Origin, Occurrence and Threats of Microplastics in Agricultural Soils: A Comprehensive Review

Microplastics in agricultural soils in China: Sources, impacts and solutions

<p>Microplastics (MPs) as polymeric environmental pollutants have been detected worldwide within arable soils. As agricultural practice poses direct input pathways for plastics to soils and carry the risk of endangering important soil functions, soils microplastic community has developed a strong focus on the investigation on MPs within arable land. However, data on large scale spatial as well as temporal MP occurrence in agricultural soils is still lacking.</p> <p>One possible way to access both, spatial and temporal variance of MPs in agricultural soils is the analysis of reserve samples from permanent soil observation (PSO) monitoring programmes. Based on the example of the PSO programme within the federal state of Hesse (Germany) we have analysed microplastics (300–5000 µm) from topsoil samples of 16 PSO locations sampled in 2003/2004 and 2014/2019. The PSO locations include 12 croplands, three grasslands and one forest soil as a control site across the federal state and its major soilscapes with typical soil formations. We used a MP extraction protocol based on density separation, Nile Red staining and fluorescent analysis coupled with a polymer analysis via ATR-FTIR. Own spiking experiments for common polymers yielded recovery rates of 100% for large MPs (>1000 µm) and 92% for MPs above our lower detection limit of 300 µm.</p> <p>We found MP concentrations of 34.80±23.37 p kg<sup>-1 </sup>with increasing concentrations by decreasing particle sizes. Overall, MPs occurred dominantly as films, followed by fragments and filaments made of PEs, synthetic rubbers or EPDMs, followed by common thermoplastic polymers. With regard to land use and soil management practice, MP concentrations were significant higher in grassland soils than cropland soils, while particle sizes and polymeric composition stay consistent. Surprisingly, we found the highest MP concentration of 65.22 p kg<sup>-1</sup> within mineral forest topsoils of a remote low mountain area. A clear temporal trend, like the MP concentration increase over time, was not detectable. Moreover, we found high temporal variances depending on PSO locations. However, MP concentrations are significant higher at PSO locations in short distances to urban areas, indicating the role of land use intensity and potential littering as MP sources.</p> <p>Our findings enable a discussion on large scale plastic input pathways and their temporal variance. Furthermore, different questions about spatial contaminant patterns and the long-term behaviour of plastics in soils have been raised, that should be discussed within our contribution.</p>

Irrigation is essential for agricultural production, serving not only to transport water but also to facilitate the migration of pollutants such as microplastics (MPs). Although the presence of MPs in agricultural soils is well documented, the effects of irrigation hydrodynamics on their distribution have rarely been explored. This study examines the occurrence and sources of MPs in various sections of paddy soils from the Quyuan Irrigation District (QID) in China. MP analysis was conducted using density separation, microscopy, and laser direct infrared spectroscopy (LDIR) methods. Results showed that MP abundance ranged from 73.30 to 3880.00 items/kg. Statistical analyses revealed that agricultural plastic residues were the primary source of MPs. As a result of irrigation activities, the abundance of < 0.5 mm MPs in paddy soils near branch canals was 2.17 times higher than that in soils near the main canal, indicating more severe MP pollution near the branch canals. In addition, the MP abundance in soil at the drainage outlet (DO) was 2560 items/kg, significantly higher than the 1440 items/kg found at the irrigation inlet (IN) ( p < 0.05). This was due to an increase in water velocity and flux, which generated stronger water impact forces that flushed most MPs into the DO soil. The irrigation hydraulic conditions and MP characteristics influenced the horizontal migration of MPs in surface paddy soils. Overall, this study elucidated the relation between MP pollution and irrigation hydrodynamics, providing valuable insights for precise monitoring and control of MP pollution in farmland.

Microplastics (MPs), defined as plastic particles ranging from 1 µm to 5 mm, have emerged as ubiquitous environmental contaminants due to the widespread use and persistence of plastics. They originate both from the degradation of larger plastic debris and from intentionally produced small particles. MPs have been detected across environmental compartments, including freshwater systems, and even within the human body, raising concerns about potential exposure and risks. This thesis aimed to investigate the occurrence of MPs in freshwater environments and related consumption products, specifically drinking water and fish, while contributing to the advancement of reliable analytical methodologies. Pyrolysis–gas chromatography–mass spectrometry (Py-GC-MS) was employed as the primary analytical technique due to its ability to provide size-independent, quantitative, and polymer-specific data. Complementary use of micro-Fourier transform infrared spectroscopy (µ-FTIR) enabled particle-based characterization. Urban surface water in Amsterdam was analyzed across seasons and locations, revealing higher MP concentrations in summer and in densely urbanized canals. Polypropylene (PP) and polyethylene (PE) were the dominant polymers, and MP concentrations were positively correlated with suspended particulate matter. In drinking water systems, raw water contained relatively high MP concentrations, while treatment processes achieved removal efficiencies of 97–98%. Consequently, tap water contained only trace levels of MPs. Methodological challenges, particularly background contamination, highlighted the importance of strict quality control. The occurrence and potential accumulation of MPs in Nile tilapia were also investigated. Low concentrations were detected in fillet tissues, with heterogeneous distribution across samples. A controlled exposure experiment demonstrated minimal translocation of MPs into edible tissues, with most particles being excreted, suggesting limited human exposure through fish consumption. Overall, this thesis provides mass-based evidence of MP occurrence across environmental and biological matrices and demonstrates the applicability of Py-GC-MS for robust MP quantification. The findings contribute to improved methodological standardization and enhance the understanding of MP distribution and potential human exposure pathways.

