Exposure to microplastics lowers arsenic accumulation and alters gut bacterial communities of earthworm Metaphire californica

Comparing the long-term responses of soil microbial structures and diversities to polyethylene microplastics in different aggregate fractions

Microplastics (MPs) alter soil aggregation stability. However, studies have yet to determine whether these alterations further affect microbial community structures and diversities within different soil aggregates and whether they influence the responses of soil microbial structures and diversities to MPs in different aggregate fractions. In this study, long-term soil incubation experiments and soil fractionation were combined to investigate the effects of polyethylene microplastics (PE-MPs) on soil aggregate properties and microbial communities in soil aggregates with different particle sizes. Results showed that the existence of PE-MPs significantly reduced the physicochemical properties of soil aggregates, inhibited the activities of soil enzymes, and changed the richness and diversity of bacterial and fungal communities. Such variations exerted notable differences in soil aggregate levels. The response sensitivity of bacteria in the silt and clay fraction was higher than that in the macroaggregate fraction, but the response sensitivity of fungi in the macroaggregate fraction was higher than that in the silt and clay fraction. Relationships and path analysis between soil aggregate properties and microbial communities after PE-MPs addition were proposed. PE-MPs affected microbial community structures by directly and indirectly influencing soil microenvironmental conditions. The relative abundances of Acidobacteria, Gemmatimonadetes, Bacteroides, Basidiomycota, Chtridiomyota, and Glomeromycota were significantly correlated with physicochemical properties and soil enzyme activities. Enzyme activities were direct factors influencing soil microbial community structures, and physicochemical properties (i.e., dissolved organic carbon, soil available phosphorus) could indirectly affect these structures by acting on soil enzyme activities. Our findings helped improve our understanding of the responses of soil microbial structures and diversities to MPs through the perspective of different soil aggregates.

Sampling, pre-treatment, and identification methods of microplastics in sewage sludge and their effects in agricultural soils: a review

Microplastics are widely detected in wastewater treatment plants. They can remove microplastics from wastewaters with a high yield, but it means that microplastics are transferred and accumulated to sewage sludge. Lately, increasing attention has been paid to microplastics in raw and treated wastewaters. However, studies about quantification and identification of microplastics in sewage sludge are very scarce and need to be further investigated. Since the sludge-based microplastics are newly studied and are a challenging matrix due to high organic content, there is limited knowledge of sampling, pre-treatment methods, identification techniques, and expression units. Besides, treated sewage sludge is mostly used for soil amendment to improve soil fertility and it gives economic advantages. This situation creates a pathway for microplastics entering the soil environment with unknown consequences. To the best of our knowledge, microplastics have a large specific surface area, small size, and hydrophobicity which makes it a good adsorbent for other pollutants. Therefore, the combined effect of microplastics with adsorbed pollutants such as heavy metals, antibiotics, and persistent organic pollutants could give serious harm to soil safety and soil organisms. Herein, new developments in the methods for sampling, pre-treatment, and identification techniques of microplastics in sewage sludge were reviewed. Then, the abundance of microplastics, major polymer types, and shapes in sewage sludge were examined. Finally, the effects and ecological risks of microplastic pollution as a result of agricultural usage of sewage sludge in the soil environment have been summarized. Also, the main points for future research were highlighted.

Toxicological interactions of microplastics/nanoplastics and environmental contaminants: Current knowledge and future perspectives

The co-occurrence of microplastics/nanoplastics (MPs/NPs) with other environmental contaminants has stimulated a focus shift of its skyrocketed research publications (more than 3000 papers during 2016-2020, Web of Science) from ubiquitous occurrence to interactive toxicity. Here, in this review, we provided the current state of knowledge on toxicological interaction of MPs/NPs with co-contaminants (heavy metals, polycyclic aromatic hydrocarbons, pharmaceuticals, pesticides, nanoparticles, organohalogens, plastic additives, and organotins). We discussed the possible interactions (aggregation, adsorption, accumulation, transformation, desorption) that played a role in influencing the toxicity of the mixture. Besides, the type of interactions such as synergistic, antagonistic, potentiating was expounded to get a deeper mechanistic understanding. Despite the wide occurrence and usage, scant studies were available on polypropylene, polyethylene terephthalate. Our analysis shows a dearth of research on common occurring heavy metals (mercury, lead, chromium), phthalates, personal care products. Considerations for environmental factors such as the presence of dissolved organic matter, pH, salinity, temperature, and effects of different colors and types of polymer are recommended.

