Gaps between Laboratory Experiments and Real-World Exposure: Toxicological Assessment of Microplastics Is Based on Inadequate Evidence

Abstract

The global significance of microplastic (MP) toxicity assessment is widely acknowledged. Current studies have enhanced our understanding of the mechanisms behind MP toxicity; however, most research mainly focused on the toxicity of individual MPs, overlooking the environmental complexity that arises from the diversity of MPs and the combined effects of multiple pollutants. Furthermore, a notable gap exists in research concerning low-dose and long-term exposure, which significantly limits the relevance of current toxicity data for risk assessments. To address these challenges, we suggest a more thorough and logical approach to evaluating MP toxicity, including: enhancing the harmonization of methods for detecting and quantifying MPs in various environmental and biological matrixes; leveraging AI to simulate real environmental exposures and to predict the complex interactions between MPs and other environmental factors; and combining insights from environmental science, toxicology, materials science, and other relevant fields to bridge the gap between laboratory findings and real-world conditions. Collectively, these efforts could transform fragmented data into risk intelligence, delivering actionable governance solutions for global MP challenges.

1. Introduction

The ubiquitous presence of microplastics (MPs) both in the environment and in the human body has raised global concerns about their adverse health effects (e.g., on the digestive, nervous, and cardiovascular systems) − (Figure ). Mounting toxicological evidence suggests that MPs can induce oxidative stress, inflammatory responses, and even neurotoxicity. − Notably, recent epidemiological studies have begun to establish direct correlations between MP exposure and human health risks; for instance, the presence of MPs in arterial plaques has been associated with a significantly increased risk of cardiovascular events. This convergence of toxicological and epidemiological findings underscores the critical importance of obtaining reliable hazard assessment data.

1.

Sources, detection methods, and environmental behavior of MPs.

However, a considerable portion of laboratory studies differed significantly from real-world exposure, which involves impractical doses, an idealized single-component exposure scenario, and an insufficient exposure period. ,, Consequently, the experimental data underpinning current risk assessments may fail to capture the true extent of the hazards, thereby impeding the formulation of robust policies to safeguard public health. Closing this gap is an urgent priority for both policymaking and risk assessment.

While the existence of a lab-field gap in MP toxicology is widely acknowledged in the literature, a comprehensive, quantitative assessment of its specific dimensions and a correspondingly innovative framework to address it are still lacking. Many reviews have qualitatively discussed the limitations, but few have systematically quantified the prevalence of these discrepancies across a large body of primary research or proposed integrated, practical solutions that leverage cutting-edge technological advancements.

In this study, we presented and discussed research findings by elaborating on the methodologies of systematic literature reviews and meta-analyses, which quantitatively reveal key gaps in current experimental designs. Subsequently, we proposed an innovative framework outlining strategic pathways to enhance environmental relevance, develop advanced behavioral simulation and toxicity assessment models, implement intelligent analysis, and leverage in situ characterization. Finally, the conclusion section summarizes core findings and outlines future directions to advance this field.

In order to elucidate this issue, this paper provides a comprehensive critique of the gap between laboratory and real-world toxicity assessments for MPs, proposing an innovative testing framework. By integrating toxicity assessment methods with interdisciplinary advances in analytical chemistry and artificial intelligence (AI), this work aims to close the gap between the intrinsic complexity of environmental systems and the normative imperatives of regulatory science.

2. Key Gaps between Laboratory Research and Real-World Exposure

2.1. Current State of MP Toxicological Research

The widespread detection of MPs in the human body has raised many concerns about their toxicity. The widely recognized mechanisms through which MP toxic exert effects can be summarized as follows: (1) The potential adverse effects are thought to be associated with the monomers and additives (added during the production or processing of plastics) released during plastic fragmentation, some of which have exhibited toxicity, carcinogenicity, or endocrine-disrupting properties. − (2) Oxidative photodegradation of plastic debris, which may result in the formation and release of harmful volatile organic compounds. (3) MPs can absorb persistent organic pollutants (POPs) and/or toxic metals from the environment and serve as vectors for pathogenic and/or antibiotic-resistant organisms microorganisms. (4) MPs at the nanoscale have toxic effects due to the ultrahigh reactivity caused by their huge specific surface area. −

However, as critical bridging evidence, current MPs’ epidemiological data are based on correlation analysis, making it difficult to establish a direct cause of morbidity (dementia cases, cardiovascular events, and inflammatory bowel disease (IBD)). ,, An epidemiologic link between MPs and human health has been shown for the first time in 2024, revealing that patients with MPs in the aorta were 4.5 times more likely to have a heart attack, stroke, or death rate than patients with no MPs found in the aorta. Another study analyzing MPs in human feces showed a correlation between fecal MPs and IBD status. , It was found that MP concentrations in the brain increased over time, higher than in the liver and kidneys. In addition, people with dementia had significantly higher concentrations of MP in the brain than people without dementia. The positive correlation between MPs in the human body and disease states suggests that exposure to MPs may be associated with the disease process or that disease may exacerbate the retention of MPs (Figure A). Nevertheless, epidemiological detection of MPs in human samples faces dual challenges: pervasive contamination risks (from clinical sampling to lab analysis), causing false positives, and technical limitations in identifying submicron/degraded particles at low concentrations within biological matrices, compromising data reliability. Future biomonitoring requires standardized ultraclean protocols (e.g., nonplastic tools and blanks), tissue-specific methods coupled with cross-validated analytical techniques (e.g., Raman and pyrolysis GC-MS), mandatory reporting of quality controls (including blanks and recovery rates), and international guidelines for exposure assessment accuracy.

