DSpace at VNU: Kinetic differences of legacy organochlorine pesticides and polychlorinated biphenyls in Vietnamese human breast milk

Chemosphere 81 (2010) 1006–1011

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Chemosphere
journal homepage: www.elsevier.com/locate/chemosphere

Kinetic differences of legacy organochlorine pesticides and polychlorinated
biphenyls in Vietnamese human breast milk
Nguyen Minh Tue a, Agus Sudaryanto b, Tu Binh Minh c, Bui Hong Nhat c, Tomohiko Isobe b, Shin Takahashi a,
Pham Hung Viet c, Shinsuke Tanabe a,⇑
a
b
c

Center for Marine Environmental Studies, Ehime University, Bunkyo-cho 2-5, Matsuyama 790-8577, Japan
Senior Research Fellow Center, Ehime University, Bunkyo-cho 2-5, Matsuyama 790-8577, Japan
Centre for Environmental Technology and Sustainable Development, Hanoi University of Science, 334 Nguyen Trai, Hanoi, Viet Nam

a r t i c l e

i n f o

Article history:
Received 2 February 2010
Received in revised form 28 July 2010
Accepted 2 September 2010
Available online 25 September 2010
Keywords:
Breast milk
Depuration

POPs
Temporal trend
Vietnam

a b s t r a c t
The present study investigated the current contamination status and evaluated several kinetic-related
features of organochlorine pesticides (OCPs) and PCBs in human breast milk collected from northern Vietnam. The variation in the levels of these contaminants was found to be strongly associated with total lactation time and dietary habits. OCPs exhibited the characteristics of steadily declining compounds: the
overall levels of DDTs and HCHs in the population decreased with a half-time of only 5 years and it
can be suggested that OCPs depurated relatively fast with breastfeeding (5% per month). PCBs were
slower in both regards, with a temporal decrease half-time of 12 years and a suggested depuration rate
via breastfeeding of 2.5% per month, indicating that the exposure level was still high relative to the
human body burden. It was found that the PCB exposure levels of infant from breastfeeding exceeded
the reference dose, and this situation may continue for the next two or three decades. Knowledge of these
kinetic-related characteristics not only is useful for risk assessment and prediction of future trends of legacy contaminants but also may provide insight regarding similar kinetic processes of emerging persistent
pollutants.
Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction
Worldwide production and intensive use of organochlorine
compounds (OCs), including organochlorine pesticides (OCPs) and
polychlorinated biphenyls (PCBs), has resulted in their widespread
contamination. These compounds have received considerable
attention in the late decades of the last century with regard to their
persistence, bioaccumulative characteristics, long-range transport
and long-term toxic effects to human (ATSDR, 2000, 2002). Despite
the global declining trends of OCs in recent years (Norén and Meironyté, 2000; Schecter et al., 2005; Jaraczewska et al., 2006; Kunisue et al., 2006; Lignell et al., 2009), elevated levels of OCPs were
still observed in human breast milk from Asian developing countries due to a later phase-out than in developed countries, suggesting further monitoring is necessary (Kunisue et al., 2004; Minh
et al., 2004; Sudaryanto et al., 2006; Subramanian et al., 2007). Vietnam was reported to be among the countries with the highest levels
of dichlorodiphenyltrichloroethane and its metabolites (DDTs) and
unlike other Asian developing countries also had relatively high

levels of PCBs (Minh et al., 2004) because of the extensive use of
⇑ Corresponding author. Tel./fax: +81 89 927 8171.
E-mail address: (S. Tanabe).
0045-6535/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.chemosphere.2010.09.013

OCPs in agriculture and imported PCB-contaminated transformer
oil before their ban in 1995 (Minh et al., 2008).
Breast milk is a convenient matrix for monitoring persistent organic pollutants (POPs) in human. The advantages include simple
and non-invasive sample collection, suitability for determination
of lipophilic POPs due to the relatively rich lipid content, and relevance with regard to the exposure of breastfeeding infants, who are
at the early stage of development and vulnerable to toxic contaminants. However, due to the transfer of the mother’s body burden to
the infant through breastfeeding (Carrizo et al., 2007; Shen et al.,
2007; Trapp et al., 2008), the contamination levels in female donors
may vary with lactation time. Indeed, the levels of legacy POPs such
as OCs in mother’s milk have been reported to decrease with the
number of children (Minh et al., 2004; Fürst, 2006; Kunisue et al.,
2006; Sudaryanto et al., 2006). Recent monitoring studies have
been designed to avoid the variation by sampling milk from only
primiparae within 3–8 weeks post-partum (WHO, 2005). With this
approach, it is difficult however to make a direct comparison with
data from past references and the survey is also more difficult to
coordinate, especially in developing countries where health assessment frameworks are scarce. There have been studies aiming to
quantify the variation due to lactation, either by temporal monitoring of the compounds in individual donors (Schecter et al., 1998;


