COUNTING WHAT LIGHT CANNOT RESOLVE

How We Measure It

Standard methods for plastic particles start at 20 µm or 1 µm, so nanoplastics are largely missing from routine monitoring. This page explains what each instrument can and cannot tell, how labs contaminate their own samples, and why careful labs given the same sample report very different numbers.

9 min readUpdated 2026-11-04ReviewedBWell supportedCLimitedDDisputedEUnknownPProvenance

Analyst in a mask and white coat at an infrared microscope, with absorbance spectra on the monitor beside it — Infrared spectra of a microplastic particle on screen beside a Thermo Nicolet Continuum FTIR microscope at Ifremer, Brest, France, 2020. The spectrum is compared with reference libraries to name the polymer; the method works routinely down to about 10–20 µm.Lesbats Stephane (2020). Analyse d'échantillons. Ifremer. https://image.ifremer.fr/data/00702/81374/CC BY 4.0Source ↗

Standard methods miss nanoplastics (below 1 µm): the EU drinking-water method counts nothing below 20 µm¹, and ISO 16094-2 starts at 1 µm². Those are scopes, not instrument limits; one specialist lab has identified particles down to 500 nm by Raman microscopy, recovering 67% of test beads (level C)³. Every step can also add plastic. In a 2026 test, touching a surface with lab gloves left a mean of about 2,000 false "microplastics" per square millimeter (level C)⁴.

≈2,000 /mm²

false microplastic hits left by dry contact with lab gloves

nitrile and latex gloves, infrared and Raman library matching; cleanroom nitrile gloves ≈100 /mm²; Clough et al. 2026⁴

one lab's test; a 2020 study of 10 glove types found the same stearate artifact (S-291)

CLimited

4 of 50

freshwater and drinking-water studies meeting every quality criterion

Koelmans et al. 2019, 50 studies of freshwater, groundwater, tap and bottled water⁵

systematic quality review; a 2018 biota review found the same weaknesses (S-315)

BWell supported

≈1,000×

modeled rise in count when the lower cutoff falls from 300 µm to 1 µm

power-law model, slope 2.2 (marine surface water median), up to 5 mm; our calculation; estimate, not a measurement⁶

Arithmetic only: extends a fitted power law below its valid range (roughly 50–350 µm in Kooi's samples); the resulting count increase is not established.

PProvenance

Sampling sets the smallest particle you can find

A nominal mesh or pore size is not an exact gate. Elongated particles slip through lengthwise, aggregates are counted as larger objects, and small particles lodge in or are lost from membranes⁷^,³. A size range means the nominal cutoff plus a shown recovery.

The EU drinking-water method samples at least 1,000 liters through 100 µm and 20 µm filters and accepts spike recoveries of 60–140%. It reports particles of 20 µm–5 mm and fibers of 20 µm–15 mm per cubic meter¹. Sediment and tissue are digested⁸, which can lose or alter particles.

Contamination is the harder problem; guidelines ask for clothing policies, cleaned glassware, clean-air cabinets and blanks treated like samples⁹. The 2025 North Atlantic survey used pre-combusted glass vials and set any signal below three standard deviations of its blanks to zero¹⁰.

Blanks vary: in a 22-laboratory exercise on clean water they carried 91 particles on average, standard deviation 141 (level C)¹¹.

In a 2024 bottled-water study, ultrapure Milli-Q water run through the whole procedure held about as much plastic as the samples. Materić argued that it was the right procedural blank and that setting it aside for clean filters makes the counts unreliable¹². The authors replied that the Milli-Q water was itself contaminated, with a different polymer profile, and that their filter blanks, exposed to the same lab air, controlled the remaining sources (level D)¹³.

