Dock bug in decayed flower
Brown dock bug in decayed flower macro close-up

A revolutionary new technique could soon be helping forensic scientists to resolve criminal investigations by analyzing the bugs in soil.

A team of scientists at New Zealand’s government-owned Institute of Environmental Science and Research (ESR) has pioneered the application of molecular technology to forensic soil analysis; the technique allows simple matching and exclusion of soil samples based on the bacterial community living within them.

Fictional detective Sherlock Holmes is credited with first realizing the value of soil in criminal investigations. In the book, The Sign of Four Holmes spotted a particular reddish mold’ on his offsider Watson’s instep and told his companion, correctly, that he (Watson) had been to the Wigmore Street post office that day. The color of the soil — from the pavement outside the post office — was the tell-tale sign.

In the real world, soil color is one of several ways that forensic scientists analyses oil at present. They also check the mineral composition and the density of the soil as well as what pollen is in the soil. But these techniques, because of the expertise needed to be able to make the scientific judgments — are expensive and only used in New Zealand for serious criminal cases.

The technique allows simple matching and exclusion of soil samples based on the bacterial community living within them. Now the ESR team, led by environmental microbiologist Dr. Jacqui Horswell, has developed a technique that identifies soil by the bugs that live within each sample. Dr. Horswell and her team aim to develop a scientifically and legally robust DNA profiling system for comparing soil from different locations.

“We see soil as being unique to a specific location and that’s because we have so many different factors that are involved in the formation of soil,” she explains. For instance, the soil under a forest will be different from soil under a rugby field pitch, and even the soil in two neighboring backyards will differ depending on what is planted in the gardens. It is that difference that the ESR technique can exploit.

To identify where suspects have been, a DNA profile could be taken from the soil at a crime scene and then compared with DNA profiles from the soil on items in a suspect’s possession, including footwear, vehicles, and clothing.

To help identify different soils, the ESR team plans to create a database of soils, which would also give the scientists the ability to say what the probability is of a fortuitous match with another soil (in the same way the probability for a match in two samples of human DNA is calculated).

The research is of international importance. The Foundation for Research in Science and Technology (FRST) has provided investment funding to develop a prototype soil-DNA fingerprinting kit.

” The technique will open up new options for evidential soil comparison. It’s a precise analytical tool and it’s quickly and easily applied,” says Dr. Horswell.

Once the research is complete ESR aims to enter product development. “We’d like to see a forensic comparison of soil using bacterial DNA profiling become routine both here and overseas,” said Dr. Horswell.

She hopes that a prototype soil-DNA analysis kit will be ready in two years and that it will be in use in New Zealand courts in about 5 years.

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