Prerpints.org logo
Preprint
Article

Biodegradation of Polystyrene by Plastic-Eating Tenebrionidae Larvae

This version is not peer-reviewed.

Submitted:

03 April 2024

Posted:

04 April 2024

You are already at the latest version

A peer-reviewed article of this preprint also exists.

Abstract
Polystyrene (PS) is an extremely stable polymer with relatively high molecular weight and a strong hydrophobic character that makes it highly resistant to biodegradation. In this study, PS was subjected to biodegradation tests by Tenebrio Molitor (T. Molitor) and Zophobas Morio (Z. Morio) larvae. Specifically, six different experimental diets were compared: (i) T. Molitor fed with bran; (ii) T. Molitor fed only PS; (iii) T. Molitor fed only PS treated with H2O2; (iv) Z. Morio fed with bran; (v) Z. Morio fed only PS and (vi) Z. Morio fed only PS treated with H2O2. Therefore, the mass change of the larvae and the survival rate were measured periodically, while the frass collected after 15 and 30 days were analyzed by different analyses, such as spectroscopy (FTIR), spectrometry (molecular weight and polydispersity), and microscopy (scanning electron microscopy observations). The obtained results suggest that in the case of T. Molitor larvae, larvae feeding on bran showed the highest survival rate of ~94 % at 30 days, while in the case of the Z. Morio larvae, the highest survival rate was exhibited by larvae eating PS-H2O2. Although not strongly pronounced, the Mw and Mn of PS frass of both T. Molitor and Z. Morio larvae decreased over 30 days, suggesting the Ps biodegradation. Finally, the morphological analysis shows that PS samples isolated from the frass of T. Molitor and Z. Morio larvae showed completely different, rough and irregularly carved surface structures, in comparison to PS before biodegradation.
Keywords: 
biodegradation
;  
polystyrene
;  
Tenebrio Molitor
;  
Zophobas Morio.
Subject: 
Chemistry and Materials Science  -   Polymers and Plastics