2.

MP size distribution, formation processes, and human health implications. (A) Detection and toxic effects of different sizes of MPs in the human body; (B) human exposure pathways and hazards of MPs; (C) the relationship between particle size distribution and particle formation processes. Smaller particles are formed through the fragmentation and erosion of larger particles, while larger particles are removed through erosion, size-dependent transport, and sedimentation, resulting in a higher abundance of smaller particles. Reproduced from ref .

In terms of toxicological studies, MPs are considered to induce various toxic effects, including neurotoxicity, oxidative stress, and inflammation based on laboratory experimental results (Figure B). , Zhang and Jin et al. found that MPs can be internalized by cells, directly causing a significant increase in intracellular ROS levels and promoting the gene expression of the inflammatory factor TNF-α. , This confirms at the cellular mechanism level that MPs can induce oxidative stress and inflammatory responses. No doubt that early studies not only provided foundational data for assessing the toxicity of MPs exposure but also pointed the way forward for research.

While MP polymers are generally considered to be biochemically inert, incomplete polymerization reactions typically leave unreacted residual monomers in the polymer materials at concentrations of 0.01%–4%, some of these can be harmful to human health and the environment (Table ). ,, It is reported that the toxicity of MP is primarily related to the preservative rather than the particles themselves. The acute toxicity of MP can be greatly reduced if the additive is extracted before organisms are exposed to it. In addition to preservatives, solvents, suspension aids, surfactants, initiators, catalysts, and other polymerization additives in polymers are also hazardous. The solvents used in polymer production, such as benzene, hexamethylphosphoramide, and N-methyl pyrrolidone, are classified as causing mutagenicity or reproductive (CMR) toxicity. However, most additives, such as initiators, catalysts, chain transfer agents, and suspension aids, are usually added at very low levels (<2 wt %), resulting in limited dissolution and reduced potential health effects due to human intake.

1. Ranking of MP Polymer Types Based on Hazard Classifications of Monomers .

Polymer	Hazard Level	Monomer 1 (wt %)	Monomer 2 (wt %)	Monomer 3 (wt %)
HDPE	II	Ethylene (100 wt %)
LDPE	II	Ethylene (100 wt %)
PP	I	Propylene (100 wt %)
PS	II	Styrene (100 wt %)
PVC	V	Vinyl chloride (50 wt %)	Benzyl butyl phthalate (50 wt %)
PC	IV	Bisphenol A (70 wt %)	Phosgene (30 wt %)
PET	II	Ethylene glycol (37 wt %)	Terephthalic acid (63 wt %)
PMMA	IV	Methyl methacrylate (100 wt %)
Nylon-6.6	III	Adipic acid (56 wt %)	Hexamethylenediamine (44 wt %)
Nylon-6	II	ε-Caprolactam (100 wt %)
Nylon-6.10	III	Sebacic acid (63 wt %)	Hexamethylenediamine (37 wt %)
Nylon-11	NC	11-Aminoundecanoic acid (100 wt %)
Nylon-12	NC	Lauryl lactam (100 wt %)
PUR	V	Propylene oxide (58 wt %)	Ethylene oxide (7 wt %)	Toluene-diisocyanate (29 wt %)

^aHDPE: high-density polyethylene; LDPE: low-density polyethylene; PP: polypropylene; PS: polystyrene; PVC: polyvinyl chloride; PC: polycarbonate; PET: polyester; PMMA: poly­(methyl methacrylate); PUR: polyurethane; wt %: percentage by weight; NC: not classified.

^bThe hazard level is divided into five levels (I–V), with each level representing a 10-fold increase in hazard severity (V being the most hazardous level).

In conclusion, before achieving a comprehensive risk assessment of MPs on human and ecosystem health, the critical knowledge gaps between controlled experimental models and the real-world environment must be bridged. Significant challenges persist across experimental design, the extrapolation of findings, and the depth of scientific understanding.

2.2. Gaps of the Existing Experiment Paradigm

We conducted a systematic literature search following PRISMA guidelines (Figure A). We searched Web of Science Core Collection, Current Contents Connect, MEDLINE, Research Commons, Chinese Science Citation Database^SM, and SciELO Citation Index (search conducted on December 1, 2025). Our search string, combining synonyms with “OR” and main elements with “AND,” was: (“microplastic” OR “nanoplastic”) AND (“toxicity” OR “adverse effect”) AND (“environmental relevant*” OR “environmentally realistic” OR “mismatch*” OR “research gap*”). The studies were selected based on these criteria: (1) original research (not reviews or perspectives); (2) exposure to MPs with toxicity end points; (3) exposure to known-component MPs samples; (4) including the physicochemical parameters of MPs; (5) including in the “microplastic-free” control group; (6) simulated real-world exposure. For studies included in the literature review, the following information was extracted: (1) publication details; (2) animal/cell models exposed; (3) type of MPs; (4) microplastic sizes; (5) exposure concentrations; (6) exposure duration; (7) end point outcomes; (8) method of simulating real-world exposure. When a measure had more than one exposure design, it was categorized into distinct groups. To investigate the gaps associated with extrapolating laboratory results to real-world environments, each study was categorized based on the types of MP polymer used for exposure, exposure duration, MP size, model organisms, and the method used to simulate environmental exposure. The initial search yielded 247 documents. After excluding duplicates, documents with titles or abstracts unrelated to the topic, and review articles, 88 research papers were ultimately included in this study (Supporting Information).

