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 Environment (CCME) and U.S Environmental Protection Agency (U.S. EPA). The PCDD/Fs concentration in fish tissue of BienHung Lake (catfish and snake-head) is superior in comparison with European Council (EC) standard. The dioxin contamination risk for local resident health is very high due to the lack of information and inconsiderable attention of responsible organizations about this problem. As BienHoa was selected as a case-study for PCDD/Fs transfer in food chain, using statistic methods (cluster analysis and Principal Component Analysis - PCA), we have showed a high similarity of PCDD/Fs profiles pattern between BienHoa Airforce Base soils, BienHung Lake sediments and fish tissue. The similarity in PCDD/Fs relative i-TEQ profiles between MWIs bottom ash and soil of industrial zone ThuDuc proves that industrial and municipal combustions are responsible sources for PCDD/Fs in the soil of such these zones. However in comparison with the sites contaminated by Agent Orange (A.O)/Dioxin, the PCDD/Fs contamination level in the industrial soil is lower and mainly dominated by PCDFs than PCDDs. The result also showed comparables i-TEQ values in BienHoa residents with inhabitants of industrial countries, however Vietnam is only developing and agricultural country. Beside that, 2,3,7,8-TCDD has been detected in many tested cases. 2,3,7,8-TCDD is the most toxic compound and related to the A.O/Dioxins from the war, unfortunately we have not enough data to assess the relationship between A.O/Dioxin residue and these samples. To find out this relationship it is necessary an integrated large-scale investigation. Result of our research serves as a base for set-up a reference laboratory for PCDD/Fs and dioxin-liked compounds research in the South of Vietnam. At present time, a small laboratory for PCDD/Fs analysis has been installed in IER and serves as a member of VietNam Dioxin Research Network.

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