Source-Sink Spatial Mismatch Characteristics and Health Risks of Soil BTEX in a Decommissioned Industrial Site on a Coastal Plain
The relocation of numerous industrial enterprises in China has left behind soil contamination, particularly by volatile organic compounds such as BTEX, whose migration and health risks are of great concern. Coastal plains, characterized by high groundwater tables and interbedded sedimentary strata, exhibit contaminant distribution and migration patterns distinct from inland regions. This study investigated a decommissioned resin plant site in the Yangtze River Delta coastal plain, systematically analyzing the spatial distribution, migration, and health risks of soil BTEX. Seven BTEX compounds were detected with detection rates ranging from 24.3% to 47.1%. Maximum concentrations of benzene, ethylbenzene, and m/p-xylene exceeded China's Class I construction land screening values. The contaminant plume was predominantly located in the southern product warehouse area, while the potential source was traced to the upstream wastewater treatment unit, indicating a 'source-sink' spatial mismatch. Vertically, contaminants exhibited a 'shallow-layer volatilization, middle-layer enrichment, and deep-layer retardation' pattern, with significant enrichment in silty clay at 3–6 m depth and sharp concentration declines in mucky clay. Membrane Interface Probe (MIP) multi-parameter detection revealed that benzene and toluene migrated as a whole, whereas chlorobenzene lagged due to strong adsorption. Benzene posed the most significant health risk, with carcinogenic risk up to 7.42×10⁻⁴ and non-carcinogenic hazard quotient up to 38.24, both exceeding acceptable levels. Inhalation of indoor air contaminated by vapor intrusion from underlying soil contributed over 87% of benzene's total risk, dominating the exposure pathway. This study elucidates the unique migration and risk formation mechanisms under high water table and interbedded strata, providing a scientific basis for precise investigation, risk assessment, and remediation of similar contaminated sites.