It’s simple. No soil means no life. Human life without soil is impossible to imagine as our wellbeing depends on its capacities and functions. As well as being a key resource for food security and human sustainability, soils can also provide chemical and biological profile characteristics, and can contain tiny secrets of great use to the investigative process. Such information can help investigators search for a missing person, and can also be presented as evidence in court.
As principal soil scientist at the James Hutton Institute and a court expert witness, I regularly work with police and forensic practitioners in the UK and abroad, on questions such as “Where could that soil have come from?”, or “Can that soil be evidentially linked to that crime scene?”
The James Hutton Institute, whose strengths in land, crop, waters, environmental and socio-economic sciences enable a broad range of disciplines to interconnect, also has a worldwide reputation in soil, microbiology, land, plant biology, physiology, analytical instrumentation and geographic location, making it an ideal place to carry out such interdisciplinary science. Soil is a complex and heterogeneous material involving customary contact with persons, vehicles and objects. That complexity can make it a useful form of contact trace evidence in crime investigation using the many powerful analytical approaches developed in our labs.
Soil is unlikely to be the only form of evidence used in an investigation, but it can be very powerful when brought together with other pieces of information in the investigative jigsaw. By working with a wide team of experts, such as with statisticians at Biomathematics and Statistics Scotland, our team is an excellent position to examine ecological or environmental samples (organics, volatile organic compounds, mineralogy, botany, diatoms, plant and microbial DNA analysis) and deliver witness reports and statements, not to mention the expert witness court presentation side of the work.
Soil has been used in several high profile cases in the past in the UK, both for intelligence for search and as evidence in court. In addition, soil has also been used to investigate environmental crime such as contamination and sewage spillage, or movement of pollutants or organic contaminants into watercourses.
In a large scale murder hunt led by Northern Constabulary (2009), soil information was used in the search phase of the investigation, to help eliminate areas of land using Geographical Information Systems (GIS) and soils data held on our soils database, which also helped with the construction of probable pattern of vehicle movements.
This information from the case also provided evidence, through a two way association – sand from the deposition site was found on the spade, and flakes of metal from the spade were found at the deposition site, making a strong contact trace association.
Two men were found guilty of murder and culpable homicide through the use of this information, along with several other threads of evidence.
Tools of the trade
Soil mineralogy, organic characterisation, botany, diatom, fungal and nematode identification, plant and seed DNA analysis, and bacterial DNA profile characterisation are some of the main characteristics that are used by our forensic team. A wide range of state of the art methods are at our fingertips: X-ray diffraction, Infrared Red Spectral Analysis, Gas Chromatography, Scanning Electron Microscopy, and light and heavy isotope analysis have all been used to great effect in many cases. Geographic Information Systems have been developed at the Institute, to allow the mapping of exclusion of areas in search, enabling police to fine tune areas on the ground for missing persons or objects.
We, along with our predecessor organisations, have been collecting data on Scotland’s soils since the 1940s, resulting in a library of information on more than 13,000 locations with more than 40,000 individual samples held in our archives.
Data are stored in a number of tables which allow users to find out information about the site, the individual horizons in the soil profile and all of the samples which have come from those geographically referenced soil horizons. Some samples have more than 1,000 individual data items associated with them, from the depth at which it was taken, to its colour, its chemistry, including isotope chemistry, physical properties, through to the soil DNA and other molecular analysis.
No two forensic cases are ever the same, and the approach taken depends on the question asked and the case situation and context. When I am contacted by the investigating authorities, I consider each individual case context and individual questions asked, and then decide upon the most appropriate approach to take.
Visiting the site can be very revealing, offering up potential solutions as to where to take the most appropriate control samples. The first laboratory stage in any case is to examine the reference soil and/or traces of vegetation on any questioned items such as footwear, vehicles or objects associated with a potential crime scene. The microscope is one of my most important tools, often revealing secrets that can link that questioned item back to having been in contact with a specific locus.
Professor Steve Hillier, head of the Mineralogy section, is an expert in characterisation and quantification of soil minerals. This provides vital information on the parent material on which the soil had developed and thus vital clues as to where a soil from an unknown location had originated.
The technique is fully accredited and offers a powerful tool to help answer the question “Where could that soil have come from?”
Professor Hillier makes extensive use of X-ray powder diffraction (XRPD) in his work and his research interests revolve around clay, soil and environmental mineralogy. This research is aimed at developing methods for clay mineral identification and quantification in soils and linking this to an understanding of soil properties and behaviour.
The innovation of the XRPD quantitative methods developed by Professor Hillier is world renowned through his consistent success in the Reynolds Cup, a biennial competition organised by the Clay Minerals Society, and many of the same methods are offered as commercial services to industry, including security. In addition, rare materials such as asbestos, fly ash and other anthropogenic materials can provide information on likely source. Professor Hillier’s great experience in the oil and gas industry delivers context, international reputation and accreditation.
A variety of applications
In addition, unknown substances are often sent to the Institute, where highly trained scientists apply the most appropriate techniques to identify with confidence what the material is. In addition, food adulteration and fake products can be identified using such approaches as stable isotopic characterisation. Searchable databases on a wide range of materials have been compiled, also using approaches such as neural network modelling.