3.

Meta-analysis of exposure experiments in simulated environmental MPs. (A) PRISMA flowchart showing publication selection procedure; research characteristics encompass exposure concentrations (B), polymer types, exposure durations, particle sizes, model organisms, and methods of environmental simulation (C).

2.2.1. Toxicity Assessment

Meta-analysis reveals considerable disparities between current MP toxicity experiments and real-world exposure conditions (Figure C). Experimentally, polystyrene (PS) is heavily overrepresented (46.67% of studies), despite the complex and diverse composition of environmental MPs. Furthermore, 64.21% of studies employ short-term exposures (0–21 days), overlooking the long-term, continuous nature of environmental MP exposure and its potential chronic effects. − Although research tends to focus on small-sized particles (0–10 μm), environmental MPs display a much broader size distribution. Model organisms are also biased toward insects/arthropods (30.68%) due to their laboratory convenience, which limits the generalizability of findings across ecosystems. While 44.32% of studies attempt to simulate real-world concentrations, laboratory settings often fail to replicate key environmental complexities such as coexposure to other pollutants and MP aging. These gaps underscore the need for future work to employ environmentally relevant MP mixtures, longer exposure durations, and multispecies designs to improve ecological realism.

MP toxicity is closely linked to bioavailability, which is influenced by polymer properties, size, shape, surface chemistry, additive composition, and weathering. However, the prevailing use of idealized MP models, particularly pristine PS spheres, limits the practical relevance of much current data. , For MPs tracing, fluorescently- or metal-labeled sphere particles were widely used. By contrast, environmental MPs exist as heterogeneous mixtures, whose behavior and toxicity likely differ significantly from those of laboratory-grade PS. , Particle shape also affects bioavailability; irregularly shaped MPs can show increased tissue penetration and induce stronger oxidative stress, synergistically enhancing cytotoxicity and systemic toxicity. , As of now, only a limited number of studies have used environmentally realistic, irregular MPs, leaving important questions about the combined effects of size, shape, and adsorbed pollutants on bioavailability largely unresolved.

Uncertainty also persists regarding exposure routes and doses. Although dietary intake, inhalation, and other pathways are widely discussed, actual MP intake appears relatively low. For example, estimated daily MP intake is 184 ng for children and 583 ng for adults, representing only ∼0.001% of total particulate intake from the diet. − Furthermore, other exposure routes are considered minor but are poorly quantified. Moreover, as MP toxicity research has expanded, so has controversy over its mechanisms. While MPs are generally regarded as inert and too large to cross biological barriers easily, studies have reported MPs up to 26.4 μm in brain tissue, contradicting models suggesting only subμm particles can traverse such barriers. − This inconsistency highlights unresolved questions regarding how larger MPs enter tissues and how their bioavailability is shaped by physical and chemical transformations in the environment.

Another major challenge is the lack of well-defined, environmentally relevant concentration thresholds for MP exposure experiments. As noted in Nature, some toxicity data may lack biological significance due to experimental artifacts. Contamination during sampling and analysis, despite precautions such as cotton coats, plastic-free workflows, and heat-treated glassware, remains a concern, especially when plastic-based instruments are used. Without standardized protocols and quality control, environmental MP concentration data vary widely, complicating cross-study comparisons and limiting their utility as benchmarks for toxicological studies.

Regardless of the medium or research system (aquatic environment, soil, sediment), laboratory concentrations are tens or hundreds of times higher than maximum environmental concentrations (in terms of number concentration or mass concentration), indicating this is a common feature in current toxicological research. The results of such high-concentration exposure experiments have limitations when directly extrapolated to assess real-world environmental risks. They may fail to accurately predict the sublethal effects that organisms may experience under long-term, low-dose environmentally relevant concentrations, effects that are equally critical to population and ecosystem health. , Experimental doses of MPs ranging from 10² to 10⁷ times higher than actual environmental levels were found to be employed (Figure B and Table ). It is worth noting that studies suggested that adverse effects in biota were rarely shown at environmentally relevant concentrations of MPs. This discrepancy underscores the critical need for future studies to adopt exposure levels that accurately reflect real-world conditions. , Compared with well-documented nanotoxicology research, which exhibits relatively higher environmental relevance in its high-dose designs, the employed concentrations in MPs research remain effect-relevant rather than environmental-relevant.

