Dirt detectives

29 July 2008

Forensic scientists can now trace a speck of soil to almost any garden in the country. But how have they cultivated their soil-sifting skills? Antenna goes digging for evidence...

This research was reported in New Scientist magazine on 24 July 2008.

Criminals will have to be extra careful to clean their boots in future.

Image: David Riley / The Macaulay Institute

Forensic experts have been sifting through soil for evidence for more than a century. They tend to inspect soil for different minerals - grains of rock, sand and clay mixed into the mulch. This can reveal the region that soil is from, but won't provide a precise location.

Traces of soil can be retrieved from shoes, clothes, car tyres and under fingernails.

Image: Lorna Dawson / The Macaulay Institute

So what's new?
Scottish scientists switched their focus from mainly mineral to vegetable - the dead and decaying plant litter in soil. The team collected soil samples from different flowerbeds and examined them for a range of plant chemicals.
Analysis of these chemicals shows differences between flowerbeds - even within the same garden! This suggests that each area of soil has its own unique chemical profile.

As well as fragments of rocks and minerals, soils contain many dead, decaying and living things.

Image: Mauro Rodrigues / Dreamstime

The identity of resident microbes is another strand of evidence the team has been teasing from topsoil. Combining information on microbes with profiles of plant chemicals could turn soil evidence into a powerful crime-busting tool.

Countless bacteria and fungi make their homes in the soil.

Image: Eye of Science / Science Photo Library

'At the moment, soil evidence is mostly used in serious crime cases like murder because it's expensive and time consuming. But if our new techniques are combined with existing types of soil analysis, soil evidence could be used much more widely in future.' Lynne Macdonald, soil expert

Lynne Macdonald, soil expert, The Macaulay Institute, Scotland.

Image: David Riley / The Macaulay Institute

'Soil has great potential for forensics but it is highly complex material. Looking at plant chemicals in this way is a new technique that offers a potentially useful means of fingerprinting soils.' Karl Ritz, soil expert

Karl Ritz, soil expert, Cranfield University.

Image: Karl Ritz