The scale of the problem begins with the sheer ubiquity of the particles themselves. Microplastics, generally defined as plastic fragments smaller than five millimeters, and nanoplastics, which measure below one micrometer, are generated through the fragmentation and degradation of larger plastic materials as well as through direct release from industrial and consumer sources. Once in the environment, these particles do not travel alone. The review emphasizes that they can interact with co-contaminants, including heavy metals and persistent organic pollutants, effectively acting as tiny rafts that concentrate other toxins. They may also alter fundamental environmental properties and biological processes in the soils where food is grown, changing the very substrate on which agriculture depends.

Plants sit at the critical interface between this environmental contamination and the food web. As primary producers, they are the first biological gate through which soil-borne plastics must pass on their way to herbivores and, ultimately, to humans. The review’s synthesis of experimental evidence indicates that both microplastics and nanoplastics can be taken up by plants through their roots, and under certain conditions through aerial tissues such as leaves. But the two size classes behave very differently. Nanoscale particles, by virtue of their diminutive dimensions, generally show a far greater potential for internalization into plant tissues and for subsequent redistribution to above-ground parts, the very portions of the plant that most often end up as food.

The technical explanation for this size-dependent behavior lies in plant anatomy. Root cell walls, with their porous structure, act as a physical sieve that excludes particles above a certain diameter while permitting much smaller particles to pass. Once inside the root, particles must navigate the endodermis, a selective barrier that normally regulates the flow of water and solutes into the vascular system. Nanoplastics small enough to breach these defenses can be transported through the xylem, the plant’s water-conducting plumbing, and deposited in stems, leaves, and fruits. This translocation pathway is what transforms a soil contamination problem into a food safety problem, because it places plastic particles directly into edible plant biomass rather than leaving them on surfaces that might be washed away.

What happens when animals consume these contaminated plants is the second half of the story, and it is here that the review is most careful to draw distinctions. Following ingestion, experimental studies indicate that nanoplastics in particular can cross biological barriers in the gut and reach tissues beyond the gastrointestinal tract. In some model organisms, exposure to these particles has been associated with oxidative stress, inflammatory responses, cellular damage, and alterations in physiological or behavioral endpoints. These findings are striking, and they have fueled viral headlines about plastics invading the bodies of virtually every organism studied. Yet the review’s authors urge restraint in interpretation, noting that the relevance of such laboratory findings to environmentally realistic exposure levels, and to human health specifically, remains uncertain.

This distinction between exposure and harm is one of the review’s central contributions. The authors place particular emphasis on separating three concepts that are often conflated in public discussion: evidence of exposure, meaning that particles are present in an organism; demonstrated trophic transfer, meaning that particles move from one organism to another through feeding; and bioaccumulation and biomagnification, meaning that particle concentrations increase within an organism or up the food chain. While plant uptake is now well supported experimentally, the extent to which plant-associated plastics subsequently undergo trophic transfer to animals under environmentally realistic conditions remains less well established. Much of the strongest evidence comes from controlled laboratory settings where particle concentrations, sizes, and polymer types may not reflect what animals actually encounter in a field or pasture.

The uncertainty stems from several interacting factors that the review dissects in detail. Particle size matters enormously, as the nanoscale fraction behaves fundamentally differently from larger microplastics. Physicochemical properties such as polymer type, surface charge, and the presence of additives and adsorbed pollutants shape how particles interact with biological membranes and immune systems. Environmental conditions, including soil chemistry, moisture, and the presence of other contaminants, influence both plant uptake and particle fate. And analytical limitations compound everything: detecting and characterizing micro- and nanoplastics in complex biological matrices remains technically difficult, and the lack of standardized methods makes it hard to compare results across studies or to distinguish genuine contamination from laboratory background noise.

The detection challenge deserves particular attention because it underpins every other conclusion in the field. Identifying plastic particles in plant roots, leaves, or animal tissue requires methods capable of confirming both the chemical identity of the polymer and the size and morphology of the particle, all at very low concentrations in matrices full of natural organic material. The review surveys the analytical approaches currently available and highlights how methodological inconsistency has produced a fragmented evidence base. Without standardized protocols, a study reporting high particle counts in one food item may not be comparable to a study reporting low counts in another, leaving regulators and the public without a clear picture of actual exposure levels in the diet.

Against this backdrop of uncertainty, the review also considers what can be done. The authors argue that improving the characterization of transfer pathways through standardized methods, environmentally realistic field studies, and interdisciplinary research spanning plant science, animal physiology, and analytical chemistry is essential for strengthening environmental risk assessment. Better science, they contend, will inform proportionate strategies for reducing plastic inputs and exposure across agricultural and terrestrial food systems. That word, proportionate, is telling. The goal is not to dismiss concern but to ensure that mitigation efforts, from reducing plastic mulch and packaging in agriculture to improving waste management, are targeted at the pathways and particle types that genuinely matter for exposure.

