Exploring the potential of earthworm gut bacteria for plastic degradation

The use of plastic mulch films in agriculture leads to the inevitable accumulation of plastic debris in soils. Here, we explored the potential of earthworm gut-inhabiting bacterial strains (Mycobacterium vanbaalenii (MV), Rhodococcus jostii (RJ), Streptomyces fulvissimus (SF), Bacillus simplex (BS), and Sporosarcina globispora (SG) to degrade plastic films (⌀ = 15 mm) made from commonly used polymers: low-density polyethylene film (LDPE-f), polylactic acid (PLA-f), polybutylene adipate terephthalate film (PBAT-f), and a commercial biodegradable mulch film, Bionov-B® (composed of Mater-Bi, a feedstock with PBAT, PLA and other chemical compounds). A 180-day experiment was conducted at room temperature (x̄ =19.4 °C) for different strain-plastic combinations under a low carbon media (0.1× tryptic soy broth). Results showed that the tested strain-plastic combinations did not facilitate the degradation of LDPE-f (treated with RJ and SF), PBAT-f (treated with BS and SG), and Bionov-B (treated with BS, MV, and SG). However, incubating PLA-f with SF triggered a reduction in the molecular weights and an increase in crystallinity. Therefore, we used PLA-f as model plastic to study the influence of temperature ("room temperature" & "30 °C"), carbon source ("carbon-free" & "low carbon supply"), and strain interactions ("single strains" & "strain mixtures") on PLA degradation. SF and SF + RJ treatments significantly fostered PLA degradation under 30 °C in a low-carbon media. PLA-f did not show any degradation in carbon-free media treatments. The competition between different strains in the same system likely hindered the performance of PLA-degrading strains. A positive correlation between the final pH of culture media and PLA-f weight loss was observed, which might reflect the pH-dependent hydrolysis mechanism of PLA. Our results situate SF and its co-culture with RJ strains as possible accelerators of PLA degradation in temperatures below PLA glass transition temperature (Tg). Further studies are needed to test the bioremediation feasibility in soils.

Pesticide Residues in Organic and Conventional Agricultural Soils across Europe: Measured and Predicted Concentrations

During the growing season of 2021, 201 soil samples from conventionally and organically managed fields from 10 European countries and 8 cropping systems were taken, and 192 residues of synthetic pesticides were analyzed. Pesticide residues were found in 97% of the samples, and 88% of the samples contained mixtures of at least 2 substances. A maximum of 21 substances were found in conventionally managed fields, and a maximum of 12 were found in organically managed fields. The number and concentration of pesticide residues varied significantly between conventional and organic fields in 70 and 50% of the case study sites, respectively. Application records were available for a selected number of fields (n = 82), and these records were compared to the detected substances. Residues from 52% of the applied pesticides were detected in the soils. Only 21% of the pesticide residues detected in the soil samples were applied during the 2021 growing season. From the application data, predicted environmental concentrations of residues in soil were calculated and compared to the measured concentrations. These estimates turned out not to be accurate. The results of this study show that most European agricultural soils contain mixtures of pesticide residues and that current calculation methods may not reliably estimate their presence.

Short-term impacts of polyethylene and polyacrylonitrile microplastics on soil physicochemical properties and microbial activity of a marine terrace environment in maritime Antarctica

Evidence of microplastic (MP) pollution in Antarctic terrestrial environments reinforces concerns about its potential impacts on soil, which plays a major role in ecological processes at ice-free areas. We investigated the effects of two common MP types on soil physicochemical properties and microbial responses of a marine terrace from Fildes Peninsula (King George Island, Antarctica). Soils were treated with polyethylene (PE) fragments and polyacrylonitrile (PAN) fibers at environmentally relevant doses (from 0.001% to 1% w w-1), in addition to a control treatment (0% w w-1), for 22 days in a pot incubation experiment under natural field conditions. The short-term impacts of MPs on soil physical, chemical and microbial attributes seem interrelated and were affected by both MP dose and type. The highest PAN fiber dose (0.1%) increased macro and total porosity, but decreased soil bulk density compared to control, whereas PE fragments treatments did not affect soil porosity. Soil respiration increased with increasing doses of PAN fibers reflecting impacts on physical properties. Both types of MPs increased microbial activity (fluorescein diacetate hydrolysis), decreased the cation exchange capacity but, especially PE fragments, increased Na+ saturation. The highest dose of PAN fibers and PE fragments increased total nitrogen and total organic carbon, respectively, and both decreased the soil pH. We discussed potential causes for our findings in this initial assessment and addressed the need for further research considering the complexity of environmental factors to better understand the cumulative impacts of MP pollution in Antarctic soil environments.

