Characterization and composition of heavy metals
and persistent organic pollutants in water and estuarine sediments
from Gao-ping River, Taiwan
Ruey-an Doong
a,*, Shih-hui Lee
a, Chun-chee Lee
a, Yuh-chang Sun
a, Shian-chee Wu
ba
Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, 101, sec. 2, Kuang-Fu Road, Hsinchu 30013, Taiwan b
Graduate Institute of Environmental Engineering, National Taiwan University, 10670 Taipei, Taiwan
Abstract
The objective of this study was to determine the concentrations and possible sources of heavy metals and persistent organic pollutants (POPs) in water and estuarine sediments from Gao-ping River in order to evaluate the environmental quality of aquatic system in south-ern Taiwan. High concentrations of heavy metals including Cr, Zn, Ni, Cu and As, ranging from 10.7 to 180 mg/kg-dry weight (dw), were detected in sediments from Gao-ping River. When normalized to the principal component analysis (PCA), swinery and electroplat-ing wastewaters were found to be the most important pollution sources for heavy metals. Of various organochlorine pesticide (OCP) residues detected, aldrin and total-hexachlorocyclohexane (HCH) were frequently found in sediments. The total concentrations of OCPs were in the range 0.47–47.4 ng/g-dw. Also, the total-HCH, total-cyclodiene, and total-dichlorodiphenyltrichloroethane (DDT) were in the range 0.37–36.3, 0.21–19.0, and 0.44–1.88 ng/g-dw, respectively. The polychlorinated biphenyl (PCB) concentrations in sediments from Gao-ping River ranged between 0.37 and 5.89 ng/g-dw. The PCB concentrations are positively correlated to the organic contents of the sediment particles. a-HCH was found to be the dominant compound of HCH in the sediments, showing that long-range transport may be the possible source for the contamination of HCH in sediments from Gao-ping River. In summary, trace amounts of POPs in estuarine sediments from Gao-ping River were detected, showing that there still exist a wide variety of POP residues in the river sedi-ments in Taiwan. These POP residues may be mainly from long-range transport and weathered agricultural soils, while heavy metal con-tamination is primarily from the swinery and industrial wastewaters.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Gao-ping River; Heavy metals; Persistent organic pollutants (POPs); Organochlorine pesticides (OCPs); Polychlorinated biphenyls (PCBs); Sediments
1. Introduction
Persistent organic pollutants (POPs) such as organo-chlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) and heavy metals are ubiquitous contaminants in different compartments of the environments (Hong et al., 1999; Doong et al., 2002a; Martin et al., 2003; Fu and Wu, 2005, 2006). In spite of numerous countries having withdrawn the registered usage of POPs for many years,
these man-made chemicals still persist at considerable lev-els worldwide (Cleemann et al., 2000; Feng et al., 2003; Verweij et al., 2004; Wurl and Obbard, 2005; Chau, 2006; Katsoyiannis, 2006). These compounds are generally gen-erated by anthropogenic processes and can be introduced into the environments through various routes. Due to their toxic, mutagenic, and carcinogenic characteristics, these persistent compounds are considered to be hazardous to the biota and environments. Also, these compounds are strongly sorbed onto the surface of particles associated with the organic content of solid-phase matrix and can be deposited to the underlying sediments. Therefore, the 0025-326X/$ - see front matterÓ 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.marpolbul.2007.12.015 *
Corresponding author. Tel.: +886 3 5726785; fax: +886 3 5718649. E-mail address:radoong@mx.nthu.edu.tw(R.-a. Doong).
www.elsevier.com/locate/marpolbul Marine Pollution Bulletin 57 (2008) 846–857
investigation of POP concentrations in aquatic environ-ments is needed to provide important information on anthropogenic impact on the environment and serve as an indicator of contaminant loading.
The input pathways of POPs into the river environments include discharge of domestic sewage and industrial waste-water, runoff from nonpoint sources, and direct dumping of wastes into the river. Although sediments do not consti-tute a direct measure of the degree of aquatic pollution, they offer an irreplaceable aid in reconstructing the histor-ical inputs of POPs based on profile descriptions of con-tamination in core samples (Hendy and Peake, 1996; Chang and Doong, 2006). Although the residual levels of the chlorinated compounds in the environments have con-siderably declined in the past thirty years, recent work has depicted that the chlorinated pesticides could be found in the range 0.04–330 ng/g-dry weight (dw) in marine and river sediments collected from Asian countries (Sarkar et al., 1997; Hong et al., 1999; Doong et al., 2002b; Hart-well, 2004; Wurl and Obbard, 2005; Minh et al., 2007). Moreover, some OCPs such as hexachlorocyclohexane (HCH), dichlorodiphenyltrichloroethane (DDT) and endo-sulfan are still used in some countries around the tropical and subtropical belts for agricultural and medicinal pur-poses (Rajendran et al., 2005). These compounds can be deposited into the sediments through long-range atmo-spheric transport (LRT), resulting in a high exposure to OCPs in the areas near the pollution sources.
In addition to the contamination of POPs in sediments from riverine and estuarine areas, the distribution of trace metals can be affected by anthropogenic inputs. Trace met-als are distributed globally with a wide range of concentra-tions in sediments and biota. High concentraconcentra-tions of heavy metals in sediments from estuarine and coastal areas in Asian countries have also been reported (Choi et al., 2006; Chen et al., 2007; Ip et al., 2007). Trace metals can be recirculated in the aquatic environments via natural or anthropogenic processes and then back to the water bodies, resulting in deterioration of the water quality and long-term implication of human health and ecosystem (Fatoki and Mathabatha, 2001; Ip et al., 2007). The change in envi-ronmental conditions such as pH, redox potential, natu-rally organic matters and sediment texture may affect the remobilization of metals from sediments (Guevara-Riba et al., 2004; Lager et al., 2005; Choi et al., 2006). The trace metals associated with coarse particles may deposit on the upstream area of the estuary, while dissolved trace metals and those associated with fine particles could be trans-ported to downstream to the surrounding coastal area by physical transportation (Ip et al., 2007). More recently, Chen et al. (2007) investigated the distribution and accu-mulation of trace metals in sediments of Kaohsiung Har-bor, Taiwan and found that the metal concentrations at the vicinity of river mouths were higher than those at other locations and metal concentrations correlated closely to the physicochemical properties of sediments. These results clearly show that the physical- and chemical properties of
river basins and anthropogenic processes have significant influence on the fate and transport of trace metals in sediments.
