Transfer of Heavy Metals in Northeast Brazil's Topsoils: Insights from Sequential Extraction and Statistical Tools

Abstract This study aimed to evaluate the distribution and mobility of trace metals (Pb, Cu, Cd, Cr, Ni, Zn) in surface soils of Pernambuco state, Northeast Brazil, applying sequential extraction techniques defined by the Community Bureau of Reference (BCR) and complemented by statistical analysis through Principal Component Analysis (PCA) and Pearson correlation matrix. Analysis of fifty topsoil samples showed that most metals predominantly reside in the residual fraction. However, Cd, Ni, and Zn were significantly present in the mobile fraction. Cd and Pb were closely associated with iron and manganese oxides, indicating their potential mobility within environmental matrices. Cu, however, was primarily detected under oxidising conditions in the residual fraction. PCA revealed a positive correlation of soil pH with Ni, Cu, and Cr and a negative correlation with Zn, Cd, and Pb. Factors such as organic matter and soil texture also play significant roles in influencing the mobility of these metals. The study highlights significant variances across different soil classes, underscoring the complex nature of soil chemistry. These findings emphasise the importance of sequential extraction and PCA in assessing metal solubility and availability, which is crucial for effective environmental management and agricultural practices.