Spatial Analysis of Cadmium and Lead in Soils of Nagaon District of Assam, India

Abstract

Aims: The study was carried out in order to find the hotspots of Cadmium and Lead accumulation in the soil due to the anthropogenic activities, so that proper management strategies can be taken on time for their remediation. Study Design: Different geospatial techniques as Normal Q-Q plot, histogram, trend analysis and semi-variogram cloud model is used. Place and Duration of Study: The study was conducted emphasizing basically in high agricultural chemicals dependent Nagaon District of Assam, India, from 2018 to 2021. Methodology: Heavy metals were assessed using a random sampling method with a 5 x 5 km2 grid, and a total of 160 samples were collected from a depth of 0 – 15 cm for soil. Choropleth maps were created to show the distribution and hotspots of pollution. Results: Geospatial analyses from different thematic maps of heavy metals revealed significant vulnerable points of elevated concentrations of Pb (>24.45 mg/kg) and Cd (>0.31 mg/kg) in soil which is presumed to be due to anthropogenic factors. The three-dimensional trend over the distribution of metals throughout the district best fitted the second-order polynomial for Cd, and Pb in soils. Significant numbers of pairs of heavy metal pairs to a certain extent were found to be spatially autocorrelated and all the pairs away from X-axis towards the extreme right corner and far above the axis reflected less influence of local characteristics of the heavy metal. Co-variance cloud with search direction from North to South revealed the existence of spatial autocorrelation and a wider spatial shift of correlation towards the southern direction. Conclusion: The current study provides baseline data to update the mitigation approaches to better manage the heavy metal contamination in soil in the entire district.