For more than a half of a century, herbicide dioxin sprayed by the Americans in the Việt Nam war has been discussed, studied and addressed due to its complexity and serious consequences on the environment and people of Việt Nam.
In addition, dioxin from industrial processes, solid waste treatment and other sources has attracted more attention because dioxin emission from these sources and their human exposure has tended to increase. Therefore, dioxin has become “a double issue” in Việt Nam.
From 1961 - 1972, American military has sprayed herbicides in the southern part of Việt Nam with three objectives: destroying the environment and forests which are bases of the opponents (offensive), establishing safe zones around their camps (defensive) and crop destruction.
Herbicides are marked by colors in their containers: orange, orange 2, purple, pink, green, blue, white and dinoxol. Of these, the main one isAgentOrange which is a combination of 50% n-butylic este 2,4,5-T and 50% n-butylic este 2,4-D.
Except for blue and white herbicides, they all contained 2,3,7,8 tetraclodibenzo-p-dioxin (2,3,7,8 TCDD), one of the most toxic chemicals produced by humans. TCDD is a by-product during 2,4,5-T production (Fig.1).
|Figure 1.Dioxin formation in 2,4,5-T production
Data on the amount ofherbicides used by the Americans in Việt Nam and the amount of dioxin in herbicides are mixed. According to Westing (1976), 72,354,000 liters of herbicides were sprayed in 2,578,502 ha, containing 170 kg dioxin. According to Stellman (2005), 73,772,262 liters of herbicides were used, containing 366 kg dioxin. Young (2009) estimates that 79,488,240 liters of herbicides used, of which 46,276,880 liters of herbicides containing dioxin (62.4%), or 130 - 144 kg dioxin were released.
Herbicide dioxin residues in the environment
After several decades, dioxin residues in sprayed areas have declined considerably. In A Lưới, ThừaThiên-Huế, only two among 140 samples had a dioxin level of 877 ppt. The other tested soil and sediment samples showed a level of from 0 to 246 ppt (Committee 10-80, Hatfield, 2000). In Sa Thầy, Kon Tum, dioxin levels in soil were from 333 to 845 ppt (three samples), in sediment from 107 to 430 ppt (five samples) (Le Xuan Canh 2010). In other sprayed areas, dioxin levels were found much lower or not detected.
Biên Hòa airport, Đồng Nai is considered as the most dioxin affected spot. In this area, in Ranch Hand campaign (herbicide spraying campaign) and Pacer Ivy campaign (herbicide collection and disposal campaign in 1972), American military stored 170,300 208-litre tanks of herbicides, of which 109,000 tanks contained Agent Orange. From 11/1969 to 3/1970, some accidents happened causing 25,000 liters of Agent Orange and 2,500 liters of agent white to release into the environment. Therefore, dioxin contamination became more complex. According to studies by Việt Nam-Russia Tropical Research Centre (1996), Steering Committee 33’s Office (2011) and some other studies, dioxin levels at Biên Hòa Airport ranges from 01 to 962,559 ppt, with an average level of 2,984 ppt with 1,020-9,658 ppt TEQ. It is estimated that 247,000 cm3 of soil and 236,000 cm3 of soil and sediment need to be treated for dioxin contamination. In 2009, Ministry of Defense of Việt Nam buried 94,000 cm3 of dioxin contaminated soil in the area of 4.7ha, of which 3,384 m3 was properly buried (combined with microbiological technology). Effectiveness of the properly buried method needs to be further studied.
Đà Nẵng Airport is considered as the second most dioxin affected in Việt Nam. During the War, the US Military stored 94,900 herbicide tanks, of which 52,700 tanks contained Agent Orange. According to a study by USAID (2011), dioxin in contaminated spots in Đà Nẵng airport ranged from 6,820ppt to 365,000ppt. It is estimated that 72,900 m3 of contaminated soil and sediment needs to be cleaned up. Since 2012, USAID has collaborated with Việt Nam’s Ministry of Defense in cleaning up dioxin in Đà Nẵng Airport, using a thermal desorption method. During the clean-up process, the real quantity of contaminated soil which needed to be remedied was double compared with an initially estimated volume. This shows complexity of dioxin contamination in the contaminated sites.
Phù Cát Airport in Bình Định is considered as the third most dioxin affected area in Việt Nam, with about 7,500 m3 of contaminated soil and the highest concentration of 238,000ppt. In 2012, with support from Global Environment Facility via United Nations Development Programme (UNDP), Steering Committee 33’s Office finished landfilling dioxin contaminated soil in this spot.
In addition to the above mentioned spots, some military airports of the former Sài Gòn government storing herbicides in the past also have dioxin contamination but with low concentration and little or no impact on the environment and local people.
Herbicide originated dioxin decontamination is a complex issue because of very high dioxin levels and TCDD (the most toxic and persistent form). Landfilling is only valid in a certain period. Bioremediation needs further research. According to USEPA (2013), success of using bioremediation has been only obtained at laboratories. Thermal adsorption is being applied in Đà Nẵng but appears some limitation due to dioxin in emission and wastewater are found to exceed permitted levels. At present, within a framework of a national program on dioxin research, Ministry of Defense is studying combination of methods for dioxin decontamination.
