Variations of sulfur isotope ratios in a single lichen thallus: A potential historical archive for sulfur pollution

Utilizing the analytical capability to measure S isotope ratios of small quantities of S in biological material without any chemical pretreatment, the variation of δ³⁴S within a lichen thallus was investigated using old and young segments of fruticose lichen thalli (Alectoria sarmentosa) from an oil refinery area in Come-By-Chance and two coastal areas, Newfoundland, Canada. Old segments of lichen samples from the oil refinery area showed significantly higher δ³⁴S values (1.0-2.5‰) than their corresponding young segments. Lichen samples from two coastal areas showed no noticeable differences in δ³⁴S values between old and young segments. These results demonstrate that lichen thalli record temporal changes in the isotopic composition of atmospheric S and hence constitute a historical archive of atmospheric S pollution.