Microplastics in agroecosystems-impacts on ecosystem functions and food chain

The paper frames micro- and nanoplastics (MNPs) as pervasive, persistent contaminants that have received extensive attention in aquatic systems but remain understudied in terrestrial soils and agroecosystems. High plastic production and mismanagement result in significant MNPs loading in agricultural environments, where they can affect soil biota, plant growth, nutrient cycling, and potentially human health via trophic transfer. The review aims to scrutinize global literature on MNPs in agroecosystems, elucidating sources, occurrence, distribution, transport and fate, ecological risks and bioavailability, plant uptake and accumulation, and biotic responses. It underscores critical knowledge gaps that hinder accurate risk assessment and management, emphasizing the importance for food security and environmental health.

The review synthesizes studies on: (1) sources and occurrence of MNPs in soils (primary sources such as pellets, microbeads, tyre wear; secondary fragmentation of larger plastics). Reported estimates include European farmlands (63–430 thousand tons) and North America (44–300 thousand tons), and measured abundances from China (e.g., Shanghai shallow soils 78 items/kg; vegetable farmlands up to 12,560 items/kg), Mexico (0.87 ± 1.9 items/g), Australia (0.03–6.7% by content). (2) Transport and fate mechanisms (vertical leaching influenced by pore size, bioturbation by earthworms and collembola, horizontal movement by wind, runoff, irrigation, sludge/compost application). (3) Impacts on soils and biota, including altered microbial communities, enzyme activities, soil structure and GHG fluxes; plant-level effects on germination, growth, photosynthesis, and oxidative stress. (4) Plant uptake mechanisms for nanoplastics via endocytosis, symplastic/apoplastic pathways, xylem translocation driven by transpiration, and foliar/stomatal entry with phloem redistribution; size, charge, and polymer type influence uptake/toxicity. (5) Food chain transfer with bioaccumulation evidence in invertebrates, vertebrates, and human samples (stool, colectomy). (6) Effects on nutrient cycling, especially nitrogen transformations and enzyme activities, and contributions to soil carbon pools. (7) Analytical detection/quantification methods in soils (visual microscopy, micro-FTIR, Raman, GC-MS, SEM/EDX, Vis-NIR/hyperspectral), including sample preparation workflows (drying, sieving, density separation, filtration) and their strengths/limitations.

This is a narrative review synthesizing global literature on micro- and nanoplastics in agroecosystems. The authors collate reported measurements of MNPs occurrence (including tabulated data by region), summarize mechanistic and experimental studies on transport, plant uptake, and ecological effects, and critically appraise analytical detection methods used for soil MNPs (sample preparation, spectroscopic and chromatographic techniques). No primary experimental procedures or systematic search protocol are described; rather, the paper aggregates findings across published studies to identify patterns, data gaps, and management/remediation implications.

