Occurrence Characteristics and Health Risk Assessment of Hexabromocyclododecanes in Soils from a Historical Production Legacy Site
Although the production and use of hexabromocyclododecanes (HBCDs) have been completely banned in China since December 2021, historical production activities may still leave high-concentration residual contamination in localized areas. This study investigated a typical legacy site of historical HBCDs production in eastern China. Surface and core soil samples were systematically collected both inside and outside the former plant area to characterize the occurrence, spatial distribution, and environmental burden of HBCDs, and to evaluate associated human health risks. Results showed that HBCD concentrations in soils outside the plant area ranged from below detection limit to 6.90×10² ng·g⁻¹ dw, while those inside the plant area were substantially higher, reaching up to 1.18×10⁶ ng·g⁻¹ dw. γ-HBCD was the dominant isomer; however, its relative abundance was lower than that reported in commercial HBCD mixtures and in previous studies conducted near production facilities. Outside the plant, HBCDs concentrations in soil generally decreased with increasing distance from the site, yet remained detectable at a distance of approximately 10 km (15.2 ng·g⁻¹ dw). Within the plant area, HBCDs concentrations in soil cores decreased with depth, declining from 1.08×10⁴–1.18×10⁶ ng·g⁻¹ dw in surface soils to 1.05–93.5 ng·g⁻¹ dw at depths of about 4 m. Analysis of the relative cumulative environmental burden indicated that although HBCDs loads were highest in the near-source area, they gradually accumulated over a broader spatial scale. Approximately 23.7%, 40.1%, 60.0%, and 87.1% of the total estimated burden accumulated within 2 km, 2.81 km, 4 km, and 6 km from the site, respectively. Health risk assessment indicated that oral ingestion of soil was the primary exposure pathway for different populations. Localized high-contamination zones within the plant area contributed significantly to non-carcinogenic risks, while overall risks for children outside the plant area were at acceptable levels.