Human cadaver decomposition islands (CDIs) and forensic taphonomy: gravesoil δ 13C and δ 15N enrichment patterns in short (30 d) and extended (900 d) postmortem intervals

Soil forensics examines edaphic properties of evidentiary value in the immediate vicinity of human remains in a region called the cadaver decomposition island (CDI). As a body decomposes, soil in the CDI is permeated with liquified human nutrients and becomes gravesoil. This study is the first to specifically investigate how stable isotopes of carbon (δ13C) and nitrogen (δ15N) change in human gravesoils during decomposition over the postmortem interval (PMI). Gravesoil samples were analysed for %C, δ13C, %N, and δ15N in CDIs over the initial 30-d PMI (PMI30) and over longer PMIs up to 900 d (PMI900). Gravesoil %C and δ13C did not show any significant changes with decomposition progression in the PMI30 study. By days 10–15, gravesoil mean %N more than doubled from 0.4% to 1.05%, while mean gravesoil δ15N increased from 3.3‰ to 8.2‰ by day 10, up to a high mean of 9.9‰ on day 20. Both %N and δ15N remained significantly elevated for the entire PMI30 period. In the PMI900 study, gravesoils increased from 0.2%–0.8% N to a high of 1.9% N after 2–3 months, then decreased to 0.5%–0.6% in the 600–900 d time frame. Gravesoil δ15N originating at 2‰–4‰ was enriched by 15‰–20‰ after the first month, eventually declining to 9‰–11‰ after 600–900 d. We conclude that δ15N in human gravesoils has promise as a forensic tool to detect a CDI and correlate it with decomposition stage that adds to existing methods in estimating PMI, even if the body is absent.