A national-scale assessment of heavy metal contamination in urban road dust across China: a synthesis of data from 82 cities

The Potential Heavy Metal Pollution Transfer to Surface Water and Groundwater in an Old Mining Area of Hubei, China

As a typical historical mining city, Daye, Hubei, faces potential heavy metal migration risks from legacy mining activities. This study conducted a grid-based survey in 2020, analyzing 389 soil and 137 water samples using the Nemerow Pollution Index (NPI) and spatial statistics to assess pollution and transfer mechanisms. Results show that soils were significantly contaminated (average NPI = 5.40), with 71.03% of samples exceeding the pollution threshold (NPI > 1), whereas surface water (0.18) and groundwater (0.11) maintained good quality. Despite limited direct soil migration, atmospheric wet deposition was identified as the probably dominant pathway driving higher concentrations of Cu, Cd, Pb, and As in surface water than in groundwater (e.g., on average, Cu and Cd levels in surface water were ~1.7-fold and ~5-fold those in groundwater, respectively, all well below Class III limits of national water quality standards). This study clarifies the mechanism protecting water bodies amid severe soil contamination and provides a scientific basis for integrated soil–water management in post-mining regions.

Multi-Compartment Pollution Assessment of Soil Metals and Air Pollutants in Lebanon’s Bekaa Valley: Integrating Geochemistry, Remote Sensing, and Multi-Scale Spatial Analysis

This study presents the first integrated multi-compartment assessment linking soil heavy- metal contamination and satellite-derived tropospheric air pollution in Lebanon’s Bekaa Valley. Six metals (Cd, Cr, Cu, Ni, Pb, Zn) were measured in 295 agricultural topsoils using DTPA extraction—which targets the labile, bioavailable pool most relevant to food-chain transfer in calcareous soils—and were compared with Sentinel-5P TROPOMI vertical columns of SO2, NO2 and HCHO extracted at point, 1000 m and 5000 m scales. Chromium was the dominant element, and composite pollution indices indicated overall good but transitional soil quality, with a majority of sites at warning level. Principal component analysis, spatial autocorrelation and land-use analysis converged on three plausible source groupings—predominantly geogenic (Cr, Ni), localized anthropogenic (Cd, Pb) and agricultural (Cu)—although, in the absence of isotopic or other direct source tracing, these assignments remain indicative rather than confirmed. Soil metals and atmospheric columns were largely uncorrelated (|r| < 0.3 for 17 of 18 pairs); this decoupling is consistent with the contrasting temporal integration and spatial support of the two compartments rather than with a single shared pathway. Multi-scale analysis supported a parsimonious dual-scale (point + 5000 m) sampling framework. The study offers a transferable assessment framework for other Mediterranean regions and underscores the need for locally calibrated, total-metal soil background values. Because these indices and threshold comparisons are computed from DTPA-extractable concentrations, they serve here as one-directional, bioavailability-based screening tools rather than regulatory determinations: an exceedance conservatively flags a site for confirmatory total-metal analysis, whereas a non-exceedance does not establish compliance.

Integrated Geochemical and Spatial Assessment of Potentially Toxic Metal Contamination in Urban Soils of Turkestan, Kazakhstan: Implications for Environmental Monitoring and Sustainable Urban Development

