Chlorinated hydrocarbon contaminants in Hong Kong surficial sediments

Chemosphere, Vol. 39, No. 6, pp. 913-923,

1999 © 1999 Elsevier Science Ltd. All rights reserved 0045-6535/99/$ - see front matter

Pergamon

PII: S0045-6535(99)00041-7

CHLORINATED HYDROCARBON CONTAMINANTS IN HONG KONG SURFICIAL SEDIMENTS

Bruce J. Richardson* and Gene J. Zheng

Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong

(Received in Germany 11 November 1998; accepted 13 January 1999)

Abstract Twenty surficiai sediments were sampled from nearshore Hong Kong waters during 1997-1998, and analyzed for a range of chlorinated pesticides and polychlorinated biphenyls (PCBs). Results showed that concentrations (on a dry weight basis) of total HCHs were in the range 0.1 - 16.7 ng g-l, and total DDTs 0.3 - 14.8 ng gl. PCBs, measured as an Aroclor 1242, 1248, 1254, 1260 (1:1:1:1) mixture, were found to be in a range of 0.5 - 97.9 ng g'~, and were at highest concentrations in Victoria Harbour. Results indicated that chlorinated pesticides and PCBs in Hong Kong nearshore sediments were most likely derived from waste discharge from a variety of sources, including agricultural, sewage, industrial waste disposal and shipping-related activities. In addition, as the north and west sides of Hong Kong are subject to influence from the Pearl River (due mainly to agricultural activities in the Pearl River Delta, and to a lesser extent developments around the Shenzhen Special Economic Zone), these inputs are also thought to be likely sources of contamination. ©1999 Elsevier Science Ltd. All rights reserved

Introduction Organochlorines, including the chlorinated pesticides and PCBs, represent an important group of anthropogenic compounds that have caused worldwide concern as toxic environmental contaminants. Although they have been largely replaced in the past 20 years by alternatives which are more easily degraded in the environment, and are not as harmful in the long term (especially to non-target organisms), the persistence of many organochlorine compounds in the environment has prompted ongoing monitoring programs aimed at ensuring environmental quality is maintained, and that wildlife and human health is adequately protected.

In the past, pesticides such as ct-, 13-, ,/-, and 8- hexachlorohexanes (total HCHs), hexachlorobenzene (HCB), dichlorodiphenylthrichloroethane (DDT), chlordane, aldrin and dieldrin have been widely used in

914

China.

Similarly, the polychlorinated biphenyls (PCBs) have been used worldwide in electrical

applications (e.g. as dielectric fluids in capacitors and transformers), in ship painting, and in carbon-free copy papers. Their use up until the 19g0s, especially in roles which ensured continued environmental input (from both deliberate and accidental sources), has resulted in a pool of these compounds remaining in many environmental compartments.

The organochlorine compounds of environmental significance are characterized by their toxicity, stability, and often their recalcitrance to degradation in natural environments. In addition, they are easily adsorbed onto suspended particulate matter in both freshwater and marine situations, and may rapidly deposit to sediments, especially in river mouths and estuaries. From such sinks, they can enter living organisms, via flux through the water phase, and eventual dissolution in tissue lipids (Hutzinger et al., 1974).

Organochlorine compounds in the environment are typically derived from agriculture, industrial discharge and sewage disposal practices. Since 1988, DDT has been banned in China, as has HCH (Hong et al., 1995). Prior to this time, however, these compounds were used on a large scale in agricultural practice. Subsequent runoff of the compounds into waterways has resulted in their accumulation in freshwater, estuarine and marine sediments (Zhou et al., 1997). On the other hand, PCBs in sediments are typically derived from industrial usage, principally via PCB-containing capacitors and electric transformers (Richardson & Waid, 1982).

In this study, total HCHs, DDTs and PCBs; HCB; aldrin; chlordane; and dieldrin in nearshore Hong Kong coastal sediments were determined.

The study formed part of a range-finding exercise for the later

deployment of mussels and semi-permeable membrane devices as monitoring tools in Hong Kong waters.

