The transfer of diatoms from freshwater to footwear materials: An experimental study assessing transfer, persistence, and extraction methods for forensic reconstruction

In recent years there has been growing interest in environmental forms of trace evidence, and ecological trace evidence collected from footwear has proved valuable within casework. Simultaneously, there has been growing awareness of the need for empirical experimentation to underpin forensic inferences. Diatoms are unicellular algae, and each cell (or ‘frustule’) consists of two valves which are made of silica, a robust material that favours their preservation both in sediments and within forensic scenarios. A series of experiments were carried out to investigate the transfer and persistence of diatoms upon common footwear materials, a recipient surface that has historically been overlooked by studies of persistence. The effectiveness of two novel extraction techniques (jet rinsing, and heating and agitation with distilled water) was compared to the established extraction technique of hydrogen peroxide digestion, for a suite of five common footwear materials: canvas, leather, and ‘suede’ (representing upper materials), and rubber and polyurethane (representing sole materials). It was observed that the novel extraction technique of heating and agitation with distilled water did not extract fewer diatom valves, or cause increased fragmentation of valves, when compared to peroxide digestion, suggesting that the method may be viable where potentially hazardous chemical reactions may be encountered with the peroxide digestion method. Valves could be extracted from all five footwear materials after 3 min of immersion, and more valves were extracted from the rougher, woven upper materials than the smoother sole materials. Canvas yielded the most valves (a mean of 2511/cm2) and polyurethane the fewest (a mean of 15/cm2). The persistence of diatoms on the three upper materials was addressed with a preliminary pilot investigation, with ten intervals sampled between 0 and 168 h. Valves were seen to persist in detectable quantities after 168 h on all three upper materials. However, some samples produced slides with no valves, and the earliest time after which no diatom valves were found was 4 h after the transfer. Analysis of the particle size distributions over time, by image analysis, suggests that the retention of diatoms may be size-selective; after 168 h, no particles larger than 200 μm2 could be found on the samples of canvas, and > 95% of the particles on the samples of suede were less than or equal to 200 μm2. A pilot investigation into the effects of immersion interval was carried out upon samples of canvas. Greater numbers of valves were extracted from the samples with longer immersion intervals, but even after 30 s, > 500 valves could be recovered per cm2, suggesting that footwear may be sampled for diatoms even if the contact with a water body may have been brief. These findings indicate that, if the variability within and between experimental runs can be addressed, there is significant potential for diatoms to be incorporated into the trace analysis of footwear and assist forensic reconstructions

The Idea of Home in Law

The idea of ‘home’ is problematic for lawyers. Although the significance of home sometimes appears to be acknowledged in legal discourse, the proposition that home can encapsulate meanings beyond the physical stricture of the house or its capital value continues to present conceptual difficulties for lawyers. Starting from the reference to ‘respect for home’ in the European Convention on Human Rights, this article considers why courts are reluctant to give effect to any recognition of the non-financial values of home, with the result that the financial claims of secured creditors and landlords overwhelmingly prevail over the ‘home’ interests of occupiers. These issues are considered in the context of law’s preference for rationality and objectively definable, ‘provable’ interests. The article suggests, however, that the idea of home in law is not unworkable, but rather underdeveloped. A number of ad hoc examples are presented as evidence of law’s capacity to recognise ideas linked to home in order to further particular policy aims, so long as this does not run counter to the overarching goals of the system. Finally, the article evaluates avenues through which lawyers could engage productively with home theorists in other disciplines to develop a more coherent legal concept of home