Evaluation of the dioxin-like toxicity in soil samples from Thua Thien Hue province using the AhR-CALUX bioassay - An update of Agent Orange contamination in Vietnam.

In this study, an AhR-responsive reporter-gene cell-based bioassay CALUX was used to assess the biological potency of dioxins and dioxin-like PCBs (dl-PCBs) in top soil samples collected from a former airbase (A-So) and remote regions from urban and agricultural areas in Thua Thien Hue, Vietnam. In top soil collected from A-So airbase, Bioanalytical EQuivalent (BEQ) concentrations of up to 2700 pg 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) per g dry weight (pg BEQ-TCDD g dw) were assessed. Interestingly, while BEQ values for dl-PCBs were found to be up to 13 pg BEQ-TCDD g dw, the dl-PCB activity was not detected in all the hotspot sample extracts. In contrasts, BEQ values for dioxin like compounds from remote regions were much lower and occasionally below the quantification limits of the method. The BEQ activities obtained in this study have a similar trend to the WHO-TEQ results for the samples collected in the A-So airbase. However, BEQ values were higher than those of TEQ, probably reflecting the presence of additional AhR ligands and/or possible non-additive interactions in the sample mixture. This study confirms that after more than 60 years, a strong residual pollution of PCDD/Fs remains on this former air base following the use and storage of Agent Orange during the Vietnam War, raising a health risk for populations exposed in this area because livestock animals graze there.