Spectacular Strawberry Science!

Garden strawberries

Yay! It’s June! Do you know what that means, Chronicle Flask readers? Football? What do you mean, football? Who cares about that? (I jest – check out this excellent post from Compound Interest).

No, I mean it’s strawberry season in the U.K.! That means there will be much strawberry eating, because the supermarkets are full of very reasonably-priced punnets. There will also be strawberry picking, as we tramp along rows selecting the very juiciest fruits (and eating… well, just a few – it’s part of the fun, right?).

Is there any nicer fruit than these little bundles of red deliciousness? Surely not. (Although I do also appreciate a ripe blackberry.)

And as if their lovely taste weren’t enough, there’s loads of brilliant strawberry science, too!

This is mainly (well, sort of, mostly, some of the time) a chemistry blog, but the botany and history aspects of strawberries are really interesting too. The woodland strawberry (Fragaria vesca) was the first to be cultivated in the early 17th century, although strawberries have of course been around a lot longer than that. The word strawberry is thought to come from ‘streabariye’ – a term used by the Benedictine monk Aelfric in CE 995.

Woodland strawberries

Woodland strawberries, though, are small and round: very different from the large, tapering, fruits we tend to see in shops today (their botanical name is Fragaria × ananassa – the ‘ananassa’ bit meaning pineapple, referring to their sweet scent and flavour.

The strawberries we’re most familiar with were actually bred from two other varieties. That means that modern strawberries are, technically, a genetically modified organism. But no need to worry: practically every plant we eat today is.

Of course, almost everyone’s heard that strawberries are not, strictly, a berry. It’s true; technically strawberries are what’s known as an “aggregate accessory” fruit, which means that they’re formed from the receptacle (the thick bit of the stem where flowers emerge) that holds the ovaries, rather than from the ovaries themselves. But it gets weirder. Those things on the outside that look like seeds? Not seeds. No, each one is actually an ovary, with a seed inside it. Basically strawberries are plant genitalia. There’s something to share with Grandma over a nice cup of tea and a scone.

Anyway, that’s enough botany. Bring on the chemistry! Let’s start with the bright red colour. As with most fruits, that colour comes from anthocyanins – water-soluble molecules which are odourless, moderately astringent, and brightly-coloured. They’re formed from the reaction of, similar-sounding, molecules called anthocyanidins with sugars. The main anthocyanin in strawberries is callistephin, otherwise known as pelargonidin-3-O-glucoside. It’s also found in the skin of certain grapes.

Anthocyanins are fun for chemists because they change colour with pH. It’s these molecules which are behind the famous red-cabbage indicator. Which means, yes, you can make strawberry indicator! I had a go myself, the results are below…

Strawberry juice acts as an indicator: pinky-purplish in an alkaline solution, bright orange in an acid.

As you can see, the strawberry juice is pinky-purplish in the alkaline solution (sodium hydrogen carbonate, aka baking soda, about pH 9), and bright orange in the acid (vinegar, aka acetic acid, about pH 3). Next time you find a couple of mushy strawberries that don’t look so tasty, don’t throw them away – try some kitchen chemistry instead!

Peonidin-3-O-glucoside is the anthocyanin which gives strawberries their red colour. This is the form found at acidic pHs

The reason we see this colour-changing behaviour is that the anthocyanin pigment gains an -OH group at alkaline pHs, and loses it at acidic pHs (as in the diagram here).

This small change is enough to alter the wavelengths of light absorbed by the compound, so we see different colours. The more green light that’s absorbed, the more pink/purple the solution appears. The more blue light that’s absorbed, the more orange/yellow we see.

Interestingly, anthocyanins behave slightly differently to most other pH indicators, which usually acquire a proton (H+) at low pH, and lose one at high pH.

Moving on from colour, what about the famous strawberry smell and flavour? That comes from furaneol, which is sometimes called strawberry furanone or, less romantically, DMHF. It’s the same compound which gives pineapples their scent (hence that whole Latin ananassa thing I mentioned earlier). The concentration of furaneol increases as the strawberry ripens, which is why they smell stronger.

Along with menthol and vanillin, furaneol is one of the most widely-used compounds in the flavour industry. Pure furaneol is added to strawberry-scented beauty products to give them their scent, but only in small amounts – at high concentrations it has a strong caramel-like odour which, I’m told, can actually smell quite unpleasant.

As strawberries ripen their sugar content increases, they get redder, and they produce more scent

As strawberries ripen their sugar content (a mixture of fructose, glucose and sucrose) also changes, increasing from about 5% to 9% by weight. This change is driven by auxin hormones such as indole-3-acetic acid. At the same time, acidity – largely from citric acid – decreases.

Those who’ve been paying attention might be putting a few things together at this point: as the strawberry ripens, it becomes less acidic, which helps to shift its colour from more green-yellow-orange towards those delicious-looking purpleish-reds. It’s also producing more furaneol, making it smell yummy, and its sugar content is increasing, making it lovely and sweet. Why is all this happening? Because the strawberry wants (as much as a plant can want) to be eaten, but only once it’s ripe – because that’s how its seeds get dispersed. Ripening is all about making the fruit more appealing – redder, sweeter, and nicer-smelling – to things that will eat it. Nature’s clever, eh?

There we have it: some spectacular strawberry science! As a final note, as soon as I started writing this I (naturally) found lots of other blogs about strawberries and summer berries in general. They’re all fascinating. If you want to read more, check out…

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Toxins and tanks: could your fishtank really be deadly?

Could a deadly poison be lurking in your fish tank?

A few days ago I came across a news story: “Fish owner tells how cleaning out tank released deadly palytoxin that poisoned family and led to closure of entire street“. Now you have to admit, as titles go that’s pretty compelling.

To begin with, for some reason, I had it in my head that this happened in Australia (in my defence, that is where most of the really deadly stuff happens, right?). But no, this happened in the U.K. Not only that, but it was even in Oxfordshire, which is my neck of the woods.