1. Introduction

Plastic products are widely used around the world because of their low cost and ease of production. Presently, over 400 million tons (Mt) of plastics are produced yearly, with exponential growth over the past 50 years, and more than 360 million tons of polymers produced per year are of fossil based. Specifically, the main products are polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), and polyvinyl chloride (PVC), materials that have very attractive characteristics, such as low density, good mechanical impact stability, resistance to chemicals and corrosion, and are commonly used for packaging, construction, automotive, agriculture, and electronic devices [1]. Increasing world population has led to increased production and consumption of plastic materials. However, the accumulation of petrol-plastic wastes in the environment has become the focus of worldwide attention because of the environmental problems caused by their improper disposal after use and decommissioning and because the natural degradation of plastics is very sluggish, resulting in the accumulation of plastic waste that poses a serious environmental threat [2,3,4].
The main disposal methods include landfill, incineration, chemical treatment, and recycling. Landfilling is the process of disposing and accumulating waste in a certain area. It is a traditional method of waste management, which is widely used in many parts of the world. However, major environmental issues like global warming and the increase of soil acid grow as CO2 and other gasses emitted from landfills. This method destroys soil, affects groundwater, and cannot effectively degrade waste plastics. Incineration is the process of burning waste in an incinerator until it gets converted to ashes and gas. The process produces a large number of toxic gases, which volatilize into the air and causes harmful effects to public health, biodiversity and ecosystems. Furthermore, the cost of chemical treatment and recycling is high. Hence, these methods are not enough to successfully solve the problem of environmental pollution from plastic products [5].
Considering that much plastic waste has not been scientifically and properly treated, through a series of physical and chemical processes, microplastics are formed and dispersed into the environment [3,6]. Furthermore, organisms can interact with plastic waste: several species of vertebrates and invertebrates have been reported to ingest or become entangled in plastic as animals are unable to distinguish food from plastic in the environment, resulting in the ingestion of plastic particles [7,8].
In recent years, several studies have explored the unusual ability of some insects to consume and even biodegrade different types of plastics. While feeding, insects come into contact with a wide range of hydrocarbon polymers in their diet, and the gut of some insects contains microbial symbionts that aid in the decomposition of these polymers. Soon, various insects, such as mealworms, meal beetles, weevils or wax moths, particularly of the orders Coleoptera and Lepidoptera, were identified as having remarkable abilities to consume and degrade a wide range of synthetic polymers such as polyethylene, polyurethane, polypropylene, polystyrene, and polyvinyl chloride into lower molecular weight, simple and nontoxic molecules, which are eventually excreted as fecula [9]. Moreover, the rate of plastic consumption by these insects is higher than that of bacteria and fungi, isolated from various sources, such as soil, garbage or sewage sludge. These insects mainly include the yellow mealworm (larvae of Tenebrio molitor), the greater wax moth (larvae of Galleria mellonella), and the superworm (larvae of Zophobas morio) among others [10]. The complete life cycle of Lepidopterans and Coleopterans insects consists of four stages: eggs, larvae, pupae, and adults; a significant portion of their life is spent in the larval stage. It is worth noting that the length of each stage of the insect life cycle can vary according to several factors, such as temperature, humidity, nutrition and age of the parents. Interestingly, the initial larval and pupal stages of Tenebrio Molitor, named also yellow mealworm larvae for their color, are rich in protein and considered a popular dish in some countries. The larval period varies from 22 to 100 days, while the pupal period lasts about 8 days. Zophobas Morio, a synonym of Zophobas atratus, is commonly known as a superworm or royal worm, associated with damaged stored foods. Z. Atratus adult beetles look very similar to T. Molitor, but are larger and measure about 2-3 cm in length [11,12]. These larvae can be easily raised on fresh oats, wheat bran, or cereals with potatoes, cabbage, carrots, or apple.
Polystyrene (PS), molecular formula [−CH(C6H5)CH2−]n, commonly known as Styrofoam, accounted for about 5.3% (c.a. 21 Mt/year) of the total plastic consumption in 2022 [13]. Although PS is considered a durable plastic, PS products are often designed for a very short service time and one-time use because of the low cost of this material. Is an extremely stable polymer with high molecular weight and strong hydrophobic character, which makes this polymer highly resistant to biodegradation. Several soil invertebrates have also been tested to determine whether they were able to degrade PS, including earthworms, isopods, slugs, millipedes or snails [14].
In this work, the larvae of yellow mealworm Tenebrio Molitor and superworm Zophobas morio, two species of Coleopterans tenebrionidae larvae, were chosen and prepared to carry out the research. Before the tests, the larvae were placed in a polypropylene plastic container and fed their usual food, then expanded PS foam was used as raw material for the larvae of both species.
The degradation of polystyrene treated with hydrogen peroxide and subjected to microwaves irradiation was also studied. The use of microwaves for polymer degradation is an excellent alternative to conventional thermal heating, offering increased reaction rates, reduced reaction times and energy savings. Typically, polymers such as PS have poor dielectric properties and are unable to absorb enough microwave energy to achieve the necessary temperature for degradation. Consequently, in order to increase absorption, it is necessary to use solvents such as hydrogen peroxide that can absorb microwave energy to achieve the required temperature [15,16,17].
Six different experimental diets were compared: (i) T. Molitor fed with bran; (ii) T. Molitor fed only PS; (iii) T. Molitor fed only PS treated with H2O2; (iv) Z. Morio fed with bran; (v) Z. Morio fed only PS and (vi) Z. Morio fed only PS treated with H2O2. The change of the larvae mass and the survival rate were measured periodically. Furthermore, a morphological analysis of frass was performed by Scanning Electron Microscopy (SEM), Mn, Mw and polydispersity (PD) were determined by Size Exclusion Chromatography (SEC) and additional characterization of the residual polymer was obtained using Fourier Transform Infrared Spectroscopy (FTIR) to identify chemical modifications resulting from PS digestion. There has been investigated an innovative aspect regarding the treatment of PS with H2O2 in order to facilitate PS biodegradation by Tenebrionidae larvae.

2. Materials and Methods

2.1. Test Materials

Tenebrio Molitor (yellow mealworms) and Zophobas Morio (superworms) at the larval stage were purchased from a local supplier (Palermo, Italy) and tanged in length from 2 to 3 cm and 4 to 8 cm, respectively. Expanded PS foam waste of electronic equipment boxes was collected and used as a feedstock for the larvae of both species. The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of PS were 133,174 Da and 236,693 Da, respectively. Hydrogen peroxide (36 volumes 100 ml) was purchased from a local supplier (Palermo, Italy). For microwave oxdidation, a block of PS was placed in a beaker with hydrogen peroxide H2O2 for 5 minutes and then microwaved into a commercial microwave oven at 800 Watt for 3 minutes, which caused the initial breakage of the polystyrene chains.

2.2. Feeding Tests

To compare the PS consumption and biodegradation between the larvae of the two species, six treatments were prepared based on feeding conditions. A group of T. molitor and Z. Morio larvae (30 as a group) were reared on PS foam (~0.4 g) and PS foam treated with H2O2 (PS H2O2) (~0.4 g) as exclusive diet in a polypropylene plastic container. As a control, other group of larvae (30 as a group) were reared on normal diet of wheat bran and fruits. Prior to the commencement of the feeding experiment, the larvae were subjected to a 48 h starvation period to empty their intestines. All containers were maintained in the climatic chamber under the controlled condition i.e., 25 ± 1°C, 60 ± 2% humidity, for a period of 30 days.

