Sources and fate of PCDDs and PCDFs in rural and urban ecosystem and food chain in southern Vietnam

Problems related to Dioxins contamination in Southern Vietnam are until now still a hot newsreel and controversy subject in international conferences as well as in many articles. The adverse effects of Dioxins residue from chemicals used by U.S. Army during the Vietnam War (Ranch Hand Operation 1961 to 1971) have caused many consequences not only to Vietnamese ecosystem and people but also to the U.S army veterans that participated in the war at that period as reported in many scientific reports. In Vietnam, since 1980 many studies have been carried out in collaboration with overseas scientists and laboratories on Dioxin contamination levels as well as its influences on ecosystem and human health. However, regardless of many efforts, up to now the problem of Dioxin contamination and its consequences is not yet completely and appropriately solved. There is still relative high Dioxins residue in the areas named as "hot spot" in Southern Vietnam and its contamination is causing the adverse effects on local residents. Nowadays, studies on this subject are relatively difficult to perform due to many factors: over 30 years passed; land use disturbance; degradation and transfer of dioxin into biological food web; population emigration; etc.. In addition, a lack of related documents and military secrets also contributed to this. With the support of SDC in frame of a collaboration project between Vietnam and Switzerland, we have carried out the research named "Sources and Fate of PCDDs and PCDFs in rural and urban ecosystem and food chains of South-Vietnam". Our research has examined integratelly the PCDD/Fs sources with special regard on the PCDD/Fs source from the war, but also consider the others possible sources such industrial and municipal combustions, agricultural used chemicals, etc. The selected locations for our research have been set up based on collected document from Division 10-80 and Office 33 (two responsible organizations for Dioxins and related problems in Vietnam): CamLo District – QuangTri Province; DaNang City; MaDa Forest and BienHoa City (BienHoa Airforce Base and BienHung Lake) – DongNai Province; and industrial zone – Thu Duc – Hochiminh City. Seventeen 2,3,7,8-PCDD/Fs congeners have been chosen for our research due to their high toxicities. Soil, sediment, municipal waste incinerator (MWI) bottom ash, fish tissue, and human adipose are selected as the matrices to examine the PCDD/Fs residue. The result showed that even after more than 30 years, the PCDD/Fs concentration based on i-TEQ value (especially for 2,3,7,8-TCDD) is still higher than guideline values in some countries: very high i-TEQ value in cultivate soil of CamLo district and DaNang City. For the area named "hot spot" such BienHoa Airforce Base and BienHung Lake, the i-TEQ value and 2,3,7,8-TCDD concentration in soil and sediment are superior than values proposed by Agency for Toxic Substance and Disease Registry (ATSDR), Canadian Council of Ministers of the Environmen