Plastic particles in soil: state of the knowledge on sources, occurrence and distribution, analytical methods and ecological impacts

Increased production and use of plastics has resulted in growth in the amount of plastic debris accumulating in the environment, potentially fragmenting into smaller pieces. Fragments <5 mm are typically defined as microplastics, while fragments <0.1 μm are defined as nanoplastics. Over the past decade, an increasing number of studies have reported the occurrence and potential hazards of plastic particles in the aquatic environment. However, less is understood about plastic particles in the terrestrial environment and specifically how much plastic accumulates in soils, the possible sources, potential ecological impacts, interaction of plastic particles with the soil environment, and appropriate extraction and analytical techniques for assessing the above. In this review, a comprehensive overview and a critical perspective on the current state of knowledge on plastic pollution in the soil environment is provided: detailing known sources, occurrence and distribution, analytical techniques used for identification and quantification and the ecological impacts of particles on soil. In addition, knowledge gaps are identified along with suggestions for future research.

The effects of high-density polyethylene and polypropylene microplastics on the soil and earthworm Metaphire guillelmi gut microbiota

As an emerging pollutant in terrestrial ecosystem, studies on the effects of microplastics on the gut microbiota of terrestrial organisms are relatively little even though gut microbiota is closely related to host health, metabolism and immunity as well as soil decomposition processes. In this study, earthworms Metaphire guillelmi were exposed to soil amended with 0.25% (w/w) high-density polyethylene (HDPE, 25 μm) or polypropylene (PP, 13 μm) microplastics for 28 d. The ingestion of HDPE and PP microplastics by M. guillelmi was clearly demonstrated by Nile Red fluorescence staining method. There were significant differences for the microbiota between the M. guillelmi gut and the surrounding soil, which may result from the influence of specific conditions in the gut habitat. HDPE and PP microplastics exposure did not induce gut microbiota dysbiosis in M. guillelmi. However, PP microplastics exposure significantly reduced bacterial diversity and altered bacterial community structure in the soil. Specifically, the relative abundance of Aeromonadaceae and Pseudomonadaceae significantly increased while the relative abundance of Nitrososphaeraceae and two unidentified families affiliated with Proteobacteria significantly decreased. This study broadens our understanding of the ecotoxicity of microplastics on the soil and gut microbiota of terrestrial organisms.

Linking effects of microplastics to ecological impacts in marine environments

Recently, efforts to determine the ecological impacts of microplastic pollutants have increased because of plastic's accelerated contamination of the environment. The tiny size, variable surface topography, thermal properties, bioavailability and biological toxicity of microplastics all offer opportunities for these pollutants to negatively impact the environment. Additionally, various inorganic and organic chemicals sorbed on these particles may pose a greater threat to organisms than the microplastics themselves. However, there is still a big knowledge gap in the assessment of various toxicological effects of microplastics in the environment. Ecological risk assessment of microplastics has become more challenging with the current data gaps. Thus, a current literature review and identification of the areas where research on ecology of microplastics can be extended is necessary. We have provided an overview of various aspects of microplastics by which they interact negatively or positively with marine organisms. We hypothesize that biogeochemical interactions are critical to fully understand the ecological impacts, movement, and fate of microplastics in oceans. As microplastics are now ubiquitous in marine environments and impossible to remove, we recommend that it's not too late to converge research on plastic alternatives. In addition, strict actions should be taken promptly to prevent plastics from entering the environment.

