O R I G I N A L A R T I C L EUtilization of soil properties to understand the vertical distribution of dioxins in the soil of Bien Hoa airbase, Vietnam Thuong Huyen Dang1•Toshifumi Igara
Trang 1O R I G I N A L A R T I C L E
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: 8 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
contam-inated 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
concen-trations, 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
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 Soil Toxicity equivalency quantity (TEQ) Grain size distribution Total organic carbon (TOC) Loss on ignition (LOI)
Introduction Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) are groups of organic com-pounds 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 (Heidelore2003) 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 neuro-developmental defects in children, immunotoxicity, and changes in thyroid and steroid hormones (WHO 2002; FAO/WHO2006) 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 nat-urally due to natural events like forest/bush fires and vol-canic eruptions (Rappe et al 1987; Rappe 1996) These
& Thuong Huyen Dang
dthuyenus1982@gmail.com
1 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
2 Faculty of Engineering, Hokkaido University, Kita-ku,
Sapporo 060-8628, Japan
3 Yagai-Kagaku Co., Ltd., Higashi-ku, Sapporo 065-0043,
Japan
DOI 10.1007/s12665-015-4803-y
Trang 2chemicals are persistent organic pollutants; and because of
their inherent stability and hydrophobicity, these
com-pounds could migrate for long distances overtime
(Al-tarawned 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 DOD2007; Young and
Andrews2007) 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 (Buckingham1982) 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 (Buckingham1982; Paul2002) 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 6 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
neces-sary 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
con-taminated with this very toxic organic compound
According to the Vietnam Red Cross, ca 3 million
Viet-namese are currently affected by dioxins, including at least
150,000 children born with birth defects (Michael2012) 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 (Hermann2006)
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
degra-dation of dioxins according to depth in Bien Hoa airbase
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 dis-solved organic carbon in situ using lysimeter Although strong correlations between TOC and PCDD/Fs in soils have been reported, correlation analyses revealed no sig-nificant 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 air-base, 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 satisfac-torily 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 air-base 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 (Dw-ernychuk et al.2002; Dwernychuk 2005: Hatfield Consul-tants 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 Committee2006,2007,2011) According to the information from a present department commander and Hatfield Consultants and 10-80 Committee
Trang 3(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 ha 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
concentra-tion of TEQ in this area was 35,900 pg-TEQ/g-dw, which
is currently used as an isolated landfill site of 94,000 m3of
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 sam-ples BH03-1, BH03-2, BH03-3, and BH03-4 were col-lected at depth of 0.55, 2.5, 4.45, and 6.4 m, respectively,
at borehole BH03 Twelve undisturbed soil samples with approximately 5 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 Envi-ronment 2009) as shown in Fig.2 After drying soil sam-ples 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 N2gas to approximately 50 ll and taken in
Fig 1 The Bien Hoa airbase (achieved from Dang et al 2015 )
Trang 4(D)
(C)
(B)
(A)
elution with n-hexane
elution with n-hexane elution with 25% DCM/n-hexane elution with toluene
addition of syringe spike exchange to n-nonane volume 50μl
addition of syringe spike exchange to n-nonane volume 50μl
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
concentration
Active charcoal silicagel column chromatography
aliphatic
hydrocarbons
PCBs etc Fr.
HRGC/HRMS mono-ortho PCBs Idn and Qnt by SIM
HRGC/HRMS PCDDs, PCDFs and non-ortho PCBs Idn and Qnt by SIM
PCDDs, PCDFs non-ortho PCBs Fr.
concentration mono-ortho PCBs Fr.
with toluene for over 16hrs
removal of toluene
Removal of toluene replace to n-hexane
concentration
crude extract division
concentration
add Internal Std (clean-up spike)
13
C-2,3,7,8 located -T 4 O 8 CDD
13
C-2,3,7,8 located -T 4 O 8 CDF
13
C-Co-PCBs
sample
Soxhlet extraction
Options; treating with sulfuric acid
Fig 2 Analytical procedure flow chart (Idn and Qnt indicate identification and quantity, respectively in the figure, modified from Dang et al 2015 )
Trang 5a 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
adop-ted (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
addi-tion, 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
Amer-ican 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
suspen-sion 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 2 h
Results and discussion
TEQ and grain size
Figure3 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
dif-ferent is found with high concentration In borehole BH01,
higher concentrations of dioxin in samples BH01-1
(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 con-centrations 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 (Table1) 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
Fig 3 Grain size distribution of 12 samples and relationship with TEQ
Trang 6TEQ and TOC
The results of TOC measurements are listed in Table1
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.4 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
cor-responded 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
TEQ and LOI Figure5 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 relation-ship 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 con-tributing LOI except TOC
Conclusion Undisturbed soil samples were collected by drilling three boreholes in Bien Hoa airbase to analyze the vertical dis-tribution of dioxins and soil properties The high concen-trations 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-Table 1 Sampling depth and dioxin concentration of 12 samples
Fig 4 Relationship between TOC and TEQ Fig 5 Relationship between TEQ and LOI
Trang 7dw 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
finan-cial 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.
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