In this episode, we talk about the analysis of drugs in hair.
The use of hair as a preferred sample for drug testing has grown in popularity over the last couple of decades. But so too has our understanding of its limitations. What can hair analysis tell us about a person's drug history?
Special thanks to Michaela Kenneally and Marc Grabowski for appearing in this episode.
Peter's recommended hair collection device
Contact us at toxpod@tiaft.org
Find out more about TIAFT at www.tiaft.org
The Toxpod is a production of The International Association of Forensic Toxicologists. The opinions expressed by the hosts are their own and do not necessarily reflect the views of TIAFT.
In this episode, we talk about the analysis of drugs in hair.
The use of hair as a preferred sample for drug testing has grown in popularity over the last couple of decades. But so too has our understanding of its limitations. What can hair analysis tell us about a person's drug history?
Special thanks to Michaela Kenneally and Marc Grabowski for appearing in this episode.
Peter's recommended hair collection device
Contact us at toxpod@tiaft.org
Find out more about TIAFT at www.tiaft.org
The Toxpod is a production of The International Association of Forensic Toxicologists. The opinions expressed by the hosts are their own and do not necessarily reflect the views of TIAFT.
[Skit] In the 1980s, the music was loud and the mullets were soft. Parachute pants were a thing. And the analysis of drugs in hair was just getting started.
Dr Jameson:[singing"Girls Just Wanna Have Fun" whilst typing]
Lab assistant:Coming Jameson?
Dr Jameson:Yeah, I'll be along shortly. Just got to finish writing this report about some cocaine I found in a hair sample.[typing] So in conclusion, the detection of cocaine in their hair demonstrates that the subject has used cocaine in the previous...[sound of time machine materialising]
Time-traveller:[out of breath] Stop!
Dr Jameson:What! How did you get in here?
Time-traveller:Are you Dr Jameson?
Dr Jameson:Yes, but who are you?
Time-traveller:I'm a toxicologist just like you and I'm from the future.
Dr Jameson:Ridiculous. There's no such thing as time travel.
Time-traveller:That's the least of your worries right now. Listen, you need to repeat this test!
Dr Jameson:What do you mean, repeat it?
Time-traveller:In the future, we've discovered that small amounts of cocaine can be found in the hair from external contamination.
Dr Jameson:Really? So it might not indicate use then?
Time-traveller:No. You need to wash the hair first to remove any contamination. Then whatever's left in the hair is from drug use.
Dr Jameson:Um, okay. Thanks, I guess.
Time-traveller:Happy to help.[sound of time machine dematerialising]
Dr Jameson:That was weird. Luckily there is still enough hair sample to...[sound of time machine materialising]
Time-traveller:[out of breath] Stop!
Dr Jameson:What? You were just here!
Time-traveller:Yes. Only a few moments have passed for you, but several years have gone by for me.
Dr Jameson:So what's the problem?
Time-traveller:Remember I said you need to wash the hair first and then whatever is left is from drug use?
Dr Jameson:Uh, yes. That was literally seconds ago.
Time-traveller:Right. Well, it turns out that the wash isn't really that reliable. What you really need is to use a higher cut off for a positive result.
Dr Jameson:What kind of cut off level are you talking about?
Time-traveller:Here. I've brought these recommendations from the future.[paper rustling]
Dr Jameson:Okay. So wash the hair first and use a higher cut off concentration and that will eliminate external contamination?
Time-traveller:Definitely!
Dr Jameson:Alright. Thanks again.
Time-traveller:My pleasure.[sound of time machine dematerialising]
Dr Jameson:This guy is something else. I'd better cancel my afternoon meeting...
Time-traveller:[out of breath] Stop!
Dr Jameson:What is it this time?
Time-traveller:You know those cut offs I gave you?
Dr Jameson:Yes. I'm still holding them. Why are you always out of breath?
Time-traveller:Oh, it's the time machine. It works by pedal power. Better for the environment apparently. Anyway, it turns out that external contamination can give much higher levels than we thought- even higher than those cutoffs.
Dr Jameson:But I'm going to wash the hair first. Isn't that enough?
Time-traveller:Forget about the wash, alright? Some of the external contamination has probably already migrated into the hair, and even if it hasn't, the wash step might push it in! No. What's important is the metabolites. You need to detect the metabolites!
Dr Jameson:Okay, metabolites. So for cocaine...
Time-traveller:Well, benzoylecgonine is a good one, I think. Probably want it to be at least five percent of the parent concentration too, just to be sure.