Sampling and Analysis Surficial sediment samples were removed from 20 sites close to the Hong Kong shoreline using an Ekman grab (Figure 1; Zheng and Richardson, In Press). Samples were obtained from each of 3 stations in northeast Hong Kong (sites 1-3); 3 sites in western Hung Kong (sites 4, 7, 8); 2 stations in Tolo Harbour (sites 5, 6); 2 sites in the Sai Kung area (sites 9, I0); 7 stations in Victoria Harbour (sites 12-18); and 3 stations to the south of Hong Kong (sites 11, 19, 20). Samples (representing approximately the top 10 cm of sediment) were carefully transferred into pre-cleaned containers, and stored at -10°C until they were analyzed. Blanks were run in addition to sediment samples in all later analyses (Table 1).

915

%

N

T

[

st,=

]

Fimare1: Map of Hong Kong showing the sampling locations, as follows: (1) Sha Tau Kok Wharf; (2) Kat O Wharf; (3) Kat O Fish Farm; (4) Tsim Bei Tsui; (5) Tai Po Market Park Wharf; (6) Chinese University; (7) Gold Coast; (8) Tsing Yi North; (9) Sai Kung Wharf; (10) Hung Kong University of Science & Technology Wharf; (11) Cheung Chau Fish Farm; (12) Hung Kong University West; (13) China-HK Ferry; (14) Tsim Sha Tsui; (15) Hung Horn; (16) To Kwa Wan Wharf; (17) Kwun Tong Wharf; (18) Sha Wan Ho Marine Police; (19) Shek O Beach; (20) Yung Shue Wan. Frozen sediments were removed from refrigeration and kept at room temperature for 2 hours. After thawing, approximately 2 g of each sediment was accurately weighed and placed in an aluminum dish for oven drying at 105°C overnight. All analytical results were subsequently expressed on a dry weight basis.

Wet sediment subsamples (about 30 g, accurately weighed) were analyzed using the methods previously reported by Zheng & Quinn (1988) and Zheng & Richardson (in press). Briefly, an internal standard consisting of 94 ng (accurate to 0.1 ng) of octachloronaphthalene (OCN) was added to each weighed sample, which was then thoroughly mixed prior to extraction. Each sediment (with internal standard) was refluxed with 120 mL methanol at 80°C for two hours. After cooling to room temperature, the mixture was passed through a glass filter; 80 mL distilled water was then added, and the aqueous-methanol solution extracted three times with 30 mL distilled hexane. The three extracts were pooled together and the volume was reduced to approximately 1 mL by rotary evaporation prior to column chromatography.

A chromatography column consisting of 2 g of activated silica gel and 1 g of activated copper powder (for sulfur removal) was washed with 15 mL methanol, followed in sequence by 15 mL of methylene chloride,

916 and 20 mL of hexane. The extraction aliquot (-1 mL) was added to the eohmm and eluted with 15 mL distilled hexane to provide Fraction 1, which contained petroleum hydrocarbon compounds. The column was further eluted with 20 mL of a mixture of methylene chloride and hexane (20:80) to obtain the chlorinated pesticides and PCBs (Fraction 2). This fraction was reduced in volume to 2 mL for gas chromatographic analysis prior to and after the separation of DDE from PCBs (USFDA, 1994). The latter was achieved in the following fashion. An aliquot of Fraction 2 solution (1 mL) was added to 1 mL of CrO 3 acetic acid solution (1 mL of distilled water added to 1.5 g of CrOs, followed by the addition of 59 mL of glacial acetic acid). This mixture was placed in a boiling water bath for 15 minutes (USEPA, 1997). After removal, it was cooled and re-extracted 3 times with 3 mL hexane on each occasion. The hexane extracts were pooled, and reduced to 50-100 ~tL for quantitation by gas chromatography.

