Cement industry contributions to soil heavy metals accumulation: spatial patterns, seasonal trends, and geochemical controls

This study examines the spatial and temporal patterns of heavy metals accumulation in soils located downwind of a cement factory in central Iran, focusing on their attenuation trends, geochemical behavior, and environmental influences. A total of 1,728 soil samples were collected over four seasons at three radial distances (1.0, 2.0, and 3.0 km) and analyzed for lead (Pb), Chromium (Cr), Copper (Cu), Zinc (Zn), Manganese (Mn), Cadmium (Cd), Arsenic (As), Nickel (Ni), and Antimony (Sb) across two depth intervals (0–15 cm and 15–30 cm). Heavy metals concentrations generally declined with distance from the factory, confirming its role as a primary pollution source, with Pb and Ni showing the strongest attenuation trends. Pb concentrations in deeper soil decreased by 54% and Ni by 37% between 1.0 km and 3.0 km. Seasonal variations were evident, with summer showing the greatest reductions, such as a 28% decline in Cd in surface soil at 3.0 km compared to 1.0 km, likely due to increased volatilization and reduced atmospheric washout under hot, dry conditions. Hotspot analysis revealed that Pb, As, and Mn accumulated heavily within a 1.0 km radius of the factory, while Cu, Zn, and Sb extended up to 3.0 km, influenced by prevailing wind patterns. Soil pH strongly governs heavy metals mobility; Cr becomes more mobile when pH drops below 6.5, whereas Cd is retained most effectively at pH values above 7.0. These patterns indicate the dominance of adsorption and precipitation processes under near-neutral to alkaline conditions. These findings emphasize the role of cement industry emissions in shaping the geochemical characteristics of surrounding soils and highlight the importance of seasonal and geochemical controls in understanding heavy metals fate and transport. Beyond this case study, the integrated geospatial and environmental approach used here offers a transferable framework for assessing heavy metal contamination in other industrial areas, particularly in arid and semi-arid climates where dry deposition dominates.