Microplastics Claims: Why Most “Plastic-Free” Labels Fail

Q: How MDL, QL, and DLR Shape a Microplastics Report

The Method Detection Limit (MDL) is the lowest concentration a method can distinguish from a blank sample at 99% statistical confidence. In plain language, it answers the question “is anything there at all.” The Quantitation Limit (QL), also called the Limit of Quantitation or LOQ, is the lowest concentration that can be measured with acceptable precision and accuracy. It answers “how much is there, reliably.” The Detection Limit for Purposes of Reporting (DLR) is the regulatory threshold below which a laboratory reports a result as non-detect rather than a number.nnA result between the MDL and QL means the analyte is likely present but cannot be reliably counted. A result below the MDL means the method cannot distinguish signal from background noise. For microplastics, these distinctions matter because a “none detected” result is only meaningful relative to the specific MDL of the method used. That floor is typically 20 µm or 50 µm, which leaves the entire sub-20 µm fraction and all nanoplastics outside the method’s view entirely.

Q: Why the 1–20 µm Size Range Is a Critical Blind Spot

The 1–20 µm range sits below the validated lower limit of both validated analytical methods, since infrared spectroscopy begins at 50 µm and Raman spectroscopy at 20 µm, yet above the nanoplastic threshold of 1 µm. This means particles in this range are neither captured by the most stringent validated public methods nor classified as nanoplastics. Research has found that this fraction may represent a substantial share of actual particle counts in water. As noted earlier, the majority of particles in real-world samples fall into this unvalidated range.nnEmerging techniques, including high-frequency ultrasound combined with machine learning, are beginning to address detection at the lower end of this range. None of these approaches has yet achieved the validated, standardized status required for defensible regulatory or verification use. Until validated methods exist for this fraction, any “none detected” result from current standard methods leaves this size range entirely unexamined.

Q: How Independent Review Turns a Lab Report into a Defensible Claim

A laboratory report records what an instrument found above its detection floor, for the polymers it screened, in the lot it tested. The report does not, on its own, assess whether the method was appropriate for the product type, whether blanks and contamination controls were adequate, whether the reporting limits are sufficient to support any claim, or what claim language the data can actually carry.nnIndependent review, such as the Wellness Quality Institute’s Plastic-Free Pathway Verification governed by WQI-CS-01, examines all of those elements against defined criteria and then produces approved claim language tied specifically to the reviewed evidence. The resulting claim is scope-locked to the product, dataset, particle-size range, polymer panel, and production period reviewed. That scope lock is what makes the claim defensible. It states exactly what was examined and makes no assertion about what was not.nnMany companies discover through this process that their existing data supports either a narrower or a stronger claim than they had assumed. They also see that the “none detected” result on their report is bounded by the method’s floor rather than by the product itself.

Written by: Scott Steveson, Specialist, Wellness Quality Institute

Key Takeaways on Microplastics Claims and Verification

Three critical limits define every microplastics lab report: Method Detection Limit (MDL), Quantitation Limit (QL), and Detection Limit for Purposes of Reporting (DLR). Together they determine what “none detected” actually means.
Validated analytical methods begin at 20 µm or 50 µm, which leaves the entire 1–20 µm fraction and all nanoplastics outside the method’s reach and unmeasurable by current standards.
Non-detect results are left-censored observations. Simple substitution methods can create misleading trends that reflect changing lab limits rather than real product improvements.
Before using any lab report for a market claim, verify the detection floor, polymer panel, blank results, reporting limits, chain of custody, matrix suitability, and spectroscopic confirmation of counted particles.
No laboratory can prove a product is free of plastic. Contact the Wellness Quality Institute for independent Plastic-Free Pathway Verification that turns real lab data into scope-locked, defensible claims.

The Measurement Gap That Makes Most Plastic-Free Claims Unverifiable

One state water resources control board has published the most stringent public reference framework for microplastics in drinking water currently available in the United States. The framework includes two validated analytical methods, and each method has a defined lower size boundary:

SWB-MP1-rev1, an infrared spectroscopy method, is validated for particles greater than 50 µm through 5,000 µm.
SWB-MP2-rev1, a Raman spectroscopy method, is validated for particles greater than 20 µm through 5,000 µm.

That state’s regulatory definition of microplastics in drinking water covers solid plastic material with particles that have at least three dimensions greater than 1 nanometer and less than 5,000 micrometers. The best validated methods begin at 20 or 50 micrometers, which are thousands of times larger than the definitional floor. That gap is not a bureaucratic oversight. It reflects a hard technical limit: the 1–20 µm fraction is not validated under either method, and everything below 1 µm, the nanoplastic range, sits beyond the reliable reach of commercially available analytical methods.