The fish tank owner, a man named Chris Matthews, was actually an experienced aquarist. He knew about palytoxin – a poisonous substance which can be released by corals – and he was aware that it can be deadly if ingested. He also knew that it can cause serious skin irritation.

What he didn’t realise was that taking his pulsing xenia coral out of the tank could cause it to release the toxin into the air.

But before I talk about palytoxin, let’s just look at the word “toxin” for a moment. It has a specific meaning, and it’s often misused. As in many, many adverts. Here’s a recent one, but these easy to find – just put “toxin free” into the search engine of your choice.

In a way, this is quite funny. You see, “toxin” specifically refers to “a poison of plant or animal origin“. In other words, a naturally occurring poison*. There are lots and lots of naturally occurring poisons. Plants make them all the time, generally to ward off pests. Most essential oils can, at a high enough dose, be toxic. The hand cream in that picture contains peppermint oil. Peppermint is, of course, pretty safe – we’ve all eaten mints after all – but guess what? Take huge dose of it and it becomes a real problem. Now, I’m not for one second suggesting that hand cream is dangerous or harmful, but technically, it’s not “toxin free”.

Beauty products which contain only synthetic ingredients are, by definition, toxin-free.

Yes, the irony or this sort of marketing is that beauty products made out of entirely synthetic ingredients definitely will be toxin-free. Nothing natural = no toxins. Whereas anything made out of naturally occurring substances almost certainly isn’t, regardless of its spurious labelling.

Anyway, back to the palytoxin. It’s naturally occurring. And incredibly dangerous. More proof, as if we needed it, that natural doesn’t mean safe. Very often, in fact, quite the opposite. The human race has spent millenia working out how to protect itself from nature and all her associated nastiness (bacteria, viruses, extreme temperatures, poor food supply, predators…. the list is long and unpleasant) and yet for some reason it’s become fashionable to forget all that and imagine a utopia where mother nature knows best. Honestly, she doesn’t. Well, maybe she does – but being kind to human beings isn’t on her agenda.

Palytoxin is especially unpleasant. Indeed, it’s thought to be the second most poisonous non-protein substance known (there are some very impressive protein-based ones, though – botulinum toxin for one). The only thing which is more toxic is maitoxin – a poison which can be found in striated surgeonfish thanks to the algae they eat.

Palytoxin is a large molecule.

Palytoxin is a big molecule, technically categorised as a fatty alcohol. It has eight carbon-carbon double bonds, 40 hydroxy groups (phew) and is positively covered in chiral centres (don’t worry students: your teacher isn’t going to expect you to draw this one. Probably). Bits of it are water-soluble whilst other parts are fat soluble, meaning it can dissolve in both types of substance. Because it’s not a protein, heat doesn’t denature it, so you can’t get rid of this toxin with boiling water or by heating it. However, it does decompose and become non-toxic in acidic or alkaline solutions. Household bleach will destroy it.

It’s mostly found in the tropics, where it’s made by certain types of coral and plankton, or possibly by bacteria living on and in these organisms. It also turns up in fish, crabs and other marine organisms that feed on these things.

In fact, story time! There is a Hawaiian legend which tells that Maui villagers once caught a Shark God with a hunger for human flesh whom they believed had been killing their fishermen. They killed the Shark God and burned him, throwing the ashes into a tide pool. The ashes caused ugly brown anemones to grow. Later, the villagers discovered that blades smeared with these “limu” would cause certain death. So the anemones came to be known as “Limu Make O Hana” or Seaweed of Death from Hana. We now know that those brown ‘anemones’ are zoanthid corals, and the ‘certain death’ was due to palytoxin poisoning.

Zoanthids are a source of palytoxin.

People don’t suffer palytoxin poisoning very often. Most cases have been in people who’ve eaten seafood and, as here, aquarium hobbyists. In a few cases people have been exposed to algae blooms.

It’s really nasty though. Palytoxin can affect every type of cell in the body (yikes) and as a result the symptoms are different according to the route of exposure. Eat it and you’re likely to experience a bitter taste in your mouth, muscle spasms and abdominal cramps, nausea, lethargy, tingling and loss of sensation, slow heart rate, kidney failure and respiratory distress. It can damage your heart muscle; in the worst case scenario, it causes death by cardiac arrest.

On the other hand, if you inhale it, the symptoms are more likely to revolve around the respiratory system, such as constriction of the airways which causes wheezing and difficulty breathing. It can also cause fever and eye-infection type symptoms. Over time, though, the result is the same: muscle weakness and eventually, death from heart failure.

The respiratory symptoms from palytoxin are easily misdiagnosed: it looks like a viral or bacterial infection. In fact, our fish tank owner initially thought he had flu. It was only when everyone in the family got ill, even the dogs, that he realised that it must be poisoning. Fortunately, the emergency services took it seriously and sent both ambulance and fire crews to his house, as well as police. They closed the street and ensured that the poison was safely removed.

There is no antidote, but the symptoms can be eased by, for example, treatment with vasodilators. If the source of exposure is removed the victim is likely to recover over time. You’ll be pleased to hear that Chris Matthews, his family, and the firefighters who attended the scene, were checked over at hospital and appear to be okay.

If you’re an aquarium owner, how to you avoid getting into this kind of predicament? As Chris Matthews said, the coral he had, pulsing xenia, was “not expensive and a lot of people have it.”

Click the image to read safety guidelines from the Ornamental Aquatic Trade Association.

According to the Ornamental Aquatic Trade Association, the most important piece of safety advice is to only handle your marine creatures underwater and fully submerged. Don’t take them out of the tank unnecessarily, and if you do need to move them, use submerged plastic bags or a bucket, so that they stay underwater at all times. You should also wear strong rubber gloves, ideally gloves specifically designed for aquarium use (such as these). If you need to dispose of a rock which contains soft coral species, soak it in a bleach solution – one part household bleach to nine parts water – for several days before you intend to dispose of it. Leaving an untreated rock outside to dry will not make it safe – it could still be highly toxic. Finally, whilst activated charcoal can help to keep palytoxin out of the water, it may not be able to cope with large quantities, and it needs to be changed frequently.

