In death, the putrefaction of a bone’s organic constituents leaves it bare from its surrounding tissues and periosteum. Perforating vessels also disintegrate to leave foramens open to its immediate environment. In this situation, bone is subject to a process of leaching, hydrolysis and recrystallization (Grupe & Dreses-werringloer, 1993). Generally, as it degrades, its mass decreases thus its porosity increases. However its decomposition rate is dependant on the variables of its environment thus its biological fate is as challenging in its understanding as its homeostasis.
Postmortem damage is variable thus the integrity of bone is subject to uncertainty. If the burial is shallow, a body can easily be affected by predation. The consumption of soft tissue and bone not only accelerates the rate of decomposition (Mann et al, 1990), but can also mimic spiral fractures (Ubelaker, 1997) where the bone is usually twisted apart in an effort to extract the marrow.
Time Time before intiment is crucial. For the duration a cadaver stays in an unprotected state, the more chance there is of greater exposure to the effects of temperature, which in turn affects the rate of putrefaction and bacterial and entomological action.
Action taken on a body Actions such as cremation can leave bone in a fragile state (Henderson, 1987). Warpage and fracture will most certainly occur in a high temperature environment. However, that there are morphological similarities between this and the pathological distortion of bone that could easily lead to a false conclusion. Depending on the temperature, bone also exhibits a variety of colour changes. Whilst black results from carbonisation of the bone, white represents calcination, which indicates a complete loss of the organic portion and the fusion of bone salts (Mayne Correia, 1997).
Location The final resting place of a cadaver greatly influences the rate of decomposition as more than often, this location will accommodate the body for the longest period of time before it is recovered. Differing soil types that accommodate cadavers have distinct affects on its rate of decomposition and preservation. The depth of the burial also contributes to the affect, where for example a shallow interment may be more susceptible to predation.
There are more obvious traits of predation such as the characteristic scores and furrows on bone made by the gnawing action of rats. (Patel & Path, 1994). This is not because they eat it, but rather they need to provide attrition to their continuously growing incisors (Haglund, 1997).
Temperature The effect temperature has on the rate of decay is very dependant on the depth of interment (Henderson, 1987). In the most general circumstance, the deeper the burial, the cooler it will be. This has a direct influence on the rate of chemical reaction, which generally increases two or more times with each 10�c rise in temperature (Gill-King, 1997). Freeze thawing can accelerate rates of disarticulation, susceptibility to entomological infestation and aerobic decay. This is primarily due to the mechanical disruption of the tissues caused by freezing, which weakens the skin, connective tissue and joints. It is important to consider though that this process is predominantly one of decay from the outside in (Micozzi, 1986).
Soil pH and composition pH is another influential factor in the preservation of human bone. In neutral soils of around 7pH, the integrity of the bone will be well kept. However, it the pH is lowered, dissolution of the bone’s inorganic matrix will begin (Henderson, 1987), as seen in the above. Soil porosity is also important in the state of cadaver preservation. If an interment is shallow and hastily done then the grave fill will consequently be more aerated than the surrounding matrix, thus enabling greater levels of oxidation. Soil at a depth of 2 metres is thermally stable due to its efficiency of obstructing solar radiation. At a depth of 4 metres predation is inhibited and the surrounding matrix remains cool. Thus the cadaver can remain virtually intact with minimal tissue loss for up to 1 year (Rodriguez, 1997).
The opening up of a bone’s microstructure in a soil environment can be immediately accelerated by the ingress of bacteria and saprophytic fungi through natural spaces such as vascular apertures (Child et al, 1993). This is termed as microscopic focal destruction (tunnelling) (Piepenbrink, 1986, Child, 1995, Grupe & Dreses-werringloer, 1993). Piepenbrink, (1986) considered saprophytic fungi as a primary invader of bone in order to utilise the energy content of its collagen matrix by excreting non-specific proteases in order to hydrolyse it. However, Child et al (1993) suggests that bacteria, which have the ability to release specific collagenase enzymes (such as the genera Pseudomonas (aerobic) and Aeromonas, (anaerobic)) may be the primary invaders whereby soil fungi benefit from the collagen being pre-digested.
Demineralisation of bone is also enhanced by acidic microbial metabolites (Grupe & Dreses-werringloer, 1993). Complimenting this idea, Gill-King, (1997) suggests that in normal pH soil environments, bacteria themselves reduce the pH through fermentation, which can consequently enhance the growth of fungi. Decomposition is limited however by a number of conditions. If the grave is water logged both microbial and fungal action will be inhibited (Nicholson, 1996).
A fall in temperature can slow microbial activity, whereas alkaline soils can buffer the microbial acids thus inhibiting dissolution. Competition between organisms can also occur where some microbial energy is directed in controlling other microorganisms, thus prolonging the life of the substrate (Child, 1995). One should also be aware that soil diatoms may not tolerate the acidic environment generated by this process, thus diatom passage may not occur when microbial activity is current. If the body was exhumed after a period and placed into a river however, microbially degraded bone will certainly be more open to the passive entry of diatoms.
It is conceivable that a permanent water flow through bone will remove its mineral at a constant rate. In a burial environment, the diagenetic changes in bone vary according to the soil’s water content, pH and drainage as well as precipitation rates. This in turn affects the uptake and dissolution of bone. In general circumstances, water will enter and move through bone in the same way it moves through soil due to the similarity of its porosity. Bone has a considerable affinity for uranium ions and if they encounter the dahllite ion’s surface, ion exchange will occur.
This process, which ultimately concludes in equilibration is potentially fast but is limited by the rate ground water is brought to the bone surface either by diffusion or hydraulic flow (Hedges & Millard, 1994). However, if a body were placed in a stream or river, hydraulic flow would be a constant, thus in theory the dissolution of bone, which refers to the rate at which the bone mineral dahllite disintegrates into a solution, would increase thus easing the passive entry of diatoms.