The Gao-ping River is one of the important rivers for water supply and irrigation in southern Taiwan. It has a total length of 171 km with a catchment basin of 3257 km2, which is the largest catchment basin in Taiwan. Gao-ping River is also one of the most contaminated rivers in Taiwan. Approx-imately 500,000 tons of domestic and industrial wastewater, mainly from swinery wastewater, are discharged daily into the river. Two petrochemical industrial parks are located near the mouth of estuary and discharge 16,000 tons of wastewater daily into the river. Also, the average sand load-ing rate is 35.6 1012
tons/year, mainly during the periods from June to October (Doong and Lin, 2004). This period is also the main flooding period of Gao-ping River, which can transport contaminant associated suspended particles from upstream to downstream. Moreover, Gao-ping River has been historically subjected to severe anthropogenic inputs of pollutants, such as heavy metals, total Kjeldahl nitrogen (TKN), total phosphorus (TP) and biochemical oxygen demand (BOD5). Despite the potential for direct
dis-charge of organic contaminants into the river, no measure-ment has been made for the content and composition of POPs and trace metals in Gao-ping River. Also, little is known regarding to the fate and potential sources of POPs and heavy metals in the aquatic environment of this region. The objective of this study was to determine the concen-trations and possible sources of POPs and trace metals in water and surface sediments from Gao-ping River in order to evaluate the pollution potential of river sediments in southern Taiwan. OCPs, PCBs and 8 metals including Cr, Cd, Pb, Ni, Zn, Cu, As and Hg were analyzed to char-acterize the distribution and fate of these compounds. Also, principal component analysis (PCA) was applied to the data in order to identify possible sources and the distri-bution of micropollutants.
2. Materials and methods
2.1. Study area and sample collection
The sampling stations are illustrated in Fig. 1. Twelve sampling stations along Gao-ping River and its tributary were selected. These sites locate from heavily contaminated (K2, K7 and K8) to background areas (K12) in order to effectively monitor the distribution of pollution throughout the catchment basin of Gao-ping River. Surface sediment samples were collected using grab sampler. A total of 72 samples, including 36 water and 36 sediment samples, was collected in April, July and November 2000, which means that each station contained three water and three sediment samples. The water samples were directly col-lected from the river using 5 L pre-cleaned glass jars with polytetrafluoroethylene (PTFE) screw caps and 1 L plastic bottles for physicochemical parameter and heavy metal analyses, respectively. The glass jar was cleaned with
bidis-tilled water first, and then rinsed with methanol, acetone and hexane in sequence to remove trace amount of organic contaminants. Field blanks containing bidistilled water only were used to control the contamination during the sampling and transportation processes. The plastic bottle was washed with deionized water, immersed in 3% nitric acid solution overnight, and then rinsed with bidistilled water. In addition, the sediment samples collected at each station were mixed and divided into three parts and were placed on ice after sampling, while the water samples for heavy metal analysis were acidified to pH < 2 using concen-trated nitric acid. All the samples were transferred to the laboratory directly. The water samples were stored at 4°C and analyzed within 2 weeks, while sediment samples were freeze-dried at18 °C and analyzed within 1 month. 2.2. Extraction and cleanup
Homogenized subsamples were freeze-dried, and OCPs and PCBs were extracted with Soxhlet apparatus separately. A 10-gram sediment was placed into a thimble filter, and POP residues in sediments were extracted with 300 mL 1:1 hexane/acetone for 24 h at a rate of 4–6 cycles/h. The extracts were firstly preconcentrated to 2–3 mL on a rotary evaporator. Activated copper powder and tetrabutyl ammo-nium (TBA) solution were then used to remove sulfur com-pounds in PCB and OCP extracts, respectively. The 2-g Florisil solid-phase extraction (SPE) cartridges were used
to cleanup both the PCB and OCP extracts. Sodium sulfate (ca. 1.0 cm) was added to a Florisil SPE cartridge to remove trace amount of water in extracts. For OCP extracts, the car-tridge was conditioned with 6 mL petroleum ether–ether (95 + 5) at a rate of 5 mL/min, and then the OCPs in SPE cartridge were eluted with 12 mL petroleum ether–ether (95 + 5) at a rate of 2 mL/min. For PCB extracts, the car-tridge was activated with 10 mL hexane, and the PCBs were eluated with 10 mL ether–hexane (6%, v/v). All the elutes were concentrated to about 1–2 mL on a rotary evaporator, and then transferred to 10 mL glass tubes with small amounts of hexane. The solvent in the glass tube was entirely evaporated under a gentle stream of nitrogen and the precipitates were redissolved in 1 mL hexane and ana-lyzed with a gas chromatograph-electron capture detector (GC-ECD) system.
