Environ Sci Pollut Res DOI 10.1007/s11356-016-7518-z LETTER TO THE EDITOR Reply to the letter to the editor “TCDD and birth weight of Vietnamese infants” Dao Van Tung 1,2 & Teruhiko Kido & Seijiro Honma & Ho Dung Manh 3,4 & Dang Duc Nhu 3,5 & Rie Okamoto & Shoko Maruzeni 1,6 & Muneko Nishijo & Hideaki Nakagawa & Pham Thien Ngoc & Ngo Van Toan & Nguyen Ngoc Hung & Nguyen Hung Minh & Le Ke Son Received: 17 August 2016 / Accepted: 23 August 2016 # Springer-Verlag Berlin Heidelberg 2016 Thank you very much for your comments on and interest in our article We appreciate the opportunity to explain our study in more detail First, regarding the small proportions of the total toxic equivalents (TEQs) that were attributable to TCDD in our study, it is true, as Dr Boffetta and Dr Scialli mentioned, that TCDD contributed only a small proportion of the total toxic equivalent (TEQ) concentration We have previously published a paper entitled “Residual congener pattern of dioxins in human breast milk in southern Vietnam” (Tawara et al., 2011) We found a higher concentration of each congener in the herbicide-sprayed commune than in the non-sprayed commune, and we used cluster analysis to investigate the PCDD/DF congener patterns in the samples from the sprayed Responsible editor: Philippe Garrigues * Teruhiko Kido kido@mhs.mp.kanazawa-u.ac.jp Hanoi Medical University, No Ton That Tung, Dong Da, Hanoi, Vietnam Viettiep Hospital, No Nha Thuong, Le Chan, Hai Phong, Vietnam Faculty of Health Sciences, Institute of Medical Pharmaceutical and Health Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa 920-0942, Japan Faculty of Pharmacy, Lac Hong University, Bien Hoa, Vietnam School of Medicine and Pharmacy, Vietnam National University, Hanoi, Vietnam Department of Public Health, Kanazawa Medical University, 1-1 Daigaku, Uchinada, Ishikawa, Japan Environment Administration, Ministry of Natural Resources and Environment, No 67 Nguyen Du Street, Hanoi, Vietnam commune The congener patterns were dominated by the more-chlorinated (hexa-, hepta-, and octa-chlorinated) PCDD/DF congeners We have also previously determined PCDD/DF concentrations in serum from older Vietnamese men (Manh et al., 2014) living in the same areas as the subjects of this study Older men are very different subjects to the lactating mothers who were the subjects of this study In the serum samples from the older men, TCDD contributed 10.0 % of the total PCDD/DF TEQ in the “hotspot region” and 13.4 % in the control region These contributions were relatively low and were similar to the contributions we found in our current study The PCDD/DFs in milk and serum were determined using a GC-HRMS method, and this analytical method was validated We cannot determine why TCDD contributed a small proportion of the total TEQ concentration However, it has been more than 40 years since herbicides containing PCDD/DFs have been sprayed on the study area The halflives of the different PCDD/DF congeners need to be taken into consideration PCDD congeners with fewer chlorine substituents generally have shorter half-lives than PCDD congeners with more chlorine substituents For example, 1,3,6,8TCDD, 1,3,7,9-TCDD, HpCDD, and OCDD in sediment have been found to have half-lives of 4.4 ± 1.7, 4.6 ± 1.9, 6.2 ± 3.1, and 6.0 ± 2.8 years, respectively (Segstro et al., 1995) Unfortunately, we cannot find any studies of biological half-lives of PCDD/DFs in Vietnam Regarding recall bias, we collected a breast milk sample from each lactating mother and asked her to report the birth weight of her child at the same time Therefore, no mother knew the PCDD/DF concentrations in her breast milk when she reported the birth weight of her child If recall bias affected our study, as Dr Boffetta and Dr Scialli suggest, most mothers in the hotspot area would have emphasized the low birth weights of their children However, we did not find any significant differences between the Environ Sci Pollut Res reported birth weights in the hotspot and control areas The birth weights (mean ± standard deviation) of male children in the hotspot area and the non-sprayed area were 3179 g ± 481 g (N = 34) and 3267 g ± 440 g (N = 28), respectively, and the birth weights of female children in the hotspot area and the non-sprayed area were 3144 g ± 453 g (N = 25) and 3234 g ± 365 g (N = 34), respectively The relationships between the birth weights and the actual weights at the sampling time were assessed with the subjects divided into two groups, 8–9 weeks old and 12– 14 weeks old We found significant relationships between birth weight and actual weight in both groups (r = 0.561 for the 8–9 weeks old group and r = 0.379 for the 12– 14 weeks old group) The actual body weights of the children were determined by skillful nurses using a digital balance (Seca 877) that was adjusted carefully to work properly at the latitude of Vietnam We are therefore very confident that recall bias did not affect the reported birth weights of the children Regarding potential confounders, the subjects of the study were lactating mothers living in the hotspot and non-sprayed areas The mothers were between 20 and 30 years old and had infants between and 16 weeks old at the time the samples were collected In Vietnam, women tend to smoke little and drink little alcohol (less than men and also less than women in some other parts of the world) Therefore, we did not examine the effects of smoking or drinking alcohol in our study The hotspot and non-sprayed areas were both rural areas with similar characteristics except for their histories of being sprayed with herbicides There are three PCDD/DF hotspots in Vietnam Of these, Da Nang is the third biggest city in Vietnam and Bien Hoa is an industrial city The third, Phu Cat, which was the hotspot our samples were collected in, has a local airport at which several airplanes land each day We are not sure whether the reviewers have visited Phu Cat, but we are not sure why the reviewers state that Phu Cat is “the site of a civilian and military airport, perhaps accounting for the evidence of industrial and incineration byproducts in human milk reported in the paper” because we not believe that this applies to Phu Cat Finally, the interpretation of our study was limited because samples from too few subjects were able to be analyzed to allow multivariate analysis results with a high level of confidence to be produced We cannot deny that there could have been confounding factors A larger study will need to be performed to overcome this limitation References Manh HD, Kido T, Okamoto R, Xianliang S, Anh le T, Supratman S, Maruzeni S, Nishijo M, Nakagawa H, Honma S, Nakano T, Takasuga T, Nhu DD, Hung NN, Son le K (2014) Serum dioxin levels in Vietnamese men more than 40 years after herbicide spraying Environmental Science & Technology 48:3496–3503 doi:10.1021/es404853h Segstro MD, Muir DCG, Servos MR, Webster GRB (1995) Long-term fate and bioavailability of sediment-associated polychlorinated dibenzo-p-dioxins in aquatic mesocosms Environ Toxicol Chem 14:1799–1807 doi:10.1002/etc.5620141021 Tawara K, Nishijo M, Maruzeni S, Nakagawa H, Kido T, Naganuma R, Suzuki H, Nhu DD, Hung NN, Thom LTH (2011) Residual congener pattern of dioxins in human breast milk in southern Vietnam Chemosphere 84:979–986 doi:10.1016/j.chemosphere.2011.05.041 ... reported birth weights in the hotspot and control areas The birth weights (mean ± standard deviation) of male children in the hotspot area and the non-sprayed area were 3179 g ± 481 g (N = 34) and. .. confounders, the subjects of the study were lactating mothers living in the hotspot and non-sprayed areas The mothers were between 20 and 30 years old and had infants between and 16 weeks old at the time... (Seca 877) that was adjusted carefully to work properly at the latitude of Vietnam We are therefore very confident that recall bias did not affect the reported birth weights of the children Regarding