Dr Jameson:Um, isn't benzoylecgonine a degradation product of cocaine? How do you know it isn't just there because of degradation?
Time-traveller:It is? Okay, forget about benzoylecgonine. What you really want is norcocaine or cocaethylene. Or both!
Dr Jameson:Fine. This is the last time you're going to appear like this, right?
Time-traveller:I'm pretty sure we've got it all worked out this time. Happy testing.[sound of time machine dematerialising]
Dr Jameson:What a day. I need a drink.[sound of time machine materialising]
Time-traveller:[out of breath] Stop!
Dr Jameson:Let me guess. You've discovered something else I need to know.
Time-traveller:Well, yes.
Dr Jameson:Let's hear it then.
Time-traveller:Okay, the thing is norcocaine and cocaethylene, they're found in cocaine powder sometimes, so they might not actually be proof of metabolism.
Dr Jameson:Uh-huh.
Time-traveller:What you need is a unique metabolite. Something that's only produced in the body that can totally exclude contamination. Something like hydroxycocaine.
Dr Jameson:Uh, it's gonna be pretty tough to analyze those low level metabolites. How am I going to do that?
Time-traveller:Yeah. You might want to think about investing in an LC/MS.
Dr Jameson:Are you serious? Like LC/MS is ever going to be useful.
Time-traveller:Oh, you'll get used to it.
Dr Jameson:Right. So you're sure that hydroxycocaine is not found in cocaine powder as well?
Time-traveller:Um, pretty sure. Hang on.[sound of time machine dematerialising and then materialising again][out of breath] So it's, here's the thing, you might just want to use hair analysis as supportive evidence rather than proof of drug use.
Dr Jameson:Okay. That's what I thought. I'm going to go to lunch now. Please don't come back.[door slams]
Time-traveller:Wow, she's even crankier when she's young.
Dr Jameson:[muffled] I heard that!
Time-traveller:[sigh][sound of time machine dematerialising]
Tim:Hello and welcome to The Toxpod, I'm Tim Scott.
Peter:I'm Peter Stockham.
Tim:And today's episode is obviously going to be focused on hair analysis. Hair analysis can be a useful tool, but there are some limitations to it and so we're going to look at some of those today.
Peter:It's easy to say some of those tongue in cheek things that was mentioned in that little skit in hindsight.
Tim:Yeah, unlike in the sketch where it portrayed things as happening in a very linear fashion, one discovery after another. It wasn't really like that.
Peter:Yeah. Even as they were developing hair testing methods, often there wasn't a real consensus on how to do hair testing and so the process evolved quite a bit over the years and to where, until we got to a point where we are now.
Tim:Yeah, I think there's definitely some consensus within the hair testing community about the way to do things and probably more importantly about the way to interpret things, but there's still a lot of things where there isn't really a consensus and there have been people right from the start when hair analysis first really started taking off, which was back in the eighties and it's just sort of gone from strength to strength really in terms of how much it's being used within the toxicological community, both workplace testing and forensic testing, and there's been people right from the start who were really bullish on the prospects of hair analysis and how it was going to be used. And then there were also people who were very cautious right from the start.
Peter:So there were promises made probably that hair testing could do more than what it actually was capable of after we realised it had a few limitations.
Tim:Yeah, I mean with any scientific advancement, there's, it always relies on the excitement about the possibilities, but then also the caution of the possible limitations. If you don't have those people who are really excited about what is possible, the science isn't going to advance.
Peter:Yeah, so you need to have those sorts of people.
Tim:That's right. That's right. We owe a lot to the people who have put a lot of work into research in hair analysis because they thought it could be useful and in doing so have exposed some of the limitations. But as I said hair analysis, it's got its place and it's just that the toxicologist needs to be very aware of what the limitations are so that they're not assuming too much about what it means.
Peter:There's also the problem with the commercialisation of hair testing as well. You know, we have third party companies who may use a laboratory, a forensic science laboratory to do the actual testing, and the advertising that they put forward is not always giving the correct information I've found just from a quick web search recently. They're still calling it things like hair follicle testing and you know the little things that always get toxicologists angry. They say things like amphetamines and methamphetamines as well.
Tim:Methamphetamines, yeah, that's an interesting one. And with hair testing as well, often because it's used quite a lot in workplace testing, you, the end user, the person who gets the report is often the person who's having their hair tested and so for them trying to interpret what it means, it's, it's really, it's impossible for them to interpret it, but it's very difficult to convey that. They see a positive result and they think that means that they've been using the drug, you know, quite recently. It doesn't always mean that.