The digestion for sediments was performed according to SW846 method 3052 (US EPA, 2004). The microwave-assisted digestion method was employed using PTFE diges-tion vessels (maximum pressure 200 psi) with pressure and temperature feedback control. An approximately 0.5 g of homogenized sediment was added into the mixture con-taining 9 mL nitric acid, 3 mL hydrochloric acid and 1 mL hydrofluoric acid, and then was transferred to diges-tion vessels. These vessels were then capped, sealed and heated in the microwave system with simultaneous temper-ature and pressure monitoring at 180°C for 10 min. After the microwave digestion, the products were transferred to
Taiwan Strait N25o E119o 120o 121o 122o Gao-ping river Taiwan Pacific Ocean 24o 23o 22o K11 K10 K9 K8 K7 K2 K1 K3 K4 K5 K6 K12 Taiwan strait Taiwan Strait
another PTFE beaker. The resultant solution was again heated in a class-100 clean bench until near dryness, and subsequently diluted to a known volume with bidistilled water and 1 mL nitric acid. Generally, the analytical errors due to the loss of analytes during the digestion process were evaluated by determining the spike recovery of heavy met-als using an inductively coupled plasma mass spectrometer (ICP-MS) (Elan 5000, Perkin–Elmer Sciex, Norwalk, CT). 2.3. Analytical procedures
The concentrations of OCPs and PCBs in the extracts were monitored with GC-ECD. A PTE-5 capillary column (30 m 0.32 mm 0.25 lm) and an SPB-608 capillary col-umn (30 m 0.25 mm 0.25 lm) were used for separating OCPs and PCBs, respectively. For OCPs, column tempera-ture increased from 140°C to 200 °C at 15 °C/min, held for 2 min, and then programmed to 250°C at 2 °C/min, held for 2 min. For PCBs, the initial temperature was set at 75°C, held for 2 min, and increased to 150°C at a rate of 15 °C/ min, held for 5 min, programmed to 270°C at a rate of 4°C/min, held for 5 min, and then again ramped to 300°C at a rate of 15 °C/min, held for 5 min. The tempera-tures of injector and detector were 250 and 310°C, respec-tively. Ultra-high purity nitrogen gas was used as the carrier and make-up gases. Pentachloronitrobenzene and decachlorobiphenyl were used as the internal standards for OCPs. Compounds identified included HCHs (a-HCH, b-HCH, c-HCH and d-HCH), cyclodienes (heptachlor, aldrin, dieldrin, endrin, endosulfan I, endosulfan II and endosulfan sulfate) and DDTs (p,p0-DDT, p,p0-DDD, p,p0
-DDET and methoxychlor). For PCB analysis, mixtures of Aroclor 1242/1254/1260 (1:1:1) were introduced as the quantification standard. Forty-two peaks (IUPAC No. 16, 18, 28/31, 33, 41, 48/47, 49, 52, 66/95, 56, 70, 83, 92, 101, 97, 99, 110, 105, 118, 128, 135, 138, 141, 146, 149, 151, 153, 158, 163, 170, 171, 174, 177, 180, 183, 185, 187, 194, 195, 201 and 203) were identified and summarized as P
PCB. Decachlorobiphenyl was spiked into the sample before the extraction as a surrogate of the target com-pounds, and 2,4,6-trichlorobiphenyl was used as the internal standard for PCBs. Only peaks within the proper range (±2%) of the retention time when compared with the stan-dards were counted for the quantification of PCB congeners (Fu and Wu, 2005, 2006). For every set of 10 samples, a pro-cedural blank and spike sample consisting of all reagents was run to check for interference and cross-contamination. No obvious interference and contamination was observed during the analytical procedures.
The quality of the analytical data of OCPs and PCBs was assured using certified reference material (CRM 804-050 soil standard) and standard reference material (NIST 1939a), respectively.Table 1shows the recoveries and lim-its of detection (LODs) of OCPs in sediments. The LODs and recoveries of OCPs were in the range 0.05–0.35 ng/g-dw and 82–120%, respectively. In addition, the recoveries of OCPs in CRM samples ranged from 75 to 98%. For
PCBs, the average recovery of the congeners in the SRM was 82 ± 6% with the range of 73% (CB118) to 90% (CB138/163). The LODs were in the range 0.032 (CB44) to 0.088 (CB18) ng/g-dw with the recovery of 96 ± 23% from spiked PCB standards, showing that the analytical protocols used in this study can effectively determine resi-dues of POPs in sediments.
Trace metals (Cr, Cd, Pb, Ni, Zn, Cu and As) in digested sediment and filtrated water samples (0.45 lm) were deter-mined by ICP-MS with a cross-flow nebulizer and double pass spray chamber under Rf power of 1150 W. In addi-tion, cold vapor atomic absorption spectrometer (CVAAS) was used for Hg analysis. A CRM sample (NIST 2704 Buf-falo river sediment) was used to assure the whole analytical and instrumental accuracy of the method. The LODs of heavy metals in water and sediment were in the range 0.037(Pb)–0.99(Ni) lg/L and 9.1(Cd)–249(As) lg/kg-dw, respectively, with the recovery of 82–107%. In addition, the recoveries of heavy metals in CRM samples ranged from 85% (Cr) to 121% (Hg).
Oxidation–reduction potential (ORP), volatile sus-pended solid (VSS), and water content in sediments were also analyzed. ORP was determined with an Orion EA 920 expandable ion analyzer (Orion Research Inc., Boston, MA.) by using an Orion model 97-78-00 Pt redox electrode. The values were expressed in terms of the ORP values of the samples relative to the Pt redox electrode, and were read out until the potential changed was less than 0.5 mV/min. Water content and VSS were determined by the weight loss at 103 ± 2°C and 550 ± 50 °C, respectively. Total organic car-bon (TOC) concentrations of water samples were obtained by a model 700 TOC analyzer (O.I. Corporation, Texas). In addition, concentrations of TKN and TP in sediments were analyzed and determined according to ‘‘Standard Methods” (APHA, 1995).
Table 1
The recoveries, limits of detection (LODs), and the analyzed results of CRM standards (840-050) of OCPs in sediments
Pesticides Recovery (%) LODs (ng/g-dw) CRM standard (lg/kg) Certified value Analyzed value a-HCH 99 0.12 –a – b-HCH 106 0.35 – – c-HCH 99 0.22 491.4 414.7 d-HCH 90 0.09 – – Aldrin 92 0.05 18.04 14.6 Dieldrin 99 0.12 1862.5 1467.7 Endrin 82 0.22 62.15 54.3 Heptachlor 101 0.15 – – Heptachlor epoxide 95 0.24 – – Endosulfan I 98 0.08 1464.3 1093.8 Endosulfan II 91 0.16 1128.2 845.0 Endosulfan sulfate 92 0.13 – – p,p0-DDD 109 0.18 1530.6 1278.1 p,p0-DDE 86 0.12 1519.6 1341.8 p,p0-DDT 120 0.18 1060.1 1042.1 Methoxychlor 120 0.31 – – a Not available.
