Spatio-temporal variations of air- and soil-borne hexachlorobenzene and pentachlorobenzene: A decadal nationwide assessment in South Korea

Abstract

Seasonal air and annual soil samples were collected across South Korea from industrial, urban, and suburban sites as part of a national monitoring campaign. Hexachlorobenzene (HCB) and pentachlorobenzene (PeCB) were analyzed in samples collected from 2008 to 2020 and 2013 to 2020, respectively. HCB showed a 13 % annual mean decline in air concentrations, but its mean concentration (255 pg/m3) remained 4.5 times higher than the mean concentration observed in the northern hemisphere. PeCB concentrations showed no significant temporal trends, indicating stabilized atmospheric levels. HCB displayed clear seasonal variations (summer > fall > spring > winter), while PeCB concentrations were slightly elevated during warmer seasons. Both compounds exhibited significantly higher air concentrations at urban and industrial sites than at suburban sites, with major industrial hubs like Ulsan, Gyeonggi, and Daegu identified as hotspots. While soil concentrations showed no temporal variation, they demonstrated distinct spatial patterns. HCB levels were potentially influenced by long-range atmospheric transport from continental Asia, while PeCB levels were attributed to soil re-volatilization. Fugacity fractions indicated that PeCB has reached stagnation levels, controlled by secondary sources (net volatilization), while HCB is approaching stagnation, exhibiting equilibrium conditions. These findings emphasize the need for sustained monitoring in urban and industrial areas to support and strengthen control measures.