JOEM Volume 46, Number 5, May 2004 

Letters to the Editor : Readers are invited to submit letters for publication in this department. Submit them to: The Editor, Journal of Occupational and Environmental Medicine, 605 Worcester Road, Towson, MD 21286-7834. Letters should be sent as hard copy with an accompanying diskette and should be designated “For Publication.” 

Food as a Source of Dioxin Exposure in the Residents of Bien Hoa City, Vietnam--Schecter et al. 

To the Editor: The article by Schecter et al. [1] uses laboratory results of 16 food samples collected from various areas in Bien Hoa City, Vietnam, “to determine if food is the route of current intake of TCDD into persons living in Vietnamese 'hotspots'” and concludes that “Clearly, food, including duck, chicken, some fish, and a toad, appears responsible for elevated TCDD in residents of Bien Hoa City, even though the original Agent Orange contamination occurred 30 - 40 years before sampling.” The methodology used and the data and information provided in the article do not appear to support the conclusion. 

The authors referred to Bien Hoa City as a dioxin “hot spot” because of “a substantial leak of over 5000 gallons of Agent Orange occurred underground at the Bien Hoa air base approximately 30 years before our sampling.” This reference is speculating and misleading. Although the article states “In the vicinity of Bien Hoa City, soil and sediment samples from the Bien Hung Lake showed areas with elevated TCDD...,” it does not provide any supporting data to link Agent Orange from the leak at the Bien Hoa airbase 30 years ago with the Bien Hung Lake, whose location could not be specified by the authors. 

The article states It is probable that consumption of food is responsible for elevation of TCDD levels in persons living near the Bien Hoa City dioxin 'hot spot',” but it does not provide supporting data

1) to link elevated TCDD levels in food samples with the dioxin “hot spot” and

2) to link elevated TCDD levels in food samples with elevated blood TCDD levels in residents of Bien Hoa City. The analytical results show only one in three fish samples collected within the dioxin hot spot having elevated TCDD concentration. But the highest TCDD concentrations were found in food samples collected from the Bien Hoa and Bien Hung markets. These samples were likely from food produced in other areas and shipped to the markets for sale; therefore, they may be contaminated by sources other than the Bien Hoa City dioxin “hot spot.” 

There are strong indicators suggesting the presence of potential sources other than Agent Orange for the current dioxin contamination in Vietnam, especially in Bien Hoa City. The first indicator is elevated concentrations of polychlorinated biphenyls (PCBs), polychlorinated dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) in all samples (soil, sediment, food, and human blood) collected for the study. Because dioxin was the only contaminant contained in the herbicides used during the Vietnam War, these polychlorinated compounds must be from a source or sources other than the Bien Hoa City dioxin “hot spot.” 

According to the article, “possible sources of PCBs include electrical transformers or capacitors and hydraulic fluid used during the Vietnam or Second Indochina war.” This interpretation appears to be bias. According to Dr Sinh N. Nguyen of the Vietnam National Environmental Agency, Vietnam has imported between 27,000 and 30,000 tons of PCBs-contaminated oil from Soviet Union, China, and Rumania for industrial uses. A portion of this imported oil was discharged directly to the environment and caused environmental pollution (United Nations Environmental Programme, Proceedings of the Regional Workshop on the Management of Persistent Organic Pollutants, Hanoi, Vietnam, 16 to 19 March 1999). The PCB products could be contaminated with PCDDs and PCDFs from the time they were shipped from the factory. When PCBs were made, PCDDs and PCDFs were created as byproducts in the mixtures. 

The other indicator is untreated industrial waste from industrial zones located within Bien Hoa City. These industrial zones include various industries such as paper, plastic, electric, electronics, and chemicals.