Technician in a face mask and white disposable coat looking through a stereo microscope at a filter in a glass dish — A technician in a face mask and disposable coat inspects a glass-fiber filter in a glass dish under a stereo microscope, Ifremer, Brest, France, 2020. Covering clothing and glassware reduce fibers shed into samples.Lesbats Stephane (2020). Analyse d'échantillons. Ifremer. https://image.ifremer.fr/data/00702/81374/CC BY 4.0Source ↗

Illustration of a lab bench: fibers trailing from a knitted sleeve, a gloved fingertip, a smear on a filter, a vent and tips — Illustration: ways plastic can enter a sample in the lab: fibers shedding from a knitted sleeve, a gloved fingertip leaving a faint smear on the filter, an air vent, and a plastic bottle and pipette tips. Particles enlarged; illustrative sizes, not to scale.Illustration · AI generatedMade with FLUX.1-schnell (fp8, Comfy-Org/Flux-1-Schnell) · ComfyUI (local), tools/content/generate_l3.pySite illustration (AI-generated, Flux)Site original

Counting and identifying particles one by one

Particle methods give count, size, shape and, with spectroscopy, polymer. Visible light cannot resolve detail finer than roughly 200–300 nm (our calculation from the Abbe limit¹⁴); smaller particles can be detected, not imaged.

Optical microscopy is cheap but has no chemistry. In the 22-lab test, recovery averaged 76% (standard error 10%), excellent mainly above 50 µm¹¹. In a 12-lab test, particles below 1 mm were undercounted by 20% even with best practice (level C)¹⁵.

Nile red dye binds to fat-loving (lipophilic) surfaces and makes plastic glow under a fluorescence microscope. The original protocol covers 20–1,000 µm¹⁶; the JRC/BAM study grouped staining with the less specific techniques¹⁷.

µFTIR matches an infrared spectrum per particle to a polymer library. Mid-infrared light cannot resolve detail finer than about 4–7 µm, and the routine range starts near 20 µm¹⁴; an 84-lab comparison put the limit at 10–20 µm⁷.

µRaman uses a visible laser and reaches about 0.5 µm¹⁴, but fluorescence from dyes, additives and matrix can swamp its spectra¹⁷. An automated 2026 workflow reached 500 nm and recovered 67 ± 10% of 500 nm test beads. It oversized particles by about 0.5 µm and needed each particle centered in the laser focus (level C)³. In potable water, only 0.36% of its 0.5–10 µm particles were plastic³.

Two Raman spectra beside two dark-field images of a tiny particle circled in red, scale bar 0.5 µm — Raman spectra of a small polypropylene particle on an aluminum-coated polycarbonate filter (scale bar 0.5 µm): recognizable with the laser centered on it (a), not slightly off center (b). Figure 6 (left) from Jüngling et al. (2026), CC BY 4.0.Figure 6 (left panel) from Jüngling I.S., Schmitt L., De Franceschi F., Da Costa Filho P.A., Lei L., Coic L., Benismail N., Dubascoux S., Ambühl M.E., Ivleva N.P. (2026), Analytical and Bioanalytical Chemistry 418:5283–5302, https://doi.org/10.1007/s00216-026-06567-2 · CC BY 4.0 · croppedCC BY 4.0Source ↗

O-PTIR (optical photothermal infrared) reads infrared absorption with a visible probe beam. A 2025 tissue study reports about 500 nm lateral resolution¹⁸, and the instrument can record a Raman spectrum from the same spot¹⁴.

Weighing plastic instead of counting it

Thermoanalytical methods heat a sample and identify polymers from breakdown products, giving mass per polymer but no number, size or shape¹⁹^,²⁰. In pyrolysis GC/MS (py-GC/MS), each polymer is quantified from indicator compounds. One 2025 blood workflow used 1-eicosene for polyethylene (PE) and reached detection limits from 14 ng/mL for polypropylene (PP) to 245 ng/mL for PE (level C)²¹.

TED-GC/MS (thermal extraction desorption GC/MS) traps gases released from a larger sample portion before analysis¹⁹. Both weigh whatever polymer reaches the instrument: polymer-related mass in a prepared fraction. py-GC/MS has reported nanoplastic mass this way in surface water, groundwater and wastewater²²^,²³. That label needs evidence that the signal came from particles, not dissolved polymer.

Limitation

Testing py-GC/MS on human blood, Rauert and colleagues found extraction recoveries of 7–109% and realistic detection limits up to 20 times higher than those calculated in pure water. Under their extraction and marker conditions, the method was not yet suitable for PE and polyvinyl chloride (PVC) in biological matrices (level C)²⁴. Nardella and colleagues report a working full-scan blood workflow with 1-eicosene as the PE marker²¹; the two studies validated different steps.