N.M. Tue et al. / Chemosphere 81 (2010) 1006–1011

Hooper et al., 2007) or by using mathematical models (Trapp et al.,
2008). Together, these studies indicate that the observed depuration kinetic of POPs during the lactation period varies for different

compounds and suggest an important influence of human intake
level. This influence may explain the lack of significant difference
in the breast milk levels of emerging POPs such as polybrominated
diphenyl ethers (PBDEs) between primiparae and multiparae
mothers (Schecter et al., 2003; Tue et al., 2010). Consequently,
while the depuration kinetics of legacy and emerging POPs through
breastfeeding may be similar, investigating the former has the
advantage because their human intake levels are low relative to
the body burden.
The present study investigated the current contamination status of legacy OCPs and PCBs in northern Vietnamese human breast
milk and assessed their different kinetic-related characteristics,
specifically the relationship between OC levels and lactation time
as well as the connection of this relationship to the declining trend
of the compound. An up-to-date assessment of infant health risk
from OCs in mother’s milk was also conducted.

2. Material and methods
2.1. Sample collection
Breast milk samples (n = 33) were collected between August
and September 2007 from Hanoi, the capital city of Vietnam and
its surrounding suburban and rural areas. All donors were nonsmokers, non-drinkers and appeared healthy. The samples were
collected by the donors or with the help of a midwife and placed
in solvent-pre-cleaned analytical-grade glass containers with Teflon-lined screw caps and kept in gel ice. Informed consents were
obtained from all donors. Questionnaires were also used to acquire
information on age, height and weight measurements, number of
deliveries, detailed history of breastfeeding, occupation and dietary
habit. General information on the donors are summarised in
Table 1. After collection the samples were kept with ice and sent
within 8 h to the Centre for Environmental Technology and
Sustainable Development (Hanoi University of Science, Hanoi,

Vietnam) to store at À20 °C. The frozen samples were later
air-transported with gel ice to the Environmental Specimen Bank
(es-BANK, Ehime University, Japan) and stored at À25 °C until
analysis.

Table 1
General characteristics of the donors of breast milk.
Parameters

Urban (n = 14)

Suburban/rural
(n = 19)

Age (year)
Weight (kg)
Height (cm)
BMI (kg mÀ2)

23–35 (28.0)
46–62 (53.0)
155–167 (160)
16.4–25.4
(19.9)
1–2 (1.6)
0.57–12 (4.5)
4.5–25 (10.0)

18–35 (25.5)
40–52 (45.0)

150–159 (155)
16.7–21.6 (19.1)

4–14 (8)
2–14 (6)
1–7 (3)
2.3–7.3 (4.4)
86% office
worker
14% housewife

0–14 (6)
0–8 (3)
0–1 (0)
1.2–6.4 (3.1)
37% farmer, 26%
housewife
37% other

Number of children
Nursing period (last child, month)
Total nursing period (all children,
month)
Food consumption (servings per
week)
Meat and meat products
Fish
Milk and dairy products
Breast milk lipid content (%)
Occupation

Values between parentheses are medians.