A Hewlett Packard 6890 gas chromatograph with a 30 m HP-5 fused silica capillary column (0.2 mm diameter and 0.33 ~tm thickness film; 95% dimethyl- 5% diphenyl-polysiloxane), and equipped with a micro-ECD was used for the quantitation of chlorinated pesticides and PCBs. A chlorinated pesticide standard containing four isomers of HCH (ct-, 13-, T,- 8-); p,p'-DDE, p,p'-DDD and p,p'-DDT; HCB; aldrin; chlordane; and dieldrin (along with the internal standard, OCN) was injected onto the micro-ECD under the following conditions. Temperature program: 100°C for 2 min, increasing at 8°C min ~ to 270°C, then held for 20 min; injector and detector: 280°C; split ratio: 1:40. A mixture of Aroclors 1242, 1248, 1254 and 1260 (1:1:1:1) was injected under the same gas chromatographic conditions.

Using these

standards, the chlorinated pesticides and PCBs were determined in the same sample; however, DDE measurement was conducted separately following acidified chromium trioxide treatment (see above; USFDA, 1994). The internal standard (OCN) was used for quantification according to peak areas in both samples and the standards. Accurate quantitation of both p,p'-DDE and PCBs in the same sample was successful under these conditions, and most compounds were represented by narrow and well separated peaks (Mitchell, 1997).

Results and Discussion

Results of sediment analyses are shown in Table l. Highest concentrations of HCHs and PCBs were found in Kowloon Bay (Victoria Harbour) close to To Kwa Wan (site 16) and Kwun Tong (site 17). The latter are industrial localities surrounded by a densely populated area. In addition, sea water exchange within Kowloon Bay is low, and thus organochlorine compounds in the area may remain for extended periods, having been deposited to the sea bottom (Phillips et al., 1992). From the data in Table 1, To Kwa Wan had the highest concentration of HCHs and PCBs: total HCH concentrations were 16.7 ng g-i and total PCBs 97.9 ng

g-1.

Kwun Tong sediments contained 15.2 ng g-~ total HCH and 48.7 ng g'~ total PCBs. As

discussed later, the results reflect similar levels to those recorded previously by Hong et al. (1995).

c~-HCH

0.23 n.d. 0.21 2.56 4.78 5.21 0.21 1.39 0.21 0.45 1.39 0.78 3.11 0.26 1.39 1.81 1.42 n.d. 0.02 0.89 0.02

LOCATIONS

1. Sha Tau Kok Wharf 2. Kat O Wharf 3. l o t O Fish Farm 4. Tsim l k i Tsui 5. Tai Po Market Park W h ar f 6. Chinese University 7. Gold Coast 8. Tsing Yi North 9. Sai Kung Wharf 10. HKUST Wharf 11. Cheung Chau Fish Farm 12. HK University West 13. China-HK Ferry 14. Tsim Sha Tsui 15. Hung Horn 16. To Kwa Wan Wharf 17. Kwun Tong Wharf 18. Sha Wan Ho Marine Police 19. Shek O Beach 20. Yung Shue Wan Blank

0.49 n.d. 0.22 1.32 0.53 2.38 0.08 0.97 n.d. n.d. n.d. 1.51 0.12 0.12 0.84 0.74 1.16 n.d. n.d. 0.31 n.d.

~-HCH

~-HCH

p,p'-DDE p,p'-DDD p,p'-DDT

ng g.l(dry wt)

TOTAL HCH

TOTAL DDTs

1.32 1.43 3.47 1.11 1.88 2.56 5.55 n.d. 0.21 0.21 n.d. n.d. 0.37 0.37 0.21 0.25 0.89 0.04 n.d. 0.22 0.27 3.11 1.25 8.24 n.d. 0.78 2.11 2.89 0.81 0.99 7.11 n.d. 0.22 4.89 5.11 7.06 1.12 15.8 1.45 2.32 11.0 14.8 0.32 0.25 0.86 0.99 4.48 3.52 8.99 3.58 3.23 9.17 1.51 3.11 3.96 8.58 0.68 1.03 1.92 0.54 3.82 5.21 9.57 0.34 0.14 0.93 n.d. n.d. 0.51 0.51 0.49 1.56 3.44 n.d. 0.59 3.46 4.05 0.68 0.65 3.62 0.33 0.12 5.21 5.66 0.38 1.13 4.74 0.24 1.44 2.15 3.83 0.28 0.32 0.98 n.d. 1.71 0.92 2.63 0.78 0.89 3.9 0.33 3.87 3.98 8.18 4.92 9.22 16.7 0.69 3.18 3.69 7.56 5.12 7.51 t5.2 0.42 2.57 3.11 6.1 0.23 0.39 0.62 0.26 1.28 1.15 2.69 0.04 n.d. 0.10 0.03 0.41 0.52 0.96 0.45 0.77 2.42 n.d. 1.45 1.53 2.98 0.01 0.05 0.09 0.01 0.02 0.02 0.05 s.1. = sample lost during analysis; n.d. = not detected; n.a. = not analyzed