Reaching the nanoscale

TD-PTR-MS (thermal desorption proton-transfer-reaction mass spectrometry) fingerprints polymers by their vapor, with a detection limit below 1 ng of polystyrene (PS) in 1 mL samples²⁵. In a 2025 survey, 1.5 mL subsamples of North Atlantic seawater passed through 1.0 µm filters held polyethylene terephthalate (PET), PS and PVC but no PE or PP. Whether PE was altered, below detection or masked stayed open (level C)¹⁰.

SRS microscopy (stimulated Raman scattering) images particles fast enough to count. Its resolution is about 365 nm; Qian and colleagues detected particles down to 100 nm against a seven-polymer library and estimated sizes below 365 nm from signal strength, assuming solid spheres: a method demonstration (level C)²⁶. Their count of about 240,000 particles per liter in 3 bottled-water brands, about 90% nanoplastics, is disputed over its blanks (level D; see the blanks dispute above)¹²^,¹³.

AFM-IR reads infrared absorption under an atomic force microscope tip. A 2026 study identified single PS particles down to 80 nm and silica down to 20 nm, but throughput was too low to confirm nanoplastics in ambient air without enrichment (level C)²⁷.

Size without chemistry. Field-flow fractionation, nanoparticle tracking analysis and dynamic light scattering size particles but cannot tell plastic from clay or protein²⁸^,¹⁹. Single-particle ICP-MS counts nanoplastics by their carbon or metal signal, so far mainly in lab tests²⁹.

Metal-doped tracers sidestep detection in lab tests: in simulated sewage sludge, over 98% of such nanoplastics ended up in sludge, with over 93% recovered³⁰; field particles carry no tag.

What each method can tell, and what it cannot

Table of ten methods and two standard scopes: output, size range shown, resolution, standard and what each cannot tell; log-axis bars only where a size range was shown. Source:¹¹^,¹⁶^,¹⁴^,³^,⁷^,¹⁸^,²⁶^,²⁷^,²¹^,²⁴^,²⁵^,¹⁰^,²⁸^,¹^,²^,¹⁵^,¹⁷^,²⁰^,¹⁹^,³¹Nanoplastics ObservatorySite original

Data table

label	value	unit	lower_um	plot	reports	shown_range	resolution	standard	cannot_tell	source
Optical microscopy	50	µm	50	bar	count, size, shape	good recovery above 50 µm (22 labs, clean water)	n/a	not alone	polymer; small, clear particles	S-039, S-037
Nile red	20	µm	20	bar	count, size	20–1,000 µm protocol	n/a	none	which polymer	S-318, S-038
µFTIR	20	µm	20	bar	count, size, polymer	routine above 10–20 µm	3.7–7.4 µm	EU from 20 µm; ISO from 1 µm	below about 10 µm; stearate look-alikes	S-319, S-326, S-291
µRaman	0.5	µm	0.5	bar	count, size, polymer	routine 1–5 µm; 500 nm beads at 67% recovery, one lab	about 0.5 µm	EU from 20 µm; ISO from 1 µm	fluorescent particles; exact size near 500 nm	S-325, S-326
O-PTIR	0.5	µm		marker	polymer, image	no recovery range reported	about 500 nm	none	shape below 500 nm; recovery	S-320
SRS microscopy	0.1	µm		marker	count, estimated size, 7 polymers	one demonstration, bottled water	about 365 nm; detects to 100 nm	none	shape below 365 nm; other polymers	S-033
AFM-IR	0.08	µm		marker	polymer per particle	test aerosols, one lab	detects 80 nm PS, 20 nm silica	none	concentrations (too slow)	S-327
py-GC/MS, TED-GC/MS		ng/mL		none	mass per polymer	size set by prior filtration; blood LOD 14–245 ng/mL	n/a	ISO 16094-3 draft, mass only	size, number, shape; particulate or not	S-043, S-042, S-041
TD-PTR-MS		ng		none	mass per polymer	fraction through a 1.0 µm filter; LOD below 1 ng PS	n/a	none	size, number; masked PE	S-031, S-067
FFF, NTA, DLS		nm		none	size distribution	not reported in cited reviews	n/a	none plastic-specific	whether it is plastic	S-028, S-027
EU 2024/1441 scope	20	µm	20	reference	particles, fibers per m³	20 µm–5 mm	n/a	legal method	below 20 µm	S-132
ISO 16094-2 scope	1	µm	1	reference	count, size, polymer	1–5,000 µm, ten polymers	n/a	ISO standard	below 1 µm	S-040

