Widespread Distribution of Toxic Trace Elements in House Sparrow (Passer domesticus) Feathers: Evidence of a Homogeneous Urban Signature in a Petroleum-Industrial Hub.

Trace element pollution in industrial urban environments poses a significant threat to wildlife and human health, yet the spatial resolution of these contaminants is often poorly defined. This study investigated the distance-dependent accumulation of toxic trace elements-lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni), and mercury (Hg)-in the feathers of the house sparrow (Passer domesticus) across urban and rural gradients in Gachsaran County, Iran, a major center for oil extraction. A stratified spatial design was employed, establishing concentric buffer zones at 500, 1000, and 1500 m from primary pollution sources (industrial nodes and high-traffic roads). Feather samples were analyzed using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The results revealed that all studied trace elements (Pb, Cd, Cr, Ni, and Hg) showed significant differences between urban and rural areas (p < 0.05), with consistently higher concentrations observed in urban settings. Conversely, no significant differences were found for any of the trace elements between the distances of 500, 1000, and 1500 m from the pollution sources. These findings suggest that the urban footprint of anthropogenic contaminants in industrial cities, such as Gachsaran County, is characterized by a pervasive and uniform distribution throughout the urban landscape rather than being confined to immediate point-source proximity. The study concludes that the house sparrow is an effective bioindicator for broad-scale urban environmental stressors and recommends that environmental monitoring programs account for the widespread nature of trace element signatures across urban zones to accurately identify associated ecological risks.