Evaluating the efficiency of laundry sanitizers on the removal and transfer of DNA in a washing machine

Abstract

DNA persistence and transfer has been a topic of much research and study over the last several years in the forensic science field. One interesting subfield that has been investigated is the field of laundered fabrics. It has been discovered that DNA is recoverable from laundered fabrics. The sources include not only biological stains but also transfer during wear. Remarkably, DNA is able to persist through the washing process, while also capable of transferring onto other pieces of fabric during the washing process. This means a piece of evidence with one person’s DNA could transfer DNA onto a piece of fabric that was initially free of DNA. Many variables affect the persistence and transfer of DNA during the washing process including the temperature of the water, hand-washing versus machine-washing, and the cleaning products used in the washing process. One laundry product that has increased use in the last several years is the laundry sanitizer, which aims to eliminate bacteria and viruses from clothing rather than dirt. The laundry sanitizer is rarely mentioned in the literature and requires more research. This thesis project focuses on two main specific aims. Specific Aim 1 is focused on the persistence of DNA from wear during the washing process. Six different laundry products were tested, along with two separate collection methods of the wet vacuum, also known as the M-Vac™, and conventional swabbing. Lastly, the set of directions used for the laundry sanitizer was also evaluated. Laundry sanitizers often have two sets of directions: one utilizing a pre-soak option and the other utilizing the sanitizer as part of the rinse cycle. Specific Aim 2 is focused on the transfer of DNA from a washcloth spotted with blood to another pristine washcloth. The same products, except for the dry-cleaning products, were tested with the same two collection methods. The last variable tested was the blood input. Half of the washcloths were spotted with three drops of blood, and the other half were spotted with one drop of blood. To account for the high frequency of zero values, a two-part hurdle model was employed. This approach utilized a logistic regression to model the probability of occurrence and a linear regression on log-transformed data to analyze the remaining non-zero concentrations. It was seen that laundry detergent tended to have a statistically significant result on DNA concentrations. The laundry products were sometimes found to have significantly higher DNA concentrations than the low control of bleach. The collection method had some contradictory findings. In Specific Aim 1, it was seen that the M-Vac™ was associated with lower DNA concentrations than the bleach control, while in Specific Aim 2 it was seen that the M-Vac™ was associated with higher concentrations than the bleach control. Neither the blood input nor the set of directions used was ever found to be statistically significant. Bacterial colonies were also assessed in Specific Aim 1 with the shirts, and it was found that only some products (OxiClean™, Silver Satin 2+, and Lysol™) never had any colonies grow. A lack of colony growth was also associated with the rinse cycle set of directions. DNA profiles of select samples were assessed to see the quality and quantity of information that could be obtained from these samples. In terms of quality, the electropherograms were for the most part clear single source profiles with few artifacts present. There was one profile that was a partial profile with significant allelic dropout. When the electropherograms were compared with the known profiles of the participants, it was found that both the participants were able to be excluded from the sample DNA profiles. It was found that a member of the household where the washing machine was located could not be excluded from the sample DNA profiles. This was despite extensive cleaning protocols before the project began and between each sample to avoid such occurrences. Altogether, there were several interesting findings from this study in terms of the importance of laundry sanitizers on the persistence and transfer of DNA in a washing machine. It also revealed some intriguing trends about the usage of the M-Vac™ on porous fabrics. However, this study would benefit from an increased number of replicates to confirm the trends identified and perhaps parse out other trends not identified in this study. Furthermore, more troubleshooting with the cleaning protocol should be conducted or perhaps other locations for washing machines explored.