2.3. Frass Collection and Characterization

The mealworms were fed with polystyrene blocks (PS) and polystyrene treated with H2O2 and microwave irradiation (PS-H2O2) as their sole diet for 30 days. Figure 1a shows the difference in length of the Tenebrio Molitor larva before and after transformation into a pupa. As mealworm pupae are not mobile, removing the dead larvae and pupae from the containers during the experiment was performed to prevent them from being eaten and to protect them from cannibalism by the remaining larvae.
Frass samples were collected from the container after 15 and 30 days of the experiment and Figure 1b shows the difference between Tenebrio Molitor frass and Zophobas Morio frass.
Figure 1c shows the evolution of T. Molitor from larva to pupa/ beetle for more than ca. 30 days, using real images of T. Molitor evolution stages. It is important to highlight that for more than ca. 30 days, all larvae turn into pupae/beetles and the experimental analysis, concerning the nutritional diet with bran or plastic, was inevitably interrupted.

2.3.1. Weight Variation and Survival Rate

The weight of the larvae was monitored by weighing them every 5 days and ended on day 30. Since not all larvae were the same size, the weight was normalized to the number of individuals and the NW normalized weight (grams of total larvae/number of larvae) was calculated. The tests were conducted in triplicate.

2.3.2. FT-IR Analysis

A Fourier Transform Infrared Spectrometer (Spectrum One, Perkin Elmer, Shelton, CT, USA) was used to record IR spectra using 16 scans at a resolution of 4 cm-1 in the range 4000–450 cm-1, using air as background. For KBr pelleting sample preparation, a press is used to make KBr pellets of the powder. The frass samples were mixed with KBr at a ratio of 1:100 and ground uniformly in a mortar and pestle. The mixture was then pressed with a hydraulic press (Mini Pellet Press, Specac, Orpington, UK) to form a 7 mm disc pellet. The mixture was then pressed into a 7 mm pellet using a hydraulic press (Mini Pellet Press, Specac, Or-pington, UK).

2.3.3. Morphological Analysis

The morphology of the surfaces of PS, PS-H2O2 and frass samples were investigated using a Scanning Electron Microscope (SEM FEI Quanta 200 FEG) equipped with an X-ray energy dispersive spectrometer (EDS). Prior to examination, samples were placed onto a conductive stub and then gold sputtered to avoid electrostatic charging effect.

2.3.4. Size Exclusion Chromatography (SEC)

The changes of molecular weight of the polymer were followed by SEC. The detection was carried out using a differential refractometer. THF was the mobile phase with a flow rate of 1 ml min−1. Calibration was performed with polystyrene standards (from 20250 to 470000 g mol−1). Preparative SEC analyzes were performed in THF with Azura GPC Knauer apparatus equipped with four TSKgel Guard Super columns using an RDI 2.1 L differential refractometer. Sixty microliters of a polymer solution (3 mg ml−1) were injected and eluted at a flow rate of 1 ml min−1.

3. Results and Discussion

3.1. Weight Variation and Survival Rate of T. Molitor and Z. Morio Larvae

The weight of the larvae was monitored every 5 days during the test and Figure 2a,b show the normalised weight (NW) of the T. Molitor and Z. Morio larvae over 30 days of testing.
The NW of T. Molitor larvae eating bran slightly decreased during the first 5 days, see Figure 2a The NW then slowly increased over the further 25 days, reaching a final increment of ~8.5 % with respect to the initial NW value. The NW of T. Molitor larvae eating PS remained almost constant during the first 5 days, while it decreased at 10 days. The NW then increased during the remaining 20 days with a final NW value similar to the initial value. T. Molitor larvae eating PS treated with H2O2 maintained similar NW value to the initial NW value all over the 30 days, suggesting that larvae ate the PS-H2O2 foams more easily than the untreated ones. Results are in line with data available in the literature. Peng et al. [18] reported a mass decrease of ~8% of T. Molitor larvae eating PS; while the same authors observed a mass increase of ~14 % when feeding the larvae with PS and bran at the same time.
The NW of the Z. Morio larvae eating bran showed a similar trend to that of the T. Molitor ones, see Figure 2b. However, a lower final NW value of ~0.5% is achieved at 30 days. Conversely, the NW of the Z. Morio larvae eating treated and untreated PS foams always decreased during the first 10 days of ~6%. The NW of larvae eating PS then slightly increased, while that of larvae eating PS-H2O2 remained almost constant. The final NW values of larvae fed with untreated and treated PS were ~2.8 % and ~5.8 % lower than the initial value (day 0).
The survival rates of the larvae of T. Molitor and Z. Morio eating bran (control), PS foam and PS-H2O2 foam are shown in Figure 3 and summarized in Table 1.
In the case of T. Molitor larvae, see Figure 3a, larvae feeding on bran showed the highest survival rate of ~94 % at 30 days. Conversely, larvae fed PS reported the lowest value of ~83 %. Larvae fed with PS-H2O2 foam had a survival rate of ~87 %. In the literature, Peng et al. [18] reported survival rates of ~90 % for T. Molitor larvae eating PS, while Yang et al. [14] observed values of ~86%. In addition, Yang et al. [14] measured survival rates of ~85 % also for larvae eating bran. The different, although similar, survival rates of T. Molitor larvae can be attributed to the genetic differences between mealworm populations around the globe [19].
In the case of the Z. Morio larvae, the highest survival rate was exhibited by larvae eating PS-H2O2. The lowest value of ~73 % was found for Z. Morio larvae eating bran, while larvae fed with PS had a survival rate of ~80 %. These results are in contrast with the NW behaviour of Z. Morio larvae, indicating that, although larvae lost weight during the tests, they had a more suitable environment where live. The lower survival rates of the Z. Morio larvae with respect to that of the T. Molitor ones were somehow expected. An et al. [3] reported a survival rate of ~70 % of PS foam-eating and normal diet (bran)-eating Zophobas atratus larvae, which belong to the family of Zophobas larvae.