3. Results and discussion 3.1. Characteristics of sediments
The Gao-ping River is one of the highly polluted rivers in Taiwan.Table 2illustrates the physicochemical parame-ters of sediments collected from Gao-ping River. These parameters included ORP, VSS, water content, TKN and TP concentrations. The ORP values ranged from 297 to 388 mV, showing that the collected sediments were mainly under anaerobic conditions. Moreover, the VSS and water contents of the sediments ranged from 0.41% to 4.07% and from 19.1% to 70.6%, respectively. The mean concentrations of TKN and TP in sediments were in the range 226–4524 and 12–797 mg/kg-dw, respectively. It is noted that the concentrations of TKN and TP in the pol-luted locations (K1–K11) were 1.8–7.9 and 2.0–6.9 times higher than that detected from the background site (K12), which means that the nutrient pollution in Gao-ping River is serious. High concentrations of TKN and TP in sediment samples were found at stations K2, K7 and K8. This may be attributed to the discharge of untreated indus-trial and swinery wastewaters into Gao-ping River. Sam-pling stations K7 and K8 are located on Niu-chou River and Wu-lo River, the highly polluted tributaries of Gao-ping River. They receive about 100,000 tons of domestic and industrial wastewaters daily. The mean TOC concen-trations in water samples at locations K7 and K8 were 3.83 ± 1.32 and 3.0 ± 1.61 mg/L, respectively. This value is two times higher than the average TOC content of the river (1.79 ± 0.83 mg/L), showing that stations K7 and K8 are seriously polluted with micropollutants.
3.2. Concentration profile of POP concentrations
Table 3 illustrates the concentration ranges, mean values and detection frequencies of POP compositions in surface sediments. The detected concentrations of OCPs and PCBs in surface sediments from Gao-ping River were <0.12–
14.2 ng/g-dw for a-HCH, <0.35–20.21 ng/g-dw for b-HCH, <0.22–15.1 dw for c-b-HCH, <0.09–1.14 ng/g-dw for d-HCH, <0.15–0.93 ng/g-ng/g-dw for heptachlor, <0.05–9.59 ng/g-dw for aldrin, <0.12–1.42 ng/g-dw for dieldrin, <0.22–0.97 dw for endrin, <0.08–1.73 ng/g-dw for endosulfan I, <0.16–1.22 ng/g-ng/g-dw for endosulfan II, <0.13–3.45 for endosulfan sulfate, <0.12–0.73 ng/g-dw for p,p0-DDE, <0.18–1.42 ng/g-dw for p,p0-DDD, <0.18–
1.88 ng/g-dw for p,p0-DDT, <0.31–0.91 ng/g-dw for
methoxychlor and 0.38–5.89 ng/g-dw for PPCBs. The mean concentrations of individual POP in sediments were
Table 2
Physio-chemical properties of sediments collected from different sampling locations along the Gao-ping River Stations Physicochemical propertya
ORP (mV) VSS (%) Water content (%) TKN (mg/kg-dw) TP (mg/kg-dw)
K1 326 to 160 1.00–2.89 37.3–43.1 819–1531 74–461 K2 365 to 235 1.19–3.03 32.4–70.6 950–4524 135–718 K3 274 to 181 0.58–1.93 28.3–36.9 727–1223 123–413 K4 174 to 132 0.85–2.24 33.7–42.7 792–904 91–638 K5 187 to 180 0.66–1.77 29.5–30.7 563–836 84–290 K6 174 to 174 0.89–2.48 28.8–41.6 649–1148 149–408 K7 388 to 194 1.34–4.07 39.4–58.3 1803–4018 335–797 K8 298 to 198 1.10–2.80 35.3–41.3 1945–2720 277–738 K9 14 to 244 0.78–1.89 28.5–41.8 594–893 118–387 K10 196 to 297 0.47–1.36 26.9–32.5 399–1356 83–609 K11 178 to 275 0.41–1.27 24.0–47.7 310–1572 70–442 K12 64 to 244 0.79–1.90 19.1–25.4 226–521 12–365 a
ORP: oxidation-reduction potential; VSS: volatile suspended solid; TKN: total Kjeldahl nitrogen; TP: total phosphorus. Table 3
The concentration ranges, mean values and detection frequencies of OCPs and PCBs POPs Range (ng/g-dw) Mean value (ng/g-dw) Detection frequency (%) April 2000 July 2000 November 2000 Mean a-HCH <0.12–14.2 1.63 42.9 35.7 42.8 40.5 b-HCH <0.35–20.21 2.93 28.6 28.6 71.4 42.9 c-HCH <0.22–15.01 4.90 35.7 7.1 21.4 21.4 d-HCH <0.09–1.14 0.50 7.1 28.6 21.4 19.0 Aldrin <0.05–9.59 2.10 57.1 42.9 35.7 45.2 Dieldrin <0.12–1.42 0.55 14.3 14.3 7.1 11.9 Endrin <0.22–0.97 0.45 7.1 35.7 42.8 28.5 Heptachlor <0.15–0.93 0.55 50.0 7.1 7.1 21.4 Endosulfan I <0.08–1.73 0.64 7.1 42.9 35.7 28.6 Endosulfan II <0.16–1.22 0.49 7.1 14.3 28.6 16.7 Endosulfan sulfate <0.13–3.45 1.24 21.4 78.6 0.0 33.3 p,p0-DDE <0.12–0.73 0.55 7.1 28.6 7.1 14.3 p,p0-DDD <0.18–1.42 0.72 50.0 21.4 7.1 26.2 p,p0-DDT <0.18–1.88 0.99 7.1 7.1 0.0 4.7 Methoxychlor <0.31–0.91 0.87 7.1 7.1 0.0 4.7 POCPsa 0.12 – 47.4 1.27 92.8 85.7 92.8 90.4 PPCBsb 0.38–5.89 1.43 83.3 91.7 83.3 86.1
a Sum of a-HCH, b-HCH, c-HCH, d-HCH, heptachlor, aldrin, dieldrin, endrin, endosulfan I, endosulfan II, endosulfan sulfate, p,p0-DDT, p,p0 -DDD, p,p0-DDE and methoxychlor.
bSum of 42 PCB congeners (IUPAC No. 16, 18, 28/31, 33, 41, 48/47, 49, 52, 66/95, 56, 70, 83, 92, 101, 97, 99, 110, 105, 118, 128, 135, 138, 141, 146, 149, 151, 153, 158, 163, 170, 171, 174, 177, 180, 183, 185, 187, 194, 195, 201 and 203).