Source-specific probabilistic risk assessment of microplastics in soils applying quality criteria and data alignment methods

The risk characterization of microplastics (MP) in soil is challenging due to the non-alignment of existing exposure and effect data. Therefore, we applied data alignment methods to assess the risks of MP in soils subject to different sources of MP pollution. Our findings reveal variations in MP characteristics among sources, emphasizing the need for source-specific alignments. To assess the reliability of the data, we applied Quality Assurance/Quality Control (QA/QC) screening tools. Risk assessment was carried out probabilistically, considering uncertainties in data alignments and effect thresholds. The Hazardous Concentrations for 5% (HC5) of the species were significantly higher compared to earlier studies and ranged between 4.0 × 107 and 2.3 × 108 particles (1-5000 µm)/kg of dry soil for different MP sources and ecologically relevant metrics. The highest risk was calculated for soils with MP entering via diffuse and unspecified local sources, i.e., "background pollution". However, the source with the highest proportion of high-risk values was sewage, followed by background pollution and mulching. Notably, locations exceeding the risk threshold obtained low scores in the QA/QC assessment. No risks were observed for soils with compost. To improve future risk assessments, we advise to primarily test environmentally relevant MP mixtures and adhere to strict quality criteria.

Intensive vegetable production under plastic mulch: A field study on soil plastic and pesticide residues and their effects on the soil microbiome

Intensive agriculture relies on external inputs to reach high productivity and profitability. Plastic mulch, mainly in the form of Low-Density Polyethylene (LDPE), is widely used in agriculture to decrease evaporation, increase soil temperature and prevent weeds. The incomplete removal of LDPE mulch after use causes plastic contamination in agricultural soils. In conventional agriculture, the use of pesticides also leaves residues accumulating in soils. Thus, the objective of this study was to measure plastic and pesticide residues in agricultural soils and their effects on the soil microbiome. For this, we sampled soil (0-10 cm and 10-30 cm) from 18 parcels from 6 vegetable farms in SE Spain. The farms were under either organic or conventional management, where plastic mulch had been used for >25 years. We measured the macro- and micro-light density plastic debris contents, the pesticide residue levels, and a range of physiochemical properties. We also carried out DNA sequencing on the soil fungal and bacterial communities. Plastic debris (>100 μm) was found in all samples with an average number of 2 × 103 particles kg-1 and area of 60 cm2 kg-1. We found 4-10 different pesticide residues in all conventional soils, for an average of 140 μg kg-1. Overall, pesticide content was ∼100 times lower in organic farms. The soil microbiomes were farm-specific and related to different soil physicochemical parameters and contaminants. Regarding contaminants, bacterial communities responded to the total pesticide residues, the fungicide Azoxystrobin and the insecticide Chlorantraniliprole as well as the plastic area. The fungicide Boscalid was the only contaminant to influence the fungal community. The wide spread of plastic and pesticide residues in agricultural soil and their effects on soil microbial communities may impact crop production and other environmental services. More studies are required to evaluate the total costs of intensive agriculture.

Pesticide residues with hazard classifications relevant to non-target species including humans are omnipresent in the environment and farmer residences

Intensive and widespread use of pesticides raises serious environmental and human health concerns. The presence and levels of 209 pesticide residues (active substances and transformation products) in 625 environmental samples (201 soil, 193 crop, 20 outdoor air, 115 indoor dust, 58 surface water, and 38 sediment samples) have been studied. The samples were collected during the 2021 growing season, across 10 study sites, covering the main European crops, and conventional and organic farming systems. We profiled the pesticide residues found in the different matrices using existing hazard classifications towards non-target organisms and humans. Combining monitoring data and hazard information, we developed an indicator for the prioritization of pesticides, which can support policy decisions and sustainable pesticide use transitions. Eighty-six percent of the samples had at least one residue above the respective limit of detection. One hundred residues were found in soil, 112 in water, 99 in sediments, 78 in crops, 76 in outdoor air, and 197 in indoor dust. The number, levels, and profile of residues varied between farming systems. Our results show that non-approved compounds still represent a significant part of environmental cocktails and should be accounted for in monitoring programs and risk assessments. The hazard profiles analysis confirms the dominance of compounds of low-moderate hazard and underscores the high hazard of some approved compounds and recurring "no data available" situations. Overall, our results support the idea that risk should be assessed in a mixture context, taking environmentally relevant mixtures into consideration. We have uncovered uncertainties and data gaps that should be addressed, as well as the policy implications at the EU approval status level. Our newly introduced indicator can help identify research priority areas, and act as a reference for targeted scenarios set forth in the Farm to Fork pesticide reduction goals.