3.2. SEC analysis

SEC analysis was conducted to characterize the depolymerization and biodegradation of ingested PS [20]. Ponderal molecular weight (Mw), numerical molecular weight (Mn) and polydispersity index (IPD) of frass of T. Molitor and Z. Morio after 15 and 30 days are shown in Figure 4a–d, respectively. Mw, Mn and IPD of PS and PS-H2O2 foams analysed at day 0 are also reported.
The Mw and Mn of PS frass of T. Molitor larvae decreased over 30 days. Specifically, Mw was 237, 215 and 197.8 kDa at 0, 15 and 30 days, respectively, with a final reduction of 16.4 %. Mn values decreased from 133, 117 to 108.4 kDa, showing again a decrease of 18.6 %. In the literature, Yang et al. [14] reported similar Mw and Mn percentage reductions. Peng et al. [18] also observed a Mn decrease of ~20 %, however, the authors reported a Mw reduction of ~60 %. IPD increased in digested samples, as a consequence of the depolymerization and degradation action of the larvae producing lower molecular weight fragments [14,21]. PS-H2O2 foams had already lower initial values of Mw and Mn with respect to those of pristine PS ones due to the action of the H2O2, which also caused an increase in the IPD index. Mw and Mn decreased in frass of T. Molitor larvae eating PS-H2O2 foam due to the action of the larvae digestion, showing similar reduction percentages as those of the PS foam case, see Figure 4b.
A lower degradation action was observed by Z. Morio larvae. Mw and Mn values remained almost constant during the first 15 days in both frass of PS and PS-H2O2 foams, while only at 30 days a decrease of ~7 % was achieved, see Figure 4c,d. The results indicate the superior depolymerization and biodegradation activity of T. Molitor larvae compared to Z. Morio larvae.

3.3. Spectroscopy Analysis

FTIR spectra of neat PS and PS-H2O2 foams before and after T. Molitor and Z. Morio larvae degradation are shown in Figure 5. Specifically, Figure 5a illustrates the FTIR spectra of neat PS and PS-H2O2 foams; Figure 5b,c refer to the frass collected after 15 and 30 days from T. Molitor and Z. Morio larvae eating PS foams; Figure 5d,e report the comparison between FTIR spectra of frasses collected at 30 days from T. Molitor and Z. Morio larvae eating PS and PS-H2O2 foams.
Peaks at 625-970 cm-1 (ring-bending vibration) were visible in all FTIR spectra, although peak intensity was slightly damped after larvae digestion. The characteristic peaks known to represent the PS benzene ring (1550-1610 cm-1 and 1800-2000 cm-1) were visible in neat PS samples, while they were considerably dampened in frass, providing evidence of ring cleavage. In addition, evidence of degradation was the appearance of carbonyl groups (1700 cm-1) in frass. The broadening of peaks at 2500-3500 cm-1 in the FTIR of frass was also associated with the hydrogen bond of hydroxyl groups and/or carboxylic acid groups, suggesting a shift from hydrophobic to more hydrophilic surface properties [12].
Frass of T. Molitor larvae showed PS degradation already after 15 days, Figure 5b. Conversely, frass of Z. Morio larvae after 15 days had the same FTIR spectrum of that of neat PS foams. The H2O2 treatment already caused a damping effect of peaks at 2500-3500 cm-1, as well as of those at 1550-1610 cm-1 and 1800-2000 cm-1, indicating the degradation of the PS material [15,17]. Treatment of the PS with H2O2 promoted the degradation action of the larvae. A more intense peak at 1700 cm-1 and a wider peak at 2500-3500 cm-1 were, in fact, reported in FTIR spectra of frass collected from larvae eating PS-H2O2 foams with respect to those collected from PS eating one, see Figure 5d.

