Investigation of DNA transfer onto clothing during regular daily activities

Abstract

Low levels of DNA from an unidentified human source, often referred to as trace DNA, are ubiquitous, can be transferred onto objects by either direct or indirect methods and have an unknown longevity in situ. Clothing items from crime scenes are often submitted for trace DNA analysis, usually in attempt to identify a person of interest. This study examined the transfer of DNA onto three 10 × 10 cm areas located on the front, back and shoulder of an individual's external clothing (n = 300) during a regular day's activity. After wearing for a day, the DNA quantity on all three areas increased approximately 8-fold, which usually corresponded with an increase in the endogenous DNA from the wearer on the front area of the shirt. However, the back area of the shirt was more likely to demonstrate mixtures of endogenous and extraneous DNA. An additional study was also carried out to examine whether domestic laundering is a possible mechanism for the transfer of foreign DNA onto freshly laundered items and revealed that 74% of UV-treated cotton swatch samples produced DNA profiles after laundry with household garments. In summary, this study highlights the ease of DNA transfer onto an individual's external clothing during a regular day, and that extraneous DNA may be already on the clothing item prior to it being worn. The study provides empirical data to assist in the interpretation of trace DNA profiles and support a Bayesian approach to estimate statistical likelihoods for the transfer of foreign DNA. Graphical abstract ᅟ.

DNA transfer in forensic science: A review

“…Personal items and clothing are often collected as evidentiary or reference material. It is usually assumed that these will provide the profile of the regular user/wearer, which they usually do; however, they often also contain DNA from other sources [64,82,104,123,137,[160][161][162][163][164]. For example:…”

“…Although both van den Berge [104] and Kamphausen et al [192] concluded that DNA persistence and transfer in a washing machine is very unlikely, further studies have found different results. Of unworn items washed in household washing machines with normal loads of dirty laundry, Voskoboinik et al [194] found that 19% gave single-source or major DNA profiles matching that of a member of the household and Ruan et al [160] found 76% gave single-source or mixed DNA profiles. As suggested by Ruan et al [160], this increase in detection of DNA transfer could be due to the use of a profiling kit with increased sensitivity (PowerPlex21® as opposed to SGM Plus™).…”

“…Of unworn items washed in household washing machines with normal loads of dirty laundry, Voskoboinik et al [194] found that 19% gave single-source or major DNA profiles matching that of a member of the household and Ruan et al [160] found 76% gave single-source or mixed DNA profiles. As suggested by Ruan et al [160], this increase in detection of DNA transfer could be due to the use of a profiling kit with increased sensitivity (PowerPlex21® as opposed to SGM Plus™). Voskoboinik et al [194] also found that no detectable DNA was recovered from unworn socks washed alone or from swabs taken directly from the interiors of several washing/drying machines, suggesting that DNA transfer occurs via the dirty clothes within a washing machine rather than via the machine itself.…”

“…These studies demonstrate that background DNA can be acquired on clothing via various means, including washing. Ruan et al [160] raise the valuable point that whilst we assume that the observed DNA transfer occurs within the washing machine itself, there are other opportunities for DNA transfer during the whole process of washing and drying clothes, such as via the mixing of clothing in a laundry basket prior or after washing and the varied modes of drying clothes. A wide range of possibilities may therefore need to be considered during the DNA evaluation process, depending on the scenarios under consideration.…”

A review of trace “Touch DNA” deposits: Variability factors and an exploration of cellular composition

“…Despite earlier doubt about the impact of secondary transfer [32], this occurrence has been repeatedly demonstrated and is now widely accepted [48,50,93]. Particularly as testing sensitivity grows, secondary, tertiary and subsequent transfer events produce detectable DNA profiles on items never handled by the DNA contributor; this detection can follow innocuous interaction such as handshakes [94] or co-laundering of clothing [65,95], or even routine movement of people and equipment around a forensic DNA laboratory and office [71].…”