Dissipation of pesticides during composting and anaerobic digestion of source-separated organic waste at full-scale plants
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semi-dry thermophilic anaerobic digestion suggests that pesticides preferentially end up in presswaterafter solidliquid separation.
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compost and digestate on soil organisms were not found (Trslvet al., 1997; Pohl et al., in preparation) the occurrence of contami-nants raises some concern since recycling products of high qualityare expected to be free of hazardous compounds.
Composting has been widely adopted as a strategy in biodegra-dation/bioremediation of organic pollutants in recent years (Sem-ple et al., 2001). It has been shown that pesticides mightdissipate during composting of organic residues (Buyuksonmez
plants. It provides a basis to better assess the potential of compo-sting and anaerobic digestion for production of compost and dige-state with a low contamination level.
2.1. Composting and digestion plants investigated
This study focuses on open windrow composting and semi-drythermophilic anaerobic digestion with subsequent aerobic
* Corresponding author. Tel.: +41 31 910 21 17; fax: +41 21 910 22 99.
Bioresource Technology 99 (2008) 79887994
Contents lists availab
lsev ier .com/ locate/bior techE-mail address: email@example.com (T. Kupper).agriculture and horticulture. However, compost and digestate con-tain a wide range of organic pollutants (Brndli et al., 2005,2007a,b). They enter compost via aerial deposition and splash orspray induced by road trafc on green waste, accidental input(mostly incorrect separation of input materials, e.g. plastic debris)and deliberate input (e.g. pesticides application on fruits, vegeta-bles, ornamental plants and lawn). Brndli et al. (2007b) and Buy-uksonmez et al. (2000) showed that pesticides widely occur incompost and digestate. Although concentrations of organic pollu-tants in compost and digestate were below the contents that im-pair terrestrial ecosystems, and clear negative impacts of
waste, is, however, still sparse. Brndli et al. (2007c) showed thatextrapolation of available laboratory-derived ndings to real worldsystems was difcult for polychlorinated biphenyls (PCBs) andpolycyclic aromatic hydrocarbons (PAHs). Therefore, the basis forassessing the potential of composting and digestion in order to re-duce the contamination level of input materials is insufcient.Moreover, knowledge of the fate of currently used pesticides suchas triazole fungicides which are widely used commercially (Bromi-low et al., 1999) and commonly occur in compost and digestate(Brndli et al., 2007b) is not available. Therefore, the present studyaims to characterize the dissipation of pesticides at full-scaleFungicidesTriazolesFateOrganic residues
Composting and digestion (i.e. aeof organic wastes) are important waEurope. The end products, compostsoil conditioner and fertilizer, there0960-8524/$ - see front matter 2008 Elsevier Ltd. Adoi:10.1016/j.biortech.2008.03.052 2008 Elsevier Ltd. All rights reserved.
nd anaerobic treatmentnagement strategies ingestate, can be used ascling nutrients back to
et al., 1999; Fogg et al., 2003; Vischetti et al., 2004; Kawata et al.,2006). Information on the fate of organic pollutants during compo-sting and digestion under full-scale conditions of green waste(originating from private gardens and public green areas) and or-ganic kitchen waste (raw organic leftovers from vegetable produc-tion and from private kitchens), i.e. source-separated organicKeywords:all pesticides detected in the input materials showed dissipation rates higher than 50% during compo-sting, whilst levels of most triazoles decreased slightly or remained unchanged. The investigation onDissipation of pesticides during compostof source-separated organic waste at full
Thomas Kupper a,*, Thomas D. Bucheli b, Rahel C. Bra Swiss College of Agriculture, SCA, Laenggasse 85, CH-3052 Zollikofen, SwitzerlandbAgroscope Reckenholz-Tnikon Research Station ART, CH-8046 Zrich, Switzerlandc Food Authority Control of Geneva, CH-1211 Geneva, Switzerland
a r t i c l e i n f o
Article history:Received 14 January 2008Received in revised form 19 March 2008Accepted 22 March 2008Available online 1 May 2008
a b s t r a c t
In the present study, concdigestion at full-scale planthe three windrows studi(d.m.) in input materials aFungicides and among the
journal homepage: www.ell rights reserved.g and anaerobic digestioncale plants
li b, Didier Ortelli c, Patrick Edder c
ation levels and dissipation of modern pesticides during composting andere followed. Of the 271 pesticides analyzed, 28 were detected. Withintotal concentrations were between 36 and 101 lg per kg of dry matterbetween 8 and 20 lg kg d.m.1 in composts after 112 days of treatment.riazoles clearly dominated over other pesticides. More than two-thirds ofle at ScienceDirect
treatment, which are widely used in the recycling of source-sepa-rated organic waste. The prevailing conditions relevant for the fateof pesticides in these systems can be considered to be representa-tive for aerobic treatment and thermophilic anaerobic digestion.Additionally, open windrow composting allows for feasible sam-pling. Dissipation of pesticides during composting was character-ized by the investigation of three different windrows on twocommercial composting plants. One windrow consisted of mostlygreen waste (windrow CG), the second of a mixture of greenand organic kitchen waste (windrow CK) and the third com-
input presswater (50 l) was simultaneously collected from its stor-age tank. After 12 days, the output material was sampled. Press-water was again taken from the storage tank. Digestate wassampled directly from the windrow at the composting plant wherethe material underwent aerobic treatment (windrow CDK).
