How do we find poisons in the body?

Is it easy to look for toxins?
04 February 2020



How hard is it to find poisons in the body?


We asked forensic toxicologist Lorna Nesbit how she goes about tracking down toxins...

Lorna - So we don't start off completely blind as forensic toxicologists. We'll get in some sort of paperwork from a pathologist that will indicate whether they want just a general toxicology screen or whether pills had been found at the scene or if the find any needle marks on them that may indicate any sort of opioid abuse, you know, like heroin users for example.

Chris - So that might give you, excuse the pun, a point, and that might point you towards something to look for.

Lorna - If we look at the amount of drugs that are now out there, we're now at the point where we're looking for a needle in a haystack. So any sort of information is really helpful for us. And so then what we will do is we will basically do, a kind of screen and we will run the blood sample or the urine sample through some of our instrumentation so it will tell us whether we might have some sort of opiate and it will lock at down into the class of drug that we're looking at.

Chris - Are there any clever crafty molecules that will escape that screen? So if I wanted to do the master plan, criminal mastermind sort of murder, I could give a drug and by the time someone like you got near the body it would've have gone. I'm not planning any of this anybody, I'm not trying to give people ideas. But is that possible?

Lorna - If you are going to try and plan the perfect murder, which you can't generally do anything, you will get caught at some point, it might just take slightly longer, try and get something that's going to be eliminated out of the body really quickly. And those drugs are typically actually used for really sinister crime. So drug facilitated sexual assault. A lot of the drugs are used for that, because by the time somebody wakes up, for example, the drugs gone out of their system. So something like GHB is really fast eliminating. Heroin is another one. So it'll start off as heroin and then within about five minutes your body will already have started to break that down. So you have to either know how long that drug is going to stay in the body and what the biomarkers that you're going to be looking for are.

Chris - Someone asked me the other day, sounds a bit macabre this, but they were saying cause carbon monoxide poisoning, the way that kills people is by asphyxia isn't it? For instance, if someone died in a hotel room that had a poor heating system and they breathed in the gas, it binds to your hemoglobin. So you can't get oxygen around your body cause there's hemoglobin blocked up with carbon monoxide rather than hemoglobin ready to receive oxygen. Do people go looking for the carbon monoxide under those circumstances? Or if you just happen to have, have access to a cylinder of carbon monoxide and you poison someone with it and there's no other reason why they might be exposed, would you get away with that or do they look for that?

Lorna - No, so carbon monoxide poisoning is actually relatively easy to spot from a toxicologist point of view. Everybody thinks that forensic science is really glam and glorious and we all run around and we solve crimes, and we go and we see lots of dead bodies and we actually don't, we just get the bits. So we get, you know, the urine samples and the blood samples come through. And when people die, funny things happen to their body. So most of the time the blood that comes through is kind of greenish, or it's really lumpy or there's large fat deposits in the top. It's, you know, it's really glam. But when somebody comes through and they've died of carbon monoxide poisoning, their blood's really cherry red. And so when you've got a really cherry red sample, that's the first thing that you're probably going to try and look for.

Chris - So someone like you would spot that?

Lorna - Yeah.


Enjoyed the podcast, it reminded me of a history of toxicology by Deborah Blum, "The Poisoner's Handbook"

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