Fluorides as Air Pollutants Affecting Plants

Abstract

/Pathological effects of fluoride have been known for nearly 1000 years when ancient disease of gaddur, or gaddjax was first described in early Icelandic literature. Later known in English as dental fluorosis of cattle, disease developed on domestic animals feeding on grass contaminated by ash deposited following volcanic eruptions (67). Fluoride has been recognized as injurious to plants only since 1883 when Schroeder & Reuss first reported damage to vegetation in Germany (75). Reports of damage in areas near superphosphate and glass factories followed shortly (42,66,89). Not until 1940s though, with tremendous expansion of alumi­ num and phosphate industries, was fluoride recognized as a threat to agri, culture and forestry in local areas of United States. Research during this period was stimulated by serious crop losses and injury to forests near major new phosphate, aluminum, and steel plants largely in Florida, Wash­ ington, and Utab. Fluoride is a natural component of earth's ernst, with concentrations in soils commonly exceeding 0.05% and occasionally 1 %. Plants normally accumulate small amounts of this fluoride; on rare occasions, toxic concen­ trations may be absorbed from acid soils, but polluted atmospheres provide main source of .fluoride accumulated by plants. Fluoride is released whenever clays, rocks, coal, or ores containing it are heated, or when fluoride is used as a flux and allowed to escape into atmosphere. Fluorides are well recognized as air pollutants, and their harmful effects on plants have received considerable attention in past two decades. Their role in plant disease , and concept of air pollutants as disease inci­ tants dates back nearly a hundred years (70) and was fully described by Darley & Middleton in 1966 (19). Their statement that the increasing im­ portance of air pollution injury to vegetation as a factor in agricultural pro­ duction emphasizes need for plant pathologists to become more aware of pollution-incite d diseases is still timely and is certainly true for fluorides.