0.50–4.90 ng/g-dw for HCHs, 0.45–2.10 ng/g-dw for cyclo-dienes, 0.55–0.99 ng/g-dw for DDTs and 1.43 ng/g-dw for P
PCBs (Table 3). In addition, the total concentrations of OCPs and PCBs in sediments ranged from 0.12 to 47.4 ng/g-dw and from 0.38 to 5.89 ng/g-dw, respectively, with mean values of 1.27 and 1.43 ng/g-dw.
The mean detection frequencies of OCPs in sediments varied from 4.7% to 45.2%. Aldrin was the most often found OCP residues in sediments (45.2%), followed by b-HCH (42.9%), a-b-HCH (40.5%), and endosulfan sulfate (33.3%). The mean concentrations of aldrin, b-HCH, a-HCH and endosulfan sulfate were 2.10, 2.93, 1.63 and 1.24 ng/g-dw, respectively. However, several OCPs includ-ing dieldrin (11.9%), endosulfan II (16.7%), p,p0-DDE
(14.3%), p,p0-DDT (4.7%) and methoxychlor (4.7%) were
only detected in a few sediment samples at low mean con-centrations of between 0.49 and 0.99 ng/g-dw. These results clearly depict that aldrin and HCH compounds were the predominant OCPs in sediments from Gao-ping River. Also, PCBs were frequently detected in the samples (83.3–91.7%). Of the 42 PCB congeners detected, PCB18, PCB20, PCB28, PCB31, PCB41 and PCB70 were found to be the dominant species because of their relatively high concentrations in major portion of the sediment samples.
Table 4 compares the POP concentrations obtained in this study with the reported data in other Asian areas. Con-centrations ofPcyclodiene were in the range 0.21–10.6 ng/ g-dw, which are comparable with those observed in Ara-bian Sea, India (Sarkar et al., 1997) and Wu-shi estuary, Taiwan (Doong et al., 2002b). Concentrations of PHCH in sediments from Gao-ping River varied from 0.37 to 36.3 ng/g-dw with the mean value of 2.49 ng/g-dw. The
lev-els ofPHCH in this study were comparable with those in sediments collected from Haihe River, China (Yang et al., 2005), Minjiang River, China (Zhang et al., 2003), coastal regions of Singapore (Wurl and Obbard, 2005) and north-ern coast, Vietnam (Nhan et al., 1999), but higher than those in sediments of Pearl River estuary, China (Hong et al., 1999), Victoria Harbor, Hong Kong (Hong et al., 1995), Masan Bay, Korea (Hong et al., 2003) and Ulsan Bay, Korea (Khim et al., 2001). It is noted that the mean concentration of PHCH in Gao-ping River (2.49 ng/g-dw) was lower than those in other locations (5.02– 8.62 ng/g-dw) having similar contamination levels, depict-ing that the concentration of HCH in sediments from Gao-ping River is slightly high.
The levels of PDDT and PPCBs were in the range 0.44–1.88 and 0.38–5.89 ng/g-dw, respectively, which are relatively low compared to those in sediments collected from other locations in Asian countries. The levels of P
DDT andPPCBs in Gao-ping River were comparable with those obtained from Pearl River estuary, China (Hong et al., 1999) and Da-han River, Taiwan (Doong et al., 2002a). However, such concentrations were much lower than those in marine and estuarine sediments collected from India, Vietnam, Singapore, China and Hong Kong (Sarkar et al., 1997; Hong et al., 1999; Zhang et al., 2003; Wurl and Obbard, 2005; Yang et al., 2005). This result is reasonable because India and China are reported to be the largest DDT consumers in Asia (Rajendran et al., 2005). In addition, Wurl and Obbard (2005) investigated the POP concentrations in marine surface sediments col-lected from the coastline of Singapore and found that concentrations of PDDT and PPCBs were in the range
Table 4
Concentration and mean values of POP residues (ng/g-dw) in sediments collected from various locations in Asian countries Locations PHCH (ng/g-dw)a P
cyclodiene(ng/g-dw)a
P
DDT (ng/g-dw)a PPCBs (ng/g-dw) References
Range Mean Range Mean Range Mean Range Mean
Gao-ping River, Taiwan 0.37–36.3 2.49 0.21–10.6 0.86 0.44–1.88 0.78 0.38–5.89 1.43 This study Pearl River estuary, China 0.28–1.23 0.68 – – 1.36–8.99 2.84 0.18–1.80 0.67 Hong et al. (1999) Haihe River, China 1.88–18.8 7.33 – – 0.32–80.2 15.9 – – Yang et al. (2005) Minjiang River, China 3.0–16.2 8.62 – – 1.5–13.0 6.70 15.1–57.9c 34.5 Zhang et al. (2003) Victoria Harbor, HK ND-2.3 0.58 – – 1.38–25.4 10.2 3.2–16.0 8.90 Hong et al. (1995)
Nearshore, HK 0.1–16.7 5.02 – – 0.27–14.8 5.06 0.48–97.9d 17.2 Richardson and Zheng (1999) Arabian Sea, India 0.85–7.87 – 1.22–4.54b – 1.47–25.2 – – – Sarkar et al. (1997)
Ulsan Bay, Korea 0.02–4.55 0.59 – – 0.05–43.4 4.20 – – Khim et al. (2001)
Masan Bay, Korea ND-1.03 0.61 – – 0.28–89.2 16.0 1.24–41.4 15.0 Hong et al. (2003) Coastal region, Singapore 3.40–46.1 18.1 – – 2.2–11.9 6.7 1.4–330e 73.9 Wurl and Obbard (2005) Wu-shi Estuary, Taiwan 0.99–14.5 3.99 0.46–13.0 – ND-11.4 2.5 – – Doong et al. (2002b) Da-han River, Taiwan ND-2.08 0.39 ND-4.51 1.05 0.06–2.91 0.90 – – Doong et al. (2002a) Northern Coast, Vietnam 1.20–33.7 8.53 – – 6.2–10.4 7.74 0.47–28.1f – Nhan et al. (1999) Mekong River delta, Vietnam <0.02–1.30 – – – <0.01–110 – 0.039–9.2 0.89 Minh et al. (2007)
a P
HCH = a-HCH + b-HCH + c-HCH + d-HCH; Pcyclodiene = heptachlor + aldrin + dieldrin + endrin + endosulfan I + endosulfan II + endo-sulfan sulfate;PDDT = p,p0-DDT + p,p0-DDD + p,p0-DDET + methoxychlor.
b
Only contain aldrin, dieldrin and endrin. c Sum of 21 PCB congeners.
d in Aroclor 1242 + 1248 + 1254 + 1260 (1:1:1:1) equivalents. e Sum of 37 PCB congeners.
