Wood & Zimmer 2014a-ApplSoilEcol Robin F14

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Applied Soil Ecology 77 (2014) 7279

Contents lists available at ScienceDirect

Applied Soil Ecology

journa l homepage: www.elsevier .com/ locate /apsoi l

Can terrestrial isopods (Isopoda: Oniscidea) make use ofbiodegradable plastics?

Camila TimmWooda,, Martin Zimmerb,1

a kologie-Zentrum, Christian-Albrechts-Universitt zu Kiel, Olshausenstr. 75, Gebude I, 24118Kiel, GermanybZoologisches Institut, Christian-Albrechts-Universitt zu Kiel, Am Botanischen Garten 1-9, 24118 Kiel, Germany

a r t i c l e i n f o

Article history:

Received16 September 2013Received in revised form 18 January 2014Accepted20 January 2014

Keywords:Feeding rateGrowth rateWoodliceStarch-basedplasticCellulose-based plastic

a b s t r a c t

Biodegradable plastics more and more replace conventional plastics, because they are considered envi-ronmentally friendly. Soil macro-invertebrates have been demonstrated to consume some of thesebiodegradable plastics, but studies usually do not go beyond notice ofconsumption and possible short-term ecotoxicological effects on organisms. This study uses the terrestrial isopod Porcellio scaberas asoil detritivore model and three biodegradable plastics (starch-, cellulose- and poly(3-hydroxybutyrate)(PHB)-based films) to evaluate both the contribution of isopods to the disintegration ofbiodegradableplastics and the effects ofplastic-feeding on isopod ecology. Consumption rate ofstarch-based plasticwas similar to that ofleaflitter (mainly beech) and on average higher than those ofthe other two plas-tic types. Digestibility, however, was highest for cellulose-based plastic. HPLC results show that isopodsbreakdownstarch-based plastic intomaltose and glucose, and cellulose-basedplastic into cellobiose. Noglucose was present in feces ofisopods having fed cellulose-based plastic, either for inability ofbreakingdown cellobiose into glucose, or due to a rapid uptake of the glucose by isopods. Growth rates werenegative, but not significantly different from zero, for all food sources; cellulose-based plastic causedthe highest biomass loss to isopods. Toughness ofstarch-based plastic diminished over time when lit-ter and/or isopods were present. Cellulose-based plastic increased in toughness over the disintegrationexperiment, possibly affecting its consumption by isopods. Overall, isopods increased the disintegration

rates ofstarch- and cellulose-based plastics, but no PHB film was consumed, and its disintegration ratewas low. We conclude that starch-based plastic is comparable to a natural low-quality food source (e.g.,beech litter), and isopods would probably consume starch- and cellulose-based plastics in the field.

2014 Elsevier B.V. All rights reserved.

1. Introduction

1.1. Plastics and fauna

Plastic litter is hazardous to a variety of living creatures (Scott,2000; Stevens, 2002). Largeplasticitemshave beenshownto causesuffocation or entanglement, or disrupt digestion in birds, fishes,turtles, mammals and invertebrates (Browne et al., 2008; Derraik,

2002; Laist, 1987, 1997; Murray and Cowie, 2011; Quayle, 1992;Ryan, 1988). Over 180 species are known to ingest plastic frag-ments (Derraik, 2002), and some animals even feed selectively on

Correspondingauthor at: Graduate Program in Animal Biology, Federal Univer-sity ofRioGrandedo Sul, Av.BentoGoncalves,9500,predio43435,91501-970PortoAlegre, RioGrande do Sul, Brazil. Tel.: +5551 33087698; fax: +55 51 33087696.

E-mail address: [email protected](C.T. Wood).1 Present address: Biodiversitt & Evolution der Tiere, AG kologie, FB Organ-

ismische Biologie, Paris-Lodron-Universitt, Hellbrunnerstr. 34, 5020 Salzburg,Austria.

plasticparticleswith specific shapesandcolorsmistaking themforpotential prey items (Moser and Lee, 1992).