1–4 (1.8)
0.43–12 (7.3)
1.3–57 (18.6)

1007

2.2. Chemical analyses
Analysis of OCs followed the method described by Minh et al.
(2004). Briefly, approximately 10 g of sample was applied to a
glass column containing 10 g of pre-cleaned diatomaceous earth
(EXtrelutÒ NT, Merck, Germany), kept for 30 min and then extracted with 250 ml diethyl ether. The extract was dried over
anhydrous sodium sulphate then concentrated and solvent-exchanged into hexane. A portion of this extract (25% in volume)
was used for gravimetric determination of lipid content. The
remaining extract was subjected to gel permeation chromatography (packed Bio-Bead S-X 3, Bio-Rad Laboratories, USA) for lipid
removal using a dichloromethane (DCM)/hexane mixture (1:1
v/v) as eluant. The lipid-free extract was then concentrated and
passed through a 12 g of activated Florisil (Florisil PR, Wako,
USA) packed in a glass column for final clean-up and separation.
The first fraction, eluted with hexane, contained PCBs, hexachlorobenzene (HCB), trans-nonaclor and p,p0 -DDE while the
second fraction, eluted with 20% DCM in hexane, contained hexachlorocyclohexane isomers (HCHs), chlordane compounds (CHLs:
oxychlordane, trans- and cis-chlordanes, trans- and cis-nonachlors) and DDTs (p,p0 -DDT, -DDE and -DDD).
Quantification with external standards was carried out using a
GC-ECD (Agilent 6890 series) equipped with an auto-injector (Agilent 7683 series) and a DB-1 fused silica capillary column (0.25 mm
i.d.  0.25 lm film thickness  30 m length, J&W Scientific, USA).
The external standard for PCBs was an equivalent mixture of 62
PCB congeners (BP-MS, Wellington Laboratories, Canada). A procedural blank was analysed simultaneously with every series of five
samples to check for interference and contamination. Recoveries

throughout the procedure (n = 5) were 99.1 ± 5.5% for DDTs,
95.7 ± 5.5% for PCBs, 94.1 ± 3.7% for HCHs, 92.6 ± 7.2% for HCB
and 98.6 ± 6.5% for CHLs. Relative standard deviations (n = 3) for
the analysis of a pooled milk sample were less than 15% for HCHs
and less than 10% for other OCs. Further details on quantification
and quality assurance have been described previously (Minh
et al., 2004). Concentrations were not recovery-corrected and were
expressed on a lipid weight basis unless otherwise specified.
2.3. Data analyses
The Wilcoxon rank sum test was used for assessing whether the
contaminant levels between groups were significantly different.
For this analysis, non-detectable levels were set to zero. Possible
associations between levels of contaminants and sociodemographic
parameters were examined using multiple linear regressions.
Compounds detected in less than 80% of the samples were not
examined. Non-detectable levels were set to half of the detection
limit and then all levels were log-transformed (base 10) to bring
the data distribution closer to normality. The parameters used as
independent variables included age, body mass index (BMI), total
lactation time, and consumption of food from animal origin (total
frequency for meat, fish and dairy products). Parity was not
included in the models due to a strong correlation with lactation
time (Spearman’s q = 0.86, p < 0.001). Parameters with a p-value
of more than 0.1 were removed from the model; those with
p < 0.05 were considered as having significant relationship with
level of the contaminant. All calculations were performed using
the statistical software package R (R Foundation for Statistical
Computing, Vienna, Austria) version 2.9.2.
First-order kinetics were assumed for both the depuration of
OCs in individual mother’s milk through breastfeeding and the

long-term decline of OCs in the population. This kinetic can be expressed using the following logarithmic equation:

log10 C 2 ¼ log10 C 1 À kt

ð1Þ


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N.M. Tue et al. / Chemosphere 81 (2010) 1006–1011

where C1 and C2 are the OC levels at the beginning and the end of
the time interval t, respectively and k is the first-order decrease rate
constant. A decrease half-time can be derived as tdec1/2 = log102/k.
3. Results and discussion
3.1. Contamination levels and patterns
DDT compounds were the predominant organochlorine contaminants in Vietnamese human breast milk. The total levels of
p,p0 -DDT and its metabolites were an order of magnitude higher
than total PCB levels (Table 2). Other OCPs followed a pattern of
HCHs > HCB > CHLs. The levels of CHLs were low; oxychlordane,
trans- and cis-nonachlor were not detected in 27%, 39% and 21%
of the samples, respectively. These results may reflect the usage
pattern of OCPs in Vietnam, as the usage of HCB and CHLs was very
limited compared with other countries (Minh et al., 2004).
As seen in Table 2, donors living in the city had significantly
higher levels of OCs than those living in suburban and rural areas.
Specifically, only p,p0 -DDE, b-HCH and several highly chlorinated
PCB congeners (CB-138, -153 and -180) accumulated at substantially higher levels in urban donors. These compounds are the predominant and more persistent of their respective groups. Thus
their elevated relative abundance suggests a long accumulation
history rather than a recent exposure. Indeed, the proportions of

