Mapping and screening risk assessment of heavy metals concentrations in soils of the Bahr El-Baker Region, Egypt

Abstract

Mapping the spatial distribution of soil pollutants is essential for delineating contaminated areas ofBahr El-Baker Soils, Egypt. Geostatistical interpolation and kriging was used to estimate pollutant levels in soils. The X- Ray Fluorescence (XRF) and X- Ray Diffraction (XRD) analyses results showed similarity of the studied soils in the most of chemical and mineralogical (dominant montmorillonite) properties; thus revealing to these exposed soils the same geological and pedological conditions. These soils exhibited that they possess both permanent and variable surface charges due to smectite minerals, amorphous iron oxides, and organic matter which ensures high metal sorption capacity thus, increasing the cation-exchange capacity (CEC) values. The spatial patterns showed the homogeneity in Cd, Pb, Cr, and Ni contents. In contrast, Cu and Zn contents, since their data distributions were characterized by great variation and high skewness (1.27 and 1.22 respectively). The best fit model for Cd and Pb were Circular and Exponential model with Mean Standardized (MS) values for them -0.0255 and 0.0600, respectively which is closest to zero. Root Mean Square Standardized (RMSS) values for Cd and Pb were 1.096 and 0.9789 respectively which are closest to 1. The best fit model for Zn was Pentaspherical model (MS = 0.0002) and Rational Quadratic model for Ni and Cr with -0.0029 and -0.0046 MS, respectively which is closest to zero. The data showed that the concentrations of heavy metals Zn, Cr, Ni, and Pb measured in these soils are still under the threshold values. However, the concentrations of Cd and Cu in some soils exceeded the threshold values for non-polluted soils. Since the whole study area (17818.93 ha) became contaminated by Cd, and 6370.23 ha only became contaminated by Cu. Although, this study is a screening presentation which helps to identify the important areas to sample in the future, the results indicate that these soils are still able to load with over concentrations of these metals and retained them, since they do not reach their saturation capacities except for Cu and Cd in some areas. But under bad management with continuous accumulation of these toxic metals in the environment, region will be exposed to real disaster. Geostatistics provides effective methods to quantify the contaminated soil which support decision-making about redevelopment scenarios or remediation techniques. Key words: Heavy metals, geostatistics, risk assessment, Egypt.