The potential ingestion of plastics by animals increases withincreasing fragmentation of plastic debris. For instance, fragmentssmaller than 1mm (microplastic fragments) have been accumu-lating for several years in the marine water column and cannow represent up to 85% of the stranded plastic debris in someplaces ashore (Browne et al., 2007; Hildago-Ruz and Thiel, 2013).

These microplastics are ingested by animals and their effects onmarine invertebrates have received increasing attention over thelastdecade(Browneet al., 2008; Teutenet al., 2007). Once ingested,theymightbe retained in thedigestivetrack,egested throughfecesor transferred through theepithelial lining of thegut into body tis-sue (translocated), and long-term toxicological effects cannot beexcluded (Browne et al., 2008).

1.2. Biodegradable plastics

Thesubstitution of conventional plastics by biodegradableoneswouldreduceenvironmentalproblems(GrossandKaira,2002;Ren,

0929-1393/$ seefrontmatter 2014 Elsevier B.V. All rightsreserved.

http://dx.doi.org/10.1016/j.apsoil.2014.01.009
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C.T. Wood, M. Zimmer / Applied Soil Ecology 77 (2014) 7279 73

2003; Rosa et al., 2004a). These polymers undergo biodegrada-tion, that is, chemical degradation through the action of naturallyoccurring microorganisms (Stevens, 2002). Although microorgan-isms are key for chemical decay,macroorganisms can also eat andevendigestbiodegradablepolymerscontributingto theirmechani-cal, chemical or enzymaticageingupon decomposition (AlbertssonandKarlsson, 1994).

A readily degradable plasticretainsallpropertiesexpectedby itsdesign during its lifetime, but rapidly disintegrates and is assimi-latedbymicroorganismsreturningit to theecosystem inaharmlessmanner (Stevens, 2002).

Unlike conventional plastics that are based on non-renewablesources, biodegradable plastics aremade from naturally occurringpolymers, such as starch, cellulose or bacterial energy stores, andthereforecan(1)bedegradedbynaturallyoccurringorganisms(seeabove), and (2) be considered sustainable.

Starch is a renewable and widely available material that can beconverted to thermoplastic using a swelling or plasticizing agent.Blends and composite materials can be produced by processingstarch with biodegradable polymers (Rudnik, 2008). Such a ther-moplastic can undergo up to 97.5% biodegradation after44 days incontrolled composting conditions (Degli-Innocenti et al., 1998).

Cellulose thermoplastic materials can be produced throughesterification of cellulose. The raw material can be derived fromcotton, recycled paper or many other sources (Rudnik, 2008), andcellulose-based plastics are being used for various commercialapplicationssuch as food packaging. In controlled composting con-ditions, up to 96.8% biodegradation of cellulose film was observedafter 47 days (Degli-Innocenti et al., 1998).

Polyhydroxyalcanoates (PHAs) form a group of biodegradablethermoplastics that are extracted from the intracellular carbonenergy store that is accumulated as granuleswithin cells by a widevariety of bacteria, being the poly(3-hydroxybutyrate) (PHB) oneof the most studied plastics from this group (Bucci et al., 2005;Maehara etal.,2001;Wangetal.,2005). PHBhas beenused insmalldisposable products and packaging materials (Rosa et al., 2004b).Tansengco and Dogma (1999) observed up to 91% degradation of

PHB films in burial after four weeks, and Krupp and Jewell (1992)demonstratedcomplete degradationwithin60 days at 37 C underlaboratory conditions.

1.3. Biodegradable plastics and the environment

In largescale, thedegradationofbiodegradable plastics involvescomposting sites and landfills, places inwhich theactivity andeffi-ciency of microorganisms is affected by interactions with otherorganisms. Several studies have tested the microbial degradationof biodegradable plastics in sludge, soil or composting conditions(Kim et al., 2000;Rosaet al., 2004a; Krneret al., 2005;Wanget al.,2005).

