Environ Earth Sci (2016) 75:18 DOI 10.1007/s12665-015-4803-y ORIGINAL ARTICLE Utilization of soil properties to understand the vertical distribution of dioxins in the soil of Bien Hoa airbase, Vietnam Thuong Huyen Dang1 • Toshifumi Igarashi2 • Takuya Shiraiwa3 Received: 13 March 2015 / Accepted: July 2015 / Published online: 19 December 2015 Ó Springer-Verlag Berlin Heidelberg 2015 Abstract During the Vietnam War, Bien Hoa airbase was utilized by the US military in the storage and transport of Agents Orange, White, and Blue, which are herbicides/ defoliants used during the war These chemicals used were highly contaminated with dioxins, which were still unknown at that time as carcinogenic chemicals Thus, accidental spills as well as deliberate disposal of contaminated items within the airbase caused the advertent dioxin problem of the airbase The relationships of soil properties and dioxin distribution have not yet been considered at this site Therefore, the objective of this paper was to clarify these relationships using soil samples from boring cores drilled from three areas of the airbase Dioxins concentrations, total organic carbon (TOC), loss on ignition (LOI), and grain size distribution were analyzed The results showed that dioxin concentration increased with the increase in TOC Silty clay with higher TOC of 0.49 % presented the highest toxicity equivalency quantity (TEQ) of 3300 pg-TEQ/g-dw at borehole BH01 Similarly, at BH02, silty clay with the highest TOC of 0.42 % showed the highest TEQ of 760 pg-TEQ/g-dw The analyzed results of this research also presented a relationship between the TEQ and particle size It seems to show that & Thuong Huyen Dang dthuyenus1982@gmail.com Earth Resources and Environment Department, Faculty of Petroleum and Geology Engineering, Ho Chi Minh City University of Technology, 106 Blg8, 168 Ly Thuong Kiet, Dist.10, Ho Chi Minh City, Vietnam Faculty of Engineering, Hokkaido University, Kita-ku, Sapporo 060-8628, Japan Yagai-Kagaku Co., Ltd., Higashi-ku, Sapporo 065-0043, Japan the higher concentration of dioxins was found with a ratio of coarse grain size to fine grain size approximately 1:1 However, correlation between dioxins and LOI was not clearly observed This indicates that mobility of dioxins is sensitive to the TOC of soils Keywords Dioxins Á Soil Á Toxicity equivalency quantity (TEQ) Á Grain size distribution Á Total organic carbon (TOC) Á Loss on ignition (LOI) Introduction Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) are groups of organic compounds generally referred to us ‘‘dioxins and dioxin-like substances.’’ They have characteristic two- or three-ring benzene structures that can be chlorinated to varying degrees (Heidelore 2003) Humans can be exposed to these organic substances either directly or indirectly via the consumption of contaminated food crops and animal products (Elskens et al 2013) Dioxins and dioxin-like substances could cause cancer, developmental and neurodevelopmental defects in children, immunotoxicity, and changes in thyroid and steroid hormones (WHO 2002; FAO/WHO 2006) Dioxins and dioxin-like compounds are also considered as cumulative poisons, i.e., the human body does not have the ability to excrete these substances out; therefore, they slowly accumulate with continuous exposure to contaminate food sources PCDD/Fs are formed industrially as by-products in the manufacture of chlorophenols and phenoxy herbicides, chlorine bleaching of paper pulp and smelting They can also be formed naturally due to natural events like forest/bush fires and volcanic eruptions (Rappe et al 1987; Rappe 1996) These 123 18 Page of chemicals are persistent organic pollutants; and because of their inherent stability and hydrophobicity, these compounds could migrate for long distances overtime (Altarawned et al 2009; Bergknut et al 2010) During the Vietnam War, Agent Orange, a herbicide/ defoliant named after the orange-striped barrels in which it was shipped, was used by the US military in the herbicidal warfare campaign code named ‘‘Operation Ranch Hand.’’ More than 22.67 million liters, 9.36 million liters, and 3.39 million liters, respectively, of Agent Orange, Agent White, and Agent Blue had been transported and stored by the Ranch Hand in Vietnam War (US DOD 2007; Young and Andrews 2007) The most widely used of these agents was Orange The aim of this program was to deprive the VietCong of food and vegetation cover in the thick jungles of southern Vietnam (Buckingham 1982) Agent Orange is a mixture of 50 % 2,4-dichlorophenoxyacetic acid (2,4-D) and 50 % 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), which was the most extensively used herbicide/defoliant in this campaign (Buckingham 1982; Paul 2002) By the end of the Vietnam War in 1971, the US military reportedly used ca 45 million liters of Agent Orange, which was sprayed within at least million acres (24,000 km2) of farm and forest areas in southern Vietnam (Buckingham 1982) The persistence of 2,4-D and 2,4,5-T in soil is limited to only a few weeks, and high dosages are necessary for these substances to have detrimental effects to humans (Buckingham 1982) Unfortunately, 2,4,5-T used in the production of Agent Orange was contaminated with 2,3,7,8-tetrachlorodibenzodioxin (TCDD), an extremely toxic PCDD compound (Buckingham 1982) As a result, large farming and forest areas, including the air bases used for their storage and transport, were inadvertently contaminated with this very toxic organic compound According to the Vietnam Red Cross, ca million Vietnamese are currently affected by dioxins, including at least 150,000 children born with birth defects (Michael 2012) In addition, women had higher rates of miscarriage and stillbirths in the dioxin-contaminated areas, as did livestock such as cattle, water buffalo, and pigs Children born in these contaminated areas also have multiple birth defects, including cleft palate, mental disabilities, hernias, and extra fingers and toes (Hermann 2006) Vertical distribution of PCDD/Fs in sediment cores was also observed above the groundwater level, indicating that they are transported downwards by percolating rain/groundwater (Czucwa et al 1984) Kakimoto et al (2006) showed that dioxins in soils are re-mobilized by dilution when irrigation in rice fields was increased The decrease in dioxins concentration in soil core had been presented in research of Bergknut et al (2010) Bulle et al (2011) and Dang et al (2015) also studied on the degradation of dioxins according to depth in Bien Hoa airbase 123 Environ Earth Sci (2016) 75:18 Brzuzy and Hites (1996) found strong correlations between total PCDD/Fs levels in soil and the content of total organic carbon (TOC), while Kim and Osako (2004) showed that the leaching concentration of dioxins correlated with dissolved organic carbon in situ using lysimeter Although strong correlations between TOC and PCDD/Fs in soils have been reported, correlation analyses revealed no significant relationship between TOC and TEQ of ball clay in the studies of Hilscherova and Kanan (2003) and Ferrario et al (2007) Surveys of PCDD/Fs concentrations of Bien Hoa airbase, one of the air bases used by the US military during the Vietnam War for their herbicidal campaign program, have been conducted several times but were limited to the analyses of surface soils only (Hatfield Consultants and 10-80 Committee 2006, 2007, 2011) Because PCDD/Fs could migrate downward and contaminate the groundwater, these previous surveys are insufficient to gage the actual scale of dioxin contamination of the area Therefore, detailed surveys of deeper soils and sediments should be conducted to understand the risks associated with dioxin contamination of the area as well as to understand the migration pattern(s) of dioxin in the subsurface satisfactorily In this paper, the authors attempt to characterize the mobility of PCDD/Fs