Distribution of organic contaminants in Lake Taihu

Distribution of organic contaminants in Lake Taihu

Pergamon PII: soo43-1354(%)ooo25-5 DISTRIBUTION HUIXIAN War. Res. Vol. 30, No. 9, pp. 200>2008, 1996 Copyright 0 1996ElsevierScience Ltd Printed in...

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Pergamon PII: soo43-1354(%)ooo25-5

DISTRIBUTION

HUIXIAN

War. Res. Vol. 30, No. 9, pp. 200>2008, 1996 Copyright 0 1996ElsevierScience Ltd Printed in Great Britain. All rights reserved 0043-1354/96$15.00+ 0.00

OF ORGANIC CONTAMINANTS TAIHU

ZOU, GUANGYAO

IN LAKE

SHENG*, CHENG SUN and OUYONG

XU

Department of Environmental Science and Engineering, Nanjing University, Nanjing 210093, P.R. China (First received June 1995; accepted in revised form January 1996)

Abstract-Water contamination in Lake Taihu and Lake Wulihu poses a threat to water supply and recreation. Water samples were collected during 1988-1989 for analysis of organic contaminants in the two lakes. Over 800 organic contaminants were detected by CC and GC-MS, and 84 of them were screened by a scoring system as priority contaminants. Results showed that the average concentration was one order of magnitude higher in Lake Wulihu than in Lake Taihu, although the number of contaminants in Lake Wulihu was only double those in Lake Taihu. Concentrations of phthalates, halohydrocarbons, and alkanes in Lake.Taihu were close to those in Lake Wulihu, whereas the concentrations of alkylaromatics, anilines, phenols, alcohols, ketones, and polynuclear aromatics in Lake Taihu were lower than in Lake Wulihu by 2-3 orders of magnitude. The average concentration of contaminants in Lake Taihu reaches the highest during the rainy season while this occurs in Lake Wulihu during the dry season because of differences in water flow patterns in the lakes, conditions of the water environment, and physico-chemical properties of contaminants. Copyright 0 1996 Elsevier Science Ltd Key words-organic

contaminant,

distribution, lake, movement

INTRODUCTION

Lake Taihu (Institute of Wuxi Environmental Science and Technology), with an area exceeding 1200 km*, is located in the southern portion of Jiangsu Province, China. At its northern tip is Lake Wulihu, a lagoon with an area of approximately 10 km* (Fig. 1). Several tributaries connect the two lakes with other bodies of water such as the Yangtze River. These two lakes differ in hydrological conditions in addition to area. Lake Wulihu receives millions of tons of industrial waste water and domestic sewage each day from Wuxi, an industrial city with a population of 1 million located approximately 2 km northeast of Lake Wulihu. On the other hand, Lake Taihu accepts some industrial and agricultural pollutants, as well as sewage, mainly from small towns on the west side of the lake. During most of the year, water flows from Lake Taihu to Lake Wulihu. However, reverse flow in winter/spring brings water from Lake Wulihu into Lake Taihu. The main geographical features of Lake Taihu are represented in Fig. 1. Lake Taihu is known for both recreational opportunities and scenic beauty. Several tap water plants were also built around the lakes. Water contamination in the lakes has threatened the sources of water supply and recreation. The objective of the *Author to whom all correspondence should be addressed. Current address: Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI 488241325, U.S.A. [Fax: (517) 353 51741. WR 3019-C

study described here was to determine the concentration distribution of organic contaminants in the lakes. Factors affecting the distribution characteristics were determined. The results presented here provided valuable information for the local decisionmakers. EXPERIMENTALSECTION Sampling and enrichment

Sampling sites are shown in Fig. 1. Sites 1, 2, and 3 are located in Lake Wulihu, and others are in Lake Taihu. Twenty water samples in Lake Taihu and 9 in Lake Wulihu were collected at three different times (May of 1988-the normal season, August of 1988-the rainy season, and February of 1989-the dry season). Samples were collected at 1 m below the water surface, and were stored, with no headspace, in 10 I or 20 1 glass bottles with glass stoppers. A total volume of 50 1at each time was collected. Water samples were immediately transported to the lab and were passed through a small filter column and an adsorption column in series within 48 h. The filter columns were packed with glass wool to remove suspended solids. The adsorption columns were filled with 70 ml (Gibs et al., 1984) of the mixed resins of XAD-4 and XAD-7 (Levesque and Mallet, 1983; Moore and Karasek, 1984) with a ratio of 1: 1. The resins were pretreated in a Soxhlet with methanol, tetrahydrofuran, acetonitrile, acetone, ether, and methylene chloride in succession. Pretreatment lasted 10 h for each solvent. The resins were free of organic compounds as indicated by gas chromatography. The resins were stored in methanol for later use. The resins with adsorbed water contaminants were extracted with 50 ml of CHICIZ in a Soxhlet. The volume of CHZCIZ extracts was then decreased to about 4 ml in a Kuderna-Danish evaporator using a modified Snyder tube. The volume was then reduced to 0.5-l ml by blowing a