The broader significance of the review lies in its sober framing of a topic prone to alarm. There is no doubt that plastic particles are present in agricultural environments and that plants can take them up, with nanoplastics posing the greater internalization risk. There is also no doubt that these particles can cause biological effects in laboratory organisms at sufficient doses. What remains to be demonstrated, with the rigor that food safety policy demands, is how efficiently these particles move through real food chains, whether they accumulate to meaningful concentrations in animal tissues, and what, if any, consequences follow for human consumers. By mapping the pathways, cataloging the uncertainties, and calling for standardized and realistic research, Karimi, Seth, and Sinha have provided both a warning and a roadmap, one that acknowledges the genuine threat of plastic pollution while insisting that the next generation of studies be designed to answer the questions that matter most.

Subject of Research: Trophic transfer of micro- and nanoplastics from plants to animals in terrestrial food chains

Article Title: Pathways of micro- and nanoplastics transfer from plants to animals in the food chain

Article References: Karimi, J., Seth, S., & Sinha, R. (2026). Pathways of micro- and nanoplastics transfer from plants to animals in the food chain. Microplastics and Nanoplastics. https://doi.org/10.1186/s43591-026-00232-2

Image Credits: AI Generated

DOI: 10.1186/s43591-026-00232-2

Keywords: microplastics, nanoplastics, plant uptake, trophic transfer, food chain, food safety, bioaccumulation, soil ecosystem, ecotoxicology, risk assessment, Pathways, micro-

The scale of the underlying waste problem in Uganda provides essential context for the results. The country’s eleven major cities are home to roughly 5.5 million residents and visitors, about 12.1 percent of the national population, and this urban concentration has driven a sharp rise in solid waste generation. Kampala Capital City alone produces approximately 28,000 tons of municipal solid waste every month, a figure that has more than doubled over the past two decades. Globally, the World Bank projects that waste generation could reach 27 billion metric tons per year by 2050, and developing countries with limited collection infrastructure and low recycling rates face the steepest challenges. In Uganda, the waste stream is dominated by food scraps, paper, cloth, plastic bags and bottles, glass, medical waste, and metals, with plastics accumulating across all landfills in forms that include polyethylene, polypropylene, polystyrene, polyethylene terephthalate, polycarbonate, polyurethane, and polyvinyl chloride.

Composting has been embraced as a practical response to this mounting waste burden. By converting biodegradable material into nutrient-rich manure, composting reduces waste volume, recycles organic matter back into farmland, lessens dependence on commercial fertilizers, and improves soil quality. The technology adopted at Ugandan landfill sites is conventional and simple, consisting mainly of open windrows in which mixed waste is left to decompose. The trouble is that very little of the incoming waste is segregated. Only three of the eleven sites studied, Mukono, Lira, and Fort Portal, perform any manual pre-treatment to remove non-compostable materials before composting begins, and even that removal is incomplete. When plastic-laden mixed waste enters the windrows, mechanical weathering, oxidation, and photocatalytic breakdown progressively fragment the larger plastic items into microplastics, defined as synthetic polymer particles smaller than 5,000 micrometers.

To quantify this contamination, the research team designed a sampling campaign that controlled for both spatial and temporal variability. All samples were collected during a single two-week window in the dry season of June 2025. At each site, three mature compost piles were independently sampled, with each pile divided into top, middle, and bottom sections sampled at a depth of 5 to 15 centimeters using a stainless-steel shovel. The sections were homogenized, and material from the three piles was combined into a single composite sample of 300 grams per site, which was then sieved through a 5-millimeter stainless-steel mesh, sealed in airtight paper bags, and transported in a cool box to the laboratory. Compost maturity was verified before analysis: every sample exceeded a germination index of 70, showed a carbon-to-nitrogen ratio below 20, total nitrogen below 3.0 percent dry weight, and a pH between 7 and 9, confirming that the material analyzed was genuinely finished compost rather than raw waste.

The laboratory extraction followed an adapted wet peroxide oxidation protocol. Twenty grams of sieved, oven-dried compost were digested with Fenton reagent, a mixture of 20 milliliters of 30 percent hydrogen peroxide and 20 milliliters of 0.05 molar acidified ferrous sulphate, heated to approximately 75 degrees Celsius in a laminar flow fume hood until the organic matter disappeared. Density separation followed, using a saturated zinc chloride solution at 700 grams per liter with a density of 1.7 grams per cubic centimeter. After an hour of settling, the supernatant was filtered through a glass microfiber filter with an 11-micrometer pore size, and the captured particles were air-dried for three to four days before examination under a ZEISS Stemi 508 stereomicroscope fitted with an Axiocam 208 color camera. The researchers distinguished genuine plastic from natural particles using the hot needle and break tests, and rigorous quality controls, including blank tests with distilled water, non-plastic sampling equipment, cotton lab clothing, and glassware cleaned three times with distilled water, confirmed that no contamination was introduced during handling. Statistical comparisons across sites used a one-way ANOVA followed by Tukey’s HSD test at a significance threshold of 0.05.