2. MP Concentrations Measured in the Environment and Concentrations Used in Experimental Studies .

MP Type	Typical Environmental Concentration	Environmental Medium	Common Experimental Concentration	Reference
PS		Blue mussel	100–200–300 mg/L
PS		ICR mice	1.5 × 105 particles/m3
Aged PS		Mouse monocyte macrophages (RAW 264.7)	1–100 mg/L
Particles, HDPE		Blue mussel	2500 mg/L
PET		Pacific white shrimp	1–100 mg/L
PE		Kale	1% (w/w)
PS, PP, PMMA		Primary rat microglia	1–100 mg/L
Fragments, lines, films spheres	0.073 mg/L	South Pacific Gyre
Pellets, flakes, spherules	0.697 mg/L	Danube
Particles, fibers	10–9000 particle/m3	Wastewater treatment plant effluent in Germany
Sheets, fibers, fragments, foam	50–1292 particle/m2	Sediments in Qinghai Lake, China
PE, CP, PET, PVA, rayon, PS, PAM, PCT, PA, PBT, PMP, PP, PSR, PDP, PSF, and PCL	0.05 ± 0.09 and 0.06 ± 0.10 items/g	Fish in Yellow Sea and East China Sea

^aPS: polystyrene; HDPE: high-density polyethylene; PET: polyester; PE: polyethylene; PP: polypropylene; PMMA: poly­(methyl methacrylate); CP: cellophane; PVA: poly­(vinyl alcohol); PAM: polyacrylamide; PCT: poly­(1,4-cyclohexanedimethylene terephthalate); PA: polyamide; PBT: poly­(1,4-butylene terephthalate); PMP: poly­(4-methyl-1-pentene); PSR: polysulfide rubber; PDP: poly­(diallyl phthalate); PSF: polysulfone; PCL: polycaprolactone.

Besides exposure concentrations, the morphology of MP is also a crucial factor to investigate. Naturally formed MPs exhibit irregular shapes, coexist with particulate fiber fragments, span a wide range of sizes, and have rough and smooth textured surfaces that are interspersed and highly irregular. However, current discourse on MP toxicity relies on standardized materials (e.g., spheres with uniform dimensions), which differ from the actual morphology of MP in real-world environments, resulting in limitations in the conclusions drawn from experimental studies. , While some studies have used aged or milled MPs to better approximate environmental conditions, standards that match real environmental MPs are still lacking. , Notably, with the rapid advancement of AI methods in the fields of morphological recognition and toxicity prediction, constructing multidimensional, high-precision morphology-toxicity correlation models is becoming feasible, offering new pathways to overcome current research bottlenecks. Even in studies using ground plastic pellets, the area-equivalent diameter is often used as the primary parameter to indicate toxicity potential. However, fibers and fragments of identical equivalent size may exhibit markedly different toxicities, with the former typically demonstrating greater toxicity. Several studies have shown that shapes with higher aspect ratios and sharper angular features are more likely to adhere to and be internalized by cells. − As a result, the reality is that for irregularly shaped particles, the key parameters influencing their toxic effects remain unclear.

2.2.2. Impact of MPs’ Environmental Behavior on Their Toxic Effects

MPs’ environmental behaviors contribute to the toxic effects. Photo-oxidation of plastic fragments by solar ultraviolet radiation makes plastics susceptible to fragmentation, which is considered the primary mechanism for plastic degradation. The process of photo-oxidation of plastic debris is accompanied by the release of toxic volatile organic compounds (VOCs), including carbonyl compounds, lactones, esters, acids, alcohols, ethers, aromatics, and other substances. While no studies have measured the amount of VOCs produced during light aging of plastic debris in real environments, nor do single VOCs pose a significant human health risk, it can be surmised that subchronic exposure to mixtures of VOCs may be harmful due to additive interactions between chemicals belonging to the same functional group. It is worth noting that different types of plastics release characteristic toxic substances during environmental degradation: thermal degradation of chlorinated plastics such as polyvinyl chloride (PVC) releases hydrogen chloride, release of hydrogen fluoride from fluorinated plastics such as polyvinylidene terephthalate (PVT) through a chain-stripping mechanism, and nitrogen-containing plastics such as polyacrylonitrile, nylon, and polyurethane can lead to the release of hydrogen cyanide.

MPs leachates refer to plastic additives, depolymerization products, and their interaction derivatives. When processed into the final plastic product, plastic polymers are blended with various additives to improve their properties, such as heat stabilizers, flame retardants, light stabilizers, plasticizers, antioxidants, lubricants, antimicrobials, pigments, antistatic, and fillers. These low molecular weight nonpolymeric additives attached to plastic polymers are either loosely bonded or not bonded to the plastic macromolecules at all, so they are leached from plastic compounds into the surrounding environment (including air, water, or food) and can accumulate through biomagnification.

MPs can also function as environmental vectors since they can absorb and transport various environmental pollutants, including metals, antibiotics, and microorganisms, a phenomenon often referred to as the “Trojan horse” effect. Both endogenous and exogenous contaminants attached to MPs have been identified as major effectors, , though their overall hazard potential remains limited unless with a high hazard score. Various chemical contaminants, such as polycyclic aromatic hydrocarbons (PAHs), dichlorodiphenyltrichloroethane (DDT), chlorinated benzenes, and BHC, have been characterized as having high adsorption capacity to plastics. Polychlorinated biphenyls (PCBs), POPs, organ halogenated pesticides (OHPs), nonylphenols, and metals were also detected in stranded plastic pellets. Quantitatively, about 300 μg/g Fe, Al, Pb, Cu, Zn, and up to 80 ng/g Co, Cr, Cd, Ni were detected adsorbed to plastic polymers. Machine learning predictions demonstrated that polyamide (PA) showed the highest adsorption capacity for commonly studied heavy metals such as Pb, Cd, Cu, and Cr, which was mainly attributed to the presence of CO and NH groups. MPs can adsorb metal cations more effectively, with Pb showing the most significant adsorption. The main factors affecting the adsorption of heavy metals onto MP were concentration, specific surface area, and pH. In addition, surface complexation and electrostatic interactions are the main mechanisms of Pb and Cd adsorption, where surface functional groups are the main factors influencing the mechanism of MPs.

