Organochlorine Pesticides in the Singapore Coastal Environment

C. Basheer and H. K. Lee

[1] Introduction

Organochlorine pesticides (OCPs) are important classes of persistent organic pollutants (POPs) that are commonly found in the environment. OCPs are long-lived organic compounds, and originate almost entirely from anthropogenic activities such as agriculture and pest control [1]. POPs are known to adversely affect the endocrine system in both wild fauna and humans, have a propensity to bioaccumulate in the lipid fraction of biological tissues and are subject to biomagnification in both terrestrial and aquatic food webs [2]. POPs are also highly recalcitrant to chemical and biological degradation, and therefore persist in the environment for long periods [3]. The OCPs are of particular concern due to their environmental and health effects which has led to the control of, or complete ban on, the use of these chemicals in many developed as well as developing countries (although it is clear that they are still being used illegally). Recently, Singapore became a signatory of the Stockholm Convention under the United Nations Environment Programme to implement measures to reduce and eliminate POPs releases into the environment, including bans on production, import, export, and use of some OCPs [4]. These microorganic pollutants are semi-volatile at atmospheric conditions, and may occur both in the gas phase and as attached to particles depending on the vapor pressure of the compound [5]. The major removal mechanism of the semivolatile organic compounds from the atmosphere is through either wet or dry deposition. Wet deposition of POPs to both aquatic and terrestrial ecosystems is particularly important in places that receive abundant rainfall like Singapore.

The OCPs are, to a variable extent, insoluble in seawater but are readily soluble in fat and adsorb strongly onto suspended particulates in the water column [6]. OCP enrichment of the surface film may be of considerable importance to surface living organisms or to birds that skim food off the sea surface. Surface plankton and other organic particulates are readily associated with OCPs and undergo subsequent sedimentation.

In this study, OCPs were monitored in Singapore’s coastal environment. This survey represents a continuing effort to identify the status and trends of OCPs contamination in the Singapore context, to acquire a better understanding of the transport and deposition processes involving these pollutants in the tropical environment.

[2] Sampling Procedure

[2.1] Selection of Locations

Surface water samples were collected from 19 locations (Figure 1) along the Singapore coastline from October 2002 to January 2003. Surface seawater was collected in 1-liter precleaned glass bottles. Locations selected for sampling including the primary industrial areas of the southwestern coast of Singapore, Jurong Island in the Singapore Straits, the northeastern coast of the island in Johor Straits, water sports recreational sites of central and eastern Singapore Straits, and western Johor Straits. Locations gradients and classifications are given in the Table 1 (see Appendix.).

[2.2] Conditions During Sample Collection

There are no seasons in Singapore. Weather conditions are generally constant, usually warm, humid and abundant rainfall can be experience throughout the year. The marinas and port areas are generally sheltered, and the tidal range is minimal. Thus, the rate of exchange of water into marina and port is relatively low. The characteristics of the water samples collected are given in Table 1. The temperature of the samples varied between 30^oC to 34.5^oC, and pH from 7.3 to 8.3.

[3] Analytical Results

[3.1] Summary of Results

OCPs were detected in all sampled locations (see Figure 1). Widespread contamination of these compounds raises concern about their accumulation in the food chain. As well, Singapore's coastal waters are increasingly used for many purposes such as desalination for drinking water, recreation and aquaculture (fish farming). There is therefore a real threat of exposure to these compounds. Results from this study illustrate the extent of pollution of these undesirable compounds and despite the relatively small size of the overall sampling area, there was considerable variation in the concentration levels from the sites. The highest amounts of individual OCPs were g-BHC (0.879 mg/L) and a-BHC (0.363 mg/L) recorded at Pasir Ris, and Endrin (0.898 mg/L) recorded at Lim Chu Kang. The lowest amounts of OCPs were recorded at south and central regions (see data on distribution region-wise).

[3.2] Mean Concentrations of OCPs in Eastern Johor Straits and Eastern Singapore Straits

Wide ranges of concentration of OCPs were detected in eastern Johor Straits, with mean total OCP concentrations ranging from 0.035 to 0.133 mg/L. The highest total OCP concentrations detected in the northeastern region were at Pasir Ris, i.e. 0.133 mg/L and in the Eastern Singapore Straits, at the Bedok Jetty, i.e. 0.112 mg/L. The individual OCP concentrations in this region ranged from 0.004 mg/L to 0.879 mg/L. The highest concentration of OCPs were g-BHC (0.879 mg/L) and a-BHC (0.363 mg/L) detected at Pasir Ris; b-BHC (0.449 mg/L) at East Coast Park; Endrin (0.376 mg/L) at Sembawang Park; and Aldrin (0.305mg/L) at Changi. The mean and concentration ranges at six locations are shown in the Table below.

