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•Micro- and nano-plastics in agricultural soils represents a major environmental threat.•Standard methods for microplastic separation and detection are urgently needed.•Microplastics ...affect agroecosystem functioning by accumulating heavy metals or organic contaminants.•Plasticizers represent a major source of pollution within microplastics.•Adoption of biodegradable films will help reduce soil microplastic accumulation.
It is now widely acknowledged that microplastic pollution represents one of the greatest anthropogenically mediated threats to Earth-system functioning. In freshwater and marine ecosystems the presence of large amounts of microplastic appears almost ubiquitous, with frequent reports of negative impacts on aquatic health. In contrast, however, the impact of plastic in terrestrial environments remains poorly understood. In agroecosystems, microplastics (particles < 5 mm) can enter the soil environment either directly (e.g. from biosolids application, irrigation water, atmospheric deposition), or indirectly through the in situ degradation of large pieces of plastic (e.g. from plastic mulch films). Although we have encouraged the use of plastics over the last 50 years in agriculture to promote greater resource use efficiency and food security, the legacy of this is that many soils are now contaminated with large amounts of plastic residue (ca. 50–250 kg ha−1). Due to difficulties in separating and quantifying plastic particles from soil, our knowledge of their behavior, fate and potential to transfer to other receptors (e.g. surface and groundwater, air) and enter the human food chain remains poor. This information, however, is critical for evaluating the risk of soil-borne microplastic pollution. In this critical review, we systematically summarize (i) the distribution and migration of microplastics in soils, (ii) highlight the separation, extraction, and identification methods for monitoring microplastics in soils, (iii) discuss the ecological effects and pollution mechanisms of soil microplastics, (iv) propose mitigation strategies to help prevent and reduce microplastic pollution, and (v) identify the most important future challenges in soil microplastics research.
Upon environmental weathering, plastic materials form smaller sized microplastics, of which the contamination in agricultural fields is of significant importance and increasing social concern. ...Plastic mulch films are considered a major source of agricultural soil microplastic pollution. However, the mechanism and kinetics of microplastic formation from plastic mulch films were rarely understood. In this study, the rate of microplastic generation from typical mulch films, such as oxodegradable, biodegradable, and conventional non-degradable (polyethylene, PE) mulch films, were quantified in soil under simulated UV irradiation. Results showed that microplastic formation was more rapid from biodegradable mulch film, followed sequentially by oxodegradable mulch film, white PE mulch film, and black PE mulch film. The kinetics of microplastic generation strictly followed the Schwarzchild's law, with exponential growth at indexes between 1.6309 and 2.0502 in the microplastic generation model. At a cumulative UV irradiation of 2.1 MJ/m2, the average quantity of microplastics released from biodegradable, oxodegradable, and white and black non-degradable mulch films were 475, 266, 163, 147 particles/cm2, respectively; with particle sizes largely distributed within 0.02–0.10 mm range. Concurrent increase in crystallinity and surface erosion of the mulch films were observed upon UV irradiation, which further determined the accessibility and activity of the materials to photo-oxidation (reflected as HI indexes), therefore played a critical role on the quantity and size ranges of microplastic debris.
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•Kinetics of microplastic generation from mulch films were studied upon UV irradiation.•Biodegradable films were most rapid in microplastic formation, followed by oxo-film and PE film.•Kinetics of microplastic generation strictly followed the Schwarzchild's law.•Crystallinity and chemical composition are critical for the size and quantity of microplastics.•At cumulative UV exposure of 2.1 MJ/m2, 147–475 microparticles/cm2 could be released.