2.2.3. Inconsistent Data of the MPs’ Bio-Occurrence

Since accurately assessing the true level of human exposure to MPs is still debated, it is challenging to conduct experiments that simulate real-life exposure in vitro. Currently, commonly used analytical methods include Raman and FTIR spectroscopies, pyrolysis and thermal desorption gas chromatography, imaging techniques, etc. − The advantages, disadvantages, limitations, and applications are summarized in Table . There is still a lack of standardized processes for MP quantification, including standardized methods for sampling, extraction, characterization, and quantification.

3. Methods for Identification and Quantification of MPs .

Method		LOD	Advantages	Disadvantages	Sample Types	Reference
1. Optical identification methods	Naked eye	≥1 mm	Simplest and cheapest method	Not suitable for laboratories or risk assessments	Lake water and sediments
	General light microscopy	≥100 μm	Wide range of applications	Unrecognized polymer type	Wastewater, sludge, sediment, and biosample
	Dye staining	≥6.5 μm	Efficient counting of small MPs	False positive results	Wastewater and biosample
	Flow cytometry	500 nm	Analyzing MPs size, quantity, and distribution	Expensive instrumentation	/
2. Chemical analysis methods	FTIR	10–20 μm	Chemical identification	Sample preparation is mandatory	Water, sludge, sediment, and biosample
	Raman qualitative	≥1 μm	Provides information on MPs type, particle number, size distribution and morphology	Laser light damage to MPs	Water, sludge, sediment, and biosample
3. Thermal degradation methods with GC-MS detection analysis	Py-GC-MS	∼1 μg	Individual polymer particle analysis	Consumption time for single particle preselection	Surface water and biosample
	TED-GC-MS	1 wt %	Simultaneous polymer identification and quantification in complex samples	Vulnerable to interference by residual organic matrix compounds	/

^aFTIR: Fourier transform infrared spectrometer; Py: pyrolysis; TED: thermo-extraction and desorption; GC-MS: gas chromatography–mass spectrometry; LOD: limit of detection; wt %: percentage by weight.

First and foremost, the representation of MP amounts (number concentrations) differs significantly from mass fluxes (mass concentrations). Differences between quantitative and qualitative MP concentrations significantly interfere with the accuracy of toxicity assessments: the split between quantity-dominant risks (e.g., small-sized particles) and quality-dominant risks (e.g., chemical toxicity) leads to mechanistic misclassification. Nanoscale particles (<1 μm) account for more than 99% of the particles in the environment, and their high specific surface area can adsorb/release large quantities of pollutants and penetrate biological barriers (Figure C). Still, due to their extremely low single-particle mass (e.g., 100 nm PS particles with a mass of only 0.05 pg), mass–concentration-based toxicity experiments (e.g., 100 μg/L) need to introduce trillions of particles, which is much higher than the actual exposure level (typically <10⁶ particles/L), leading to experiments that overestimate chemical toxicity and underestimate physical damage. In contrast, millimeter-sized particles, although high in mass percentage, are sparse and low in bioaccessibility, and reliance on mass concentration assessment may mask the true risk of physical obstruction (e.g., intestinal sludge). A study developed a rapid mass transformation method for different shapes of environmental MPs. However, the accuracy and comparability of some studies’ data are questionable, highlighting an urgent need to standardize testing methods in the future.

Meanwhile, MP contamination poses a major challenge in the analytical process of human tissue research. MP contamination may be introduced at almost every step of the process, including sampling, transportation, storage, handling, and analysis. Of particular concern is the widespread use of plastics in clinical settings, which may introduce MP directly into human blood. A key methodological challenge is that modern laboratories are themselves significant sources of contamination of MPs, and it is difficult to recognize experimental contamination with existing detection techniques. To enhance the quality of the study, it is recommended that standardized procedures be adopted throughout the sample collection to analyze and reduce the risk of contamination and quantify the uncertainty of the results by setting up multiple controls.

Research on MPs focusing on the quantification of human exposure pathways and the characterization of tissue distribution is developing fast. Advances in high-resolution analysis and in situ tracking techniques, such as single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) and near-infrared two-region (NIR-II) in vivo imaging, , have enabled highly sensitive detection and real-time dynamic tracking of MPs at the nanoscale. Leveraging SP-ICP-MS for nanoscale imaging and molecular tracking further enables the localization of MPs at the vascular plaques, neuronal cells, and other subcellular levels.

