Spatial zoning of the territory of Almaty City based on the concentration and level of heavy metal contamination of soils

Almaty, the largest city in Kazakhstan, has a long history of industrial activity and heavy traffic, yet no systematic assessment of soil heavy metal contamination has ever been conducted across the entire urban territory. To fill this gap, we collected ۴۱۲ soil samples from the top ۰–۱۰ cm layer between April and September ۲۰۲۵, covering all administrative districts of Almaty on a ۱ km × ۱ km grid. Concentrations of lead (Pb), cadmium (Cd), zinc (Zn), copper (Cu), and chromium (Cr) were measured using ICP‑OES after aqua regia digestion. Background values were established from ۲۵ reference sites outside the city. The results show wide spatial heterogeneity: Pb ranged from ۴.۲ to ۳۴۷.۸ mg kg-۱ (mean ۴۸.۶), and Cd from ۰.۰۵ to ۳.۹۲ mg kg-۱ (mean ۰.۶۴). Strong positive correlations among Pb, Cd, Zn, and Cu (r = ۰.۶۹–۰.۸۴, p < ۰.۰۰۱) indicate common anthropogenic sources, while Cr showed only moderate enrichment (median enrichment factor ۱.۲). Using the threshold of background mean + ۲SD, we classified the city into four zones: Class I (clean, ۳۳% of area), Class II (moderate, ۳۸%), Class III (high, ۲۲%), and Class IV (very high, ۷%). Very high zones are concentrated in the northern industrial belt and near the former battery plant, where Pb averaged ۱۲۴.۵ mg kg-۱ and Cd ۱.۹۲ mg kg-۱, close to Kazakh maximum allowable concentrations. Industrial areas and old residential districts displayed significantly higher contamination than new residential zones (p < ۰.۰۰۱). This study provides the first evidence‑based soil contamination map for Almaty, enabling targeted remediation, urban planning, and public health interventions.

کلیدواژه ها:

Heavy metal contamination ، Soil zoning ، Almaty ، Urban geochemistry