By Steve Down

The aftermath of hurricane Katrina has reminded the world, if reminders were needed, of the fragility of human life. Within a relatively short space of time, thousands of people died in a horrific natural disaster. A far worse episode was the Asian tsunami, in which more than 180,000 people are known to have perished and 42,000 are listed as officially missing. But aside from the sad and extensive loss of life, the sheer number of dispersed bodies poses another problem.

Corpses begin to decompose almost immediately after death by spontaneous processes. Cells die and release enzymes which, along with bacteria and fungi, attack the tissue causing it to soften and liquefy. The actions of external agents, such as insects, animals, or extreme weather can accelerate decomposition. The overall result is the release of gases and liquids from the decaying body which seep into the air, soil and water. Along with bacteria and pathogens, they constitute a serious health hazard, fouling the air and threatening water supplies.

The evolving gases are believed to direct search-and-rescue dogs to bodies and a different set of evolved gases from living people guides them to trapped survivors. These gas profiles have been studied in part by Greek researchers who have characterised the gases given off by living and dead people in an effort to try and differentiate them for the purpose of developing a chemical sensor.

Agapios Agapiou and colleagues from the University of Athens have identified the volatile organic compounds (VOCs) emitted by two dead bodies found in the sea. These have been compared with the VOC profiles in the breath, blood and urine of healthy subjects and in the breath of fasting monks, used to simulate people who have been trapped without food or water. In addition, the characteristic profiles of urban air and household waste have been determined, as these create the general background.

Now, Agapiou and the team have turned their attention to the potential environmental impact of the VOCs. They acquired a body that was found near the beach in the Attica region of Southern Greece with an estimated time since death of 3 days. After one further day in a refrigerated morgue, the corpse was placed in a sealed body bag for 2 hours so that the VOCs could equilibrate, then they were measured at intervals over the next 24 hours to see how the gas profile developed over time.

A Teflon tube was inserted into the bag through which the accumulated headspace gases were pumped. The VOCs were trapped on a sorbent tube for analysis by thermal desorption GC/MS with electron ionisation. The desorbed compounds were collected in a cryotrap to maximise both the recovery and the mass spectral signals, then desorbed into the GC column with a short heating pulse. The peak areas were corrected for background levels of gases originating from the body bag and the ambient air.

The VOC profile changed with time, with some compounds not observed until the 24-hour sampling point. It is not clear whether this pattern can be extrapolated to the time of death, since the body was approximately 4 days old when sampling began, or whether collection and refrigeration affected the rate of decomposition. It would have been informative to repeat the analysis after refrigerating the body for another 24 hours to see whether the VOC profile matched that of the first tests, or continued from where it left off, but medico-legal restrictions prevented this.

A total of 30 VOCs were identified, including alkanes, alkenes, alcohols, aldehydes, ketones, simple benzene derivatives and sulphides. Of this group, 11 were present in all samples, suggesting that prevailing processes are occurring during decomposition over the whole period.

The most abundant compound emitted after 24 hours was dimethyl disulphide, with significant concentrations of dimethyl sulphide, dimethyl trisulphide and methyl ethyl disulphide also found. Sulphides have been observed in other studies of human decomposition.

The researchers were surprised at the lack of nitrogen-containing compounds among the VOCs. Volatile amines are produced by the breakdown of proteins and amino acids and are usually associated with human decay. The team suggested that their low volatility or rapid metabolism by bacteria might be responsible for their absence.

The environmental impact of these evolving compounds could be estimated by examining their physicochemical properties. In preliminary work, Agapiou and his colleagues noted that the median molecular mass of the compounds was 108 but the molecular mass range increased with time. Similarly, the vapour pressure range of the evolved VOCs broadened over time from 6.4-232 to 0.048-502 mm Hg, as did the Henry's law constants. The octanol-water partition coefficients indicated that more polar and intermediate polar compounds were produced over time.

Taken together, data of this type will be useful for determining the extent by which the emitted VOCs are taken up in air, water or soil, leading to a more detailed assessment of their toxicological impact. In the meantime, the team recognise that longer testing periods of up to several weeks are required for a better understanding of the chemistry of death.

http://www.spectroscopynow.com/coi/cda/detail.cda?id=17008&type=Feature&chId=4&page=1