Some biodegradable plastics are developed for agricultural

purposes, undergoing degradation in the same environment andbecoming available to a variety of soil invertebrates. The use ofbiodegradablematerials is thought to be already an improvementin relation to petroleum-based plastics. However, their effects onthe environment and wildlife are not yet known, risking the sub-stitution of one problem for another.

1.4. Biodegradable plastics and soil fauna

Invertebrates have been recorded to consume some of thesepolymers that present enhancingagents(suchas starch) (Andersonet al., 1995; Fritz et al., 2003; Rudnik, 2008; Tsao et al., 1993;Wool,1988), but these studies rarely go beyond notice of consumption.

Studies using macroinvertebrates that consume biodegradable

plastics mainly focus on possible toxicological effects of one type

of biodegradable plastic, while their ecological effects on the faunaare usually not approached. Fritz et al. (2003) approached fur-ther potential toxic effects by applying ecotoxicological tests withbiodegradable plastics using earthworms, the water flea Daphniaand some plant seeds and found no inhibition in growth of earth-worms as well as possible benefits from the consumption anddigestion of the undegraded organic matter. Similar results havebeen also reported by Rudnik (2008). Nonetheless, earthwormscannot actively tear plastics into pieces like soil arthropods.

Terrestrial isopods, orwoodlice, have been shown to ingestcer-tain biodegradable plastics under artificial laboratory conditions(Anderson et al., 1995; Fritz et al., 2003; Rudnik, 2008; Tsao et al.,1993; Wool, 1988) and they fragment their food sources prior toingestion. As terrestrial isopods play an important role in decom-position processes in many ecosystems (Hassall et al., 1987; Kautzand Topp, 2000; Sousa et al., 1998; Zimmer and Topp, 1999) andare among the most abundant groups of macro-decomposers inmanycommunities(Hassall andDangerfield, 1990; Zimmer, 2002),theyare appropriatemodel organisms to understand the effectsofbiodegradable plastic consumption by the soil fauna.

This study uses the well-studied woodlouse species PorcellioscaberLatreille 1804 (Crustacea: Isopoda: Oniscidea) asa soildetri-tivore model and three biodegradable plastics (starch-, cellulose-and PHB-based) to answer the following questions: (1) do ter-restrial isopods have the potential to promote disintegration rateof biodegradable plastics in the soil; (2) how does the consump-tion of different biodegradable plastics affect isopods feeding andgrowthrates;and(3)would isopods feed onbiodegradable plasticsifanotherfoodsourcewasavailable?Wehypothesizethatwoodlicefeeding on biodegradable plastics would increase the disintegra-tion rate of plastics frommaterials that occur in their natural foodsource (starch andcellulose).We also hypothesize that biodegrad-able plastic consumption when another food source is availablewould indicate that animals might partially digest it. In addition,this would suggest that isopods can feedon them innatural condi-tions.

2. Material andmethods

2.1. Isopods and biodegradable plastics

Specimens of P. scaberwere collected in home compost inSalzburg-Nonntal, Thumegger Bezirk (13.05E, 47.79N), and keptunder laboratory conditions for three to four weeks prior to exper-iments.Ovigerous femaleswere excluded in thedisintegration andfeeding rates experiments.

Three different biodegradable plastics were used in the experi-ments: starch-, cellulose- andPHB-based. The starch-basedplasticwas bought commercially as doggy bags (BioBag Dog, made inNorway) andmade from Mater-Bi granules (Novamont, Italy). Thecellulose-based films were kindly supplied by Innovia (England)(Nature Flex NE30, suitable use for food packaging). PHB powderwas kindly supplied by Biomer (Germany) and transformed intofilms in the laboratory by pouring 3mLof 3% chloroform solutionin a Petri dish (7cm diameter) over a hotplate at 120 C in a hood,until chloroformhadevaporatedcompletely.Allfilmswere cutintosquares of 4 cm2 for the experiments.

