The Search for a Volatile Human Specific Marker in the Decomposition Process

Abstract

In this study, a validated method using a thermal desorber combined with a gas chromatograph coupled to mass spectrometry was used to identify the volatile organic compounds released during decomposition of 6 human and 26 animal remains in a laboratory environment during a period of 6 months. 452 compounds were identified. Among them a human specific marker was sought using principle component analysis. We found a combination of 8 compounds (ethyl propionate, propyl propionate, propyl butyrate, ethyl pentanoate, pyridine, diethyl disulfide, methyl(methylthio)ethyl disulfide and 3-methylthio-1-propanol) that led to the distinction of human and pig remains from other animal remains. Furthermore, it was possible to separate the pig remains from human remains based on 5 esters (3-methylbutyl pentanoate, 3-methylbutyl 3-methylbutyrate, 3-methylbutyl 2-methylbutyrate, butyl pentanoate and propyl hexanoate). Further research in the field with full bodies has to corroborate these results and search for one or more human specific markers. These markers would allow a more efficiently training of cadaver dogs or portable detection devices could be developed.

Fig 1. Sample overview.

Number of decomposition days (a) and of samples taken (b) of every species after one (blue), three (red) and six months (green) with minimum, maximum and mean of respectively decomposition days (a) and samples taken (b).

Fig 2. PCA plots of compounds per chemical class.

Score- and loadingplots of relative number of compounds in chemical classes after one (a), three (b) and six (c) months.

Fig 3. PCA plots of observations per chemical class.

Score- and loadingplots of relative number of observations of compounds in chemical classes after one (a), three (b) and six (c) months.

Fig 4. Nitrogen-containing compounds over time.

Percentage of nitrogen-containing compounds identified over a time of six months for human remains a (a) and mouse b (b).

Fig 5. PCA plots of sulphur-containing compounds.

Score- and loadingplot of sulphur-containing compounds after six months of decomposition.

Fig 6. PCA plots of nitrogen-containing compounds.

Score- and loadingplot of nitrogen-containing compounds after six months of decomposition.

Fig 7. PCA plots of esters.

Score- and loadingplots of esters after one (a), three (b) and six (c) months of decomposition.

Fig 8. PCA plots of specific markers.

Score- and loadingplots of possible human and pig specific markers after six months of decomposition (a) and without frozen remains and with extra samples after one month (b).

Fig 9. PCA plots of specific markers.

Score- and loadingplots of possible omnivore specific compounds after six months (a) and pig specific compounds after one month (b).