Assessment of DNA transfer and degradation in washing machines: forensic implications

DNA transfer caused by the use of a washing machine is a topic of great importance in the forensic field, as it can have significant implications in collecting genetic evidence at crime scenes. Understanding DNA transfer during the washing process is important since this process can affect the accuracy and reliability of the recovered DNA samples. In this study, two experiments were carried out on 53 volunteers, one studied the transfer of touch DNA and the other studied the transfer of blood DNA. Fabrics were washed with clean acceptor fabric in a washing machine. Mixtures of alleles were obtained, especially in acceptor fabrics, partially matching with the profile of the corresponding volunteer. Complete profiles were not recovered in any case. The age of the volunteers, the type of sample, the small volume of blood, or the short contact with the piece of cloth seem to be factors to consider regarding the low recovery rate of the POI (person of interest) alleles. The presence of extra alleles and the low rate of recovered POI alleles, require the criteria for the interpretation of these profiles to be more restrictive. So, the profiles derived from clothes that have been washed in a washing machine in their interpretation should be considered as LTDNA (Low Template DNA) with the criteria used in the interpretation of mixtures.