Degradation of Forensically Important Biological Fluids: A Comparative Study on Different Surfaces, Temperatures, and Time Intervals
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Abstract
Biological fluids recovered from crime scenes are vulnerable to environmental and microbial degradation, which can reduce their forensic value before laboratory examination. Although previous studies have examined individual factors affecting biological evidence, limited experimental research has systematically investigated the combined influence of temperature, exposure duration, substrate characteristics, and microbial activity on the degradation of blood and saliva. This study addresses this gap by examining the microbial degradation of blood and saliva deposited on five commonly encountered substrates: soil, glass, wall, floor, and ceramic tile, under three temperature conditions (4–9°C, 20–25°C, and 40–45°C). Samples obtained from five healthy volunteers were examined at 6, 12, 18, 24, and 48 hours. Microbial growth and degradation were evaluated using conventional culture methods, staining techniques, selective media, and standard biochemical tests.
The findings indicated that temperature, exposure duration, and substrate characteristics substantially influenced microbial growth and biological-fluid degradation. Soil exhibited the greatest microbial diversity and degradation, whereas non-porous surfaces generally demonstrated comparatively limited microbial growth. Moderate temperature conditions (20–25°C) produced pronounced degradation, particularly between 12 and 24 hours. Reduced detectable amylase activity was associated with saliva degradation, while folate-dependent haemolytic Streptococcus species were identified among the major contributors to blood degradation. The study demonstrates that biological-fluid persistence is governed by the interaction of environmental and substrate-related factors. The findings address an important research gap and provide practical implications for the timely recovery, packaging, preservation, and forensic interpretation of biological evidence..
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