Fragmentation and depolymerization of microplastics in the earthworm gut: A potential for microplastic bioremediation?

The accumulation of microplastics poses potential risks to soil health. Here, we did a preliminary exploration on the potential of Lumbricus terrestris (Oligochaeta) to reduce low-density polyethylene (LDPE), polylactic acid (PLA), and polybutylene adipate terephthalate (PBAT) microplastic (20-648 µm) contamination in soils. The ingestion of microplastics-contaminated soil (1% of microplastics, dw/dw) in a mesocosm system and the ingestion of pure microplastics in the Petri Dish by earthworms were studied. Results show that earthworms survived in the microplastics-contaminated soil (0% mortality in 35 days) but barely when exposed solely to microplastics (30-80% mortality in 4 days). Size-dependent ingestion of microplastics was not observed. The fragmentation of LDPE microplastics in the gizzard facilitated by soil was confirmed by the significantly increased ratio of small-sized (20-113 µm) microplastics from the bulk soil to the gut (from 8.4% to 18.8%). PLA and PBAT microplastics were fragmented by gizzard without the facilitation of soil, the ratios of small-sized (20-113 µm) PLA and PBAT microplastics in the gut were 55.5% and 108.2% higher than in respective pristine distributions. Substantial depolymerization of PLA (weight-average molar mass reduced by 17.7% with shift in molecular weight distribution) and suspected depolymerization of PBAT were observed in the worm gut, while no change in the molar mass was observed for PLA and PBAT microplastics buried in the soil for 49 days. Our results suggest that ingested microplastics could undergo fragmentation and depolymerization (for certain polymers) in the earthworm gut. Further research is needed to reveal the mechanisms of polymer depolymerization in the earthworm gut and to evaluate the feasibility of microplastic bioremediation with earthworms.

Microplastic appraisal of soil, water, ditch sediment and airborne dust: The case of agricultural systems

Although microplastic pollution jeopardizes both terrestrial and aquatic ecosystems, the movement of plastic particles through terrestrial environments is still poorly understood. Agricultural soils exposed to different managements are important sites of storage and dispersal of microplastics. This study aimed to identify the abundance, distribution, and type of microplastics present in agricultural soils, water, airborne dust, and ditch sediments. Soil health was also assessed using soil macroinvertebrate abundance and diversity. Sixteen fields were evaluated, 6 of which had been exposed to more than 5 years of compost application, 5 were exposed to at least 5 years of plastic mulch use, and 5 were not exposed to any specific management (controls) within the last 5 years. We also evaluated the spread of microplastics from the farms into nearby water bodies and airborne dust. We found 11 types of microplastics in soil, among which Light Density Polyethylene (LDPE) and Light Density Polyethylene covered with pro-oxidant additives (PAC) were the most abundant. The highest concentrations of plastics were found in soils exposed to plastic mulch management (128.7 ± 320 MPs.g-¹ soil and 224.84 ± 488 MPs.g-¹ soil, respectively) and the particles measured from 50 to 150 μm. Nine types of microplastics were found in water, with the highest concentrations observed in systems exposed to compost. Farms applying compost had higher LDPE and PAC concentrations in ditch sediments as compared to control and mulch systems; a significant correlation between soil polypropylene (PP) microplastics with ditch sediment microplastics (r² 0.7 p < 0.05) was found. LDPE, PAC, PE (Polyethylene), and PP were the most abundant microplastics in airborne dust. Soil invertebrates were scarce in the systems using plastic mulch. A cocktail of microplastics was found in all assessed matrices.