Urban soils are sensitive indicators of environmental quality and anthropogenic pressure, particularly in arid regions where pollutant accumulation is enhanced by limited precipitation and intense evaporation. This study aimed to assess physicochemical properties, heavy metal contamination, spatial heterogeneity, and potential pollution sources in urban soils of Turkestan, Kazakhstan. Surface soil samples were collected from 15 representative sites covering industrial, transport, residential, peripheral, and recreational land-use zones. The samples were analyzed for pH(H2O), total dissolved solids, petroleum hydrocarbons, organic matter, and total concentrations of Cu, Zn, Pb, and Cd. Spatial distribution mapping, Pearson correlation analysis, principal component analysis (PCA), and heatmap visualization were applied to identify contamination patterns and likely pollution sources.  The investigated soils exhibited stable alkaline conditions, with pH values ranging from 8.52 to 8.74, typical of arid urban environments. Zinc showed the highest variability, with concentrations ranging from 68.0 to 203 mg kg-1 and a coefficient of variation exceeding 50%, indicating localized enrichment. Cadmium displayed pronounced spatial heterogeneity (0.14-2.80 mg kg-1) and enrichment near industrial and transport-related areas. Copper concentrations ranged from below the detection limit to 61.3 mg kg-1, whereas lead exhibited comparatively lower spatial variability. Spatial distribution maps revealed contamination hotspots associated with transport corridors, industrial facilities, and fuel stations. Multivariate statistical analysis demonstrated relationships among metals, petroleum hydrocarbons, and urban infrastructure, while PCA distinguished metal-enriched sites from mixed urban and low-impact areas. Urban soils of Turkestan are influenced by localized anthropogenic activities and can serve as useful indicators of technogenic pressure in arid urban environments. The integrated application of spatial mapping and multivariate statistical approaches provides a practical framework for environmental monitoring, pollution management, and sustainable urban development in data-limited Central Asian cities.

Evaluating the pollution footprint of traffic-derived trace elements in roadside soil and the associated risks in a non-metropolitan city

This study evaluated the influence of multiple traffic-related conditions, including proximity to a road, car parking, highway, road junction, and transport stop, commonly observed yet largely overlooked in many non-metropolitan cities of developing nations, on trace element (TE) contamination in roadside soil and the associated risks in a secondary South African city. Among the evaluated TEs (As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sb, Zn), mean Cu and Pb concentrations exceeded national soil quality guidelines at 100% and 86% of sites, respectively, whereas pollution assessment revealed generally moderate Sb, Pb, Cr, Ni, Co, Mn, and Zn contamination at > 71% of sites; indicating 73% of TEs as potential environmental threats. Of the seven examined localities, a mean pollution load index above 1 suggested soil pollution at a site affected by most traffic conditions. Regression analysis indicated positive relationships between road proximity and concentrations of all TEs, with significant (p < 0.05) associations for 75% of the identified contaminants, along with As and Ba. Significant positive correlations between TEs exhibiting higher contamination suggested shared sources. This was further supported by principal component analysis, which associated 73% of TEs with one or more traffic variables, primarily road proximity, transport stop, and highway, and secondarily car parking. Moreover, origin from multiple traffic sources was suggested for most TEs. Nearly moderate ecological risks for Cd and Pb at two sampling points, and potential cancer risks for children from As, require follow-up investigation. The findings provide valuable insights into the globally underexamined pollution footprint of multiple traffic-related factors and highlight the need for their management to promote ecosystem sustainability in comparable cities.

Human health risk assessment of heavy metal pollution in airborne dust from Zakho City, Iraq

Soil heavy metals in a typical coal mining cluster of Northern China: Pollution, source apportionment, and eco-health risks

Summary Coal mining activities can alter soil heavy-metal accumulation and risk patterns. To identify pollution characteristics, sources, and ecological and health risks, 88 surface soil samples from Tongchuan Town, Ordos City, were analyzed using enrichment factor, potential ecological risk index, positive matrix factorization, soil physicochemical analysis, and Monte Carlo-based health risk assessment. Heavy-metal concentrations were generally low and regional pollution risk was controllable, although Cd exceeded the agricultural soil risk screening value at some sites. Cd and Hg showed local enrichment and dominated ecological risk, with over 60% of sites at moderate or higher risk. Industrial-traffic sources contributed the most (44.09%), followed by natural sources (34.06%), coal-related emission-atmospheric deposition (16.35%), and mining disturbance-agricultural inputs (5.50%). Soils were strongly alkaline, with low organic matter and nitrogen and potassium deficiencies. Health risks were acceptable; oral ingestion was dominant, Cr and As were key contributors, and children were more sensitive.