Bioremediation of Cd-spiked soil using earthworms (Eisenia fetida): Enhancement with biochar and Bacillus megatherium application

In this study, we evaluated the influence of biochar and Bacillus megatherium on Cd removal from artificially contaminated soils using earthworms (Eisenia fetida). Within a 35-days remediation period, over 30% of Cd was removed by earthworms from the contaminated soil (with Cd at ∼ 2.5 mg kg^-1), and both additives facilitated Cd removal. Additionally, over 22% reduction in the extractable Cd contents was also achieved by earthworms. Cd accumulated in earthworms steadily increased through remediation, and the accumulated Cd decreased in the order of earthworm + biochar (T3) > earthworm + Bacillus megatherium (T4) > earthworm alone (T2). The bioaccumulation factors (BCF) were above 1, indicating the enrichment of Cd in earthworms, and there were higher BCF for both T4 (944%) and T3 (845%). The ingestion of metal-bonded biochar particle and the elevated Cd mobility would be the main reason for the enhanced Cd-remediation by earthworms under T3 and T4, respectively. Through remediation, microbiota communities in both, soil and earthworm guts, demonstrated high similarity, while a lower level of bacterial abundance was observed in earthworm guts compared with that in soils. Eventually, soils became more fertile and demonstrated higher enzyme activities after remediation. Therefore, we concluded that earthworm, alone or combined with biochar or Bacillus megatherium could be an alternative method for Cd-contaminated soil remediation.

Microplastics aggravate the joint toxicity to earthworm Eisenia fetida with cadmium by altering its availability

Microplastics (MPs) have become a global environmental issue, however, the threats of metal-associated MPs to soil ecosystems and their involved processes have not been fully disclosed. In this study, a microcosm experiment with co-exposure of polyethylene and cadmium was conducted to determine their joint effects on the earthworm Eisenia fetida and to explore their relationship with the soil Cd availability that affected by MPs. The results showed that 28-day co-exposure of MPs and Cd significantly induced higher avoidance responses, weight loss and reduced reproduction of earthworms with the increasing content of pollutants. MPs and Cd jointly inhibited the superoxide enzyme (SOD) and peroxidase (POD) activities while increasing the glutathione (GSH) and malondialdehyde (MDA) activities in E. fetida. Histopathological changes and DNA damage to earthworm sperm also occurred in an MPs-dose-dependent manner. In addition, the presence of MPs significantly increased the soil diethylenetriaminepentaacetic acid (DTPA)-Cd concentrations by 1.20-fold and 1.43-fold while increasing the Cd bioaccumulation in E. fetida by 2.65-fold and 1.42-fold in low- and high-Cd-contaminated soil, respectively, which potentially contributed to the aggravation of the joint toxicity to E. fetida. In conclusion, this study demonstrated that microplastics could enhance the cadmium availability in the co-exposure soil which resulted in the joint toxicity of metal-associated MPs to soil organisms. CAPSULE: MPs increased soil Cd availability and potentially aggravated the joint toxicity with Cd to Eisenia fetida.

Microplastic digestion generates fragmented nanoplastics in soils and damages earthworm spermatogenesis and coelomocyte viability

Despite concerns about the ecotoxicological effects of microplastics in soils, there is a limited understanding of the reproductive toxicity of microplastics to soil organisms and the production of nanoplastics through biological fragmentation. We used the earthworm Eisenia andrei to investigate the generation of nanoplastics from polyethylene microplastics in soil ecosystems and to determine the negative effects of microplastic exposure on soil invertebrates. Earthworms were exposed to two different sizes of microplastic for 21 days, and various physiological features, including those pertaining to reproduction, were subsequently analyzed. Exposure to microplastics affected coelomocyte viability and caused damage to male reproductive organs, while having negligible effects on female reproductive organs. Earthworm-induced fragmentation of microplastics to nanoplastics was confirmed using scanning electron microscopy and energy dispersive X-ray analysis. These nanoplastics were introduced into soils through cast excretion. We provide the evidence of nanoplastic generation from ingested microplastics and damage caused to earthworm spermatogenesis through microplastic exposure.