as functions of soil properties by drilling three boreholes and taking undisturbed soil cores in the airbase Study site and methods Study site The study area is located in Bien Hoa city of Dong Nai province (Fig 1) Bien Hoa airbase is very close (ca 500 m) to the Dong River, which is the primary water source of water for residents of Dong Nai province, Ho Chi Minh City, and other provinces The elevation of the airbase is higher than its surrounding areas, so groundwater and surface run off with substantial concentrations of dioxins flow from the airbase to Bien Hung Lake, Dong Nai River, and residential areas (Dang et al 2015) Surveys of dioxins have been done since 2001 (Dwernychuk et al 2002; Dwernychuk 2005: Hatfield Consultants and 10-80 Committee 2006, 2007, 2011), but these were limited to the shallow ground surface ([10 cm) Some soil samples showed several thousand times higher dioxin concentrations than the Vietnamese standards These reports recommended that the contaminated soils be treated immediately in the airbase (Vu-Anh et al 2008, Hatfield Consultants and 10-80 Committee 2006, 2007, 2011) According to the information from a present department commander and Hatfield Consultants and 10-80 Committee Environ Earth Sci (2016) 75:18 Page of 18 Fig The Bien Hoa airbase (achieved from Dang et al 2015) (2006, 2007, 2011), Bien Hoa airbase has three hot spot zones The first is Pacer Ivy with an area of 20 ha, which was used as a garrison and dumpsite of soldiers’ used clothes The highest concentration of TEQ measured in this area was 28,600 pg-TEQ/g-dw The previous research also showed that at a depth of 3.6 m the highest concentration of dioxins was 3300 pg-TEQ/g-dw in the Pacer Ivy (Dang et al 2015) The second is in the Southwest Corner of the airbase (known as football stadium) with an area of ca 1.2 and was formerly used as an infirmary of wounded soldiers The highest concentration of TEQ in this area was 65,500 pg-TEQ/g-dw The third is Z1 with an area of about 4.7 ha, which was used during the war as a storage area of Agents Orange, White, and Blue The highest concentration of TEQ in this area was 35,900 pg-TEQ/g-dw, which is currently used as an isolated landfill site of 94,000 m3 of contaminated soil Methods Sampling Three boreholes, BH01, BH02, and BH03, were drilled in the study site to collect undisturbed soil samples Two of them were in the Pacer Ivy area, while the third one was in the Southwest Corner of the airbase Distances from BH01 to BH02 and from BH01 to BH03 are 170 and 1360 m, respectively The groundwater levels (GLs) were shallow: GL-1.2 m at BH01, GL-1.1 m at BH02, and GL-5.1 m at BH03 All of the cores were collected and transported to the Ho Chi Minh City University of Technology Four soil samples at BH01 (BH01-1, BH01-2, BH01-3, and BH01-4) were collected at depths of 1.95, 2.55, 3.5, and 5.65 m, respectively Soil samples of BH02-1, BH02-2, BH02-3, and BH02-4 were collected at a depth of 0.65, 2.6, 3.6, and 5.5 m, respectively, at borehole BH02 The last four samples BH03-1, BH03-2, BH03-3, and BH03-4 were collected at depth of 0.55, 2.5, 4.45, and 6.4 m, respectively, at borehole BH03 Twelve undisturbed soil samples with approximately cm in thickness were collected based on visual differences in soil texture These samples were then sealed with aluminum foil and sent to Japan for analysis The sampling process had been presented in research of Dang et al (2015) Chemical analysis Dioxins in soil samples were measured based on the Japanese standard analytical method (Ministry of Environment 2009) as shown in Fig After drying soil samples under room temperature, eight grams were placed in a thimble filter and then treated by Soxhlet extraction using toluene for more than 16 h (part A in Fig 2) The extracted crude solvent was evaporated, messed up to 100 ml, and divided into several aliquots (i.e., primarily by 0.1 ml and secondary by 90 ml) After adding internal