Fish tank owner Chris also said: “The information is not readily available online in a way people can easily understand” and “I want to use this experience to educate people about the risks and the measures people need to take.” Hopefully this blog post (and all the associated news coverage) will help with that. Be careful with your corals!

* Note that while ‘toxin’ specifically refers to poisonous substances from plants and animals, this restriction doesn’t extend to the word “toxic”. The definition of that is “containing or being poisonous material” (regardless of whether it’s a naturally-occurring substance or not). So “non-toxic” labels are fine, if a little bit meaningless – no matter what the woo-pushing sites say, your hand cream really isn’t poisonous.

Like the Chronicle Flask’s Facebook page for regular updates, or follow @chronicleflask on Twitter. All content is © Kat Day 2018. You may share or link to anything here, but you must reference this site if you do.

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Where did our love of dairy come from?

The popularity of the soya latte seems to be on the rise.

A little while ago botanist James Wong tweeted about the myriad types of plant ‘milk’ that are increasingly being offered in coffee shops, none of which are truly milk (in the biological sense).

This generated a huge response, probably rather larger than he was expecting from an off-hand tweet. Now, I’m not going to get into the ethics of milk production because it’s beyond the scope of this blog (and let’s keep it out of the comments? — kthxbye) but I do want to consider one fairly long thread of responses which ran the gamut from ‘humans are the only species to drink the milk of another animal’ (actually, no) to ‘there’s no benefit to dairy’ (bear with me) and ending with, in essence, ‘dairy is slowly killing us‘ (complicated, but essentially there’s very little evidence of any harm).

Humans have been consuming dairy products for thousands of years.

But wait. If dairy is so terrible for humans, and if there are no advantages to it, why do we consume it at all? Dairy is not a new thing. Humans have been consuming foods made from one type of animal milk or another for 10,000 years, give or take. That’s really quite a long time. More to the point (I don’t want to be accused of appealing to antiquity, after all), keeping animals and milking them is quite resource intensive. You have to feed them, look after them and ensure they don’t wander off or get eaten by predators, not to mention actually milk them on a daily basis. All that takes time, energy and probably currency of some sort. Why would anyone bother, if dairy were truly detrimental to our well-being?

In fact, some cultures don’t bother. The ability to digest lactose (the main sugar in milk) beyond infancy is quite low in some parts of the world, specifically Asia and most of Africa. In those areas dairy is, or at least has been historically, not a significant part of people’s diet.

But it is in European diets. Particularly northern European diets. Northern Europeans are, generally, extremely tolerant of lactose into adulthood and beyond.

Which is interesting because it suggests, if you weren’t suspicious already, that there IS some advantage to consuming dairy. The ability to digest lactose seems to be a genetic trait. And it seems it’s something to do, really quite specifically, with your geographic location.

Which brings us to vitamin D. This vitamin, which is more accurately described as a hormone, is a crucial nutrient for humans. It increases absorption of calcium, magnesium and phosphate, which are all necessary for healthy bones (not to mention lots of other processes in the body). It’s well-known that a lack of vitamin D leads to weakened bones, and specifically causes rickets in children. More recently we’ve come to understand that vitamin D also supports our immune system; deficiency has been meaningfully linked to increased risk of certain viral infections.

What’s the connection between vitamin D and geographic location? Well, humans can make vitamin D in their skin, but we need a bit of help. In particular, and this is where the chemistry comes in, we need ultraviolet light. Specifically, UVB – light with wavelengths between 280 nm to 315 nm. When our skin is exposed to UVB, a substance called 7-dehydrocholesterol (7-DHC to its friends) is converted into previtamin D3, which is then changed by our body heat to vitamin D3, or cholecalciferol – which is the really good stuff. (There’s another form, vitamin D2, but this is slightly less biologically active.) At this point the liver and kidneys take over and activate the chloecalciferol via the magic of enzymes.

We make vitamin D in our skin when we’re exposed to UVB light.

How much UVB you’re exposed to depends on where you live. If you live anywhere near the equator, no problem. You get UVB all year round. Possibly too much, in fact – it’s also linked with skin cancers. But if you live in northerly latitudes (or very southerly), you might have a problem. In the summer months, a few minutes in the sun without sunscreen (literally a few minutes, not hours!) will produce more than enough vitamin D. But people living in UK, for example, get no UVB exposure for 6 months of the year. Icelanders go without for 7, and inhabitants of Tromsø, in Norway, have to get by for a full 8 months. Since we can only store vitamin D in our bodies for something like 2-4 months (I’ve struggled to find a consistent number for this, but everyone seems to agree it’s in this ballpark), that potentially means several months with no vitamin D at all, which could lead to deficiency.

In the winter northern Europeans don’t receive enough UVB light from the sun to produce vitamin D in their skin.

In the winter, northern Europeans simply can’t make vitamin D3 in their skin (and for anyone thinking about sunbeds, that’s a bad idea for several reasons). In 2018, this is easily fixed – you just take a supplement. For example, Public Health England recommends that Brits take a daily dose of 10 mcg (400 IU) of vitamin D in autumn and winter, i.e. between about October and March. It’s worth pointing out at this point that a lot of supplements you can buy contain much more than this, and more isn’t necessarily better. Vitamin D is fat-soluble and so it will build up in the body, potentially reaching toxic levels if you really overdo things. Check your labels.

Oily fish is an excellent source of vitamin D.

But what about a few thousand years ago, before you just could pop to the supermarket and buy a bottle of small tablets? What did northern Europeans do then? The answer is simple: they had to get vitamin D from their food. Even if it’s not particularly well-absorbed, it’s better than nothing.