- Occurrence and sources: Global plastic production was ~335 million tons in 2016 with ~79% landfilled or mismanaged, contributing to soil MNPs. Estimated agricultural MNP loads: Europe 63–430 thousand tons; North America 44–300 thousand tons. Reported soil abundances include Shanghai shallow soils 78.0 items/kg and deep soils 62.5 items/kg; Campeche, Mexico 0.87 ± 1.9 items/g; industrial areas in Australia 0.03–6.7% MNPs. - Transport/fate: MNPs move vertically (leaching influenced by pore size, cracks, root activity) and horizontally (wind, runoff, floods, compost/sewage sludge/irrigation). Soil fauna (earthworms, collembola) facilitate redistribution via adhesion, ingestion, and excretion. - Soil and biota impacts: MPs negatively affect plant growth (e.g., lettuce growth and chlorophyll reduced by PE exposure; inhibited shoot/root growth; delayed germination due to pore blockage). Specific reports include decreased root and fruit biomass in Allium fistulosum with PP/PA/HDPE; reduced wheat growth metrics with LDPE/biodegradable MPs; tomatoes showed enhanced vegetative growth but delayed/reduced fruiting when exposed to MPs. - Microbial and enzymatic effects: Shifts in bacterial taxa (e.g., increased Acidobacteria/Bacteroidetes; decreased Deinococcus-Thermus/Chloroflexi) reported with certain MPs. MPs can form plastisphere biofilms that may harbor pathogens. Mixed findings exist, from increased microbial activity (PA/PE) to decreases (polyester/PMMA), and inhibitory effects on enzyme activities (urease, glucosidase, phosphatase) and antibiotic dissipation. - Biogeochemical cycles and GHGs: MPs increased soil CO2 emissions by ~28.67% at 18% MP concentration; PP at ~30% w/w enhanced dissolved organic matter C/N/P, increased soil respiration ~3-fold, and stimulated SOM decomposition. MPs can alter soil porosity, water/nitrate migration, pH, and C:N ratios. Effects on N2O and CH4 fluxes depend on particle type/size and soil structure changes; some studies show reduced N2O enhancement under fertilization due to MPs. - Plant uptake: Nanoplastics (e.g., PS 20–50 nm) can enter cells via endocytosis, translocate through xylem driven by transpiration, and move via phloem after foliar/stomatal entry. Size and surface charge modulate uptake and distribution; submicrometre plastics can enter via crack-entry modes. - Food chain/human exposure: Evidence of trophic transfer from soils to invertebrates to poultry (e.g., increasing MNP abundance from soil to earthworm casts to chicken feces). MNPs detected in mouse organs (liver, kidney, gut) and in human stool and colectomy specimens. Estimated annual MP intake: ~1063 particles (adults) and ~3223 (children). - Detection methods: Visual microscopy suitable for 0.5–5 mm; micro-FTIR for 20–50 μm; Raman for 1–20 μm; GC-MS provides polymer identification/quantification but destroys size/number information; SEM/EDX for morphology/composition; Vis-NIR/hyperspectral enables rapid, economical screening but limited size resolution. - Management/remediation: The review points to bio-based plastics, microbial remediation, regenerative agriculture, legislation to curb single-use plastics, and awareness campaigns as elements to mitigate MNPs in agroecosystems.

The compiled evidence demonstrates that agroecosystems are significant sinks for micro- and nanoplastics, with multiple agricultural pathways (mulching films, sludge/compost application, irrigation) contributing to inputs. Once in soils, MNPs alter physical structure, microbial community composition and function, and nutrient and carbon cycling, leading to variable but often adverse effects on plant growth and yield and potentially enhancing greenhouse gas emissions. Mechanistic insights into plant uptake (size- and charge-dependent entry via roots and leaves) indicate potential for MNP translocation into edible tissues and subsequent trophic transfer, raising food safety concerns. However, findings remain heterogeneous due to differences in polymer types, particle sizes/shapes, concentrations, and experimental conditions; many studies are laboratory-based and may not reflect complex field scenarios. The review highlights the urgent need for standardized detection and quantification protocols and comprehensive occurrence datasets to enable risk assessment, monitoring, and effective mitigation strategies in agricultural soils.

MNPs are pervasive in agroecosystems, impacting soil biota and function, plant development, nutrient cycling, greenhouse gas fluxes, and potentially human health through food chain transfer. To mitigate their impacts, the authors advocate for broader adoption of bio-based plastics, microbial/biological remediation strategies, regenerative agricultural practices, regulations limiting single-use synthetic plastics, and enhanced waste management awareness. Key future priorities include: (1) developing standardized, efficient methods for sampling, isolating, quantifying, and characterizing diverse MNPs in organic-rich agricultural soils; (2) elucidating MNPs roles as vectors for persistent pollutants and assessing cytotoxic and transgenerational effects on soil flora/fauna and humans; (3) building robust regional/global inventories of MNP concentrations, types, and transformations under varying climates and cropping systems; and (4) clarifying long-term fate, transport, and degradation pathways in soils and the rhizosphere. Behavioral changes by producers and consumers will be essential to achieve sustainable plastic waste management.

- The body of evidence on MNPs in agroecosystems is limited by sparse field data and a heavy reliance on laboratory experiments that may not capture real-world complexity (mixtures of polymers, co-pollutants, variable soil conditions). - Lack of standardized sampling, extraction, and analytical protocols complicates cross-study comparisons and accurate quantification, especially in organic-rich soils. - Occurrence and distribution data are geographically uneven, hindering global assessments and projections. - Mechanistic understanding of soil property changes (e.g., pH shifts), long-term fate and degradation, and interactions with contaminant vectors remain incomplete.