Collection of human and environmental data on pesticide use in Europe and Argentina: Field study protocol for the SPRINT project

Current farm systems rely on the use of Plant Protection Products (PPP) to secure high productivity and control threats to the quality of the crops. However, PPP use may have considerable impacts on human health and the environment. A study protocol is presented aiming to determine the occurrence and levels of PPP residues in plants (crops), animals (livestock), humans and other non-target species (ecosystem representatives) for exposure modelling and impact assessment. To achieve this, we designed a cross-sectional study to compare conventional and organic farm systems across Europe. Environmental and biological samples were/are being/will be collected during the 2021 growing season, at 10 case study sites in Europe covering a range of climate zones and crops. An additional study site in Argentina will inform the impact of PPP use on growing soybean which is an important European protein-source in animal feed. We will study the impact of PPP mixtures using an integrated risk assessment methodology. The fate of PPP in environmental media (soil, water and air) and in the homes of farmers will be monitored. This will be complemented by biomonitoring to estimate PPP uptake by humans and farm animals (cow, goat, sheep and chicken), and by collection of samples from non-target species (earthworms, fish, aquatic and terrestrial macroinvertebrates, bats, and farm cats). We will use data on PPP residues in environmental and biological matrices to estimate exposures by modelling. These exposure estimates together with health and toxicity data will be used to predict the impact of PPP use on environment, plant, animal and human health. The outcome of this study will then be integrated with socio-economic information leading to an overall assessment used to identify transition pathways towards more sustainable plant protection and inform decision makers, practitioners and other stakeholders regarding farming practices and land use policy.

Cocktails of pesticide residues in conventional and organic farming systems in Europe - Legacy of the past and turning point for the future

Considering that pesticides have been used in Europe for over 70 years, a system for monitoring pesticide residues in EU soils and their effects on soil health is long overdue. In an attempt to address this problem, we tested 340 EU agricultural topsoil samples for multiple pesticide residues. These samples originated from 4 representative EU case study sites (CSS), which covered 3 countries and four of the main EU crops: vegetable and orange production in Spain (S-V and S-O, respectively), grape production in Portugal (P-G), and potato production in the Netherlands (N-P). Soil samples were collected between 2015 and 2018 after harvest or before the start of the growing season, depending on the CSS. Conventional and organic farming results were compared in S-V, S-O and N-P. Soils from conventional farms presented mostly mixtures of pesticide residues, with a maximum of 16 residues/sample. Soils from organic farms had significantly fewer residues, with a maximum of 5 residues/sample. The residues with the highest frequency of detection and the highest content in soil were herbicides: glyphosate and its main metabolite AMPA (P-G, N-P, S-O), and pendimethalin (S-V). Total residue content in soil reached values of 0.8 mg kg^-1 for S-V, 2 mg kg^-1 for S-O and N-P, and 12 mg kg^-1 for P-G. Organic soils presented 70-90% lower residue concentrations than the corresponding conventional soils. There is a severe knowledge gap concerning the effects of the accumulated and complex mixtures of pesticide residues found in soil on soil biota and soil health. Safety benchmarks should be defined and introduced into (soil) legislation as soon as possible. Furthermore, the process of transitioning to organic farming should take into consideration the residue mixtures at the conversion time and their residence time in soil.

Global data on earthworm abundance, biomass, diversity and corresponding environmental properties

Earthworms are an important soil taxon as ecosystem engineers, providing a variety of crucial ecosystem functions and services. Little is known about their diversity and distribution at large spatial scales, despite the availability of considerable amounts of local-scale data. Earthworm diversity data, obtained from the primary literature or provided directly by authors, were collated with information on site locations, including coordinates, habitat cover, and soil properties. Datasets were required, at a minimum, to include abundance or biomass of earthworms at a site. Where possible, site-level species lists were included, as well as the abundance and biomass of individual species and ecological groups. This global dataset contains 10,840 sites, with 184 species, from 60 countries and all continents except Antarctica. The data were obtained from 182 published articles, published between 1973 and 2017, and 17 unpublished datasets. Amalgamating data into a single global database will assist researchers in investigating and answering a wide variety of pressing questions, for example, jointly assessing aboveground and belowground biodiversity distributions and drivers of biodiversity change.

