Arch. Environ. Contam. Toxicol. 50, 153–165 (2006)
DOI: 10.1007/s00244-005-7001-1
Organochlorine Insecticides in Mudflats of Hong Kong, China
H. L. Wong,1 J. P. Giesy,1,2 P. K. S. Lam1
1
Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong
Zoology Department, National Food Safety and Toxicology Center and Center for Integrative Toxicology, Michigan State University, East Lansing,
Michigan 48824-1311, USA
2
Received: 4 January 2005 /Accepted: 14 May 2005
Abstract. Organochlorine (OC) insecticides were measured in
different environmental compartments (including seawater,
sediment, and biota) at six sites within the Mai Po Marshes
Nature Reserve (MPMNR) and at one site in A Chau (AC) in
Hong Kong in June 2002 (wet season) and January 2003 (dry
season). MPMNR is a Wetland of International Importance
(Ramsar site) situated in the western part of Hong Kong,
whereas AC is a relatively remote island in Starling Inlet on
the eastern side of the New Territories of Hong Kong. Generally, concentrations of OC insecticides in water, sediment,
and biota were greater at MPMNR than at AC. Hexachlorobenzene, dichloro-diphenyl-trichloroethane, and hexachlorocyclohexanes were detected in all samples collected from
MPMNR. Preliminary risk assessments were performed by
comparing the measured concentrations of OCs in different
environmental compartments with the corresponding guidelines promulgated by various environmental protection
authorities. Concentrations of some OCs in sediments from
certain locations in MPMNR were consistently greater than
their corresponding sediment guideline values. These results
suggest that the sediment OC concentrations in the sediments
of MPMNR might pose a risk to aquatic organisms. Despite
this, concentrations of OCs in biota samples were much lower
than the relevant guideline values promulgated by government
agencies to protect the health of human consumers. It is postulated that the management practices adopted at MPMNR
have been effective in limiting the bioaccumulation window
(duration) for OCs. This situation may have been aided by a
frequent exchange of water between the tidal shrimp ponds at
MPMNR and the open sea, again attributable to management
practices. The low-cost maintenance practices adopted at
MPMNR may potentially be applicable to wetlands in other
southeastern Asian countries, thus allowing sustainable fishery
production and wildlife conservation.
Organochlorine (OC) insecticides have been widely used in
China. Although most applications have ceased, the residues of
OC insecticides still persist in many environmental compartCorrespondence to: P. K. S. Lam; email: bhpksl@cityu.edu.hk
ments in the southern region of China. In the Pearl River Delta,
it has been estimated that OC pesticide use was approximately
76,000 to 100,000 tons/y from 1972 to 1982 (Hua and Shan
1996). These OC insecticides, which have leached into the
Pearl River (Zhang et al. 2002), have resulted in relatively
great historical concentrations in water birds and sediments
from the mudflats and mangrove stands at the Mai Po and
Inner Deep Bay (ID) Ramsar sites of Hong Kong (Liang et al.
1999; Zheng et al. 2000; Connell et al. 2003). Discharge from
the highly polluted Shenzhen River and its catchment is another source of pollution to Deep Bay (Hong Kong Environmental Protection Department 2003). These compounds are
classified by the United Nations Environment Program as
being of ‘‘great concern’’ because of their persistence, toxicity, and wide distribution in the southeast Asian region
(United Nations Environmental Programme [UNEP]
2003). Because of the positioning of the ecologically
important Ramsar site near the heavily industrialized area
of southern China and the fact that China is a signatory to
the Stockholm Convention, it was necessary to prepare an
inventory of the current status of contamination at the site.
Situated within the Mai Po and ID Ramsar sites, the Mai Po
Marshes Nature Reserve (MPMNR) occupies an area of
380 ha and is composed of five main wetland habitat types:
mangroves, fishponds (FPs), reed beds, mudflats, and intertidal
shrimp ponds. Intertidal shrimp ponds (or gei wais [GWs]) are
established with flooding at selected high tides through regulation by a single sluice, which facilitates the material exchange with the open sea area. The central area of a GW is
mainly covered by mangroves and reeds and is an important
habitat for water birds. To counter pollution stress, the management authority of the MPMNR—the World Wildlife Fund
for Nature Hong Kong (WWFHK)—performs various lowcost traditional practices to maintain the habitat.
The present study was conducted to determine the current
status of OC contamination and assess the efficiency of these
low-cost management practices, especially regarding their
potential for decreasing hazards to humans who might consume fish from these areas. In addition, preliminary risk
assessment was conducted by comparing the measured OC
concentrations in water, sediment, and fish with relevant
guidelines promulgated by various jurisdictions to estimate the
potential ecologic risk of OCs to wildlife at MPMNR.
H. L. Wong et al.
154
Fig. 1. Map showing the Mai Po and AC study sites. Sampling locations in the Mai Po area: 1 = FPs; 2 = GWs; 3 = the gate of GWs; 4 = MM;
5. mudflat near the NB; 6. ID. Dotted lines represent the tidal flushing direction. FPs = fishponds; GWs = gei wais; NB = near the bird-watching
blind; ID = Inner Deep Bay; MM = middle part of the mangrove.
Materials and Methods
Seawater, sediment, and biota (including polychaetes, shrimp, and
fish) were collected from six sites in MPMNR and one site in A Chau
(AC) in June 2002 and January 2003 (Fig. 1 and Table 1). The sampling periods corresponded to the wet and dry seasons as defined by the
Hong Kong Observatory based on rainfall records (Hong Kong
Observatory 2003). The six sampling sites in MPMNR were selected to
represent different hydrological characteristics. The outer part of the
Mai Po marshes (i.e., ID [location no. 6] and near the bird-watching
blind [NB; location no. 5]; Fig. 1) is heavily influenced by tidal
flushing, whereas the inner part (i.e., location nos. 1 through 4) is
predominantly affected by artificial flushing of GW water. Two seawater samples were analyzed from each site. No water samples were
collected from ID during the dry season. Four surface sediment samples were collected with a stainless steel grab. Large objects such as
leaves, rubbish, and rocks were removed by hand. Twenty g sediments
were weighed and freeze-dried for subsequent OC analysis. Dichlorodiphenyl-trichloroethane and its metabolites (DDTs), hexachlorocyclohexanes (HCHs a, b, and c), and 11 cyclodiene insecticides—
including chlordanes (a and c), endosulfans (I and II), aldrin, dieldrin,
endrin, heptachlor, kepone, methoxychlor, and mirex—were measured
using previously described methods (Khim et al. 1999; Snyder et al.
2001). Concentrations of OC insecticides were measured in composite
samples of surface sediments. Dried samples were weighed and then
ground with a precleaned mortar and pestle. Total organic carbon
(TOC) was determined using a Perkin Elmer 2400 Series II CHNS/O
analyzer (Perkin Elmer, CT) after acidification for carbonate removal
(National Oceanic and Atmospheric Administration 1993). Biota
samples (n = 5) were collected from the Mai Po mudflat (near the NB
and GWs) and AC. Polychaetes, shrimp, and fish were collected from
both sites subject to their availability. The shrimp (Metapenaeus ensis)
from Mai Po were only available for collection during the wet season.
Mudskippers (Boleophthalmus boddaerti) were collected from the
mudflat near NB in both the wet and dry season. Three fish species—
Mugil cephalus (flathead mullet), Mylio macrocephalus (black porgy),
and Tilapia zilla (redbelly tilapia)—were collected from GWs during
the wet season. Two unidentified species of Gobiidae and the bivalve
Cyclina orientalis were collected from AC in both seasons. Shrimp
(Acetes spp.) and other species of fish were collected from AC during
the wet season only (Table 1).