Of couse it helps if you have access to lots of foods which are sources of vitamin D. Which would be…  fatty fish (tuna, mackerel, salmon, etc) – suddenly that northern European love of herring makes so much more sense – red meat, certain types of liver, egg yolks and, yep, dairy products. Dairy products, in truth, contain relatively low levels of vitamin D (cheese and butter are better than plain milk), but every little helps. Plus, they’re also a good source of calcium, which works alongside vitamin D and is, of course, really important for good bone health.

A side note for vegans and vegetarians: most dietry sources of vitamin D come from animals. Certain mushrooms grown under UV can be a good source of vitamin D2, but unless you’re super-careful a plant-based diet won’t provide enough of this nutrient. So if you live in the north somewhere or you don’t, or can’t, expose your skin to the sun very often, you need a supplement (vegan supplements are available).

Fair skin likely emerged because it allows for better vitamin D production when UVB levels are lower.

One thing I haven’t mentioned of course is skin-colour. Northern Europeans are generally fair-skinned, and this is vitamin D-related, too. The paler your skin, the better UVB penetrates it. Fair-skinned people living in the north had an advantage over those with darker skin in the winter, spring and autumn months: they could produce more vitamin D. In fact, this was probably a significant factor in the evolution of fair skin (although, as Ed Yong explains in this excellent article, that’s complicated).

In summary, consuming dairy does have advantages, at least historically. There’s a good reason Europeans love their cheeses. But these days, if you want to eat a vegan or vegetarian diet for any reason (once again, let’s not get into those reasons in comments, kay?) you really should take a vitamin D supplement. In fact, Public Health England recommends that everyone in the UK take a vitamin D supplement in the autumn and winter, but only a small amount – check your dose.

By the way, if you spot any ‘diary’s let me know. I really had to battle to keep them from sneaking in…

Like the Chronicle Flask’s Facebook page for regular updates, or follow @chronicleflask on Twitter. All content is © Kat Day 2018. You may share or link to anything here, but you must reference this site if you do.

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Chemical du jour: how bad is BPA, really?

BPA is an additive in many plastics

When I was writing my summary of 2017 I said that there would, very probably, be some sort of food health scare at the start of 2018. It’s the natural order of things: first we eat and drink the calorie requirement of a small blue whale over Christmas and New Year, and then, lo, we must be made to suffer the guilt in January. By Easter, of course, it’s all forgotten and we can cheerfully stuff ourselves with chocolate eggs.

Last year it was crispy potatoes, and the year before that it was something ridiculous about sugar in ketchup causing cancer (it’s the same sugar that’s in everything, why ketchup? Why?). This year, though, it seems that the nasty chemical of the day is not something that’s in our food so much as around it.

Because this year the villain of the piece appears to be BPA, otherwise known as Bisphenol A or, to give it its IUPAC name, 4,4′-(propane-2,2-diyl)diphenol.

BPA is an additive in plastics. At the end of last year an excellent documentary aired on the BBC called Blue Planet II, all about our planet’s oceans. It featured amazing, jaw-dropping footage of wildlife. It also featured some extremely shocking images of plastic waste, and the harm it causes.

Plastic waste is a serious problem

Plastic waste, particularly plastic waste which is improperly disposed of and consequently ends up in the wrong place, is indisputably something that needs to be addressed. But this highlighting of the plastic waste problem had an unintended consequence: where was the story going to go? Everyone is writing about how plastic is bad, went (I imagine) editorial meetings in offices around the country – find me a story showing that plastic is even WORSE than we thought!

Really, it was inevitable that a ‘not only is plastic bad for the environment, but it’s bad for you, too!’ theme was going to emerge. It started, sort of, with a headline in The Sun newspaper: “Shopping receipts could ‘increase your cancer risk’ – as 93% contain dangerous chemicals also linked to infertility. Shopping receipts are, of course, not made of plastic – but the article’s sub-heading stated that “BPA is used to make plastics”, so the implication was clear enough.

Then the rather confusing: “Plastic chemical linked to male infertility in majority of teenagers, study suggests” appeared in The Telegraph (more on this in a bit), and the whole thing exploded. Search for BPA in Google News now and there is everything from “5 Ways to Reduce Your Exposure to Toxic BPA” to “gender-bending chemicals found in plastic and linked to breast and prostate cancer are found in 86% of teenagers”.

Yikes. It’s all quite scary. It’s true that right now you can’t really avoid plastic. Look around you and it’s likely that you’ll immediately see lots of plastic objects, and that’s before you even try to consider all the everyday things which have plastic coatings that aren’t immediately obvious. If you have young children, you’re probably drowning in plastic toys, cups, plates and bottles. We’re pretty much touching plastic continually throughout our day. How concerned should we be?

As the Hitchiker’s Guide to the Galaxy says, Don’t Panic. Plastic (like planet Earth in the Guide) can probably be summed up as mostly harmless, at least from a BPA point of view if not an environmental one.

BPA is a rather pleasingly symmetrical molecule with two phenol groups. (A big model of this would make a wonderfully ironic pair of sunglasses, wouldn’t it?) It was first synthesized by the Russian chemist Alexander Dianin in the late 19th century. It’s made by reacting acetone – which is where the “A” in the name comes from – with two phenol molecules. It’s actually a very simple reaction, although the product does need to be carefully purified, since large amounts of phenol are used to ensure a good yield.

It’s been used commercially since the fifties, and millions of tonnes of BPA are now produced worldwide each year. BPA is used to make plastics which are clear and tough – two characteristics which are often valued, especially for things like waterproof coatings, bottles and food containers.

The concern is that BPA is an endocrine disruptor, meaning that it interferes with hormone systems. In particular, it’s a known xenoestrogen, in other words it mimics the female hormone estrogen. Animal studies have suggested possible links to certain cancers, infertility, neurological problems and other diseases. A lot of the work is fairly small-scale and, as I’ve mentioned, focused on animal studies (rather than looking directly at effects in humans). Where humans have been studied it’s usually been populations that are exposed to especially high BPA levels (epoxy resin painters, for example). Still, it builds up into quite a damning picture.

