Fig. 19.

Coefficient of variation (CV) of the concentrations and D/L values of THAA in unbleached and bleached fossil samples. Upper: 15 individual unbleached (■) and bleached (□) Valvata piscinalis shell powders from Funthams Lane. Lower: CVs of bleached samples as a percentage of the CVs for unbleached samples, for the THAA concentration and D/L values from Funthams Lane (FL) Valvata piscinalis, Bithynia tentaculata and from Purfleet (P) Bithynia tentaculata. Inter-shell variability is reduced in all measures of the amino acid composition, except for D/L Ala in shells from Purfleet, where the CVs are low.