No need for slime panic: it’s not going to poison anyone

This is one of my favourite photos, so I’m using it again.

The school summer holidays are fast approaching and, for some reason, this always seems to get people talking about slime. Whether it’s because it’s a fun end-of-term activity, or it’s an easy bit of science for kids to do at home, or a bit of both, the summer months seem to love slimy stories. In fact, I wrote a piece about it myself in August 2017.

Which (hoho) brings me to the consumer group Which? because, on 17th July this year, they posted an article with the headline: “Children’s toy slime on sale with up to four times EU safety limit of potentially unsafe chemical” and the sub-heading: “Eight out of 11 popular children’s slimes we tested failed safety testing.”

The article is illustrated with lots of pots of colourful commercial slime pots with equally colourful names like Jupiter Juice. It says that, “exposure to excessive levels of boron could cause irritation, diarrhoea, vomiting and cramps in the short term,” and goes on to talk about possible risks of birth defects and developmental delays. Yikes. Apparently the retailer Amazon has removed several slime toys from sale since Which? got on the case.

The piece was, as you might expect, picked up by practically every news outlet there is, and within hours the internet was full of headlines warning of the dire consequences of handling multicoloured gloopy stuff.

Before I go any further, here’s a quick reminder: most slime is made by taking polyvinyl alcohol (PVA – the white glue stuff) and adding a borax solution, aka sodium tetraborate, which contains the element boron. The sodium tetraborate forms cross-links between the PVA polymer chains, and as a result you get viscous, slimy slime in place of runny, gluey stuff. Check out this lovely graphic created by @compoundchem for c&en’s Periodic Graphics:

The Chemistry of Slime from cen.acs.org (click image for link), created by Andy Brunning of @compoundchem

And so, back to the Which? article. Is the alarm justified? Should you ban your child from ever going near slime ever again?

Nah. Followers will remember that back in August last year, after I posted my own slime piece, I had a chat with boron-specialist David Schubert. He said at the time: “Borax has been repeated[ly] shown to be safe for skin contact. Absorption through intact skin is lower than the B consumed in a healthy diet” (B is the chemical symbol for the element boron). And then he directed me to a research paper backing up his comments.

Borax is a fine white powder, Mixed with water it can be used to make slime.

This, by the way, is all referring to the chemical borax – which you might use if you’re making slime. In pre-made slime the borax has chemically bonded with the PVA, and that very probably makes it even safer – because it’s then even more difficult for any boron to be absorbed through skin.

Of course, and this really falls under the category of “things no one should have to say,” don’t eat slime. Don’t let your kids eat slime. Although even if they did, the risks are really small. As David said when we asked this time: “Borates have low acute toxicity. Consumption of the amount of borax present in a handful of slime would make one sick to their stomach and possibly cause vomiting, but no other harm would result. The only way [they] could harm themselves is by eating that amount daily.”

It is true that borax comes with a “reproductive hazard” warning label. Which? pointed out in their article that there is EU guidance on safe boron levels, and the permitted level in children’s’ toys has been set at 300 mg/kg for liquids and sticky substances (Edited 18th July, see * in Notes section below).

EU safety limits are always very cautious – an additional factor of at least 100 is usually incorporated. In other words, for example, if 1 g/kg exposure of a substance is considered safe, the EU limit is likely to be set at 0.01 g/kg – so as to make sure that even someone who’s really going to town with a thing would be unlikely to suffer negative consequences as a result.

The boron limit is particularly cautious and is based on animal studies (and it has been challenged). The chemists I spoke to told me it’s not representative of the actual hazards. Boron chemist Beth Bosley pointed out that while it is true that boric acid exposure has been shown to cause fetal abnormalities when it’s fed to pregnant rats, this finding hasn’t been reproduced in humans. Workers handling large quantities of borate in China and Turkey have been studied and no reproductive effects have been seen.

Rat studies, she said, aren’t wholly comparable because rats are unable to vomit, which is significant because it means a rat can be fed a large quantity of a boron-containing substance and it’ll stay in their system. Whereas a human who accidentally ingested a similar dose would almost certainly throw up. Plus, again, this is all based on consuming substances such as borax, not slime where the boron is tied up in polymer chains. There really is no way anyone could conceivably eat enough slime to absorb these sorts of amounts.

These arguments aside, we all let our children handle things that might be harmful if they ate them. Swallowing a whole tube of toothpaste would probably give your child an upset stomach, and it could even be dangerous if they did it on a regular basis, but we haven’t banned toothpaste “just in case”. We keep it out of reach when they’re not supposed to be brushing their teeth, and we teach them not to do silly things like eating an entire tube of Oral-B. Same basic principle applies to slime, even if it does turn out to contain more boron than the EU guidelines permit.