Microplastics (MPs) accumulation can potentially influence soil fertility and plant productivity. MP pollution and spatial distribution in terrestrial environments, particularly in agricultural soils surrounding the municipal solid waste (MSW) dumping site in southwest Bangladesh, is still not investigated. The objective of this study was to quantify, characterize, and assess the ecological risks of MPs in agricultural soils surrounding the MSW dumpsite of Khulna City Corporation (KCC) in southwest Bangladesh. Ten (10) composite agricultural soil samples surrounding the MSW dumping site were collected and processed for MPs and trace metals analysis. We investigated the abundance, spatial distribution, characteristics, polymer types, and ecological risk of observed MPs. The results exhibited that the mean abundance of MPs was 5567 items kg-1 (range from 1667 to 11,000 items kg-1), and the dominant shape, size, and color were found in fibers (~ 43%), < 1 mm, and blue, respectively. Polyvinyl chloride (PVC) was the dominant polymer followed by HDPE and nylon among the 14 identified polymer types across the study site's soils. Spatial analysis showed that the old dumpsite, along with agricultural soils in the vicinity of the active dumpsite, was polluted with the MPs and heavy metals. The investigated sites were classified as risk category I due to MP pollution, and thefindings indicate a decrease in MP abundance as the distance from the dumping site increases. Principal component and correlation analysis indicate different anthropogenic sources of MPs and heavy metals pollution, namely the solid waste dumpsite and improper agricultural activities (p < 0.05). The findings highlight the need for integrated management strategies to prevent microplastic pollution in agricultural soils to ensure soil health and crop productivity.

Microplastic content prediction in agricultural soils using a mixed variable selection combined with Transformer-LSTM fusion architecture.

Due to the ecological risk posed by plastic pollution, biodegradable plastics (BDPs) usage in agriculture has gained attention as an alternative to conventional plastics. However, agricultural soil remains a major reservoir of microplastics (MPs) in today&amp;#8217;s global environment. Given the persistence of MPs, few studies have focused on the fate and transport of conventional MPs from agricultural topsoil. However, understanding the transport of biodegradable MPs is largely unknown. The aim of this study is to analyze the erosion and transport behavior of biodegradable polylactic acid (PLA) MPs (size 250 &amp;#8211; 300 &amp;#956;m) under simulated heavy rainfall events on fallow and crusted agricultural soils. The experiment used fluorescent PLA filament to obtain the MPs. Based on the fluorescent property of the PLA MPs, a simple, reliable, and cost-effective method using darkroom photography under a 365nm UV lamp, and an Image J script was developed for quantification. The study was conducted on three plots (1m &amp;#215; 1m) of loamy soil at an agricultural field in the Czech Republic. A concentration of 4 g m-2 of PLA MPs was incorporated into the top 5 cm of the soil in each plot. Rainfall simulations with an intensity of 60 mm h-1 were carried out twice within one week in April 2022. The results showed a general depletion of biodegradable PLA MPs in the delivered sediment. Eroded sediments showed mean enrichment ratios of 0.59 &amp;#177; 0.05 in the fallow plot and 1.45 &amp;#177; 0.37 in the crusted plot. Higher MP enrichment and sediment delivery were observed on crusted soil compared to fallow soil, suggesting a more conservative erosion and transport for the latter. Overall, our study highlights that a relatively high-density biodegradable MP, such as PLA, tends to remain within the topsoil and is negligibly affected by rainfall-induced surface runoff and very low infiltration capacity.