2003

2004

H. Zou et

steam of NZ gas across the surface of samples. Preliminary experiments showed that the recoveries of model compounds ranged from 72 to 96%. Gas chromatography

Quantitative determination of organic contaminants was performed using a Varian 3700 gas chromatograph equipped with a flame ionization detector and an SE-54 fused-silica capillary column (25 m x 0.25 mm). Several n-alkanes were used as internal standards to calculate the concentrations of organic contaminants by the following equation (Lee et al., 1984):

ws = w0 (A,,A~I~~~‘~~~~~~~~)~~~~ where i and ref represent an organic contaminant to be determined and the internal standard, respectively. The internal standard is carefully selected so that its peak is close to but completely separated from the peak of i. (A,/A,&n.r is the ratio of the peak areas of i and the internal standard after the internal standard is added to the sample being analyzed. (A,/&&,, is the ratio of the peak areas of i and the internal standard before the internal standard is added. W, is the amount of internal standard added (pg). W, is the calculated amount of the organic contaminant (l(g). The relative response factors and recovery factors of some model compounds (relative to the n-alkane internal standards) were also determined. The relative response factors and recovery factors of other organic contaminants were approximated by those of the model compounds with similar structures. Concentrations of organic contaminants were then adjusted for their recoveries. Gas chromatography-mass

spectromeiry

A finnigan MAT GC-MS-COM (ITD-706B) with Incas data system was used for the qualitative identification of organic contaminants. The EPA priority pollutants were identified by mass chromatography.

al.

RESULTS

More than 800 organic contaminants were detected in the concentrates of water samples. Figure 2 compares the diagrams of the total ion current (TIC) corresponding to organic contaminants in two water samples collected during the normal season from Lake Taihu (above) and Lake Wulihu (below), respectively. The larger number of peaks in the water sample from Lake Wulihu than from Lake Taihu demonstrates that Lake Wulihu has a greater variety of contaminants than Lake Taihu. Based on their frequency of occurrence, average concentrations, and toxicity (Center for the Biology of Natural Systems, 1985; Sitting, 1985; Zhu, H., 1987; Zhu, Z., 1987), 84 priority organic contaminants in the lakes were identified. Those priority organic contaminants were assigned to 13 classes according to their chemical structures and uses (Table 1). The concentration and number of organic contaminants in each class are shown in Tables 1 and 2. The concentration in Table 1 is expressed as the sum of the concentrations of all contaminants in that class in a single water sample. The average concentration in Table 2 is expressed as the sum of the concentrations of all contaminants in that class in all water samples either over three sampling times (first 2 columns) or at a single sampling time (last 6 columns) divided by the number of water samples. The average number of organic contaminants in Table 2 is expressed as the sum of the number of organic contaminants in that class in all water samples either over three sampling times (first 2 columns) or at a single sampling time (last 6 columns) divided by the number of water samples. There are several interesting observations based on the data in Tables 1 and 2. Average concentrations and number of contaminants

The average concentration of organic contaminants in Lake Wulihu was approximately one order of magnitude higher than that in Lake Taihu, whereas the average number of organic contaminants in Lake Wulihu was only about twice that in Lake Taihu, as illustrated in Table 2. Taihu

II 0

Lake

“‘II

0 ” 10 km

Time-dependent number

0

1 20 km

N A

Fig. 1. Sampling sites in Lake Taihu and Lake Wulihu, Jiangsu Province.

variation

of

concentrations

and

The ratio of the average concentrations of organic contaminants in Lake Wulihu to those in Lake Taihu varies with the sampling time. The average concentration of organic contaminants in Lake Wulihu was only twice as high as that in Lake Taihu during the rainy season, while it was up to 25 times higher in Lake Wulihu during the dry season. The average concentration of organic contaminants was about 14 times higher in Lake Wulihu than in Lake Taihu during the normal season. Independent of the sampling times, the average number of organic contaminants in Lake Wulihu remained at twice the level found in Lake Taihu, as illustrated in Table 2.

2005

Distribution of contaminants in Lake Taihu Chromtagrar, SltfPLE99 Acquired: Apr-25-1999 ’ Comment: TH-ZeShan CC:50(6)3/MIN258(30) Fc=.63al/mtn SE54 25bW.k#4#28*1 Scan Range: 288 - be Scan: 208 Inf = 1793145 I! 3:21 RIC: 160X 4293154

“.,.‘..

..,.,....

1808

16:41

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2em 33:21

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3080 50:01

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,.,.