Mean and Concentration Ranges of OCPs (Eastern Johor Straits & Eastern Singapore Straits)

Concentrations in mg/L
OCPs	Mean	Standard deviation	Minimum	Maximum
a-BHC	0.189	0.124	0.050	0.363
b-BHC	0.239	0.167	0.038	0.449
g-BHC	0.381	0.325	0.081	0.879
δ-BHC	0.050	0.018	0.034	0.078
Heptachlor	0.018	0.004	0.013	0.023
Aldrin	0.073	0.114	0.013	0.305
Heptachlor epoxide	0.012	0.003	0.009	0.016
a-Chlorandane	0.009	0.004	0.004	0.014
g-Chlorandane	0.010	0.002	0.007	0.014
p-p'-DDE	0.005	0.001	0.004	0.006
Dieldrin	0.044	0.010	0.030	0.059
p-p'-DDD	0.009	0.003	0.005	0.015
Endrin	0.241	0.087	0.141	0.376
p,p'-DDT	0.022	0.036	0.004	0.094
Endosulfan sulfate	0.032	0.011	0.020	0.046

See the Appendix (Table 2a and 2b) for details on site-specific levels

The Eastern Johor Straits and the Singapore Straits are more contaminated than the other regions. This is probably due to the confined configuration of the coast, and the presence of the Pasir Gudong river estuary, which limits hydrodynamic dispersion. This river runs across agricultural, commercial and industrial land in Malaysia and into the Straits of Johor, adjacent to Singapore. Among the seven locations the Pasir Ris park site was more contaminated than the other locations; the lowest amount was recorded in Ponggol (see Table 2).

[3.3]. Mean OCPs Concentrations in the Singapore Straits (South and Central Regions)

The mean total OCPs concentrations ranged from 0.031 to 0.117 mg/L. Both highest and lowest total mean OCPs concentrations were detected in the central region i.e. 0.117 mg/L at Sentosa, and 0.031 mg/L at Labrador Park respectively. The individual OCPs concentrations in these south and central regions ranged from 0.004 mg/L to 0.644 mg/L. The highest concentration of individual OCPs were detected at Raffles Place (g-BHC, 0.644 mg/L; β-BHC, 0.362 mg/L and a-BHC, 0.257 mg/L); Sentosa (Endrin, 0.563 mg/L) and St. John’s Island (Aldrin, 0.121 mg/L).

The eastern and central locations in the Singapore Straits support activities such as Singapore port itself with shipping industries (near the World Trade Centre (WTC) Complex), recreational and tourist activities (Sentosa) and further to the west, petrochemical refineries near the Southern Islands. Among the seven locations Sentosa and Raffles Place were more heavily contaminated than the others; the lowest concentration of OCPs was recorded in Labrador Park (see Table. 3). Compared with other regions, relatively low concentrations of OCP were detected here.

Mean and Concentration Ranges of OCPs (Singapore Straits (South and Central Regions))

Concentrations in mg/L
OCPs	Mean	Standard deviation	Minimum	Maximum
a-BHC	0.116	0.088	0.019	0.257
β-BHC	0.175	0.124	0.061	0.362
γ-BHC	0.276	0.268	0.013	0.644
δ-BHC	0.062	0.022	0.031	0.094
Heptachlor	0.028	0.019	0.016	0.067
Aldrin	0.070	0.042	0.024	0.121
Heptachlor epoxide	0.011	0.004	0.005	0.016
a-Chlorandane	0.007	0.002	0.004	0.011
g-Chlorandane	0.010	0.001	0.009	0.013
p-p'-DDE	0.005	0.001	0.004	0.008
Dieldrin	0.039	0.020	0.023	0.081
p-p'-DDD	0.006	0.002	0.003	0.010
Endrin	0.228	0.152	0.108	0.563
p,p'-DDT	0.013	0.016	0.004	0.049
Endosulfan sulfate	0.026	0.004	0.020	0.031

See the Appendix (Table 3a and 3b) for details on site-specific levels

[3.4] Mean Concentrations of OCPs in the Western Johor Straits and Western Singapore Straits

In the western part of Johor Straits, the waters mainly support recreational activities and fish farms, with some minimal agriculture that do not generally involve extensive use of the types of pesticides discussed in the present work. The mean total OCPs concentrations ranged from 0.067 to 0.105 mg/L. The highest total OCPs concentrations were detected in the northeastern region at Lim Chu Kang i.e. 0.105 mg/L and the lowest total OCP concentration was detected at Kranji (0.067 mg/L). Individual OCPs concentrations in this region ranged from 0.005 mg/L to 0.617 mg/L. The highest concentrations of individual OCPs were recorded at Tuas Jetty (g-BHC, 0.617 mg/L, a-BHC, 0.333 mg/L, p-p’-DDT, 0.173 mg/L); Jurong Pier (b-BHC, 0.278 mg/L); and Lim Chu Kang (Endrin, 0.898 mg/L). Among the six locations, the highest levels of OCPs were detected in Lim Chu Kang, probably due to fresh water input from a Malaysian river opposite this location (see Table 4).

