An investigation into the use of riverine mesocosms to analyse the effect of flow velocity and recipient textiles on forensic fibre persistence studies

Textile fibre evidence can provide important activity level information in criminal cases. To date, very few studies have investigated fibre persistence on fabrics exposed to aquatic conditions, even though items of evidence and victim's bodies can regularly be found in aquatic environments. This lack of research on whether fibres (and other trace evidence) persist on evidence submerged in water, has shown to impact practice as it is reported that crime scene examiners do not attempt to recover this evidence, due to the belief that it would not be present. The dynamic nature of aquatic environments mean that the studies are difficult to conduct in situ and variables, such as water flow rate are not possible to control and thought to be difficult to monitor. To address these challenges, artificial streams (also known as mesocosms) were employed in this study to investigate the persistence rate of polyester fibres on different fabric types (Woollen/nylon mix carpet, 100% polyester fleece, and 95% polyester/5% elastane sports vest) for a four week exposure time (1, 8, 24, 48, 120, 168, 264, 336, 504 and 672 hrs). The effect of water flow rate on the persistence of fibres was investigated by conducting the experiment with two flow velocities; 'high' (∼2.75 L/s) or 'low' (∼0.7 L/s). Significant differences between textile type were seen at 504 hrs under low flow conditions and 8, 24, 168 and 264 hrs under high flow conditions. When comparing flow velocities, a significant difference was seen at 1 hr exposure for the fleece textile only, indicating that the two flow rates used in this study do not significantly affect fibre persistence. Initial loss rates were highest for the first hour of submergence for the carpet, fleece and sports vest. Fibre persistence rates were highest on the carpet, followed by fleece and then sports vest. Persistence rates remained mostly constant after 24 hrs for all textiles but with redistribution of fibres between textiles being seen after this exposure time. The use of artificial flumes in this study provided a balance between realistic experimentation and a controlled study; key experimental variables could be continously and safely monitored. This study provides the first fibre persistence data in river type environments and proposes a new method for testing persistence in aquatic environments. This approach is not limited to fibres evidence and could be employed for other evidence such as glass, pollen, fingerprints and DNA.