Gut microbiota protects honey bees (Apis mellifera L.) against polystyrene microplastics exposure risks

Microplastic contamination is not only a pressing environmental concern in oceans, but also terrestrial ecosystems. However, little is known about its potential impacts on pollinators. Here, we reported the effects of 25 μm-diameter spherical polystyrene microplastics (PS-MPs) alone or in combination with the antibiotic tetracycline on honey bees (Apis mellifera L.) in the laboratory. We noticed that PS-MPs exposure for 14 d had sublethal effects, with low mortalities (up to 1.6 %) across three different treatments (0.5, 5, and 50 mg/L) and no changes to the body weight gains compared to the control bees. Nevertheless, PS-MPs exposure led to significant decreases in the α-diversity of bees' gut microbiota accompanied by changes to the core microbial population structure. Additionally, PS-MPs lead to alterations in the expression of antioxidative (Cat), detoxification (CypQ1 and GstS3), and immune system-related genes (Domeless, Hopscotch, and Symplekin) in guts. More interestingly, we observed that PS-MPs accumulated and degraded inside of the hindgut and interacted with gut bacteria. The depletion of the normal gut microbiota using tetracycline dramatically increased the lethality of microplastics. These results provide a resource for future research on microplastic-microbiome interactions in other insects and also shed light on understanding the potential effects of microplastics in terrestrial ecosystems.

Microplastics in soils: A review of methods, occurrence, fate, transport, ecological and environmental risks

The global prevalence of microplastics (MPs) poses a potential threat and unpredictable risk to the function and health of environmental systems. However, the research progress of soil MPs is restricted by the inherent technical inconformity and difficulties in analyzing particles in complex matrices. Here, we reviewed a selection of papers and then extrapolated a tentative standardized method for such analyses. The multiple sources of soil MPs in soil need to be quantified. Global monitoring data of soil MPs is far from sufficient. The interaction between MPs and different properties and environmental factors controls the migration and retention of MPs in soil. The migration behavior and key mechanisms of MPs in real-world environments remain to be determined. The presence of MPs threatens soil microbial-plant-animal ecosystem function and health, and may enter the human body through the food chain, although the extent of these hazards is currently debated. In particular, attention should be paid to the potential transport and ecotoxicological mechanisms of contaminants derived and adsorptive from MPs and of harmful microorganisms (such as pathogens) attached as biofilms. Although there exist preliminary studies on soil MPs, it is urgent to consider the diversity of MPs as a suite of contaminants and to systematically understand the sources, flux and effects of these artificial pollutants in time and space from the perspective of plastic environmental cycle. More comprehensive quantification of their environmental fate is undertaken to identify risks to global human and ecological systems. From the perspective of controlling soil MP pollution, the responsibility assignment of government manage-producer-consumer system and the strategy of remediation should be implemented. This review is helpful for providing an important roadmap and inspiration for the research methods and framework of soil MPs and facilitates the development of waste management and remediation strategies for regional soil MP contamination.

Global trends and prospects in microplastics research: A bibliometric analysis

Microplastic pollution is a global enviromental issues. This is the first time in recent decades that quantitative and qualitative evidence from bibliometrics and Altmetric has been used to conduct an in-depth statistical analysis of global microplastics research knowledge and demonstrate research progress, trends and hotspots. We comprehensively searched the Web of Science Core Collection scientific database from its inception (1986) to September 21, 2019. The study shown that the number of papers on microplastics has increased significantly since 2011. Worldwide, researchers in the field come mostly from Western Europe, mainly spread in the UK, Netherlands and Belgium. With the exception of China, the contribution of developing countries was very limited. Moreover, this study systematically elaborated the hotspots in this field (especially in ecological toxicity and human health risks). The results shown that research on marine systems and marine plankton is still dominant. Since human beings are the ultimate consumers of the food chain, microplastics may have potential effects on the human respiratory system and gastrointestinal tract. Towards that end, some topics and perspectives are noted that could indicate the current scientific hotspots and guide future research directions.

Microplastics could be a threat to plants in terrestrial systems directly or indirectly

Microplastics (MPs) are an emerging threat to ecosystem functioning and biota. The major sources of MPs are terrestrial and agricultural lands. But their fate, concentration in the terrestrial environment, and effects on soil and biota are poorly understood. There is a growing body of concern about the adverse effects of MPs on soil-dwelling organisms such as microbes in mycorrhizae and earthworms that mediate essential ecosystem services. Environmental concentrations and effects of MPs are considered to increase with increasing trend of its global production. MPs in the soil could directly impact plants through blocking the seed pore, limiting the uptake of water and nutrient through roots, aggregation, and accumulation in the root, shoot, and leaves. However, MPs can also indirectly impact plants by affecting soil physicochemical characteristics, soil-dwelling microbes, and fauna. An affected soil could impact plant community structure and perhaps primary production. In this article, we have assessed the potential direct and indirect impacts of MPs on plants. We have discussed both the positive and negative impacts of MPs on plants in terrestrial systems based on currently available limited literature on this topic and our hypothetical understandings. We have summarized the most current progress in this regard highlighting the future directions on microplastic research in terrestrial systems.

