Microbial neoformation of volatiles: implications for the estimation of post-mortem interval in decomposed human remains in an indoor setting

Abstract

The objective of this study was to determine if a relationship between microbial neoformation of volatiles and the post-mortem interval (PMI) exists, and if the volatiles could be used as a tool to improve the precision of PMI estimation in decomposed human remains found in an indoor setting. Chromatograms from alcohol analysis (femoral vein blood) of 412 cases were retrospectively assessed for the presence of ethanol, N-propanol, 1-butanol, and acetaldehyde. The most common finding was acetaldehyde (83% of the cases), followed by ethanol (37%), N-propanol (21%), and 1-butanol (4%). A direct link between the volatiles and the PMI or the degree of decomposition was not observed. However, the decomposition had progressed faster in cases with microbial neoformation than in cases without signs of neoformation. Microbial neoformation may therefore act as an indicator of the decomposition rate within the early decomposition to bloating stages. This may be used in PMI estimation based on the total body score (TBS) and accumulated degree days (ADD) model, to potentially improve the model's precision.

Keywords: 1-Butanol; Acetaldehyde; N-Propanol; Neoformation of ethanol; Post-mortem interval; Total body score.

Fig. 1

a The distribution of total body score (TBS) among cases without neoformation of volatiles (n = 321, non-neo) and cases with neoformation (n = 91, neo) based on detected N-propanol and/or 1-butanol in femoral vein blood. b The distribution of the relative amount of acetaldehyde in femoral vein blood among cases without external decomposition (n = 209, non-decomp) and cases with external decomposition (n = 203, decomp). c The distributions of the relative amount of acetaldehyde among cases with neoformation (n = 91) divided into non-decomposition cases (n = 6) and decomposition cases (n = 85). The horizontal lines represent medians. The crosses represent means. The top and bottom box lines show the first and third quartiles. The whiskers show the maximum and minimum values, with the exception of outliers (circles)

Fig. 2

Scatter plots illustrating the correlation and linear regression in the neoformation group adjusted for ante-mortem intake (n = 56). A total of 52 cases were positive for N-propanol (a, b), 38 cases were positive for ethanol (c, d), and 56 cases were positive for acetaldehyde (e, f). Solid lines represent linear regression and dashed lines represent the 95% confidence interval

Fig. 3

The rate of decomposition (calculated as TBS/log₁₀ADD) illustrated for the four volatiles: 1-butanol (log₁₀butanol), neoformated ethanol (log₁₀etOH), N-propanol (log₁₀propanol), and acetaldehyde (log₁₀acetaldehyd). Solid black circles indicate cases with detected volatiles. Below the dashed lines, the open circles indicate cases without detected volatiles

Fig. 4

Comparison between the two regression models. a The original model: TBS~log₁₀ADD, comprising the actual log₁₀ADD values of each case. b The rate-modified model: TBS~rate-modified log₁₀ADD model