standards as a clean-up spike in the separated solvent, the aliquot was evaporated, replaced to hexane, injected into a multilayer column chromatograph with normal hexane (part B in Fig 2) (Dang et al 2015) After the elution, effluent from the multilayer column chromatograph was evaporated again, and the resulting product was injected into an active charcoal column chromatograph first with hexane, followed by 25 % dichloromethane/hexane (for mono-ortho PCBs fraction), and then finally with toluene (for non-ortho PCBs fraction and PCDD and PCDFs) Each eluted fraction for analysis was purged by N2 gas to approximately 50 ll and taken in 123 18 Page of Environ Earth Sci (2016) 75:18 sample Soxhlet extraction (A) concentration with toluene for over 16hrs removal of toluene add Internal Std (clean-up spike) C-2,3,7,8 located -T4 O8CDD 13 crude extract 13 C-2,3,7,8 located -T4 O8CDF 13 C-Co-PCBs division Options; treating with sulfuric acid concentration Removal of toluene replace to n-hexane (B) Multi-layer silicagel column chromatography Sodium sulfate (dehydrates) 6.0g 10% Silver nitrate silicagel 3.0g Silicagel 0.9g 22% Sulfuric acid silicagel 6.0g 44% Sulfuric acid silicagel 4.5g Silicagel 0.9g 2% Potassium hydroxide silicagel 3.0g Silicagel 0.9g elution with n-hexane concentration Active charcoal silicagel column chromatography elution with n-hexane aliphatic hydrocarbons PCBs etc Fr elution with 25% DCM/n-hexane elution with toluene (C) mono-ortho PCBs Fr PCDDs, PCDFs non-ortho PCBs Fr concentration waste concentration addition of syringe spike exchange to n-nonane volume HRGC/HRMS mono-ortho PCBs Idn and Qnt by SIM (D) 50μl addition of syringe spike exchange to n-nonane volume 50μl HRGC/HRMS PCDDs, PCDFs and non-ortho PCBs Idn and Qnt by SIM Fig Analytical procedure flow chart (Idn and Qnt indicate identification and quantity, respectively in the figure, modified from Dang et al 2015) 123 Environ Earth Sci (2016) 75:18 a vial bottle (part C in Fig 2) The sample was provided for a gas chromatograph–mass spectrometer (GC–MS, JEOL, Japan) WHO-TEF (2006) for TEQ calculation was adopted (Dang et al 2015) Quality assurance and quality control (QA/QC) To enhance the quality of analyzed data, the authors checked a blank value regularly and analyzed the same sample three times for evaluating the variability In addition, the recovery of samples within 50–120 %, according to the Japanese standard method, was calculated (Dang et al 2015) Soil properties analysis Three common soil properties were examined in this study and compared with the distribution of PCDDs and PCDFs: particle size distribution, TOC, and loss on ignition (LOI) Particle size distribution was analyzed based on American Society for Testing and Materials D421 and D422 (ASTM D421 and D422) Gravel and sand particles are typically measured using sieve analysis A stack of sieves with accurately dimensioned holes between a mesh of wires is used to separate the particles into size bins There are various holes diameters such as 4.750, 2.000, 0.850, 0.4250, 0.25, 0.106, and 0.075 mm The finer grain size was analyzed by hydrometer analysis The soil particles are mixed with water and shaken to produce a dilute suspension in a glass cylinder, and then, the cylinder is left to sit Then, Stock’s law was applied to calculate the relationship between sedimentation velocity and particle size for 0.02 and 0.005 mm The TOC was determined from the total carbon (TC) at 900 °C and total inorganic carbon (IC) at 450 °C with phosphate solution using the TOC analyzer attached to a solid sample combustion unit (TOC-VCSN-SSM-5000A, Shimadzu Corporation, Japan) The LOI was measured by the difference in weight before and after ignition at 600 °C for h Page of 18 (370 pg-TEQ/g-dw) and BH01-2 (3300 pg-TEQ/g-dw) were found with a ratio of coarse grain size to fine grain size of 54.2:45.8 and 63.6:36.4, respectively, while lower concentrations of dioxins in BH01-3 (52 