the main ingredients of pesticides technical mixtures, p,p0 -DDT

and a-HCH, within their groups of compounds were only 1.3–
8.5% (median 3.1%) and <1–8.0% (median <1%), respectively in
the urban donors. These values were as low as those reported in
the countries where the bans on these pesticides were effectively
implemented such as in Japan (Kunisue et al., 2006). The ratios of
p,p0 -DDT/DDTs and a-HCH/HCHs in the suburban/rural donors
were slightly higher (2.1–23.6%, median 6.1% and <1–28%, median
3.3%, respectively), probably related to more recent exposure to
technical mixtures of these pesticides used in agriculture in the
suburban/rural areas. The higher accumulation of OCs in urban donors may be explained by their richer diets and shorter total lactation times (Table 1), as levels of the contaminants were found to
increase with the consumption of food from animal origin and decrease with the duration of lactation (Table 3). These two factors
represented respectively the main intake and depuration pathways
of OCs, as discussed in the subsequent section.
3.2. Influence by lactation time and other factors
Significant relationships between levels of several OC compounds and sociodemographic parameters were found using multiple linear regressions (Table 3). The logarithm (base 10) of the
levels of p,p0 -DDE, p,p0 -DDT, b-HCH, HCB, CB-138, -153 and -180
correlated negatively with total lactation time. This correlation
was also significant in univariate regressions (R2 > 0.3, p < 0.005)
with an exception of p,p0 -DDT, indicating that the depuration

Table 2
Concentrations (ng gÀ1 lipid wt.) of organochlorine pesticides, indicator and total PCBs in human breast milk collected from Hanoi and surrounding areas.
Compound

DDTs
p,p0 -DDT
p,p0 -DDE
p,p0 -DDD

RDDTs

Urban

Suburban/rural

Median

Range

Median

Range

% Detected

pa

20
(27)
720
(1000)
1.8
750
(1100)

14–70
(19–79)
370–1300

(840–3800)
0.96–9.4
390–1300
(890–3900)

14
(23)
220
(510)
2.1
240
(540)

4.8–53
(6.6–100)
38–690
(170–1100)
0.35–15
46–710
(190–1200)

100

0.014
(0.057)
<0.001
(<0.001)
0.439
<0.001
(<0.001)

ND
18
(35)
ND
18
(35)
3.0
(4.3)

ND–0.39
6.0–48
(8.3–67)
ND
6.0–48
(8.3–67)
1.6–4.4
(2.1–9.6)

0.2
5.1
(15)
0.055
5.8
(16)
1.8
(3.5)

ND–2.5
1.9–17

(4.0–42)
ND–1.8
2.1–17
(4.2–42)
ND–5.6
(ND–14)

64
100

0.51
0.38
0.20
0.96

0.26–1.2
ND–0.94
0.10–0.32
0.42–2.0

0.26
0.097
0.13
0.40

ND–1.5
ND–0.56
ND–0.39
0.14–2.0

73
61
79

0.009
0.110
0.021
0.007

1.1
0.16
0.40
5.7
8.4
(11)
8.1
(11)
3.6
(5.0)
47
(54)

0.48–6.3
ND–1.3
0.12–3.2
2.4–13
3.7–13
(4.1–18)
3.9–11
(4.3–17)

1.9–5.0
(2.1–9.8)
22–84
(23–89)

1.8
0.20
0.36
4.2
5.1
(7.0)
4.7
(6.7)
1.6
(2.4)
33
(38)

ND–32
ND–2.8
ND–0.96
ND–7.7
1.2–9.7
(2.9–17)
1.2–9.7
(2.5–17)
0.36–4.0
(1.0–7.7)
6.7–77
(11–95)

94
48
97
94
100

0.129
0.114
0.314
0.012
0.003
(0.010)
0.002
(0.008)
<0.001
(<0.001)
0.022
(0.025)

100
100

HCHs

a-HCH
b-HCH

c-HCH
RHCHs

HCB
CHLs
Oxychlordane
trans-Nonachlor
cis-Nonachlor
RCHLs
PCBs
CB-28
CB-52
CB-101
CB-118
CB-138
CB-153
CB-180

R62PCBs

45

97

100
100

Values between parentheses were obtained by adjusting concentrations for lactation time: log10Cadjusted = log10Cunadjusted À b lactation (see models in Table 3).
ND: not detected.
a
p-values of the Wilcoxon test comparing urban and suburban groups.

