Fluoride was measured in samples of lichen collected in 1990 from 68 sites on the island of Hawaii; in addition, fluoride levels were measured in 8 rainfall samples collected at the same time. The levels of fluoride in the lichens range from 6 to 332 ?g g?1, which are similar to the levels measured on Etna.
The highest levels of fluoride were detected close to Kilauea, and the concentration generally decreases with increasing distance from this volcano. This overall pattern of distribution is modified by local variations in wind direction, which relate to the topographic features of the island.
Close to Kilauea, there are more localised controls on the fluoride levels, caused by circulating groundwaters and degassing lavas.