Microplastics & nanoplastics
Nanoplastics: the plastic you'll never see
Nanoplastics are plastic particles smaller than one micron — a thousand times thinner than a human hair. They are the smaller, more dangerous half of the plastic in your water. Microplastics you can stain, filter, and count at home. Nanoplastics slip through all of it — through filters, through your gut lining, through the blood-brain barrier, and into the cells themselves. When people talk about “plastic in water,” they almost always mean microplastics. The bigger story is the part nobody can see.
Microplastics vs nanoplastics: it's all about size
Microplastics
1 µm – 5 mm
Big enough to trap on a filter and stain pink under blue light. Mostly stay in the gut and pass through. This is what an at-home kit counts.
Nanoplastics
< 1 µm
Below the resolution of any optical method. Small enough to cross cell membranes and the blood-brain barrier. Detectable only with lab instruments.
One micron is the dividing line, and it's not arbitrary. Above it, a particle behaves like debris — it gets caught, counted, and mostly excreted. Below it, plastic starts behaving like a dissolved substance: it moves through barriers that stop larger particles cold. That single order-of-magnitude difference in size is the difference between “in your water” and “in your bloodstream.”
Why nanoplastics are the part that matters
They cross into your body. Microplastics are largely trapped in the digestive tract and excreted. Nanoplastics are small enough to pass through the intestinal wall, enter the bloodstream, and reach organs. Researchers have now found plastic particles in human blood, placenta, testes, and brain tissue — and the particles small enough to get there are overwhelmingly nanoplastics.
There are far more of them. In 2024, a Columbia University team (Qian et al., PNAS) used a new laser-imaging technique and found bottled water averages ~240,000 plastic particles per liter — 10 to 100 times higher than every previous count. Roughly 90% were nanoplastics, which older methods literally could not see. The plastic was always there. The instruments finally caught up.
The number to remember
~240,000 particles per liter of bottled water — and about 9 out of 10 are nanoplastics. When you count microplastics, you're seeing the tip of a much larger iceberg.
What it takes to detect nanoplastics
Here's the honest part. Nanoplastics are below the resolution of any optical method — including the Nile Red fluorescence staining our at-home kit uses. No consumer product counts nanoplastics, and anything claiming to is selling you a number it can't back up. Detecting them requires lab-grade instruments:
py-GC/MS
Pyrolysis gas chromatography–mass spectrometry. Burns the sample and identifies the plastic by its chemical signature. Measures mass, not particle count — and works below the optical limit.
Stimulated Raman scattering (SRS) microscopy
The technique behind the 2024 Columbia bottled-water study. Uses laser light to fingerprint individual particles down to ~100 nm, fast enough to count hundreds of thousands per liter.
Electron microscopy
Resolves individual nanoplastic particles by firing electrons instead of light. Extremely high resolution, extremely low throughput — one sample at a time, in a specialized lab.
All three live in a lab and cost hundreds to thousands of dollars per sample. That's the trade-off: labs catch nanoplastics; an at-home kit catches the microplastics you can act on — today, for $50.
So why count microplastics at all?
Because the two travel together. Where a water source sheds a lot of microplastics, it's shedding far more nanoplastics you can't see — same bottle, same pipe, same filter failure. The microplastic count is the visible, measurable proxy for a much larger invisible load. You can't count the nanoplastics at home, but you can find the source that's producing both — and that's the thing you can actually change. Test your tap against your filter, your bottled water against your tap, and follow the plastic back to where it's coming from.
FAQ
What is the difference between microplastics and nanoplastics?
It's purely a question of size. Microplastics are plastic fragments between 1 micron (1 µm = 1,000 nanometers) and 5 millimeters. Nanoplastics are smaller than 1 micron — down to a few nanometers. The cutoff matters because below ~1 µm, particles start behaving less like debris and more like a dissolved substance: they pass through filters, cross biological membranes, and travel into tissues and cells that microplastics can't reach.
Why are nanoplastics considered more concerning than microplastics?
Because they go places microplastics can't. Microplastics are mostly trapped in the gut and excreted. Nanoplastics are small enough to cross the intestinal lining, enter the bloodstream, pass the blood-brain barrier, and accumulate inside individual cells. Studies have detected plastic particles in human blood, placenta, testes, and brain tissue — and the particles small enough to get there are overwhelmingly in the nano range.
How many nanoplastics are in bottled water?
A landmark 2024 study from Columbia University (Qian et al., PNAS) used a new laser-based imaging technique and found that a liter of bottled water contains on average ~240,000 detectable plastic particles — roughly 10–100× more than earlier microplastic-only counts. Crucially, about 90% of those particles were nanoplastics, which prior methods couldn't even see. The plastic was always there; the instruments just couldn't detect it until now.
Can an at-home kit test for nanoplastics?
No — and any kit that claims to is misleading you. The Water Test at-home kit detects microplastics down to about 1 micron, the lower bound of conventional microplastic counting. Nanoplastics are below the resolution of any optical method, including the Nile Red staining the kit uses. Counting nanoplastics requires lab instrumentation: py-GC/MS, stimulated Raman scattering (SRS) microscopy, or electron microscopy. The honest answer is that no consumer product detects nanoplastics, and we'd rather tell you that than sell you a number we can't stand behind.
If the kit can't see nanoplastics, why is it still useful?
Because microplastics are a proxy you can act on. Where there's a high microplastic count, there's almost always a far larger nanoplastic load you can't see — the two travel together. Counting the microplastics you can measure tells you which water source, filter, or bottle is shedding plastic, and lets you compare options side by side. You fix the source; you reduce both fractions at once.
Do water filters remove nanoplastics?
Some do, partially. Reverse osmosis membranes have pore sizes small enough to reject a large fraction of nanoplastics; most pitcher and faucet filters do not. But filter performance on the nano scale is hard to verify outside a lab. What you can verify at home is the microplastic reduction — test your tap, test the filtered output, and compare the counts. A filter that slashes the microplastic count is your best available signal that it's also catching the nano fraction.