In conclusion: pots of pre-made slime are safe, certainly from a borax/boron point of view, so long as you don’t eat them. The tiny amounts of boron that might be absorbed through skin are smaller than the amounts you’d get from eating nuts and pulses, and not at all hazardous.

Making slime at home can also be safe, if you follow some sensible guidelines like, say, these ones:

Stay safe with slime by following this guidance

Slime on, my chemistry-loving friends!


Notes:
* When I looked for boron safety limits the first time, the only number I could find was the rather higher 1200 mg/kg. So I asked Twitter if anyone could direct me to the value Which? were using. I was sent a couple of links, one of which contained a lot of technical documentation, but I think the most useful is probably a “guide to international toy safety” pamphlet which includes a “Soluble Element Migration Requirements” table. In the row for boron, under “Category II: Liquid or sticky materials”, the value is indeed given as 300 mg/kg.

BUT, there is also ” Category I: Dry, brittle, powder like or pliable materials” and the value there is the much higher 1,200 mg/kg. Which begs the question: does slime count as “pliable” or “sticky”? It suggests to me that, say, a modelling clay product (pliable) would have the 4x higher limit. But surely the risk of exposure would be essentially the same? If 1,200 mg/kg is okay for modelling clay, I can’t see why it shouldn’t be for slime. In the Which? testing, only the Jupiter Juice product exceeded the Category I limit, and then not by that much (1,400 mg/kg).

Also (the notes are going to end up being longer than the post if I’m not careful), these values are migration limits, not limits on the amount allowed in the substance in total. Can anyone show that more than 300 mg/kg is able to migrate from the slime to the person handling it? Very unlikey. But again, don’t eat slime.

This is not an invitation to try and prove me wrong.

I suppose it’s possible that someone could sell slime that’s contaminated with some other toxic thing. But that could happen with anything. The general advice to “wash your/their hands and don’t eat it” will take you a long way.


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The Chronicles of the Chronicle Flask: 2017

We’ve made it! Not only to 2018 (which was starting to look doubtful earlier in the year), but also to the Chronicle Flask’s 100th post. Which doesn’t seem that many, really, but since posts on here frequently run to 1500 words, that adds up to a rather more impressive-sounding 150,000 words or so. I mean, that’s like… half a Brandon Sanderson novel. Oh.

Anyway, it’s time for a yearly round-up. Here goes!

Last January I began with a post about acrylamide. We’d all been enjoying lots of lovely crispy food over Christmas; it was time to tell us about the terrible dangers of such reckless indulgence. The newspapers were covered with pictures of delicious-looking chips, toast and roast potatoes alongside scary headlines such as:  “Crunchy toast could give you cancer, FSA warns”. The truth was not quite so dramatic. Acrylamide does form when foods are cooked to crispiness, and it is potentially harmful, but the quantities which form in food are tiny, and very unlikely to cause you any serious harm unless you literally live on nothing but burnt toast. The FSA (Food Standards Agency) hadn’t significantly revised their guidelines, it turned out, but were in fact only suggesting that the food industry should be mindful of acrylamide levels in food and seek to reduce them as much as possible. That wouldn’t have made for quite such a good “your food is going to killllll you!” story though, I suppose.

In February the spikey topic of vaccination came up. Again. Vaccines are awesome. They protect us from deadly diseases. No, I don’t want to hear any nonsense about “Big Pharma“, and I definitely don’t want to hear how “natural immunity” is better. It’s not. At best, it might provide a similar level of protection (but not in every case), but it comes with having to suffer through a horrible, dangerous disease, whereas vaccination doesn’t. It ought to be a no-brainer. Just vaccinate your kids. And yourself.

It was Red Nose Day in the UK in March, which brought some chemistry jokes. Turns out all the best ones aren’t gone, after all. Did you hear about the PhD student who accidentally cooled herself to absolute zero? She’s 0K now.

April brought a post which ought to have been an April Fool’s joke, but wasn’t. Sceptics often point out that homeopathy is just sugar and water, but the trouble is, sometimes, it’s not. There’s virtually no regulation of homeopathy. As far as I’ve been able to establish, no one tests homeopathic products; no one checks the dilutions. Since a lot of the starting materials are dangerously toxic substances such as arsenic, belladona, lead and hemlock, this ought to worry people more than it does. There has been more than one accidental poisoning (perhaps most shockingly, one involving baby teething products). It really is time this stuff was banned, maybe 2018 will be the year.