Peter:That's right. So even at this point though Tim, there's still no international standard for hair testing, is there?
Tim:Not a standard, no. There's guidelines and there's consensus that's been reached by various groups, but no standard. No.
Peter:So why do you think that is? What's, what's the problem there with hair testing as compared to urine testing or blood testing?
Tim:Well, I mean hair testing's a newer science, so it's been changing so much. Our interpretation of it's been changing so much over the last 20 years or so. I think it's been hard for consensus to kind of keep up with that and there's been, like the Society of Hair Testing for example, has put out a number of statements over the years and they've updated them from time to time, but even the last one that was put out, which was quite a few years ago now, the research since then has really highlighted more issues. So at some point there will need to be an update of that, but it's really hard trying to keep up with the current research.
Peter:And there's also a lot of difference between the laboratories in the manner that they do the testing too, so some methods are much better at extracting a larger amount of drug out of a hair than others.
Tim:Yeah, and if you're doing forensic testing, that's what you want. You want to extract as much drug as you possibly can because you might be trying to detect a single dose of a drug in a sexual assault case for example, but workplace testing, you don't want to find a trace amount of the drug that might have been present that the person might even have just been exposed to and not necessarily taken, many months in the past. So let's take a look at some of the particular issues. The first issue comes along when you're actually sampling the hair, cutting the hair off the head. There's a number of ways that this can be done and there's recommendations in the various guidelines, but many times we've seen hair which has come in to our laboratory and it's been cut at an angle, so you know that completely throws off the timeline of the hair analysis or it's, you can see that it hasn't been cut close to the root...
Peter:But you're already talking about issues that we're getting in the laboratory. I think there's lots of issues before we even get to the laboratory, so we call these pre-sampling aspects, so there's still some uncertainty about how fast hair grows. I mean we've got a fairly good idea, but it may vary between different people. There's also, how do drugs incorporate differently between people? What about very young people? How does the drug incorporate into hair in those people compared to adults? So there are a lot of issues outside of the actual laboratory that we have to think about and always remember when we're trying to interpret them.
Tim:Yeah, there's been a lot of work into trying to determine whether a dose of a drug relates to a hair concentration.
Peter:I don't think anyone's suggesting that's a viable approach at the moment, are they?
Tim:No, nothing that I've seen, but obviously different drugs are incorporated to different extents. It's very individual dependent. So if you've got darker hair, you might incorporate some drugs better than someone else who's got lighter hair.
Peter:So, and of course when we're talking about for most laboratories anyway, when we're, when we're doing hair drug testing, we're talking about analysis of multiple individual strands of hair aren't we. And by strand I don't mean a lock I mean individual hairs.
Tim:Yeah, multiple hairs, yep.
Peter:And so each, within a certain lock of hair that's sampled, some of those hairs may have been growing faster than others because they go through the different stages of development.
Tim:Oh yeah. Undoubtedly they are.
Peter:Yeah, so hair goes through different phases of development and growth. So it goes through a growing phase, which I think is called the anagen stage and also through the telogen stage where it starts resting and then it gets shed. So within a certain area of the scalp, different hairs are in different phases. So that means after a length of time, because each hair is growing at a different rate, within a lock the drug can be spread out quite a bit over time depending on what sort of period you're looking at.
Tim:Yeah. Which is why segmental analysis is actually a pretty important thing, but it's not always done because there's a cost factor involved for every segment you're analyzing. It's another test that you're doing, but that's really the best way to get the whole picture of what's going on within that strand of hair.
Peter:And so there's never a, even with segmental analysis, there's never a clear cut off between one month and the next month. It's always going to be a fuzzy borderline there. And particularly also when we're talking about sampling the hair, as we mentioned before, cutting the hair at an angle can vary between different people. So there's always a danger that the person sampling the hair can take too large a tuft and in doing that it's very difficult to get a very straight cut across that area of scalp. Yeah, so the root end may not be aligned as well as it could be, so it's very difficult then to make an accurate prediction of timeframes.
Tim:Yeah, and then the securing of the hair as well within the envelope or the kit, whatever it's being submitted in, is not always done properly as well and you can have all the guidelines in the world, but when you're trying to train a very large body of collectors, some of whom are not very well trained, it's difficult to get them to always do the right thing.
Peter:Yeah and they may not do it very often either, so that's the other problem with any procedure.
Tim:Yeah.
