We found a higher concentration of each congener in the herbicide-sprayed commune than in the non-sprayed com-mune, and we used cluster analysis to investigate the PCDD/DF congener patte
Trang 1LETTER TO THE EDITOR
Dao Van Tung1,2&Teruhiko Kido3&Seijiro Honma3&Ho Dung Manh3,4&
Dang Duc Nhu3,5&Rie Okamoto3&Shoko Maruzeni1,6&Muneko Nishijo6&
Hideaki Nakagawa6&Pham Thien Ngoc1&Ngo Van Toan1&Nguyen Ngoc Hung1&
Nguyen Hung Minh7&Le Ke Son7
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
pub-lished 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
com-mune, and we used cluster analysis to investigate the
PCDD/DF congener patterns in the samples from the sprayed
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 sub-jects of this study Older men are very different subsub-jects 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 half-lives of the different PCDD/DF congeners need to be taken into consideration PCDD congeners with fewer chlorine sub-stituents generally have shorter half-lives than PCDD conge-ners with more chlorine substituents For example, 1,3,6,8-TCDD, 1,3,7,9-1,3,6,8-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 sug-gest, most mothers in the hotspot area would have empha-sized the low birth weights of their children However, we did not find any significant differences between the
Responsible editor: Philippe Garrigues
* Teruhiko Kido
kido@mhs.mp.kanazawa-u.ac.jp
1
Hanoi Medical University, No 1 Ton That Tung, Dong Da,
Hanoi, Vietnam
2 Viettiep Hospital, No 1 Nha Thuong, Le Chan, Hai Phong, Vietnam
3
Faculty of Health Sciences, Institute of Medical Pharmaceutical and
Health Sciences, Kanazawa University, 5-11-80 Kodatsuno,
Kanazawa 920-0942, Japan
4
Faculty of Pharmacy, Lac Hong University, Bien Hoa, Vietnam
5
School of Medicine and Pharmacy, Vietnam National University,
Hanoi, Vietnam
6
Department of Public Health, Kanazawa Medical University, 1-1
Daigaku, Uchinada, Ishikawa, Japan
7 Environment Administration, Ministry of Natural Resources and
Environment, No 67 Nguyen Du Street, Hanoi, Vietnam
Environ Sci Pollut Res
DOI 10.1007/s11356-016-7518-z
Trang 2reported 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
sub-jects 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
chil-dren 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 7 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
char-acteristics 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 do 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 confi-dence to be produced We cannot deny that there could have been confounding factors A larger study will need to be per-formed 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
Environ Sci Pollut Res