3.4. Scanning Electron Microscopy

The surface erosion of the plastic by the larvae was evaluated by SEM analysis of the frass. Firstly, the action of the H2O2 and microwave irradiation on the PS foam was investigated. Figure 6 shows the SEM images of the original PS samples and those treated with PS-H2O2 at different magnifications, i.e., 150x, 1200x and 20,000x.
A small sphere of PS foam can be seen in Figure 6a, which probably imploded due to the high vacuum pressure applied during the gold spatter process. At higher magnification, in Figure 6d,g, the smooth surfaces of the PS material can be clearly seen, as typically reported in the literature [19]. Similar structures and smooth surfaces can also be observed in the PS-H2O2 samples, Figure 6b,d,f. This indicates that the action of H2O2 did not affect the surface of the PS foam. Based on this result, only SEM images of the frond collected after 15 and 30 days from T. Molitor and Z. Morio larvae that fed on PS foam will be discussed below.
Figure 7a,c,d are SEM images of T. Molitor frass after 15 days, while Figure 7b,d,f refer to SEM images of T. Molitor frass after 30 days.
PS samples isolated from the frass of T. Molitor larvae showed completely different, rough and irregularly carved surface structures. PS foam, see Figure 6.
PS flaskes can be observed at magnification of 1200 x, Figure 7c,d. In addition, pores can be identified at a magnification of 20000 x on PS surface, Figure 7e,f, demonstrating the degradation action of the larvae. Surface alterations of the plastics are characteristic of the aging processes occurring under the influence of microorganisms present in the intestines of insects or, more specifically, enzymes secreted by them. The folding of the previously smooth surface of the polymer and the formation of pitting was observed during the biodegradation of the polymers [19].
SEM observations of frasses collected from Z. Morio larvae after 15 and 30 days are shown in Figure 8.
SEM images of PS samples collected from the frass of the Z. Morio larvae after 15 days, Figure 8a,c,e, showed a very similar structure with respect to that of the PS one, Figure 6. This indicates that Z. Morio larvae did not interact with PS material during the first 15 days of tests, as also discussed in Section 3.1–3.4.
PS degradation can be noticed only after 30 days, namely PS shreds and holes can be observed Figure 8b,d,f. However, comparing Figure 7b and Figure 8b, it can be always observed that large pieces of PS materials are still found in trass of Z. Morio larvae confirming the lower degradation action of the Z. Morio larvae with respect to that of the T. Molitor ones. Interestingly, traces of microorganisms were observed in frass of Z. Morio larvae as shown in Figure 9.
Spherical cocci bacteria are observed. The presence of cocci bacteria is in accordance with evidence reported by Yang et al. [22]. The authors attributed the ability of the Z.morio larvae to depolymerize PS to the presence of microbiota, such as the cocci, in their gut. Cocci bacteria were also found in frass after 30 days of tests, here omitted for the sake of brevity.

4. Conclusions

In this work, the biodegradation of PS by T. Molitor and Z. Morio has been investigated, considering also treatment of PS with H2O2 in order to facilitate PS degradation. As discussed before, six different experimental diets were compared: (i) T. Molitor fed with bran; (ii) T. Molitor fed only PS; (iii) T. Molitor fed only PS treated with H2O2; (iv) Z. Morio fed with bran; (v) Z. Morio fed only PS and (vi) Z. Morio fed only PS treated with H2O2. The change of the larvae mass and the survival rate were monitored periodically and obtained results suggest that both T. Molitor and Z. Morio larvae are able to biodegrade the PS and their mass changes and survival rate are similar to that of larvae fed with bran. The analysis of T. Molitor and Z. Morio frass after 15 and 30 days show slightly decreased PS molecular weight and increase of polydispersity, suggesting the reduction of PS chain weight and length. Further, the data coming from FTIR analysis support this thesis highlighting the changes of PS compositions after the digestion.
Therefore, all these results highlight the ability of both larvae to survive using as fed plastic rather than bran.

Author Contributions

Conceptualization, R.P. and N.T.D.; methodology, R.P. and N.T.D.; validation, G.B., E.A.D.L. and N.T.D.; formal analysis, E.A.D.L., G.B. and G.C.; investigation, E.A.D.L., R.P., G.B. and N.T.D.; resources, N.T.D.; data curation, E.A.D.L., G.B. and G.C.; writing—original draft preparation, E.A.D.L., G.B. and N.T.D.; writing—review and editing, N.T.D.; supervision, N.T.D.; funding acquisition, E.A.D.L. and N.T.D. All authors have read and agreed to the published version of the manuscript.