Colorful plastic fragments in water inside a laboratory petri dish. — Microplastics are particles smaller than five millimeters. Current methods can count and identify them at the upper end of that range, but reliable measurement falls away as particles get smaller — a limit that shapes every honest claim.

The following table shows how the validated measurement range for each method leaves most of the regulatory definition unmeasurable in practice.

Method	Validated Lower Limit	Validated Upper Limit	Status of 1–20 µm Fraction
SWB-MP1-rev1 (Infrared)	>50 µm	5,000 µm	Not validated
SWB-MP2-rev1 (Raman)	>20 µm	5,000 µm	Not validated
Regulatory Definition	>1 nm	<5,000 µm	Defined but unmeasurable by current validated methods
Nanoplastics (below regulatory floor)	<1 µm	—	Beyond reliable commercial detection

A 2026 critical review of micro- and nanoplastics in environmental waters confirmed that major challenges remain in achieving standardized and comparable measurements across studies, especially for particles below 20 µm. A French study found that 98% of detected particles in a tap-water sample were below 20 µm, which is the precise fraction that current validated methods cannot reliably capture. The implication is direct. A “none detected” result from either method describes only what was found above the method’s floor, not what exists below it.

Fragments of plastic suspended in blue water below the surface. — Plastic doesn’t disappear — it fragments. These secondary microplastics are the breakdown products of everyday objects, and independent research now detects them across the water supply. Detection, though, establishes presence, not absence.

Learn how WQI verification converts your existing lab reports into scope-locked, defensible claims.

How Censored Results Distort Trends and Consumer Confidence Reports

Laboratories record a non-detect result when they cannot detect an analyte above the reporting limit. Statisticians call this a left-censored observation, which means the true value lies somewhere between zero and the reporting limit, but the exact number is unknown. In water quality datasets, these results are typically flagged as “< RL” (less than the reporting limit). Problems begin when analysts need to calculate averages or track trends across multiple monitoring periods.

Simple substitution, such as replacing every non-detect with zero, half the reporting limit, or the full limit, introduces systematic bias. Simulated monitoring data shows that lowering a detection limit from 1.0 to 0.1 across a 20-year program caused half-limit substitution to produce an apparent 32.8% concentration decline that was entirely an artifact of the changing laboratory limits, not a real environmental change. The same simulation showed that censored maximum-likelihood estimation, a statistical approach that treats non-detects as interval observations rather than fixed values, recovered the true zero trend on identical data.

For Consumer Confidence Reports and monthly monitoring summaries, EPA guidance recommends Cohen’s method (or trimmed or Winsorized means) for 15–50% non-detects and substitution methods below 15%. When the proportion of non-detects exceeds 75%, no reliable method exists for estimating upper confidence limits, so utilities should report the detection frequency and compute a bounding upper confidence limit by replacing non-detects with the detection limit. A dataset that is 75% non-detect is not evidence of a clean product. It is evidence of a method that cannot see most of what may be present.

For brands, the practical consequence is clear. A trend line built on substituted non-detects can show improvement that reflects a laboratory’s upgraded instrument rather than a cleaner product. Independent review of the statistical handling of non-detects matters as much as the detection results themselves.

Practical Checklist for Evaluating a Microplastics Lab Report

Any microplastics lab report used for a market claim needs a structured review of the following elements.

Detection floor stated explicitly. The report must identify the MDL and QL for the specific method and product type. A result without a stated floor cannot be interpreted, because you cannot know what “none detected” means if you do not know where the method’s vision begins.
Polymer panel documented. Once you know the method can see particles above its floor, you need to know which types of plastic it was looking for. The report must list every polymer type screened. A panel covering only four polymers leaves others unexamined. The Wellness Quality Institute’s standard WQI-CS-01 specifies a minimum panel of PE, PP, PET, PS, PVC, PA, PC, and PMMA.
Blank results reported. Procedural blanks are samples processed exactly like the test sample but containing no plastic. These blanks must be run and reported. A 2024 PNAS commentary found that a high-profile nanoplastics study’s procedural blanks appeared contaminated, which undermined its reported concentrations. Blank data is not optional.
Reporting limits below any applicable standard. If a reporting limit exceeds the applicable regulatory standard, the result cannot be used to demonstrate compliance. The same logic applies to voluntary brand standards.
Chain of custody documented. Sample integrity from collection through analysis must be traceable. Breaks in chain of custody introduce contamination risk that can invalidate results.
Matrix suitability confirmed. The method must be validated for the specific product type, such as drinking water, a functional beverage, or another liquid. A method validated for tap water is not automatically suitable for a carbonated or high-mineral-content product.
Chemical confirmation of counted particles. Visual identification without spectroscopic confirmation can lead to overestimation or underestimation. Counted particles must be chemically verified by FTIR or Raman spectroscopy.