2.2–11.9 and 1.4–330 ng/g-dw, respectively. These results clearly depict that contamination of DDTs and PCBs in sediments from Gao-ping River is low relative to the other Asian areas.
3.3. Spatial and temporal distribution of POPs
Fig. 2illustrates the concentrations of POPs in surface sediments from Gao-ping River collected in different sam-pling seasons. High concentrations of POCPs (PHCH, P
cyclodiene and PDDT) ranging from 93.3 to 99.7 ng/ g-dw in Gao-ping River were observed in the dry sampling seasons (April and November 2000), while low POCP concentration (47.8 ng/g-dw) was detected in rainy season (July 2000). This distribution is similar to that in sediment from Wu-shi River, Taiwan (Doong et al., 2002b), and the dilution effect during the rainy season may account for the low concentration of OCPs. The contamination levels of P
HCH in sediments from Gao-ping River were, in gen-eral, higher than those ofPcyclodiene andPDDT. How-ever, thePHCH concentrations in sediments collected in July 2000 is lower than that of Pcyclodienes. It is noted that thePHCH concentration collected in the rainy season (July 2000) is also lower than those collected in the dry sea-sons (April and November 2000), while the levels of P
cyclodiene are similar. These results reflect the fact that the contamination sources and environmental fates of HCHs and cyclodienes may be different.
Fig. 3illustrates the total concentration profiles of PCBs and OCPs from 12 sampling sites in Gao-ping River among different sampling seasons. The spatial distribution of OCPs was site-specific. High concentrations of POCPs were found in sediments collected from locations K1, K2, and K7. The total concentrations of OCPs were 0.48–18.3 ng/ g-dw at station K1, 1.19–33.7 ng/g-dw at station K2, and 6.12–47.4 ng/g-dw at station K7. These values were one order of magnitude higher than those in upstream region
(K12). The highest contamination levels ofPHCH at sta-tions K1, K2 and K7 can be up to 18.02, 31.67 and 36.22 ng/g-dw, respectively, showing that the contamina-tion is mainly from HCHs. The total concentracontamina-tions of OCPs collected in dry season were generally higher than that in rainy season. Similar results were also observed for PCBs. Relatively high concentrations of PCBs were measured at sampling sites of K2 and K7, which ranged from 1.60 to 5.89 ng/g-dw and from 3.09 to 5.30 ng/g-dw with the mean values of 3.11 and 3.86 ng/g-dw, respectively. These results are in accordance with the physicochemical properties of sediments (Table 2). Station K7 is located on the highly pol-luted tributary of Gao-ping River, while station K2 is located near the mouth of the estuary of Gao-ping River. The high concentrations of OCPs detected at stations K2 may be attributed to the emission of atmospheric deposits and the change in salinity of river water. Two big petro-chemical industrial parks are located near the mouth of the Gao-ping River and discharge large amounts of waste-water into the river. The mixing of river waste-water and seawaste-water causes the change in salinity. Particles in river water can thus be rapidly removed by the flocculation in the estuarine mix-ing zone, leadmix-ing to the accumulation of micropollutants in
HCH cyclodiene DDT PCBs 0 10 20 30 40 50 60 Σ Σ Σ Σ Concentration (ng/g-dw) April 2000 July 2000 November 2000
Fig. 2. The total concentrations ofPHCH, Pcyclodiene,PDDT and P
PCBs in sediments from Gao-ping River in different sampling seasons. The total concentrations of HCH, cyclodiene and DDT are summed of each contaminant from all stations in one sampling period.
K1 K2 K3 K4 K5 K6 K7 K8 K9 K10 K11 K12 0 10 20 30 40 50 60 70 OCPs OCP concentration (ng/g-dw) April 2000 July 2000 November 2000 K1 K2 K3 K4 K5 K6 K7 K8 K9 K10 K11 K12 0 2 4 6 8 10 12 PCBs PCBs concentrations (ng/g-dw) April 2000 July 2000 November 2000
Fig. 3. The (a) OCP and (b) PCB concentrations in sediments from 12 sampling sites in Gao-ping River.
the sediments of estuary. In addition, High concentrations of POCP and PPCBs in sediments samples were found at station K7. This result is in good agreement with those of TKN, TP and VSS (Table 2), which indicates that the contamination at K7 is attributed to the discharge of untreated industrial and swinery wastewater into Gao-ping River.
3.4. Environmental fate of POPs in sediments
The relative concentrations of the parent compound and its metabolite can provide useful information on the pollu-tion source. DDT can be biodegraded by microorganisms to DDE and DDD under aerobic and anaerobic conditions, respectively. Therefore, ratios of (DDE + DDD)/PDDT and DDE/DDD can be used as indicative indices for assess-ing the long-term weatherassess-ing and biotransformation of DDT under various redox conditions, respectively (Zhang et al., 1999; Doong et al., 2002a; Wurl and Obbard, 2005; Yang et al., 2005).Fig. 4illustrates the relationship between
(DDE + DDD)/PDDT and DDE/DDD in surface
sedi-ments collected from Gao-ping River. Most values of DDE/DDD ratio were in the range 0.09–0.94, indicating that the collected samples were mainly under anaerobic con-ditions. These results are also in good agreement with the result of ORP values in sediments (388 to 297 mV). More-over, the ratio of (DDE + DDD)/PDDT can be used to indicate the long-term weathering (>0.5) or recent introduc-tion of DDT compounds to the environments (<0.5). Most ratios of (DDE + DDD)/PDDT ranged from 0.62–0.99, which means that the concentration of metabolites (DDD + DDE) is higher than that of parent compound (DDT), and the detected PDDT concentrations may be derived from the aged and weathered agricultural soils.
