Composition and distribution of organochlorine pesticide residues in surface sediments from the Wu-Shi River estuary, Taiwan

https://doi.org/10.1016/S0025-326X(02)00102-9Get rights and content

Abstract

The contamination of organochlorine pesticides (OCPs) in sediments from the Wu-Shi River estuary was investigated to evaluate the pollution potentials and distribution of OCPs in central Taiwan. A total of 19 sediment samples were collected at five sampling stations along the River estuary. The concentrations of OCPs were in the range of 0.99–14.5 ng/g-dry weight (dw) for ΣHCH (α-, β-, γ-, δ-HCH), 0.46–13.4 ng/g-dw for Σcyclodiene and 0.53–11.4 ng/g-dw for ΣDDT (p,p-DDD, p,p-DDE, p,p-DDT). The mean concentrations of ΣHCH, Σcyclodiene and ΣDDT were 3.79, 4.87 and 2.51 ng/g-dw, respectively. The total concentrations of OCPs correspond to 1.73–71.9 μg/g-OC when normalized to TOC contents. Among the organochlorine pesticides, endosulfan sulfate, β-HCH, and p,p-DDD were the most dominant compounds in the sediments with the average concentrations of 1.97, 3.43 and 2.08 ng/g, respectively. Also, different contamination patterns among sampling seasons were observed. The measured concentrations of OCPs collected in spring were higher than those in autumn and winter. A linear relationship between sediment characteristics and OCP residues was also demonstrated. The results obtained in this study show that there still exist a variety of organochlorine pesticide residues in the sediments from the near shore of central Taiwan.

Introduction

A large variety of hydrophobic organic substances, such as organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs) are transported into riverine and estuarine environments through different input pathways, such as discharge of domestic sewage and industrial wastewater, runoff from nonpoint sources, and atmospheric deposition. Although sediments do not constitute a direct measure of the degree of aquatic pollution, they offer an irreplaceable aid in reconstructing the historical inputs of anthropogenic pollutants based on spatial and temporal profile descriptions of contamination in sediment samples (Hendy and Peake, 1996). Therefore, the investigation of distribution of anthropogenically hydrophobic organic compounds in sediments can provide a valuable record of contamination in the river or estuary environments.

The understanding of the contamination of organochlorine pesticides in the riverine and estuarine environments is of great concern because of the detection of the pesticide residues in various environmental media (Pereira et al., 1996; Hong et al., 1999; Doong et al., 1999). In spite of numerous countries have withdrawn the registered usage of OCPs for many years, these man-made chemicals still persist at considerable levels worldwide (Fowler, 1990; Hendy and Peake, 1996; Sarkar et al., 1997). In Taiwan, a broad spectrum of pesticides was used for agricultural activities as well as vector controls. Hexachlorocyclohexane (HCH), endosulfan and DDT were employed extensively from the early 1950s for the control of soil-dwelling insects until the production ban commenced in 1974. It is estimated that 2.5×107 kg of pesticides was released into the environments annually since the 1950–1970s and constituted a long-term source of contamination to aquatic ecosystem via soil erosion and agricultural runoff.

Long-range transport (LRT) is also another possible route for the contamination of organochlorine pesticides in sediments. Some organochlorine pesticides, such as endosulfan, heptachlor and HCH are still used in some developing countries around the tropical belt and may be transported through the atmosphere and gradually deposited into the river at higher latitudes. Oehme et al. (1996) measured the seasonal concentration changes of organochlorines in the European Arctic and found that long-range air transport from more polluted areas might lead to a significant concentration change in the Arctic air. A study conducted in India examining the flux of HCH also indicated that most of the HCH applied annually was lost to the atmosphere (Takeoka et al., 1991).

The Wu-Shi River drainage basin covers approximately of 2026 km2 and has a total length of 117 km, ranking as the fourth largest river basin in Taiwan. This river, which flows into Taiwan Strait, is located in a temperate area characterized by intense agricultural activities and only slightly industrialized. Also, the Wu-Shi River catchment is an important water supply source for central Taiwan. However, little information on the contamination of OCPs in the riverine and estuarine environments is available. This study first documented the composition and distribution of OCPs residues in surface sediments from the riverine and estuarine environments of the Wu-Shi River. Furthermore, the spatial and temporal changes and the environmental fate of OCPs were discussed.

Section snippets

Study area and sampling

Samples of surface sediment were collected from October 1997 to May 1998. Five sampling stations along Wu-Shi River estuary were selected. The locations of these sampling stations are shown in Fig. 1. At all sample sites surface sediments were collected from a boat using a sediment grabber in areas of low flow velocity (<0.3 m/s). Immediately after collection sediments were preserved in deep freeze in order to avoid degradation.

Extraction and cleanup

Homogenized subsamples were freeze-dried and organochlorine

Contamination profiles of OCPs

Concentrations of organochlorine pesticides in surface sediments from the Wu-Shi River estuary are shown in Table 2. Compounds identified included hexachlorocyclohexane (α-HCH, β-HCH, γ-HCH, δ-HCH), cyclodiene (aldrin, dieldrin, endrin, endosulfan I, endosulfan II and endosulfan sulfate) and diphenyl aliphatic (p,p-DDE, p,p-DDD, p,p-DDT and methoxychlor) pesticides. The concentrations of ΣOCPs were in the range of 2.62–33.6 ng/g-dry weight (dw) with an average value of 13.98 ng/g-dw.

Conclusions

This study first documented the composition and distribution of OCPs in sediments collected from Wu-Shi River estuary. Sediment OCP concentrations were generally low to medium relative to other areas of the world. The high detection frequencies and concentration of the biological metabolites, such as endosulfan sulfate, p,p-DDD from the parent OCPs in sediments depict that the organochlorine pesticide contamination was mainly from the aged and weathered agricultural soils.

The hydrological

Acknowledgements

The authors would like to thank Environmental Protection Administration (EPA) and National Science Council, Taiwan, ROC for the financial supports under the Contract No. EPA-87-E3L1-03-02 and NSC89-2621-Z-007-001, respectively.

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