Analytical Methods:Biomolecules

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Biomolecules
The term 'biomolecules' is often used to refer to specific biomarkers of faecal and other organic materials. Coprostanol is formed by the microbial breakdown of cholesterol in the gut of higher mammals. Hence, coprostanol is a specific biomarker for faecal matter. Animals consume compounds called stenols from the plants they consume. These too are broken down in the gut into a new series of compounds known as 5&szlig;-stanols (Bull et al. 1999). Other biomarkers that have been applied to archaeological materials include wax esters, alkanols and n-alkanoic acids that have been used to identify turf inputs (Simpson et al. 1998).

Questions
Biomolecules have been used to identify manuring in archaeological soils, whilst the relative proportion of different 5&szlig;-stanols provides information about diet and may help identify the animal that is the source of the faecal material. Comparison of other biomarkers such as alkanols and n-alkanoic acids between archaeological and reference soils may also help to identify other manure inputs such as turf. Biomolecules have also been used to study the abandonment of a wastewater course in Athens (Bull et al 2003) and the identification of middens and less successfully animal pens at &Ccedil;atalh&ouml;y&uuml;k (Bull et al. 2005).

Examples of situations where biomolecules have been successfully used include:
 * The identification of faecal and manure materials in archaeological soils from Crete, Turkey, Athens and Orkney.

Samples and storage
Specialist advice should be sought before sampling to ascertain the potential for preservation of biomarker compounds and to identify suitable sample sizes and sampling strategy. Samples should be kept refrigerated and analysed as soon as possible after sampling. Control and reference samples are important for the subsequent interpretation of results.

Analysis
Analysis is a specialist procedure that involves the use of solvent extraction and gas chromatography to isolate organic compounds and mass spectrometry to identify them.

Data and interpretation
Confident interpretation of organic data requires a good knowledge of the origin and formation of different compounds and the likely taphanomic effects of burial. Organic molecules are susceptible to further decay in the soil, which can limit their sensitivity and usefulness. Identification of specific inputs ot soils where a mixture of manure materials have been added. Interpretation of signatures requires specialist knowledge, but the involvement of the archaeologist in this process is important to ensure that the history of the site is fully understood and considered.