4000 66:41

,,.,

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5090 83:21

.,,,

6990 100: 81

Ic uired: f&v-28-1989 ’ : ?c=.83nl/min SE54 25W%n’d %=2e:l = 2900322 I? 3:21 RIC: 188% =363844

Fig. 2. Comparison of TICS for sampling site 8 (Taihu, above) and sampling site 2 (Wulihu, below) during

the normal season (*internal standards). On the other hand, Lake Wulihu is more contaminated during the dry season than during the rainy season, while Lake Taihu is more contaminated during the rainy season than during the dry season. As indicated in Table 2, the average concentrations in Lake Wulihu were 7.786 and 5.799 fig/l during the dry season and the rainy season, respectively, whereas the average concentrations in Lake Wulihu were 0.307 and 2.725 pg/l during the dry season and the rainy season, respectively. [email protected] in the concentrations of different classes of contaminants between the lakes

The concentration distribution of different classes of organic contaminants is not always consistent with the distribution of average concentration in the lakes. Each class of organic contaminants has its own concentration distribution, depending on its general chemical properties. As shown in Table 2, the average concentration of phthalates in Lake Taihu (0.203 fig/l) was only five-fold higher than that in Lake Wulihu (0.915 pg/l). The average concentration of halogenated aliphatic compounds in Lake Taihu (0.634 pg/l) was even higher than that in Lake Wulihu (0.353 pg/l), due to their concentration in Lake Taihu (1.467 pg/l) being much higher than that in Lake Wulihu (0.149 pg/l) during the rainy season. During the dry season, the average concentration of aliphatic

halohydrocarbons in Lake Taihu (O.O56/1g/l) was much lower than that in Lake Wulihu (0.417 pg/l). In other words, the concentration of aliphatic halohydrocarbons in Lake Taihu fluctuates significantly with season. The concentration of aliphatic halohydrocarbons in Lake Wulihu during the rainy season (0.149 pg/l) was lower than that during the dry season (0.417 @g/l). The concentration of alkanes in the two lakes was similar during the rainy season and the normal season, although it was considerably lower in Lake Taihu (0.001 pg/l) than in Lake Wulihu (1.687 pg/l) during the dry season. Distributions of pesticides, esters, ethers, hydrazines, and amides could not be determined due to the fact that their concentrations in both lakes were quite low and close to the detection limit of GC. The concentrations of other contaminants (including alkylaromatics, anilines, phenols, alcohols, ketones, halo- and nitro-aromatic compounds, organic phosphates, PAHs, etc.) in Lake Wulihu were higher than that in Lake Taihu by, typically, 2-3 orders of magnitude during all seasons. DISCUSSION

The concentration distribution of organic contaminants in Lake Taihu and Lake Wulihu is governed by the chemical properties of organic contaminants and the environmental conditions in the lakes.

A B C A B C A B C A B C A B C A B C A B C A B C A B C A B C A B C A B C

Pesticides

Alkylaromatics

Anilines

Phenols

Carbonyl and hydroxy hydrocarbons

Esters, ethers, and amide, etc.

Halo-and nitrobenmnes

Phosphate

Phthalates

Halogenated aliphatic ethers

Polunuclear aromatics

Total/j concentration/ total number of compounds

0.113/2 0.057/l ND 0.001/l 0.034/l 0.025/l 0.32211 ND ND ND ND ND ND

0.034,2 ND ND ND

0.092,2 0.001/l ND ND ND ND ND

3.4917 0.447,2 5.07,5 0.684/2 0.180/l 0.02 I ,2 0.39411 I.9312 0.003/l I.2412 ND ND 0.15913 0.001/l ND

ND 5.2815 2.8615 0.030/l 0.140/l 0.003,2 0.123/l I .053/3 ND O.O4U,l ND ND ND ND 0.001/l

0.306/2 ND ND ND 0.001/l ND

0.002/l 0.002/l 0.002/l 0.254/l ND 0.43412 ND ND 0.006/l 0.001/l 0.001/l 0.001/l 2.13/8 1.79/11 0.514/12

0.003,3 ND 0.002/l 0.581/2 0.008,2 0.111/3 0.006/l ND 0.012,2 0.003,3 0.117/I 0.002,2 5.01/19 0.28718 0.587,16

0.11 l/4 0.002/l ND 0.491/z 0.087/l 0.015/Z ND O.&l 0.001/l 0.001/l O.OJOl/l 3.13/15 1.15,12 0.047,lO

0.18313 0.52212 0.049,3 0.26812 0.214,4 0.077/l 0.190/l 0.219/2 0.138/2 I.2812 0.001/l 0.200/l

