Troubleshooting #1: Nail Polish Remover on Table

Reader Lyn asks:

Hi Dr Chemical, thanks for this – hope you can assist me to bring my favourite table back to presentable..

Am attaching photo – I tipped nail polish remover on it  – looking at the label on the bottle it doesnt say much – black and gold brand – pinky colour.

Kind regards & have a good day.

Lyn

Good question Lyn!

I’m afraid you have a problem.  You have managed to spill on to your table, the most aggressive solvent that is available over the counter (acetone).  The only over-the-counter chemical that was more aggressive and this was trichloroethane, which was in Preen aerosol, but that has now gone by the board.

The acetone is an extremely aggressive solvent to lacquers and varnishes, and I’m afraid that what has happened in this case is that it has actually dissolved the varnish.  So you can’t just rub the pink stuff off – even if you are able to do so, you would still see the scoring of where the acetone had attacked the varnish.

So it depends on how deep the scoring is and how good a job you want to do. you might find that you will be able to remove the pink stuff with a bit of toothpaste on a stiff toothbrush.  If you can, and the scoring of the acetone is not too bad, that might be all you want. But it looks like a large surface area, so the toothpaste is probably not an option.

You could also try Mr Sheen – if the pink is only lightly adsorbed it might lift it.

If Mr Sheen doesn’t work, what you want is an automotive cutting compound – these are designed to gently lift off the coating on old paint to refresh it by exposing the paint underneath – it does this with the use of a mild abrasive compound.  And it is the perfect stuff to use in this regard.  Go to an automotive accessory shop and buy Kitten #2 cutting compound.  Don’t get it mixed up with the #1 compound, which is just the ordinary polish.  The cutting compound is normally red and you can expect to pay about $11 for a tin.

Follow the instructions on the tin for how you use it – the job you want to do is remove the upper layer of the varnish, exactly the same as if you were removing the old coating of paint on the car.

A gentle circular rubbing motion is what you want, and if you’re lucky you will see the pink stuff lift off pretty quickly. Be a bit careful, as varnish is softer than the automotive paint that it was designed for – so gently at first. Once you see the pink stuff come off, wipe the polish off and see how it looks.  If you can still see scoring in the varnish, you may need to polish it a bit more.

But the Kitten product is an excellent abrasive polish with many uses, like cleaning stainless steel, so hopefully it will do the job for you.  And of course when you finish, hit with my favourite Mr Sheen.

Let me know you get on.

 

Do Cast Iron Saucepans Contain Lead?

Last week on my radio show I was asked whether cheaper brand cast iron saucepans might contain lead?

It’s quite a common question – there are also websites where people asked this question, which is no doubt the source of the listeners query.  It appears to be based on the fact that often when people pick up cast-iron saucepans they feel particularly heavy – they therefore wonder whether the increased weight might be caused by lead.

As it happens, this fear is ungrounded.  Cast-iron saucepans will not contain any lead.

Here’s why:

Cast iron saucepans, as the name suggests, are made by being “cast” into a mould.  The iron must therefore be heated hot enough not only to melt it, but hot enough so that there is time to pour it into the mould before it starts to cool and solidify.  It is therefore heated substantially hotter than its actual melting point.

The melting point of iron is 1,535° C.

To cast it, they would therefore heat it no doubt several hundred degrees past this temperature.

Now, let’s look at lead.  Lead melts at a mere 327.5 °C and by the time you reach the melting point of iron is very close to its actual boiling point of 1,750°C

So when the lion is hot enough to be cast, it would actually be above the boiling point of lead.  So what little lead there may be in the iron, would simply boil out of it before it was cast, in exactly the same way that when you use beer or red wine in a recipe, the alcohol all boils out very quickly and you are left with the taste of the wine, but not the alcohol.

But there is one word of caution here.  In years gone by lead was used as a pigment in paints.  It is possible that very old saucepans with enamel coatings may have lead in their pigment.  But most cast-iron saucepans are bare cast-iron, so this is not a problem.

So why do are people have this impression that cast iron feels “heavier” than stainless steel saucepans?  The reason simply is that since cast iron is a more brittle metal than stainless steel, it must be made thicker to give it the mechanical strength.  So it is simply this – cast-iron saucepans feel heavier because they’re thicker.

Ammonium Nitrate: the Jekyll and Hyde Chemical

Chemistry contains a few Jekyll and Hydes.

There are chemicals, like DDT, that are capable of achieving great good and great evil.  At the top of this list is ammonium nitrate.