BPA has been banned from baby bottles in many countries, including the USA and Europe

Of course, we don’t normally eat plastic, but BPA can leach from the plastic into the food or drink that’s in the plastic, and much more so if the plastic is heated. Because of these concerns, BPA has been banned from baby bottles (which tend to be heated, both for sterilisation and to warm the milk) in several countries, including the whole of Europe, for some years now. “BPA free” labels are a fairly common sight on baby products these days. BPA might also get onto our skin from, for example, those thermal paper receipts The Sun article mentioned, and then into our mouths when we eat. Our bodies break down and excrete the chemical fairly quickly, in as little as 6 hours, but because it’s so common in our environment most of us are continually meeting new sources of it.

How much are we getting, though? This is a critical question, because as I’m forever saying, the dose makes the poison. Arsenic is a deadly poison at high levels, but most of us – were we to undergo some sort of very sensitive test – would probably find we have traces of it in our systems, because it’s a naturally-occuring mineral. It’s nothing to worry about, unless for some reason the levels become too high.

When it comes to BPA, different countries have different guidelines. The European Food Safety Authority recommended in January 2015 that the TDI (tolerable daily intake) should be reduced from 50 to 4 µg/kg body weight/day (there are plans for a new assessment in 2018, so it might change again). For a 75 kg adult, that translates to about 0.0003 g per day. A USA Federal Drug and Administration document from 2014 suggests a NOAEL (no-observed-adverse-effect-level) of 5 mg/kg bw/day, which translates to 0.375 g per day for the same 75 kg adult. NOAEL values are usually much higher than TDIs, so these two figures aren’t as incompatible as they might appear. Tolerable daily intake values tend to have a lot of additional “just in case” tossed into them – being rather more guidance than science.

The European Food Standards Authority published a detailed review of the evidence in 2015 (click for a summary)

So, how much BPA are we exposed to? I’m going to stick to Europe, because that’s where I’m based (for now…), and trying to look at all the different countries is horribly complicated. Besides, EFSA produced a really helpful executive summary of their findings in 2015, which makes it much easier to find the pertinent information.

The key points are these: most of our exposure comes from food. Infants, children and adolescents have the highest dietary exposures to BPA, probably because they eat and drink more per kilogram of body weight. The estimated average was 0.375 µg/kg bw per day.  For adult women the estimated average was 0.132 µg/kg bw per day, and for men it was 0.126 µg/kg bw per day.

When it came to thermal paper and other non-dietary exposure (mostly from dust, toys and cosmetics), the numbers were smaller, but the panel admitted there was a fair bit of uncertainty here. The total exposure from all sources was somewhere in the region of 1 µg/kg bw per day for all the age groups, with adolescents and young children edging more toward values of 1.5 µg/kg bw per day (this will be important in a minute).

Note that all of these numbers are significantly less than the, conservative, tolerable daily intake value of 4 µg/kg bw per day recommended by EFSA.

Here’s the important bit: the panel concluded that there is “no health concern for BPA at the estimated levels of exposure” as far as diet goes. They also said that this applied “to prenatally exposed children” (in other words, one less thing for pregnant women to worry about).

When it came to total exposure, i.e. diet and exposure from other sources such as thermal paper they concluded that “the health concern for BPA is low at the estimated levels of exposure”.

The factsheet that was published alongside the full document summarises the results as follows: “BPA poses no health risk to consumers because current exposure to the chemical is too low to cause harm.”

Like I said: Don’t Panic.

What about those frankly quite terrifying headlines? Well, firstly The Sun article was based on some work conducted on a grand total of 208 receipts collected in Southeast Michigan in the USA from only 39 unique business locations. That’s a pretty small sample and not, I’d suggest, perhaps terribly relevant to the readership of a British newspaper. Worse, the actual levels of BPA weren’t measured in the large majority of samples – they only tested to see if it was there, not how much was there. There was nothing conclusive at all to suggest that the levels in the receipts might be enough to “increase your cancer risk”. All in all, it was pretty meaningless. We already knew there was BPA in thermal receipt paper – no one was hiding that information (it’s literally in the second paragraph of the Wikipedia page on BPA).

The Telegraph article, and the many others it appeared to spawn, also weren’t based on especially rigorous work and, worse, totally misrepresented the findings in any case. Firstly, let’s consider that headline: “Plastic chemical linked to male infertility in majority of teenagers, study suggests”. What does that mean? Are they suggesting that teenagers are displaying infertility? No, of course not. They didn’t want to put “BPA” in the headline because that, apparently, would be too confusing for their readers. So instead they’ve replaced “BPA” with “plastic chemical linked to male infertility”, which is so much more straightforward, isn’t it?

And they don’t mean it’s linked to infertility in the majority of teenagers, they mean it’s linked to infertility and it’s in the majority of teenager’s bodies. I do appreciate that journalists rarely write headlines – this isn’t a criticism of the poor writer who turned in perfectly good copy – but that is confusing and misleading headline-writing of the highest order. Ugh.

Plus, as I commented back there, that wasn’t even the conclusion of the study, which was actually an experiment carried out by students under the supervision of a local university. The key finding was not that, horror, teenagers have BPA in their bodies. The researchers assumed that almost all of the teenagers would have BPA in their bodies – as the EFSA report showed, most people do. No, the conclusion was actually that the teenagers – 94 of them – had been unable to significantly reduce their levels of BPA by changing their diet and lifestyle. Although the paper admits the conditions weren’t well-controlled. Basically, they asked a group of 17-19 year-olds to avoid plastic, and worked on the basis that their account of doing so was accurate.

