CROOKS beware, a scraping of mud on your shoe could link you to a footprint at the scene of a crime, thanks to a technique that uniquely identifies different soils within a small area by their organic material.
Soil is a tried-and-tested source of forensic information. To determine where it came from, investigators usually try to identify the inorganic components, such as the minerals, or the size, shape and colour of grains. That鈥檚 fine as long as you鈥檙e comparing samples over a wide geographical area. But what if you are trying to catch a thief who has been operating in one town, where these characteristics are likely to be very similar?
Lorna Dawson at the Macaulay Institute in Aberdeen, UK, and her colleagues have been to see how much it varies within a local area. The team took soil samples from seven flower beds in four gardens in and around Aberdeen. For each sample they measured the levels of organic molecules including n-alkanes, fatty alcohols and fatty acids, which are all found in the waxy outer layer of plant matter. Some of these compounds can remain in the soil for thousands of years, so that each area should have a unique organic profile.
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鈥淓very garden has a different history of ownership, with different plants, woodchips and fertilisers. These all build up to give an additional level of organic information,鈥� says Dawson. What鈥檚 more, the team found noticeable differences between soils from the different beds, even those within the same garden.
Further studies have shown that combining this organic analysis with traditional mineral analysis can pinpoint soil samples to different parks within the same town, as well as linking soils to larger geographical areas with more accuracy.
Dawson鈥檚 team also thinks that comparing DNA fragments from bacteria and fungi living in the soil could provide another layer of soil evidence. 鈥淵ou can never say with absolute certainty that two samples come from the same place, but the more markers you have, the stronger the likelihood is,鈥� says Dawson, who presented the results at the in London last week.
鈥淭his has phenomenal potential to increase the power of soil as a forensic tool,鈥� says , a forensic soil expert from the University of Oxford. While the size and shape of soil grains often correlate with its mineral content, its organic content does not and so acts as 鈥渁n independent witness鈥� that two soil samples came from the same place, Bull says. But he cautions that the technique could fall down when soils are introduced from a central location such as a gardening shop.
鈥淭he organic content of soil acts as an independent witness that two soil samples came from the same place鈥�
The team would also like to be able to trace soil samples back to any location, which will mean building a comprehensive database of samples.
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