Evaluation of the rainwater acidity of a rural region due to a coal-fired power plant in Brazil

Rainwater samples (73) of a rural region surrounding a coal plant in the northeast of Paraná State (Brazil) were evaluated. Samples of bulk and wet deposition were analysed during a 1-year period (June 1999–June 2000). A large number of rain samples (51) presented pH values below 5.6 (volume weight mean (VWM) was pH=4.7±0.7), indicating that the region rainwater was slightly acidic. The anions and cations concentrations in rainwater samples showed a high sulphate concentration (69 μeq l−1), followed by sodium, calcium and ammonium (35, 32 and 30 μeq l−1, respectively). The analysis of different data of the region indicates that one probable source of the high sodium concentration is fly ash, after the coal burning process. Due to a large contribution of these cations to the sulphate neutralization action, the rainwater of this region displays only a moderate acidity, which does not cause significant environmental impact.