"f-HCH

16.5 n.d. 3.06 7.26 23.6 16.8 3.49 21.2 5.96 3.14 3.17 17.2 34.4 3.72 25.0 97.9 48.7 7.98 1.00 2.86 0.91

TOTAL PCBs

T a b l e 1: C o n c e n t r a t i o n s o f o r g a n o c h l o r i n e c o m p o u n d s i n H o n g K o n g s e d i m e n t s n g g l ( d r y vet). F o r l o c a t i o n s , se e F i g u r e 1.

2.46 0.84 0.17 0.54 0.83 4.23 0.26 1.82 5.92 0.47 1.14 2.10 0.54 0.14 0.95 s.l. 9.78 0.98 n.d. n.a. n.d.

HCB

n.d.

n.a.

0.54 0.34 0.37 0.51 1.19 n.d. n.d. 2.85 n.d. 0.27 0.57 3.01 n.d. 0.29 0.48 1.16 4.27 1.05 n.d.

Aldrin

2.11 2.01 0.64 0.93 1.96 11.3 0.40 2.23 7.07 0.64 0.80 2.00 1.18 0.78 1.23 5.02 6.35 n.d. n.d. n.a. 0.05

Chlordane

0.04

n.&

2.01 1.68 0.70 0.55 2.63 19.4 0.80 0.96 8.32 0.59 2.38 2.46 7.79 0.50 1.19 0.77 7.48 n.d. 0.06

Dieldrin

918 Also within Victoria Harbour, Hung Hom sediment (site 15) contained lower concentrations of HCHs and PCBs (3.9 ng g~ and 25.0 ng g~ respectively) than those found in To Kwa Wan and Kwun Tong. In this area, a large population lives alongside the coast, and there are several local waste water discharge outlets. In addition, there is the possibility that organochlorine compounds in Hung Hom may have been derived from the To Kwa Wan region, being moved westward via typical water currents in Victoria Harbour (Wu, 1988). Hung Horn sediments were much sandier than those from both To Kwa Wan and Kwun Tong, presumably due to the stronger sea water current in the area. This fact would also account for the lower concentrations observed.

Sediments from the China-Hong Kong Ferry station (site 13) also contained significant concentrations of both HCHs (4.7 ng g~) and PCBs (34.4 ng g-~). It is believed that the large number of ships in this locality, combined with waste water discharge outlets, provide the major sources of these compounds. By the same token, Tsim Sha Tsui sediment (site 14) should have contained high concentrations of PCBs as well, but the sediment in this area was very sandy and in addition is subject to strong currents, as well as localized (and frequent) shipping and ferry traffic. Therefore, PCBs adsorbed to particulate matter may not deposit to the bottom, or may not remain for long periods in this locality (Wu, 1988), thus accounting for the relatively low levels encountered (HCHs: 0.98 ng g~; PCBs: 3.72 ng g~).

However, higher PCB

concentrations (17.2 ng g~) were found at Hong Kong University West (site 12), where there are a number of important anchorages for ships.