2.2. Biodegradable plastic disintegration (mass loss)

Starch-, cellulose- and PHB-based plastics were used as treat-ments, along with conventional plastic films with comparablepresentation to the three biodegradable plastics (color and hand-felt texture). Experimental units containing ca 10g of soil,

one 4cm2

piece of plastic and two P. scaberwere kept in a


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74 C.T. Wood, M. Zimmer / Applied Soil Ecology 77 (2014) 7279

temperature-controlledchamber at 15 C and12:12hphotoperiod.The soil was taken from abandoned agricultural grasslandwith pHof 5.50.2, water holding capacity of 0.510.03g of water per gsoil (dry mass) and organic matter content of 174%. Water wassprinkled every two days to keep soil moist but with no accumu-lation of water droplets in units. Animal-free controls consisted ofunits with soil and plastic (N=7 for both treatments and controls).

Units were maintained for 14 days or until only 1020% of theplastic remained visible. After the experiment, soil was thoroughlysearched for plastic remains, and water was added to retrieve lostplastic that could not be collected during visual search. Plasticswere washed, air-dried and reweighed for plastic mass loss cal-culation inmg per day.

Biodegradable plastic mass loss without and with isopodswas compared by one-sided t-test (normal distribution) orMannWhitney (non normal distribution) for each plastic type inorder to access the effect of isopods on plastic disintegration.

2.3. Feeding and growth rates of isopods on biodegradableplastics

Experimental units (N=11 for each treatment and correspond-ing isopod-free controls) containing a bottom of plaster of Paris(to keep humidity), one 4 cm2 piece of the biodegradable plastic(or leaf litter (Fagus sylvatica) fragment of approximate size) andone P. scaberwere kept at 15C and 12:12h photoperiod for 15days. After theexperiment, isopodswere kept foranotherday witha piece of carrot as food source in order to make them egest allconsumed biodegradable plastic (Wood et al., 2012). Feeding andgrowth ratesfromfeeding onbiodegradableplasticwerecomparedto mixed leaf litter (dominated by beech, F. sylvatica L.) collectedat Kapuzinerberg in Salzburg, Austria (oven-dried at 40 C for 48hbefore being offered to the isopods). We used a low-quality nat-ural food source in order not to underestimate consumption ofplastics in comparison to a high-quality leaf litter. Isopod weightwas recorded every three days, and linear regression was used tocalculate initial and final mass (to account for weight fluctuation

due to change in bodywater content). Three isopods of each treat-ment were sacrificed and oven-dried overnight at 60C after theexperiment inorderto correctwetweight to dry weight. Fecal pel-lets were collectedevery twodays, kept frozenduringexperiment,and oven-dried overnight at 60C at the end of the experiment.Consumption of plaster of Paris happened on occasion and feceswere visually distinguished and eliminated from units. Biodegrad-able plastic remains were washed and air-dried (and leaf remainsoven-dried) and reweighed.

Relativeconsumptionrate (RCR),approximatedigestibility(AD)and relative growth rate (RGR) were calculated as proposed byWaldbauer (1968). Data are presented as RCR, AD and RGR, butAnalysis of Covariance (ANCOVA)wasused to analyze feeding andgrowth data, as suggested by Raubenheimer and Simpson (1992)

provided that statistical problems may occur from the analysisof indices that are obtained as ratios. Consumption was analyzedthrough the amount of ingested food, using the duration of theexperiment and initial isopodmass as covariates. Digestibilitywasanalyzed through the mass of egested feces, using the ingestedamount, the duration of the experiment and initial isopodmass ascovariates. Growthwas analyzed through final isopodmass, usingthe duration of the experiment and initial isopod mass as covari-ates.

2.4. Quasi-natural conditions: Simulation of biodegradableplastic in the soil

Abundant soil (enough to cover the base of the experimental

units, ca 350 g) and mixed leaf litter (same type from experiment

Table 1

Biodegradable plastic mass loss (mg per day) in units with one piece of starch-cellulose- or poly(3-hydroxybutyrate) (PHB)-based plastic, soil and two Porcellioscaber, and in control units without isopods for 414 days.

