Spatial and Temporal Patterns of Trace Element Deposition in Urban Thessaloniki: A Syntrichia Moss Biomonitoring Study

Urban air pollution, especially from heavy metal (HM) contamination, poses significant risks to human health and environmental sustainability. This study investigates the spatial and temporal distribution of HM contamination in Thessaloniki, Greece, using Syntrichia moss as a bioindicator to inform urban environmental management strategies. Moss samples were collected from 16 locations representing diverse urban activity zones (motorway, industrial, city center, airport) in March, May, and July 2024. The concentrations of 12 HMs (Al, Sb, As, Ba, Cd, Cr, Co, Cu, Pb, Ni, V, and Zn) were analyzed using ICP-MS, and the contamination factors were calculated relative to controlled moss samples. The results revealed significant spatial variation, with elevated levels of As, Cd, Cr, Pb, and Zn, particularly in high-traffic and industrial zones, exceeding the background levels by up to severe and extreme contamination categories. Temporal trends showed decreases in Al, Ba, and Ni from March to July 2024, while Cr and Cu increased, suggesting seasonally varying sources. Multivariate analyses further distinguished the contamination patterns, implicating traffic and industrial activities as key contributors. Syntrichia effectively captures HM contamination variability, demonstrating its value as a cost-effective bioindicator. These findings provide critical data that can guide urban planners in developing targeted pollution mitigation strategies, ensuring compliance with the European Green Deal's Zero Pollution Action Plan.