0.001

<0.001
(0.006)
0.002
0.001
(0.006)
0.047
(0.251)


N.M. Tue et al. / Chemosphere 81 (2010) 1006–1011
Table 3
Coefficients (b) and p-values of sociodemographic parameters in linear models of
P
contaminant concentrations log10C = b0 + bi parameteri.
Parameters

Age

Lactationa

Dietb

Model

p,p -DDE

b
p

0.0263

0.071

À0.0199
<0.001

0.0195
0.006

R2 = 0.653
p < 0.001

p,p0 -DDT

b
p

0.0303
0.039

À0.0085
0.035

NS

R2 = 0.265
p = 0.017

b-HCH

b

p

0.0401
0.002

À0.0203
<0.001

0.0076
0.023

R2 = 0.782
p < 0.001

HCB

b
p

NS

À0.0192
0.012

NS

R2 = 0.386
p = 0.012

CB-138

b
p

NS

À0.0115
0.001

0.0142
0.011

R2 = 0.480
p < 0.001

CB-153

b
p

NS

À0.0113
0.001

0.0154
0.007

R2 = 0.477
p < 0.001

CB-180

b
p

NS

À0.0138
<0.001

0.0196
0.001

R2 = 0.569
p < 0.001

0

NS: non significant, p > 0.1.
a
Lactation time, in months.
b
Consumption of food from animal origin (total frequency for meat, fish and
dairy products, in servings per week).

through breastfeeding plays an important role in the variation of
these POPs levels in northern Vietnamese women. The depuration
of lipophilic compounds from breast milk has been assumed to follow a first-order kinetic (Trapp et al., 2008) and the depuration rate
can be derived experimentally by monitoring temporally the levels

in individual donors. Although such an approach was not attempted in this study, the regression coefficients b of lactation
time (Table 3) could be interpreted approximately as general
first-order depuration rate constants (base 10, Eq. (1)) of OCs in
the study cohort. Despite the modest sample size, the regression
results obtained were fairly consistent across the compounds analysed. The b coefficients of lactation time in the regression models
of OCP compounds such as p,p0 -DDE, b-HCH and HCB were nearly
identical (approximately À0.02 monthÀ1) regardless of the different concentration ranges (Table 3). This value is equivalent to a
depuration rate of 5% per month or a half-time of 15 months. It
is noteworthy that these coefficients were twofold lower in abso-

Log adjusted concentration (ng g−1 lipid)

3.5
DDE
β−HCH
CB153

3.0

2.5

2.0

1.5

1.0

0.5

0.0

0

10

20

30

40

50

60

Lactation time (month)
Fig. 1. Relationship between total lactation time and levels of p,p0 -DDE, b-HCH and
CB-153. Organochlorine levels were adjusted for age and diet habit.

1009

lute value in the models of highly chlorinated PCB congeners,
equivalent to a depuration rate of 2.6% per month. This slower decrease (Fig. 1) suggests that the current intake levels of PCBs, relative to the human body burden, may be higher than those of OCPs.
Our results are in agreement with those obtained in a depuration
study by Schecter et al. (1998). The authors observed a decrease
in levels of p,p0 -DDE, HCB and PCBs in an American mother’s milk
over a 38 month period of breastfeeding by respectively 81%, 92%
and 78%, which would correspond to a first-order rate of 4%, 6%
and 4% per month. The slow depuration rate of highly chlorinated
PCBs derived in the present study is closer to those of emerging
POPs such as polybrominated diphenyl ethers (2–3%), calculated