Plastic film mulch (PFM) is a double-edged-sword agricultural technology, which greatly improves global agricultural production but can also cause severe plastic pollution of the environment. Here, ...we characterized and quantified the amount of macro- and micro-plastics accumulated after 32 years of continuous plastic mulch film use in an agricultural field. An interactive field trial was established in 1987, where the effect of plastic mulching and N fertilization on maize yield was investigated. We assessed the abundance and type of macroplastics (>5 mm) at 0–20 cm soil depth and microplastic (<5 mm) at 0–100 cm depth. In the PFM plot, we found about 10 times more macroplastic particles in the fertilized plots than in the non-fertilized plots (6796 vs 653 pieces/m2), and the amount of film microplastics was about twice as abundant in the fertilized plots than in the non-fertilized plots (3.7 × 106 vs 2.2 × 106 particles/kg soil). These differences can be explained by entanglement of plastics with plant roots and stems, which made it more difficult to remove plastic film after harvest. Macroplastics consisted mainly of films, while microplastics consisted of films, fibers, and granules, with the films being identified as polyethylene originating from the plastic mulch films. Plastic mulch films contributed 33%–56% to the total microplastics in 0–100 cm depth. The total number of microplastics in the topsoil (0–10 cm) ranged as 7183–10,586 particles/kg, with an average of 8885 particles/kg. In the deep subsoil (80–100 cm) the plastic concentration ranged as 2268–3529 particles/kg, with an average of 2899 particles/kg. Long-term use of plastic mulch films caused considerable pollution of not only surface, but also subsurface soil. Migration of plastic to deeper soil layers makes removal and remediation more difficult, implying that the plastic pollution legacy will remain in soil for centuries.
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•N fertilization aggravated the abundance of macroplastic and film microplastic.•Microplastics consisted of films, fibers, and granules in long film-mulched soil.•Film microplastic was identified as originating from the plastic mulch films.•Plastic film-derived microplastics can readily migrate down the soil profile.•Plastic films contributed 33%–56% to total microplastics for 0–100 cm profile.
Enteric viruses represent a global public health threat and are implicated in numerous foodborne and waterborne disease outbreaks. Nonetheless, relatively little is known of their fate and stability ...in the environment. In this study we used carefully validated methods to monitor enteric viruses, namely adenovirus (AdV), JC polyomavirus (JCV), noroviruses (NoVs), sapovirus (SaV) and hepatitis A and E viruses (HAV and HEV) from wastewater source to beaches and shellfish beds. Wastewater influent and effluent, surface water, sediment and shellfish samples were collected in the Conwy catchment (North Wales, UK) once a month for one year. High concentrations of AdV and JCV were found in the majority of samples, and no seasonal patterns were observed. No HAV and HEV were detected and no related illnesses were reported in the area during the period of sampling. Noroviruses and SaV were also detected at high concentrations in wastewater and surface water, and their presence correlated with local gastroenteritis outbreaks during the spring and autumn seasons. Noroviruses were also found in estuarine sediment and in shellfish harvested for human consumption. As PCR-based methods were used for quantification, viral infectivity and degradation was estimated using a NoV capsid integrity assay. The assay revealed low-levels of viral decay in wastewater effluent compared to influent, and more significant decay in environmental waters and sediment. Results suggest that AdV and JCV may be suitable markers for the assessment of the spatial distribution of wastewater contamination in the environment; and pathogenic viruses can be directly monitored during and after reported outbreaks to prevent further environment-derived illnesses.
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•The TFUF concentration method is suitable for quantifying viruses in water samples.•For the first time, sapovirus was found in UK waters.•Enteric viruses were traceable from source to beaches and shellfish beds.•Norovirus concentrations in the environment agreed with local outbreaks.•PGM assay is useful to study norovirus degradation in the environment.
Biochar application has become a novel and emergent technology for sequestering C, improving soil quality and crop production, and is a potential win–win strategy for ecosystem service delivery. ...Biochar addition can also stimulate soil microbial activity, and although it is unclear exactly why biochar should benefit soil microorganisms, it is thought that the large surface area and volume of pores provide a significant habitat for microbes. The aim of this study was to determine the level of microbial colonisation of wood-derived biochar that had been buried in an agricultural soil for three years. We have examined the level of colonisation on the internal and external surfaces of field-aged biochar by scanning electron microscopy, and used 14C-labelled glucose to quantify the rates of microbial activity in different spatial niches of the biochar and the surrounding soil. Microbial colonisation of field-aged biochar was very sparse, with no obvious differences between the external and internal surfaces. At the high field application rate of 50 t ha−1, biochar contributed only 6.52 ± 0.11% of the total soil pore space and 7.35 ± 0.81% of the total soil surface area of the topsoil (0–30 cm). Further, 17.46 ± 0.02% of the biochar pores were effectively uninhabitable for most microbes, being <1 μm in diameter. The initial rate of microbial mineralization of 14C-labelled glucose was significantly greater in the control bulk soil and the soil immediately surrounding the biochar than on the biochar external and internal surfaces. However, lower C use efficiency values of microbes on, or within, the biochar also suggested lower available C status or differences in the structure of the microbial community in the biochar relative to the surrounding soil. This study suggests that, at least in the short term (≤3 y), biochar does not provide a significant habitat for soil microbes. While biochar is extremely recalcitrant and largely unavailable to soil microbes, changes in soil physicochemical properties and the introduction of metabolically available labile compounds into the surrounding soil (the ‘charosphere’) may significantly alter soil microbial activity and structure, which could ultimately affect soil–plant–microbe interactions. Therefore, before the wide-scale application of biochar to agricultural land is exploited, it is important that we understand further how the properties of biochar positively or negatively affect soil microbial communities, and in turn, how they interact with, and colonise biochar.