Peter:I think there should be a hair collection device, a standardized device that, it's disposable, it, somehow you put it on the scalp and it grabs a certain area of scalp and then it's got a little razor blade that cuts cuts through parallel to the scalp...
Tim:[laughing] I'm getting flashbacks to Wayne's World, the Suck and Cut or whatever it's called.
Peter:And I think also the incorporation of drug into the hair, it doesn't just happen as the hair's growing. It also happens through sebum as well. So secretions on the outside of the hair can incorporate the drug.
Tim:Yeah, and sweat from a drug user. It can sort of contaminate other parts of the hair as well. Yeah, there's multiple ways that drugs can get into hair, but then I mean some of the research that's happening in the last few years is questioning whether some drugs even get into the hair via the traditional routes that have been thought of through the body, through the blood, into the hair. Something like THC, now people are questioning whether that even gets into the hair through the blood or is it all just external contamination?
Peter:All of it's environmental contamination are you saying?
Tim:Maybe, maybe. I don't know. I think there's still research going on in these areas to find out.
Peter:So basically hair analysis is not a final science as yet, there's still some development continually going on it.
Tim:Yeah, I mean is anything ever a final science?
Peter:Probably not.
Tim:But yeah, hair analysis is definitely newer than some of these other specimens that have been tested. It's only recently, in fact, that hair has stopped being regarded as an alternative specimen compared to something like blood or urine, which are the traditional specimens.
Peter:So the problem with developing hair methods is they're very difficult to validate because it's impossible to spike a hair with a known amount of drug. The only authentic hair that you can get is from a person who's been using drugs and you never actually know how much drug is in that hair in the first place, so you never know how effective your method is except by comparison with other people's methods.
Tim:Yeah, you know how much you're extracting obviously, but this is part of the problem is that there is no standardized analysis for hair and different methods extract different amounts and you see that in proficiency testing samples and so on. There's a bit of a difference between laboratories.
Peter:The range of results that you get back from laboratories is often a lot wider than it would be for blood or urine for example.
Tim:Yeah, for sure, much wider. But it's very hard to standardize tests across all laboratories everywhere because everyone's constantly developing their methods as well and everyone's doing the best job that they can. But there are different perspectives and as we were saying before about workplace testing versus forensic testing, for example, some laboratories want to cover really low amounts of drugs, some want to only target high amounts, some want to target these particular drugs, you know, drugs vary from region to region in the world, so the drugs that we're looking at here in Australia, they might not be so concerned about looking at in Europe, they might be concerned about other ones, so you can't just have a method that is transferable to all laboratories everywhere.
Peter:Exactly. When you're talking about commercializing, you want to have one method that does everything if, in the ideal world, but unfortunately you can't get one method that will reliably extract all drugs out.
Tim:And that brings us to washing as well, which is the first step in hair analysis to try and remove some of the external contamination, but it's a real balancing act because on the one hand you don't want to remove any drug that's actually inside the hair that's come from within the person, but it's very hard to remove all the external contamination and still leave all the drug there that was there inside the hair in the first place.
Peter:And there's also the potential of some washes pushing the drug into the hair, as we mentioned in the skit.
Tim:Yeah, that's been a really interesting finding just in the last few years. The advance of new, uh, instrumental techniques has actually really helped in working out some of these aspects of hair analysis.
Peter:And so that work was done using, uh, using mass spectral imaging on a single hair analysis.
Tim:Yeah. Which wouldn't have been possible 20 years ago to do that kind of testing on a single hair strand, so...
Peter:I do like that concept of analyzing a single hair because it was pointed out to me once that you tend to think of drugs in hair being at a very, very low concentration. But if there's an acute ingestion, the concentration of the drug at a specific spot on the hair is actually quite high because when you think if you're analyzing a whole centimetre of hair, the actual drug is being diluted through that segment.
Tim:And most of the time people are analyzing more than one centimetre. It might be two or three centimetres at a time. Because of that uncertainty in the timeframe, as we were talking about before, you want to make sure you're capturing the timeframe in question, but if it, if it was just a single dose, then you're really diluting it out by analyzing that much hair.
Peter:That's right, that's half the problem with detecting these low doses.
Tim:So with the wash, some labs do a really extensive wash to try and remove any external contamination and I guess if you're focused on getting as few false positives as possible, then you would go for that approach, but then other labs, and maybe forensic labs are in this category, are erring more on the side of not getting false negative results and they figure, well we'll detect what we'll detect and then we'll interpret it afterwards. Yeah, there's gonna be some issues but... and so they might opt for a lesser wash step, a less rugged wash step so that they actually are not extracting the drug that's in the hair.
