Utilization of soil properties to understand the vertical distribution of dioxins in the soil of Bien Hoa airbase, Vietnam

During the Vietnam War, Bien Hoa airbase was utilized by the US military in the storage and transport of Agents Orange, White, and Blue, which are herbicides/defoliants used during the war. These chemicals used were highly contaminated with dioxins, which were still unknown at that time as carcinogenic chemicals. Thus, accidental spills as well as deliberate disposal of contaminated items within the airbase caused the advertent dioxin problem of the airbase. The relationships of soil properties and dioxin distribution have not yet been considered at this site. Therefore, the objective of this paper was to clarify these relationships using soil samples from boring cores drilled from three areas of the airbase. Dioxins concentrations, total organic carbon (TOC), loss on ignition (LOI), and grain size distribution were analyzed. The results showed that dioxin concentration increased with the increase in TOC. Silty clay with higher TOC of 0.49 % presented the highest toxicity equivalency quantity (TEQ) of 3300 pg-TEQ/g-dw at borehole BH01. Similarly, at BH02, silty clay with the highest TOC of 0.42 % showed the highest TEQ of 760 pg-TEQ/g-dw. The analyzed results of this research also presented a relationship between the TEQ and particle size. It seems to show that the higher concentration of dioxins was found with a ratio of coarse grain size to fine grain size approximately 1:1. However, correlation between dioxins and LOI was not clearly observed. This indicates that mobility of dioxins is sensitive to the TOC of soils.