•Microbial colonisation of field-aged biochar was very sparse.•Lower C use efficiency of biochar-associated microbes suggested lower available C status.•In the short term (<3years) biochar does not provide significant habitat for soil microbes.•The charosphere supports higher microbial activity than the surfaces of biochar.
The long term survival of fecal indicator organisms (FIOs) and human pathogenic microorganisms in sediments is important from a water quality, human health and ecological perspective. Typically, both ...bacteria and viruses strongly associate with particulate matter present in freshwater, estuarine and marine environments. This association tends to be stronger in finer textured sediments and is strongly influenced by the type and quantity of clay minerals and organic matter present. Binding to particle surfaces promotes the persistence of bacteria in the environment by offering physical and chemical protection from biotic and abiotic stresses. How bacterial and viral viability and pathogenicity is influenced by surface attachment requires further study. Typically, long-term association with surfaces including sediments induces bacteria to enter a viable-but-non-culturable (VBNC) state. Inherent methodological challenges of quantifying VBNC bacteria may lead to the frequent under-reporting of their abundance in sediments. The implications of this in a quantitative risk assessment context remain unclear. Similarly, sediments can harbor significant amounts of enteric viruses, however, the factors regulating their persistence remains poorly understood. Quantification of viruses in sediment remains problematic due to our poor ability to recover intact viral particles from sediment surfaces (typically <10%), our inability to distinguish between infective and damaged (non-infective) viral particles, aggregation of viral particles, and inhibition during qPCR. This suggests that the true viral titre in sediments may be being vastly underestimated. In turn, this is limiting our ability to understand the fate and transport of viruses in sediments. Model systems (e.g., human cell culture) are also lacking for some key viruses, preventing our ability to evaluate the infectivity of viruses recovered from sediments (e.g., norovirus). The release of particle-bound bacteria and viruses into the water column during sediment resuspension also represents a risk to water quality. In conclusion, our poor process level understanding of viral/bacterial-sediment interactions combined with methodological challenges is limiting the accurate source apportionment and quantitative microbial risk assessment for pathogenic organisms associated with sediments in aquatic environments.
Summary During the past 10 years, multidrug-resistant Gram-negative Enterobacteriaceae have become a substantial challenge to infection control. It has been suggested by clinicians that the ...effectiveness of antibiotics is in such rapid decline that, depending on the pathogen concerned, their future utility can be measured in decades or even years. Unless the rise in antibiotic resistance can be reversed, we can expect to see a substantial rise in incurable infection and fatality in both developed and developing regions. Antibiotic resistance develops through complex interactions, with resistance arising by de-novo mutation under clinical antibiotic selection or frequently by acquisition of mobile genes that have evolved over time in bacteria in the environment. The reservoir of resistance genes in the environment is due to a mix of naturally occurring resistance and those present in animal and human waste and the selective effects of pollutants, which can co-select for mobile genetic elements carrying multiple resistant genes. Less attention has been given to how anthropogenic activity might be causing evolution of antibiotic resistance in the environment. Although the economics of the pharmaceutical industry continue to restrict investment in novel biomedical responses, action must be taken to avoid the conjunction of factors that promote evolution and spread of antibiotic resistance.
