A comparison of packaging materials for wet biological evidence
Lake, Anneliese Elizabeth
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When considering what packaging material is optimal for a piece of biological evidence there are two vital things to consider: degradation and contamination (1). Biological evidence collected from a crime scene is brought to the laboratory, however, immediate testing upon arrival is highly unlikely (2). Therefore, the packaging must be suitable for transportation as well as storage. During the storage phase, if improper packaging is utilized, degradation and/or contamination could occur. General forensic practice is to dry biological samples before packaging, then package the evidence in a paper (breathable) container. This study investigated the use of kraft stock envelopes, plastic bags, glassine envelopes, Tyvek envelopes, evidence/syringe tubes, knife pouches, and Cap-Shure® plastic swab caps to package wet blood and semen samples. The packaging materials were evaluated in a humidity study, degradation study, and transfer study to determine if the biological specimen would remain intact and contained within the packaging. In the humidity study, it was determined that the kraft paper, glassine paper, and Tyvek® allowed for the passage of moisture, enabling the enclosed sample to readily dry. The plastic bag, evidence tube, and knife pouch created a difference in relative humidity above 20%, thus increasing the ambient moisture concentration the samples were exposed to. In the degradation study, all samples were positive for their respective biological substance when tested with screening, presumptive, and confirmatory methods, however, bacteria were observed on samples that were packaged in plastic bags evidence tubes, and plastic caps. Additionally, only one sample, packaged in an evidence tube, yielded a DNA degradation index that implied degradation had occurred. The packaging materials were also tested to determine if the biological fluid would transfer through them, permitting cross-contamination. The kraft paper and one glassine paper did not provide a true barrier, as blood transferred through the envelopes onto a surrounding surface. The Tyvek®, knife pouch, and plastic bag all kept the wet blood contained within the package and no transfer to the surrounding surfaces occurred, although bloodstains on the interior of the Tyvek® and knife pouch could be visualized from the exterior. Overall, Tyvek® envelopes were determined to be an optimal packaging material for wet biological samples when compared to the other packaging materials used in this limited study due to their relative strength, ability to allow fluids to air dry and the lack of penetration of wet blood to the exterior surface.