# Fun with mathematics

A new analysis of some of the world’s most popular bottled water brands says more than 90% contain tiny pieces of plastic.

Analysis of 259 bottles from 19 locations in nine countries across 11 different brands found an average of 325 plastic particles for every litre of water being sold.

The paper is here.

Looks rather like contamination from the packaging process – it’s higher than in tap water for example.

My own reaction was we’ve an average of 23 pieces per litre of water (median, I think) and pieces are divided into more than 100 nm and less than (so, perhaps 50 nm on average for the smaller group). nm is a millionth of a metre.

Me, I’m going to go with this being equal to nothing in the vernacular. But I’ll admit that I get lost in 10-6, volume and length measurements and so on. Anyone like to tell us all what this actually is as contamination in ppm, or ppb?

It would be fun if this plastics concentration was less than, say, the allowable levels of As in drinking water…..

## 17 thoughts on “Fun with mathematics”

1. Nit pick: particles were divided into more or less than 100 µm, not nm. A µm is a millionth of a metre.

The small particles (<100 µm) come in at roughly 1 ppb. (US EPA and WHO rules on arsenic require <10ppb in drinking water.)

For the bigger ones it doesn’t really make much sense to think that way, it’s more like the odd bit of tea leaf in your cuppa.

2. I also wonder what other “nasties” are found in tap water, or food, or fresh air. Sure, none of us want turtles dining on plastic bags, but that’s in a different league. Looking forward to any answers to Tim’s questions.

3. Arthur’s right. But if we do it by density assuming that the larger particles have an average diameter of 200µm while the smaller have an average diameter of 50µm then we get a density of 61 ppb.
Unless plastic is highly chemically active at these scales or crosses the blood-brain barrier (and is significantly chemically active) I think we can fairly safely say “meh”. Or even “go and get a real experiment!”

4. For some time now I’ve read stories like this as being mostly about how much better instruments are becoming at detecting ever-smaller quantities of things.

5. Published on same day Stephan Hawking died. Coincidence? I think not.

6. Getting units right always helps understanding this sort of thing. Even a very very tiny bit of plastic is a gajillion times larger than a water molecule. The term ‘parts per billion’ is essentially meaningless when used to describe small bits of stuff suspended in a liquid. The ratio of the number of bits of plastic to number of water molecules could be 1:An unfeasibly large number.
Bits of shit per cc – that might work.
% by volume – hmmm
% of the recommended amount of plastic shit in water according to the gummint – hmmm
We need some units to work with…..

7. Correct, TN. I worked in pollution control in the early 1970s. There was nothing we could measure aT concentrations below parts per MILLION.

8. So the bottled water, packaged in plastic, contains a microscopically small amount of synthetic dietary fibre.

So what?

9. Patrick, concentration is about 10 to the minus 9 by volume. That’s what I mean by ppb (as do most people).

10. File under, ‘So what?’

Plastic is slow (millions of years slow) to biodegrade, and is insoluble so those particles will pass through the intestine. A very small amount of very, very, very small particles might collect in body tissue, but since they do not break down… so what?

There are plasticisers in plastics which can leach out over time and these chemicals are harmful, but in such tiny amounts they would pose no risk in a lifetime.

So we have a ‘gizza grant’ report. And a topic for the political slime and envirofreaks to demand ‘something be done’… let’s ban bottled water, or better still tax it or ban/tax water.

Any news on glass particles in liquids?

11. The relevant comparison to make is with sand.

Natural erosion by rivers and seas batters rocks on cliffs and mountains, and grinds them down to powder, which settles on the bottom of the sea, and is compacted to form rock again. Plastic has just joined this natural cycle.

Rocks are generally made or ores of various frequently toxic chemicals. The stuff we dig up in mines, erosion grinds up and drops in the sea. Uranium ores. Radium ores, Arsenic ores, Copper, Beryllium, Cadmium, Lead, Mercury, Lithium, Manganese, Thallium … the whole periodic table. And the insoluble stuff makes up sand and sediment, which animal life also eats and absorbs, and can potentially also build up in their bodies.

So you need to compare the toxicity and prevalence of plastic with that of sand and silt if you want to make a rational assessment of risks. Nobody does, though.

12. ‘Natural erosion by rivers and seas batters rocks on cliffs and mountains, and grinds them down to powder’

I hope you are not in a teaching position.

13. *counts* naught dot 4 units per milliliter…

That’s less than the most stringent bacteriological requirements for water, except maybe for biomolecular work.

14. “I hope you are not in a teaching position.”

Weird hope to have.

It’s first-year GCSE geography. Or it is in our universe at least. I don’t know about yours…

15. As per all the comments above. but one point escapes me.100microns (µm) is a large particle. a human hair is around 17 -100. typical micro water filter will removal particle down to 1 micron. So this begs the question – is this stuff not filtered at sourced (or bottled) and how dirty are the bottles? it terms of ppm – particles in fluid are measure in counts/ml. in a range of sizes ie . Size range: 2 µm – 100 µm; so 8 size channels would be: 2, 5, 10, 15, 20, 25, 50, 100 µm.

16. “So this begs the question – is this stuff not filtered at sourced (or bottled) and how dirty are the bottles?”

I think when plastic is molded, you get protrusions squeezing out at the edges of the mold which have to be trimmed off. or some parts are cut out after molding, leading to plastic ‘sawdust’ in the factory. Some of these will inevitably end up in the product.

It depends what you class as “dirty”.

17. Those amounts are what engineers call as near to F-all as makes no differences. For those of us who live surrounded by a soup of harmful stuff, by which I mean all of us, this thing, which was always with us but we didn’t know, will also make no difference.