Microplastic pollution alters forest soil microbiome

The impact of microplastic pollution on terrestrial biota is an emerging research area, and this is particularly so for soil biota. In this study, we addressed this knowledge gap by examining the impact of aged low-density polyethylene (LDPE) and polyester fibres (i.e. polyethylene terephthalate, PET) on a forest microbiome composition and activity. We also measured the corresponding physicochemical changes in the soil. We observed that bacteria community composition diverged in PET and LDPE treated soils from that of the control by day 42. These changes occurred at 0.2% and 0.4% (w/w) of PET and at 3% LDPE. Additionally, soil respiration was 8-fold higher in soil that received 3% LDPE compared to other treatments and control. There were no clear patterns linking these biological changes to physicochemical changes measured. Taken together, we concluded that microplastics aging in the environment may have evolutionary consequences for forest soil microbiome and there is immediate implication for climate change if the observed increase in soil respiration is reproducible in multiple ecosystems.

Low density-microplastics detected in sheep faeces and soil: A case study from the intensive vegetable farming in Southeast Spain

One of the main sources of plastic pollution in agricultural fields is the plastic mulch used by farmers to improve crop production. The plastic mulch is often not removed completely from the fields after harvest. Over time, the plastic mulch that is left of the fields is broken down into smaller particles which are dispersed by the wind or runoff. In the Region of Murcia in Spain, plastic mulch is heavily used for intensive vegetable farming. After harvest, sheep are released into the fields to graze on the vegetable residues. The objective of the study was to assess the plastic contamination in agricultural soil in Spain and the ingestion of plastic by sheep. Therefore, three research questions were established: i) What is the plastic content in agricultural soils where plastic mulch is commonly used? ii) Do livestock ingest the microplastics found in the soil? iii) How much plastic could be transported by the livestock? To answer these questions, we sampled top soils (0-10 cm) from 6 vegetable fields and collected sheep faeces from 5 different herds. The microplastic content was measured using density separation and visual identification. We found ~2 × 10³ particles∙kg^-1 in the soil and ~10³ particles∙kg^-1 in the faeces. The data show that plastic particles were present in the soil and that livestock ingested them. After ingesting plastic from one field, the sheep can become a source of microplastic contamination as they graze on other farms or grasslands. The potential transport of microplastics due to a herd of 1000 sheep was estimated to be ~10⁶ particles∙ha^-1∙y^-1. Further studies should focus on: assessing how much of the plastic found in faeces comes directly from plastic mulching, estimating the plastic degradation in the guts of sheep and understanding the potential effects of these plastic residues on the health of livestock.

Impact of plastic mulch film debris on soil physicochemical and hydrological properties

The plastic mulch films used in agriculture are considered to be a major source of the plastic residues found in soil. Mulching with low-density polyethylene (LDPE) is widely practiced and the resulting macro- and microscopic plastic residues in agricultural soil have aroused concerns for years. Over the past decades, a variety of biodegradable (Bio) plastics have been developed in the hope of reducing plastic contamination of the terrestrial ecosystem. However, the impact of these Bio plastics in agroecosystems have not been sufficiently studied. Therefore, we investigated the impact of macro (around 5 mm) and micro (<1 mm) sized plastic debris from LDPE and one type of starch-based Bio mulch film on soil physicochemical and hydrological properties. We used environmentally relevant concentrations of plastics, ranging from 0 to 2% (w/w), identified by field studies and literature review. We studied the effects of the plastic residue on a sandy soil for one month in a laboratory experiment. The bulk density, porosity, saturated hydraulic conductivity, field capacity and soil water repellency were altered significantly in the presence of the four kinds of plastic debris, while pH, electrical conductivity and aggregate stability were not substantially affected. Overall, our research provides clear experimental evidence that microplastics affect soil properties. The type, size and content of plastic debris as well as the interactions between these three factors played complex roles in the variations of the measured soil parameters. Living in a plastic era, it is crucial to conduct further interdisciplinary studies in order to have a comprehensive understanding of plastic debris in soil and agroecosystems.