Bioremediation of Cd-contaminated soil by earthworms (Eisenia fetida): Enhancement with EDTA and bean dregs

The remediation of cadmium (Cd) contaminated soil has become a global problem due to its toxicity to living organisms. In this study, earthworm (Eisenia fetida) alone or combined with EDTA or bean dregs were used for Cd removal from soils. The total and available Cd in soils, soil physicochemical and biological (soil enzyme) properties, Cd accumulation in the earthworm and its antioxidant responses towards Cd, were determined during the 35 days of soil incubation experiment. Our results showed that earthworms were capable of removing Cd from soils, and the remediation process was accelerated by both EDTA and bean dregs. By translocation of Cd from soils, the content of Cd in earthworm steadily increased with the exposure time to 8.11, 12.80, and 9.26 mg kg^-1 on day 35 for T2 (earthworm alone), T3 (EDTA enhancement), and T4 (bean dregs enhancement), respectively. Consequently, a great reduction in the Cd contents in soils was achieved in T3 (36.53%) and T4 (30.8%) compared with T2 (28.95%). The concentrations of water/DTPA extractable Cd were also reduced, indicating the low Cd mobility after amendment. Finally, the soil became more fertile and active after wermi-remediation. The soil pH, EC, NO₃^--N, available P, and K contents increased, while soil SOM, DOC, and NH₄⁺-N contents were decreased. There were higher soil enzyme activities (including acid phosphatase activity, β-glucosidase activity, and urease activity) among treatments with earthworms. Additionally, the operational taxonomic units (OTUs) increased by 100-150 units, and the higher chao1 and Shannon indexes indicated the enhanced microbial community after wermi-remediation, especially among treatment with EDTA and bean dregs. Therefore, we concluded that earthworms, alone or combined with EDTA and bean dregs, are feasible for the remediation of Cd-contaminated soil.

Ecological role of earthworm intestinal bacteria in terrestrial environments: A review

Increasing evidence demonstrated the critical role the earthworm gut played in sustaining earthworm's metabolism and transformation of nutrients and pollutants in the environment. Being rich in nutrients, the earthworm gut is favorable for the colonization of (facultative) anaerobic bacteria, which bridge the host earthworm gut with adjacent terrestrial environment. Therefore, the status quo of earthworm gut research was primarily reviewed in this work. It was found that most studies focused on the bacterial composition and diversity of the earthworm gut, and their potential application in nutrient element and pollutant transformation, such as nitrification, methanogens, heavy metal detoxification, etc. Yet limited information was available about the specific mechanism of intestinal bacteria in nutrient and pollutant transformation. Therefore, in this work we highlighted the current problems and concluded the future prospect of worm's intestinal bacteria research. On one hand, high throughput sequencing and bioinformatics tools are critical to break the bottleneck in the intestinal bacteria research via clarifying the molecular mechanism involved in the transformation processes described above. In addition, a global dataset concerning worm gut bacteria will be needed to provide comprehensive information about intestinal bacteria pool, and act as a communication platform to further encourage the progress of worm gut research.

Interactions of microplastics and cadmium on plant growth and arbuscular mycorrhizal fungal communities in an agricultural soil

