High Levels of PCDDs in Vietnamese Breast Milk from Historical Agent Orange Spraying

(LONDON Base Peak) - One of the unfortunate legacies of the futile Vietnam War in the 1960-70s is linked directly to the decision to undertake large-scale defoliation in order to remove ground cover for the opposing troops and destroy crops. The principal herbicide used was Agent Orange which was contaminated with toxic impurities that continue to exert their influence even today.

The defoliant comprised a 50:50 mixture of esters of 2,4-D and 2,4,5-T and was shipped in drums marked with an orange stripe, hence the name. But 2,4,5-T was not pure. During its manufacture, small but significant amounts of dioxins were also produced and the most abundant was 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD), which just happened to be the most toxic.

2,3,7,8-TCDD is rated a known human carcinogen by the International Agency for Research on Cancer and the risk from the defoliants was compounded by the fact that both 2,4-D and 2,4,5-T are possible human carcinogens. Once a research study revealed in 1970 that 2,4,5-T might cause birth defects in lab animals, its use in Vietnam was brought to a halt.

But by then the damage had been done. About 48 million gallons of Agent Orange had been sprayed over a ten-year period in what was then South Vietnam, with an estimated 600 kg of 2,3,7,8-TCDD.

Even now, the levels of this dioxin remain elevated in soils and sediments from the sprayed areas, despite the long rainy season which might be expected to wash it away over time.

Polychlorodibenzodioxins (PCDDs) are known to infiltrate and climb the food chain, eventually ending up in humans. They accumulate in fats and breast milk and are passed from mother to child during breastfeeding. The elevated levels were confirmed in Vietnamese mothers in a study published in 2001, but that study cannot be extrapolated to the general population, according to a second team of researchers.

Pham The Tai, who is affiliated to Kanazawa Medical University, Japan, and the Vietnam Military Medical University, Ha Noi, with co-researchers from five other organisations in Japan and Vietnam, thought that pooling of samples and the preferential targeting of people in the high-exposure was not representative of the country as a whole. Consequently, they have undertaken their own study which aims to provide an overall picture by measuring the PCDDs and the related polychlorodibenzofurans (PCDFs) in the breast milk of mothers from different areas of Vietnam.

Breast milk was collected 3-22 weeks after birth from a total of 520 mothers from three categories of geographical location. Some were living in the old North Vietnam where defoliant spraying had not occurred. The two other types were from areas that were heavily sprayed during the war or from known hot spots near air bases, where the herbicides were known to have been stored for distribution.

The PCDDs and PCDFs were extracted from the milk samples and spiked with carbon-13-labelled internal standards for the analysis of 17 congeners by GC/MS with electron ionisation. A high resolution mass spectrometer operated in selected ion monitoring mode was used for quantification.

The data did reveal a strong Agent Orange effect, even 40-50 years after the defoliant was sprayed across the countryside, with levels covering a broad range. However, the toxic equivalency factors (TEQs) of PCDDs & PCDFs in first-time mothers (primiparae) within the three types of region were greater than those of multiparae in each region. This is consistent with the fact that breastfeeding is an important route of dioxin release in nursing mothers.

In the non-sprayed regions, the TEQs were relatively low at 4.09 and 2.84 pg/g for primiparae and multiparae, respectively. These levels are consistent with the lowest values published in a WHO< multi-country dioxin exposure study from 2002-2003.

In the old South Vietnam where spraying was prevalent, the TEQ values for breast milk were markedly higher, being approximately 3- and 4-fold higher in the sprayed areas and hot spots, respectively.

The congener profiles of the PCDDs and PCDFs were similar to each other for the sprayed and hot spot locations but were different to those from the non-sprayed areas. This is consistent with a common source for the contaminated areas, which was different to that from the far north, and defoliant spraying during the war fits the bill.

The overall levels were lower than those observed in the 2001 study, which Tai and the team attributed to a general depletion in environmental concentrations in the intervening period, as well as the targeting of high-exposure individuals such as fish eaters in the earlier study.

The team also detected a correlation between the length of time the women lived in a contaminated area and the TEQ values for their breast milk, which indicated that those residing near the hot spots were still exposed to high dioxin levels.

The results have strong implications for the mothers as well as their children. Breastfeeding in this region usually takes place for several months after birth and is often extended beyond one year.

The daily dioxin intakes for the infants were estimated from the new data as 94.4, 64.5 and 25.4 TEQ/kg/day in the hot spots, sprayed and non-sprayed areas, respectively. The significance of the levels can be seen by comparison with the values for adults in the USA and Japan, which are 42 and 60 TEQ/kg/day.

So, Vietnamese infants from dioxin-contaminated areas do appear to be more vulnerable to adverse health risks, although more research is required to establish the facts.

What is certain is that the effects of Agent Orange spraying are still being felt in Vietnam and the long-term health legacy of the contaminant dioxins remains a problem.