Freshwater diatom persistence on clothing I: A quantitative assessment of trace evidence dynamics over time

Freshwater diatoms offer valuable circumstantial forensic indicators, with a growing empirical research base aiming to identify and understand some of the spatial and temporal factors affecting their validity as trace evidence. Previous studies demonstrated that recipient surface characteristics, environmental variability, and individual species traits influence the initial transfer of freshwater diatoms to clothing. However, no previous research has sought to consider the impact of these and other variables on the persistence of transferred diatoms over investigative timescales. Therefore, this study aimed to identify and explore diatom retention dynamics on clothing following wear over time (hours to weeks). A series of experiments were designed to examine the impact of clothing material, seasonality, and time since wear (persistence interval) on the total number and species-richness of diatoms recovered and their relative retention (%) over time. Nine clothing swatches were immersed in a freshwater environment and then worn for one month in the spring. Subsamples were retrieved at regular intervals (e.g. 30 mins, 1 h, 8 h, 24 h) up to one month, diatoms were extracted using a H₂O₂ method, and examined microscopically. Three clothing materials were subject to the same experiment in the winter to generate a seasonal comparison. The results broadly identified three stages of diatom persistence on clothing - rapid initial loss, variable intermediate decay, and sustained long-term presence. Clothing material significantly impacted the number of diatoms recovered and retention dynamics over time, with complex interactions identified with seasonality. Although fewer diatoms were recovered in the winter, overall retention trends were consistent at the different times of year. The findings demonstrate that diatoms can be recovered from clothing, even weeks or months after an initial transfer, yielding a useful environmental trace indicator for forensic reconstructions over investigative timescales. The impact of clothing material and seasonality on persistence identified cotton, acrylic, and viscose clothing as the most reliable temporal repository of diatom trace evidence, with a more abundant forensic assemblage available for forensic comparisons in the spring.