Emily C. Lennert
DNA, recovery, quantification, blood, bloodstain, fabric, washed, PCR
Salahuddin, Z.; Zahoor, M. Y.; Kalsoom, S.; Rakha, A. You can’t hide encoded evidence: DNA recovery from fabrics after washing. Australian Journal of Forensic Sciences. 2018, 50(4), 355-360.
The opinions expressed in this review are an interpretation of the research presented in the article. These opinions are those of the summation author and do not necessarily represent the position of the University of Central Florida or of the authors of the original article.
DNA is a common form of forensic evidence. DNA may be recovered from blood on fabrics; however, in some instances, criminals have attempted to wash blood from clothing. This study aimed to determine the effect of washing bloodstains from fabrics on the recovery of DNA.
Several fabrics were studied to determine the effect of washing on a variety of substrates. Fabrics included 100% cotton, 100% khaddar (natural fiber cloth), 100% polyester, 100% wool, denim, tropical (composition unspecified), 65% wool 35% rayon blend, 65% khaddar 35% linen blend, 80% denim 20% rayon blend, and 50% polyester 50% cotton blend. All fabrics were soaked and washed in water prior to sample preparation, and cut into 7.62 x 7.62 cm squares.
Two sets of experiments were prepared. In the first experiment, a sample set containing one of each fabric was hand washed with tap water for 5 minutes, and another set was washed for 10 minutes. In the second experiment, a sample set containing one of each fabric was soaked in detergent for 5 minutes, and a second set was soaked for 10 minutes, then all were hand washed with tap water. Controls were also made which were not washed by either preparation method. After the initial washing, all samples were sterilized under UV light for 20 min. Then 100 μL of human blood, obtained from a female volunteer, was deposited onto each fabric sample. Bloodstain boundaries were marked to allow for the identification of the bloodstain site after washing. The samples were allowed to dry at room temperature for 24 hours before being washed again following the same washing procedures. Fabrics were hung to dry for 24 hours after washing, then packaged in paper envelopes and stored at -20 ˚C until DNA analysis was performed.
DNA extraction from each fabric sample was performed following a Chelex 100 extraction method, previously established, with slight modifications. A detailed, step-by-step description of the extraction process is provided in the study. Following extraction, samples were quantified using a Quantifiler Human DNA Quantification Kit with amplification performed by polymerase chain reaction (PCR) using a 7500 Real-Time PCR System. 7500 System Sequence Detection Software was used to evaluate the data. Data was presented as mean DNA concentration recovered from bloodstains after washing.
Regardless of washing method or fabric type, DNA was successfully recovered from all samples. Blended fabrics showed higher DNA yields than pure fabrics, i.e. 100% cotton. Overall, wool and the wool/rayon blend produced the lowest yield of DNA recovered after washing. For unwashed, i.e. control, fabrics the highest DNA yield was reported for polyester/cotton blend at 6775 ng/250 μL, while the lowest was reported for wool/rayon blend at 0.675 ng/250 μL. Water washed fabrics showed a similar pattern across wash times, with the denim/rayon blend producing the greatest yield at both time points, 229 5ng/250 μL at 5 minutes and 2225 ng/250 μL at 10 minutes. Wool/rayon blend produced the lowest yield for water washed fabrics at both time points, 0.3 ng/250 μL at 5 minutes and 0.285 ng/250 μL at 10 minutes. Detergent washed fabrics showed slightly different trends at each time point. At 5 minutes, the denim/rayon blend produced the highest DNA yield (2675 ng/250 μL) while the lowest DNA yield came from the wool/rayon blend (0.49 ng/250 μL). However, at 10 minutes, the denim rayon blend produced the highest yield (2227.5 ng/250 μL) and the 100% wool produced the lowest yield (0.152 ng/250 μL). Lower DNA yields were reported with increased washing time. The detergent did not appear to interfere with DNA recovery.
- DNA was recovered from all fabric, regardless of washing time or method.
- The denim/rayon blend yielded the highest DNA recovery in all washing methods and times.
- Wool and the wool/rayon blend yielded the least DNA recovery in all washing times and methods.
Offenders may attempt to wash blood from clothing to destroy evidence; however, this study shows that despite washing DNA may still be recovered.
The type of fabric, time of washing, and method of washing will affect the amount of DNA recovered from a fabric.