Bien
Hoa airbase is a known
dioxin-contaminated hotspot in Vietnam. The contamination occurred during the Vietnam War at the site where
dioxins were transported, stored, sprayed, and spilled in the area.
Dioxins, which are
cancer inducing substances, may transfer from the soil to food crops and finally to human beings living around the area. Many surveys of
dioxins in soil, water, organisms, and human have been carried out in this study area since 2002. In this paper vertical distribution of
dioxins in undisturbed soil cores were examined. Twelve soil samples from three drilled cores were collected to analyze
dioxin levels according to the standard Japanese analytical method. The results showed that the toxicity equivalency quantity (TEQ) in one soil sample at a depth of 2.6 m reached 3,300 pg-TEQ/g-dw. High TEQs were also observed in the
clay layer. This anomaly of
dioxin concentrations could be attributed to the affinity of
dioxins for the
clay layer. The isomer patterns in the
soils were different from those in the soil of Hokkaido in that 2,3,7,8-tetrachlorinated
dibenzo-p-dioxin (
TCDD) was the most dominant in the soil sample. This indicates that the
dioxins originate from a defoliant
Agent Orange disposed at the site after the Vietnam War.