In May I turned to something which was to become a bit of a theme for 2017: alkaline water. It’s not so much that it doesn’t do anything (although it really doesn’t), more the fact that someone is charging a premium for a product which you could literally make yourself for pennies. It’s only a matter of dissolving a pinch of baking soda (sodium bicarbonate) in some water.

June brought a selection of periodic tables because, well, why not? This is a chemistry blog, after all! And now we’ve finally filled up period seven they do have a rather elegant completness. 2019, by the way, has just been announced as the International Year of the Periodic Table of Chemical Elements, to coincide with IUPAC’s 100th anniversary and the 150th anniversary of Mendeelev’s discovery of periodicity (his presentation, The Dependence Between the Properties of of the Atomic Weights of the Elements, was made on 6th March 1869). Looks like 2019 will be an exciting year for chemists!

In July it was back to the nonsense of alkaline diets again, when Robert O. Young was finally sentenced to 3 years, 8 months in custody for conning vulnerable cancer patients into giving him large sums of money for ineffective and dangerous treatments. Good. Moving on.

August brought me back to a post that I’d actually started earlier in the year when I went to a March for Science event in April. It was all about slime, and August seemed like a good time to finally finish it, with the school holidays in full swing – what could be more fun on a rainy day at home than making slime? Slime was a bit of a 2017 craze, and there have been a few stories featuring children with severely irritated skin. But is this likely to be caused by borax? Not really. Turns out it’s actually very safe. Laundry detergents in general, not so much. In short, if you want to make slime the traditional way with PVA glue and borax, fill your boots. (Not really – your parents will be uninpressed.)

In September it was back to quackery: black salve. A nasty, corrosive concoction which is sold as a cancer cure. It won’t cure your cancer. It will burn a nasty great big hole in your skin. Do not mess with this stuff.

October carried on in a similar vein, literally. This time with a piece about naturopaths recommending hydrogen peroxide IVs as a treatment for lots of things, not least – you guessed it – cancer. Yes, hydrogen peroxide. The stuff you used to bleach hair. Intraveneously. Argh.

The puking pumpkin!

The end of the month featured a far better use for hydrogen peroxide, that of the puking pumpkin. Definitely one to roll out if, for any reason, you ever find yourself having to demonstrate catalysis.

November brought us, somewhat unseasonally, to tomatoes. Where is the best place to store them? Fridge or windowsill? Turns out the answer involves more chemistry than you might have imagined.

And then, finally, December. Looking for a last-minute Christmas gift? Why not buy a case of blk water? I mean, other than it’s an exorbitantly priced bottle of mysterious black stuff which doesn’t do any of the things it claims to do, and might actually get its colour from coal deposits, that is.

And that, dear friends and followers, is it for 2017! Happy New Year! Remember to be sceptical when the inevitable “deadly food” story appears in a few weeks….


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Unsafe slime? How bad is borax, really?

Slime is a fun bit of chemistry that anyone can do – but how safe is it?

It’s August, which means it’s the school summer holidays in the UK and, as is traditional, it’s been pouring with rain. This has left many a cabin-fevered child searching for ways to amuse themselves.

Start hunting around the internet for things to do and it’s not long before the concept of the “kitchen science” experiment turns up. There are actually loads of these, and it’s even possible to do some of them without permanently damaging anyone’s eardrums, dusting every surface with cornflour and leaving a parent rocking in the corner muttering “why did I encourage this?” over and over to themselves.

Which brings me to slime – surely the go-to fun science experiment. What’s not to love about taking some of that white, runny PVA glue found in gallon bottles in school classrooms everywhere and magically turning it into glorious, gloopy slime? Add some food colouring and you can even have coloured slime! Add glitter and… well you get the idea.

Many YouTubers love this stuff. A quick search for “make your own slime” turns up pages and pages of videos, giving instructions as to how to do just that.

In fact, it seems that slime-making is currently a bit of a craze, with children all over the world making all kids of different types. There’s unicorn slime, rainbow slime, fluffy slime – you name it. Brilliant, you might think, a whole generation of youngsters interested in chemistry. What’s not to like about that?

Well, as a few news reports have recently pointed out, there might be a problem if children are handling lots of borax, or certain other chemicals.

Polyvinyl alcohol

Slime, you see, is a really nice example of polymerisation – the same process that goes on when plastics are made. PVA glue, the usual starting material, is a polymer itself. The letters PVA stand for polyvinyl alcohol (its systematic name is poly(1-hydroxyethylene)), but literally no one calls it that, not even A-level chemistry teachers forced, kicking and screaming, to follow IUPAC naming conventions).

PVA is a long chain of carbon atoms with alternating CH2 groups and alcohol, OH, groups. As anyone who’s ever handled it will know, it’s quite runny. Thick, yes, but still runny. Basically, it’s a liquid.