The results painted a picture of pervasive but uneven contamination. Hoima’s compost site exhibited the highest microplastic abundance, more than double the eleven-site average, and was identified as a statistical outlier, significantly exceeding Jinja (p = 0.030), Mbale (p = 0.013), Soroti (p = 0.012), Kabale (p = 0.010), and Fort Portal (p = 0.0027). Jinja, which deploys an advanced Komptech Cribus 3800 mobile screening machine for post-composting processing, recorded a high abundance of 3,050 ± 304.63 particles per kilogram with relatively low variation, suggesting that mechanical screening without upstream segregation may actually break plastics down further and distribute them through the compost. At the low end, Mukono (1,250 ± 312.77 particles/kg) and Kasese (1,300 ± 316.58 particles/kg) showed statistically indistinguishable levels (p = 0.86), while Gulu and Hoima displayed the greatest variability, pointing to intermittent plastic inputs. The Ugandan average sits close to figures reported elsewhere: 2,400 ± 358 particles per kilogram in rural domestic waste compost in Zhejiang Province, China, and 2,800 ± 616 particles per kilogram in municipal organic waste compost in the Netherlands.

Perhaps the most telling result concerned particle shape. Fibres dominated at every site, accounting for 54.98 percent of all identified microplastics, followed by pellets at 15.37 percent, fragments at 15.15 percent, films at 6.06 percent, filaments at 5.41 percent, and foams at just 3.03 percent. Fibrous particles are strongly associated with synthetic textiles, ropes, and sacks, and Soroti’s profile was almost entirely fibrous, suggesting a single dominant source such as woven packaging material. Pellets, which are industrially manufactured primary microplastics often used in personal care products, featured prominently in Jinja, Fort Portal, Gulu, and Mbale. Fragments arise from the degradation of hard plastics such as high-density polyethylene, while films trace back to plastic bags and food packaging. The overwhelming presence of secondary microplastics, particles formed by the breakdown of larger plastic items, led the authors to conclude that poor waste management and inadequate segregation practices are the root cause of the contamination, rather than any single industrial source.

The environmental implications extend well beyond the compost pile itself. Previous research has shown that microplastics alter soil physical properties, including porosity, water-holding capacity, structure, and bulk density, and that polypropylene additions to loess soils can raise concentrations of nitrogen, phosphorus, and dissolved organic matter. Microplastic surfaces also adsorb hydrophobic organic compounds and heavy metals, acting as vectors that transport toxic chemicals through soil, and they can host distinct microbial communities that facilitate the spread of pathogens. Because compost is applied directly to farmland, the particles it carries enter the soil-plant system, where they may influence crop growth rates and nutrient uptake. Studies in both China and Europe have further demonstrated that the composting process itself can increase microplastic abundance by fragmenting larger plastics, with one study recording a rise from 5,133 particles per kilogram in raw material to as much as 11,200 particles per kilogram in finished compost, which helps explain why even screened compost retains substantial plastic loads.

The human health dimension adds urgency to the findings. Microplastics in compost can enter the food chain, and growing research interest now focuses on how these particles are absorbed, distributed, metabolized, and excreted in the human body. Continuous exposure has been linked to inflammation, and microplastics are suspected of interfering with metabolic processes. The authors of the Ugandan study acknowledge important limitations, including the compositing of three piles into a single site-level sample, which prevented assessment of within-site variability, the reliance on stereomicroscopy and the heated needle test rather than advanced techniques such as micro-Raman spectroscopy, FTIR, or pyrolysis-GC/MS for polymer verification, and the absence of recovery-efficiency testing. They also note the lack of standardized protocols for microplastic sampling and extraction. Even so, the central message is unambiguous: compost from municipal solid waste sites across Uganda is considerably contaminated with microplastics, and the most effective remedy lies upstream. Enhancing source segregation at the household and municipal levels, the researchers argue, would reduce the plastic entering composting facilities in the first place and lower microplastic concentrations in the final product applied to the nation’s farmland.

Subject of Research: Microplastic contamination of compost produced from municipal landfill waste in Uganda

Article Title: Identification and quantification of microplastics in compost from municipal landfills in Uganda

Article References: Tumwebaze, A., Twinomujuni, D., Baluku, E., Ogwal, F. S., Akankwasah, B., & Komakech, R. (2026). Identification and quantification of microplastics in compost from municipal landfills in Uganda. BMC Environmental Science, 3(1), Article 22. https://doi.org/10.1186/s44329-026-00064-8

Image Credits: AI Generated

DOI: 10.1186/s44329-026-00064-8

Keywords: microplastics, compost, Uganda, municipal solid waste, landfills, waste management, soil contamination, food chain, plastic pollution, composting, environmental science, zinc chloride density separation