THE GREENHOUSE EFFECT: DECOMPOSITION RATES IN HUMAN REMAINS WRAPPED IN PLASTIC

Determining an accurate estimation of the postmortem interval (PMI) of human remains is important for several reasons. First, it is used to determine whether the individual is recently deceased, and therefore of medicolegal concern. If so, the estimated PMI is used in narrowing the possible identities of the deceased. PMI can also be used in excluding, or convicting, a murder suspect.

Though deviations may occur, it has been found that PMI can be calculated from the decomposition stages with reasonable accuracy (Galloway 1989, Megyesi 2001, Megyesi et al. 2005, Schiel 2008, Simmons et al. 2010). Some factors, such as low temperatures, desiccation, or delay of insect access have been shown to produce a ‘minimum’ estimated PMI much shorter than the actual PMI, and this must be considered when estimating PMI.

This experiment explores whether conditions exist that might cause an estimated PMI to significantly over-estimate the true time-since-death. The study addresses variables involved in decomposition of a body wrapped in plastic in early spring. It investigates the differences in estimated and actual PMI between six subjects, in two sets of three treatments: black plastic, translucent plastic, or no plastic. PMI was calculated from Accumulated Degree Days (ADD) from temperatures measured both internally and next to the body at 30 days. These are compared with PMI calculated from Total Body Scores (TBS) assessed visually using Megyesi’s methodology (Megyesi 2001, Megyesi et al. 2005). PMI calculated from weather station data are compared with PMI from TBS after visual assessment of the subjects at two months.

The study finds that spring weather can produce a significant ‘greenhouse effect’ for remains wrapped in plastic. Results suggest Megyesi’s TBS method may be contra-indicated in cases of extensive mummification, or when covering or enclosure may have accelerated the decomposition process by elevating temperatures or slowed it by excluding insects.

In conclusion, decomposition rates are affected by variables other than time and recorded ambient temperature, leaving significant potential for error. Megyesi’s Total Body Score (TBS) method does have utility in estimating a possible postmortem interval, but such estimates should not be used for exclusionary purposes or alibis.