Furthermore, the integrated solution consisting of different methods is gradually gaining recognition for the detection of MP. The combination of pyrolysis gas chromatography–mass spectrometry (Py-GC/MS) with spectroscopic or microscopic techniques serves as a key method for the detection of MPs in biological samples, enabling comprehensive toxicological assessments in epidemiological studies. Notably, regarding the highly concerning issue of nanoplastics (NPs), Py-GC/MS demonstrates superior reliability. However, the Py-GC/MS assay has its limitations. First, residual impurities in samples may interfere with analysis. Second, pyrolysis of nonplastic substances can produce compounds that indicate the presence of plastics, which can interfere with experimental results. For example, fatty acids (e.g., triglycerides) can break down into the same compounds PE.

2.2.4. The Distinctive Case of Biodegradable MPs: A Promise with Potential Pitfalls

Biodegradable plastics (BPs), which include both biobased polymers and petroleum-based varieties, are increasingly promoted for their ability to degrade via microorganisms, offering environmental benefits, thereby reducing plastic pollution and dependence on fossil resources. They are widely adopted in sectors such as medicine, automotive manufacturing, and packaging. , However, despite their green reputation, BPs are more likely to degrade into MPs and release additives, which may have similar or even worse impacts than MPs. Moreover, biodegradable microplastics (BMPs), which are produced by the degradation of biodegradable plastics, possess rougher and more complex surface morphologies, which enhance their potential to inflict mechanical damage on organisms and facilitate further fragmentation, all of which may trigger cascading adverse effects. , Toxicity studies indicate that high concentrations of PLA-derived MPs can induce significant oxidative stress and alter gene expression in vital organs. Comparative analyses also suggest that degradable MPs may pose a higher global risk of antibiotic resistance than nondegradable ones, partly due to the enrichment of multidrug resistance genes. Evidence from earthworms also demonstrates the greater acute toxicity of biobased fibers at high concentrations. Given that PLA-MPs demonstrate lipid metabolism disruption and toxicity comparable to conventional MPs, future regulatory approaches must prioritize the development of targeted testing standards and establish precautionary safety evaluations for biodegradable plastics to safeguard ecosystem health adequately.

Currently, BMPs share research gaps with conventional MP, including the absence of a systematic toxicity assessment framework and insufficient data on long-term and low-dose exposure effects. However, BMPs also face unique challenges, particularly the critical issue of unclear mechanisms linking degradation behavior to toxicity. Although BMPs and MP share similarities in physical toxicity effects and pollutant carrier functions, the degradable nature of BMPs, along with the release of chemically toxic substances and the dynamic environmental behavior changes that accompany this process, makes their toxicological characteristics more complex.

3. Strategies to Bridge the Gaps

Key gaps between laboratory and real-world exposure conditions undermine the reliability of experimental results. In laboratories, the most popular experimental paradigm employs high doses of single pollutants, such as PS microspheres, using traditional models like cell lines and model animals. Real-world environments, however, highlight complex factors including UV-induced degradation, irregularly shaped MPs, copollutants, and authentic exposure pathways, emphasizing low-dose, long-term exposure, and multisystem interactions. To bridge these gaps, it is essentialthough not sufficientto deploy state-of-the-art resources such as certified MP reference materials, standardized analytical protocols, high-resolution computational models, and next-generation bioassay platforms (Figure ).

4.

Bridging the gaps: a framework for assessing real-world MP risks.

3.1. Research Driven by Environmental Relevance

Environmental relevance primarily refers to the use of MPs derived from real environmental samples or those subjected to natural weathering, with exposure concentrations that span environmentally realistic levels and exposure durations that are sufficiently long to capture ecologically significant effects. Future toxicological studies on MPs must be grounded in practical environmental relevance to provide data and reliable recommendations for environmental management policy formulation.

The use of MPs that closely approximate the physical and chemical states encountered in natural environments is fundamental to ensuring the reliability of their toxicological and environmental behavior research results. Chen et al. identified potential health risks associated with dietary exposure to irregular PS-MPs at environmentally relevant doses. Nevertheless, the MP-related reference materials are still dominated by monodisperse spherical particles. Irregularly shaped MP reference materials, which serve as an efficient tool for analysis and toxicity evaluation, remained in the developing stage. Currently, the International Organization for Standardization (ISO) and major metrology institutes, such as the Bundesanstalt für Materialforschung and -prüfung (BAM), the National Institute of Standards and Technology (NIST), and the National Institute of Metrology of China (NIM), are gradually establishing a systematic preparation and application system. The most popular products available are MPs with controllable particle sizes (1 μm–5 mm) prepared by the mechanical pulverization-screening method and the precipitation method (Figure ). Functionalized treatment processes such as surface oxidation modification, pollutant loading, and biofilm coating have been developed to meet the needs of complex environmental simulations. In the coming future, developing reference materials with clear environmental relevance, including those with shapes, concentrations, and sizes more closely aligned with actual environmental conditions, and applying them in environmental monitoring and toxicity assessment experiments, represents an effective technical approach to address the current lack of environmental relevance in research.

5.

Preparation and characterization of the MPs reference material. (A) mechanical grinding workflow; (B) SEM images and microfluidic imaging results of PS MPs prepared by mechanical grinding; (C) precipitation method workflow; (D) microfluidic imaging results of PS MPs prepared by precipitation method.