Microplastics (MPs) as emerging contaminants have attracted attention worldwide, but little is known on their interactions with metallic contaminants in soil-plant systems. Here, we investigated the interactions between MPs, i.e., polyethylene (PE) and polylactic acid (PLA), and cadmium (Cd) on plant performance and arbuscular mycorrhizal fungal community in an agricultural soil. PE showed no noticeable phytotoxicity, while 10% PLA decreased maize biomass and chlorophyll content in leaves. A significant interaction on root biomass occurred between PE and Cd, but not between PLA and Cd. Both PE and PLA caused increase in soil pH and DTPA-extractable Cd concentrations, but no alterations in Cd accumulation in plant tissues. Different numbers of endemic and total OTUs were observed in various treatments. The relative abundance of arbuscular mycorrhizal fungi (AMF) genera highly varied with MPs and Cd. MPs altered AMF community structure and diversity, depending on their type and dose. Coexisting Cd produced slight but significant interactions with MPs on the dominant AMF genera. Overall, plant growth and AMF community varied with MPs type and dose, Cd, and their interactions, and the high dose of PLA produced stronger phytotoxicity. In conclusion, coexisting MPs and Cd can jointly drive shifts in plant performance and root symbiosis, thereby posing additional risks for agroecosystems and soil biodiversity.

Effects of Co-Contamination of Microplastics and Cd on Plant Growth and Cd Accumulation

Microplastics (MPs) occur widely in terrestrial ecosystems. However, information on the interaction of MPs with metals in terrestrial ecosystems is lacking in the literature. The present study investigated the effects of two types of MPs (high-density polyethylene (HDPE) and polystyrene (PS)) with different dosages (i.e., 0, 0.1%, 1%, and 10%) on the uptake and effects of Cd in maize plants grown in an agricultural soil. Results showed that addition of Cd at a 5 mg/kg caused inhibited plant growth and resulted in high Cd accumulation in plant tissues. Polyethylene alone showed no significant phytotoxic effects, but a high-dose of HDPE (10%) amplified Cd phytotoxicity. Polystyrene negatively affected maize growth and phytoxicity further increased in the presence of Cd. Both HDPE and PS caused soil diethylenetriaminepentaacetic acid (DTPA)-extractable Cd concentrations to increase but did not significantly affect Cd uptake into plant tissues. In the soil without Cd addition, HDPE decreased soil pH, while PS did not significantly alter soil pH. However, in the soil spiked with Cd, both HDPE and PS increased pH. Overall, impacts on plant growth and Cd accumulation varied with MP type and dose, and PS induced substantial phytotoxicity. In conclusion, co-occurring MPs can change Cd bioavailability, plant performance, and soil traits. Our findings highlight the ecological impacts that could occur from the release of MPs into soil.

Environmental fate and impacts of microplastics in soil ecosystems: Progress and perspective

The wide and intensive application of plastics and their derived products has resulted in global environmental contamination of plastic waste. Large-sized plastic litter can be fragmented into microplastics (<5 mm), which have attracted increasing concerns from the general public and scientific communities worldwide. Until recently, the majority of microplastics research reported in literatures has been focusing on the aquatic settings, especially the marine environment, while information about microplastics contamination in terrestrial soil systems is highly insufficient. In this paper, we reviewed the latest data regarding the occurrence of microplastics in terrestrial soils and discussed their potential pathways into the soil environment. We also summarized the currently used methodologies for extraction and characterization of microplastics in soil matrices and evaluated their advantages and limitations. Additionally, we assessed the ecotoxicological consequences of microplastics contamination on soil ecosystems, including the effects on soil physiochemical properties, terrestrial plants, soil fauna, and soil microbes. Finally, based on the most current progress summarized in this review, we suggested several directions for future research on microplastics in soil ecosystems.

Focus topics on microplastics in soil: Analytical methods, occurrence, transport, and ecological risks

Microplastics with extremely high abundances are universally detected in marine and terrestrial systems. Microplastic pollution in the aquatic environment, especially in ocean, has become a hot topic and raised global attention. However, microplastics in soils has been largely overlooked. In this paper, the analytical methods, occurrence, transport, and potential ecological risks of microplastics in soil environments have been reviewed. Although several analytical methods have been established, a universal, efficient, faster, and low-cost analytical method is still not available. The absence of a suitable analytical method is one of the biggest obstacles to study microplastics in soils. Current data on abundance and distribution of microplastics in soils are still limited, and results obtained from different studies differ significantly. Once entering into surface soil, microplastics can migrate to deep soil through different processes, e.g. leaching, bioturbation, and farming activities. Presence of microplastics with high abundance in soils can alter fundamental properties of soils. But current conclusions on microplastics on soil organisms are still conflicting. Overall, research on microplastics pollution in soils is still in its infancy and there are gaps in the knowledge of microplastics pollution in soil environments. Many questions such as pollution level, ecological risks, transport behaviors and the control mechanisms are still unclear, which needs further systematical study.

