The effects of various household cleaning methods on DNA persistence on mugs and knives

With the prevalence of forensic science in popular media, offenders are becoming more forensically aware and can employ precautionary methods, such as cleaning used items or rubbing away fingermarks, to reduce their traces left at a crime scene. This study examined the effects of various cleaning methods on DNA persistence on commonly encountered casework exhibits, specifically knives and mugs. Aliquots of acellular DNA were added to the knife handles or mug rims, allowed to dry, and then the substrates were either sampled directly or were cleaned and then sampled. The plastic- and wood-handled knives were cleaned with a cloth in a sink of water, diluted dish washing liquid or diluted household bleach, whereas the ceramic, glass and steel mugs were cleaned with a dry or wet cloth, or by wiping with a cloth after applying a cleaning product (dish washing liquid or household bleach spray) directly into the mug and then rinsing it with water. DNA samples were collected with wet and dry swabs, in triplicate, and extracted and quantified. In both experiments, DNA was not detected on items after cleaning with dish washing liquid or household bleach, irrespective of the differences in amounts of DNA initially deposited, substrates, and cleaning methods. Even without a cleaning product, rubbing with a dry cloth decreased DNA recovery from the mugs, regardless of the mug substrate. These results contribute to our understanding of the impact of various cleaning methods on DNA recovery at the crime scene and will help inform DNA recovery strategies.