For the analysis of biota samples, whole-body tissues were completely homogenized, and 20 g homogenized tissue was used for OC
determination. The samples were freeze-dried and mixed with 3x
volume precleaned sodium sulfate. Dried samples were Soxhlet extracted for 16 hours using 400 mL distilled 75% dichloromethane
(Tedia) with hexane (LabScan, Thailand). Sediment extracts were
treated with activated copper to remove sulfur. All extracts were
concentrated to 1 mL by rotary evaporation at approximately 40C.
Twenty L seawater was filtered through precleaned 0.5-lm glass fiber
filters (GC-50; Toyo, Japan). The filters were Soxhlet extracted in a
manner similar to that for sediments. The remaining filtrates were
extracted three times with 1 L dichloromethane. The lipid contents of
biotic samples were determined gravimetrically. Extracts were passed
through 10 to 12 g activated Florisil (60- to 100-mesh size; Sigma) for
the removal of impurities and fractionation (Khim et al. 1999).
Polychlorinated biphenyls (PCBs), dichlorodiphenyldichloroethane
(DDDs), dichlorodiphenyldichloroethylene (DDEs), and a- and bHCHs were eluted in fraction 1 by 80 to 100 mL hexane. Other OC
pesticides and PCB 169 were eluted in fraction 2 by 100 mL dichloromethane and hexane (1:4). The extracts were concentrated by
rotary evaporation and blow-down with high-purity nitrogen gas. OC
insecticides were quantified using a Hewlett Packard 5890 series II
gas chromatograph equipped with an 63Ni electron-capture detector. A
fused silica capillary column (60 m · 0.25 mm diameter) coated with
DB-5MS (J &W Scientific, Folsom, CA) at 0.25-lm film thickness
was used. The column oven was programmed from an initial temperature of 100C with a 3-minute hold time to 210C at a rate of
25C/min and then ramped at a rate of 1C/min to 270C with a final
hold time of 60 minutes. The injector and detector temperatures were
maintained at 250C and 280C, respectively. Accuracy and precision
were determined by use of matrix spikes, matrix spike duplicates, and
analysis of standard reference materials (SRM-2978, National Institute of Standards and Technology). Method detection limits
(MDLs) were determined as the concentrations of spiked standards in
various environmental samples that give rise to a peak with a signalto-noise ratio of 3 (United States Environmental Protection Agency
[USEPA] 1996). Procedural blanks were included to check for potential contamination.
Statistical Analysis and Calculations
Concentrations in sediment and biota samples were compared among
locations and seasons using nonparametric Mann-Whitney U and
155
Organochlorine Insecticides In Mudflats of Hong Kong, China
Table 1. Details of samples collected from Mai Po and AC during 2002 and 2003
Location and matrix
N
Collection date
Body length (cm)
Mai Po (wet season)
Seawater
Plankton
Sediment
Polychaetes
Shrimp
Mudskipper
2
2
4
4
4
4
6/15/2002
6/15/2002
6/15/2002
6/16-18/2002
6/17/2002
6/20/2002
NA
NA
NA
0.5–6.1
12.3–13.5
12.1–12.9
20.0
20.0
20.0
20.0
9.4
13.4
€
€
€
€
€
€
0.1 L
0.1 L
0.01 g
0.01 g
1.3 g
1.5 g
Collected in six sampling points
Filter 20 L seawater with 63-lm pore size net
Collected in six sampling points
Scientific name: unknown (pooled sample)
Scientific name: Metapenaeus ensis
Scientific name: Boleophthalmus boddaerti
Mai Po (dry season)
Seawater
Plankton
Sediment
Polychaetes
Mullet
Black porgy
Redbelly tilapia
Mudskipper
2
2
4
4
4
4
4
4
1/15/2003
1/15/2003
1/15/2003
1/14-19/2003
1/19/2003
1/19/2003
1/19/2003
1/14/2003
NA
NA
NA
0.5–5.0
37.9–39.0
19.5–26.1
21.8–23.5
12.1–13.6
20.0 €
20.0 €
20.0 €
20.0 €
20.0 €
20.0 €
20.0 €
15.7€
0.1 L
0.1 L
0.01 g
0.01 g
0.03 g
0.02 g
0.02 g
1.4 g
Collected in five sampling points
Filter 20 L seawater with 63-lm pore size net
Collected in six sampling points
AC (wet season)
Seawater
Plankton
Sediment
Polychaetes
Clam
Shrimp
Gobiidae sp. A
Gobiidae sp. B
Shortnose ponyfish
2
2
4
4
4
4
4
4
4
6/23/2002
1/15/2003
6/23/2002
6/23–30/2002
6/24/2002
6/23–27/2002
6/23–27/2002
6/23–27/2002
6/23–27/2002
NA
NA
NA
0.5–3.2
6.5–7.5
NA
11.9–12.5
12.5–14.2
3.0–4.0
20.0
20.0
20.0
20.0
7.5
20.0
12.8
10.8
20.0
0.1 L
0.1 L
0.01 g
0.01 g
1.3 g
0.01 g
1.7 g
1.2 g
0.01 g
Hawaiian Islands silverside
4
6/23–27/2002
1.5–2.0
20.0 € 0.01 g
Reeve's shad
Konoshiro gizzard shad
4
4
6/23–27/2002
6/23–27/2002
6.2–8.5
10.5–12.7
8.6 € 1.3 g
10.4 € 1.8 g
2
2
4
4
4
4
4
1/20/2003
1/15/2003
1/20/2003
1/20–31/2003
1/22/2003
1/20–25/2003
1/20–25/2003
NA
NA
NA
0.5–2.5
5.4–8.5
8.3–9.6
10.5–11.3
20
20
20
20
6.1
10.7
12.4
AC (dry season)
Seawater
Plankton
Sediment
Polychaetes
Clam
Gobiidae sp. A
Gobiidae sp. B
Volume or WW
€
€
€
€
€
€
€
€
€
€
€
€
€
€
€
€
0.1 L
0.1 L
0.01 g
0.01 g
1.9 g
2.3 g
1.6 g
Remarks
Scientific
Scientific
Scientific
Scientific
name:
name:
name:
name:
Mugil cephalus
Mylio macrocephalus
Tilapia zilla
Boleophthalmus boddaerti
Filter 20 L seawater with 63-lm pore size net
Scientific name: unknown (pooled sample)
Scientific name: Cyclina orientalis
Scientific name: Acetes spp. (pooled sample)
Scientific name: Unknown
Scientific name: Unknown
Scientific name: Leiognathus brevirostris
(pooled sample)
Scientific name: Atherinomorus insularum
(pooled sample)
Scientific name: Tenualosa reevesii
Scientific name: Konosirus punctatus
Filter 20 L seawater with 63-lm pore size net
Scientific
Scientific
Scientific
Scientific
name:
name:
name:
name:
Unknown (pooled sample)
Cyclina orientalis
Unknown
Unknown
AC = A Chau.
NA = Not applicable.
Kruskal-Wallis tests because of failure in normality and homogeneity
of variance tests (Sigmastat 3.0; SPSS, Chicago, IL). Hierarchical
cluster analysis was applied to classify the relationship of concentrations among different sites with different seasons for sediment and
biota samples (Systat 11.0; Systat). To facilitate comparisons of OC
concentrations in different matrices with environmental guidelines,
sediment concentrations were expressed on a dry-weight (dw) basis.
