Persistence and detection of touch DNA and blood stain DNA on pig skin exposed to water

As it is unclear if and how long DNA evidence can persist on submerged skin, we examined the potential for recovery of touch DNA and blood stain DNA from skin samples immersed in different aquatic environments and temperatures for forensic purposes in this proof-of-concept study. We used pig skin, either smeared with human blood or held firmly for 30 s by two test-persons, before immersing it in either cold, room-temperature or warm water as well as in a stream and a pond for up to seven days prior to DNA testing. The samples were then typed at 16 STR loci. Cold water samples yielded the most promising results, as shown by the recovery of the full set of 16 reproducible STR loci from the touch DNA sample of one test-person after 7 days. For blood stains, we were able to recover all 16 reproducible STRs after 2 days. Room-temperature water and warm water yielded varying results for both blood stain DNA and touch DNA. For pond and stream samples, DNA recovery was possible only within two days. While the pond and stream samples were at relatively cold temperatures, DNA recovery may have been affected by the presence of water insects and snails in the pond and mud in the stream. Our findings show the potential of using immersed samples, particularly those immersed in cold water, as we could detect a complete DNA profile from blood stains and from touch DNA after several days. Our study opens the way for future in-depth studies, examining larger datasets and a wider range of conditions.