In the laboratory, samples collected on day 0 and 14 were cut bya shredder (Althaus, Ersigen, Switzerland, Model 300 K1) andmixed thoroughly in a concrete mixer before sub-samples(1000 g) for analysis were taken. The drying procedure was per-formed as gently as possible (at 40 C until the weight remained
T. Kupper et al. / Bioresource Technology 99 (2008) 79887994 7989prised output material from a thermophilic anaerobic digestionplant (windrow CDK; Table 1). In order to prepare the windrowsto be investigated, waste materials were shredded, thoroughlymixed and heaped up to windrows with a front loader. All threewindrows were covered with air-permeable fabric, irrigated withfresh water if necessary and turned regularly during composting.
The study of pesticides dissipation during thermophilic anaero-bic digestion took place at a plant that employed the Kompogasprocess (for details on this process: see Brndli et al., 2007c). Theoutput of the fermenter undergoes solidliquid separation result-ing in digestate (solid phase with a dry matter (d.m.) content ofabout 35%) and presswater (liquid phase with a d.m. content ofabout 12%). The digestate was submitted to subsequent aerobictreatment (open windrow composting: CDK; see above).
Details of the composting process parameters, such as temper-ature development, turning and irrigation frequencies, content ofwater, organic matter, nutrients and heavy metals, are providedin Brndli et al. (2007c).
2.2. Sampling and processing of the samples
Sampling periods at the composting plants reected the threephases of the process: thermophilic, cooling and maturation stage(Semple et al., 2001). Accordingly, sampling took place on day 0(input material) and on day 14, 56 and 112 of composting. Beforeeach sampling, the windrows were turned at least twice. The mostsuitable sampling techniques for obtaining composite sampleswere used according to the structure of the material: digging atransect or collection of drilling cores on both sides of the windrowover the entire transect about every 3 m of the windrow. The vol-ume of aliquots was large (>>1 l) and the number thereof plentiful(>100). The composite sample was thoroughly mixed and reducedto 600 l for input material and to 60 l of material collected on day14, 56 and 112 for transport to the laboratory.
At the digestion plant input material was sampled on day 0from every shovel of the front loader lling the feeding tank (vol-ume: 54 m3) which continuously loads the fermenter over 24 h.Mixing and volume reduction of the gathered composite samplewas performed as for compost samples (see above). Material forinoculation of the fermenter (i.e. the output of the fermenter beforesolidliquid separation) could not be sampled directly because thefermenters output pipe was not accessible. Instead, the digestatewas sampled continuously over half a day and the corresponding
Table 1Input material composition of the windrows investigated (further information is give
Acronym of thewindrows
CG Green waste: 35% trimmings from trees and shrubs, 20%4% soil, 34% residues from processing of cereals, Copaz
CK Mixture of green and organic kitchen waste: 50% greenmature compost
CDK Output material from a thermophilic anaerobic digestion
of a mixture of green waste, kitchen waste and approx. 10%
* Parts of the input material has been chopped and stored on a large heap over severalconstant, i.e. up to seven days). This low drying temperature pre-vents evaporation of the mostly non-volatile pesticides. A furtherdegradation during sample treatment and storage seems unlikelysince a signicant reduction of the water content is achieved with-in the rst day of drying. The samples were stored at room temper-ature in the dark. Before analysis, the samples were milled in a ballmill at a particle size of
For organophosphorous pesticides analysis by gas chromatographywith nitrogen phosphorous detection (GCNPD), 10 ml of organicsupernatant was evaporated to dryness on a rotary evaporatorand then dissolved in 2 ml of hexane before analysis on GCNPD.A conrmation of pesticides identity was carried out by gas chro-matography with ion trap mass spectrometry detection (GCMS)in case of positive samples using at least three characteristic ionsfor identication. Limits of detection ranged between 5 and50 lg kg d.m.1.