Peter:Yeah, because often the extraction procedure is pretty similar to the procedure anyway, so you can actually be extracting drugs out of the hair in the wash. It may not all be external contamination that you're removing.
Tim:Yeah, if it's a solvent extraction and a solvent wash, sometimes the solvents are very similar or even identical and it's just the timeframe and the temperature and so on that's different.
Peter:So it's a pretty difficult balance, isn't it, and there's not really a right answer.
Tim:Yeah, it just highlights the importance of the final interpretation and knowing about all the limitations as you go. So another thing that was mentioned in the sketch was about cutoffs and this is where there's some disagreement as well between experts on what cut off should actually be used, what cutoffs are appropriate and it might differ depending on your different circumstances.
Peter:So often cut offs are mainly to differentiate frequent users from one off users.
Tim:Yeah. I think the terminology that's used in the Society Of Hair Testing guidelines is regular use. So you're trying to differentiate people who've been using it regularly from... you're trying not to capture people who just maybe used it once over the last several months.
Peter:So what do these cutoffs actually mean Tim? Because as we all know, depending on the method that you use, you're going to get at a different extraction efficiency. So a 400 cut off in one laboratory may not be the same as a 400 cut off on another laboratory.
Tim:No, it depends on your method and having a set cut off across all methods everywhere really doesn't make a lot of sense, but I guess in trying to standardize a little bit, some of the testing, you've got to start somewhere and so having even a cut off as a rough guideline, I think is, it's useful to have it, but really if you're using a particular method in your laboratory, you want to be comparing those concentrations that you're getting to similar methods either in your own laboratory or in another laboratory.
Peter:And the other thing about relying on cut offs is that you can still get concentrations greater than the cutoff from the root end of a hair after they've stopped using for several months.
Tim:Yeah, many months after someone stopped using you can find, if they were a chronic user of cocaine, for example, you can find cocaine in their hair many months later at higher concentrations than the cut off and it does decrease over that time, but if you just did one segment, one 3 centimetre or 2 centimetre segment, you're not going to know about how it's decreasing over time, all you're going to know is what you find in that time period.
Peter:So you're saying the more segments the better to try to get a better trend of what's happening in that person's hair?
Tim:The more segments the better, but also I think it's just not, it's not just about the cut offs. I think that's become pretty clear. The cutoffs are not the be all and end all. And I'm not sure anyone ever really said that they were. They're always meant to be taken in conjunction with everything else, but sometimes you do get so called experts talking about the cutoffs as if they are a concrete thing that you can use and they're just not.
Peter:It's difficult to have a reliable benchmark.
Tim:Which is why the metabolites are a really important part of hair analysis, finding the metabolites, because if someone's actually taken the drug, they're going to have the metabolites in their system and then they're going to, in most cases they're gonna find their way into the hair as well. Whereas if the drug has just come from external exposure outside the hair, you're not going to find the metabolites.
Peter:But there's also, the problem with that is that metabolites are almost always more polar than the parent drug and so because the hair's a fairly non-polar matrix it makes them more difficult to incorporate into hair so that you need very, very sensitive instrumentation to get down to some metabolites.
Tim:Yeah. Which we do have now. The instrumentation now I think has become sensitive enough that we can detect really trace amounts of metabolites. It wasn't always in the past. It's only, I think it's only been in the last 10 years, even five years that the technology has got to a state where we can reliably detect these really trace levels of unique metabolites and that's the key,, unique metabolites because it's no good using something like norcocaine, as we mentioned in the sketch, which is also found in cocaine seizures at concentrations, at a similar proportion to what you might find in a cocaine user.
Peter:So hydroxy metabolites are quite important because apparently they're not, well, they're not usually a degradation product or not usually a metabolic product produced in the plant that the drug may be coming from, but then again, they're much more polar than the parent, so they will be hard to detect.
Tim:Yeah, so hydroxycocaine, there's several hydroxycocaines: meta, ortho, para. And all of them have been used and are being used to identify cocaine use as opposed to just external exposure, but trace amounts of these have been found in cocaine seizures as well, and I guess it just comes down to the likelihood that that's going to happen. You know, they're not present in all cocaine seizures. Maybe toxicologists are just a little bit to used to talking about things in black and white terms. It's definitely this or it's definitely that. If you get a DNA scientist, for example, they talk in likelihoods all the time, so it might come down to just whether a toxicologist is prepared to say, yeah, it's unlikely to be from external contamination due to all of these different things and yes, it's possible that those have come from external contamination, but it's unlikely. It's hard to say how unlikely, I think that's what makes people uncomfortable about it.