And how much did the teenagers have in their samples? The average was 1.22 ng/ml, in urine samples (ng = nanogram). Now, even if we assume that these levels apply to all human tissue (which they almost certainly don’t) and that therefore the students had roughly 1.22 ng per gram of body weight, that only translates to, very approximately, 1.22 micrograms (µg) per kilogram of body weight.

Wait a second… what did EFSA say again…. ah yes, they estimated total exposures of 1.449 µg/kg bw per day for adolescents.

Sooooo basically a very similar value, then? And the EFSA, after looking at multiple studies in painstaking detail, concluded that “BPA poses no health risk to consumers”.

Is this grounds for multiple hysterical, fear-mongering headlines? I really don’t think it is.

It is interesting that the teenagers were unable to reduce their BPA levels. Because it’s broken down and excreted quite quickly by the body, you might expect that reducing exposure would have a bigger effect – but really all we can say here is that this needs to be repeated with far more tightly-controlled conditions. Who knows what the students did, and didn’t, actually handle and eat. Perhaps their school environment contains high levels of BPA in dust for some reason (new buildings or equipment, maybe?), and so it was virtually impossible to avoid. Who knows.

In summary, despite the scary headlines there really is no need to worry too much about BPA from plastics or receipts. It may be worth avoiding heating plastic, since we know that increases the amound of BPA that makes its way into food – although it’s important to stress that there’s no evidence that microwaving plastic containers causes levels to be above safe limits. Still, if you wanted to be cautious you could choose to put food into a ceramic or glass bowl, covered with a plate rather than clingfilm. It’ll save you money on your clingfilm bills anyway, and it means less plastic waste, which is no bad thing.

Roll on Easter…

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Just what is blk water, and should you drink it?

Christmas is almost here! Are you ready yet? Are you fed up with people asking if you’re ready yet? Have you worked out what to buy for Great-uncle Nigel, who says he neither needs nor wants anything? Always a tricky scenario, that. Consumables are often a safe fallback position. They don’t clutter up the house, and who doesn’t enjoy a nice box of luxury biscuits, or chocolates, or a bottle of champagne, or spirts, or a case of blk water.

Wait, what?

Yes, this mysterious product turned up in my feed a few weeks ago. It’s water (well, so they say), but it’s black. Actually black. Not just black because the bottle’s black, black because the liquid inside it is… black.

It’s black water.

A bit like… cola. Only blacker, and not fizzy, or sweet, or with any discernable flavour other than water.

It raises many questions, doesn’t it? Let’s start with why. Obviously it’s a great marketing gimmick. It definitely looks different. It also comes with a number of interesting claims. The suppliers claim it contains “no nasties” and “only 2 ingredients”, namely spring water and “Fulvic Minerals” (sic). (Hang on, I hear you say, if it’s minerals, plural, surely that’s already more than two ingredients? Oh, but that’s only the start. Stay with me.)

It claims to “balance pH levels” and help “to regulate our highly acidic diets”. Yes, well, I think I’ve covered that before. Absolutely nothing you drink, or eat, does anything to the pH in any part of your body except, possibly, your urine – where you might see a small difference under some circumstances (but even if you do it doesn’t tell you anything significant about the impact of your diet on your long-term health). And bear in mind that a few minutes after you drink any kind of alkaline water it mixes with stomach acid which has a pH of around 2. Honestly, none of that alkaline “goodness” makes it past your pyloric sphincter.

Finally, blk water apparently “replenishes electrolytes”. Hm. Electrolytes are important in the body. They’re ionic species, which means they can conduct electricity. Your muscles and neurons rely on electrical activity, so they are quite important. Like, life or death important. But because of that our bodies are quite good at regulating them, most of the time. If you run marathons in deserts, or get struck down with a nasty case of food poisoning, or have some kind of serious health condition (you’d know about it) you might need to think about electrolytes, but otherwise most of us get what we need from the food and drink we consume normally every day.

Besides which, didn’t they say “only 2 ingredients”? The most common electrolytes in the body are sodium, potassium, magnesium, chloride, hydrogen phosphate and hydrogen carbonate. Most spring waters do contain some, if not all, of these, in greater or smaller amounts, but it’s not going to be enough to effectively “replenish” any of them. If, say, you are running marathons in the desert, the advice is actually to keep a careful eye on your water intake because drinking too much water can dangerously lower your sodium levels. Yes, there are sports drinks that are specifically designed to help with this, but they taste of salt and sugar and/or flavourings which have been added in a desperate attempt to cover up the salty taste. This is apparently not the case with blk water which, to repeat myself, contains “only 2 ingredients”.

And, according to the blk website the drink contains “0 mg of sodium per 500ml” so… yeah.

Speaking of ingredients, what about those so-called fulvic minerals? Maybe they’re the source of those all-important electrolytes (but not sodium)? And maybe they’re magically tasteless, too?

And perhaps, like other magical objects and substances, they don’t actually exist – as geologist @geolizzy told me on Twitter when I asked.

It’s not looking good for blk water (£47.99 for a case of 24 bottles) at this point. But hang on. Perhaps when they said fulvic minerals, what they meant was fulvic acid – which is a thing, or possibly several things – in a the presence of oh, say, some bicarbonate (*cough* 2 ingredients *cough*).

That could push the pH up to the stated 8-9, and didn’t we learn in school that:
acid + alkali –> salt + water
and maybe, if we’re being generous, we could call the salts of fulvic acids minerals? It’s a bit shaky but… all right.

So what are fulvic acids?

That’s an interesting question. I had never heard of fulvic acids. They do, as it turns out, have a Wikipedia page (Wikipedia is usually very reliable for chemical information, since no one has yet been very interested in spoofing chemical pages to claim things like hydrochloric acid is extracted from the urine of pregnant unicorns) but the information wasn’t particularly enlightening. The page did inform me that fulvic acids are “components of the humus” (in soil) and are  “similar to humic acids, with differences being the carbon and oxygen contents, acidity, degree of polymerization, molecular weight, and color.” The Twitter hive-mind, as you can see, was sending me down the same path…

A typical example of a humic acid.

