Combined effects of air and soil pollution by fluoride emissions on Tibouchina pulchra Cogn., at Cubatão, SE Brazil, and their relations with aluminium

Abstract

High deposition of gaseous/particulate fluorides and other air pollutants has resulted in an acidification and probable formation of soluble AlFx complexes in the soil in the vicinity of the industrial complex of Cubatao, SE Brazil. With the present field study we aimed at determining the contribution of F and Al uptake from fluoride-contaminated soil, supposedly as AlFx complexes, to the increase of foliar F and Al contents in saplings of an Al-accumulator tree species (Tibouchina pulchra) which were concomitantly exposed to fluoride-contaminated air and also the proportional contribution of both air and soil contamination to the mentioned foliar accumulation of these elements. The seasonal variations in F and Al accumulation and possible metabolic changes in the plants due to F and Al accumulation were also investigated. The saplings were exposed during three consecutive periods of 16 weeks to: (a) air and soil from a reference site (PVnoF); (b) air or soil from two polluted sites (CM-high air pollution, low F and MV-high air pollution, high F); and (c) both air and soil from these polluted sites. After exposure, the changes in the foliar concentrations of F and Al, the relations between both element contents and their relationships with oxidative stress indicators were determined. The data were grouped in three matrices: PVnoF–CMlwF and PVnoF–MVhgF, taking in account the possible air/soil exposure combinations in each, and soil/air from all sites. The slight F accumulation in plants of PVnoF–CMlwF matrix was a result of higher uptake from soil than from air (54 and 46%, respectively). At PVnoF–MVhgF matrix, the extremely high F accumulation in leaves of T. pulchra could be attributed to the combination of both air and soil contamination (83 and 17%, respectively). T. pulchra always showed higher foliar Al concentrations than 1000 μg g−1 dry mass, mainly after exposure to air and soil of both polluted sites (CMlwF and MVhgF). A highly significant linear regression was estimated between molar Al and F contents, taking in account the data obtained for saplings of T. pulchra cultivated in the different soils and exposed to ambient air of PVnoF, suggesting that both elements were taken as Al–F complexes from soil. The uptake of fluorides from air and/or soil of MVhgF caused significant metabolic changes in T. pulchra, but visible injury supposedly induced by fluorides were observed only when the foliar F contents surpassed 700 μg g−1 dry mass. On the contrary, Al did not cause any metabolic stress to the plants.