Environmental and Tissue-Specific Determinants of DNA Degradation in Forensic Evidence: A Systematic Literature Review of Temperature, Moisture, and pH Effects

Abstract

DNA evidence remains one of the most powerful tools in forensic science; however, its evidential value is highly dependent on the preservation of genetic material following deposition or death. DNA degradation is a complex process influenced by both environmental conditions and the intrinsic biological characteristics of the tissue from which DNA is recovered. This systematic review examines the combined effects of temperature, moisture, and pH on DNA degradation and understands how preservation patterns differ among major forensic tissue types, including blood, saliva, soft tissues, bone, teeth, hair, and nails. DNA degradation occurs through multiple molecular pathways, including hydrolytic cleavage, depurination, oxidative damage, nuclease activity, microbial decomposition, and ultraviolet radiation-induced strand breakage. ¹˒²

 Available evidence demonstrates that elevated temperatures significantly accelerate the DNA degradation by increasing rates of depurination, strand fragmentation, and oxidative damage, particularly under prolonged exposure conditions.³˒⁴ Likewise, extreme acidic or alkaline environments destabilise the DNA molecule and contribute to the breakdown of phosphodiester bonds and nucleobases.⁵ Moisture further increases degradation by promoting hydrolysis and facilitating microbial proliferation, leading to increased nuclease-mediated DNA destruction.⁶˒⁷ In contrast, cool, dry, and near-neutral pH environments consistently provide the most favourable conditions for long-term DNA preservation.³˒⁶ Marked differences in DNA preservation are observed     among biological tissues. Soft tissues such as liver, spleen, and brain generally undergo rapid post-mortem degradation due to autolysis, high enzymatic activity, and microbial invasion.⁸ On the other hand, mineralised tissues such as bone and teeth provide physical protection against environmental insults and often retain recoverable DNA for extended periods, making them valuable sources in highly decomposed or skeletal remains.⁹˒¹⁰ Hair roots may yield substantial quantities of nuclear DNA when present, whereas hair shafts and keratinised tissues frequently contain limited and degraded genetic material.¹¹˒¹²

The reviewed literature further indicates that progressive DNA degradation adversely affects forensic DNA profiling by reducing template quantity, increasing fragmentation, and increasing the risk of allelic dropout, particularly for larger short tandem repeat (STR) loci. ³˒¹³  These effects may compromise individual identification and influence interpretations relating to post-mortem interval estimation and evidential reliability. Although substantial evidence exists regarding individual environmental factors, comparatively few studies have investigated their combined or synergistic effects under realistic forensic conditions. Methodological heterogeneity, variation in tissue types, and limited long-term experimental studies remain significant challenges within the field.

Understanding the interactions between environmental stressors and tissue-specific preservation characteristics is essential for optimising evidence collection, storage, laboratory processing, and interpretation of forensic DNA profiles. Future research should focus on integrated degradation models, standardised experimental designs, and the development of improved analytical approaches for highly degraded biological evidence.