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

The δ34S 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 δ34S values of the sulfate- and organic-S, respectively, of Brassicaceae and Allium species vegetables showed differences between 3 and 6‰, and differences in glucosinolates were between 0 and 14‰. δ34S-value differences of total-S between individual tissues of the same plant were ∼3‰. 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 δ34S values of herbivore muscle meat and milk relative to the diet and between an animal and its child had trophic shifts of ∼1.5‰. 34S enrichments of up to 4‰ were observed for hair, hooves, and horn, an isotope fractionation of −5‰ between the diet sulfate and cartilage. Therefore, the reported agreements between δ34S value of biomass and primary S sources are true for only bulk material and not for individual compounds or tissues.