In the early years of the 20th century, the world had a problem.  Fertilisers were hard to make.  The only source of saltpetre, the chemical that was used as the basis of most fertilisers, was in Chile.  Digging it out, and transporting it around the world, was an expensive and time-consuming process.

The problem was the nitrogen.  Nitrogen is required to make nitrates, and of course ammonium nitrate, which contains two nitrogen atoms.

And while there is plenty of it around us – the air we breathe is 70% nitrogen – no one had worked out a way to get it out of the air, and so the only way left was digging it out of the ground in Chile.

Along came Fritz Haber.

Haber worked out a way to get nitrogen out of the air, and convert it to nitrates.  And so suddenly the world had a plentiful and cheap supply of fertiliser, and vast tracts of land could be made arable, and millions of people could be fed.

That is the Dr Jekyll part.

This all happened in 1913, which you may notice was the year before the First World War started.

As it happened, the Germans had another problem.  Explosives.  They couldn’t make them in any great amount, because they were nitrate-based, and the British had cut off their supply of saltpetre from Chile.  The only source they had was urine and bird droppings, which was never going to yield much.

Suddenly, as if by magic, along came the Haber process.  Suddenly, now the Germans had a plentiful supply of nitrates, and they could make as many explosives as they wanted.

That is the Mr Hyde part.

In fairness to Haber, who developed it as a fertiliser, he was not to know that this chemical would be used to make the explosives that were killing millions of people. But let’s be realistic about this – were it not for the Haber process, World War I would not be what it was – the British would have had the ability to make explosives, and the Germans wouldn’t, and the war would have been much, much shorter.

And today the ammonium nitrate is used for both sources.  It is used by terrorists, and it is used by mines as an explosive.  It is also used by farmers as a fertiliser.

Incidentally, although it was known as explosive compound, this knowledge was not very widely disseminated, and it led to the second greatest industrial accident of all time.

In fact, it has led to a few industrial accidents – in years gone by, before people knew how explosive it was, they would actually break it up with a hammer and chisel if it had caked together.

The Chemistry of Pollution #4

We have seen that there are several mechanisms by which chemicals degrade in the environment.  There is chemical oxidation, UV oxidation, and biodegradation.

There are two types of biodegradation – aerobic and anaerobic.  By far the more common of these two processes is aerobic because there is lots of oxygen around.  But, as we are about to see sometimes anaerobic processes take over.

Despite the efficiency of aerobic biodegradation, it is essentially confined to natural compounds.  And sometimes we as humans put chemicals in the environment which are not natural – but are synthetic, and these compounds can sometimes be very difficult to break down.

These chemicals go by several terms – “recalcitrant”, “persistent”, or “refractory”

As it happens, there is a common thread amongst many of these chemicals.  So let’s look at a few and see if you can work it out.  Consider each of the following chemicals: dichlorodiphenyltrichloroethane (DDT), carbon tetrachloride, chloroform, hexachlorobenzene, chlorofluorocarbons, trichloroethylene.

That’s right – they are all chlorinated compounds.  Each of these is a chemical that was at one stage considered useful, but is now banned (although DDT because of its incredible effectiveness in killing malaria carrying mosquitoes, is still used in some parts of the world).

But the rest of them are no longer used industrially, except in laboratory applications.  You may have heard about the scare recently when some road workers found the residue of a truck spill on the Pacific Highway, north of Sydney that occurred in 1980.  The initial concern was that it had been carrying radioactive material, but mentioned in the fine print also, was that it had been carrying DDT and hexachlorobenzene.  And the nature of these chemicals is that they will not have degraded much in the 32 years since a truck accident.

Why is that?  Why are chlorinated compounds so difficult to degrade biologically?  The reason is simple chemistry.  Aerobic degradation of the chemical by bacteria is nothing more than biological oxidation.  The bacteria oxidise chemicals to turn it into CO2.  But the problem with chlorinated chemicals is that the chlorination makes them resistant to oxidation, for reasons that I will not bore you with (but if you really want to know, it’s to do with the electron withdrawing effect of the chlorine atom).

But there is a second problem with chlorinated compounds.  They are heavier than water.  That is if they get into waterways, they sink to the bottom.

Now we’ve all seen the mess created by the Exxon Valdeez, and the recent oil spill in the gold of Mexico – but at least the oil floated, so it was accessible to clean up.  If the chemical in question sinks to the bottom, it is very inaccessible, and will sit there for many years, poisoning aquatic life and concentrating up through the food chain.

So this is why chlorinated chemicals are essentially a thing of the past – even trichloroethylene which was an exceptionally good drycleaning fluid is no longer used.