The organic carbon–normalized values were calculated based on
concentrations on a dw basis and the corresponding TOC values listed
in Table 4. Concentrations of biota samples were expressed on a wetweight basis. The lipid-normalized values were calculated based on
concentrations on a wet weight basis and the corresponding lipid
weights listed in Table 5.
Preliminary Risk Assessment
Preliminary risk assessments were performed by comparing the
measured concentrations of OCs in different compartments with the
corresponding guidelines from various environmental protection
authorities. Typical and worst-case risk quotients were estimated by
calculating the ratios of the means and the highest concentrations of
OCs to their corresponding guideline values, respectively (Tables 4
and 5) (DHHS 1994; USEPA 1995a, 1995b, 1995c, 2004; Environmental Canada 2002; Ontario Ministry of Environment and Energy
1997; ZHB 1999).
Results and Discussion
Extraction Efficiency and Recoveries
External standards of OC pesticides—100 ng/L, 20 ng/g dw,
and 20 ng/g dw—were added to water, sediment, and biota
samples, respectively. OC pesticides had recoveries ranging
from 90% to 102% in sediment and biotic samples. The
average recoveries of chlordanes, DDTs, endosulfans, aldrin,
H. L. Wong et al.
156
Table 2. Comparison of measured and listed OC insecticide concentrations (ng/g dw) in SRM2978
OC insecticides
Measured
values
c-chlordane
o,pÕ-DDD
p,pÕ-DDD
o,pÕ-DDE
p,pÕ-DDE
o,pÕ-DDT
p,pÕ-DDT
a-chlordane
Endrin
11.38
4.4
37.5
10.5
38.8
9.2
3.9
14.6
5.3
€
€
€
€
€
€
€
€
€
0.83a
0.6
1.5
1.0
2.3
1.6
0.3
0.9
0.7
Listed
values
8.9
3.9
38.3
7.6
39.4
7.7
4.3
13.9
4.8
€
€
€
€
€
€
€
€
€
Mean
deviation (%)
0.84
2.0
2.7
1.6
4.3
1.9
0.4
1.0
0.3
+28
+13
)2
+38
)2
+19
)9
+5
+10
a
Mean € SD.
DDD = dichloro-diphenyl-dichloroethane.
DDE = dichloro-diphenyl-dichloroethylene.
DDT = Dichloro-diphenyl-trichloroethane.
OC = Organochlorine.
SRM = Standard reference material.
dieldrin, endrin, and HCHs were >90%, and the recoveries of
heptachlor, mirex, kepone, and methoxychlor were 75% to
85% in seawater samples. The MDLs of chlordanes, DDTs,
endosulfans, aldrin, dieldrin, endrin, and HCHs in seawater
were 0.01 to 0.5 ng/L. The MDLs of the other OCs in seawater
were 1 ng/L. The MDLs of OCs in sediment and biota samples
were 0.01 to 0.05 and 0.01 to 0.1 ng/g dw, respectively.
Concentrations were not corrected for recoveries. The measured and listed values of standard reference material (SRM)
2978 are listed in Table 2. Most of the measured values were
in close agreement with the listed values except for c-chlordane and o,p-DDE, for which the measured concentrations
were higher than the listed values. c-chlordane and o,p-DDE
(10 lg/L) were spiked into different environmental matrices—
including particulates in water, sediments, and all biota species
(n = 4)—to act as a supplementary test. The recoveries of cchlordane and o,p-DDE were 86.5% to 105.3% and 75.2% to
106.8%, respectively.
Spatial and Temporal Variations of OC Concentrations
OCs were detected in most samples analyzed (Tables 3, 4, and
5). In general, DDTs were the predominant contaminants in
most samples. Cyclodienes, hexachlorobenzene (HCB), and
HCHs showed a large variation in concentrations in various
species and among sampling locations. Generally, concentrations of OC pesticides in water, sediment, and biota were
greater at MPMNR than at AC (Tables 3, 4, and 5). Sediments
from MPMNR contained finer particles and greater TOC
contents than those from AC (Table 4). Concentrations of total
DDTs and total HCHs in water samples from all of the sampling sites (Table 3) were relatively small compared with the
no-hazard levels for surface waters (1000 ng/L for DDTs and
5000 ng/L for HCHs) as promulgated by the State Environmental Protection Administration of China (ZHB 1999). Sediments from MPMNR (total OC insecticides = 7.0 to 96 ng/g
dw) were generally more contaminated than those from AC
(3.4 to 5.7 ng/g dw). In MPMNR, GWs, the mudflat (near NB),
and ID were most contaminated in terms of DDTs, HCB,
HCHs, and cyclodienes (Fig. 2 and Table 4). Concentrations
of OCs were lower in areas with strong tidal and artificial
flushing. Concentrations of OC residues in fish from MPMNR
(15 to 55 ng/g ww) were generally higher than those from AC
(1.1 to 3.6 ng/g ww) (Fig. 3). Concentrations of OC pesticides
in plankton samples were all less than those of MDLs.
No significant temporal variations in concentrations of OC
insecticides in seawater were observed (Kruskal-Wallis test p
>0.05) except for HCHs. Among the OC insecticides, HCB
occurred at the greatest concentrations in both seasons (wet
season = 0.05 to 0.61 ng/L and dry season = 0.14 to 0.34 ng/
L), with the greatest concentrations found in GWs. Concentrations of OCs in sediments varied among sampling sites
(Table 4 and Fig. 2). Concentrations of HCB in the water
samples from FPs were twice as great during the dry compared
with the wet season. The spatial patterns were dissimilar for
different insecticides, with HCHs and cyclodienes showing
marked variations between the dry and wet seasons (Fig. 3).
DDTs. Concentrations of total DDTs in the sediments
ranged from 1.4 to 19 ng/g dw (dry season) to 2.0 to 31 ng/g
dw (wet season). DDT concentrations varied with sampling
locations in MPMNR and were generally greater than those
at AC (1.4 and 2.0 ng/g dw) (Table 4). GWs, ID, and FPs
were classified as a different group from the middle part of
the mangrove (MM) and AC by cluster analysis (Fig. 2).
DDT levels recorded in this study were comparable with the
concentration ranges found in surface sediments from the
Pearl River Delta (38.3 € 1.7 ng/g dw; Zhang et al. 2002),
Daya Bay (0.14 to 20.7 ng/g; Zhou et al. 2001), and Lake Tai
(0.33 to 1.8 ng/g dw) and Shanghai (13 to 33 ng/g dw)
(Nakata et al. 2005).
DDEs were the dominant DDT metabolites in the sediments
from both MPMNR and AC. Ratios of (DDDs + DDEs)/total
DDTs in the surface sediments collected from MPMNR were
generally close to unity (Fig. 4), and approximately half of the
DDTs were metabolic products. In this study, the proportion of
DDEs and DDDs relative to total DDTs were greater than
those in samples collected from various Chinese estuaries
during the 1980 s (DDDs + DDEs)/total DDTs = 0.5 to 1) (Fu
et al. 2001; Mai et al. 2002) and 2001 (0.81) (Nakata et al.
2005). Specifically, the proportion of p,pÕ-DDE was larger in
the inner part of GWs at Mai Po, where there was relatively
little tidal flushing compared with the outer areas (NB and ID)
(Table 3). Although the ratios (close to unity) recorded in this
study might suggest that a great proportion of the existing
DDTs were related to historical input rather than fresh discharge, the substantial amount of DDTs found in seawater still
pointed to the possible existence of fresh sources of DDTs
(Table 3).
