The impact of airborne fluoride (F) on forests, plants and soil have been the subject of several studies in India and abroad 1-4. The purpose of this paper is to present a brief on the Indian studies documented around fluoride polluting industries with special reference to the aluminium industries and in comparison with studies done abroad.
The most important phytotoxic pollutant emitted in the aluminium reduction process is F and it is found as Hydrogen fluoride (HF), particulate fluoride (e.g. Cryolite, Na3AIF6; and Calcium fluoride, CaF2). These are produced mainly by volatilization of Fcontaining electrolytes. HF is by far the most phytotoxic of the common air pollutants5. Particulate F, such as cryolite, is from 5 to 10% as phytotoxic as HF, depending upon temperature and relative humidity6. But particles as a group, whether F-containing or not, can have direct or indirect environmental effects.

INDIAN EXPERIENCE

The studies and experience, in India,of the impact of atmospheric fluoride pollution on vegetation and animals are very little. This is not because of lack of awareness and existence of the problem but mainly due to the insufficient resources and hardware inputs. However, with the advent of Air (Prevention and Control of Pollution) Act, 1981 and Environment Protection Act, 1986, in India new thrust and impetus is being given to the air pollution control in fluoride polluting industries including aluminium industry.

LABORATORY STUDIES

Fluoride generator and fumigation chamber : A simple apparatus for generating volatile fluoride, in controlled amounts, has been developed in 1972. A suitable dilution of HF or H2SJF6 is atomised and passed through a heating tube maintained at 150°C in order to obtain gaseous fluoride7. The apparatus is portable and is convenient for fumigating plants in fumigation chamber as well as in green-house.By exposing the plants species to different con­centrations and doses of gaseous F it has been shown that number of useful plants have depleted growth and production due to exposure of fluoride8,9.

FIELD STUDIES

Soil : The effect of fluoride contamination of soil and litter by an aluminium factory on the organic matter content of the soil was investigated. It was found that increase in F content of soil and litter causes accumulation of organic matter content in the surface soil. It was sug­gested that the presence of F in the soil and litter decreases the growth and activity of micro-organisms resulting in greater accumulation of organic matter in the soil (Tablel)3.

in another study the soil samples obtained from within 1 km of aluminium factory showed 855 ppm of total fluoride and 755 ppm available fluoride10. The total fluoride of the samples collected from 5 km away from the factory had shown lower value of total fluoride (71.44 ppm) and available fluoride (0.5 ppm).

Fluoride in plants : The fluoride concentration in herbaceous vegetation decreased with the in crease in the distance from the aluminium factory. The maximum and minimum F levels of 423 ppm and 20 ppm were recorded at the respective distances of 0.5 km northeast and 2 km south of aluminium factory (Table 2}4. In an another study visible symptoms were observed on vegetation due to atmospheric fluoride in 1980 (Table 3)11.

Table 1 : Fluoride content of soil and litter samples and organic matter content of soil samples collected at various sites in northeast of the aluminium factory at Renukoot.

Site locationfrom the factory, km.	Fluoride content, ppm		Organic matter content in the soil (% dry weight)
	Soil	Litter
0.5	1803	619	3.90
1.0	1678	602	3.63
2.0	1301	410	2.43
3.5	1080	176	2.67
5.0	864	73	1.85
7.0	623	30	1.68
10.5	556	36	1.72
16.0	468	21	1.80
Control sites	380	5	1.71

Table 2 : Fluoride concentration in her baceous plants growing in the region around the aluminium factory.

Site No.	Location from the factory		Fluoride con­centration (ppm)
	Direction	Distance (km)
1.	North east	0.5	423.2
2.	-do-	1.0	240.2
3.	-do-	2.0	175.1
4.	-do-	3.5	102.3
5.	-do-	5.0	62.2
6.	East-northeast	1.0	204.0
7.	-do-	2.0	25.1
8.	East	1.0	194.9
9.	-do-	1.5	108.8
10.	-do-	2.5	78.0
11.	Southeast	1.0	83.2
12.	-do-	2.0	38.3
13.	South	1.0	34.8
14.	-do-	2.0	20.0
15.	Southwest	1.5	81.0
16.	-do-	3.0	32.5
17.	West	1.0	128.3
18.	-do-	1.5	72.0
19.	Northwest	1.0	67.1
20.	-do-	2.5	40.0
21.	North	0.8	88.4
22.	-do-	1.5	43.0
Control	-do-	40.0	5.2