All of these industries are considered as potential sources of dioxin contamination. The untreated industrial waste, including wastewater, has been discharged directly into the environment and has caused serious environmental pollution, especially the Dong Nai River, the receiving water for wastewater from the Bien Hoa industrial zones. According to the National Environmental Agency 's State of Environment in Vietnam 2001, “most of the monitored rivers are found to be polluted with substances like N and P, from 4 to nearly 200 times compared with water resource of category A [for potable water] and from 2 to 20 times in comparison with water source of category B [for non-potable water]. Organic pollution in Sai Gon River, Vam Co Dong River and canals is very serious while it is rather severe in Dong Nai River.” In addition to organic substances and nutrients, toxic chemicals have also been found in wastewater. For example, studies for the Bai Bang Paper Mill in the Vinh Phu province revealed dioxins accumulated in sludge from the receiving waters and the sedimentation basin, and PCBs were found in municipal sewage from Ho Chi Minh City

In summary, the authors should use a more appropriate method to determine whether food is the route of current intake of TCDD into persons living in Vietnamese “hot spots” such as the leak of Agent Orange at the Bien Hoa Airbase in 1970. Regardless the method used, adequate and appropriate supporting data should be provided 1) to link the Bien Hoa dioxin “hot spot” with the TCDD contaminated areas where food are produced, 2) to link elevated TCDD levels in soil and sediment samples with elevated TCDD levels in food grown within the contaminated areas, and 3) to link elevated TCDD levels in food consumed by persons living in the contaminated areas with elevated TCDD levels in their blood. If other persistent organic pollutants are detected, additional potential sources should be evaluated to determine the “true” route of the dioxin contamination in the studied area. 

Truyet T. Mai, PhD

Vietnamese American Science and Technology Society, Orange County, California 


1. Schecter A, Quynh HT, Pavuk M, Papke O, Malisch R, Constable JD. Food as a source of dioxin exposure in the residents of Bien Hoa City, Vietnam. J Occup Environ Med. 2003;45:781-788. 


We thank Dr Truyet T. Mai for his interest in our recently published article on dioxin from Agent Orange as a continuing source of current contamination of food in one location in Vietnam.[1] We appreciate his interest in the environmental and health effects of dioxin exposure in Vietnam. [2]  

Although Dr Mai voices no criticisms of our analytical methods, we feel that it is appropriate to reemphasize what method we used to examine human blood, soil, sediment, wildlife, and food for 2,3,7,8-TCDD (TCDD) where Agent Orange had been sprayed or stored. After cleanup, all samples were analyzed by high-resolution gas chromatography-high resolution mass spectroscopy (GC-MS) with the use of appropriate chemical standards conducted by ERGO Research Laboratory, which is certified by the World Health Organization for the determination of congener specific dioxins, dibenzofurans, and PCBs in human tissue and food. This method is the current “gold standard” for determination of dioxin exposure regardless of the original source of the dioxin. [3-8] 

2,3,7,8-TCDD, unquestionably from Agent Orange, has been identified in humans and their food sources since 1970 when one of us (J.D.C.) collected human milk and fish from heavily Agent Orange sprayed areas of Vietnam for dioxin analyses. These pioneer dioxin analyses showed as much as 1850 parts per trillion of 2,3,7,8-TCDD on a lipid basis in some nursing mothers' milk, which is the highest human milk level ever recorded and which can be compared to the US and south of Vietnam current background level of approximately 2 ppt; whereas in fish up to 1020 ppt wet weight (ww) was detected compared with a usual background of less than 0.01 ppt ww. [9-12] Subsequently, blood and fat samples were used to estimate Agent Orange exposure. As a result, some US Vietnam veterans were shown to be carrying elevated levels of the specific dioxin (2,3,7,8-TCDD), which contaminates Agent Orange. [7,13-15] 

Part of Bien Hoa City is a dioxin “hot spot” not only because of the history of herbicide spraying and of a major Agent Orange spill as documented by the US Department of Defense but also by the determination of elevated 2,3,7,8-TCDD (and only this of many dioxin congeners measured) in selected inhabitants chosen for greater likelihood of herbicide exposure. Contamination of human or environmental samples with products of incineration,16,17 pentachlorophenol, [8,18] contaminated rice oil19-21 or, as here, Agent Orange, results in characteristic patterns of the 7 chlorinated dioxin, 10 chlorinated dibenzofuran, and 12 PCB congeners, which characterizes or “fingerprints” the source of the exposure. The elevation of only this specific dioxin, and no dibenzofurans or PCBs, [3,4,6,22-27] is persuasive evidence that the material originated from Agent Orange either sprayed, spilled, or inadequately stored with resulting leakage.  

