The Distribution of Mercury and Other Trace Elements in the Bones of Two Human Individuals from Medieval Denmark - the Chemical Life History Hypothesis

Article excerpt

Authors: Kaare Lund Rasmussen (corresponding author) [1]; Lilian Skytte [1]; Christian Pilekaer [1]; Anne Lauritsen [1]; Jesper Lier Boldsen [2]; Peter Mygind Leth [2]; Per Orla Thomsen [3]

Introduction

Indicators of diet, provenance, occupation and medical treatment of medieval humans are increasingly being investigated by trace element analyses in the skeletal remains procured from archaeological excavations. These analyses are normally performed on a single sample from the skeleton of an individual, often a tooth or the compact part of the largest bone in the human body - the femur. However, little attention has been given to the distribution of the trace elements between different bone elements in the same skeleton. Grupe [1] discriminated between compact and trabecular bone tissues and reported average trace element concentrations of Mg, P, Ca, Zn, Sr and Ba in the two types of tissue. Concentrations in different tissue types in modern man were reported in the comprehensive report Reference Man [2]. In this work we present trace element analyses of 36 different parts of the skeletons of two medieval human individuals excavated in Denmark. The two individuals were selected based on a larger survey by Rasmussen et al.[3] reporting the Hg concentrations in single samples of compact bone tissue in each individual, mostly from the femur, and including more than hundred individuals. The first individual selected for this study exhibited an elevated Hg concentration in the analysis of a single sample from the femur, indicating that this individual had been exposed to Hg, probably through medical treatment with Hg. The other individual was selected because the single femoral sample featured an Hg concentration at the background level, which indicated that the individual was not exposed to Hg above the environmental background level.

The samples were subjected to two analytical methods: CV-AAS for Hg and ICP-MS for Mg, Al, Ca, Mn, Fe, Zn, As, Sr, Ba and Pb. Our results show significant differences between the trace element concentrations in the various bone tissues, most notably between compact and trabecular tissue. It is the first time that a study of the bone trace element chemistry has been conducted to this level of detail on Danish medieval skeletons.

Excavation site and bone material

The Franciscan Friary in Svendborg was founded in 1236 (Figure 1). Svendborg is situated on the south coast of the island of Fyn in Denmark (Additional file 1). The buildings of the friary were modified and enlarged over the centuries and in 1361 a new gothic church was consecrated by Bishop Niels Jonsen from Odense. A layman cemetery was situated to the south of the friary?s church [4]. To the east, the premises of the friary were bordered by the coastline. To the west was an elevated ground where the medieval city was situated. Excavations in 1975-1977 and again in 2007 revealed extremely well preserved burials in the laymen cemetery; in some individuals even brain tissue was preserved. The reason for the fine state of preservation was undoubtedly the highly anoxic and groundwater saturated low-porosity clay-rich soil.

Figure 1: The archaeological site, the Franciscan Friary in Svendborg, Demark. a: The Franciscan Friary in Svendborg just prior to demolition in 1828. Watercolour by C.F. Thorin 1828 now at the National Museum of Denmark; b: The excavation plan of the lay cemetery at Svendborg Franciscan Friary (field A) showing the excavation level 3 and the position of AG93 at depth 6.11 m (violet rectangle); c: Same field, excavation level 4, the position of AG104 at depth 5.94 m is indicated by a violet rectangle; from Svendborg County Museum 1977. [see PDF for image]

Additional file 1: Franciscan Friary Svendborg Denmark.

A series of individuals excavated from the cemetery in 1975-77 have previously been sampled for compact bone tissue which were analysed in triplicate for Hg by Cold Vapour Atomic Absorption Spectroscopy (CV-AAS) [3]. …

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