2.4. Uncertainties of sampling, processing and analysis
Considering the heterogeneity of input material and compost, itis clear that artifacts are difcult to avoid in such eld studies evenif optimal methods for sampling, sample processing and analysisare used. Experiments on sampling errors inuencing analytical re-sults of organic compounds were conducted earlier by Breuer et al.(1997). They found total errors, i.e. combined sampling and analyt-ical errors, resulting from a compost eld study of about 30% forPCBs and PAHs. Analytical errors determined by Brndli et al.(2006) for single PCBs and PAHs were in the same range. The over-all precision for the pesticide data reported here was assumed tobe similar. For the calculation of sum concentrations (Tables 2and 3), a worst case scenario was selected, i.e. detected but not
quantiable compounds (3 < signal to noise ratio < 10) were setequal to method quantication limits. Similarly, to follow pesticidedissipation more quantitatively, i.e. to include pesticides that wereoriginally detected (3 < signal to noise ratio < 10) but disappearedduring further treatment, all data with a signal to noise ratio >3were considered quantiable.
2.5. Calculation of dissipation rates
To follow dissipation of organic pollutants during organic mat-ter degradation, normalization of the measured concentrations to aconservative tracer is necessary. Crude ash turned out to be themost reliable reference parameter as compared to other potentiallysuitable candidates such as heavy metals (Brndli et al., 2007c).The concentrations measured were converted to lg kg1 crudeash as follows:
ci;norm ci;meascash 1000
where ci,norm denotes the normalized concentration of the com-pound i (lg kg crude ash1), ci,meas is the quantied concentrationof the compound i (lg kg d.m.1) and cash is the crude ash content(g kg d.m.1) in the same sample. A dissipation rate (in %) was usedto quantify the concentration change of a compound in the sub-strate. It was calculated as follows:
Table 2Concentrations (lg kg d.m.1) of pesticides at two composting plants in windrows consisting of green waste (CG), a mixture of green and organic kitchen waste (CK) and outputmaterial from a thermophilic anaerobic digestion plant (CDK) on day 0 and after 14, 56 and 112 days of composting, respectively
Plant Composting plant 1 Composting plant 2
Substrates in windrows Green waste (CG) Green waste and kitchen waste(CK)
Output material from a thermophilic anaerobicdigestion plant (CDK)
Day 0 14 56 112 0 14 56 112 0 14 56 112
Concentrations in lg kg d.m.1
Pesticides Sum 36 14 14 8 43 28 10 14 101 44 19 20
Fungicides Sum 30 11 11 7 29 27 10 13 94 41 19 19Triazole Cyproconazole 1
testate used forculation
Presswater used forinoculation
Presswater (sampled after 12days)
173 1435 57 83 34 42 26 39 82 1
16 167 9
echnology 99 (2008) 79887994 7991Table 3Concentrations (lg kg d.m.1) of pesticides in a thermophilic anaerobic digestion plan
Substrates Input material (mostly kitchenwaste)
Concentrations in lg kg d.m.1
Pesticides Sum 92 36
Fungicides Sum 70 13Triazole Cyproconazole 2
echnTotal pesticide concentrations were between 36 and 101 lgkg d.m.1 in input materials of the windrows CG, CK and CDK,and in the range of 820 lg kg d.m.1 in composts on day 112 (Ta-ble 2). Such numbers are lower by a factor of 37 than the averageconcentration reported by Brndli et al. (2007b). Like Brndli et al.(2007b) total pesticide concentrations in compost containingkitchen waste (windrows CK, CDK) were higher than in greenwaste compost (windrow CG).