recently by Hooper et al. (2007) in American breast milk, suggesting continuing exposure to PCBs in Vietnam. This exposure may be
considerable for lower-chlorinated PCBs (CB-28, -52, -101, -118),
as the levels of these congeners did not correlate with lactation
time. The low absolute value of b coefficient of lactation time in
the model of p,p0 -DDT may also be explained by a more recent
exposure in suburban/rural residents.
Although the consumption rate of food from animal origin was
introduced in the regression models only as a pseudo-quantitative
parameter to simulate the influence of the variation in dietary intake, significant positive correlations were found between this
parameter and the levels of p,p0 -DDE, b-HCH and highly chlorinated PCBs (Table 3), suggesting diet as the major exposure pathway for these compounds. On the other hand, the lack of such
correlations in the case of p,p0 -DDT and lower-chlorinated PCBs
may be explained by non-dietary exposure, such as direct exposure
to pesticides containing DDT or inhalation of air-borne PCBs.
The influence of long-term accumulation was observed only in
the models of p,p0 -DDT and b-HCH which showed significant positive correlations with age of the donor whereas such a relationship
was either weakly significant for p,p0 -DDE (p = 0.071) or absent for
PCBs (Table 3). Possible explanations for this lack of correlation
may include a generally longer nursing period lowering OC levels
in older women or a recent and continuing exposure in case of
PCBs. BMI did not have any significant influence on contaminant
concentrations (details not shown).
3.3. Temporal trends
In order to assess the temporal trends of OC levels in human
breast milk from Hanoi, the results obtained in this study were
compared with those from the survey in 2000 by Minh et al.
(2004) who employed the same analytical methods to investigate
primiparae and multiparae living in urban Hanoi and having a similar average number of children. The overall arithmetic mean levels
of all OCs were found to decrease: DDTs from 2100 to 810 ng gÀ1
lipid wt., HCHs from 58 to 22 ng gÀ1 lipid wt., HCB from 3.9 to
2.9 ng gÀ1 lipid wt., CHLs from 2.0 to 1.1 ng gÀ1 lipid wt. and PCBs

from 74 to 49 ng gÀ1 lipid wt. in a 7-year span. Assuming an exponential decline of POPs following a first-order kinetic (Norén and
Meironyté, 2000), the decrease half-times tdec1/2 of DDTs, HCHs
and PCBs during this period were 5, 5 and 12 years, respectively.
These results are consistent with the declining trends of DDTs
and PCBs in human milk reported in southern Vietnam and Europe
towards the end of the 1990s (Table 4). The slower decrease of PCB
levels in human, which peaked around the early 1980s in the case
of European countries (Jaraczewska et al., 2006; Polder et al., 2008)
may be explained by a late phase-out of these chemicals and their
continuous release from old or waste electrical and electronic
equipment (ATSDR, 2000). However, the decline of PCBs may be
accelerating in recent years, as suggested by the shorter tdec1/2 reported in Swedish breast milk and river sediment in southern Vietnam (Table 4). By contrast in case of on-going contamination, the
temporal decrease of POPs levels can be slower, and DDTs have


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N.M. Tue et al. / Chemosphere 81 (2010) 1006–1011

Table 4
Declining half-times (year) of DDTs and PCBs in different countries.
Country

Period

Matrix

DDTs

PCBs

References

Poland
Sweden
Sweden
USA (Great Lakes)
Vietnam (south)
Vietnam (south)
Vietnam (north)

1973–2004
1967–1997
1996–2006
1994–2005
1987–2001
1990–2004
2000–2007

Human milk
Human milk
Human milk
Human serum
Human milk
River sediment
Human milk

7.5
6

15.2
14
8.5
12.4
11–18
7
12

Jaraczewska et al. (2006)
Norén and Meironyté (2000)
Lignell et al. (2009)
Knobeloch et al. (2009)
Minh et al. (2004)
Minh et al. (2008)
This study

been reported to decline as slow as PCBs in the populations living
around the Great Lakes (Table 4). Together these data suggest a
steady decline in the contamination levels of DDTs as opposed to
a recent exposure to PCBs in the Vietnamese population.
3.4. Potential health implication for breastfeeding infants
OCs in mother’s milk represent a potential hazard for breastfeeding infants, who are in their early stages of development. Postnatal exposure to PCBs has been associated with altered cognitive
function and motor development during childhood (Jacobson et al.,
1990; Walkowiak et al., 2001; Vreugdenhil et al., 2002). Exposure
to elevated concentrations of OCs including DDTs, HCB and PCBs
in breast milk was also suggested to weaken the immune system
of breastfed babies (Dewailly et al., 2000). It is important to note
that a high concentration of POPs in breast milk also implies a significant prenatal exposure. In the scope of the present study only
the risk for infants by postnatal exposure to contaminants in
mother’s milk was assessed. The daily intake doses (DIs) of OCs

