Assessment of the levels of heavy metal pollution in roadside soils of Termiz – Taskent, Uzbekistan

Abstract

This study investigates the contamination of roadside soils by heavy metals (Pb, Zn, Ni, and Mo) along the Tashkent- Termiz International M-39 highway, utilizing indices such as the enrichment factor (EF), geo-accumulation index (Igeo), and pollution load index (PLI). Soil samples collected at 21 distances (5–1000 m) indicate that metal concentrations decrease with distance from the road, with rapid reductions observed within the 5–100 m range. Pb levels decline from 24 mg kg-1 at 5 m to 1.4 mg kg-1 at 1000 m, while Zn reduces from 26.3 mg kg-1 to 2.1 mg kg-1. Ni and Mo follow similar trends, but Mo exhibits lower mobility. Pb, Zn, and Ni stand out as indicators of anthropogenic pollution, with high correlation values between their DTPA-extractable and total concentrations (R2: Pb = 0.953, Zn = 0.930, Ni = 0.932). The Igeo values reveal moderate to high contamination near the road, particularly for Pb and Zn. The EF values for Mo (2.06) suggest moderate enrichment due to anthropogenic sources, such as traffic emissions, while Pb (0.76), Zn (0.89), and Ni (0.93) show minimal enrichment. PLI values of 4.24, 4.03, 3.63, and 4.87 for Pb, Zn, Ni, and Mo, respectively, classify the area as “highly polluted” for most metals. These findings highlight the significant anthropogenic contribution to heavy metal accumulation, driven by vehicular emissions, tire wear, and industrial activities. The contamination poses risks to soil health, biodiversity, and human safety through bioaccumulation in the food chain. Sustainable environmental management and pollution mitigation strategies are urgently required to address these concerns and safeguard agricultural productivity and ecosystem functions.