To elaborate, as a result of municipal waste incineration, many other dioxins and dibenzofurans are characteristically formed, especially octachlorodibenzodioxin. [16] If chlorine is used for bleaching, paper and pulp effluents typically contain 2,3,7,8-TCDF and 2,3,7,8-TCDD. Pentachlorophenol is typically contaminated with higher chlorinated dioxins and dibenzofurans with eight, seven, and six chlorines, not tetrachlorinated dioxins or dibenzofurans. [8,18]  

The fact that food of animal origin is the route of intake of over 95% of the intake of dioxins in humans is now well documented. [28-32] The purpose of our article was to document, in this location and at this time, the link between the dioxin-contaminated population and the contamination of their food. The food that we sampled was, in fact, representative of that eaten by our human subjects. All our higher levels of TCDD were found in food from the contaminated lake or nearby in this study, consistent with findings from previous work. [24,25,33,34]  

The Bien Hoa “hot spot” is quite similar to the one in the central highlands studied by a Canadian environmental team which shows similar elevation of 2,3,7,8-TCDD in human tissue, soil, sediment, and food. [5,6]  

In his reference to PCBs, Dr Mai seems to be mistaken in describing them as being characteristically contaminated with dioxins and dibenzofurans. In fact, their characteristic contaminants are dibenzofurans. [35] When heated to certain temperatures in the presence of oxygen, even more dibenzofurans are typically formed. [36,37] Although there is considerable similarity between dioxins and dibenzofurans, they are different compounds. It was the dibenzofurans in rice oil resulting from heated PCBs that were primarily responsible for the Yusho rice oil poisoning of 1969 in Japan and the Yucheng rice oil poisoning of 1979 in Taiwan. [21,22]  

From a public health perspective, we agree that it would be useful to determine the history of PCB importation in Vietnam and the current levels of contamination in humans and the environment because these and their contaminants are very persistent compounds. 

We certainly agree with Dr Mai that Agent Orange is not the only toxic chemical that is to be found in Vietnam. Since the 1980s we and others have reported the presence of contaminating chemicals other than TCDD in Vietnam. [38-43] However, the report under discussion was mainly confined to the study of Agent Orange. We can refer to our previous studies of sediment or silt performed many years ago, which found elevated TCDD in areas that had been sprayed whereas none was found in Hanoi (unsprayed), but at the same time we found other dioxins than 2,3,7,8-TCDD in both locations, presumably from incineration or other industrial sources. Since then, the article under discussion joins others in showing many dioxins as well as other chlorinated organics not from Agent Orange in the Vietnamese population and environment. These may also contribute to adverse health outcomes. We have focused much of our work on 2,3,7,8-TCDD in Vietnam because the TCDD contamination from Agent Orange is, to the best of our knowledge, the largest and potentially most significant dioxin exposure that has occurred to date and which has the potential to have caused serious health effects on exposed Vietnamese and also American and other Vietnam veterans. 

The evidence is overwhelming that, although it has been 30 years since the last direct contamination with Agent Orange in Vietnam, there is continued exposure of the population and that these high levels come through food because many of those with high levels of TCDD, up to 413 ppt, which is the highest blood level ever found in a Vietnamese, were born long after the use of Agent Orange had ceased. Levels of TCDD above current background of approximately 2 ppt were found in 95% of the population tested. Bien Hoa remains a dioxin hot spot, currently with high levels of TCDD in human blood, soil, food, and sediment samples. Because most dioxin enters humans through the food chain and because we found many food samples with elevated levels of 2,3,7,8-TCDD, and this particular dioxin only, among the more than 20 dioxins, dibenzofurans and PCBs we studied, we can feel very confident that their food is the continuing route of intake in the people of Bien Hoa, regardless of the precise origin of every food tested. Although our research focuses mainly on TCDD exposure in Vietnam, the reason for our concern is the known human toxicity of dioxins and dioxinlike compounds to Vietnamese or others exposed to these compounds. [19,20,23,30,31,44-47] 

This letter was prepared with the assistance of K.C. Tung and Ana Nguyen. 

Arnold Schecter - Hoang Trong Quynh - Marian Pavuk - Olaf Papke - Rainer Malisch - John D. Constable 


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