Funding

This work has been financially supported by MUR - Italy (Ministry of University and Research of Italy), in the field of “Next Generation EU” - PNRR M4 - C2 -investimento 1.1: Fondo per il Programma Nazionale di Ricerca e Progetti di Rilevante Interesse Nazionale (PRIN) - PRIN 2022 cod. 20229BHA75 dal titolo “FUnctional Technology Unlocking Recycling and VALorization of Personal Protective Equipment production scrap and waste” (FUTUREVAL-PPE). CUP B53D23005690006. The APC was funded by E.A. Di Liberto and N.Tz. Dintcheva.

Institutional Review Board Statement

Ethical review and approval were waived for this study, as the use of invertebrate animals, like insects, for laboratory experiments do not require approval of bioethics committees and are not subject to procedures in accordance with Directive 2010/63/EU of the European Parliament and of the Council of 22 September 2010 on the protection of animals used for scientific purposes, amended by Regulation (EU) 2019/1010 of the European Parliament and of the Council of 5 June 2019.

Data Availability Statement

All data are available.

Acknowledgments

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Pastic Europe Plastics – The Fast Facts 2023. Https://Plasticseurope.Org/Knowledge-Hub/Plastics-the-Fast-Facts-2023/ (Accessed 20 February 2024) 2023.
  2. Beghetto, V.; Gatto, V.; Samiolo, R.; Scolaro, C.; Brahimi, S.; Facchin, M.; Visco, A. Plastics Today: Key Challenges and EU Strategies towards Carbon Neutrality: A Review. Environmental Pollution 2023, 334, 122102. [Google Scholar] [CrossRef] [PubMed]
  3. An, R.; Liu, C.; Wang, J.; Jia, P. Recent Advances in Degradation of Polymer Plastics by Insects Inhabiting Microorganisms. Polymers 2023, 15, 1307. [Google Scholar] [CrossRef] [PubMed]
  4. Di Bartolo, A.; Infurna, G.; Dintcheva, N.T. A Review of Bioplastics and Their Adoption in the Circular Economy. Polymers 2021, 13, 1229. [Google Scholar] [CrossRef] [PubMed]
  5. Alqattaf, A. Plastic Waste Management: Global Facts, Challenges and Solutions. In Proceedings of the 2020 Second International Sustainability and Resilience Conference: Technology and Innovation in Building Designs(51154); IEEE: Sakheer, Bahrain, November 11, 2020; pp. 1–7. [Google Scholar]
  6. Ferreira-Filipe, D.A.; Paço, A.; Duarte, A.C.; Rocha-Santos, T.; Patrício Silva, A.L. Are Biobased Plastics Green Alternatives?—A Critical Review. IJERPH 2021, 18, 7729. [Google Scholar] [CrossRef] [PubMed]
  7. Enyoh, C.E.; Shafea, L.; Verla, A.W.; Verla, E.N.; Qingyue, W.; Chowdhury, T.; Paredes, M. Microplastics Exposure Routes and Toxicity Studies to Ecosystems: An Overview. Environ Anal Health Toxicol 2020, 35, e2020004. [Google Scholar] [CrossRef] [PubMed]
  8. Khan, S.; Dong, Y.; Nadir, S.; Schaefer, D.A.; Mortimer, P.E.; Xu, J.; Ye, L.; Gui, H.; Wanasinghe, D.N.; Dossa, G.G.O.; et al. Valorizing Plastic Waste by Insect Consumption. C 2021, 1, 1–9. [Google Scholar] [CrossRef]
  9. Mitra, B.; Das, A. The Ability of Insects to Degrade Complex Synthetic Polymers. In Arthropods - New Advances and Perspectives; D.C. Shields, V., Ed.; IntechOpen, 2023 ISBN 978-1-80355-612-3.
  10. Jiang, S.; Su, T.; Zhao, J.; Wang, Z. Biodegradation of Polystyrene by Tenebrio Molitor, Galleria Mellonella, and Zophobas Atratus Larvae and Comparison of Their Degradation Effects. Polymers 2021, 13, 3539. [Google Scholar] [CrossRef] [PubMed]
  11. Pivato, A.F.; Miranda, G.M.; Prichula, J.; Lima, J.E.A.; Ligabue, R.A.; Seixas, A.; Trentin, D.S. Hydrocarbon-Based Plastics: Progress and Perspectives on Consumption and Biodegradation by Insect Larvae. Chemosphere 2022, 293, 133600. [Google Scholar] [CrossRef] [PubMed]
