Developing a method for exploiting soil bacterial communities as evidence in environmental forensic investigations

In environmental forensic investigations, soil is often considered as the evidence associated with a crime scene in court. A major challenge is minimizing the uncertainty in linking sets of matched soil to a suspected offender. This article examined the potential methods of analyzing soil bacterial communities via high throughput sequencing, which could generate information of great importance to environmental forensic investigations. Here, we simulated local, regional, and large-scale scenarios, in addition to unknown samples, to investigate the potential of using soil as physical evidence in environmental forensics. At the broad-scale, using heatmap cluster and principal coordinate analyses, we observed that the microbial communities in samples were significantly different across different spatial distances based on Bray-Curtis dissimilarity distances. In soil samples obtained within 20 m of each other, the microbial communities revealed the detailed information based on the numbers of specific operational taxonomic units (OTUs) and biomarker species. In the criminal contexts, soils can be obtained and used to decode the origin information. To trace the soil samples to their origins, we analyzed the dissimilarity distances and matched sources of suspected soil samples to simulate crime investigation activities. In our study, source tracker was used to locate the sources of samples obtained from of a shoe or a tool according to soil microbial communities, and the method could be an effective auxiliary approach in forensic soil source tracking based on microbial data. The results demonstrated that high-throughput sequencing combined with the source tracker approach could make soil a powerful source of evidence to facilitate environmental forensic investigations.