ACTUALISTIC TESTING OF THE INFLUENCE OF GROUNDWATER CHEMISTRY ON DEGRADATION OF COLLAGEN I IN BONE

Though recent reports have heightened our understanding of biomolecular stabilization reactions in early diagenesis, little is known about how groundwater chemistry can aid or hinder preservation of bone biomolecules through geologic time. To examine this topic, we conducted actualistic experiments employing varied fluid compositions simulating a suite of groundwater conditions. Chicken (Gallus gallus) femora were placed in a matrix of unsterilized natural river sand. To simulate groundwater flow, fluid solutions were percolated through separate trials for a period of three months. Four trials were conducted: 1) deionized water, as the control; 2) water supersaturated with calcium carbonate; 3) water enriched in phosphate; and, 4) water enriched in iron. After three months, degradation of each bone was examined via thin sectioning and histologic study, as well as immunofluorescence and enzyme-linked immunosorbant assays against collagen I, the primary structural protein of bone. We found that in higher pH trials overall bone degradation accelerated, with the rate of degradation for soft tissue components increasing the most. The iron trial found cementation of sediment over bone surfaces preferentially occurring over more porous regions of bone tissue, perhaps due to interaction with decay products from such regions. Though collagen I was still present and recognizable in all four trials after three months, collagen concentrations remained higher in bones that experienced early diagenetic permineralization. Thus, our results demonstrate that early diagenetic permineralization may hinder long-term microbial attack, and hence increase the potential for a bone to retain endogenous biomolecules through late diagenesis. Future variations of this actualistic taphonomy experiment employing varying solution metal concentrations, bacterial floras, pH values, host sediments, and types of bone tissue are needed to reveal how early diagenetic environments control the initial decay of bone biomolecules.