Higher concentrations of DDTs were detected in the biological samples from the MPMNR compared with AC. Concentrations of total DDTs ranged from 7.9 to 12.9 ng/g ww in
fish and from 0.1 to 6.9 ng/g ww in other biota samples from
MPMNR (Table 5). These levels were similar to the concentration range (3.9 to 76 ng/g ww) reported for Hong Kong
fishes (Chan et al. 1999). Cluster analysis classified the
mudskipper (Boleophthalmus boddaerti) as a separate group
from other species in GWs within the same season (Fig. 4).
Compared with MPMNR, lower concentrations were found in
0.010
0.005
0.013
0.024
0.014
€
€
€
€
0.018
0.018
0.002
0.111
€ 0.012
€
€
€
€
€
AC = A Chau.
FP = Fishpond.
GW = Gei wai.
HCB = Hexachlorobenzene.
HCH = Hexachlorocyclohexane.
ID = Inner Deep Bay.
MDLs = Method detection limits.
MM = Middle part of the mangrove.
NB = Mudflat near Bird-watching blind.
NG = Gate of geiwai.
ND = Samples with concentrations less than the MDLs.
OC = Organochlorine.
€ 0.012
€ 0.005
€ 0.052
€ 0.012
€ 0.022
29.5
ND
ND
ND
ND
0.021
0.012
0.080
0.067
0.084
ND
ND
0.036
ND
ND
0.029
0.041
0.092
0.341
ND
ND
ND
ND
Salinity (psu)
Aldrin
a-chlordane
c-chlordane
o,pÕ-DDD
p,pÕ-DDD
o,pÕ-DDE
p,pÕ-DDE
o,pÕ-DDT
p,pÕ-DDT
Dieldrin
Endrin
Endosulfan I
Endosulfan II
Endosulfan sulfate
a-HCH
b-HCH
c-HCH
HCB
Heptachlor
Kepone
Methoxylor
Mirex
5.9
ND
ND
ND
ND
ND
0.009
0.085
ND
0.247
ND
ND
0.041
ND
ND
ND
ND
ND
0.271
ND
ND
ND
ND
GW
Insecticides and salinity FP
Dry season
30.4
ND
ND
ND
ND
0.016
0.012
0.080
0.067
0.092
ND
ND
0.028
ND
ND
ND
0.009
0.153
0.332
ND
ND
ND
ND
NG
0.003
0.005
0.013
0.024
0.007
€ .003
€ 0.011
€ 0.153
€ 0.006
€
€
€
€
€
33.4
ND
ND
ND
ND
0.008
ND
0.064
ND
0.046
ND
ND
0.032
ND
ND
0.015
0.009
0.153
0.222
ND
ND
ND
ND
MM
€
€
€
€
0.010
0.003
0.011
0.160
€ 0.003
€ 0.008
€ 0.006
€ 0.002
34.1
ND
ND
ND
ND
0.048
ND
0.062
0.017
0.020
ND
ND
0.012
ND
ND
0.040
0.026
0.020
0.137
ND
ND
ND
ND
NB
€
€
€
€
0.002
0.014
0.021
0.057
€ 0.001
€ 0.003
€ 0.024
€ 0.016
€ 0.004
35
0.122
ND
ND
ND
0.010
0.001
0.117
0.041
0.030
ND
ND
ND
ND
ND
ND
ND
ND
0.121
ND
ND
ND
ND
AC
5.3
€ 0.052 ND
ND
ND
0.068
€ 0.001 0.086
€ 0.001 0.080
€ 0.023 0.130
€ 0.009 0.030
€ 0.004 0.102
ND
ND
0.058
ND
ND
0.081
0.020
0.096
€ 0.015 0.407
ND
ND
ND
ND
FP
0.022
0.045
0.005
0.045
0.019
0.007
€
€
€
€
0.007
0.011
0.022
0.073
€ 0.007
€
€
€
€
€
€
Wet season
8.1
ND
ND
ND
0.142
0.072
0.054
0.459
0.013
0.214
ND
ND
0.091
ND
ND
0.052
0.024
0.085
0.608
ND
ND
ND
ND
GW
0.059
0.014
0.002
0.020
.011
0.012
€
€
€
€
0.001
0.003
0.003
0.020
€ 0.036
€
€
€
€
€
€
10.2
ND
ND
ND
0.053
0.118
0.077
0.098
0.017
0.097
ND
ND
0.053
ND
ND
0.086
0.012
0.080
0.356
ND
ND
ND
ND
NG
0.084
0.054
0.084
0.162
0.044
0.107
€
€
€
€
0.076
0.028
0.111
0.458
€ 0.063
€
€
€
€
€
€
Table 3. Concentrations (ng/L € SD) of OC insecticides and salinity in water samples from Mai Po and AC during the dry and wet seasons
18.3
ND
ND
ND
ND
0.010
ND
0.023
0.009
0.053
ND
ND
0.059
ND
ND
0.042
0.008
0.048
0.165
ND
ND
ND
ND
MM
€
€
€
€
0.029
0.011
0.002
0.108
€ 0.004
€ 0.023
€ 0.012
€ 0.008
€ 0.001
18.3
ND
ND
ND
ND
0.034
0.005
0.023
0.004
0.067
ND
ND
0.039
ND
ND
0.031
0.009
0.049
0.047
ND
ND
ND
ND
NB
0.013
0.001
0.017
0.005
0.017
€
€
€
€
0.011
0.012
0.044
0.030
€ 0.020
€
€
€
€
€
20.0
0.053
ND
ND
0.016
0.026
0.043
0.084
0.004
0.073
ND
ND
0.054
ND
ND
0.095
0.015
0.081
0.372
ND
ND
ND
ND
ID
30
€ 0.020 0.022
ND
ND
€ 0.015 ND
€ 0.006 ND
€ 0.001 ND
€ 0.001 ND
€ 0.002 ND
€ 0.006 0.041
ND
ND
€ 0.066
ND
ND
€ 0.008 0.006
€ 0.011 0.006
€ 0.015 0.066
€ 0.174 0.065
ND
ND
ND
ND
AC
€
€
€
€
0.008
0.001
0.015
0.047
€ 0.009
€ 0.014
1900c
—
2a
2.26b
2.26b
1.22b
1.22b
2.07b
2.07b
1.19b
1.19b
Wet season
TOC (% dw)
Aldrin
a-chlordane
c-chlordane
o,pÕ-DDD
p,pÕ-DDD
o,pÕ-DDE
p,pÕ-DDE
o,pÕ-DDT
p,pÕ-DDT
0.32b
0.32b
0.32b
22e
6d
—
2a
2.26b
2.26b
1.22b
1.22b
2.07b
2.07b
