Microplastics are commonly described as plastic particles or fragments smaller than 5 mm, including weathered fragments, industrial pellets, and microbeads. As research moved from oceans to freshwater, soil, air, food, and human exposure, ISO 24187:2023 introduced finer size classes for more precise sampling, identification, and risk assessment.
Thompson and colleagues drew broad attention to small plastic fragments and fibers in the marine environment, helping shape the modern microplastics concept.
The NOAA international workshop and its proceedings formalized microplastics as plastic particles smaller than 5 mm, creating a practical research boundary for sampling and analysis.
ISO 24187:2023 separates 1-5 mm large microplastics from 1 µm-1 mm microplastics, supporting more precise and comparable environmental analysis.
1 mm - 5 mm
Water-insoluble solid plastic particles with at least one dimension between 1 mm and 5 mm. This size class often includes visible fragments, pellets, flakes, and larger particles that still require polymer confirmation.
1 µm - 1 mm
Water-insoluble solid plastic particles between 1 µm and 1 mm. MPs have been reported in marine, freshwater, terrestrial, atmospheric, food, drinking-water, and biological samples.
< 1 µm
Plastic particles below 1 µm. This size range is difficult to quantify in complex environmental matrices and may include particles small enough to cross biological barriers.
Microplastics are now recognized as a diverse and globally distributed group of contaminants. They are present in marine, freshwater, terrestrial, atmospheric, and biological systems, with reported evidence of transport through wind, water, food webs, and human exposure pathways. The field has also learned that particle size, shape, polymer type, color, aging state, and chemical additives all influence how microplastics move, persist, and interact with organisms.
Microplastics have been reported from surface waters and deep-sea sediments to farmland, lakes, rivers, sea ice, mountain regions, air, food, drinking water, and human tissues.
Microplastics are not a single contaminant. Their behavior depends on polymer chemistry, particle size, morphology, density, additives, and environmental weathering.
Different instruments, size cutoffs, pretreatment protocols, and reporting metrics still limit comparability between studies, making method standardization essential.
Particles intentionally produced or added to products, including microbeads, industrial abrasives, paint and coating particles, and pre-production pellets or flakes.
Particles generated during product use and environmental fragmentation, including tire-wear particles, synthetic textile fibers, packaging debris, and plastics broken down by UV exposure, abrasion, water movement, and heat.
Waste-to-energy incineration, municipal solid-waste combustion, open burning, pyrolysis, and other industrial thermal processes can release or transform plastic particles, producing aged microplastics with altered spectral and chemical signatures.
Without accurate detection, we cannot assess risk, trace sources, evaluate mitigation measures, or design effective regulations. Spectroscopic and mass-based methods have advanced the field, but degraded, dark, small, or chemically transformed particles remain difficult to identify consistently. OpenMNP exists to help close this gap.
Reliable identification of MPs and NPs in human tissues, food, air, and water is essential for exposure assessment, toxicological studies, and public health policy.
Tracking MP pollution in air, water, and soil, and understanding how particles move through ecosystems, depends on consistent detection methods.
As policy action grows, detection workflows must produce comparable evidence across laboratories, matrices, and particle types, not just isolated measurements.