Misuse and overuse of antibiotics have contributed to the rise of antimicrobial resistance as one of the top public health threats. Antibiotics and antibiotic resistance genes (ARGs) are prevalent in ...agricultural soils due to the widespread application of livestock and organic wastes. However, information about the occurrence, distribution, and risk of antibiotics and ARGs in agricultural soils is lacking for many scenarios. In this study, based on 2225 observations from 135 independent studies, we summarized the concentration or abundance of antibiotics or ARGs under different fertilizer sources and land-use patterns, analyzed the contributions of key environmental factors to the occurrence of antibiotics and ARGs in agricultural soils, and highlighted the potential ecological risk of typical antibiotics and the relationship between ARGs and mobile genetic elements (MGEs). Our results showed that cattle manure, chicken manure, swine manure, and sewage sludge were the primary pollution sources of antibiotics and ARGs in agricultural soils, and sulfonamides, tetracyclines, fluoroquinolones, and their corresponding ARGs were the main pollution types. Land-use type, soil, and climatic factors affected antibiotics concentration and ARG abundances. MGEs play a vital role in promoting the dissemination of ARGs, especially the sul1 gene is closely related to intI1. In conclusion, our findings and future research exploring these topics will contribute to better management of antibiotic and ARG contamination in agricultural soils and their risk to human health.
Waterborne enteric viruses are an emerging cause of disease outbreaks and represent a major threat to global public health. Enteric viruses may originate from human wastewater and can undergo rapid ...transport through aquatic environments with minimal decay. Surveillance and source apportionment of enteric viruses in environmental waters is therefore essential for accurate risk management. However, individual monitoring of the >100 enteric viral strains that have been identified as aquatic contaminants is unfeasible. Instead, viral indicators are often used for quantitative assessments of wastewater contamination, viral decay and transport in water. An ideal indicator for tracking wastewater contamination should be (i) easy to detect and quantify, (ii) source-specific, (iii) resistant to wastewater treatment processes, and (iv) persistent in the aquatic environment, with similar behaviour to viral pathogens. Here, we conducted a comprehensive review of 127 peer-reviewed publications, to critically evaluate the effectiveness of several viral indicators of wastewater pollution, including common enteric viruses (mastadenoviruses, polyomaviruses, and Aichi viruses), the pepper mild mottle virus (PMMoV), and gut-associated bacteriophages (Type II/III FRNA phages and phages infecting human Bacteroides species, including crAssphage). Our analysis suggests that overall, human mastadenoviruses have the greatest potential to indicate contamination by domestic wastewater due to their easy detection, culturability, and high prevalence in wastewater and in the polluted environment. Aichi virus, crAssphage and PMMoV are also widely detected in wastewater and in the environment, and may be used as molecular markers for human-derived contamination. We conclude that viral indicators are suitable for the long-term monitoring of viral contamination in freshwater and marine environments and that these should be implemented within monitoring programmes to provide a holistic assessment of microbiological water quality and wastewater-based epidemiology, improve current risk management strategies and protect global human health.
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•Human mastadenoviruses are robust indicators for human-associated pollution in water.•Bacteroides-associated phages and crAssphage are promising indicators.•Multiple indicators should be used to assess wastewater treatment efficiency.•Survival and abundance of indicator viruses should be further assessed.
•Presence of SARS-CoV-2 in feces and wastewater constitutes a paradigm shift in surveillance.•WBE has potential as a surveillance and predictive tool during the COVID-19 pandemic.•Validated protocols ...for concentration and quantification of SARS-CoV-2 and other markers are needed.
The presence of SARS-CoV-2 in the feces of infected patients and wastewater has drawn attention, not only to the possibility of fecal-oral transmission but also to the use of wastewater as an epidemiological tool. The COVID-19 pandemic has highlighted problems in evaluating the epidemiological scope of the disease using classical surveillance approaches, due to a lack of diagnostic capacity, and their application to only a small proportion of the population. As in previous pandemics, statistics, particularly the proportion of the population infected, are believed to be widely underestimated. Furthermore, analysis of only clinical samples cannot predict outbreaks in a timely manner or easily capture asymptomatic carriers. Threfore, community-scale surveillance, including wastewater-based epidemiology, can bridge the broader community and the clinic, becoming a valuable indirect epidemiological prediction tool for SARS-CoV-2 and other pandemic viruses. This article summarizes current knowledge and discusses the critical factors for implementing wastewater-based epidemiology of COVID-19.
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