It was very interesting to read the results of ESR’s recent media release: Hair samples reveal P lab kids’ long term exposure to methamphetamine. I’ve seen many cases involving meth labs and manufacture, using swabs from surfaces to determine whether or not methamphetamine could have been manufactured in a given location. Using hair analysis results to link drugs with child neglect is something that seems to becoming more common here in New Zealand and so I have also been asked a few times about methods and results – this is a new aspect of science reaching again from the realms of criminal casework into Family Court casework (hair analysis is relatively common for adults wanting to obtain or maintain custody of children).
Concentrations of drugs in hair is something that needs to be considered when looking at results. It is not possible to differentiate between single or multiple occurrences of a drug during the period represented by the hair sample – a result from a six centimetre length of hair will be the result for the entire length of hair: could be one occurrence or several.
When interpreting results from hair samples it is of course important to consider not only the concentrations of drugs that are detected but also the period of time that each hair sample represents and also take into account the speed at which the hair grows. Growth rates in adults is documented in Harkey (1993) who advises that ,”The range of hair growth rates reported.for scalp hair alone is between 0.2 mm/day and 1.12 mm/day (0.6-3.36 cm/month or 0.27- 1.53 inches/month). Hair type and anatomical location are the most important factors which determine growth rate. Scalp hair grows faster than pubic or axillary hair which in turn grows faster than beard hair. In addition, growth rate is somewhat dependent on race, sex and age. Scalp hair in women grows faster than in men. Caucasian hair grows faster than Asian hair, and hair growth rate generally decreases with age.” Less is known about the growth rates of children’s hair.
So the results from ESR are encouraging but, as with all areas of science (particularly I think in forensic science), we need to know more in order to be able to interpret our findings and case circumstances are critical – different cases will have different significant factors. Further details are available in:
Harkey, M. 1993. Anatomy & physiology of hair. Forensic Science International, vol 63 , pp 9-18.
Kronstrand & Scott. 2006. Chapter 1: Drug incorporation into hair. Analytical and Practical Aspects of Drug Testing in Hair. Kintz, P (Ed.). CRC Press.
Thanks also to Dr Karen Scott for her recent assistance in these cases.