Plastic t ype Without i sopods ( control) With i sopods

Starch-based 0.060.01 (0.50.1%)* 1.40.4(114%)*

Cellulose-based 0.160.01 (0.990.05%) 0.170.01 (1.030.09%)PHB-based 0.010.01 (0.050.03%) 0.0100.003 (0.050.01%)

Numbers are expressed in meanSE in mg per day and percentage per day in

parenthesis and* indicates significant difference (p


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Fig. 1. Consumption rate (left) and approximate digestibility (right) of biodegrad-able plasticsor mixedleaf litterby Porcellioscaberafter15 days.DataaremeanSE;

letters indicate significant differenceof bothparameters among treatments.

p=0.318) (Table 1). The conventional plastic films had no signs ofconsumption by isopods in any presentation.

3.2. Feeding and growth rates

Consumption rates were significantly higher when isopods fedon leaf litter or starch-based plastic (F3,34 =19.77; p


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Fig. 3. Starch-basedfilmtoughness (gmm2) in animal-freecontrol units andunitswith Porcellio scaber, from the different experiments conducted in this study andplastic on its initial condition. Data is represented as mean; SE is not shown sinceit could not be calculated due to low number of remaining plastic pieces in someexperiments.

consumption had different effects on the animals. Wewill discussin turn the effects of the isopods on the plastic disintegration andthe effects of plastic consumption to the animals.

4.1. Effects of terrestrial isopods on biodegradable plasticdisintegration

Physical disintegration is an essential part of the biodegra-dation process and the starch-based plastic presented increaseddisintegration rates upon isopod activity. The direct consumptionof starch-based plastics even when litter was available indicatesthat isopods have a potential to increase disintegration rate ofstarch-based plastics if disposed in environments where animalsarepresent.Wool(1988)and Tsaoet al. (1993)havealso shown theinvolvementof certainsoilmacroinvertebrates suchas cockroachesand crickets in the primary biodegradation of starch-enhancedpolyethylene (PE) films. However, they have only visually evalu-ated consumption in categories (no consumption, less than 50%, orgreater than 50%) and theeffect of animals in this process was notquantified.

Cellulose-based plastic consumption could also be noticed inall conditions, although in smaller proportion than that of starch-based plastic. Provided that the toughness of the cellulose-basedplastic had increased by the end of the disintegration experi-ment, isopods did not affect the disintegration rate of this plastic

Fig. 4. Cellulose-based film toughness (gmm2) in animal-free control units andunits with Porcellio scaberfrom the different experiments conducted in this studyand plastic on its initial condition. Data is represented as mean; SE is not shownsince it could not be calculated due to low number of remaining plastic pieces insome experiments.

in plastic-only treatment. This might have been due to interac-tions with the water from the soil, since cellulose fibers tendto form a network upon wetting that can entrap water mak-ing it thicker and less flexible (Lee and Fan, 1982). This increasein toughness might have hindered cellulose plastic consumptionby isopods in the disintegration experiment. Such increase in

toughness did not occur during the experiment with cellulosebased-plastic and leaf litter, and isopods could consume the plas-tic,contributing toanincrease indisintegrationrate ofplastic films.This suggests that isopods can also speed up the disintegration ofcellulose-based plastic, depending on presentationattributes suchas toughness.

The effect of the presence of litter on the increased disintegra-tion rate of the plastics can be attributed to its higher microbialactivity in relation to other soil layers as previously shown inthe literature (Andersson et al., 2004). Alternatively, plastic piecesmay have been attached to the leaf litter and were then sim-ply co-consumed along with the latter (authors pers. obs.: seebelow).

The lack of consumption by isopods and low disintegration

rates of PHB films in the experiments might have been due to thepreparation method that requires dissolution of PHB powder inchloroform, andperhaps PHBfilms retained traces of the chemicalthat couldbeavoidedby isopods.Wemighthaveobtaineddifferentresults, had we used commercially available PHBfilms.