Effects of plastic mulch film residues on wheat rhizosphere and soil properties

Plastic residues could accumulate in soils as a consequence of using plastic mulching, which results in a serious environmental concern for agroecosystems. As an alternative, biodegradable plastic films stand as promising products to minimize plastic debris accumulation and reduce soil pollution. However, the effects of residues from traditional and biodegradable plastic films on the soil-plant system are not well studied. In this study, we used a controlled pot experiment to investigate the effects of macro- and micro- sized residues of low-density polyethylene and biodegradable plastic mulch films on the rhizosphere bacterial communities, rhizosphere volatile profiles and soil chemical properties. Interestingly, we identified significant effects of biodegradable plastic residues on the rhizosphere bacterial communities and on the blend of volatiles emitted in the rhizosphere. For example, in treatments with biodegradable plastics, bacteria genera like Bacillus and Variovorax were present in higher relative abundances and volatile compounds like dodecanal were exclusively produced in treatment with biodegradable microplastics. Furthermore, significant differences in soil pH, electrical conductivity and C:N ratio were observed across treatments. Our study provides evidence for both biotic and abiotic impacts of plastic residues on the soil-plant system, suggesting the urgent need for more research examining their environmental impacts on agroecosystems.

Global distribution of earthworm diversity

Soil organisms, including earthworms, are a key component of terrestrial ecosystems. However, little is known about their diversity, their distribution, and the threats affecting them. We compiled a global dataset of sampled earthworm communities from 6928 sites in 57 countries as a basis for predicting patterns in earthworm diversity, abundance, and biomass. We found that local species richness and abundance typically peaked at higher latitudes, displaying patterns opposite to those observed in aboveground organisms. However, high species dissimilarity across tropical locations may cause diversity across the entirety of the tropics to be higher than elsewhere. Climate variables were found to be more important in shaping earthworm communities than soil properties or habitat cover. These findings suggest that climate change may have serious implications for earthworm communities and for the functions they provide.

Predicting soil microplastic concentration using vis-NIR spectroscopy

Microplastic accumulation in soil may have a detrimental impact on soil biota. The lack of standardized methods to identify and quantify microplastics in soils is an obstacle to research. Existing techniques are time-consuming and field data are seldom collected. To tackle the problem, we explored the possibilities of using a portable spectroradiometer working in the near infrared range (350-2500 nm) to rapidly assess microplastic concentrations in soils without extraction. Four sets of artificially polluted soil samples were prepared. Three sets had only one polymer polluting the soil (low-density polyethylene (LDPE), polyethylene terephthalate (PET), or polyvinyl chloride (PVC)). The fourth set contained random amounts of the three polymers (Mix). The concentrations of microplastics were regressed on the reflectance observed for each of the 2150 wavelengths registered by the instrument, using a Bayesian approach. For a measurement range between 1 and 100 g kg^-1, results showed a root-mean-squared-deviation (RMSD) of 8, 18, and 10 g kg^-1 for LDPE, PET, and PVC. The Mix treatment presented an RMSD of 8, 10, and 5 g kg^-1 for LDPE, PET, and PVC. The repeatability of the proposed method was 0.2-8.4, 0.1-5.1, and 0.1-9.0 g kg^-1 for LDPE, PET, and PVC, respectively. Overall, our results suggest that vis-NIR techniques are suitable to identify and quantify LDPE, PET, and PVC microplastics in soil samples, with a 10 g kg^-1 accuracy and a detection limit ≈ 15 g kg^-1. The method proposed is different than other approaches since it is faster because it avoids extraction steps and can directly quantify the amount of plastic in a sample. Nevertheless, it seems to be useful only for pollution hotspots.

Biogenic transport of glyphosate in the presence of LDPE microplastics: A mesocosm experiment

The accumulation of plastic debris and herbicide residues has become a huge challenge and poses many potential risks to environmental health and soil quality. In the present study, we investigated the transport of glyphosate and its main metabolite, aminomethylphosphonic acid (AMPA) via earthworms in the presence of different concentrations of light density polyethylene microplastics in the litter layer during a 14-day mesocosm experiment. The results showed earthworm gallery weight was negatively affected by the combination of glyphosate and microplastics. Glyphosate and AMPA concentrated in the first centimetre of the top soil layer and the downward transport of glyphosate and AMPA was only detected in the earthworm burrows, ranging from 0.04 to 4.25 μg g-1 for glyphosate and from 0.01 (less than limit of detection) to 0.76 μg g-1 for AMPA. The transport rate of glyphosate (including AMPA) from the litter layer into earthworm burrows ranged from 6.6 ± 4.6% to 18.3 ± 2.4%, depending on synergetic effects of microplastics and glyphosate application. The findings imply that earthworm activities strongly influence pollutant movement into the soil, which potentially affects soil ecosystems. Further studies focused on the fate of pollutants in the microenvironment of earthworm burrows are needed.