1.19b
1.19b
0.72b
4200c (ng/g
TOC)
290c (ng/g
TOC)
1400c (ng/g
TOC)
Endosulfan
sulfate
a-HCH
b-HCH
c-HCH
HCB
Heptachlor
Kepone
Methoxylor
Mirex
Endosulfan II
Endosulfan I
TOC (% dw)
Aldrin
a-chlordane
c-chlordane
o,pÕ-DDD
p,pÕ-DDD
o,pÕ-DDE
p,pÕ-DDE
o,pÕ-DDT
p,pÕ-DDT
Dieldrin
Endrin
Dry season
TEL/SQAL/
AET-L/LEL/
ISQG (ng/g)
(2.05)
(17.00)
(0.15)
(0.88)
(3.73)
(1.85)
(0.87)
(0.21)
(1.37)
(17.94)
(1.87)
(0.35)
(1.95)
0.01 (0.10)
0.29 (10.03)
0.11 (1.33)
0.01 (0.13)
1.12–1.23
1.83 € 0.08
ND
ND
ND
ND
1.30 € 0.06
12.93 € 5.10
1.68 € 0.14
0.33 € 0.03
0.11 €
ND
0.09 €
9.97 €
1.17 €
ND
ND
ND
0.25 € 0.07 (0.35)
0.96 € 0.09 (1.08)
ND
1.05–1.18
ND
ND
0.76 € 0.07
0.19 € 0.03
ND
1.87 € 0.16
16.02 € 0.75
0.78 € 0.07
0.12 € 0.02
3.29 € 0.35
1.73 € 0.08
FP
(2.34)
(28.01)
(3.81)
(1.32)
(10.71)
(6.94)
(1.29)
(9.62)
(5.33)
(0.96)
(4.52)
(2.54)
(2.27)
(1.42)
(5.16)
(17.22)
(5.82)
(1.25)
0.99 (24.94)
0.07 (1.02)
0.05 (0.64)
0.02 (0.91)
1.09–1.14
0.81 € 0.12
4.47 € 0.07
2.40 € 0.14
1.97 € 0.21
1.25 € 0.11
5.07 € 0.09
16.39 € 0.87
5.38 € 0.31
1.21 € 0.04
0.58 €
0.89 €
ND
24.12 €
0.93 €
ND
ND
ND
0.15 € 0.12 (0.29)
2.59 € 0.07 (2.67)
0.80 € 0.07 (0.88)
1.10–1.25
1.24 € 0.04
9.47 € 0.12
5.17 € 0.18
ND
ND
2.28 € 0.06
25.38 € 3.81
3.55 € 0.19
1.29 € 0.03
10.49 € 0.21
6.73 € 0.16
GW
0.13
0.02
0.01
0.67
0.03
0.05
0.56
(1.94)
(0.33)
(0.29)
(15.54)
(0.19)
(0.65)
(12.23)
1.05–1.17
ND
1.92 € 0.06 (2.01)
ND
ND
ND
ND
0.33 € 0.08 (0.41)
ND
ND
1.76 €
0.30 €
0.28 €
14.93 €
0.16 €
0.59 €
11.50 €
ND
1.15 € 0.03 (1.17)
2.86 € 0.09 (2.97)
2.59 € 0.09 (2.67)
1.22–1.48
ND
ND
1.64 € 0.10 (1.72)
0.43 € 0.01(0.44)
ND
2.83 € 0.48 (3.51)
9.92 € 0.30 (10.34)
ND
ND
0.86 € 0.01 (0.87)
0.12 € 0.08 (0.20)
NG
(2.19)
(0.11)
(2.02)
(0.09)
0.01 (0.06)
0.16 (4.49)
0.09 (0.87)
0.04 (0.15)
0.04 (0.70)
1.18–1.28
ND
ND
ND
ND
ND
ND
3.20 € 0.28 (3.55)
ND
ND
0.10 €
0.65 €
ND
0.05 €
4.35 €
0.76 €
ND
ND
0.22 € 0.02 (0.24)
ND
0.15 € 0.06 (0.19)
1.12–1.59
ND
0.09 € 0.01
ND
1.99 € 0.04
ND
ND
ND
2.18 € 0.13
0.10 € 0.02
ND
ND
MM
(1.72)
(3.47)
(4.08)
(1.09)
(2.76)
(1.36)
(5.17)
(3.09)
(0.90)
0.24
0.04
0.15
0.38
0.05
0.01
0.93–1.14
ND
6.79 € 0.12
4.31 € 0.32
1.13 € 0.11
1.27 € 0.11
4.55 € 0.35
10.17 € 0.33
6.66 € 0.21
5.45 € 0.27
2.52 €
0.54 €
2.32 €
7.46 €
1.09 €
0.20 €
ND
ND
(6.91)
(4.73)
(1.25)
(1.38)
(4.96)
(10.63)
(6.92)
(5.66)
(2.87)
(0.57)
(2.53)
(8.00)
(1.15)
(0.20)
0.32 € 0.18 (0.58)
ND
0.15 € 0.04 (0.19)
0.84–1.06
ND
4.53 € 0.59
2.43 € 0.53
0.80 € 0.08
ND
1.48 € 0.28
3.15 € 0.30
3.52 € 0.46
1.06 € 0.04
2.70 € 0.05
1.24 € 0.09
NB
(2.06)
(3.60)
(2.24)
(0.88)
(1.05)
(7.08)
(8.60)
(5.60)
(4.77)
(2.27)
(2.80)
€
€
€
€
€
€
€
€
0.51
0.35
0.05
0.90
0.04
0.10
0.01
0.02
0.56–0.6
0.60 € 0.21
1.99 € 0.02
2.43 € 0.48
0.74 € 0.11
1.40 € 0.29
4.04 € 1.12
7.09 € 0.49
0.35 € 0.12
3.25 € 0.16
5.49
1.29
1.80
10.67
2.37
0.32
0.50
0.31
(0.81)
(2.01)
(3.09)
(0.90)
(1.79)
(5.49)
(7.75)
(0.52)
(3.47)
(6.00)
(1.46)
(1.85)
(11.87)
(2.41)
(0.47)
(0.51)
(34)
0.12 € 0.07 (0.21)
0.63 € 0.04 (0.66)
ND
0.67–0.85
1.93 € 0.10
3.52 € 0.06
1.91 € 0.24
0.82 € 0.08
1.02 € 0.03
6.71 € 0.46
8.02 € 0.39
5.37 € 0.39
4.07 € 0.53
2.18 € 0.11
1.83 € 0.68
ID
0.57–0.85
0.36 € 0.36 (0.86)
ND
ND
ND
ND
ND
2.04 € 0.26 (2.37)
ND
ND
0.41 € 0.05 (0.46)
ND
ND
1.48 € 0.16 (1.64)
ND
ND
ND
ND
0.08 € 0.05 (0.13)
ND
ND
0.27–0.53
ND
ND
ND
ND
ND
ND
1.40 € 0.06 (2.00)
ND
ND
ND
ND
AC
Table 4. Concentrations (ng/g dw) of OC pesticides in sediment samples in dry and wet seasonsa Concentrations are reported as mean € standard derivation. Maximum concentrations are given in
parentheses. Locations are abbreviated as fish pond (FP); gei wai (GW); the gate of the gei wai (NG); middle part of the mangrove (MM); mudflat near the bird watching blind (NB); Inner Deep Bay (ID).
Typical and worst-case risk quotients larger than unity are in bold.