Why two honest labs disagree

Size cutoffs. Small particles vastly outnumber large ones: above a lower size limit of roughly 50–350 µm, depending on the sample type, counts follow power laws; below it, measured counts fall short of the fitted line (level B)⁶^,¹⁶^,³². Across more than 60,000 particles measured by FTIR imaging, median slopes ran from 2.2 in marine surface water to 3.1 in organisms (level C)⁶.

Take a constructed example: one lab counts above 300 µm, another down to 1 µm, in the same water. A slope of 2.2 gives the second about 970 times more particles, a slope of 3.1 about 160,000 times (our calculation, up to 5 mm; level P). This calculation extends a fitted power law down to 1 µm; in Kooi's samples, the fit already fails below roughly 50–350 µm. The factors illustrate that assumption, not a measured increase (level E; searched S-314, S-313, S-026, S-027 and S-028, 3 November 2026).

Same water, different cutoff: modeled count relative to a 300 µm cutoff

Model line on log axes, not a measurement: counts rise about 27-fold at 20 µm and about 970-fold at 1 µm for slope 2.2, and 160,000-fold at 1 µm for slope 3.1; values below the fitted range (roughly 50–350 µm depending on sample type) are extrapolated, so every point below 300 µm is marked extrapolated. Source:⁶Nanoplastics ObservatorySite original

How this was calculated

Our calculation. Count between the cutoff L and 5,000 µm, proportional to L^(1−α) − 5000^(1−α), with α = 2.2 (median, marine surface water) and α = 3.1 (median, biota) from Kooi et al. 2021. Model, labeled 'model'; extrapolation below the fitted lower limit (roughly 50–350 µm, sample-type dependent; Kooi et al. 2021) is not established, so the 100 µm point and all smaller cutoffs are marked extrapolated. No laboratory icons: the comparison is a constructed example.

Data table

label	value	unit	cutoff_um	value_slope_3_1	extrapolated
300 µm	1	× count at 300 µm	300	1	false
100 µm	3.8	× count at 300 µm	100	10	true
20 µm	27	× count at 300 µm	20	296	true
10 µm	61	× count at 300 µm	10	1268	true
1 µm	972	× count at 300 µm	1	159638	true

Count versus mass. One 1 mm PE sphere weighs about 0.5 mg, as much as a trillion 100 nm spheres (our calculation, density 0.95 g/cm³; level P); see How to Read the Numbers.

Sample volume. The EU method samples at least 1,000 liters and must analyze at least 10% of the recovered material, so at least 100 liters¹. The North Atlantic survey collected 2 liters and analyzed 1.5 mL subsamples¹⁰: about 67,000 times less analyzed volume (our calculation; level P). Each stray particle weighs more in a small portion.

Method

Same sample, many answers: a real test. In 2025, 84 laboratories registered to receive identical tablets of PET and aged PE particles of about 10–200 µm, and 56 reported results. All that reported identified both polymers; reproducibility standard deviations, in percent of the reference value, were 62–117% (PE) and 46–62% (PET) with thermal methods and 121–129% and 64–70% with spectroscopy. Dissolving and filtering the tablets was one of the most critical steps (level C)⁷.

Between-lab spread. In the JRC/BAM comparison, 98 datasets on one PET-in-water sample spread almost evenly between the lowest and highest values. Libraries, match thresholds and data treatment varied strongly, and only 69% of labs reporting counts said how they sized particles¹⁷. A 2026 comparison across seven countries with shared protocols found identification accuracy from 54% to 93% and PE recovery from below 5% to above 130%³³. Large spread recurs across exercises (level B)¹⁵^,¹¹^,⁷.

Look-alikes. Leachates of 10 glove types read as PE under µRaman, µFTIR and py-GC/MS, because stearates and fatty acids share PE's long hydrocarbon chains (level B)³¹^,⁴. Biological matrices can also yield common py-GC/MS markers for PE and PVC²¹^,²⁴. A 2026 framework asks for two orthogonal techniques before plastic is reported in human samples³⁴.