Tolo Harbour is a semi-enclosed embayment in which water exchange is low (taking _>1 month; Wu, 1988). Sediments from the Chinese University station (site 6) and Tai Po Market Park (site 5) contained PCBs in concentrations of 16.8 and 23.6 ng g-t respectively. Several wastewater discharge outlets can be found in this area. At Tai Po Market, there is an industrial site, which has a waste water discharge of a dark lateritic colour. The Chinese University site is at the mouth of the Shing Mun River, draining a partially rural area, which may account for the consistently higher concentrations of pesticides found at this location. In general, Tolo Harbour is surrounded by rural land, which must also be considered to be a contributory factor to the pesticide concentrations recorded. Although only two sites were sampled in Tolo Harbour, our results indicate the need for greater surveillance of organochlorines in this area.

To the west of Hong Kong, Tsing Yi North sediments (site 8) contained HCH and PCB concentrations of 9.2 ng g~ and 21.1 ng g-t respectively. Although other western sites (4, 7) had lower concentrations, they were still higher than those to the east of Hong Kong, suggesting that the influence of the Pearl River Delta and the Shenzen Economic Zone provided a significant contribution in these localities. Of interest in this regard were the concentrations of DDTs and PCBs at the Gold Coast location (site 7). This is largely a residential area, and it is unlikely that these compounds could have come from local sources.

919

!,o

[a] Total HCH$

1

14

!12 10 6

8

6 t'2

8

0 [c] Total PCBs

[d] HCB

!:20 ~

2

5 o

[e]Aldrin

[f] Chlordane

5 4 3 2 1

1.51~

0.5 I

[b]TotalDDT$ 2 ~

Io

o z"'

~:

-~° I.- ~

~

[g]Dieldrin

g o

< F i e u r e 2:

Average organochlorine compound concentrations in different localities around Hong Kong. In the individual diagrams, NE = north east; W = west; Tolo = Tolo Harbour; SK = Sai Kung; V H = Victoria Harbour; S = south.

1992 1995/96 1995/96

Typhoon Shelters

Other Hong Kong Waters Average (SD) Deep Bay (sites=4) Eastern Buffer (sites=4) Junk Bay (sites=l) Mirs Bay (sites=7) North Western (sites=5) Port Shelter (sites=7) Southern (sites=7) Tolo Harbour (sites=5) Western (sites=2)

Victoria Harbour (Mean) 1997

1992 1995/96

(n=6)

Victoria Harbour Range (n=9)

Date 1997/98

Location

10.25 (3.7) 12.9 (13.3) 9.0 (2.7) 6.7 (1.5) 9. l (3.4) 7.5 (3.2) 7.6 (3.9) 8.99 (3.9) 9.1 (1.9)

38-81 n.d.- 169

27.2 (w. w./

3.2-27 9.5-25.5

0.48-97.9 17.2 6.68 10.6 20.2 4.55 33.6 2.34

Total PCBs

w. w. = wet weight

56-97

24.0

1.4-30.3

0.27-14.8 5.06 2.06 6.82 9.95 5.04 5.24 2.66

Total DDTs

5.4-9.4

2.93

n.d.-2.3

0.1-16.7 5.02 1.52 6.09 11.4 1.43 6.54 1.99

Total HCHs

Connell et al. (1998a)

Connell et al. (1998a)

Connell et al. (1998b)

Connell et al. (1998a)

Source

A comparison o f total PCB, D D T and H C H concentrations (ng g~ dry weight, unless otherwise stated) in H o n g K o n g sediments during the period 1992-1998.

This Study, Range This Study, Mean (n=20) North East, Mean (n=3) West, Mean (n=3) Tolo Harbour, Mean (n=2) Sai Kung, Mean (n=2) Victoria Harbour, Mean (n= 7) South, Mean (n=3)

Table 2:

o

921 Although the north east sites (1-3) contained lower concentrations of the analyzed organochiorines, Sha Tau Kok sediments (site 1) contained relatively high concentrations of total PCBs (16.8 ng g-l). This may be related to the busy shipping within this area, and may also be associated with cross-border inputs. Similarly, levels in the Sai Kung area (9, 10) were relatively low, although total DDTs and PCBs were elevated at the Sai Kung Wharf station (site 9). PCB levels may have been associated with local shipping activities (the area contains a busy marina), but the sources of DDTs in this area are unclear. Of all the regions from which samples were taken, levels of PCBs and organochlorine pesticides were generally lowest in the region south of Hong Kong Island (sites 11, 19, 20).