Fig. 5illustrates the composition profiles of HCH spe-cies in sediments from Gao-ping River. The HCH concen-trations were summarized from the 12 sampling sites. The dominant isomers of HCH in sediments collected in April
and July 2000 were a- and b-HCH, while b- and c-HCH were found as the dominant species collected in November 2000. Recent studies have shown that the contamination of HCH isomers is a serious problem worldwide (Fellin et al., 1996; Walker et al., 1999). HCH pesticide has been used for agricultural purpose to control the insects in fruit, grain and vegetable crops and is still used in some developing countries around the tropical belt. Among the HCH iso-mers, a-HCH is more likely to partition to the air and transport for a long distance, while b-HCH is more resis-tant to hydrolysis and environmental degradation, and is the predominant isomer in soils and animal tissues and flu-ids. Recently, considerable unused stockpiles of technical-grade HCH was found in dump sites in Africa and Near East (FAO, 1998). Some of the containers have been dam-aged and resulted in leakage. In this study, the most often found isomers are a- and b-isomers, inferring that the con-tamination of HCH in the collected sediments from Gao-ping River may be attributed to the long-range transport and the erosion of the weathered agricultural soils contain-ing HCH compounds.
3.5. Concentration profiles of heavy metals
Table 5 shows the range, mean and median concentra-tions of heavy metals in water and sediments from Gao-ping River from 12 sampling sites. Most heavy metal con-centrations in water samples were lower than those values of water quality standards promulgated by Taiwan Envi-ronmental Protection Administration (EPA). Although the mean value of Cr in water samples was lower than the water quality standards (50 lg/L), some detected values in sampling locations K7 and K8 were higher than those of the water quality standards. It is noted that Gao-ping River is one of the major rivers for water supply in south-ern Taiwan. The high Cr concentration in Gao-ping River
DDE DDD DDT (DDE+DDD)/DDT DDE/DDD 0.0 0.2 0.4 0.6 0.8 1.0 Ratio April 2000 July 2000 November 2000 Sum
Fig. 4. The fractions of DDT compositions and the ratios of DDE/DDD and (DDE + DDD)/DDT in surface sediments collected from Gao-ping River.
April July November
0 20 40 60 80 100 Composition (%) Sampling Season α-HCH β-HCH γ-HCH δ-HCH
Fig. 5. The composition profiles of HCH species in sediments from Gao-ping River.
infers the possible hazard to human health. In addition, very high concentrations of trace metals were detected in sediments from Gao-ping River. Since Taiwan has not pro-mulgated the sediment quality criteria (SQC) yet, the SQC in Hong Kong was used for comparison (Ip et al., 2007). It is surprised that the mean concentration of Ni has exceeded the trigger (B) level of the SQC in Hong Kong (35 mg/kg-dw). In addition, the mean concentrations of Cr and Zn
were 171 ± 439 and 203 ± 289 mg/kg-dw, respectively, which are much higher than the Action (C) level of SQC in Hong Kong (80 mg/kg-dw for Cr and 200 mg/kg-dw for Zn). These results clearly show that the sediments from Gao-ping River are highly contaminated with heavy metals.
Fig. 6 displays the site variations of the selected metal concentrations (Cr, Cu, Ni and Zn) in sediments collected Table 5
The concentration range, mean values and median of heavy metals in water and sediment samples collected from Gao-ping River Metals Water quality standarda(lg/L) Water samples (lg/L) Sediment samples (mg/kg-dw)
Range Mean ± SD Median Range Mean ± SD Median
Cr 50 0.47–338 19.2 ± 63.4 1.80 35.7–2714 171 ± 439 57.5 Cd 5 0.08–0.95 0.25 ± 0.22 0.16 0.01–1.0 0.21 ± 0.23 0.12 Pb 50 0.77–13.8 2.29 ± 2.31 1.77 18.3–92.9 28.2 ± 11.5 24.9 Cu 1000 0.90–34.3 5.12 ± 7.72 2.49 14.5–197 46.9 ± 41.7 32.8 Ni 100 3.64–35.8 7.54 ± 6.14 5.59 18.9–184 38.6 ± 26.4 33.7 Zn 5000 5.14–354 29.6 ± 56.3 15.5 65.9–1535 203 ± 289 122 As 50 0.63–4.32 2.29 ± 0.97 2.13 5.12–25.8 11.3 ± 3.94 11.2 Hg 2 <0.33 <0.33 <0.33 0.20–1.72 1.01 ± 0.44 1.11
a Promulgated by Taiwan Environmental Protection Administration (EPA).
K1 K2 K3 K4 K5 K6 K7 K8 K9 K10 K1 1 K 12 0 100 200 300 400 1000 1500 2000 2500 Cr Concentration (mg/kg-dw) Sampling station April 2000 July 2000 November 2000 K1 K2 K3 K4 K5 K6 K7 K8 K9 K10 K11 K12 0 50 100 150 200 Cu Concentration (mg/kg-dw) Sampling station April 2000 July 2000 November 2000 K1 K2 K3 K4 K5 K6 K7 K8 K9 K10 K11 K12 0 20 40 60 80 100 120 140 160 180 Ni Concentration (mg/kg-dw) Sampling station April 2000 July 2000 November 2000 K1 K2 K3 K4 K5 K6 K7 K8 K9 K10 K11 K12 0 100 200 300 400 1200 1400 1600 Zn Concentration (mg/kg-dw) Sampling station April 2000 July 2000 November 2000
from 12 sampling sites in Gao-ping River. The detected concentrations from most sampling stations were, in gen-eral, similar to those of the background station (K12), which located in the upstream of Gao-ping River. It is noted that the metal concentrations (Cr, Cu, Ni and Zn) detected from sampling locations K2, K7 and K8 were higher than that of location K12, which is in good agree-ment with the distribution patterns of POPs. The high con-centrations of trace metal detected at stations K2 may be attributed to the emission of atmospheric deposits and wastewater discharge from factories located near the mouth of the estuary of Gao-ping River and from the sur-face runoff of Kao-hsiung metropolitan, the biggest city located in the catchment of the Gao-ping River (Doong and Lin, 2004). The mixing of river water and sea water causing a change in salinity may be another possibility for the higher metal concentrations at location K2. Trace metals are usually associated with fine particles (Birch and Taylor, 2000; Singh et al., 2003). When fine particles move downstream to the mouth of Gao-ping River, the change in salinity enlarges the particle diameters by floccu-lation, resulting in the deposition of metal concentrations in the sediments of estuary.
