δ34S-Value Measurements in Food Origin Assignments and Sulfur Isotope Fractionations in Plants and Animals

The delta S-34 values of biological material, especially food commodities, serve as indicators for origin assignments. However, in the metabolism of higher plants sulfur isotope fractionations must be expected. As a matter of fact, the delta S-34 values of the sulfate- and organic-S, respectively, of Brassicaceae and Allium species vegetables showed differences between 3 and 6 parts per thousand and differences in glucosinolates were between 0 and 14 parts per thousand. delta S-34-value differences of total-S between individual tissues of the same plant were similar to 3 parts per thousand. It is believed that these relatively small and variable fractionations are due to the partition of individual S-metabolism steps to different plant compartments, where they may occur independently and quantitatively. The delta S-34 values of herbivore muscle meat and milk relative to the diet and between an animal and its child had trophic shifts of similar to 1.5 parts per thousand. S-34 enrichments of up to 4 parts per thousand were observed for hair, hooves, and horn, an isotope fractionation of -5 parts per thousand between the diet sulfate and cartilage. Therefore, the reported agreements between delta S-34 value of biomass and primary S sources are true for only bulk material and not for individual compounds or tissues.