The impact of environmental variability and clothing type on the transfer of marine diatoms as trace evidence indicators in coastal locations

Diatoms are a species-rich group of microalgae, abundant in freshwater, marine, and soil environments. Subsequently, they may be used as a form of trace evidence, reconstructing links between persons and places involved in crime. Despite previous studies demonstrating the forensic value of diatoms in freshwater and soil habitats, no previous research has explored their transfer and persistence dynamics in marine environments. This study therefore aimed to assess diatom transfer to clothing following immersion in five coastal and one freshwater location, offering a novel contribution to the rapidly expanding empirical research base within forensic ecology. Experiments were designed to consider the impact of recipient surface characteristics, environmental variability, and diatom valve characteristics (morphology and species-specific features) on the abundance, species richness, and whole assemblage composition of marine diatoms recovered from clothing. Three common materials - cotton, polyester, and acrylic - were submerged in two marine lakes, two tidal beaches, and one estuary along the Merseyside coast (NW England), and one inland pond to provide a freshwater comparison. Diatoms were recovered from all environmental and clothing transfer samples using a H₂O₂ extraction protocol before microscopic analysis including species identification. The results demonstrate significant differences in the diatom communities present within the six environmental samples, with multiple site-specific marker taxa and a variable species assemblage between coastal sites. Clothing type and environmental variability significantly influenced the abundance, species richness, morphology, and species composition of marine diatoms transferred to clothing. Notably, the whole species assemblage retrieved from each subset of transfer samples demonstrated relative similarity to the corresponding environmental control sample, supporting forensic comparisons and exclusions with questioned sites. These findings highlight that marine diatoms offer useful circumstantial trace evidence indicators during crime reconstructions involving coastal environments. Furthermore, and similarly to the findings of freshwater research, care must be taken when interpreting marine diatoms as trace evidence indicators in forensic investigations. The complexity of variables influencing the abundance and representativeness of a diatom sample transferred to clothing necessitates exclusionary interpretations to ensure robust and reliable conclusions of evidential significance.