Given the chemical inertness and widespread distribution of MPs, conducting long-term low-dose exposure experiments to investigate their combined toxicity mechanisms is of significant importance. A study introduced an MNP exposure protocol that incorporates particle-specific properties and dynamic behavior. It includes a top-down synthesis of environmentally relevant MNPs, characterized via techniques such as thermal extraction desorption–GC/MS, along with adapted exposure systems for short- and long-term toxicity tests in soil and aquatic organisms, based on modified chemical ecotoxicity guidelines. The protocol lasts from 24 h to 2 months. It is also necessary to conduct epidemiological studies on long-term, low-dose exposure, establish monitoring networks, and perform correlation analysis with health data.

3.2. Development of Behavior Simulation and Toxicity Evaluation Modeling

MPs are not only physical pollutants but also carriers of chemical toxicants. Future research should pay attention to pH-, temperature-, and microbial-based dissolution kinetics models to predict the release rate of additives under different environmental conditions; the use of organoid models to simulate the desorption of MPs-pollutant complexes in vivo; and consider the phenomenon of enhanced cross-barrier toxicity, e.g., the fact that NPs may carry pollutants across the blood-brain barrier. “Eco-corona”, a surface layer on MPs formed by the sequential adsorption of organics and contaminants, should be investigated owing to its capacity to alter toxic effects by modulating immune recognition pathways. For example, when MPs adsorbed reactive proteins, there can be a 40% decrease in their macrophage phagocytic efficiency, which increases the risk of chronic inflammation.

To solve the problem of chemical exposure and biological interactions, exposure-effect prediction models should be constructed, and multiomics linkage (macro-genome, metabolome) can be used to reveal the toxicity mechanism of MPs. For example, microphysiological Systems constructed biomimetic organ chips by microfluidic technology can simulate the microenvironments of the heart, liver, kidney, and other organs, and accurately track the toxic pathways of MPs in cross-organ interactions. Additionally, organoid models and organ chips accurately simulate the toxicity of multitissue interactions. Organoid models are based on the differentiation of human induced pluripotent stem cells (hiPSCs) to construct 3D organoids, which can visually observe the toxicity of MPs. Research findings using 3D kidney organoids, PS MPs can induce renal autophagy and apoptosis by up-regulating the DDIT4 gene. The integration of microphysiological systems with hiPSCs significantly enhances the human relevance of toxicity data, supporting high-throughput screening and real-time monitoring of biomarkers. This platform enables tracking of molecular events such as MPs uptake, intracellular localization, and oxidative stress, while simulating low-dose chronic exposure scenarios in humans to assess cumulative toxicity. It serves as a critical platform for achieving precision toxicology.

Additionally, standardized toxicity test indicators should be developed to assess the toxic effects of MPs comprehensively. In-depth studies on the effects of leachates exposure are required, including laboratory simulations of compound exposure scenarios and joint toxicity experiments, to ensure that exposure doses reflect real-world conditions.

3.3. In Situ and Online Characterization

In situ online detection is driving a paradigm shift in toxicology research by enabling real-time, dynamic, environmentally relevant, and high-throughput toxicity assessments. The rapid advancement of in situ portable testing technology has solved the problems of long cycle time and the high cost of traditional laboratory analysis. In situ detection techniques (e.g., Raman spectroscopy, infrared spectroscopy) can directly analyze the composition and distribution of MPs in environmental samples, while online monitoring systems (e.g., flow cytometry combined with fluorescent labeling) can track the dynamic behavior of MPs in real time.

In recent years, a variety of portable instruments for on-site MP analysis have been developed and widely used for the on-site detection of MP in diverse environmental matrices, including complex samples such as wastewater, sludge, and sediments. Current portable instruments for MP analysis include near-infrared spectrometers, surface-enhanced Raman scattering (SERS), fluorescence instruments, hyperspectral imaging (HIS), and laser-induced breakdown spectroscopy (LIBS), demonstrating broad detection capabilities ranging from nanometers to millimeters, with a limit of detection (LOD) down to μg/L or lower. Electrochemical sensors, including resistive pulse sensors with integrated microfluidics, have been used to achieve highly sensitive in situ detection of MPs in liquid samples. Furthermore, portable pyrolysis mass spectrometry (py-MS) has been successfully applied for the efficient identification of MP types and concentrations. However, in situ detection of MP is also affected by various factors, including environmental factors and sample complexity.

Currently, new techniques such as single-particle hyperspectral Raman imaging combined with deep learning algorithms enable high-throughput and accurate identification of the chemical composition, particle size, and morphology of MPs in complex biological samples (e.g., blood, tissues). Additionally, Nano Secondary Ion Mass Spectrum (Nano SIMS) can be used to track the in situ distribution of contaminants adsorbed on the surface of MPs and their interactions with cellular components. Moreover, the importance of “heterogeneity analysis”, in which the chemical additives, aging, and biological canopy of MPs combine to determine their toxic effects, needs to be emphasized. The development of in situ online detection could not only complement traditional methods but also represent an essential requirement for establishing proactive environmental health risk management systems.

3.4. Intelligent Analysis for MP Toxicity

In the toxicological assessment of MPs, AI and big data technologies play a key role in analytical detection and toxicity calculation, which is trending in a multidimensional way. It can enhance detection accuracy, expedite the analysis of toxicity mechanisms, and refine risk assessment models.

