How was this forensic science result determined?

I was reading at this site the following:

I can easily believe that the hair strands like a ring of a tree, can show diet changes over time. But how can they single out with such astonishing accuracy where the person had been? I would be impressed with “Went from a clean rural place to a polluted urban inner city”, but police in the UK can tell when someone had been to TAMPA by their hair? :dubious:

This is just a WAG, but I seem to recall that differences in drinking water can sometimes be used to pinpoint a person’s whereabouts from their hair (e;g some areas have a specific mineral signature).

That sounds plausible, but is there some database of worldwide drinking water mineral signatures that forensic investigators have access to?

This was Isotope Analysis. Geologists have pretty good databases of isotope distribution, as it can be used for a range of analysis. Forensic Scientists just tap in to that data.

Si

What isotopes would they use? Organic material like hair is mostly made up of lightweight elements like carbon, hydrogen, oxygen, and nitrogen, and most of those only have one stable isotope. Do they use the trace amounts of heavier elements, or is there something useful they can get out of the common ones?

Strontium and Oxygen, according to wiki.

Si

So a little of each, then. Hm, I hadn’t realized that there were other stable isotopes of oxygen.

[sup]16[/sup]O/[sup]18[/sup]O ratios are used to study historical climate effects from ice cores, because there is a temperature dependent variation.

Si

They do it like with all DNA. The figure out what probably happened, then get a hair and confront the person with what they think happened.

:slight_smile: