Spatial dependence in road dust lead accumulation: quantifying the contribution of urban structural variables using...

Urbanization transforms land use and environmental processes, often concentrating potentially toxic elements in surface dust. However, the influence of urban morphology (beyond simple density measures) on spatial patterns of lead (Pb) accumulation in road dust remains insufficiently understood, particularly in arid-region landscapes. This study evaluated how urban structure and landscape configuration influence Pb enrichment in road dust across 70 urban settlements in Isfahan Province, central Iran. Road dust samples from 100 locations (70 urban, 30 non-urban) were analyzed for Pb concentration. A spatial lag model assessed relationships between Pb excess (urban minus background) and 12 predictors representing built-up intensity, road networks, fragmentation, and soil properties. Urban Pb concentrations (127.77 ± 31.09 mg kg^-1) exceeded non-urban levels (29.93 ± 6.69 mg kg^-1) by more than fourfold. The spatial lag model explained 93.4% of variance in Pb excess, with a spatial autoregressive parameter (ρ = 0.983) indicating dominant spillover effects. Major road length (β = 1.364) and built-up proportion (β = 0.903) showed the strongest positive associations, while fragmentation (patch number) was negatively associated (β = -0.213, p = 0.058). Nighttime light intensity (β = 0.769) and soil CaCO₃ (β = 0.343) were also significant positive predictors. These findings demonstrate that Pb contamination in arid-region urban dust is governed by both local structural attributes and strong spatial spillover processes, with road networks and built-up intensity as primary drivers, while fragmentation may mitigate accumulation.