But if you mix it with borax, aka sodium tetraborate, some magic happens. And when I say magic, I mean chemistry. The chains of atoms become linked together (edit July 2018: I originally said via hydrogen bonds but turns out that’s not quite right – check out this page on c&en for more info), and as a result the new substance is a lot more solid. But it’s not quite solid. At least, not in the sense of something that keeps its own shape. No, this is weird, peculiar, stuff that sits somewhere in between solid and liquid.

Borax joins the chains of PVA together.

There’s something tactilely pleasing about slime. Put it in your hands and it feels cool and slightly moist – your fingers slide over and through it with a sort of squeaky sensation. Leave it alone for a few minutes and it flows to take the shape of its container, forming a perfect, mirror finish on its surface. Tip the pot over, and it will gradually creep toward the edge.

It is safe to handle. Here are my hands, handling it (we made this at the March for Science in Bristol back in April). You will notice that my skin is not falling off.

It’s white unless you dye it. We went for red, which is pleasingly disturbing.

I did, though, wash my hands after I took that photo. And that’s because, while the PVA is pretty harmless (as you know if, like me, you spent your primary school days painting your hands with glue just so you could peel it off later) the borax isn’t. At least, not entirely.

Before I go any further, let’s be clear: lots of things aren’t “entirely” safe. Most of the cleaning products in the average kitchen and bathroom have warning levels of varying degrees of severity on them, and we don’t think too much about it. Even things that are designed to be in contact with skin, like hand soap and shampoo, usually have warnings about eye irritation and statements like “if irritation occurs, discontinue use”. Even water is deadly in the wrong context (don’t try inhaling too much of it, for example). So when I say not entirely safe, I don’t mean to suggest that panic needs to ensue if your child has so much as looked at a borax solution.

Borax has traditionally been used in several household products, although admittedly more in the US than in the UK. Most people know it as a laundry additive, where it softens water, brightens whites and inhibits the growth of the bacteria and fungi which can make clothes stinky.

It’s not considered a lethal compound, in the sense that you’d have to eat a large quantity – far more than anyone might reasonably consume by accident – before it became deadly, and you’d almost certainly throw up long before then. Borax can irritate the skin (but see note at the end), and inhalation of the dust is well known to irritate the lungs. This is more of a concern for people working with borax on an industrial scale day in and day out – but it could become an issue if, say, someone were making slime every single day using large quantities of borax (not recommended).

Then there’s another concern. If borax is exposed to hydrochloric acid, it forms boric acid. Long-term exposure to boric acid can cause kidney damage and fertility problems, both in men and women. It’s also potentially teratogenic, which means it could cause harm to an unborn child. Borax and boric acid are not the same thing but, of course, our stomachs contain hydrochloric acid. Therefore, if you swallow borax, you’re effectively exposed to boric acid.

Frequent exposure to borax might cause skin irritation (see note at end)

These risks are the reason borax was added to the Substance of Very High Concern (SVHC) candidate list on 16 December 2010, which is the first step in restricting use of the chemical within the European Union. As far as I can establish, it’s still a “candidate”, but the European Chemicals Agency substance information card does state that borax may “damage fertility or the unborn child”.

Now, the chances of achieving the levels involved in “long-term exposure” from occasionally handling borax solutions are slim to none. It’s safe to handle dilute borax solutions (see notes at the end). Indeed, borax is even approved as a food preservative in the EU (E285). To put it into context, alcohol (ethanol) also causes organ damage and is a known teratogen and a carcinogen (which borax isn’t) and that turns up in all sorts of things we’re regularly in contact with, everything from antiseptic hand gels to mouthwashes to drinks (and it’s also approved as a food additive, E1510 – which is good news if you like liqueur chocolates).

I personally have no concerns about handling dry borax in small quantities to make up solutions myself. However, I wouldn’t let children do that part. Once made I’d consider the solution safe, so long as children were supervised and weren’t doing anything really silly like drinking it. I’d also tell children to wash their hands after handling the slime and, if I thought they had sensitive skin for any reason (eczema, say) I’d suggest plastic gloves.

Borax is easy to buy online.

Because of the European Regulations, it theoretically shouldn’t be that easy to get hold of borax in the UK. But I found it for sale on Amazon.co.uk. The listing says that it “can only be purchased by Professionals and by trade and business users,” (sic) but I ordered some and there were no checks. A plastic bag full of borax powder (the decahydrate, Na2B4O7.10H2O) arrived within a few days.

