Abstract
The goal of this study was to determine the symptoms and microscopic damage caused by fluoride on Spondias dulcis, a fluoride-sensitive species. The plants were exposed to simulated fog with fluoride (0, 5, 10, 15 and 20 mg L(-1)) for 20 min daily during four consecutive days. Samples from leaflets without any apparent fluoride injury were collected to microscopic analysis. The percentage of necrosed leaf area was measured, and the level of pollutant in the dry matter from the basal and apical portions of the plant was determined. The necroses began 24 h after the first simulation mainly from the base of the leaflets. A higher level of necrosis was observed at the apical portion of the plants, a region of higher fluoride accumulation. The damage on the surface of the leaflets was characterized as plasmolysis, erosion of the epicuticular waxes and epidermal rupture. Structurally, the noticeable accumulation of granules and droplets green stained by toluidine blue in the spongy parenchima and the boundaries of ending veinlets was observed. The limb thickness reduction occurred due to plasmolysis in the mesophyll, showing an apparent correlation with the damage observed on the surface. The parameters observed in the laboratory are promising for field biomonitoring studies.
Highlights
Fluoride, an extremely phytotoxic atmospheric pollutant (Smith and Hodge 1979), can be released into the atmosphere during the production of aluminium, bricks, glass, and steel (Fornasiero 2001)
In the plants exposed to fluoride, necrosis occurred in all leaflets in marginal areas, as well as in interveinal areas, mainly at the base of the leaflets (92.5% of the leaflets showed necrosis) (Fig. 1BE)
The symptoms of the ex posure to fluoride are described as marginal necrosis and apical necrosis
Summary
An extremely phytotoxic atmospheric pollutant (Smith and Hodge 1979), can be released into the atmosphere during the production of aluminium, bricks, glass, and steel (Fornasiero 2001). In Brazil there is little data regarding the concentration of fluoride in the atmosphere, most of them restricted to Cubatão city, São Paulo. The aluminium industry has been blamed for the emission of this pollutant, for instance, at the metallurgical zone in Minas Gerais State (Divan Junior et al 2007, 2008). Some plant species, such as Panicum maximum cv. Colonião and Chloris gayana, have been used in Brazil as bioindicators for detecting the presence of fluoride in the atmosphere (Divan Junior et al 2007). When carrying out field studies, it is essential to have a prior knowledge on plant-
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