Nov 16 2023
Not as Clean as You Wish: DNA Persistence and Transfer in a Laundry Scenario
Today’s blog is written by guest bloggers Margherita Andalò, Jasmine Nguyen, Brooke Sutton, Lauren Hernandez, Lev Voskoboinik, Mark Barash.
Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden. Justice Studies Department, San Jose State University, San Jose, USA. DNA and Forensic Biology Laboratory, Division of Identification and Forensic Science, Israel Police, National HQ, Jerusalem, Israel.
Touching an object can lead to biological traces deposition. Subsequently, the traces might be transferred onto another object(s) that wasn’t in direct contact with the original person (e.g. secondary transfer). This indirect transfer may involve an intermediary individual or object (e.g. tertiary transfer) and can occur under various circumstances. In legal contexts DNA evidence is highly regarded for its credibility, often serves as a crucial link between a suspect and a crime and it’s often to be perceived as “infallible”. However, the nuances of indirect DNA transfer scenarios, especially regarding how DNA is deposited, remain largely unexplored despite their significance in trials.
This study represents a part of my Master’s research project conducted under supervision of Dr. Mark Barash at San Jose State University. This experiment was planned to mimic the real-life scenarios which would assist forensic DNA experts in their operational casework. Public and private (household) washing machines were tested for DNA retention in the machine drums. Subsequently, we explored potential DNA transfer from the biological material left in a washing machine/dryer onto the next load. In the first stage the drums of public washing machines and dryers were sampled via wet and dry swabbing method. As second stage, clean UV-treated socks were washed or dried in public washing machines or dryers and sampled with an adhesive tape. The samples were then extracted using PrepFiler BTA™ kit (Thermo Fisher Scientific) and quantified using either a qPCR Investigator Quantiplex Pro kit (Qiagen) on a 7500 Real-Time Instrument or using QubitTM dsDNA HS Assay Kit. Samples quantified over a minimum threshold (>0.013 ng/ul) were amplified using a 24plex QS kit (Qiagen). The fragments were separated on a 3500xl genetic analyzer. The analysis was performed under an analytical threshold of 300 rfu.
I have conducted this project under supervision of Dr. Mark Barash at San Jose State University, Justice Studies Department. Our key collaborator was Dr. Lev Voskoboinik from the Forensic DNA Laboratory of the Israel Police. My fellow undergraduate students at San Jose State University Jasmine Nguyen, Brooke Sutton and Lauren Hernandez also helped this research, especially the wet-lab part of the project. Results were surprising to us and many of the attendees of ISHI 34 meeting who read our poster. For the first experiment of DNA retention in the machine’s drums, amplifiable DNA with a minimal concentration of 0.013 ng/ul and a maximum concentration of 2.76 ng/ul was detected in 30 out of 100 washing machines tested and 7 out of 50 dryers tested. All the amplified samples produced DNA profiles of various qualities. None of the genotyped samples showed potential presence of inhibitors based on the qPCR CT-IPC values. However, most of the samples (83.7%) showed various levels of degradation (DI > 1.5, max = 21.91). Single source profiles or simple mixtures with a major profile were obtained in five (17%) and eleven (37%) washing machine samples respectively. For the dryer samples, one (14%) yielded a single source profile and two samples (28%) yielded simple mixtures with a major donor. The rest of the samples yielded various types of mixtures with a minimum of two contributors.
The experiment on the potential transfer of biological material demonstrated that among the 60 samples collected from socks after a washing/drying cycle, 70% of samples from washing machine washed socks (6 cold and 15 hot water cycle) and 80% of samples from dryers socks produced DNA yield between 0.04 ng/ul and 0.41 ng/ul. The genotyping of the positively quantified samples is currently ongoing.
Therefore, the results were surprising, considering the very good quality of the DNA profiles. The outcome of this experiment should especially be taken into consideration in cases with DNA as the sole incriminating evidence. The potential for DNA transfer and the case context should always be considered to prevent potential misjustice.
I got interested in the forensic field since young age, perhaps a bit of CSI syndrome along with my passion for science and strong belief in justice. I always dreamed about putting my knowledge in service for law enforcement. My grandfather was also part of police forces and he raised me with a big sense of work ethic. Specifically, this project appealed me as it could be of importance within the investigative and of actual applicability in the courtroom. I wanted to carry on my first research project in forensic genetics, that’s for sure, but I wanted also to build a study potentially relevant to professionals in the field. The idea of building and researching something that could prevent wrongful convictions and could raise the awareness on the implication of DNA transfer made me eager to work on it.
This work could potentially have a wide impact on the field given that DNA evidence is currently one of the most incriminating evidences. This research emphasizes the need of considering DNA not as the sole crucial proof but as part of an holistic investigative approach. During the poster presentation I was already approached by several law enforcement workers which were “concerned” by the results of the study itself. Potential transfer scenarios are not easy to identify as the pattern of trace transfer are endless and still to be fully investigated. Consequently, this study contributes to a better comprehension of the dynamics of DNA retention and transfer within the context of activity-level propositions and their implications for the criminal justice system.
The ISHI meeting was an amazing experience for me! The next step in my professional career would be either keep contributing to forensic research with a PhD program or starting to move my first steps in the job market. Hopefully new opportunities are awaiting me in the near future. As a young graduate I am both eager and “scared” of moving alone within the field but every day that passes by I am more convinced of the career path I chose. Now I will also continue working on this research to hopefully benefit the forensic field. Hopefully seeing you in ISHI 35 next year in Texas with new discoveries!
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