Fungicides also clearly dominated over other pesticides in termsof concentration. Total concentrations ranged from 29 to94 lg kg d.m.1 for input materials and from 7 to 19 lg kg d.m.1
for composts on day 112 (Table 2). Again, these numbers areroughly 27 times lower than the average concentration of42 lg kg d.m.1 reported by Brndli et al. (2007b). In addition tothe dominating triazoles accounting for up to 100% of the totalamount of pesticides determined (windrows CG, CK on day 112),the post-harvest fungicides imazalil and thiabendazole were otherimportant compounds. Together, they constituted up to 37% of to-tal pesticides concentrations in input material and up to 11% incompost on day 112 for windrow CDK. It should be noted that onlyone of the 28 detected compounds belongs to the 24 most widelyused pesticides in Switzerland (SGCI, 2006), namely mecoprop,which was detected only once and which ranks 20th in the 2006list. Moreover, the most prevalent triazoles play a minor role inSwitzerland, accounting for 4% at most of all fungicides sold. A rel-evant fraction of the pesticides found in composts (mainly imazalil,thiabendazole and probably triazoles) are usually used in tropicalfruits and vegetables. This indicates that they may stem fromabroad.
The sum of pesticides concentration in the input material at thedigestion plant was 92 lg kg d.m.1 (Table 3). The concentrationsof the digestate used for inoculation and submitted to subsequentaerobic treatment (windrow CDK on day 0; Table 2) were 36 and101 lg kg d.m.1, respectively. This coincides with the numbersof Brndli et al. (2007b) who found concentrations for digestateranging from 30 to 257 lg kg d.m.1. There were higher concentra-tions of presswater, ranging up to 182 lg kg d.m.1. Due to thelarge portion of kitchen waste in the input material, fungicides rep-resented the most signicant fraction of pesticides in digestate andpresswater (between 76% and 95% of the total, respectively). Incontrast, herbicides accounted for 56% of the sum of pesticides indigestate used for inoculation with mecoprop as the dominantcompound. This compound is commonly used on lawns (Gereckeet al., 2002) and, therefore, it can be assumed that this digestatecontained a high portion of lawn trimmings or other materialstreated with mecoprop.
This study provides for the rst time information on the dis-tribution of pesticides between digestate and presswater. Thesetwo output products from thermophilic anaerobic digestion arematrices with different properties. Presswater contains a largeamount of ne particles. Moller et al. (2002) found that morethan 80% of the particles were in the ne fraction (225 lmin diameter) for separated liquids from a decanting centrifugeand a screw press of digested and non-digested pig manure. Itcan be assumed that the portion of ne particles is higher inpresswater compared to the corresponding digestate and conse-quently, exhibits a larger number of sorption sites. This wouldexplain the d.m. concentration of pesticides in presswater whichaccounts on average more than double the content in digestate(Table 3). Accordingly, higher concentrations in presswater havebeen observed for other organic compounds (e.g. PAHs) and alsofor elements such as phosphorous or copper, which preferen-tially partition onto solids (Brndli et al., 2007c). The physical
7992 T. Kupper et al. / Bioresource Tchemical properties of pesticides such as water solubility oroctanolwater partition coefcient (KOW) did not correlate withthe distribution of the pesticides between presswater and dige-state and, therefore, seem to be of minor importance for pesti-cide levels in the output products of thermophilic anaerobicdigestion.
3.2. Dissipation of pesticides
3.2.1. Determining processesPesticides are subject to a series of physicalchemical and bio-
logical processes during composting or anaerobic digestion such assorption, leaching, volatilization, biotic and abiotic transformationor mineralization, which determine the extent of their dissipation.Sorption can lead to the formation of bound residues. A part ofthese is non-extractable and thus cannot be captured by chemicalanalysis. This is a well-known process governing the fate of pesti-cides in soil (Gevao et al., 2000) and during composting (Hartliebet al., 2003; Michel et al., 1995, 1997). For propiconazole, it hasbeen suggested that the formation of bound residues contributesto the persistence of this fungicide in soil (Kim et al., 2003). Michelet al. (1995) have found that almost 50% of 14C-ring-labeled 2,4-Dwas complexed with humic acids or the humin fraction of compostderived from yard trimmings. The dissipation rates found in thisstudy are probably driven by a combination of the processes listedabove but the experimental design did not allow for assigning therelevant processes. Knowledge obtained from former studies sug-gests, however, that biotic transformation or mineralization playsan important role, but the formation of bound residues should alsobe considered (Hartlieb and Klein, 2001; Michel et al., 1995, 1997).Volatilisation and/or leaching were found to be of minor impor-tance for certain pesticides (Ertunc et al., 2002; Michel et al.,1995) and other organic compounds (Hund et al., 1999; Sempleet al., 2001).