were estimated based on the assumption that an infant weighs
5 kg and consumes daily 700 g breast milk in average (Oostdam
et al., 1999). OC levels were adjusted to the first month of nursing
the last child. The DIs of DDT, total PCBs, total HCHs, HCB and total
CHLs were then compared with the corresponding reference doses
for human (RfDs), of 500 (ATSDR, 2000), 30 (ATSDR, 2002), 300,
270 and 50 ng kgÀ1 dÀ1 (Oostdam et al., 1999), respectively. These
values were derived from the no/lowest observed adverse effect
level doses in animal studies by applying uncertainty factors for
extrapolation from animals to human and for human variability.

1000

Estimated Daily Intake (ng kg−1 d−1)

500
200
100
50
20
10
5

11.4
6
5
5

As shown in Fig. 2, the majority of DI estimates of DDT and
HCHs were below their respective RfDs. Only with the highest levels in breast milk, intake levels were close to or over the threshold

levels. The DIs of HCB and CHLs were also lower than their RfDs by
at least one order of magnitude. Therefore it can be inferred that
the current health risk for Vietnamese infants related to OCPs in
mother’s milk is generally low. On the other hand the majority of
DI estimates of PCBs were higher than the RfD, up to a factor of
17, suggesting significant risk. The difference between this and
the previous risk assessment (Minh et al., 2004) is the use of the
highly conservative threshold level for PCBs, recommended by
the ATSDR, as reference in the present study; this level is considerably lower than the RfD of 1000 ng kgÀ1 dÀ1 used in the previous
study. On account of the short temporal decrease half-times tdec1/2
of DDTs and HCHs, their intake level range can be expected to
decrease to below the RfDs 5 or 6 years later. However, it would
take approximately 30 years for the median PCB intake levels to
reach the ATSDR’s threshold level, assuming the current tdec1/2 of
12 years, or 18 years if the decrease rate of PCB levels in the
Vietnamese population can be comparable with the recent rate
in sediments (tdec1/2 = 7 years).
4. Conclusions
The present study reported the current contamination status
and distinct kinetic characteristics of organochlorine pesticides
and PCBs in human breast milk in northern Vietnam. OCPs were
in a steady temporal decline and seemed to depurate from
mother’s milk with a rate of approximately 5% for every month
of lactation. Owing to possible continuing exposure, the depuration
by lactation of PCBs as well as their temporal decline were both
approximately twofold slower than in case of OCPs. In view of
some relatively high intake levels of DDTs, HCHs and especially
PCBs estimated for breastfeeding infants, these compounds still
need further monitoring in the future. The strong influence of lactation time on the levels of legacy POPs reaffirms the importance of
sampling from primiparae mothers during the early months after

delivery for a more relevant assessment of contamination status.
Nevertheless, the effect may be significant only in the case of
declining compounds and can be compensated by adjusting the
levels for lactation time. It is also suggested that knowledge of
the rate of POPs depuration through lactation may provide useful
information on the declining trend of the compounds in the population, as the two processes were found to be kinetically related.

2

Acknowledgements

1
0.5
RfD

0.2
DDT

HCHs

HCB

CHLs

PCBs

Fig. 2. Comparison of the estimated daily intake of organochlorine compounds and
their respective reference doses.

This study was partly supported by Grants-in-Aid for Scientific

Research (S) (No. 20221003) from Japan Society for the Promotion
of Science (JSPS) and the Waste Management Research Grants
(K2062, K2129 and K2121) from the Ministry of the Environment,
Japan, grants from Global COE Program and program ‘‘Promotion of
Environmental Improvement for Independence of Young Researchers” under the Special Coordination Funds for Promoting Science


N.M. Tue et al. / Chemosphere 81 (2010) 1006–1011

and Technology from the Japanese Ministry of Education, Culture,
Sports, Science and Technology (MEXT).
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.chemosphere.2010.09.013.
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