Microplastic Testing: What a Lab Can Actually Measure — and Why “None Detected” Isn’t Clean

What “testing” actually means

There is a gap between two questions that sound identical. Are there particles in this water? is easy, and you can almost answer it with a coffee filter and a cheap microscope. Are those particles plastic, and which plastic? is the hard one, and it is the only one that counts.

A fibre under a microscope can be polyester, cotton, wool or rayon, and at 20 micrometres they look broadly alike. A fragment can be polyethylene or it can be a grain of silica. Identification requires reading the material’s chemistry, not its shape, and that is what separates a laboratory result from a photograph of some specks on a filter.

Three instruments do that job. They work in genuinely different ways, and — this is the part that gets lost — they answer genuinely different questions.

Read the last column and the awkwardness becomes obvious. The method with the best size resolution is the one most easily defeated by ordinary dirt, and the method that gives you a clean mass number destroys the particles to get it. There is no single instrument that answers every question at once, which is why serious studies often run two and why two labs can hand you different-looking numbers for the same bottle without either being wrong.

What you can actually buy in 2026

Mail-in water testing is a real, functioning consumer market, and the reputable end of it is not a scam. You collect a sample in supplied bottles under fairly strict instructions, post it to an accredited laboratory, and receive a report some weeks later. The better services combine optical and polarised-light microscopy for counting with Raman confirmation for polymer identification, which is the step that makes it a microplastic test rather than a particle count.

What you should expect for your money, and what you should not:

The third row is the one worth paying for. A single test of your water tells you a number you cannot interpret. Two tests — one before your filter and one after — tell you something you can act on immediately. Whatever the absolute counts are, the ratio between them is a direct measurement of whether the device on your counter is doing its job. If you are going to spend money on testing once, spend it that way. Our comparison of water filters covers which technologies should be expected to show a difference.

The floor problem, which is the real story

Here is the tension nobody selling a test is keen to explain.

The research that made people care about microplastics in the first place is research on small particles. The studies finding plastic in placenta, in blood, in arterial plaque and in brain tissue are overwhelmingly working at the bottom of the size range and below it, in the sub-micrometre and nanoplastic region. That is precisely because small particles are the ones that cross membranes. A 50-micrometre fragment does not enter a cell. A 200-nanometre one is a different physical proposition entirely.

Now put that next to the detection floors. The consumer test you can buy sees down to about 1 to 10 micrometres. The particles that drove the health concern are, in large part, below that line.

This does not make testing worthless — knowing your filter works is genuinely useful, and the larger fraction is real. But it does mean a reassuring report should be read carefully. “None detected” is a statement about an instrument, not a clean bill of health for your water. Any laboratory worth using will state its limit of detection somewhere on the report. That number is the most important thing on the page, and it is almost always in the smallest type.

For what is known about the particles that do get into people, see microplastics in the brain and what the health evidence actually shows.

Why older results do not compare

Until very recently there was no international standard for this at all. Every laboratory made its own defensible choices about filter pore size, the smallest particle it would count, how it removed organic matter, and how it controlled for the polyester fibres shedding off the analyst’s own clothing. Those choices move the final number by more than the differences between water sources do.

ISO 16094-2 was published in September 2025, covering microplastic analysis of clean water, with Parts 3 and 4 still to come. It is the beginning of comparability rather than the arrival of it. The practical consequence for anyone reading numbers today:

• Two results from different labs are not directly comparable unless both state the same method and the same size cut-off. A lab counting from 1 µm will always report more particles than one counting from 10 µm, testing the identical bottle.
• Headline figures from before 2025 carry method variation inside them. This is a large part of why published bottled water counts range across orders of magnitude.
• Ask which standard was used. A laboratory that answers “ISO 16094-2” is telling you something meaningful. One that cannot name a method is telling you something too.

The test that does not exist

This is the most common question we get and the answer is unambiguous. You cannot pay anyone to tell you how many microplastics are in your body. There is no accredited clinical assay, no direct-to-consumer blood panel, and no validated stool test for microplastics. Where you see one offered, treat it as a red flag rather than a breakthrough.

The reason is not squeamishness — it is contamination control. Detecting a handful of plastic particles in a few millilitres of blood means proving they did not come from the sample tube, the needle, the lab air or the analyst’s sleeve. Research groups manage it with blank controls, filtered air and glass everything, and even then the field argues about the results. That level of control cannot survive a postal-service workflow, which is exactly why the studies you have read about are studies and not services.

What to actually do

• Test the filter, not the water. A before-and-after pair on the same day, same tap, same lab is worth more than any single absolute number you will ever receive.
• Read the limit of detection first. Before the headline count, find the size cut-off. It reframes everything above it, and a report without one should not be trusted.
• Insist on polymer identification. If the method is microscopy alone with no FTIR or Raman step, you have bought a particle count and not a microplastic test.
• Ignore any at-home kit promising instant results. The identification step requires instruments that cost more than a car. Nothing arriving in an envelope with a colour chart is doing it. Our honest guide to at-home testing goes through what the DIY options can and cannot show.
• Do not buy a body test. It does not exist. If someone is selling one, that fact tells you what you need to know about them.
• Consider skipping the test entirely. For most households the money is better spent on a filter with published particulate performance than on measuring a problem whose remedy you already know. Testing is for verifying a fix, not for deciding whether to bother.

For where the exposure actually comes from, see microplastics in tap water and microplastics in bottled water. For the filter question specifically, see do Brita filters remove microplastics.