pg-TEQ/g-dw) and BH01-4 (1.8 pg-TEQ/g-dw) were found with 76.2:23.8 and 41.1:58.9 in the same borehole (BH01) In borehole BH02, higher concentrations of dioxins in samples BH02-1 (320 pg-TEQ/g-dw), BH02-2 (450 pg-TEQ/g-dw), and BH02-3 (760 pg-TEQ/g-dw) were found with ratios of coarse grain size to fine grain size of 51.3:44, 53.5:39.7, and 47.6:48.1, respectively In borehole BH03, low concentrations of dioxins were found in four samples with ratios of coarse grain size to fine grain size of 86.9:13.1, 90.5:9.5, 93:7, and 84.5:15.5 from shallow to deeper borehole BH03 Therefore, the grain size distribution may affect on the presence of dioxin in soil The highest concentration of dioxins was observed below the groundwater table (Table 1) At borehole BH01, the groundwater table was 1.2 m deep, while the highest dioxin concentration of BH01-2 (3300 pg-TEQ/g-dw) was found at a depth of 2.55 m Similarly, at borehole BH02, groundwater table was located at GL-1.1 m, whereas the highest concentration of dioxins was observed at a depth of 3.6 m Even though dioxins are generally considered as relatively immobile in soils due to the presence of organic matter, they can, nonetheless, flow slowly to downstream in shallow groundwater and induce risks to surrounding habitats (Kurniawan and Jinno 2007) This means that dioxins from the airbase may move with the groundwater flow downstream into Dong Nai River, which is only about 500 m away Results and discussion TEQ and grain size Figure shows the relationship of TEQ and grain size distribution Concentration of dioxin is in good agreement with regulation distribution of grain size The presence of dioxins in soil samples in which distribution of grain size from coarse grain size to fine grain size is not much different is found with high concentration In borehole BH01, higher concentrations of dioxin in samples BH01-1 Fig Grain size distribution of 12 samples and relationship with TEQ 123 18 Page of Environ Earth Sci (2016) 75:18 Table Sampling depth and dioxin concentration of 12 samples Bore hole BH01 BH02 BH03 ID of core soil sample 4 Depth of sampling (m) 1.95 2.55 3.5 5.65 0.65 2.6 3.6 5.5 0.55 2.5 4.45 6.4 Water table depth (m) 1.2 1.1 5.2 2,3,7,8-TCDD (pg/g-dw) 360 3200 51 1.8 320 450 750 4.4 32 4.3 TEQ (pg-TEQ/g-dw, ND = 0) 370 3300 52 1.8 320 450 760 4.4 32 0.011 4.3 0.0024 TOC (%) 0.52 0.49 0.2 0.04 0.37 0.32 0.42 0.06 0.26 0.06 0.03 0.02 LOI (%) 3.2 2.8 5.8 3.4 3.0 3.4 3.2 7.2 3.9 7.2 6.6 3.5 TEQ and TOC TEQ and LOI The results of TOC measurements are listed in Table TOC decreased with depth in boreholes BH01 and BH03 The highest TOC is 0.52 % at a depth of 1.95 m of sample BH01-1 and decreased with depth BH03 had the same distribution of TOC to that of BH01 However, almost identically, the same TOC values were observed at a depth of 0.65, 2.6, and 3.6 m of BH02 The relationship between TOC and TEQ for all samples is shown in Fig A statistically significant strong positive correlation of TEQ with TOC was observed (R = 0.840; p \ 0.005), indicating that the increase in TOC also corresponded to the increase in TEQ Hilscherova and Kanan (2003) pointed out that concentrations of PCDD/Fs in soils and sediments were not correlated with TOC in sediments or soils of Tittabawassee River, Michigan However, the presence of higher TOC indicates higher concentration of dioxins in this site Therefore, dioxins have a possibility to accumulate in soil layers with higher TOC Figure presents the relationship between LOI and TEQ Although it appears that a negative correlation exists between TEQ and LOI, this relationship is not statistically significant These results are contradictory to the relationship between TOC and TEQ Ozaki et al (2005) also found that TEQ concentration increased with LOI in sediment samples This may be due to the other materials contributing LOI except TOC Fig Relationship between TOC and TEQ 123 Conclusion Undisturbed soil samples were collected by