Macro- and micro- plastics in soil-plant system: Effects of plastic mulch film residues on wheat (Triticum aestivum) growth

Plastic residues have become a serious environmental problem in the regions with intensive use of plastic mulching. Even though plastic mulch is widely used, the effects of macro- and micro- plastic residues on the soil-plant system and the agroecosystem are largely unknown. In this study, low density polyethylene and one type of starch-based biodegradable plastic mulch film were selected and used as examples of macro- and micro- sized plastic residues. A pot experiment was performed in a climate chamber to determine what effect mixing 1% concentration of residues of these plastics with sandy soil would have on wheat growth in the presence and absence of earthworms. The results showed that macro- and micro- plastic residues affected both above-ground and below-ground parts of the wheat plant during both vegetative and reproductive growth. The type of plastic mulch films used had a strong effect on wheat growth with the biodegradable plastic mulch showing stronger negative effects as compared to polyethylene. The presence of earthworms had an overall positive effect on the wheat growth and chiefly alleviated the impairments made by plastic residues.

Influence of microplastic addition on glyphosate decay and soil microbial activities in Chinese loess soil

The intensive use of pesticide and plastic mulches has considerably enhanced crop growth and yield. Pesticide residues and plastic debris, however, have caused serious environmental problems. This study investigated the effects of the commonly used herbicide glyphosate and micrometre-sized plastic debris, referred as microplastics, on glyphosate decay and soil microbial activities in Chinese loess soil by a microcosm experiment over 30 days incubation. Results showed that glyphosate decay was gradual and followed a single first-order decay kinetics model. In different treatments (with/without microplastic addition), glyphosate showed similar half-lives (32.8 days). The soil content of aminomethylphosphonic acid (AMPA), the main metabolite of glyphosate, steadily increased without reaching plateau and declining phases throughout the experiment. Soil microbial respiration significantly changed throughout the entirety of the experiment, particularly in the treatments with higher microplastic addition. The dynamics of soil β-glucosidase, urease and phosphatase varied, especially in the treatments with high microplastic addition. Particles that were considerably smaller than the initially added microplastic particles were observed after 30 days incubation. This result thus implied that microplastic would hardly affect glyphosate decay but smaller plastic particles accumulated in soils which potentially threaten soil quality would be further concerned especially in the regions with intensive plastic mulching application.

An overview of microplastic and nanoplastic pollution in agroecosystems

Microplastics and nanoplastics are emerging pollutants of global importance. They are small enough to be ingested by a wide range of organisms and at nano-scale, they may cross some biological barriers. However, our understanding of their ecological impact on the terrestrial environment is limited. Plastic particle loading in agroecosystems could be high due to inputs of some recycled organic waste and plastic film mulching, so it is vital that we develop a greater understanding of any potentially harmful or adverse impacts of these pollutants to agroecosystems. In this article, we discuss the sources of plastic particles in agroecosystems, the mechanisms, constraints and dynamic behaviour of plastic during aging on land, and explore the responses of soil organisms and plants at different levels of biological organisation to plastic particles of micro and nano-scale. Based on limited evidence at this point and understanding that the lack of evidence of ecological impact from microplastic and nanoplastic in agroecosystems does not equate to the evidence of absence, we propose considerations for addressing the gaps in knowledge so that we can adequately safeguard world food supply.

Decay of low-density polyethylene by bacteria extracted from earthworm's guts: A potential for soil restoration

Low-density polyethylene (LDPE) is the most abundant source of microplastic pollution worldwide. A recent study found that LDPE decay was increased and the size of the plastic was decreased after passing through the gut of the earthworm Lumbricus terrestris (Oligochaeta). Here, we investigated the involvement of earthworm gut bacteria in the microplastic decay. The bacteria isolated from the earthworm's gut were Gram-positive, belonging to phylum Actinobacteria and Firmicutes. These bacteria were used in a short-term microcosm experiment performed with gamma-sterilized soil with or without LDPE microplastics (MP). We observed that the LDPE-MP particle size was significantly reduced in the presence of bacteria. In addition, the volatile profiles of the treatments were compared and clear differences were detected. Several volatile compounds such as octadecane, eicosane, docosane and tricosane were measured only in the treatments containing both bacteria and LDPE-MP, indicating that these long-chain alkanes are byproducts of bacterial LDPE-MP decay.

