Study of the acid rain influence on the aluminium soil concentration near a coal fired power plant

Rainwater samples of a rural region around a coal plant in the northeast of Parana State (Brazil) were evaluated. Samples of bulk and wet deposition were analyzed during a one-year period (June 1999 - June 2000). A great number of rain events (70%) presented pH values below 5.6 (volume weight mean - VWM was pH = 4.9 ± 0.7), indicating that the region rainwater was lightly acid. The anions and cations concentrations results in the sampled rainwater showed a high sulphate concentration (69 μeq L-1), followed by the cations concentration of sodium, calcium and ammonium (35, 32 and 30 μeq L-1, respectively). The analysis of different data of the region showed that one probable source of the high sodium concentration could be from adsorbed sodium at the fly ash after the coal burning process. Due to the great contribution of these cations in the sulphate neutralization action, the rainwater of this region had only a lightly acid characteristic, which not caused a significant environmental impact. The study of the local soil showed that the soil characteristic was of an acid soil and bioavailable concentration of the alkaline (calcium, magnesium and potassium) and acid (aluminium) cations presented high calcium concentration [(1001± 357) mg kg-1] compared with the other cations. The determination of the soil sensitivity to acid rain was calculated by the ratio BC/Al3+ (BC is the sum of the alkaline cations) and presented an average value of (5.1 ± 3.3). The preliminary evaluation of the soil susceptibility to acid rain by the ratio BC/Al3+, showed that the local soil and type of vegetation (tropical savannah) were sensitive to acid deposition. A long term of this impacting condition (acid rain) could be harmful to the soil and vegetation quality. (author)