Most of the news reports doing the rounds have involved children suffering from severe skin irritation. For example, in February this year a woman from Manchester posted photos of chemical burns on her daughter’s hands online as a warning to other parents. However, looking into the details of that story it turns out that she wasn’t using borax. In fact, she used fabric detergent “as an alternative”.

Take a look at pretty much type of fabric detergent and you’ll find hazard warnings, usually indicating it’s corrosive and definitely saying “keep out of reach of children”. Those are there for a reason. Fabric detergent is designed to remove grease and  stains. In other words, to break down fats and proteins, and guess what your skin is made of? Yep. Don’t get neat fabric detergent on your hands. Even if your skin isn’t particularly sensitive, it’s almost certainly going to irritate it.

Fabric detergents are usually labelled corrosive.

Bottom line: don’t use fabric detergent as a borax alternative to make slime, because there’s a real risk that enough of it could get onto your (or your child’s) skin that it could irritate.

When it comes to borax itself, if I understand things correctly, it’s not actually restricted in the EU – including the UK – yet. (I might have this wrong – do correct me if you think I have.) It’s not something you can pop to the supermarket and buy, but as we’ve established you can buy it online fairly easily.

Borax solutions are extremely unlikely to cause harm, if used sensibly (boron chemist David Schubert agrees, see note at the end). But, once again: if you’re doing this experiment it’s best not to let children make up the solution – an adult should do that part.

A sensible quantity is about 1 gram of borax in 25 millilitres of warm water (for those without a metric scale: one level teaspoon of borax in half a cup measure of water). This will actually polymerise quite a bit of PVA – you don’t need that much. I recommend making the borax solution in a labelled plastic cup which you should throw away afterwards. Don’t leave it anywhere where someone might mistake it for their drink! Once the solution is made just add a little bit to some PVA in another plastic cup, give it a good stir with a spoon or a lolly stick, and the magic (chemistry) will happen. Add food colouring if you like (be aware that it can stain!) and enjoy the slimy goodness. (See additional note for teachers & technicians at the end.)

Do supervise any and all slime-making, don’t let children handle slime all day, every day, and if you know they have sensitive skin, make them wear plastic gloves. Make them wash their hands before they eat or drink anything.

If a child has made slime somewhere else, at a party or a science club, say, and they bring it home, again, there’s no need to worry. They can play with it perfectly safely. Don’t let them leave it on a radiator, though. That will end in disaster.

I am not a fan of the “it might be a bit dangerous, so no one should ever try it” mentality. I mean, that’s just no fun, is it? But I’m also not a fan of unnecessary risks – because trips to hospital are equally no fun. So if you want to try this experiment, I’ve summarised my guidance in this graphic.

Stay safe with slime by following this guidance

And if you want a even safer slimy experiment, and you can bear the mess, I suggest mixing cornflour with just enough water to make a thick paste in a shallow tray. Then let your kids stick their fingers in it, bounce things off it, and generally play with it. (Check out this link to find out more about why it behaves as it does.) I’m told it makes an even better mixture if you add basil seeds.

Have fun this summer, stay safe, and don’t eat the slime!

Note for teachers and technicians:
This post is aimed at people who might be making slime at home, and hence not have easy access to CLEAPSS guidelines. Anyone doing the experiment with students in school should, of course, refer to their department’s risk assessments and policies. For the record, at the time of writing, CLEAPSS classify 0.2M or 40g/dm³ (or more dilute) borax solutions as “low hazard”.

Edit: 15th August 2017:
After I wrote and published this post I was contacted by someone who specialises in boron chemistry, David Schubert. Now, if anyone knows about boron safety, it’ll be the guy who spends all day working with boron-based chemicals! He told me that borax has been shown to be safe for skin contact. He also said that you absorb less boron through intact skin than you consume by eating a normal, healthy diet (boron is a naturally-occurring trace-mineral – nuts and pulses are good sources), and even provided me with a link to a research paper on the subject. I asked him about the high pH of boron solutions, since alkaline solutions can be irritating in general, and he told me that borax solutions are less alkaline than sodium carbonate and not at all irritating to skin. At this point I will stress that when we’ve seen reports of children suffering skin irritation after making slime, it hasn’t been clear exactly what they’ve been handling. It’s very likely they were adding other chemicals to their slime, and it was actually one of those causing the irritation. Perhaps they developed an allergy to something. It’s impossible to say. Either way, the bottom line is that borax solutions are pretty safe – there’s no need to worry. (Still don’t drink them though!)


Like the Chronicle Flask’s Facebook page for regular updates, or follow @chronicleflask on Twitter. All content is © Kat Day 2017. You may share or link to anything here, including the images, but you must reference this site if you do.


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