1900c
2.20 €
1.31 €
0.85 €
8.01 €
ND
ND
ND
ND
0.32b
0.32b
0.32b
22e
6d
€
€
€
€
€
2.09
2.87
1.14
0.46
0.19
0.72b
4200c (ng/g TOC)
290c (ng/g TOC)
1400c (ng/g TOC)
FP
0.04
0.06
0.06
0.22
0.09
0.18
0.09
0.09
0.09
(2.23)
(1.37)
(0.91)
(8.16)
(2.16)
(3.01)
(1.25)
(0.59)
(0.30)
€
€
€
€
€
0.95 €
2.22 €
1.47 €
20.73 €
1.26 €
ND
ND
ND
3.90
1.64
0.39
1.73
0.41
GW
0.05
0.25
0.11
0.82
0.08
0.23
0.09
0.07
0.27
0.03
(1.01)
(2.48)
(1.57)
(21.69)
(1.34)
(4.16)
(1.77)
(0.45)
(2.03)
(0.49)
0.44 € 0.03 (0.47)
ND
ND
3.76 € 0.20 (3.99)
ND
ND
ND
ND
ND
ND
ND
0.44 € 0.02 (0.47)
ND
NG
€
€
€
€
€
0.01
0.04
0.09
0.06
0.10
(0.17)
(0.69)
(0.19)
(0.58)
(1.79)
1.11 € 0.09 (1.23)
ND
ND
3.93 € 0.21 (4.16)
ND
0.65 € 0.06 (0.68)
ND
ND
0.17
0.64
0.15
0.49
1.67
MM
€
€
€
€
€
5.43 €
1.53 €
2.01 €
1.47 €
2.28 €
0.10 €
ND
ND
2.00
2.33
0.06
0.80
0.51
NB
0.34
0.15
0.21
0.24
0.21
0.01
0.10
0.18
0.02
0.09
0.04
(5.79)
(1.70)
(2.20)
(1.72)
(2.51)
(0.10)
(2.20)
(2.57)
(0.08)
(0.92)
(0.55)
€
€
€
€
€
3.07 €
2.30 €
1.26 €
14.46 €
ND
ND
0.38 €
0.36 €
1.57
1.82
0.22
0.45
0.34
ID
(3.36)
(2.49)
(1.81)
(17.55)
(1.80)
(2.80)
(0.50)
(0.60)
(0.36)
0.20 (0.63)
0.14 (0.52)
0.21
0.23
0.38
2.80
0.27
0.69
0.21
0.16
0.02
d
Canadian
ND
ND
ND
3.25 € 0.05 (3.30)
ND
ND
ND
ND
ND
ND
ND
ND
0.04 € 0.03 (0.07)
AC
Used at contaminated sites sediments-LEL (ng/g); b USEPA threshold effects levels (TEL) (ng/g); c USEPA sediment quality advisory levels (SQAL ng/g Total organic carbon (TOC));
Interim Sediment Quality Guideline (ISQG) (ng/g); e USEPA apparent effects threshold-low (AET-L) (ng/g).
AC = A Chau.
FP = Fishpond.
GW = Gei wai.
HCB = Hexachlorobenzene.
HCH = Hexachlorocyclohexane.
ID = Inner Deep Bay.
MDLs = Method detection limits.
MM = Middle part of the mangrove.
NB = Bird watching blind.
NB = Mudflat near NB.
ND = Samples with concentrations less than the MDLs.
OC = Organochlorine.
TOC = Total organic carbon.
a
Dieldrin
Endrin
Endosulfan I
Endosulfan II
Endosulfan
sulfate
a-HCH
b-HCH
c-HCH
HCB
Heptachlor
Kepone
Methoxylor
Mirex
Wet season
TEL/SQAL/
AET-L/LEL/
ISQG (ng/g)
Table 4. Continued
100
300
300
300
3000
300
300
300
ND
ND
ND
8.36
0.33
0.02
0.72
0.13
0.33
0.22
ND
33.8
0.68
ND
ND
0.3
ND
ND
ND
0.8
0.02
0.004
1.4
0.01
0.05
0.1
€ 1 0.04
€ 0.70
€ 0.64
€
€
€
€
€
€
€
ND
9.6 € 0.4
ND
ND
2.78 € 0.1
ND
ND
0.19 € 0.02
8.81 € 0.2
0.69 € 0.1
0.21 € 0.03
0.13 € 0.01
0.12 € 0.03
0.61 € 0.01
0.23 € 0.08
ND
18.38 € 0.61
1.42 € 0.1
ND
ND
0.31 € 0.04
0.08 € 0.01
ND
ND
ND
ND
0.78
ND
ND
ND
8.41
0.32
0.02
0.34
0.31
0.29
0.39
ND
3.82
ND
ND
ND
0.04
ND
ND
ND
0.8
0.02
0.01
0.02
0.04
0.05
0.1
€ 0.02
€ 0.2
€
€
€
€
€
€
€
€ 0.1
0.37 €
0.71 €
2.81 €
ND
ND
1.60 €
11.19 €
ND
0.06 €
ND
ND
0.81 €
0.43 €
0.08 €
9.82 €
0.05 €
0.19 €
0.05 €
0.10 €
ND
ND
ND
0.05
0.02
0.01
0.57
0.01
0.01
0.01
0.01
0.01
0.09
0.64
0.02
0.04
0.17
0.38 €
0.72 €
2.75 €
ND
ND
0.78 €
9.59 €
1.43 €
0.71 €
ND
30.32 €
0.39 €
0.38 €
2.34 €
9.61 €
0.23 €
0.44 €
ND
0.49 €
ND
ND
ND
0.43
0.24
0.32
0.23
0.50
7.04
0.21
0.33
0.72
6.51
1.10
0.49
0.33
0.04
1.63
0.02
0.27
0.31
ND
0.17
1.43
0.17
0.04
0.12
ND
0.11
0.11
0.07
ND
1.17
0.01
0.04
0.12
0.05
0.06
ND
ND
0.05
0.38
0.04
0.01
0.03
€
€
€
€
€
€
0.31
0.03
0.01
0.03
0.02
0.02
€ 0.02
€ 0.03
€ 0.09
€
€
€
€
€
€ 0.01
€ 0.07
€ 0.09
0.01
0.12
0.16
ND
0.10
0.97
0.05
0.01
0.05
0.01
0.05
0.07
0.12
0.03
0.79
ND
0.05
0.08
0.05
0.04
ND
ND
Risk for carcinogenicity is considered significant if the risk quotient is greater than 10-5 by comparing OC concentrations with relevant USEPA guideline values.
D = Dry.
FDA = Food and Drug Administration.
MDLs = Method detection limits.
ND = Sample with concentrations less than the MDLs.
OC = Organochlorine.
US EPA = United States Environmental Protection Agency.
W = Wet.
a
Aldrin
320
a-chlordane
650
c-chlordane
650
o,p'-DDD
p,p'-DDD
o,p'-DDE
p,p'-DDE
o,p'-DDT
p,p'-DDT
Dieldrin
Endosulfan I
65000
Endosulfan II
65000
Endosulfan sulfate
Endrin
HCB
8600
a-HCH
b-HCH
c-HCH
Heptachlor
5400
Kepone
Methoxylor
Mirex
2200
Mai Po biota
€
€
€
€
€
€
€
€
€
€
€
€
€
€
€
0.01
0.01
0.01
0.01
0.01
0.19
0.01
0.01
0.01
0.01
0.02
0.1
0.02
0.01
0.16
€ 0.01
€ 0.02
€ 0.03
ND
ND
0.74
0.29
ND
ND
8.17
0.33
0.07
2.41
0.33
0.31
0.04
ND
3.30
0.09
ND
ND
0.04
0.38
0.14
0.04
1.17
0.01
0.01
0.32
0.04
0.03
0.05
€
€
€
€
0.01
0.03
0.01
0.01
€ 0.42
€ 0.01
€
€
€
€
€
€
€
€ 0.08
€ 0.57
US EPA
FDA guidance
noncancer
action/tolerance
Boleophthalmus Boleophthalmus
Metapenaeus
hazard level level
Mugil cephalus Mylio macrocephalus Tilipia zillia boddaerti (W) boddaerti (D)
Polychaetes (W) Polychaetes (D) ensis (D)
Table 5. Concentrations of OC insecticides (ng/g ww € SDs) in the biota from Mai Po and AC in the dry and wet seasonsa