3.2.2. Dissipation rates during compostingTwenty ve compounds of the windrows CG, CK and CDK were
detected in the input material and, therefore, enabled the calcula-tion of dissipation rates as presented in Table 4. Sixteen com-pounds exhibited dissipation rates of 96% to 6100% in at leastone windrow. Fifteen of them were not detectable after 56 daysof composting and in some cases even after 14 days (Table 2). Thisapplied to carbendazim, pyrifenox, spiroxamine and primicarb forall three windrows. On the other hand, difenoconazole, propico-nazole and tebuconazole persisted in one or two windrows. Insome cases, negative dissipation rates (i.e. higher normalized con-centrations in the compost on day 112 compared to the inputmaterial) were observed, probably due to sampling uncertainties(see Section 2.4). For comparison, levels of PCBs and high-molecu-lar-weight PAHs analyzed in the same samples remained stablewhereas less recalcitrant low-molecular-weight PAHs declined(Brndli et al., 2007c).
Out of the seven recalcitrant compounds (i.e. dissipation ratesof 650%), triazoles dominated with ve representatives. This is inline with known half lives of several triazoles in soil of up to 200days or more (Bromilow et al., 1999; Gardner et al., 2000; Buergeet al., 2006). Triadimenol was described as being very persistentwhilst propiconazole dissipated to a higher extent (Bromilowet al., 1999). This conicts with the present study, where triadime-nol was completely removed and propiconazole appeared to per-sist. Triadimenol was found more often than triadimefon andwhen occurring concomitantly, the former exhibited higher con-centrations. The same pattern was observed by Brndli et al.(2007b). This might be due to the reduction of triadimefon to tria-dimenol (Bromilow et al., 1999). Recalcitrant compounds duringcomposting such as triazoles tended to exhibit considerably higher
ology 99 (2008) 79887994half lives in soils than those of readily dissipating compounds(Tomlin, 1997). However, correlations between dissipation ratesand available soil half lives were not found.
Table 4Dissipation rates of pesticides during composting of green waste (CG), a mixture of greendigestion plant (CDK) after 112 days of composting
Chemical class Compound
Fungicides Triazole CyproconazoleDifenoconazoleFenbuconazoleFlusilazoleMyclobutanilPropiconazoleTebuconazoleTriadimefonTriadimenol
Imidazole ImazalilPyridine PyrifenoxSpiroketalamine SpiroxamineStrobilurine Azoxystrobin
Herbicides Triazine Terbuthylazine-2-h.Terbutryn
T. Kupper et al. / Bioresource TechnDissipation rates varied between the three windrows (Fig. 2). Inwindrow CG and CDK, about half of the initially detected pesticidesexhibited dissipation rates of 96% to 6100% whilst the portion of
Oxadiazole OxadiazonUrea Diuron
Insecticides Carbamate CarbofuranPrimicarb
Growth regulator Triazole Paclobutrazol
n.a., not available.pesticides which was not detectable in CK until day 112 was at67%. About one-third of the compounds were reduced by 5195%in CDK. The same extent of reduction was achieved by less than10% of the substances in CG and CK. The portion of pesticidesexhibiting a dissipation rate of 650% was higher for CG and CKthan for CDK. The highest dissipation rates were observed in CDKfor compounds detected in all three windrows. This was most pro-nounced for some of the recalcitrant compounds (mainly triazoles).It seems therefore that processes driving dissipation of pesticides
Fig. 2. Percentage of total numbers of pesticides exhibiting different dissipationrates (i.e. 96% to 6100%, 5195%, 150% and 0%) during composting of green waste(CG), a mixture of green and organic kitchen waste (CK) and output material from athermophilic anaerobic digestion plant (CDK) after 112 days.were enhanced in CDK, compared to CG and CK. Since parameterscharacterizing the composting process (e.g. content of water, or-ganic matter or nutrients and temperature) did not differ signi-
and organic kitchen waste (CK) and output material from a thermophilic anaerobic
CG CK CDK
150% 5195% 150%0% 0% 5195%n.a. 96% to 6100% 96% to 6100%n.a. n.a. 5195%150% n.a. 150%0% 0% 5195%150% 0% 5195%n.a. n.a. 96% to 6100%n.a. n.a. 5195%96% to 6100% 96% to 6100% 5195%n.a. n.a. 96% to 6100%n.a. n.a. 96% to 6100%96% to 6100% 96% to 6100% 96% to 6100%n.a. 96% to 6100% 96% to 6100%n.a. 96% to 6100% 5195%96% to 6100% 96% to 6100% 96% to 6100%96% to 6100% 96% to 6100% 96% to 6100%n.a. 96% to 6100% n.a.