Peter:The difference between DNA and this sort of approach in terms of likelihood, there's no Bayesian analysis you can do on that sort of probability.
Tim:No, I've never seen anything like that. I'm not even sure if that would be possible. And then something like amphetamine, which is a metabolite of methamphetamine and obviously amphetamine is a drug itself so it could be present from external contamination, but amphetamine's also produced during pyrolysis of methamphetamine and in one paper I've seen they found up to 10 percent of the methamphetamine was converted to amphetamine and the reason that's important is because it's turning it into a vapor which is the most likely thing to contaminate your hair, and so if you've got higher concentrations of a metabolite in the vapor than what you had in the actual powder to start with, that's going to skew your interpretation of it.
Peter:And it's also been observed that sweat from parents can actually incorporate drugs into the hair of the children.
Tim:Yeah, little children obviously, you know, come into close contact with their parents all the time, so if the parent's a drug user they're going to have the drug and metabolites in their sweat at obviously the level of the ratios that you'd expect to find them in a drug user. So if their sweat's coming into contact with the child's hair and it's absorbed into the child's hair, it makes it look as if the child's used the drug. They may not have, and I mean adding to all of that as well as that children's hair is more porous than adults. So the drug's more easily incorporated.
Peter:I'm starting to wonder why we do hair analysis Tim.
Tim:[laughing] Well, I think hair analysis is useful to determine exposure to drugs. It has limitations when you're trying to determine whether someone has actually taken the drug, but I think it can actually still be done with some confidence. A lot of labs use a combination of all these different things, you've got, you've got a wash step which you've designed to be quite thorough. You've got a cut off which is reasonably high, which is going to eliminate small amounts of recent external contamination. You've got some unique metabolites there and a lot of labs use ratios as well for those metabolites, so you might have to have a certain ratio of this metabolite and a certain ratio of this metabolite and all of that together builds the case I think that the drug has actually been used, but there is always some uncertainty because of all these things that we've been talking about.
Peter:Those limitations may be at odds to what the court might expect, or the person who's getting their hair tested may expect or the company that's selling the hair test may be telling their clients so it's often left to the toxicologist to advise of these issues.
Tim:Yeah, and I think this is what we know about all toxicology, but especially with hair analysis, the toxicologist has to be proactive about letting the clients know what the issues are because the clients aren't necessarily going to ask about all of these things. They're not gonna understand enough to ask. The toxicologist has to be on the front foot and putting some of this information out there to say, this is what we can say from this test. We've detected the drug, it could be from exposure, there's a variety of ways that it could have gotten into the hair or onto the hair. Don't assume that it's drug use without consulting further with an expert.
Peter:So there's obviously still a fair bit of work to do in hair analysis. So in terms of some recent interesting applications of hair analysis, what have you seen recently, Tim?
Tim:I mean one interesting idea is to try and have time markers for hair analysis. So if you're trying to detect a single dose, you give the person a drug which acts as a marker to see how long, how fast they hair grows, give it to them at two different time points and then rather than just relying on the average growth rate of the population, now you've got a growth rate for that individual and then you can use that to track back to the, pretty much the exact time.
Peter:So in that way they're focusing on a particular region of hair growth. So that could be quite a reliable way to ensure that you're actually looking at the right point in time of the person's hair. But then you've got problems with the variations in hair growth between strands, and I think it's going to be a lot better doing it that way than it would be without having the temporal marker in there, but still going to be some doubt.
Tim:Yeah. It reminds me of the studies that have been done on alcohol elimination rates because when we're trying to work out what the concentration of alcohol was in a person's blood at some time in the past, you can just rely on the average elimination rate of the population, but some people have done some research to try and work out whether if you give the person some alcohol at a couple of different times and measure their blood, then you can actually work out what their elimination rate is. But what's been found is that there's quite significant differences at different times, even in one person and a similar thing could be found in hair analysis.
Peter:That's true, but if you're going to do this sort of temporal analysis, you might start with something like deuterated paracetamol, or a deuterated drug that's relatively harmless, like caffeine and that would provide a good temporal marker. So we haven't covered everything in hair analysis here obviously because it's a pretty broad field. And of course if you've got some topics or some suggestions for what we should be talking about, please let us know.
Tim:You can contact us at thetoxpod@sa.gov.au.
Peter:Thanks for listening to The Toxpod.
Tim:See you next time.