Forensic taphonomy and stable isotopes: An examination of δ13C and δ15N in decomposing skin, muscle, and grave soil as an indicator of post mortem interval.

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University of New Brunswick


Forensic taphonomy studies the circumstances surrounding death and subsequent processes of decomposition. In medicolegal death investigations, two pieces of information are essential- the identity of the deceased and the post-mortem interval (PMI). Current methodology uses stable isotopes in hard, decomposition-resistant tissues to provenance the remains for identification. Stable isotopes have not yet, however, been examined as a forensic tool for estimating PMI in soft tissues from recovered remains. This dissertation reports unique data on stable isotope ratios of δ13C and δ15N in three studies. The first study examined human skin and muscle stable isotope ratios from nine human donor bodies over the first 20 days of outdoor decomposition in Texas. I found δ15Nmuscle, with mean starting values of 9.5‰, increased by 2.5‰ by day 10 and plateaued beyond the 20-day study. Second, I measured δ13C and δ15N in two studies using underlying grave soils in an area known as the cadaver decomposition island (CDI) in the first 30 days of decomposition (PMI30) and over longer periods up to 900 days PMI (PMI900). In the PMI30 study, surface gravesoil δ15N increased from a mean value of 3.3‰ to 8.2 ‰ by days 10-15, peaking at 9.9‰ at day 20, and remained elevated beyond 30 days. In the PMI900 study, gravesoils starting with 2-4‰ δ15N increased by 15-20‰ after the first month, eventually declining to 9-11‰ by 600-900 days. The third study in New Brunswick, Canada generated preliminary regionally specific data for porcine analogues. As with the first Texas human decomposition study, the porcine analogue tissues confirmed δ15Nmuscle showed the greatest promise as a forensic tool with mean starting values of 4.1‰ increasing by 0.5‰ by day-6 and remained elevated beyond the end of the 18-day experiment. My novel work provides baseline data confirming the potential of using stable isotopes in soft tissues, specifically δ15Nmuscle, to provide quantifiable information applicable to medicolegal death investigations. Future research can use my data as a proof-of-concept framework to refine methodologies that provide more accurate PMI estimates that are a key piece on real-world forensic casework.