n.a. n.a. 150%96% to 6100% n.a. n.a.n.a. 150% n.a.96% to 6100% n.a. 96% to 6100%
n.a. 96% to 6100% n.a.96% to 6100% 96% to 6100% 96% to 6100%
5195% n.a. 96% to 6100%
ology 99 (2008) 79887994 7993cantly between the windrows, it can be hypothesized that thehigher dissipation of CDK was due to the different properties ofthe input materials. The preceding anaerobic treatment of CDK in-put material might have resulted in a higher degradation orsequestration potential during subsequent composting. A possibleexplanation is the better accessibility of pesticides for micro-organisms after anaerobic treatment. It might also be hypothesizedthat anaerobically digested material provides a lower portion ofeasily degradable substrates compared to fresh organic waste,thereby enhancing co-metabolism of organic compounds such aspesticides. In contrast to the present study, Vorkamp et al. (2003)did not observe any degradation of dodemorph during subsequentaerobic treatment of anaerobically digested substrate on labora-tory scale over eight days. This discrepancy might be due to a high-er efciency of microbial processes at a full-scale plant, the shortperiod for aerobic treatment and/or the composition of digestedmaterial used by Vorkamp et al. (2003).
3.2.3. Dissipation rates during anaerobic digestionThe mass balance resulted in negative dissipation rates for 20
out of 24 compounds detected in the input material, and 15 ofthem were out of the range of usual uncertainties due to sampling,processing and analysis of about 30%. This points to methodologi-cal difculties leading to biased results. It seems likely that the res-idence time in the fermenter was not appropriately determined.This is supported by the calculated mass loss during digestionbeing lower (9.6% based on d.m.) than the normal degradation rateof 13% (Leisner, M., Kogas, A.G., personal communication; for fur-ther information see Brndli et al., 2007c). Similar problems oc-curred for PCB and PAH in identical samples (Brndli et al.,2007c). Additionally, it should be noted that anaerobic digestionof organic waste is a continuous process with internal ows. Thecharacterization of the fate of organic compounds in similar sys-
tems such as wastewater treatment requires repeated samplingcampaigns. Future studies should take this into consideration.
In the present study, dissipation of currently used pesticidesduring composting at full-scale plants was observed. More thantwo-thirds of all pesticides detected in the input materials showeddissipation rates higher than 50%. In contrast, levels of triazoles re-
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The investigation on semi-dry thermophilic anaerobic digestionsuggests that pesticides preferentially end up in presswater com-pared to digestate. However, further research is needed to assessthoroughly the fate of pesticides during anaerobic digestion usingan appropriate experimental design.
The Federal Ofce for the Environment and the Swiss FederalOfce of Energy are acknowledged for the nancial support, andthe personnel from the plants at Oensingen, Fehraltorf and Oetwilam See are thanked for their good collaboration. We are grateful toT. Poiger Agroscope Changins-Wdenswil Research Station ACWfor revision of the manuscript.
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Dissipation of pesticides during composting and anaerobic digestion of source-separated organic waste at full-scale plantsIntroductionMethodsComposting and digestion plants investigatedSampling and processing of the samplesAnalytical methodsUncertainties of sampling, processing and analysisCalculation of dissipation rates
Results and discussionPesticide prevalence and concentrationsDissipation of pesticidesDetermining processesDissipation rates during compostingDissipation rates during anaerobic digestion