Detection Is Not Absence: Why No Lab Can Prove a Product Is Plastic-Free

The World Health Organization’s 2019 assessment, Microplastics in Drinking-Water remains the clearest institutional statement of where the evidence stands. The report concludes that there is low concern on limited evidence, with more research urgently needed. The phrase “limited evidence” is the key point. Detection can establish presence. Detection cannot establish absence.

Finding a particle requires one confirmed observation. Proving that no particle is present would require certainty about everything the method cannot see. Three structural limits make that certainty unavailable.

Particle-size limits. No validated method detects every particle size. As shown earlier, the most stringent validated methods begin at 20 or 50 µm, which leaves everything smaller, including the entire nanoplastic range, outside the method’s reach.
Polymer diversity. No single test screens every polymer type. A result of “none detected” applies only to the polymers on the tested panel.
Lot-to-lot variability. A clean result on one production lot does not guarantee the next. The EPA declined to add microplastics to the proposed UCMR 6 list because no validated EPA or consensus drinking-water test method with the required quality control, accuracy, and precision currently exists for national monitoring.

Rolf Halden, director of the Biodesign Center for Environmental Health Engineering at Arizona State University, has stated that when a non-detect value is produced with methods that have high particle-size detection limits, significant health risks may still lurk from nanosized particles that go undetected. The honest position, and the one the scientific literature supports, is that plastics are effectively present throughout the environment. Any absolute claim of absence is a claim the science cannot currently carry.

Get independent verification that turns detection limits into honest, defensible pathway claims.

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Frequently Asked Questions

How MDL, QL, and DLR Shape a Microplastics Report

The Method Detection Limit (MDL) is the lowest concentration a method can distinguish from a blank sample at 99% statistical confidence. In plain language, it answers the question “is anything there at all.” The Quantitation Limit (QL), also called the Limit of Quantitation or LOQ, is the lowest concentration that can be measured with acceptable precision and accuracy. It answers “how much is there, reliably.” The Detection Limit for Purposes of Reporting (DLR) is the regulatory threshold below which a laboratory reports a result as non-detect rather than a number.

A result between the MDL and QL means the analyte is likely present but cannot be reliably counted. A result below the MDL means the method cannot distinguish signal from background noise. For microplastics, these distinctions matter because a “none detected” result is only meaningful relative to the specific MDL of the method used. That floor is typically 20 µm or 50 µm, which leaves the entire sub-20 µm fraction and all nanoplastics outside the method’s view entirely.

Why the 1–20 µm Size Range Is a Critical Blind Spot

The 1–20 µm range sits below the validated lower limit of both validated analytical methods, since infrared spectroscopy begins at 50 µm and Raman spectroscopy at 20 µm, yet above the nanoplastic threshold of 1 µm. This means particles in this range are neither captured by the most stringent validated public methods nor classified as nanoplastics. Research has found that this fraction may represent a substantial share of actual particle counts in water. As noted earlier, the majority of particles in real-world samples fall into this unvalidated range.

Emerging techniques, including high-frequency ultrasound combined with machine learning, are beginning to address detection at the lower end of this range. None of these approaches has yet achieved the validated, standardized status required for defensible regulatory or verification use. Until validated methods exist for this fraction, any “none detected” result from current standard methods leaves this size range entirely unexamined.

How Independent Review Turns a Lab Report into a Defensible Claim

A laboratory report records what an instrument found above its detection floor, for the polymers it screened, in the lot it tested. The report does not, on its own, assess whether the method was appropriate for the product type, whether blanks and contamination controls were adequate, whether the reporting limits are sufficient to support any claim, or what claim language the data can actually carry.

Independent review, such as the Wellness Quality Institute’s Plastic-Free Pathway Verification governed by WQI-CS-01, examines all of those elements against defined criteria and then produces approved claim language tied specifically to the reviewed evidence. The resulting claim is scope-locked to the product, dataset, particle-size range, polymer panel, and production period reviewed. That scope lock is what makes the claim defensible. It states exactly what was examined and makes no assertion about what was not.

Many companies discover through this process that their existing data supports either a narrower or a stronger claim than they had assumed. They also see that the “none detected” result on their report is bounded by the method’s floor rather than by the product itself.

Conclusion: Using Real Data for Honest Plastic-Free Pathway Claims

National Water Quality Month offers a clear moment to look closely at what water quality data actually proves and what it cannot. Every microplastics result is bounded by the method that produced it, including its detection floor, its polymer panel, its product type, and the lot it sampled. \