Mean and Concentration Ranges of OCPs (Western Johor Straits and Western Singapore Straits)

Concentrations in mg/L
OCPs	Mean	Standard deviation	Minimum	Maximum
a-BHC	0.211	0.089	0.077	0.333
β-BHC	0.135	0.104	0.036	0.278
γ-BHC	0.336	0.180	0.157	0.617
δ-BHC	0.059	0.032	0.028	0.119
Heptachlor	0.025	0.007	0.020	0.036
Aldrin	0.041	0.019	0.017	0.065
Heptachlor epoxide	0.012	0.003	0.008	0.016
a-Chlorandane	0.010	0.003	0.006	0.014
g-Chlorandane	0.010	0.004	0.006	0.015
p-p'-DDE	0.007	0.002	0.005	0.010
Dieldrin	0.047	0.007	0.037	0.055
p-p'-DDD	0.036	0.067	0.006	0.173
Endrin	0.334	0.285	0.134	0.898
p,p'-DDT	0.017	0.009	0.009	0.028
Endosulfan sulfate	0.028	0.014	0.015	0.054

See the Appendix (Table 4a and 4b) for details on site-specific levels

[3.5] Comparison of OCPs in Seawater Samples

The land area under agricultural use in Singapore is negligible and there is no direct application of these pesticides in the country. All OCPs are banned in Singapore. However pesticides may be easily transported through the ambient environment by different mechanisms including volatilization from soil and spray drift during application to crops [7]. The presence of OCPs in Singapore’s marine waters is probably a function of their use in neighbouring countries, including Malaysia and Indonesia. Concentrations of OCPs measured in our study were comparatively lower than those detected in water from the Selangor River in Malaysia i.e. Aldrin, up to 0.884 mg/L; Dieldrin, up to 0.850 mg/L; Endrin, up to 10.970 mg/L; b-Endosulfan, up to 12.270 mg/L; Heptachlor, up to 13.710 mg/L; Lindane, up to 40.950 mg/L; p,p'-DDT, up to 44.770 mg/L; p,p'-DDE up to 2.310 mg/L [8]; However, OCPs levels in Singapore’s coastal waters are higher than those found in the Coral Sea, Australia where total OCP concentrations have been measured at 1.21 ng/L [9], and 5.5 ng/L [10]. There does not appear to be any noticeable trend in the levels of the pollutants detected at various sampling locations.

[3.6] Summary of Quality Assurance and Control Measurements

The calibration curve was constructed with a linearity of 0.99. Extraction was performed using the proposed UNU procedure with 0.130 mg/L of OCPs-spiked concentration. Most of the compounds exhibited recoveries of greater than 80%. The recovery results are summarized in Table 5. Reappearance of OCPs was performed as suggested, and summarized in Table 6. Blank experiments were performed to check for interferences.

[3.7] Problems Encountered

We encountered no major problems in the use of the stipulated procedures in this monitoring programme.

[4] Conclusions

Monitoring studies of Singapore coastal waters indicate the presence of organic micropollutants of environmental and toxicological interest, among which the OCPs play an important role. Levels of OCPs measured can be said to be in the moderate range. This is not surprising, as extensive agricultural activities in Singapore have been phased out for more than two decades. However, these OCPs are persistent and atmospheric deposition could be the source of entry to our environment [11]. In order to understand the fate of these compounds, it is necessary to continue to monitor their presence in order to elucidate the distribution and behavior of these compounds in various environmental compartments in the Singapore context, and compare data with its immediate neighbours.

[5] References

[1] UN-ECE (1994) State of Knowledge Report of UN ECE Task Force on Persistent Organic Pollutants for the Convention on Long-range Transport Air Pollution

[2] National Research Council: 1999, Hormonally Active Agents in the Environment, National Academic Press, Washington, D.C.

[3] P. De Voogt, D. E. Wells, L. Reutergardh, U. A Th. Brinkman, Int. J. Environ. Anal. Chem. 40 (1990) 1

[4] Ministry of the Environment, Singapore: http://www.env.gov.sg/faq/faq2.htm#q8

[5] F. D. Wania, D. Mackay, Environ. Sci. Technol. 30 (1996) 390A

[6] J. L. Zhou, S. J. Rowland, Water Res. 31 (1997) 1708

[7] U. Dörfler, I. Scheunert, Chemosphere 35, (1997) 77

[8] A.M. Mustafa, C. Melissa, L. Pui, L. Cheng, A. Abdul Rani, (2000). Pesticide Residues in Water from the Selangor River, Malaysia. The UNU International Symposium on Endocrine Disrupting Chemicals (EDCs), Environmental Governance and Analytical Techniques - EDCs in East Asian Coastal Hydrosphere. University of Malaya, Kuala Lumpur, Malaysia, April 17 – 18.

[9] S. Tanabe, H. Tanaka, R. Tatsukawa., Arch. Environ. Contam. Toxicol. 13 (1984) 731

[10] D. A. Kurtz, E. L. Atlas, (1990) Distribution of Hexachlorocyclohexanes in the Pacific Ocean Basin, Air, Water, 1987. In Long Range Transport of Pesticides, ed. D.A. Kurtz, pp. 143-160. Lewis Publishers, MI, USA.

[11] S. Harrad, (2000) Persistent Organic Pollutants. Environmental Behavior and Pathways for Human Exposure. Kluwer Academic Publishers, UK.

Figure 1- Baseline Monitoring Locations 2002-2003