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| Last Updated:: 06/01/2017

Fluoride

 

 

Fluoride

 

Introduction

The air borne fluoride (F) usually in the form of hydrogen fluoride HF is a primary gaseous pollutant other gases like silicon fluoride SiF4 and fluorine (F2) are also reported as phytotoxic. It is released in the atmosphere mainly from aluminium industries, steel manufacturing industries and phosphate fertilizer plants. Like SO2, it is an accumulative poison. Most soil contain some soluble fluoride, background concentration in the soil may reach 1%, although it is generally less than 0.05% (500 ppm) in typical agriculture soils. Soil fluoride is normally taken up by plants only in small amounts. The background concentration in plants is low, often as low as 1 and less than 10 ppm in most species (Weinstein, 1977). However a few species such as hickory and dogwood as well as members of Theaceae, Diapensiaceae, Melastomataceae, Rubiaciae and others (Davison, 1983) have the capacity to accumulate hundreds, even thousands of parts per million, even when the atmospheric and soil available F concentrations are at background levels. (Weinstein, 1977, Davison 1982, Weinstein et al 1999). Generally no relation exists between the fluoride content of the soil and fluoride in the plants growing in it (Fluhler et al 1981). Rather it is the atmospheric fluorides that are most critical to excessive accumulation and plant response.

 

 

 

 Injury SymptomsIntroduction

Fluoride enters the plant primarily through the stomata and passes into the transpiration stream where it is carried to its final site of accumulation in the tips and margins of leaves (Romell 1941, Jacobson et al 1969). If the accumulation of F exceeds a threshold for that species, marginal & interveinal chlorosis are usually the first symptoms observed. Depending on the species, anthocyanosis, necrosis and growth distortion may also occur. Little F moves downward in plants to roots, from leaf to leaf or from leaves to fruits (Led better et al, 1960). In addition to foliar injury, fluoride can damage fruits. For example, on peaches it causes a problem known as suture (a seamlike join on the fruit) soft spot that makes the fruit unmarketable.