Table 3

Consumption rate ofPorcellio sacberon starch-, cellulose-or poly(3-hydroxybutyrate) (PHB)-based plastic under different experimental conditions.

Experiment Conditions Consumption rate (mgg1 day1)

Starch Cellulose PHB

Feeding and growth rates (15 days) Plastic and isopod 91 4.90.4 0.080.04Plastic disintegration (414 days) Plastic, isopod and soil 124 1.40.2 0.110.03Quasi-natural conditions (28 days) Plastic, isopod, soil and litter 4.80.7 4.10.5 0.020.01

Data expressedas meanSE.


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Fig. 5. Chromatograms from cellobiose, maltose and maltodextrine standards, and from the fecal pellets from consumption of starch- or cellulose-based plastics by theterrestrial isopod Porcellio scaber.

4.2. Effects of biodegradable plastic to terrestrial isopods

The isopods consumption of and growth rates from starch-based plastic were comparable to those of animals fed leaf litter.Both theleaf litterused inthisstudyandstarch-basedplastic canbeconsideredlow-qualityfood sourceswith lownitrogencontent andanimalswere notexpected to gainweightona strictbiodegradableplastic diet.

Although the digestibility of starch-based plastic was lowerthan that of leaf litter, growthrateswere notsignificantlydifferent.This is an indication that despite its lowdigestibility, isopods couldutilize the digested portion (i.e., glucose) of the starch-basedplastic. HPLC analysis indicated that isopods break down thestarchinto maltose and glucose. Obviously the amount of maltose and

glucose digestively released from starch-based plastic exceeded

the ability to absorb these nutrients from the food bolus insidethe gut, and excess of maltose and glucose were egested. Thesesmaller molecules egested in the feces should be rapidly used bymicroorganisms in the soil or by other coprophagous animals.

Thecellulose-basedplasticwashighlydigestible buthadlowestconsumption rate and caused the highest isopodmass loss (signif-icantly different only from growth on starch-based plastic). HPLCanalysis of feces fromcellulose-basedplastic consumptionshowedthat cellulose was broken into cellobiose, but no glucose peakwasobserved. This lackof glucose in the fecesmight mean that animalsdonothavecellobiasestobreakthecellobioseintotwomoleculesofglucose, or that glucose is taken upby isopods at thesamerateas itis released fromcellobiose. Breakingdowna complexmolecule likecellulose and not being able to break themoleculedown to glucose

would not be advantageous to isopods, meaning to have the cost


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of reducing cellulose to a smaller molecule, but not the benefit ofutilizing the glucose to produce biomass. Therefore, it is likely thatisopods rapidly use theavailableglucose andthusthe glucose peakcould not be detected. Furthermore, the conversion of cellubioseto glucose might be slower than the breakdown of maltose intoglucose due to lower enzymatic activity for cellobiose substrates.Earthwormshavebeenshowntohavesymbioticbacteriathatbreakdown celluloseand thenuseendogenous cellobiases tobreakdownthe cellobiose, and this enzymatic activity was lower than whenconsuming maltose-based substrates (Lattaud et al., 1999). Thus,the process of reducing cellulose might be more time consuming,affecting the feeding rates on cellulose-based plastic and causingbiomass loss to isopods.

The low consumption of PHB-based plastic was probably duetopreparation (with additionof chloroform).However, weight lossnotsignificantlyhigherthanotherplastics testedorleaf littermightbe due to slow activity of animals in conditions where there is noadequate food source. Moreover, the lower consumption of starchplastic in units without soil in comparison to unitswith soil mightalso be related to activity since theanimals were notprovidedwithany option to shelter in our experiments.