160
H. L. Wong et al.
ND
0.04 € 0.01
300
300
300
100
5400
2200
b-HCH
c-HCH
Heptachlor
Kepone
Methoxylor
Mirex
ND
ND
ND
ND
0.03 € 0.04
a-HCH
0.3 € 0.02 0.2 € 0.4
ND
ND
0.1 € 0.03
0.1 € 0.02
0.1 € 0.03
0.2 € 0.04
ND
0.13 € 0.04
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
0.1 € 0.02 ND
0.1 € 0.02 0.02 € 0.02 0.1 € 0.02 ND
0.1 € 0.1
0.7 € 0.03 0.3 € 0.02 0.4 € 0.4
0.1
0.1
0.03
0.03
0.02
0.1
0.5 € 0.1
3000
€
€
€
€
€
€
0.01 € 0.02 0.1 € 0.02 0.1
0.1 € 0.03 0.1 € 0.02 0.1
0.1 € 0.02 0.02 € 0.02 0.1
0.1 € 0.04 0.1 € 0.03 0.1
0.1 € 0.02
0.1
0.1 € 0.01 0.1 € 0.1 0.1
0.03 € 0.03
0.1 € 0.1
0.02 € 0.02
0.04 € 0.05
0.05 € 0.04
0.01 € 0.01
o,p'-DDT
p,p'-DDT
Dieldrin
Endosulfan I 65000
Endosulfan II 65000
Endosulfan
sulfate
Endrin
HCB
8600
0.13 € 0.05
ND
0.04 € 0.03
0.08 € 0.03
ND
0.53 € 0.03
ND
0.13 € 0.05
0.02 € 0.01
0.11 € 0.02
0.02 € 0.01
ND
ND
ND
ND
ND
ND
ND
0.2 € 0.03 0.1 € 0.01 0.1 € 0.01 0.04 € 0.01 ND
0.1 € 0.01 0.04 € 0.03 0.1 € 0.1 0.1 € 0.02 1.09 € 0.45
0.3 € 0.2 0.1 € 0.02 0.3 € 0.2 0.7 € 0.01 ND
0.1 € 0.03 0.1 € 0.02 0.1 € 0.1 0.1 € 0.01
0.1 € 0.01 0.1 € 0.02 0.1 € 0.1 ND
ND
ND
0.02 € 0.03 ND
0.1 € 0.01 0.1 € 0.01 0.1 € 0.01 0.04 € 0.02
0.2 € 0.1
ND
0.3 € 0.2
0.2 € 0.02
0.1 € 0.02
ND
ND
p,p'-DDD
o,p'-DDE
p,p'-DDE
300
300
300
€
€
€
€
0.05
0.03
0.01
0.16
€
€
€
€
0.07
0.04
0.02
0.04
€ 0.09
ND
2.87 € 0.23
0.12 € 0.03
0.08 € 0.05
0.13 € 0.03
0.27 € 0.14
ND
ND
0.15
ND
0.31
0.14
0.03
0.05
0.05 € 0.04
1.42 € 0.21
0.10 € 0.01
0.08
0.04
0.12
0.62
0.04 € 0.01
ND
0.86 € 0.09
0.03 € 0.02
0.14 € 0.12
0.02 € 0.02
ND
ND
ND
ND
ND
ND
ND
ND
0.97 € 0.72
ND
0.04 € 0.01
ND
ND
0.57 € 1.06
€
€
€
€
0.11
0.12
0.01
0.08
€
€
€
€
0.10
0.10
0.03
0.03
€ 0.08
ND
3.21 € 0.88
0.11 € 0.02
0.13 € 0.11
0.07 € 0.03
0.23 € 0.11
ND
ND
0.17
ND
0.09
0.18
0.04
0.05
0.04 € 0.04
0.71 € 0.42
0.10 € 0.07
0.13
0.16
0.11
0.07
0.08
€ 0.02
0.04
€ 0.01
ND
0.06
€ 0.01
ND
ND
ND
ND
ND
ND
0.17
€ 0.01
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
0.06
€ 0.01
ND
ND
ND
ND
0.41
€ 0.03
ND
ND
ND
0.20
€ 0.01
ND
ND
ND
ND
ND
0.01
€ 0.01
ND
ND
ND
ND
ND
ND
ND
0.05 0.27 ND
€ 0.05 € 0.07
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
1.22 0.65 0.20
€ 0.12 € 0.07 € 0.08
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
0.08
€ 0.03
ND
ND
ND
ND
ND
ND
0.49 0.34 0.11
€ 0.17 € 0.20 € 0.05
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
FDA
US EPA guidance
Noncancer action/
Atheri
Cyclina Cyclina Poly Poly
hazard
tolerance Hyporhamphus Konosirus Tenualosa nomorus Leiognathus Gobiddae spp. Gobiddae spp. Gobiddae spp. Gobiddae spp. orientalis orientalis chaetes chaetes Acetes
level
level
quoyi
punctatus reevesii
insularum brevirostris A (D)
A (W)
B (D)
B (W)
(D)
(W)
(W)
(D) spp.
Aldrin
320
a-chlordane 650
g-chlordane 650
o,p'-DDD
AC biota
Table 5B.
162
H. L. Wong et al.
Fig. 2. Cluster analysis of concentrations of total DDTs, HCHs, cyclodienes, and HCB in sediments. Separate groups are clustered by linked
lines. DDTs = dichloro-diphenyl-trichloroethane and its metabolites; HCB = hexachlorobenzene; HCHs = hexachlorocyclohexanes.
fish (0.39 to 2.6 ng/g ww) and other biota samples (0.02 to 0.2
ng/g ww) from AC.
Although large-scale application of DDTs has been banned
in China for >20 years, the long half-lives and potential ecological impacts of these chemicals still warrant continuous
monitoring. The occurrence of detectable concentrations of
DDTs in the water column in this area (Luo et al. 2004)
indicated that some fresh inputs might still be present.
HCB. Measurable concentrations of HCB were found in all
environmental compartments at MPMNR and AC. The greatest concentrations of HCB were observed in sediments from
GWs (>20 ng/g dw), and these were greater than those from
other locations in MPMNR during both seasons (Fig. 3).
Overall, HCB contamination was found to be higher in the
samples from GWs, ID, and FPs in MPMNR (0.05 to 24 and
1.5 to 21 ng/g dw during the dry and wet seasons, respectively)
than AC (1.5 and 3.3 ng/g dw during the dry and wet seasons,
respectively). These values were comparable with concentrations recently reported from Lake Tai (0.1 to 3.2 ng/g dw)
(Nakata et al. 2005). In addition, detectable levels of HCB
were found in fish and other biota samples, possibly reflecting
consistent contamination by HCB in MPMNR and AC. In
general, cluster analysis classified fish collected from
MPMNR as a distinct group containing higher concentrations
of HCB (Concentration less than the method detection limit
[ND] to 33.8 ng/g ww) compared with fish from AC (ND to
0.7 ng/g ww) (Table 5).
The relatively great concentrations of HCB recorded in this
study might be related to its intense use in the heavily industrialized Pearl River Delta. These chemicals might conceivably
be transported to the study areas by water and tidal currents
and aerial deposition (Louie et al. 2004; Wong et al. 2004).