Soil organic markers are very useful for characterising the spatial scale of an individual locus. They have been used to compare soils from questioned items with those from crime scenes in a range of cases. For example, comparison of the shape of petroleum hydrocarbon UCM hump shape in soil samples was used to link motor vehicles to a crime scene beside a muddy track; soil from a suspect’s car had a very similar UCM hump shape and unusually high faecal stanol concentrations (typically of human sewage) to soil from a rural crime scene; analysis of faecal stanols and bile acids analysis confirmed that pig faeces were present on the shoe from a person, suspected of entering a pig paddock; objective comparison of soil and dung n-alkane and fatty alcohol composition linked a vehicle to a crime scene located in a cattle field; and an unusual compound (15-nonacosanone) in mixed-source soil samples from a suspect’s car was also found in soils from a crime scene.
Metal theft, murder, rape, burglary and assault are the main types of crime where soil is used as evidence. Recently, soil left behind in a pair of gloves in the boot of the suspect’s vehicle helped police find a missing lady to within 700m of the locus; I presented evidence in 2013 in Newcastle Crown Court, contributing to the successful conviction for manslaughter in this case.
In the lab
The soil organic analysis is carried out from the laboratories of Dr Bob Mayes, where he has perfected a range of approaches to quantify the ranges of organic compounds found in soil both naturally from the plant vegetation that builds the soil below it, and also anthropogenically derived compounds, such as PAHs or hydrocarbons.
Dr Mayes has developed methodologies for measuring dietary intake, digestibility and plant species composition in grazing herbivores. These techniques, which use the chemical compounds in the wax of dietary plants as faecal markers, are now used by researchers worldwide. The applications of these markers (hydrocarbons, fatty alcohols and fatty acids) have been extended to study the diets of wild animals, including non-ruminant herbivores and insectivorous birds and mammals, and more recently have been applied to plant wax compounds in soil samples. Dr Mayes’ lab also brings much experience in faecal analysis, in determining animal source and diet of the offending animal.
This organic characterisation is crucial both in research, to determine the vegetation composition at the locus, and as evidence – the organic signatures often vary at the scale appropriate for a contact point. Long lived lipids, analysable in soil and related materials, can be useful as biomarkers in criminal forensic investigations, both for intelligence and evidential purposes, having been accepted by UK criminal courts. Acceptable organic marker analyses (plant alkanes, fatty alcohols and sterols) can now be obtained from samples of weights of 10mg, using glass SPE columns to isolate different fractions prior to GC–MS analysis. Further fourfold reduction in sample size has been achieved by using miniature syringes containing silica-gel.
It’s in the minutiae
We also work on civil cases, from contaminated land to sewage sludge deposition onto land or into river courses. Food and drink provenancing is another area where we provide intelligence and evidence, e.g. whisky, beef, garlic and characterising mixed meat products.
In addition, physical features within a soil sample such as hairs, fibres, flakes of paint, plastic shards and even flakes of skin have been characterised and contributed to the determination of the evidential value of a soil sample.
Vehicles, footwear, clothing, spades and tools, as well as trace amounts of material, e.g. found under a fingernail, can be examined and analysed in our laboratories, potentially turning around a sample analysis and interpretation in fewer than 24 hours.
Soil also contains a range of clues such as volatile organic compounds, cholesterol and DNA, that can help suggest the presence of human material which could assist police in the location and recovery of bodies. This technology originated from plant herbivore research, applied in a contrasting context – that of crop growth and pest control – but to an equal if not greater benefit.
Volatile compounds have most widely been used to indicate location and time of death, but less volatile compounds would be desirable as longer term indicators. 10-Hydroxystearate, from adipocere, can be present in wet grave soils, but is unlikely to be produced from bodies in, or on well drained soils.
From pig carcass experiments, we have shown that cholesterol and coprostanol are decomposition products, remaining in associated soil for a number of months. We have also found these compounds in ancient (ca. 3,000 years BP) and more recent (27 years BP) grave soils. Although not specifically associated with decomposed bodies, they can act as useful indicators.
We are always considering and developing new approaches and methods to this important area of forensic science. A recently awarded grant from the EU, MiSAFE, is testing an approach to use DNA fingerprinting methods to characterise soil in a cost effective way. The MiSAFE project, coordinated by the Hebrew University of Jerusalem (Israel), with partners Libragen (France), CLCbio (Denmark), Ecole Centrale de Lyon (France), Israeli Police (Israel), Guardia Civil Española (Spain) and the James Hutton Institute in Scotland, aims to provide forensic practitioners with a microbial genetic profiling tool that could bring soil into routine forensic investigation and judicial proceedings.
This would also provide opportunities for European high tech enterprises to lead this new field of environmental genetic forensics. Hopefully, MiSAFE will also lead to a better understanding of the impact of storage, sample handling and soil variability on such genetic attributes – essential before being used in a criminal court of law. It will also test the analysis of even smaller sample sizes using molecular tools, thus increasing the range of cases where it can be of use to the investigating authorities.
This soil information can now be made available to the investigator relatively easily. The development and implementation of novel and evolving technologies, such as genetic information, would enable the more routine use of soil in investigations, whether that is in a civil or criminal legal context, and thus bridge a security gap, benefiting civil UK, European and global security.
The new research work involves a range of scientists, legal and forensic experts, police practitioners and industrial stakeholders, will deliver a useable genetic forensic tool, with associated operating practise guidelines, while also widening its application to environmental and ecological disciplines. As the secrets are revealed, the future looks increasingly bright for forensic soil science.
Published: 27th May 2014 in AWE International