Exploring Heavy Metals Exposure in Urban Green Zones of Thessaloniki (Northern Greece): Risks to Soil and People's Health

Abstract

This study investigates the heavy metal contamination in urban and peri-urban soils of Thessaloniki, Greece, over a two-year period (2023-2024). A total of 208 composite soil samples were systematically collected from 52 sites representing diverse land uses, including high-traffic roadsides, industrial zones, residential neighborhoods, parks, and mixed-use areas, with sampling conducted both after the wet (winter) and dry (summer) seasons. Soil physicochemical properties (pH, electrical conductivity, texture, organic matter, and calcium carbonate content) were analyzed alongside the concentrations of heavy metals such as Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn. A pollution assessment employed the Geoaccumulation Index (I_geo), Contamination Factor (Cf), Pollution Load Index (PLI), and Potential Ecological Risk Index (RI), revealing variable contamination levels across the city, with certain hotspots exhibiting a considerable to very high ecological risk. Multivariate statistical analyses (PCA and HCA) identified distinct anthropogenic and geogenic sources of heavy metals. Health risk assessments, based on USEPA models, evaluated non-carcinogenic and carcinogenic risks for both adults and children via ingestion and dermal contact pathways. The results indicate that while most sites present low to moderate health risks, specific locations, particularly near major transport and industrial areas, pose elevated risks, especially for children. The findings underscore the need for targeted monitoring and remediation strategies to mitigate the ecological and human health risks associated with urban soil pollution in Thessaloniki.

Keywords: contamination indices; health risk; heavy metals; source apportionment; urban soils.

Figure 1

Study area and sampling points of urban soils in the city of Thessaloniki.

Figure 2

Variations in heavy metal contents among sampling periods for urban soils from Thessaloniki, Greece.

Figure 3

Contamination assessment results. (a) Boxplot of Geoaccumulation Index (I_geo) of heavy metals. (b) Boxplot of Contamination Factor (C_f) and Pollution Load Index (PLI) of heavy metals. (c) Proportion chart of I_geo of heavy metals. (d) Proportion chart of Cf of heavy metals. Different colors indicate different levels of heavy metal pollution.

Figure 4

Spatial distribution of Pollution Load Index—PLI (up) and Potential Ecological Risk Index—RI (down).

Figure 5

Potential ecological risk (Er) and cumulative ecological risk index (RI) for the studied heavy metals in urban soils from the city of Thessaloniki.

Figure 6

Hierarchical Cluster Analysis (HCA) classification of heavy metals in groups based on z-score similarities.

Figure 7

Average non-carcinogenic health risks (HQs) of exposure via ingestion (up) and dermal contact (down) to heavy metals in urban soils from the city of Thessaloniki.

Figure 8

Spatial distribution of cumulative HQ through ingestion for adults (up) and children (down).