ISOTOPIC BIOGEOCHEMISTRY OF HAIR

Stable isotope compositions of several elements in hair have proved diagnostic in foodweb studies and a variety of forensic investigations. Its desirable properties include ease of analyses of H, C, N, O, and S isotopes and high resistance to isotopic alteration. The latter is suggested by the similar isotopic data for hair from mammoths and modern Arctic muskoxen. The isotopic composition of hair is dominantly determined by diet and in turn basic biogeochemical processes at the lowest trophic level.

Meteoric water displays general trends of becoming isotopically lighter at higher latitudes and increasing distance from oceans (continentality). Although there is further fractionation during photosynthesis and small shifts in going to successively higher trophic levels, H and O-isotope compositions of hair display similar latitude and continentality trends. The C-isotope composition of hair reflects consumption at various trophic levels of vegetation produced by C3 and C4 photosynthesis. Because of increasing percentages of C3 plants, total vegetation becomes isotopically lighter with increasing latitude. This trend is reflected in hair although it may be affected by dietary selectivity. For example, South American Indians living in a forest environment have a higher C3 component in their diet than residents in a nearby city. The isotopic compositions of S and N in diets are dependent upon ions containing these elements in surface and soil waters. Hence their isotopic compositions in hair are dependent upon processes such as weathering and atmospheric deposition. Consequently factors such as locations of outcrops and industrial emitters can cause considerable variation in the isotopic composition of hair over short distances. The stable isotope composition of one element in a hair sample has a low uniqueness factor. Uniqueness can be improved by multi-dimensional cross plotting of data from several elements.