HCB concentrations in the Mai Po sediments were similar to
those in other estuaries near urban and industrial areas (Lee et
al. 2000; UNEP 2002; United Nations University 2003). It
should be noted that HCB is still being used in various
industrial processes in China and has been detected in various
locations in China (Wu et al. 1999; Kunisue et al. 2003;
Nakata et al. 2005).
HCHs. Low concentrations of HCHs in mixture form were
found in both biota and abiotic samples from the study areas.
The concentrations of HCHs in sediments were comparable
with or higher than those reported in Xiamen Harbour (<0.01
to 0.15 ng/g dw; Zhou et al. 2000) and Daya Bay (0.32 to
4.16 ng/g; Zhou et al. 2001), but they were lower than the
historical concentrations in the Pear River Estuary (42 to 101
ng/g; Wu et al. 1999) in China. The spatial and temporal
Organochlorine Insecticides In Mudflats of Hong Kong, China
163
Fig. 3. Cluster analysis of concentration of total DDTs, HCHs, cyclodienes, and HCB in fish. Separate groups are clustered by linked lines.
DDTs = dichloro-diphenyl-trichloroethane and its metabolites; HCB = hexachlorobenzene; HCHs = hexachlorocyclohexanes.
variations of HCHs were less marked than other OCs as
shown in Figure 3. Concentrations of total HCHs in biota
samples were similar for both MPMNR and AC (Fig. 4),
which were apparently lower than those reported for biota
from India, where technical HCH is still being used (Kannan
et al. 1995; Pandit et al. 2002). The sum of a- and b-HCH
accounted for >50% of total HCHs in sediments from
MPMNR (Table 4). In general, the b- and c-isomers were
dominant in samples collected from AC. The ratios of aHCH to c-HCH in the abiotic and biotic samples from
MPMNR were generally greater than unity (Fig. 3), which
might indicate the greater use of HCH mixtures than lindane
(Willet et al. 1998). In samples from ID, which experienced
the greatest tidal flushing, a-HCH was the predominant isomer. b-HCH, with the slowest degradation rate in sediments,
tended to accumulate in areas with relatively low flushing
rates such as GWs (Willet et al. 1998). In general, the relatively small concentrations of b-HCH observed probably
reflected the decreasing use of technical HCHs and lindane in
the Pearl River Delta area.
Cyclodienes. Concentrations of cyclodienes were greater in
sediment and fish samples from MPMNR compared with AC
(Tables 4 and 5). Sediments from GWs were the most con-
Fig. 4. The relationship between (DDDs + DDEs)/total DDTs and
DDDs/DDEs in sediments from AC and Mai Po. Points where DDT
levels are below the detection limit are omitted. AC = A Chau;
D = dry season; DDTs = dichloro-diphenyl-trichloroethane and its
metabolites;
FP = fishponds;
HCB = hexachlorobenzene;
HCHs = hexachlorocyclohexanes; ID = Inner Deep Bay; GW = gei
wais; MM = middle part of the mangrove; NB = mudflat near the
bird-watching blind; NG = the gate of GW; W = wet season.
H. L. Wong et al.
164
taminated for cyclodienes (38 and 17 ng/g dw during the dry
and wet seasons, respectively). GW samples formed a distinct
group relative to other locations based on cluster analysis,
especially during the dry season (Fig. 2). Approximately 20%
to 40% of cyclodienes detected in MPMNR were aldrin,
dieldrin, and endrin (Table 4). Chlordanes were detectable
(ND to 11.2 ng/g dw) in some sampling locations at MPMNR.
Endosulfans accounted for 5% to 20% of the cyclodienes
measured in sediments. This result is consistent with previous
data reported for the Pearl River Delta area (Mai et al. 2002).
Low concentrations of endosulfans (<0.1 ng/L) were commonly found in seawater samples from MPMNR. Concentrations of cyclodienes varied considerably with different biota
species collected from MPMNR. For example, fish (2.0 to 13
ng/g ww) were more contaminated by cyclodienes than other
animals (0.05 to 3.4 ng/g ww). Chlordanes and dieldrin were
important contaminants among the cyclodienes in biota samples from MPMNR (Fig. 4c). The levels of cyclodienes in fish
from MPMNR were close to the concentrations in fish from
tropical Asian countries (Kannan et al. 1995). Lower concentrations of cyclodienes were generally detected in various
environmental compartments at AC compared with those at
MPMNR, except seawater (Tables 3, 4, and 5). The compositions of cyclodienes were dissimilar for the two study areas,
and this might be related to differences in input sources
(Fig. 4).
Preliminary Risk Assessment
Recoveries for OCs in water samples in this study were generally
between 80% and 90%. Concentrations reported in this study
were not corrected for recoveries. However, even if the concentrations were corrected for recoveries (data not shown), they
were still below the acceptable levels promulgated by various
environmental protection authorities (e.g., ZHB 1999; USEPA
2002). Thus, it could be concluded that the risks related to OC
concentrations in seawater at the two study sites were low.
Concentrations of p,pÕ-DDE, a-HCH, b-HCH, chlordanes,
and heptachlor in sediments from GWs and ID were consistently greater than their corresponding sediment guideline
values under both typical and worst-case scenarios (Table 4).
These results suggest that the concentrations of OC insecticides in the sediments of the Mai Po area did pose a risk to
aquatic life, especially sediment-dwelling organisms.
Although concentrations of a number of OCs in the Mai Po
sediments were greater than their corresponding sediment
guideline values, concentrations of OCs in biota samples were
much lower than the relevant guideline values promulgated by
government agencies to protect the health of human consumers
(Table 5). It is worth noting that GWs at MPMNR have been
managed by WWFHK for >20 years according to a standard
procedure. Principally, GWs are completely drained twice a
year, and fish are removed. The GWs are restocked with fingerlings after the drain-down process. This operation may have
the overall effect of decreasing the concentrations of toxic
contaminants in the fish tissues by limiting the bioaccumulation window (duration) for OCs, thus decreasing the risk of
exposure to these toxic contaminants by way of fish consumption. During shrimp harvesting from GWs during the wet
season, the sluice gates are opened, and water is allowed to
flush out during low tides on a regular basis (>100 times/y).
The strong flushing currents create an upwelling force between
the surface sediments and water, which may increase the
amount of particle-bound OCs in the water being flushed out
of GWs. During high tide on the same day, GWs are reflooded
to allow recolonization by juvenile shrimp (Cha et al. 1997).
These operations allow an efficient and regular circulation and
exchange of water between GWs and the open sea during a
prolonged period, and this may potentially be effective in
decreasing the accumulation of OCs in biota tissues.
We speculate that the current low-cost maintenance practices adopted by WWFHK may be effective in decreasing the
potential hazards caused by OC contamination in MPMNR.
Such an approach may potentially be applicable to wetlands in
other locations, e.g., in other southeastern Asian countries,
thus allowing sustainable fishery production and wildlife
conservation. In theory, it may be possible to decrease the
quantity of insecticides accumulated in GWs by periodic removal of the contaminated sediments. However, such operations may exacerbate the resuspension of sediment particles
and increase the concentrations of OCs in the water column.
This could worsen the situation, particularly if water circulation is restricted. Further studies will need to be carried out to
examine and ascertain the relative merits of these management
options.
Acknowledgments. This study was supported by a Central Allocation
Grant (Grant No. 8730020) awarded by the Research Grants Council,
Hong Kong; and the Area of Excellence Scheme under the University
Grants Committee of the Hong Kong Special Administration Region,
China (Project No. AoE/P-04/2004).
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