The effect of bleaching agents on the DNA analysis of bloodstains on different floor coverings

Blood at crime scenes is one of the most significant traces of evidence in investigation proceedings. Cleaning up these traces with household cleaning products, often containing bleaching agents, inhibits or complicates the detection of DNA. In this study, human blood was applied onto different floor coverings (carpet, laminate, parquet, PVC, tile) and subsequently cleaned with water and bleaching agents (hydrogen peroxide, sodium hypochlorite, DanKlorix®, Vanish Oxi Action®) at different times. Samples have been collected afterwards from the floors. The samples underwent a quantitative and qualitative DNA analysis. Cleaning smooth surfaces with water is usually sufficed to prohibit retrieving a DNA profile in most of the cases. Cleaning carpets was more difficult due to their absorbent surface whereas the use of bleaching agents caused an additional reduction of verifiable DNA concentrations. Retrieving partial or complete profiles after the use of bleaching agents was only possible when cleaning with low concentrations of 3% hydrogen peroxide.