Next stop, humic acids. Now we’re getting somewhere. These are big molecules with several functional groups. The chemists out there will observe that, yes, they contain several carboxylic acid groups (the COOH / HOOC ones you can see in the example) so, yes, it makes sense they’d behave as acids.

“No nasties”, blk said. “Pure” they said. When you hear those sorts of things, do you imagine something like this is in your drink? Especially one that, let’s be clear, is a component of soil?

Oh, hang on, I should’ve checked the “blk explained” page on the blk water website. There’s a heading which actually says “what are Fulvic Minerals”, let’s see now…

“Fulvic minerals are plant matter derived from millions of years ago that have combined with fulvic acid forming rare fulvic mineral deposits. They deliver some of the most powerful electrolytes in the world.”

“Fulvic minerals contain 77 other trace minerals, most of which have an influence on the healthiness of our body. They are very high in alkaline and when sourced from the ground contain a pH of 9.”

I don’t know about you, but I’m not totally convinced. I mean, as @geolizzy says in her tweet here (excuse the minor typo, she means humic, not humid),  it sounds a bit like… water contaminated with hydrocarbon deposits?


And, by the way, the phrase “very high in alkaline” is utterly meaningless. Substances are alkaline, or they contain substances which are alkaline. “Alkaline” is not a thing in itself. This is like saying my tea is high in hot when sourced from the teapot.

There’s one more thing to add. So far this might sound a bit weird but… probably safe, right? What could be more wholesome than a bit of soil? Didn’t your granny tell you to eat a pinch of soil to boost your immune system, or something? At worst it’s harmless, right?

Tap water is chlorine-treated to keep it free of nasty bacteria.

Maybe. But then again… water is often treated with chlorine compounds to keep it bacteria-free. Now, blk water is supposedly spring water, which isn’t usually treated. But hypothetically, let’s consider what happens when humic acids, or fulvic acids, or whatever we’re calling them, come into contact with chlorine-treated water.

Oh dear. It seems that dihaloacetonitriles are formed. (See also this paper.) This is a group of substances (possibly the best known one is dichloroacetonitrile) which are variously toxic and mutagenic. Let’s hope that spring water is totally unchlorinated, 100% “we really got it from out of a rock” spring water, then.

To sum up: it is black, and that’s kind of weird and a fun talking point – although if you like the idea of a black drink you can always drink cola. It doesn’t balance your pH levels – nothing does. I don’t believe it replenishes electrolyte levels either – how can it when it doesn’t contain sodium? – and I’m dubious about the “2 ingredients” claim (could you tell?). And the oh-so-healthy-sounding fulvic minerals are most likely due to contamination from coal deposits.

All in all, whilst it might not be quite such a conversation piece, I think it would be better to get Great-uncle Nigel a nice box of chocolates this year.

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In the fridge or on the windowsill: where’s the best place to keep tomatoes?

Fresh fruit and vegetables are great, but where’s the best place to store them?

I’ve mentioned before that my Dad is a professional plant-wrangler (if you’ve never read the electric daisies post, do go and have a look – it’s a little-read favourite) and he often brings me home-grown fruit and vegetables.

What follows is an inevitable disagreement about storage, specifically, my habit of putting everything in the fridge.

In my defence, modern houses rarely have pantries (boo) and we don’t even have a garage. We do have a shed, but it’s at the bottom of our poorly-lit, somewhat muddy garden. Do I want to traipse out there on a cold, dark, autumn evening? No, I do not. So the fabled “cool, dark place” is a bit of problem. My fridge is cool and dark, I have argued, but here’s the thing – turns out, it’s too cool. And quite probably too dark.

This I have learned from the botanist James Wong (@botanygeek on Twitter), whose talk I attended on Monday this week at the Mathematical Institute in Oxford. James, it turns out, had a rather similar argument with his Mum, particularly regarding tomatoes.

We should’ve listened to out parents, because they were right. A lot of fruit and vegetables really are better stored outside of the fridge, and for tomatoes in particular “better” actually means “more nutritious”.

Lycopene is a very long molecule with lots of double C=C bonds.

Tomatoes, James explained, contain a lot of a chemical called lycopene. It’s a carotene pigment, and it’s what gives tomatoes their red colour.

Lycopene has lots of double bonds between its carbon atoms which form something chemists call a conjugated system. This has some rather cool properties, one of which is an ability to absorb certain wavelengths of light. Lycopene is especially good at absorbing blue and green wavelengths, leaving our eyes to detect the red light that’s left.

Lycopene absorbs blue and green light, which is why tomatoes appear red.

Tomatoes and lycopene also seem to have a lot of health benefits. There’s some evidence that lycopene might reduce the risk of prostate and other cancers. It also appears to reduce the risk of stroke, and eating tomato concentrate might even help to protect your skin from sun damage (don’t get any ideas, you still need sunblock). Admittedly the evidence is currently a bit shaky – it’s a case of “more research is needed” – but even if it turns out to that the causative relationship isn’t terribly strong, tomatoes are still a really good source of fibre and vitamins A, C and E. Plus, you know, they taste yummy!

But back to the fridge. Surely they will keep longer in the fridge, and the low temperatures will help to preserve the nutrients? Isn’t that how it works?

Well, no. As James explained, once tomatoes are severed from the plant they have exactly one purpose: to get eaten. The reason, from the plant’s point of view, is that the critter which eats them will hopefully wander off and – ahem – eliminate the tomato seeds at a later time, somewhere away from the parent plant. This spreads the seeds far and wide, allowing little baby tomato plants to grow in a nice, open space with lots of water and sun.

