results of the water and solventextractions to assess the dissipation kinetics of the different OPs,supposing that the measured 14C in the extracts correspond tothe initial non degraded OP. This hypothesis implies an overesti-mation of OP persistence since probably a part of measured 14Ccorresponded to metabolites formed during composting. Total dis-sipation over 83 d of composting was calculated from the differ-ence between the initial and final amount of extractable OP perreactor taking into account the mass loss of wastes during com-posting. The dissipation results expressed in % of initial amountof OP applied were: 84 ± 4 for LAS, 82 ± 4 for NP, 70 ± 10 for gly-phosate and 18 ± 8 for fluoranthene. Based on dissipation results,half-life duration (in days) were approached supposing first-orderkinetics: 22 ± 8 for LAS, 15 ± 4 for NP, 31 ± 19 for glyphosate and286 ± 188 for fluoranthene. These values were in the ranges ofhalf-lives reported in soil for fluoranthene (150–300 d, Van Brum-melen et al., 1996) and LAS (7–27 d, Jensen, 1999), in biosolid-amended soil for NP (7–19 d, Hseu, 2006) but were higher thanthe ranges reported in soil for glyphosate (1–4 d, Mamy et al.,2005).

It is important to point out that very often in the literature theestimation of OP dissipation does not take into account the massloss during composting, comparing directly the OP concentrationexpressed in mg kg�1 DM between two sampling dates. That caninduce an overestimation of the persistence. In our experiment,dry matter losses related to organic matter mineralization duringcomposting mainly occurred during the thermophilic phase, andreached on average 41%, 43% and 52% of the initial DM after 13,41, and 83 d of composting, respectively. As a consequence, the flu-oranthene concentration (in mg kg�1 DM) increased during com-posting meaning that the compost organic matter was degradedmore rapidly than the fluoranthene disappeared.

The percentages of OP dissipation found in the present study atthe end of composting were within the 25th and 75th percentileranges of the dissipation reported in the literature for LAS (Moeller

Percentage of dissipation (%)

-100 -50 0 50 100

Dissipation (decrease in OP concentration) in the literatureDissipation (decrease in OP concentration) in this studyDissipation (decrease in OP amount) in this study Disapearance (mineralization as CO2) in this study

FLT

NP

LAS

GLY

7 referencesn = 19

4 referencesn = 12

4 referencesn = 7

0 reference

Fig. 2. Distribution of the percentages of dissipation of fluoranthene, LAS, NP andglyphosate at the end of composting reported in the literature (box) and from thisstudy (symbols). The dissipation percentages were calculated from the initial (Ci)and final (Cf) concentrations in extractable OP (mg kg�1 DM) as ½ðCi � Cf Þ=Ci� � 100or from the initial (Qi) and final (Qf) amount in extractable OP (mg) per reactor as½ðQi � Qf Þ=Qi� � 100. The percentages of OP mineralization measured in the presentstudy are also shown. The boxes correspond to the 25th and 75th percentiles; thebars correspond to the 10th and 90th percentiles. The vertical continuous line in thebox is the median and closed circles are the extreme experimental data reported inthe literature.

142 G. Lashermes et al. / Chemosphere 87 (2012) 137–143

and Reeh, 2003b; Sanz et al., 2006; Pakou et al., 2009) and NP(Jones and Westmoreland, 1998; Gibson et al., 2007; Das and Xia,2008; Pakou et al., 2009) during composting whose duration variedfrom 14 to 60 d for LAS, and from 49 to 70 d for NP (Fig. 2). Nostudy on the evolution of glyphosate concentrations has beenfound. On the other hand, composting appeared to be inefficientto significantly reduce fluoranthene contamination, even with sim-ilar duration of composting in this study than in the literature(from 50 to 112 d) (Lazzari et al., 2000; Amir et al., 2005;Oleszczuk, 2006; Brändli et al., 2007; Oleszczuk, 2007; Hafidiet al., 2008; Hua et al., 2008).

4. Conclusion

The dissipation pathways of 14C-labeled fluoranthene, NP, LASand glyphosate and their availability in final composts were as-sessed during the composting of sewage sludge and green waste.Dissipation mainly occurred during the early stages of compostingduring which both mineralization and NER formation mainly oc-curred while both volatilization and lixiviation were negligible.The dissipation of LAS was largely due to mineralization. For NPand glyphosate, both mineralization and NER formation equallycontributed to dissipation. The low dissipation of fluoranthenewas only related to NER formation. In all cases, OP availability, esti-mated by the proportion of water soluble 14C-residues, was low inthe final compost, whereas the proportion of solvent extractableOPs considered to be potentially available, was very small for NPand LAS, and intermediate for glyphosate. Composting appearedto be ineffective at degrading fluoranthene and decreasing itsavailability, with no mineralization and most 14C-fluorantheneremaining solvent extractable in the final compost and thereforepotentially available.

Such procedure to evaluate the evolution of OP availabilityduring composting could be used to optimize the process anddetermine the best conditions to reduce OP availability in final

compost, thus the risks related to the application of compost inagriculture. The dissipation mainly occurred during the thermo-philic phase rather than during maturation. Thus, the initial ther-mophilic phase of composting should be carefully managed forfeedstock contaminated with these OPs.

Acknowledgments

We would like to thank ADEME (French Environment and En-ergy Management Agency), INRA (French National Institute forAgricultural Research) for the grant, and Veolia Environment, Re-search and Development, for their financial support for theseexperiments. We thank Valérie Bergheaud and Valérie Dumenyfor their assistance with experiments using 14C-labeled pollutantsand Maelenn Le Villio-Poitrenaud for her constructive comments.

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