drilling three boreholes in Bien Hoa airbase to analyze the vertical distribution of dioxins and soil properties The high concentrations were observed with a ratio of coarse grain size and fine grain size approximate 1:1 in each borehole The highest dioxin concentration was found 3300 pg-TEQ/g- Fig Relationship between TEQ and LOI Environ Earth Sci (2016) 75:18 dw with higher TOC of 0.49 % at the depth of 2.55 m at borehole BH01, and 760 pg-TEQ/g-dw with the highest TOC of 0.42 % at the depth of 3.6 m at borehole BH02 However, there were not clear correlations between TEQ and LOI The TOC in the soil samples may control the mobility of dioxins The transference and absorption of dioxins may be affected by TOC The existence of high TOC at deeper zones in the dioxin-contaminated areas is important to evaluate the mobility of dioxins Acknowledgments The authors gratefully acknowledge the financial support from AUN/Seed-Net, permission from the Vietnam Ministry of National Defense and Commander of Bien Hoa airbase for taking sample collection, and permission from the Ministry of Agriculture, Forestry and Fisheries of Japan for the importation of the samples References Altarawned M, Dlugogorski BZ, Kennedy EM, Mackie JC (2009) Mechanisms for formation, chlorination, dechlorination and destruction of polychlorinated dibenzo-p-dioxins and dibenzonfurans (PCDD/Fs) Prog Energy Combust Sci 35:245–274 Bergknut M, Laudon H, Wiberg K (2010) Dioxins, PCBs, and HCB in soil and peat profiles from a pristine boreal catchment Environ Pollut 158:2518–2525 Brzuzy LP, Hites RA (1996) Global mass balance for polychlorinated dibenzo-p-dioxins and dibenzofurans Environ Sci Technol 30:1797–1804 Buckingham WA Jr (1982) The air force and herbicides in Southeast Asia (1961–1971) Office of Air Force, United States Air Force, Washington Bulle CSM, Samson R, Descheˆnes L (2011) Transport of chlorinated dioxins and furants in soil columns: modeling pentachlorophenol pole-treating oil influence Chemosphere 83:117–123 Czucwa JM, McVeety BD, Hites RA (1984) Polychlorinated dibenzop-dioxins and dibenzofurans in sediment from Siskiwit Lake, Isle Royale Science 226:568–569 Dang TH, Igarashi T, Shiraiwa T (2015) Vertical distribution of dioxins in soil of Bien Hoa Airbase, Vietnam SpringerPlus 4:300 Dwernychuk LW (2005) Dioxin hot spots in Vietnam Chemosphere 60:998–999 Dwernychuk LW, Cau HD, Hatfield CT, Boivin TG, Hung TM, Dung PT, Thai ND (2002) Dioxin reservoirs in southern Vietnam: a legacy of agent orange Chemosphere 47:117–137 Elskens M, Pussemier L, Dumortier P, Van Langenhove K, Scholl G, Goeyens L, Focant JF (2013) Dioxin levels in fertilizers from Belgium: determination and evaluation of the potential impact on soil contamination Sci Total Environ 454–455:366–372 FAO/WHO (2006) Code of practice for the prevention and reduction of dioxin and dioxin-like PCB contamination in foods and feeds Rome, Food and Agriculture Organization of the United Nations and World Health Organization, Joint FAO/WHO Food Standards Programme, Codex Alimentarius Commission, CAC/RCP 62-2006 Ferrario J, Christian B, Schaum J (2007) Concentrations of polychlorinated dibenzo-p-dioxins in processed ball clay from the United States Chemosphere 67:1816–1821 Hatfield Consultants and 10-80 Committee (2006) Identification of new agent orange/dioxin contamination hotspot in southern Vietnam Report and appendices Hatfield Consultants Ltd., Page of 18 West Vancouver, BC, Canada; 10-80 Committee, Hanoi, Vietnam Hatfield Consultants and 10-80 Committee (2011) Environmental and human health assessment of dioxin contamination at Bien Hoa Airbase, Vietnam Report and appendices Hatfield Consultants Ltd., West Vancouver, BC, Canada; 10-80 Committee, Hanoi, Vietnam Hatfield Consultants and 10-80 Committee (Hatfield Consultants Ltd and Office 33) (2007) Assessment of dioxin contamination in the environment and human population in the vicinity of Da Nang Airport Report