For this reason once the tomato fruit falls, or is cut, from the tomato plant it doesn’t just sit there doing nothing. No, it carries on producing lycopene. Or rather, it does if the temperature is above about 10 oC. Below that temperature (as in a fridge), everything more or less stops. But, leave a tomato at room temperature and lycopene levels increase significantly. Plus, the tomato pumps out extra volatile compounds – both as an insect repellant and to attract animals which might usefully eat it – which means… yes: room temperature tomatoes really do smell better. As if that weren’t enough, chilling tomatoes can damage cell membranes, which can actually cause them to spoil more quickly.

In summary, not only will tomatoes last longer out of the fridge, they will actually contain more healthy lycopene!

Anecdotally, once I got over my scepticism and actually started leaving my tomatoes on my windowsill (after years of refrigeration) I discovered that it’s true. My windowsill tomatoes really do seem to last longer than they used to in the fridge, and they almost never go mouldy. Of course, it’s possible that I might not be comparing like for like (who knows what variety of tomato I bought last year compared to this week), but I urge you to try it for yourself.

James mentioned lots of other interesting bits and pieces in his talk. Did you know that sun-dried shiitake mushrooms are much higher in vitamin D? Or that you can double the amount of flavonoid you absorb from your blueberries by cooking them? (Take that, raw food people!) Storing apples on your windowsill is likely to increase the amount of healthy polyphenols in their skin, red peppers are better for you than green ones, adding mustard to cooked broccoli makes it more nutritious, and it would be much better if we bought our butternut squash in the autumn and saved it for Christmas – it becomes sweeter and more flavoursome over time.

In short, fascinating. Who wants to listen to some “clean eater” making it up as they go along when you can listen to a fully-qualified botanist who really knows what he’s talking about? Do check out the book, How to Eat Better, by James Wong – it’s packed full of brilliant tidbits like this and has loads of recipes.

And yes, Dad: you were right.

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Puking pumpkins: more hydrogen peroxide

It was Halloween yesterday and, unusually for the UK, it fell in school term time. As it turned out, I was teaching chemistry to a group of 12-13 year olds on that day which was too good an opportunity to miss.

Time for the puking pumpkin!

A side note: there’s loads of great chemistry here, and the pumpkin isn’t essential – you could easily do this same experiment during a less pumpkin-prolific month with something else. Puking watermelon, anyone?

Carve a large mouth, draw the eyes and nose with marker pen.

First things first, prepare your pumpkin! Choose a large one – you need room to put a conical flask inside and put the pumpkin’s “lid” securely back in place.

Carve the mouth in the any shape you like, but make it generous. Draw the eyes and nose (and any other decoration) in waterproof marker – unless you want your pumpkin to “puke” out of its nose and eyes as well!

Rest the pumpkin on something wipe-clean (it might leak from the bottom) and put a deep tray in front of it.

To make the “puke” you will need:

  • 35% hydrogen peroxide (corrosive)
  • a stock solution of KI, potassium iodide (low hazard)
  • washing up liquid

The puking pumpkin!

You can also add food colouring or dye, but be aware that the reaction can completely change or even destroy the colours you started with. If colour matters to you, test it first.


  1. Place about 50 ml (use more if it’s not so fresh) of the hydrogen peroxide into the conical flask, add a few drops of washing up liquid (and dye, if you’re using it).
  2. Add some KI solution and quickly put the pumpkin’s lid back in place.
  3. Enjoy the show!

Check out some video of all this here.

What’s happening? Hydrogen peroxide readily decomposes into oxygen and water, but at room temperature this reaction is slow. KI catalyses the reaction, i.e. speeds it up. (There are other catalysts you could also try if you want to experiment; potassium permanganate for example.) The washing up liquid traps the oxygen gas in foam to produce the “puke”.

The word and symbol equations are:

hydrogen peroxide –> water + oxygen
2H2O2 –> 2H2O + O2

There are several teaching points here:

  • Evidence for chemical change.
  • Compounds vs. elements.
  • Breaking the chemical bonds in a compound to form an element and another compound.
  • Balanced equations / conservation of mass.
  • The idea that when it comes to chemical processes, it’s not just whether a reaction happens that matters, but also how fast it happens…
  • … which of course leads to catalysis. A-level students can look at the relevant equations (see below).

Once the pumpkin has finished puking, demonstrate the test for oxygen gas.

Some health and safety points: the hydrogen peroxide is corrosive so avoid skin contact. Safety goggles are essential, gloves are a Good Idea(™). The reaction is exothermic and steam is produced. A heavy pumpkin lid will almost certainly stay in place but still, stand well back. 

But we’re not done, oh no! What you have at the end of this reaction is essentially a pumpkin full of oxygen gas. Time to crack out the splints and demonstrate/remind your students of the test for oxygen. It’s endlessly fun to put a glowing splint into the pumpkin’s mouth and watch it catch fire, and you’ll be able to do it several times.

And we’re still not done! Once the pumpkin has completely finished “puking”, open it up (carefully) and look inside. Check out that colour! Why is it bluish-black in there?

The inside of the pumpkin is blue-black: iodine is produced which complexes with starch.

It turns out that you also get some iodine produced, and there’s starch in pumpkins. It’s the classic, blue-black starch complex.

Finally, give the outside of the pumpkin a good wipe, take it home, carve out the eyes and nose and pop it outside for the trick or treaters – it’s completely safe to use.

Brace yourselves, more equations coming…

The KI catalyses the reaction because the iodide ions provide an alternative, lower-energy pathway for the decomposition reaction. The iodide reacts with the hydrogen peroxide to form hypoiodite ions (OI). These react with more hydrogen peroxide to form water, oxygen and more iodide ions – so the iodide is regenerated, and hence is acting as a catalyst.

H2O2 + I –> H2O + OI
H2O2 + OI –> H2O + O2 + I

The iodine I mentioned comes about because some of the iodide is oxidised to iodine by the oxygen. At this point we have both iodine and iodide ions – these combine to form triiodide, and this forms the familiar blue-black complex.

Phew. That’s enough tricky chemistry for one year. Enjoy your chocolate!

Trick or treat!




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