Environmental DNA monitoring: beware of the transition to more sensitive typing methodologies

Abstract

Background DNA on surfaces and equipment utilised during forensic examination of exhibits poses a contamination risk. Many laboratories have established environmental DNA monitoring (EDM) programmes to generate awareness of locations, levels and origins of background DNA to identify contamination risk reduction opportunities. To evaluate the impact on contamination risk of introducing new DNA profiling systems we have analysed 134 EDM samples from surfaces within our forensic biology laboratory. The samples were profiled for our current system (Profiler Plus) and the new systems PowerPlex 21 and Yfiler. Many samples deemed clean using Profiler Plus yielded alleles using PowerPlex 21 and those with few alleles using Profiler Plus yielded many with PowerPlex 21. The detectability of alleles in multiple samples with negative quantification results using Quantifiler suggests that items able to be deemed free of detectable DNA by the newly introduced standard, AS 5483-2012, are not so when utilising DNA typing systems as sensitive as PowerPlex 21. Current cleaning procedures are shown to be less adequate when operating with PowerPlex 21. This study highlights the need for a range of issues pertaining to contamination risk to be addressed prior to the introduction of more sensitive profiling systems such as PowerPlex 21 into casework.