  12. Yang, S.-S.; Brandon, A.M.; Andrew Flanagan, J.C.; Yang, J.; Ning, D.; Cai, S.-Y.; Fan, H.-Q.; Wang, Z.-Y.; Ren, J.; Benbow, E.; et al. Biodegradation of Polystyrene Wastes in Yellow Mealworms (Larvae of Tenebrio Molitor Linnaeus): Factors Affecting Biodegradation Rates and the Ability of Polystyrene-Fed Larvae to Complete Their Life Cycle. Chemosphere 2018, 191, 979–989. [Google Scholar] [CrossRef] [PubMed]
  13. Plastic Europe Plastics – the Facts 2022 Https://Plasticseurope.Org/Knowledge-Hub/Plastics-the-Facts-2022/ (Accessed 20 February 2024).
  14. Yang, Y.; Yang, J.; Wu, W.-M.; Zhao, J.; Song, Y.; Gao, L.; Yang, R.; Jiang, L. Biodegradation and Mineralization of Polystyrene by Plastic-Eating Mealworms: Part 1. Chemical and Physical Characterization and Isotopic Tests. Environ. Sci. Technol. 2015, 49, 12080–12086. [Google Scholar] [CrossRef] [PubMed]
  15. Achilias, D.S. Polymer Degradation Under Microwave Irradiation. In Microwave-assisted Polymer Synthesis; Hoogenboom, R., Schubert, U.S., Wiesbrock, F., Eds.; Advances in Polymer Science; Springer International Publishing: Cham, 2014; Vol. 274, pp. 309–346; ISBN 978-3-319-42239-8. [Google Scholar]
  16. Chandrasekaran, S.; Ramanathan, S.; Basak, T. Microwave Material Processing—a Review. AIChE Journal 2012, 58, 330–363. [Google Scholar] [CrossRef]
  17. Calles-Arriaga, C.A.; López-Hernández, J.; Hernández-Ordoñez, M.; Echavarría-Solís, R.A.; Ovando-Medina, V.M. Thermal Characterization of Microwave Assisted Foaming of Expandable Polystyrene. Ingeniería, Investigación y Tecnología 2016, 17, 15–21. [Google Scholar] [CrossRef]
  18. Peng, B.-Y.; Su, Y.; Chen, Z.; Chen, J.; Zhou, X.; Benbow, M.E.; Criddle, C.S.; Wu, W.-M.; Zhang, Y. Biodegradation of Polystyrene by Dark ( Tenebrio Obscurus ) and Yellow ( Tenebrio Molitor ) Mealworms (Coleoptera: Tenebrionidae). Environ. Sci. Technol. 2019, 53, 5256–5265. [Google Scholar] [CrossRef]
  19. Bulak, P.; Proc, K.; Pytlak, A.; Puszka, A.; Gawdzik, B.; Bieganowski, A. Biodegradation of Different Types of Plastics by Tenebrio Molitor Insect. Polymers 2021, 13, 3508. [Google Scholar] [CrossRef]
  20. Puglisi, C.; Samperi, F.; Carroccio, S.; Montaudo, G. Analysis of Poly(Bisphenol A Carbonate) by Size Exclusion Chromatography/Matrix-Assisted Laser Desorption/Ionization. 2. Self-Association Due to Phenol End Groups. Rapid Commun. Mass Spectrom. 1999, 13, 2268–2277. [Google Scholar] [CrossRef]
  21. Di Natale, M.V.; Carroccio, S.C.; Dattilo, S.; Cocca, M.; Nicosia, A.; Torri, M.; Bennici, C.D.; Musco, M.; Masullo, T.; Russo, S.; et al. Polymer Aging Affects the Bioavailability of Microplastics-Associated Contaminants in Sea Urchin Embryos. Chemosphere 2022, 309, 136720. [Google Scholar] [CrossRef]
  22. Yang, Y.; Wang, J.; Xia, M. Biodegradation and Mineralization of Polystyrene by Plastic-Eating Superworms Zophobas Atratus. Science of The Total Environment 2020, 708, 135233. [Google Scholar] [CrossRef] [PubMed]
Preprints 103082 g001
Figure 1. (a) Length measurement of the pupa and larva of T. Molitor; (b) Frass excreted by the T. Molitor and Z. Morio larvae after being fed with polystyrene and (c) T. Molitor evolution from larvae to pupa/ beetles for more than ca. 30 days (there are shown real images).
Figure 1. (a) Length measurement of the pupa and larva of T. Molitor; (b) Frass excreted by the T. Molitor and Z. Morio larvae after being fed with polystyrene and (c) T. Molitor evolution from larvae to pupa/ beetles for more than ca. 30 days (there are shown real images).
Preprints 103082 g001
Preprints 103082 g002
Figure 2. Weight variation during the time: (a) NW of T. Molitor and (b) NW of Z. Morio fed with bran (control), foam PS and foam PS-H2O2.
Figure 2. Weight variation during the time: (a) NW of T. Molitor and (b) NW of Z. Morio fed with bran (control), foam PS and foam PS-H2O2.
Preprints 103082 g002
Preprints 103082 g003