Extraction and decontamination of microplastics from high organic matter soils: A simple, cost-saving and high efficient method

Microplastics (MPs) have become a major concern for the general public. Although their sources and sinks have been studied, the fate of MPs in the environment remains unclear. Understanding their fate is essential for governments to develop effective countermeasures against MP pollution. In this study, MP pollution was investigated at 22 rivers and 11 beaches in Shizuoka Prefecture, Japan. Polyethylene (PE)-, polypropylene (PP)-, and polystyrene (PS)-MP concentrations in sediments ranged from 0.411 to 423, 0 to 206, and 0 to 45.1 particles kg-1, respectively. In river water and seawater, concentrations ranged from 0 to 14.7, 0 to 21.1, and 0 to 6.00 particles m-3, respectively. MP concentrations were rescaled to align with the 1 to 5,000-μm size range used to define the hazardous concentration for 5% of species (HC5). All aligned concentrations in this study were below the HC5 threshold. Population density was found to be significantly correlated with the PE-, PP-, and PS-MP concentrations in river water and with PE- and PP-MP concentrations in sediments, suggesting that local pollution sources drive MP pollution. The estimated ages of PE-MPs in river water, seawater, and sediments ranged from 0.061 to 5.5, 0.25 to 0.63, and 0.0 to 4.3 years, respectively. No significant differences in age were observed among sample types or sampling sites. These findings suggest that effective measures to reduce MP emissions could significantly decrease MP pollution within 1 year in Shizuoka Prefecture.

Effects of conventional versus biodegradable microplastic exposure on oxidative stress and gut microorganisms in earthworms: A comparison with two different soils

Vertical distribution and multi-source pathways of microplastics in agricultural soils: A study of typical irrigation areas in the upper Yellow River basin.

Microplastics (MPs) are an emerging environmental issue that might endanger the health of agricultural soil. Even though several research on the particular toxicity of MPs to species have been carried out, there is little information on MPs' impacts on soil physicochemical properties and heavy metals (HMs) availability of HMs contaminated and without contaminated soils. This study examined the changes in soil characteristics for both HMs contaminated and without contaminated soils by five distinct MPs, including Polyethylene (PE), Polyethylene terephthalate (PET), Polystyrene Foam (PS), Polyamide (PA), and a combination of these four types of MPs (Mixed MPs), at two different concentrations (0.2% and 1%; w/w), where soil incubation experiments were setup for this studies and the standard analytical techniques employed to measure soil characteristics and toxic metal availability. After the ending of soil incubation studies (90 days), significant changes have been observed for physicochemical properties [bulk density, porosity, water holding capacity, pH, electrical conductivity (EC), organic carbon (OC), and organic matter (OM)]. The soil nutrients change in descending order was found as NH4+ -N> PO43+ > Na > Ca > NO3- > Mg for lower concentrations of MPs compared to higher concentrations. The HMs availability is reducing with increasing MPs concentration and the descending order for metal availability was as follows Pb > Zn > Cd > Cr > Cu > Ni. Based on MP type, the following descending order of MPs PS > Mix (MPs) > PA > PET > PE, respectively act as a soil properties influencer. Usually, effects were reliant on MPs' category and concentrations. Finally, this study concludes that MPs may modify metal movements, and soil quality; consequently, a possible threat will be created for soil health.

Tackling microplastic contamination in sewage sludge: Optimizing organic matter degradation, quantifying microplastic presence, and evaluating ecological risks for sustainable agriculture.

Due to the copious disposal of plastics, marine ecosystems receive a large part of this waste. Microplastics (MPs) are solid particles smaller than 5 millimeters in size. Among the plastic polymers, polystyrene (PS) is one of the most commonly used and discarded. Due to its density being greater than that of water, it accumulates in marine sediments, potentially affecting benthic communities. This study investigated the ingestion of MP and their effect on the meiofauna community of a sandy beach. Meiofauna are an important trophic link between the basal and higher trophic levels of sedimentary food webs and may therefore be substantially involved in trophic transfer of MP and their associated compounds. We incubated microcosms without addition of MP (controls) and treatments contaminated with PS MP (1-µm) in marine sediments at three nominal concentrations (103, 105, 107particles/mL), for nine days, and sampled for meiofauna with collections every three days. At each sampling time, meiofauna were collected, quantified and identified to higher-taxon level, and ingestion of MP was quantified under an epifluorescence microscope. Except for Tardigrada, all meiofauna taxa (Nematoda, turbellarians, Copepoda, Nauplii, Acari and Gastrotricha) ingested MP. Absorption was strongly dose dependent, being highest at 107 particles/mL, very low at 105 particles/mL and non-demonstrable at 103 particles/mL. Nematodes accumulated MP mainly in the intestine; MP abundance in the intestine increased with increasing incubation time. The total meiofauna density and species richness were significantly lower at the lowest MP concentration, while at the highest concentration these parameters were very similar to the control. In contrast, Shannon-Wiener diversity and evenness were greater in treatments with low MP concentration. However, these results should be interpreted with caution because of the low meiofauna abundances at the lower two MP concentrations. At the highest MP concentration, abundance, taxonomic diversity and community structure of a beach meiofauna community were not significantly affected, suggesting that MP effects on meiofauna are at most subtle. However, lower MP concentrations did cause substantial declines in abundance and diversity, in line with previous studies at the population and community level. While we can only speculate on the underlying mechanism(s) of this counterintuitive response, results suggest that further research is needed to better understand MP effects on marine benthic communities.

Microplastics pollution modulated by farming regimes under multi-scenarios