Anderson et al. (1995) observed that radio-labeled starch-enhanced PE films consumed by terrestrial isopods appear to havebeenmetabolized tosomedegree from thepresenceof degradationproductsofPEandradioactivity levelsabovebackground.However,since radioactive levels could have been found in the isopods dueto the retention of PE/starch blends in the gut, it is debatable if theisopods could usethese plastics to produceor maintainbiomass. Inthis study, isopods were not able to gain biomass but maintainedweightwhile feeding on low-quality food sources.Asnosinglefoodsource is sufficient for terrestrial isopods if eaten alone (Rushtonand Hassall, 1983a), and growth rates of terrestrial isopods aregreatly affected by the available food source (Rushton andHassall,1983b; Kautz et al., 2000), biodegradableplastics alone arenotsuf-ficient forpositivegrowth. AlthoughNwaslackingon thediet, highsurvivorshipindicated that animals didnot obtainN fromcannibal-ism. As isopods fedon starchand celluloseplastics evenwhen litter

wasavailable, theymayusetheseplastics asa complementaryfoodsource, at least if the available litter is low quality.

Under natural conditions, the water in the soil may cause theadherence between biodegradable plastic pieces and leaf litter (asit happened in the quasi-natural condition experiment: authorspers. observation) raising the questionwhether isopods consumedthe plastic by mistake while feeding on leaf litter. Nonetheless,in some cases, the only part of the leaf consumed was the partwithplasticattached.Then,it ispossiblethattheisopodsselectivelyfed on that specific area that might represent an enhanced leafdue to higher starch or cellulose content or possibly different localmicrobial community. More detailed studieson natural conditionswould be necessary to clarify this issue

4.3. Further considerations

This study showed that terrestrial isopods have the potentialto increase disintegration of starch- and cellulose-based plasticsand that they can break down the plastic to smaller molecules. Incaseswheretheamountofmaltoseandglucosedigestivelyreleasedfromplastic exceeded theanimalsability toabsorbthesenutrients,the excess ofmaltose and glucose was egested. Isopods are knownto contribute directly to leaf litter decomposition by consumptionand indirectly by returning great amounts of the consumed litteras feces (Quadros and Araujo, 2008) that are rapidly colonized bymicroorganisms due to its increased surface (Hassall et al., 1987;Loureiro et al., 2006). Hence, these smaller molecules egested inthe feces should be rapidly used by microorganisms in the soil or

by other coprophagousanimals producingan indirect effect on the

plastic disintegration rate beside the direct consumption. Study-ing the degradation rate of these feces and if coprophagy of thesefeces occur would provide further evidence of the indirect effectsof isopods on biodegradable plastic disintegration.

Isopod consumption of biodegradable plastics might changewith increasing biodegradation stage and long-term ecologicaleffects are not yet known. At later stages of biodegradation,a noticeable growth of microorganisms on the film surface isobserved and someof the natural components from the plastic arestill available (Bastioli et al., 1993). Later biodegradation stages arealso associated with thinner and therefore less tough films. There-fore, contribution of animals is expected to change throughout thedecomposition of the plastic as well as the nutritional value ofthe plastic to the animals. Studying the feeding and growth ratesof plastic films that have decomposed for different time periodsalso would help to better understand these interactionsof animalsandplastics.More detailed studies on natural conditions would benecessary to determine whether similar results could be expectedwhen high quality food sources were available to isopods andlonger studies to see effects on reproduction would help under-stand long term effects to individuals andpopulations.

Acknowledgments

We are grateful to Prof. Karl Treibelmayer (Salzburg) for pro-viding access to his garden compost for collecting isopods and toProf.RaimundTenhaken(Salzburg)whoenabledus toanalyze fecalcompoundsthroughHPLC.We alsowishtothankProf.PaulaBeatrizAraujoandDr.Aline FerreiraQuadrosfor help inconductingprelim-inary experiments on this topic and three reviewerswhoprovidedvaluable comments on an earlier version of this manuscript. CTWwas financially supported by the European Commission throughthe program Erasmus Mundus Master CourseEuropean Masterin Applied Ecology (EMMC-EMAE) (FPA 2008-0092/001 FRAMEMUNDB123).

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Wood & Zimmer 2014a-ApplSoilEcol Robin F14