Figure 3. Survival rate of (a) T. Molitor and (b) Z. Morio larvae fed with bran (control), foam PS and foam PS-H2O2.
Figure 3. Survival rate of (a) T. Molitor and (b) Z. Morio larvae fed with bran (control), foam PS and foam PS-H2O2.
Preprints 103082 g003
Preprints 103082 g004aPreprints 103082 g004b
Figure 4. Data related to the changes of ponderal molecular weight (Mw), numerical molecular weight (Mn) and polydispersity (PD) of PS and PS-H2O2 (0 days), and frass of (a, b) TM and (c, d) ZM after 15 and 30 days.
Figure 4. Data related to the changes of ponderal molecular weight (Mw), numerical molecular weight (Mn) and polydispersity (PD) of PS and PS-H2O2 (0 days), and frass of (a, b) TM and (c, d) ZM after 15 and 30 days.
Preprints 103082 g004aPreprints 103082 g004b
Preprints 103082 g005
Figure 5. FTIR spectra of (a) neat PS and PS-H2O2 before the experiments (0 days) and FTIR of (b) frass of TM and (c) frass of ZM for the larvae fed with PS and PS-H2O2 after 15 and 30 days. (d) and (e) are the comparison of the spectra after 30 days for frass of TM and ZM feeding with PS and PS-H2O2, respectively.
Figure 5. FTIR spectra of (a) neat PS and PS-H2O2 before the experiments (0 days) and FTIR of (b) frass of TM and (c) frass of ZM for the larvae fed with PS and PS-H2O2 after 15 and 30 days. (d) and (e) are the comparison of the spectra after 30 days for frass of TM and ZM feeding with PS and PS-H2O2, respectively.
Preprints 103082 g005
Preprints 103082 g006
Figure 6. SEM observations at different magnifications, i.e., 150x, 1200x and 20000x, of PS (a, c, e) and PS-H2O2 (b, d, f) frass samples, respectively.
Figure 6. SEM observations at different magnifications, i.e., 150x, 1200x and 20000x, of PS (a, c, e) and PS-H2O2 (b, d, f) frass samples, respectively.
Preprints 103082 g006
Preprints 103082 g007
Figure 7. SEM observations at different magnifications of frass of T. Molitor larvae fed with PS foam.
Figure 7. SEM observations at different magnifications of frass of T. Molitor larvae fed with PS foam.
Preprints 103082 g007
Preprints 103082 g008
Figure 8. SEM observation at different magnifications of the frass of Z. Morio larvae fed with PS foam.
Figure 8. SEM observation at different magnifications of the frass of Z. Morio larvae fed with PS foam.
Preprints 103082 g008
Preprints 103082 g009
Figure 9. (a, b) SEM observation at different magnifications of organic matter in frass of Z. Morio larvae fed with PS foam.
Figure 9. (a, b) SEM observation at different magnifications of organic matter in frass of Z. Morio larvae fed with PS foam.
Preprints 103082 g009
Table 1. Summary of PS biodegradation by T. Molitor and Z. Morio larvae.
Table 1. Summary of PS biodegradation by T. Molitor and Z. Morio larvae.
Worm source Initial weight (g) Feedstocks Survival rate (%) Mw of frass (kDa) Mw reduction (%) Mn of frass (kDa) Mn reduction (%) PDI
T. Molitor 3.8 Bran
PS
PS-H2O2 		94 n.d. n.d. n.d. n.d. n.d.
83 197.8 16.4 108.4 18.6 1.83
87 186.0 17.3 101.8 18.7 1.83
Z. Morio 8.3 Bran 73 nd nd nd nd nd
PS 80 221.9 6.3 122.3 8.1 1.81
PS-H2O2 100 208.5 7.3 116.2 7.1 1.79
Note: n.d. means not determined.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.
Copyright: This open access article is published under a Creative Commons CC BY 4.0 license, which permit the free download, distribution, and reuse, provided that the author and preprint are cited in any reuse.

Downloads

115

Views

127

Comments

0

Subscription

Notify me about updates to this article or when a peer-reviewed version is published.

Email

Prerpints.org logo

Preprints.org is a free preprint server supported by MDPI in Basel, Switzerland.

facebook logotwitter logolinkedin logo
MDPI Initiatives
Important Links
Subscribe

Disclaimer

Terms of Use

Privacy Policy

© 2025 MDPI (Basel, Switzerland) unless otherwise stated