Is it possible to poison someone with antifreeze? 

Yes. In 2007, in the US, Lynn Turner was sentenced to life in prison without parole for murdering her boyfriend, Randy Thompson, in 2004 by putting antifreeze in his Jell-O, the same way she had killed her husband, Maurice Glenn Turner, in 1995. In the UK, Kate Knight of Stoke-on-Trent was found guilty in January 2008 of trying to kill her husband by putting antifreeze in his curry and red wine. Although he survived, her husband has severe sight and hearing loss, and badly damaged kidneys. Knight got a 30-year prison sentence. 

What is the poisonous molecule? 

Three different molecules are commonly used in antifreeze: ethylene glycol (ethane-1,2-diol) (1), diethylene glycol ((2-hydroxyethoxy)ethan-2-ol) (2) and propylene glycol (propane-1,2-diol) (3). Ethylene glycol is responsible for most poisonings, accidental or otherwise. 

Ethylene glycol is toxic but tastes sweet, so thousands of children and animals are poisoned every year by accidentally drinking it. In a few parts of the world, a bitter-tasting agent is added to make the liquid taste less attractive. In the liver, the enzyme alcohol dehydrogenase converts ethylene glycol first into glycoaldehyde (4) and then into other toxic molecules. Ultimately, the resultant oxalic acid (ethanedioic acid) (5) removes calcium from the body as insoluble calcium oxalate, which is deposited in the kidneys and causes kidney failure. 

How can such poisoning be treated? 

If diagnosed early enough, doctors can administer an antidote, such as ethanol (vodka). This binds to the alcohol dehydrogenase enzyme more strongly than ethylene glycol. This prevents the build-up of ethylene glycol in the liver, which passes through to the kidneys and is excreted from the body. 

What about propylene glycol? 

This chemical is not regarded as toxic because the body breaks down the molecule to harmless lactic acid (2-hydroxypropanoic acid), which is produced naturally in the body during exercise. However, propylene glycol is not used more widely because it is more expensive than ethylene glycol. 

And diethylene glycol? 

Diethylene glycol is less toxic than ethylene glycol, but has been linked with several poisoning cases. For example, cough syrup containing Chinese diethylene glycol killed over 50 Panamanians in 2006. 

What happened? 

It is thought that a Chinese company exported a syrup containing diethylene glycol but labelled as containing 99.5 per cent glycerine. Glycerine (propane-1,2,3-triol or glycerol) (6) is widely used as a safe solvent in the food and drug industry. But glycerine costs about three times as much as diethylene glycol, and it also seems that the person responsible may have had no chemical training. 

So this was a one-off? 

No. Diethylene glycol-contaminated cough syrups and expectorants have been blamed for poisoning children from Haiti, Bangladesh, India, South Africa, Nigeria and Argentina.