Dioxin consequences on human health
Main studies on herbicide dioxin consequences on human health were carried out by National Committee on Investigating American wartime chemical consequences (Committee 10-80) and National Steering Committee on Overcoming American wartime chemical consequences, with participation of some international organizations and scientists. Epidemiological studies show that disease structure and rate of the exposed groups are different from those of controlled groups, in particular birth defect rates in younger generations and maternity complications (Nguyen Thi Ngoc Phuong, Le Bach Quang, and Nguyen Van Tuong).
In addition, Vietnamese scientists have studied hematological changes, hematological production organs and immune systems, in particular generic and ADB changes. The studies show some generic changes in dioxin exposed families that relate to cancers, in particular lung cancers. Dioxin impact mechanisms are shown in Figure 2.
|Figure 2.Dioxin impact on genes
However, so far, cause-effect relations between dioxin and typical diseases have not been well established for determined diagnosis.
Dioxin from other sources
Within a framework of project “Dioxin decontamination in hotspots”, scientists have taken samples from some incinerators in Hà Nội, Hải Dương, Thanh Hóaand HCM City. TEQs of air samples were found to range from 14.1 - 46,800 pg WHO-TEQ/Nm3 (m3 of air measured in a standard condition). Seven of 18 samples from industrial incinerators had TEQ exceeding 0.6 TEQ/Nm3. Of these, some samples exceeded permitted levels some thousand times.
The highest dioxin found in the samples mainly is OCDD. TCDDs were found at small concentrations, with TCDD/TEQ ranged from 4.1-25.3%. This is a basic difference between herbicide dioxin and dioxin from other sources.
Wastewater from the above mentioned solid waste treatment facilities was also tested for dioxin. Results showed that TEQ of the tested wastewater ranged from 0.84-50,080pg WHO-TEQ/L. Dioxins with high concentrations in the tested samples mainly were 1,2,3,4,5,6,7,8-HpCDD and OCDD while 2,3,7,8-TCDD was found at a small level. Compared with Japanese permitted levels of dioxin and related compounds of 10pg TEQ/L, up to nine of 15 samples were found to exceed the levels. Some samples even had up to 50,075pg TEQ/L.
Some samples from cement factories, metallurgy factories and thermal power plants had dioxin exceeding permitted levels.
Some soil and sediment samples in Hà Nội, Thái Nguyên and Thanh Hóa were found to have dioxin lower than QCVN45:2012/BTNMT, which was a standard on dioxin in soils.
In Việt Nam, dioxin standards for water have not been established. Dioxin in water samples taken in Hà Nội, Nam Định and Thanh Hóa all were lower than 1pg/L with an average level of 0.76pg/L.
Dioxin and related compound analyses in air samples taken in Hà Nội, Thái Nguyên, Nam Định, HảiDương, QuảngNinh and Thanh Hóa showed that 16 of 17 samples had TEQ lower than 01pg/Nm3.
Consequences of herbicide dioxin used by the US Army during Việt Nam war are serious. Dioxin decontamination in Đà Nẵng Airport is planned to finish by the end of 2016. However, this deadline seems difficult to be met as some complexity has arisen during treatment process. Decontamination in Biên Hòa Airport is only at an environmental assessment stage. Funding sources and technology types have not been determined.
Figure 3.Since 2012, USAID and Ministry of Defense of Việt Nam have used thermal adsorption for dioxin decontamination in Đà Nẵng Airport
It is necessary to conduct further studies to have a more comprehensive assessment of herbicide dioxin contaminated sites in some other military airports and select suitable measure to clean up dioxin contaminated soil and sediment.
It is necessary to develop a regular and long term monitoring plan for heavily contaminated sites which have and have not been remedied. Arsenic and dioxin monitoring for groundwater should be paid more attention, as some wartime herbicides contain arsenic.
It is mandatory to have a comprehensive monitoring plan for dioxin from other sources, in particular from industrial and domestic solid waste incinerators. Outdated incinerators should be removed. Dioxin permitted levels at different sources should be reviewed and updated.
It is necessary to continue study and selection for dioxin treatment technologies which are suitable for the Vietnamese context.
For humans, health care and checkup for those who have been exposed to dioxin should be prioritized. Dioxin levels and diseases in these people should be regularly monitored. Further studies on generic, immune and hormone changes should be carried out. Detoxification for dioxin affected people should be expanded.
Law on Environmental Protection 2014 has regulations on dioxin contamination management. Detailed regulations should be issued.
Report on dioxin contamination in hot spots of Biên Hòa, Đà Nẵng and Phú Cát Airports. Steering Committee 33’s Office and UNDP, Hà Nội 2011.
Report on dioxin contamination in Việt Nam. Steering Committee 33’s Office and UNDP, Hà Nội 2011.
Overview of studies on agent orange/dioxin impact on the environment. Office of Science and Technology 33/11-15, Hà Nội 2012
The History, Use, Disposition and Environmental Fate of Agent Orange. Alvin L.Young. Springer, 2009.