Quantificação de íons metálicos nas frações TFSA, areia, silte e argila de solos no entorno do Parque Nacional do Iguaçu - PR

Abstract

Metal ions occur naturally in soils. Anthropogenic activities such as mining and agriculture have, however, contributed to increase the concentration of these elements. Studies in native forest areas are reference data for soils exposed to degradation, requiring the determination of metal ions by soil class and region, since soils of the same geological origin but of different uses and classes have different concentrations. This study aimed to determine the concentration of metal ions (Al, Cd, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb, Zn) in sand, silt, clay, and air-dried fine earth (ADFE) fractions of agricultural and forest soils around the Iguazu National Park, State of Paraná. For this, soils were collected, and their characterization was performed through determinations of pH, organic carbon (OC), organic matter (OM), available phosphorus, cation exchange capacity, and granulometry (Embrapa). Soil fraction separation was performed according to Gee and Bauder's methodology (1986) and Stokes' law. The mineralogical characterization of clays was made by XRay Diffractometry. Pseudo-total metal concentrations (USEPA 3051a) of sand, silt, clay, and ADFE were quantified, as well as available metals (Mehlich-1: Embrapa) in the ADFE fraction. The quality reference values (QRVs) for forest soils were indicated through pseudo-total metal concentrations. Among the soils collected, there was a predominance of moderately acidic soils and clayey and very clayey textures. Due to the use of phosphate fertilizers, high levels of available phosphorus were found in agricultural soils. In contrast, the levels of OM and OC were higher in the forest soils. For base saturations (V%), 68.75% of soils presented V% < 50%, indicating low fertility. The clays of the Neosols, Latosols, and Nitisols presented kaolinite, hematite, maghemite, and quartz. Gleysols presented kaolinite, quartz, vermiculite, anatase, and rutile. In general, the pseudo-total average values found in the ADFE fraction of forest soils are close only to studies with soils of the same geological origin. According to its use, the levels of Al, Cr, and K were higher in agricultural soils, and the levels of Fe, Mn, Ni, and Zn were higher in forest soils, showing the richness of these ions in such grounds. The levels of metal ions concentrated in the sand fraction, and this can be related to the source material, ferrimagnetic minerals, and the methodology used to separate the soil fractions. The QRVs in the 75th percentile were: Cd (1,00), Cr (73,35), Cu (203,30), Ni (45,26), Zn (152,12); in the 90th percentile, they were: Cd (1,16), Cr (105,88), Cu (226,96), Ni (47,48), Zn (188,02). The values found were close to the studies with soils of basaltic origin, and this research evidenced the need for taking soil classes into account while defining the QRVs.