Mean individual organochlorine concentrations in each of the areas sampled are shown in Figure 2. They suggest that Victoria Harbour may have unique sources for PCBs, probably via Kowloon Bay. These are likely derived from waste water discharge from local industrial areas and the busy shipping lanes immediately offshore. Concentrations in the area remain high as a result of the relatively stagnant nature of Kowloon Bay (Zheng and Richardson, In Press). As shown in Table 1, the concentrations of HCHs, DDTs and PCBs were relatively high in north-east part of Victoria Harbour, but concentrations reduced from east to west. The western waters of Hong Kong receive effluent from the Pearl River and contain relatively high concentrations of HCHs and DDTs. The Pearl River is believed to carry a considerable load of chlorinated pesticides, up to 863 tonnes per annum (Zhou et al., 1997), which is the highest amongst China's rivers.

Overall, sediments in eastern, northern, western and southern reaches of Hong Kong had lower concentrations of organochlorine compounds compared to Victoria Harbour (with the exception of Tolo Harbour in certain instances; see above and Figure 2). Because DDT has been banned for a longer period than HCH, DDT in the local marine environment is more dispersed, and in lower concentrations. Figure 2 indicates that average concentrations of pesticides and PCBs in the areas sampled can be generally ranked as follows: Tolo Harbour > Victoria Harbour > Western Hong Kong > North Eastern Hong Kong > Sai Kung > Southern Hong Kong. However, as sample numbers were low in many areas, various anomalies exist. For instance, the Tolo Harbour figures are heavily influenced by the Chinese University site (6), obviously skewing the data. Even in terms of individual compounds there are anomalies, including dieldrin concentrations in the Western area, and aldrin concentrations in both the Western area and Tolo Harbour. The data thus beg further analyses to clarify the true sources and distributions of the various compounds, which may be extremely localized, and dependent upon inputs from sources close to the sampling stations in many instances.

Although few long-term data exist for many organochlorines in Hong Kong sediments, comparisons can be made for HCHs, DDTs and PCBs, especially within Victoria Harbour (Table 2). In this regard, our

922 results are comparable to those reported by Council et al. (1998a, b). However, in contrast to our data, Cormell et al. (1998a, b) relied upon information obtained from sites offshore, which were originally reported by the Hong Kong EPD (1997) and by Hong et al. (1995). Trends in our nearshore samples (see Tables 1 and 2) are the opposite of those reported by us for petroleum hydrocarbons (PHCs) and polycyclic aromatic hydrocarbons (PAHs) at the same sites (Zheng & Richardson, In Press). In the case of the petroleum related compounds, major sources were shown to be nearshore, and continuing. Sources of organochlorines, on the other hand, appear to be diminishing (especially for substances such as HCHs, DDTs and PCBs; see also Connell et al., 1998b). It is probable that mixing of sediments over time has resulted in a more even spread of organochlorine contaminants within both nearshore and offshore Hong Kong sediments. As a result, contaminated areas such as Victoria Harbour show a more generalized pattern of sediment organochlorine contamination than that recorded for PHCs and PAHs.

Connell et al. (1998a) concluded that substances such as PCBs, DDTs, HCHs, petroleum hydrocarbons and PAHs in Hong Kong sediments were the result of trace discharges in stormwaters, sewage and industrial discharges, and were of long-term significance to the health of Hong Kong waters, especially within Victoria Harbour (Council et al., 1998b). Our data reinforce this notion, although we would also add the influence of localized agricultural activities (e.g. in areas surrounding Tolo Harbour), and the influence of the Pearl River Delta to the West, including the rapidly developing industrial and agricultural activities in the Shenzhen Special Economic Zone. Our data also suggest that further in-depth studies of organochlorine inputs are required in Hong Kong and neighbouring waters to truly identify sources of these compounds to the local environment.

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