Poster - #VH-86017 - Keywords: forensic DNA, DNA transfer, activity level, STRs, criminal justice

Not as clean as you think: DNA persistence and transfer in a laundry scenario.

Margherita Andalo, 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.

ABSTRACT:
Biological traces left on objects through handling can undergo a series of transfers, where they move from one object to another, often involving intermediary individuals or objects. Despite the critical role of understanding how DNA is deposited on objects or persons in legal trials, the complex landscape of indirect DNA transfer scenarios remains largely elusive. In line with the importance of better understanding the dynamics of DNA transfer, this study explored the possibility of DNA retention in the machine and dryer drums and subsequent transfer onto the next load. The study involved swabbing the drums of 100 public washing machines and 50 dryers. Additionally, 60 samples were collected from 20 new unworn socks individually washed in 20 public washing machines, and from 10 socks dried in 10 public dryers. The samples collected in both experiments were extracted, quantified, and genotyped for a standard set of STR markers. Results revealed amplifiable DNA in 30% of washing machine drums and 14% of dryer drums, with a concentration ranging between 0.013ng/ul and 2.76 ng/ul. Surprisingly, over half of the genotyped samples resulted in a single source profile or simple mixtures with a major profile, suitable for statistical interpretation and inclusion in a DNA database. In the DNA transfer experiment, 21 samples from washing cycles and 8 samples from drying cycles yielded DNA between 0.04 ng/ul and 0.41 ng/ul, currently awaiting genotyping. This study confirms DNA can persist in washing machines and dryers, potentially transferring to subsequent loads, highlighting the risk of detecting unrelated and misleading traces. Therefore, caution is essential when assessing DNA profiles from garments.