prepared for the Ford Foundation, Hanoi, Vietnam Hatfield Consultants Ltd., West Vancouver, BC, Canada; Office 33, Hanoi, Vietnam Heidelore F (2003) Chapter dioxins and furans (PCDD/PCDF) In: Fiedler H (ed) The handbook of environmental chemistry, vol 3, part O persistent organic pollutants Springer, Berlin Hermann KJ (2006) Killing me softly: how agent orange murders Vietnam’s children In: Political affairs Retrieved 25 May 2014 Hilscherova K, Kanan H, Nakata N, Hanari N, Yamashita N, Bradley PW, John MM, Taylor AB, John PG (2003) Polychlorinated dibenzo-p-dioxin and dibenzofuran concentration profiles in sediments and flood-plain soils of the Tittabawassee River, Michigan Environ Sci Technol 37:468–474 Kakimoto H, Oka H, Miyata Y, Yonezawa Y, Niikawa A, Kyudo H, Tang T, Toriba A, Kizu R, Hayakawa K (2006) Homologue and isomer distribution of dioxins observed in water samples collected from Kahokugata Lagoon and inflowing rivers, Japan Water Res 40:1929–1940 Kim YJ, Osako M (2004) Investigation on the humidification of municipal solid waste incineration residue and its effect on the leaching behavior of dioxins Waste Manag 24:815–823 Kurniawan B, Jinno K (2007) Numerical modeling for risk assessment of groundwater contamination under river and pumping effects J Environ Hydrol 15(12):1–13 Michael FM (2012) Vietnamese victims of agent orange and U.S.– Vietnam relations CRS report for congress Ministry of Environment (2009) http://www.env.go.jp/chemi/dioxin/ manual/dojo-manual/main.pdf Ozaki H, Taniguchi S, Takanami R, Shimomukai N, Hamasaki T, Sugahara M, Giri RR (2005) Quantification of dioxin in the sieved fraction of river sediment Water Sci Technol 52(9):225–233 Paul LS (2002) The history of agent orange use in Vietnam—an historical overview from the veteran’s perspective United State– Vietnam scientific conference on human health and an environment effects of agent orange/dioxins, Hanoi, Vietnam, 3–6 March Rappe C (1996) Sources and environmental concentrations of dioxins and related compounds Pure Appl Chem 68(9):1781–1789 Rappe C, Andersson R, Bergquist P-A, Brohede C, Hansson M, Kjeller L-O, Lindstrom G, Arklund S, Nygren M, Swanson SE, Tysklind M, Wiberg K (1987) Overview on environmental fate of chlorinated dioxins and dibenzofurans: sources, levels and isomeric pattern in various matrices Chemosphere 16(8/ 9):1603–1618 US Department of Defense (DOD) (2007) Presentation made at the second agent orange and dioxin remediation workshop, Hanoi, Vietnam, 18–19 June 2007 Co-sponsored by US Department of Defense and Vietnam Ministry of Defense Vietnam Embassy in Japan http://www.vnembassy-japan.gov.vn/vi/ nr070521170056/ Accessed 20 Aug 2014 Vu-Anh L, Tuyet-Hanh TT, Ngoc-Bich N, Duc-Minh N, Thanh-Ha N, Minh-Son N (2008) Knowledge, attitude and practice of local residents at Bien Hoa City–Vietnam on preventing dioxin exposure through foods Organohalogen Compd 70:000535–000538 123 18 Page of WHO (2002) Polychlorinated dibenzodioxins, polychlorinated dibenzofurans, and coplanar polychlorinated biphenyls In: Safety evaluation of certain food additives and contaminants Geneva, World Health Organization (WHO) Food Additives Series, No 48 123 Environ Earth Sci (2016) 75:18 Young AL, Andrews WB (2007) The history, science and risks of defoliants used in the Vietnam war Environ Inf Syst Res 3:121–125 ... dioxin contamination of the area as well as to understand the migration pattern(s) of dioxin in the subsurface satisfactorily In this paper, the authors attempt to characterize the mobility of. .. Concentration of dioxin is in good agreement with regulation distribution of grain size The presence of dioxins in soil samples in which distribution of grain size from coarse grain size to fine grain size... LOI The TOC in the soil samples may control the mobility of dioxins The transference and absorption of dioxins may be affected by TOC The existence of high TOC at deeper zones in the dioxin-contaminated