Multimedia monitoring of heavy metals in a large industrial city of Korea: Spatial distributions, source apportionment, and risks

Abstract

Metal contamination across various environmental media poses significant health and environmental risks to populations living in industrial cities; however, multimedia monitoring approaches remain limited. This study presents the first comprehensive assessment of metal contamination in Ulsan, the largest industrial city in South Korea, through monitoring of the atmosphere, soil, and pine needles. The primary objectives were to develop and optimize passive air sampling methods, investigate spatio-temporal distributions of metals across different environmental media, identify major pollution sources using advanced analytical techniques including isotope analysis, and assess health and ecological risks associated with metal exposure. A multimedia monitoring network was established across Ulsan, covering industrial, urban, and suburban areas. Passive air sampling methods were optimized for gaseous mercury measurement using different sulfur-impregnated activated carbon contents (16.3% and 26.3%), sampling containers, and deployment periods (1-3 months). Atmospheric mercury concentrations and mercury isotope ratios (δ202Hg, Δ199Hg, Δ200Hg, Δ201Hg, Δ204Hg) were analyzed to identify pollution sources using a ternary mixing model. The concentrations of 11 metals (aluminum (Al), arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), vanadium (V), and zinc (Zn)) were measured by analyzing passive air samplers, soils, and pine needles. Soil and pine needle samples were also sequentially extracted to determine geochemical fractions. Health risk assessments for carcinogenic and non-carcinogenic effects and ecological risk evaluations using the indices of risk assessment code (RAC), individual contamination factor (ICF), and modified ecological risk index (MRI) were conducted. Atmospheric mercury uptake rates increased significantly with higher sulfur content in activated carbon (26.3% and 16.3%), whereas they were unaffected by sampling containers. Deployment periods of at least two months were recommended due to overestimation during the first month with 1.25 times higher concentration. GEM concentrations ranged from 3.13 to 11.2 ng/m3 (mean: 4.65 ng/m3), with the highest levels at the non-ferrous industrial complex, where zinc smelting was identified as the dominant mercury source. TGM concentrations across 30 sites ranged from 2.26 to 68.5 ng/m3 (mean: 6.89 ng/m3), with industrial areas (9.88 ng/m3) significantly higher than urban (4.99 ng/m3) and suburban (4.72 ng/m3) sites. The concentrations were highest in summer (9.28 ng/m3), followed by spring (7.31 ng/m3), winter (6.57 ng/m3), and fall (4.41 ng/m3). The non-ferrous industrial complex exhibited the highest TGM levels (21.9 ng/m3). Through the mercury isotope analysis, the mean contributions of anthropogenic emissions, surface evasion, and background effects were calculated as 73%, 2%, and 25% in summer and 49%, 12%, and 39% in winter, respectively. Seasonal wind patterns significantly influenced pollutant dispersion, with southeasterly winds in summer spreading emissions inland and northerly winds in winter dispersing them seaward. The atmospheric concentrations of nine metals (excluding Al and Fe) were highest in spring (1,069 ng/m3) and summer (993 ng/m3), compared to fall (381 ng/m3) and winter (305 ng/m3). The non-ferrous industrial complex showed the highest concentrations (3,338 ng/m3), followed by petrochemical (823 ng/m3) and automobile (263 ng/m3) complexes. Among trace nine metals, Zn was predominant (391 ng/m3), followed by Pb (102 ng/m3) and Mn (70.1 ng/m3). While average risks remained below acceptable levels across most areas, the non-ferrous industrial complex (2.85E-05 and 3.34, respectively) exceeded both cancer risk thresholds (1.0E-05) and non-cancer risk limits (1.0). As contributed 85% of total cancer risk, while Mn accounted for 45% of non-cancer risk. Heavy metal concentrations in both soils and pine needles were significantly elevated in industrial areas, specifically the non-ferrous industrial complex, with Cu, Pb, and Zn concentrations often exceeding suburban and urban levels by an order of magnitude. The elevated Cr and V concentrations were characterized by pollution from the petrochemical complex and widespread Cd, Cu, Pb, and Zn pollution from various industrial sources. Atmospheric deposition was the dominant contamination pathway, with significant correlations between exchangeable fractions (F1) in soils and total concentrations in pine needles for As (r = 0.45), Cd (r = 0.53), Cr (r = 0.48), Cu (r = 0.42), Ni (r = 0.47), Pb (r = 0.42), and Zn (r = 0.53). Bioavailability was consistently higher in pine needles than in soils, with RAC and ICF values indicating medium to high ecological risks, particularly for Mn, Ni, and Zn. Soils serve as long-term contamination repositories considering higher overall ecological risks (max: 1,114), while pine needles provide more sensitive indicators of contemporary atmospheric pollution. This comprehensive multimedia monitoring study identified the non-ferrous industrial complex, particularly zinc smelting operations, as the dominant metal pollution source in Ulsan, with clear concentration gradients extending from industrial to residential areas across all environmental matrices. The passive air sampling for metals and mercury stable isotopes and geochemical fractionation in soils and pine needles characterized pollution sources and investigated source-receptor relationships in the largest industrial city, Ulsan. Seasonal meteorological variables significantly influence contaminant dispersion patterns, with monsoon-driven wind systems controlling the spatial distribution of anthropogenic emissions. While health and ecological risks in urban and suburban areas were below acceptable limits, those at the non-ferrous industrial complex exceeded the limits, requiring enhanced emission controls and continuous monitoring. The study demonstrates that comprehensive approaches combining geochemical fractionation from soil and pine needle biomonitoring with atmospheric measurements and analysis are essential for effective environmental monitoring and risk assessment in industrial cities, providing fundamental data for pollution management strategies and public health protection.