In an operation by United States Armed Forces during 1961 to 1971, large quantities of herbicides were sprayed in South Vietnam. These herbicides contained 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-tetraCDD), the most toxic congener of dioxins. Several decades after the herbicide spraying ceased, dioxin concentrations in the environment and human remained elevated in the sprayed areas. Breast milk samples from 520 nursing mothers residing in areas including the hot spots as well as the sprayed and unsprayed areas were collected to quantify the levels of dioxins. The total toxic equivalents of 2,3,7,8-substitued PCDDs/PCDFs in breast milk of mothers living in the hot spots, and the sprayed and unsprayed areas were 14.10 pg/g lipid, 10.89 pg/g lipid, and 4.09 pg/g lipid for primiparae and 11.48 pg/g lipid, 7.56 pg/g lipid, and 2.84 pg/g lipid for multiparae, respectively, with significant differences in the values among the three areas. In the hot spots, dioxin levels were highly correlated with the residency of mothers after adjustment for their age and parity.

Objective Nearly 40 years after Agent Orange was last sprayed, we conducted a cross-sectional study to evaluate the impact of dioxin exposure on salivary hormones in Vietnamese primiparae. Our previous studies found higher levels of salivary cortisol and cortisone in one of the most highly dioxin-contaminated areas, known as a ''hot-spot'', than in a non-exposed area. As a result, we suggested that further research with a larger number of participants would be needed to confirm whether dioxin affects steroid hormone levels in Vietnamese primiparae. Methods The concentration of steroid hormones in saliva was determined by liquid chromatography (electrospray ionization tandem mass spectrometry), whereas the concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in breast milk were determined by gas chromatography-high resolution mass spectrometry, for a sample of the population from a ''hot-spot'' (n = 16) and a non-exposed area (n = 10). All subjects were aged between 20 and 30 years and had children aged between 4 and 16 weeks. Results The mean toxic equivalence of PCDDs, PCDFs and PCDDs ? PCDFs in breast milk in the hot-spot area was found to be significantly higher than in the nonexposed area (p \ 0.001). Likewise, salivary cortisol, cortisone and dehydroepiandrosterone (DHEA) levels were significantly higher in the hotspot area than in the nonexposed area (p \ 0.05). As a result, herein we report, for the first time, that salivary DHEA levels in primiparae are higher in a hot-spot than in a non-exposed area, and that this may be the result of dioxin exposure. Conclusions Our findings highlight the long-term effects of Agent Orange/dioxin on steroid hormones in Vietnamese primiparae in the post-war period.

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