How far this affects brain-tissue figures is disputed (level D). Monikh, Materić and colleagues argue that the 2025 brain study lacked adequate contamination controls and validation, and that undigested lipids can inflate the PE signal³⁵. Campen and colleagues reply that the lipid comparison mixes dry- and wet-weight percentages, that polymers without known lipid interference rose over time too, and that procedural blanks held no detectable polymer³⁶^,³⁷.

They concede that tissue digestion has no agreed method and that alkaline digestion may overestimate polymer content³⁷. We read only the reply's opening paragraph, which acknowledges uncertainty "in even the best current methods"³⁶; the points above follow a 2026 paper's summary³⁷. For health questions, see Human Body.

Standards cover microplastics in clean water, not nanoplastics

ISO/TR 21960:2020 summarizes the state of knowledge, ISO 24187:2023 sets principles for microplastic analysis³⁸^,³⁹, and

ISO 16094-2:2025 covers drinking water and other low-solids water by microscopy and vibrational spectroscopy, sizing and counting particles of 1–5,000 µm and identifying ten named polymers². Its thermo-analytical sister, ISO 16094-3, gives polymer mass without a size range. Its final draft (FDIS) went to ballot on 15 September 2026, and it was not published when we checked on 3 November 2026⁴⁰^,²⁰.

ASTM D8332-20 and D8333-20 cover collecting and preparing water samples for Raman, infrared or py-GC/MS⁴¹^,⁴². Legal status is on Policy and Regulation.

Quality criteria came first: biota studies scored an average reliability of 0 on ten criteria⁴³. A 2019 review found only 4 of 50 freshwater and drinking-water studies meeting every criterion (level B)⁵. In 2021 the JRC/BAM report named the missing tools: method validation, reference materials and proficiency testing¹⁷.

Of the plastic-specific documents listed here (ISO 16094-2 and -3, ISO 24187, ISO/TR 21960, ASTM D8332 and D8333, EU 2024/1441), none sizes and counts plastic below 1 µm (level P; checked 3 November 2026). General nanoparticle-sizing standards, which do not identify polymers, were not searched. See Knowledge Gaps.

Questions

Can any lab measure nanoplastics routinely?

Not with a standardized method: the standards we checked start at 1 µm or 20 µm, or give mass without size. Specialist labs run submicrometer workflows, such as automated Raman to 500 nm or TD-PTR-MS below 1 µm, each validated for particular particles and matrices (level C,³,²,¹⁰).

If gloves and lipids create false positives, are microplastic findings wrong?

Not as a whole. The artifacts mainly inflate PE and some PVC signals (level B,⁴,³¹,²⁴). Cleanroom gloves, matrix-matched blanks and a second technique reduce them (³⁴), but one assessment found py-GC/MS not yet suitable for PE and PVC in blood (level C,²⁴).

Why not convert particle counts into grams?

It needs assumed size, shape and density distributions. Koelmans and colleagues published such a conversion; its output is an estimate, not a measurement (level B,³²).

What makes a measured number more trustworthy?

A stated size range with its recovery, procedural blanks processed like samples, polymer identification by spectrum or marker and, for tissue, a second method (level B,⁹,⁴³,³⁴).

Where to go next

Size classes are defined on What Is Nanoplastic. How to Read the Numbers turns these limits into questions for any headline, and Landmark Studies shows which instruments produced the best-known results.

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Evidence levels and provenance

AConsensus: Multiple independent studies or a systematic review plus a statement by a scientific body.
BWell supportedUsed on this page: Several independent studies with concordant findings.
CLimitedUsed on this page: Few studies, narrow conditions, or methodological caveats.
DDisputedUsed on this page: Conflicting results; both sides are shown.
EUnknownUsed on this page: No reliable evidence found; the search scope is stated.

PProvenanceUsed on this page: Provenance: checked against the primary record. A separate category, not an evidence grade: used for bibliographic facts, legal texts, official metadata, definitions quoted from a standard, the site's own arithmetic and statements about the site's process.

Editorial categories of this site. A–E grade scientific findings, per claim, with a one-line rationale; D and E are not lower rungs of the A–C scale. P is not a grade: it marks facts checked against their primary record.