The interpretation of the trace element results can be very challenging and should be collaborated by other types of dietary reconstruction or palaeopathological studies. The combination of multiple methods to address sample questions has always been the strength of bioarchaeology.
The elements of interest for dietary reconstruction are those that are known to travel through terrestrial or marine trophic pathways concentrating in tissues of different organisms as related to their level in these pathways. Therefore, the focus has been on nonessential elements for human health. Essential elements are regulated by the physiology of the body and are less likely to reflect trophic-level differences. They may, however, show differences among pathological and normal tissues or even changes with age of the individual. Even the interpretation of the distribution of nonessential elements in archaeological bone samples is complicated. Strontium exchanges with calcium in bone tissues during life and is often reported as a ratio. These ratios have been used to assess whether plants, animals, or combinations of plant and animal foods were present in the diets of past peoples. Because plants tend to have higher strontium concentrations than animal foods, intake of a diet that relied on gathered plants or agricultural resources results in higher ratios of strontium to calcium in bone. Strontium is absorbed more slowly into the human body; however, once incorporated into bone, the turnover is much less rapid, leading to a higher ratio of strontium to calcium for terrestrial foragers and early agriculturalists. Studies of strontium to calcium ratios for archaeological remains may be compared with the comprehensive study of the relationship of dietary supplements of strontium, plasma levels, and outer and inner bone strontium enrichment in living people.
Zinc and copper concentrations are higher in animal foods than in plant diets and animal foods are rich in magnesium and barium. Attempts to apply simple analysis or ratio models to studies of ancient diet proved to yield ambiguous results, since simple relationships are not usually found in the reconstruction of early diets. In order to understand the complex relationships that exist, multielement analysis approaches need to reach beyond simple ratios. For example, in the case of marine diets, strontium levels incorporated into bone should increase, since these diets are richer in strontium than terrestrial diets. However, the use of strontium to calcium ratios may be unreliable indicators of seafood consumption because these ratios may fall close to the values for terrestrial foods. Barium is very low in marine foods, much lower than in terrestrial foods. Therefore, the barium-to-strontium ratios and the barium-to-calcium ratios might be considered as possible indicators of marine versus terrestrial diets. Unfortunately, raw ratios from bone analyses have been shown to be inaccurate and may have larger errors than their original measurements. Additionally, ratios do not approximate normal distributions (see Stable Isotope Analysis).
It has become more obvious during recent years that multielemental analyses provide a better approach to the study of archaeological human remains since there is a need for sophisticated comparisons with surrounding environmental samples, as well as analysis of elements that may be interdependent or related in complex ways. These issues may be approached through the application of nonlinear multivariate statistical techniques. Statistical analyses of multivariate data can be cautiously applied to provide information that may help to eliminate or minimize the effects of diagenesis, to compare data sets to each other, and to explore the reliance of early people on marine or terrestrial resources, and to test archaeological data against modern data. An example utilizing multivariate statistical modeling of trace element analysis data, SEM, soil extraction, and comparison of ancient and modern bones can be seen in our work on diet and diagenesis at the Tutu Site, US Virgin Islands. We were able to identify contaminants inside the bone matrix using SEM and eliminate any significant contamination of the dietary variables Sr and Ba. The levels seen in those variables were consistent with mixed marine and terrestrial diets when compared to levels from other more marine-reliant sites in South America.
See also: Archaeometry; Bioarchaeology; Burials: Dietary Sampling Methods; Chemical Analysis Techniques; Neutron Activation Analysis; Sampling Methods, Theory and Praxis; Stable Isotope Analysis; Statistics in Archaeology.
World History