Even the humble prewash – Preen – had to be reformulated, because it contained trichloroethylene.

So what does happen to these compounds?  Well they mostly broken down by a completely different mechanism – anaerobic biodegradation.

Anaerobic biodegradation as the name suggests, occurs in the absence of oxygen.  These processes are very slow and take a long time – which is why these chemicals persist so much in the environment.

We have all experienced anaerobic degradation – because when you smell something that is rotting and smells really bad thing you know it has become anaerobic.  That is, the aerobic processes ran out of oxygen, and the system had to change over to an anaerobic mechanism.  And the reason they stink is simply because the chemicals they produce (mostly sulphides) have very strong odour – for example, rotten egg gas.

so when you drive past the carcass of a rotting kangaroo and you can smell it for the next 5 km, it is because in the internals of the animal the bacteria have run out of oxygen, and the system has become anaerobic

We have seen the shift away from chlorinated compounds in the insecticide industry.  The use of organochlorine (there’s that word again) insecticides are a thing of the past – these days, at least in Australia, they have mostly been replaced by the synthetic pyrethroids ( which are all chemicals ending in “thrin”).  And the advantage of the pyrethroids is that they are ultimately extracts of a natural compound from the pyrethrum daisy, and they are therefore biodegradable.

The Chemistry of Pollution #3

We have seen that there are several processors by which material degrades in the environment.

Whereas metals are prone to oxidation by the oxygen in air, and plastics, fibreglass, rubber, clothes and other materials are prone to oxidation by UV light, by far the most common mechanism of degradation is biodegradation, specifically of organic material.

Stated simply, this explains how things rot.  When food goes off in the fridge, it is biodegradation.  When you see the carcass of a rotting kangaroo by the side of the road, that is biodegradation.

There are two types of biodegradation – aerobic and anaerobic.

As the name suggests, aerobic degradation occurs when there is oxygen present, and anaerobic degradation occurs when there isn’t.

The way it works is this – microorganisms (commonly referred to as simply bugs) convert large organic (carbon-based) molecules into carbon dioxide.  This is an aerobic process because they require the oxygen to make the carbon dioxide.  This is why if you accidentally leave a carton of milk on the table for a few days, it is all bloated when you discover it.  The expansion is caused by the CO2 that is generated by the degradation process.

This is an extremely important process which is widely used in the industrial sector.  The most common place is in waste treatment plants, both domestic and industrial.

By domestic, we are simply talking about sewerage plants.  In these plants, using a process known as the activated sludge process, naturally occurring bacteria convert human waste, and other domestic waste into CO2, nitrogen, sulphates, and biomass.  The role of the plant operator is to manage the plant such that there is sufficient oxygen available for the bacteria to do their job.  If you were to visit one of these plants you would typically see large blowers blowing air into the water like a giant aquarium bubbler in your fish tank.  This is simply to provide enough oxygen for the aerobic bacteria to do the job.

This biodegradation is also extremely important industrial process, and has become more so in recent years.  Now, when an industry wishes to process the waste from an industrial process, the use of biological plants (often in conjunction with chemical plants) is very common.  These of course are used widely mostly in areas where the waste is organic in nature – food processing and so on.

it is also used to regenerate contaminated groundwater or soil.  Where an industrial pollutant has leaked into groundwater or soil, often the best way to degrade it is the naturally occurring bacteria in the soil – all they need is enough oxygen to do the job.  A common approach at these sites, therefore, is to drill holes in the ground and insert huge air blowers which just blast area into the ground.  The air allows the bacteria to do their job (and their population increases as a result and the process becomes more efficient) and often all but the most recalcitrant chemicals (which will look at tomorrow) can be removed.  It is, for example, a common process where petroleum solvents are the culprit.

So what sort of chemicals can be biodegrade, and which ones can’t?

In general, any naturally occurring chemical will be prone to biodegradation – this includes even crude oil as we have seen before.  The danger, of course, is that synthetic materials are not prone to biodegradation readily.  Plastic bags are a good example – the polymer chains are extremely stable and resist the action of bacteria.  But they are not so much of a problem, as they are chemically inert – the worst to say about them is that they are unsightly if they cause litter – but there are no toxicity issues.

Of much greater concern, are synthetic chemicals, which were made (and put into the environment) in an age where people just didn’t care about whether they were biodegradable or not.  They were made, and used, because they were cheap, they did the job, and they were stable – that is they didn’t degrade this time.  So the very thing that made them attractive in the first place, now is causing a problem.

This is a large topic in itself, and targets chemicals in several different industries – and we will look at it tomorrow.