3.4.1. Analytical Detection

By integrating machine learning (ML) and deep learning (DL) algorithms, spectral and image data of MPs can be intelligently analyzed to achieve automatic identification, classification, and counting, significantly improving the accuracy and efficiency of detection. Combined with high-resolution imaging technology, it can deeply analyze the surface characteristics of MPs and their interaction mechanisms with organisms at the single-particle level. On this basis, MPs’ feature database can be further constructed to provide reliable data support for pollution assessment and environmental impact analysis. Future developments will focus on creating more efficient algorithms and comprehensive databases to address complex detection demands. This will be coupled with the integration of microfluidics and Surface Enhanced Raman Scattering (SERS) to achieve real-time monitoring at the single-particle level.

3.4.2. Toxicity Calculation and Mechanism Prediction

By integrating toxicological data from model organisms through transfer learning (TL), it is possible to predict organ-specific toxicity in humans effectively. With the help of leveraging AI neural networks and multiomics (such as metagenomics and metabolomics) correlation analysis, it is possible to systematically reveal the mechanisms of toxicity and significantly accelerate the progress of mechanism research. , Further application of ensemble learning models (such as decision tree ensembles) can identify key factors influencing toxicity and enable precise prediction of toxic effects. , Future development trends focus on combining quantum chemical calculations with molecular docking technology to simulate molecular interactions between MP surface functional groups and biological receptors or DNA, thereby revealing the mechanisms by which they induce oxidative stress or genetic damage at the atomic/molecular level.

3.4.3. Risk Assessment and Modeling

The integration of ML-powered detection and TL-powered toxicity prediction forms the foundation for a next-generation risk assessment framework. Future developments will optimize toxicity testing parameters, enabling targeted assessment of high-risk MP categories and scenarios while enhancing resource efficiency. Furthermore, multidimensional system models will be established to comprehensively analyze the synergistic effects of MPs’ physicochemical properties, environmental aging, and coexposure with other pollutants, thereby advancing the shift in research paradigms from single-factor analysis to dynamic multifactorial interactions. ,

4. Conclusion

MP pollution is a pressing global concern. However, existing research indicates that consistent or equivalent quantitative data on human exposure to MPs remains limited, which complicates the assessment of their toxicity at environmentally relevant levels. Importantly, the identified research gaps are not only persisting but appear to be widening, as experimental approaches continue to diverge from real-world exposure scenarios. While current results have not provided direct evidence linking MPs to specific diseases, it is undeniable that MPs have been detected in both the environment and human bodies. , Our analysis distinguishing it from a mere summary of the status quo, specifically underscores that the intrinsic toxicity of MPs as inert particles may have been misestimated, and highlights the critical need to systematically identify and address these knowledge gaps. We further suggested that the critical role of MP-attached contaminants (e.g., pathogens, heavy metals, organic pollutants) should be carefully assessed.

In the future, it is necessary to improve data quality based on existing analytical frameworks, further investigate the toxicity mechanisms, conduct full life cycle assessments, and promote policy regulations. Failure to bridge these foundational gaps will severely hinder evidence-based policymaking, leaving regulators without the robust, comparable data needed to set effective exposure limits, manage risks, and prioritize mitigation strategies.

The following research priorities were identified as the most urgent: First, there is an imperative need to develop and validate harmonized methods for quantifying MP exposure in humans. Minimizing intermethod variability is the essential first step toward enabling reliable quantitative comparisons and establishing dose–response relationships. Second, future toxicity research must prioritize investigations at environmentally relevant concentrations. Key focus areas include elucidating the mechanisms of copollutant transfer (e.g., vector effects), the long-term biodistribution and accumulation of MPs, and their potential for inducing cascading health effects across organ systems. Third, research efforts should be combined with the development of life cycle assessments for plastic materials. Such evidence is essential for formulating effective policies and regulations to restrict the production and use of MP products and develop environmentally friendly alternative materials.

Biographies

Shanjun Song is an Associate Professor at the National Institute of Metrology, China (NIM). As an analytical chemist, he primarily engages in metrology of environmental health and the development of certified reference materials. His research focuses on high-accuracy measurement techniques for emerging pollutants in the environment and associated health risk assessments. He has participated in and completed international comparisons in the field of environmental metrology, providing support for enhancing pollutant measurement capabilities and achieving international mutual recognition.

Qian Liu is a Professor at the Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences (RCEES, CAS). He obtained his B.Sc. in 2004 and Ph.D. in 2009 from Hunan University. Thereafter, he obtained postdoc training at RCEES, CAS, in 2010–2012 and Trent University in 2013–2014. Dr. Liu is a recipient of the National Science Fund for Distinguished Young Scholars and the NSFC Science Fund for Excellent Young Scholars. He has won the XPLORER Prize and MIT Technology Review Innovators Under 35 China. He now serves as the Executive Editor for Environment & Health and an Associate Editor for Environmental Science: Processes & Impacts. His research interests include environmental analytical chemistry, air pollution, exposomics, and effects of environmental pollution on health.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/envhealth.6c00030.

• The meta-analysis ultimately included the research papers (XLSX)

The authors declare no competing financial interest.