High concentrations of trace metals in sediment samples were also found at stations K7 and K8. The mean concen-trations of Cr, Cu, Ni and Zn at location K8 were 269 ± 147, 102 ± 56, 30.1 ± 5.8 and 234 ± 62 mg/kg-dw, which are 2.5–6.0 times higher than that of the background station (K12). The contamination of sediments from sam-pling site K7 is more serious and the mean concentrations of trace metals were 2–3 orders of magnitude (29–104 times) higher than those from uncontaminated sites, pre-sumably attributed to the discharge of untreated industrial and swinery wastewater into Gao-ping River.
3.6. Principal component analysis
The distribution patterns of heavy metals were analyzed by a principal component analysis (PCA). PCA is a multi-variate statistical technique that can simplify large data sets and allow to reduce the number of variables to a smaller set of orthogonal factors of easier interpretation by displaying the correlations existing among the original variable ( Ash-ley and Baker, 1999). This analysis was performed with the S-PLUS 2000 statistical software package. Due to the low residual concentration of POPs in sediments from Gao-ping River, only trace metals and several physicochemical pollution indices including TKN, TP, water content, TOC and BOD5were involved. In order to minimize the
effect of absolute concentration on the first principal com-ponent, trace metals and pollution indices used for PCA analysis were normalized to the total amounts of the parameters (percent of total amount) (Woodhead et al., 1999).
The loading plot of PCA of trace metals in water sam-ples from Gao-ping River is illustrated inFig. 7a. Compo-nent 1 (PC1) can explain 42.71% of the total variance, with
high loadings on TKN, TP, BOD5, TOC, and some trace
metals (Cr, Cu and Zn). High loadings were observed at sampling locations K7 and K8, reflecting the high pollution potential on these sites. Since the pollution indices (TKN, TP, and BOD5) and trace metals of Cu and Zn are highly
related to the contamination of swinery wastewater (Ismail and Ramil, 1997), this result confirms that swinery waste-water is the main pollution source of Gao-ping River. Component 2 (PC2) can explain 11.7% of the total vari-ance. High loadings on Pb, As and particulates (SS) were observed, inferring that the mobility of As and Pb would be associated with particulates and could be moved easily downstream. From the distribution of sampling locations, high loadings of PCA were observed for stations K2 and K4 and K5, which are all located in the downstream of the main river. This also depicts that the major sources of the Pb and As contamination in aquatic environments are different from those of Zn and Cu.
Similar to the results obtained in water samples, most of the total variances in the data set in sediment samples were accounted for by two principal components. As illustrated in Fig. 7b, PC1 can explain 44.2% of the total variance,
-0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 -0.4 -0.2 0.0 0.2 0.4 0.6 water NH 3-N TKN BOD 5 TOC Cr TP Zn Cu As SS Pb Cd Ni Comp. 2 (11.66%) Comp.1 (42.71%) -0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 -0.4 -0.2 0.0 0.2 0.4 0.6 Cr Zn Ni Cu Pb Cd TKN water content TP Hg Size Al Fe Mn Comp. 2 (18.05%) Comp.1 (44.23%) sediment
Fig. 7. The loading plot of principal component analysis (PCA) of (a) water and (b) sediments from Gao-ping River.
with the high loadings on water content, TKN, and most trace metals (Cd, Cr, Ni, Zn and Cu), which is in good agreement with the results obtained in water samples. PC2 can account for 18% of the total variance, with geo-chemical elements (Mn, Fe and Al) as the abundant com-pounds. However, the characteristics of some pollution indices including grain size and TP are indistinguishable. Therefore, factor analysis (FA) was further employed.
Fig. 8shows the factor analysis of trace metals and pol-lution indices in sediment samples from Gao-ping River. FA1 can explain 30.8% of the total variance with high loadings (>0.7) on heavy metals (Cu, Pb, Zn, Cr and Ni). High loadings were observed for sampling location K7, reflecting that FA1 may be highly related to the pollution sources. It is noted that the major source of Cu and Zn is swinery wastewater, while the contamination of Pb, Ni and Cr may result from the discharge of electroplating wastewater, showing that the serious contamination in Gao-ping River may mainly be due to the discharge of industrial and swinery wastewaters. FA2 can explain 18.9% of the total variance. High loadings on TP, TKN and water content were observed for sampling site K2,
which reflects that FA2 represents the nutrient pollution. It is noted that this result is a little different from that in water sample, presumably due to that the trace metals are associated with particulates and deposited on the sedi-ments, while the water soluble TP and TKN are easily moved downstream to the mouth of Gao-ping River (K2) by physical transportation. In addition, FA3 and FA4 can explain 12.8% and 10.6% of the total variance, respec-tively, with high loadings on geochemical elements and particle size, showing that these two factors represent the geochemical characteristics of Gao-ping River.
4. Conclusions
The results obtained in this study first document the compositions and distribution of heavy metals and POPs in sediments from Gao-ping River. The mean concentra-tions of TKN and TP in sediments ranged from 339 to 2650 and 134 to 624 mg/kg, respectively. The VSS concen-trations ranged between 0.99% and 2.74%, clearing show-ing that the nutrient pollution in Gao-pshow-ing River is serious. In addition, there still exists trace amounts of OCPs and PCBs in estuarine sediments from Gao-ping River. The detected total concentrations of OCPs and PCBs were in the range of 0.12–47.4 and 0.37–5.89 ng/g, respectively, which are generally low to medium relative to the other Asian areas. HCHs and aldrin are the most abundant compounds in sediments. In addition, high con-centrations of Cr, Cu, Ni and Zn in sediment samples were detected. The concentrations were 2–3 orders of magnitude higher than those of the uncontaminated sites. PCA analy-sis showed that the contamination of heavy metal is related to the pollution indices of the Gao-ping Rivers. The distri-bution patterns observed in this study reflects the fact that POP residues in surface sediments may be mainly from long-range transport and weathered agricultural soils, while the contamination of heavy metals is attributed to the discharge of industrial and swinery wastewaters into Gao-ping River.
Acknowledgement
The authors thank the National Science Council, Tai-wan, ROC for the financial support under Contract No. NSC 95-2113-M-007-008.
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