Sediment and soil environmental forensics: What do we know?

Abstract

Environmental forensic practitioners have been identifying the source of contamination in the environment for many years. In some cases, their results have been used successfully to prosecute offenders. The use of DNA in criminal cases has led to a considerable advance in the ability of the scientist to identify the source of materials; in environmental forensics the same may be true, but the 'DNA' may be the chemical fingerprint or the biological assemblage. Legislation dictates that the correct source of compounds in the environment is identified or the source apportioned between potentially responsible parties. The implementation of the Environmental Liability Directive in the European Union may require remediation of damaged sites to their baseline condition but those conditions may not be quite so easy to define. Chemical composition of multi-compound materials such as oil may enable fingerprints to be developed based on the internal relationship between groups of chemicals: this may be considered as its 'DNA' and enable it to be tracked in the environment. Chemicals have a whole range of water solubilities and hence mobilities in the environment. In some cases, the partitioning between the solid and solution phase is dependent on the prevailing environmental conditions, such as pH or salinity. These compounds, known as hydrophobic ionogenic organic compounds, include Triclosan, a widely used anti-microbial agent in domestic products. In highly variable environments such as estuaries, this compound may not be where you initially expect it to be. In a similar manner, the biota that make up an assemblage may provide a unique signature for that environment or those conditions; this may also be tracked in the environment. In a study using the meiofauna of surface sediments of a lagoon in Portugal, the sewage-signature based on the species assemblage near known discharge sites was able to indicate the position of previously unrecognised discharges to the lagoon. The ability to use these data may also rely on multivariate statistical methods that enable signatures to be defined and then quantifiably extracted from environmental data. These methods have become relatively simple to use with the development of dedicated computer programs, but there is still the need to ensure that the data are appropriate for the method and vice versa. Over-reliance on statistical results may be undesirable in court presentations but, if used together with a whole range of methods, may help explain the situation to the lay judiciary. Stable isotopes have provided considerable advances in source identification and apportionment. In one example, lead isotopes were able to show that in the Conwy Estuary, North Wales, there was no simple single source (e.g. mine tailings) and that multiple sources contributed to the receptor site at the mouth of the estuary. As with any other branch of forensic science, the ability to identify the source of materials is paramount and, in the case of environmental forensics, methods based on a whole range of chemical, biological and statistical data have become the 'DNA' of source apportionment.