Contributions of enzymes and gut microbes to biotransformation of perfluorooctane sulfonamide in earthworms (Eisenia fetida)

Perfluorooctane sulfonamide (FOSA) is known as a key intermediate of perfluorooctane sulfonic acid (PFOS) precursors, which can be frequently detected in the environment and biota. FOSA could be bioaccumulated in earthworms from soil, but the contributions of enzymes and gut microbes involved in the biotransformation of FOSA in earthworms have not been identified. Therefore, the effects of enzyme inhibitors and intestinal microflora on biotransformation of FOSA in earthworms were investigated in the present study. FOSA was biotransformed to form PFOS by earthworms obtained from in vivo and in vitro tests. The addition of FOSA had significantly positive effects on cytolchrome P450 (CYP450) and glutathione-s-transferase (GST) activities, suggesting CYP450 and GST are likely involved in the enzymatic transformation. In addition, both 1-Aminobenzotriazole (ABT) and ezatiostat hydrochloride (TLK199), which were selected to inhibit the CYP and GST enzymes, respectively, demonstrated inhibition effects on biotransformation of FOSA in earthworms with a dose-dependent relationship. However, the concentrations of FOSA weren't changed by the bacteria isolated from worm gut, suggesting that gut bacteria did not contribute to FOSA biotransformation in earthworms. The results of this study confirm that the transformation of FOSA in earthworms is mediated mainly by enzymes rather than by gut microbes.

Microplastic particles reduce reproduction in the terrestrial worm Enchytraeus crypticus in a soil exposure

Terrestrial environments are subject to extensive pollution by plastics and, based on the slow degradation of plastics, are likely to act as long term sinks for microplastic debris. Currently the hazards of microplastics in soil and the potential impacts on soil organisms is poorly understood. Particularly the role of particle characteristics, such a size or polymer type, in dose-response relationships for microplastics is not known. The aim of this study was to assess the ingestion and toxicity of nylon (polyamide) particles, in three different size ranges, to Enchytraeus crypticus in a soil exposure. Effects were also compared with those of polyvinyl chloride (PVC) particles, in a single size range. Nylon particle ingestion was confirmed using fluorescence microscopy, with greatest ingestion for particles in the smallest size range (13-18 μm). To investigate how particle size affected survival and reproduction, E. crypticus were exposed to nylon particles in two well-defined size ranges (13-18 and 90-150 μm) and concentrations of 20, 50, 90 and 120 g/kg (2-12% w/w). An intermediate nylon size range (63-90 μm) and a larger sized PVC particle (106-150 μm), both at 90 g/kg, were also tested. Survival was not affected by either of the polymer types or sizes. Reproduction was significantly reduced, in a dose-dependent manner, by the nylon particles at high exposure concentrations (>90 g/kg). Smaller size ranges (13-18 μm) had a greater effect compared to larger size ranges (>63 μm), with a calculated EC₅₀ for the 13-18 μm size range of 108 ± 8.5 g/kg. This greater hazard could be qualitatively linked with the ingestion of a greater number of smaller particles. This study highlights the potential for toxic effects of plastics in small size ranges to soil organisms at high exposure concentrations, providing understanding of the hazards microplastics may pose in the terrestrial environment.

Microplastics as contaminants in the soil environment: A mini-review

Microplastics (MPs) have become a global environmental concern because of their ubiquitous presence. While extensive microplastic researches have focused on the marine environment, pervasive MPs contamination in soil and their detrimental impacts have been largely overlooked. Excessive concentrations of MPs and additives have been found in soil derived from the use of plastic mulches and the application of sewage sludge to fields. They may pose directly or indirectly as adverse effects on flora and fauna. The objectives of this review are (1) to summarize the abundance, sources, and properties of MPs in soil; (2) to analyze combined effects of MPs and various other environmental pollutants on soil system; and (3) to discuss the possible risks posed by MPs to soil biodiversity, food safety and human health. This review will highlight key future research areas for scientists and policymakers, and increase overall understanding of soil MPs pollution and its potential environmental impacts.