Incorporation of microplastics from litter into burrows of Lumbricus terrestris

Pollution caused by plastic debris is an urgent environmental problem. Here, we assessed the effects of microplastics in the soil surface litter on the formation and characterization of burrows built by the anecic earthworm Lumbricus terrestris in soil and quantified the amount of microplastics that was transported and deposited in L. terrestris burrows. Worms were exposed to soil surface litter treatments containing microplastics (Low Density Polyethylene) for 2 weeks at concentrations of 0%, 7%, 28%, 45% and 60%. The latter representing environmentally realistic concentrations found in hot spot soil locations. There were significantly more burrows found when soil was exposed to the surface treatment composed of 7% microplastics than in all other treatments. The highest amount of organic matter in the walls of the burrows was observed after using the treatments containing 28 and 45% microplastics. The highest microplastic bioturbation efficiency ratio (total microplastics (mg) in burrow walls/initial total surface litter microplastics (mg)) was found using the concentration of 7% microplastics, where L. terrestris introduced 73.5% of the surface microplastics into the burrow walls. The highest burrow wall microplastic content per unit weight of soil (11.8 ± 4.8 g kg-¹) was found using a concentration of 60% microplastics. L. terrestris was responsible for size-selective downward transport when exposed to concentrations of 7, 28 and 45% microplastics in the surface litter, as the fraction ≤50 μm microplastics in burrow walls increased by 65% compared to this fraction in the original surface litter plastic. We conclude that the high biogenic incorporation rate of the small-fraction microplastics from surface litter into burrow walls causes a risk of leaching through preferential flow into groundwater bodies. Furthermore, this leaching may have implications for the subsequent availability of microplastics to terrestrial organisms or for the transport of plastic-associated organic contaminants in soil.

Microplastics in the Terrestrial Ecosystem: Implications for Lumbricus terrestris (Oligochaeta, Lumbricidae)

Plastic debris is widespread in the environment, but information on the effects of microplastics on terrestrial fauna is completely lacking. Here, we studied the survival and fitness of the earthworm Lumbricus terrestris (Oligochaeta, Lumbricidae) exposed to microplastics (Polyethylene, <150 μm) in litter at concentrations of 7, 28, 45, and 60% dry weight, percentages that, after bioturbation, translate to 0.2 to 1.2% in bulk soil. Mortality after 60 days was higher at 28, 45, and 60% of microplastics in the litter than at 7% w/w and in the control (0%). Growth rate was significantly reduced at 28, 45, and 60% w/w microplastics, compared to the 7% and control treatments. Due to the digestion of ingested organic matter, microplastic was concentrated in cast, especially at the lowest dose (i.e., 7% in litter) because that dose had the highest proportion of digestible organic matter. Whereas 50 percent of the microplastics had a size of <50 μm in the original litter, 90 percent of the microplastics in the casts was <50 μm in all treatments, which suggests size-selective egestion by the earthworms. These concentration-transport and size-selection mechanisms may have important implications for fate and risk of microplastic in terrestrial ecosystems.

Using earthworms to test the efficiency of remediation of oil-polluted soil in tropical Mexico

This study focuses on the medium-term effects of soil bioremediation on mortality and reproduction rates of Eisenia fetida (laboratory experiment) and of the tropical earthworm Polypheretima elongata (field experiment). We compared soils restored with the two bioremediation technologies landfarming (LF) and compost-bioremediation (BI) with control soils and with soils contaminated with 1% and 2% of petroleum. Control and restored soils both were fertile and showed low hydrocarbon contents. The mortality of E. fetida was not influenced by soil restoration and by contamination with 1% petroleum; it only increased in soils contaminated with 2% petroleum. However, the reproduction rate of E. fetida was significantly lower in the soils restored with LF and in those contaminated with 1% crude oil and significantly higher in the soils restored with BI. P. elongata showed the same reaction as E. fetida. We conclude that it is important to include reproduction or other sub-lethal tests for earthworms when estimating the efficiency of restoration techniques.