0.099/l 1.84/l 0.028/l 0.017/2 0.002,2 ND

5.66122 27.7121 12.2123

0.72611 0.121,2 ND 1.17,16 16.9123 4.17119

0.167/l 0.560/2 0.07913

1.08/l 5.5714 0.222/l 0.54312 15.411 0.336/l

0.27411 0.37212 0.005/Z

IO.7126 8.71,20 6.95120

ND ND 0.005,2

o&3

ND 4.4713 0.54312

0.095/l ND 0.005,2

1

ND 0.002/ 1 0.005/2

ND 0.001/l 0.002/2

O.&

ND

ND ND ND

ND ND 0.001/l

0.&2 ND

ND ND ND

1.5612 0.006/l ND

0.308,3 I.7815 [email protected],1

6

detected

0.&2

0.01 l/4 5.81,4 ND

0.350/2 0.002/l ND

0.52912 4.1313 0.002/l

0.001/l 0.603,2 ND

0.57213 1.00/2 I .08/6

1.0714 0.16612 6.3318

O.E,l

0.004/l 0.024, I ND

0.004/l ND ND

0.446/3 0.006/l ND 0.034/l ND ND

0.007/2 0.004/I ND

O.E,2 1.25/l

1.80/Z I.1915

0.004/l ND ND

5

3.6412 ND 0.264/l

4

0.580/l 0.84412 ND

2.8112 ND 0.84813 ND 0.72612 ND

3

compounds

classes

8

9

2.50/l I 1.57,9 0.374/10

2.83/10 2.7611 I 0.15518

0.001/l 0.052/l 0.001,1

1.32/l I 0.256111 0.159/S

0.002/2 0.019/l 0.001/l

ND ND 0.006/I ND ND 0.006/l ND 0.006/l 0.006/I 0.002/2 O.lSS,I 0.001,1

0.26811 0.060,3 0.133/l

0.004,2 ND ND

ND ND 0.002/l 0.415/2 0.005/l 0.138/2

ND ND 0.006/2

ND 0.001/1 ND 0.067/l 0.140/l 0.008,3

ND ND ND

ND ND ND

0.102/l 0.016/l ND

ND 0.021/l ND ND ND ND

ND ND 0.001/l

ND ND ND

ND ND ND

0.69212 ND 0.012/2

0.248,3 0.160/5 ND

ND ND ND

0.047/l ND ND

0.101/l ND ND

2.0413 I.4312 ND

0.163/l I.1115 ND

0.43314 0.220/l 0.30613

ND ND ND

ND ND 0.005,2

ND ND ND

ND ND ND

ND ND 0.001/l

0.001/l ND O.OOl/l

ND 0.32313 ND

ND ND ND

0.334,2 ND 0.054,l

I.7312 0.83513 ND

7

Taihu

in various

*Sampling site. tA, 8, and C stand for sampling times in the rainy season (Aug. 1988), the normal season (May 1988), and the dry season (Feb. 1989). respectively. tEach data was shown as the sum of concentration @g/l) and number of all detected contaminants in that class. §ND means that contaminants in the class was identified by GC-MS but have a concentration summation below the detection limit of GC. IlTotal = the sum of each column for the corresponding sampling season.

A B C

Halogenated aliphatic compounds

B C

2

NW

of organic

0.24412 0.047,2 0.002/l

At

sum (~g/l)/number

1.7912 0.208,5 0.002/l

1* 0.473121 ND 3.0215

Period

hydrocarbons

Class

Wulihu

1. The concentration

Alkane

Table

10

0.314/13

2.14113

0.001/l

0.001/l

0.006/l

ND

0.230,2

0.004/2

0.005/Z

0.048,2

0.008,3

ND

0.001/l

ND

ND

0.001/l

ND

ND

0.001/l

0.105/2

ND

0.001,1

ND

ND

0.062/2

1.42/l

ND

0.56413

Distribution of contaminants in Lake Taihu Table 2. Comparison of different classes of organic contaminants Class Alkane hydrocarbons Halogenated aliphatic compounds Pesticides Alkylaromatics Anilines Phenols Carbonyl and hydroxy hydrocarbons Ester, ethers, and amide, etc. Halo-and nitrobenzenes Phosphates Phthalates Halogenated aliphatic ethers Polynuclear aromatics Totalf

Averages over three sampling times

2007

between Lake Taihu and Lake Wulihu’ The normal season (B)

The rainy season (A)

The dry season (C)

Wulihu 0.601/0.67 0.493/1.67

Taihu 0.68914.17 0.379/0.83

Wulihu 1.68714.33 0.417/0.33

Taihu 0.001/0.43 0.056/0.86

0.001/0.33 I.96413 O&IO/l.33 1.19512.33 ND

0.004/o. 17 0.064/l 0.006/O. 17 0.006/0.5 ND

NDt 4.75316 0.368/3.33 0.001/0.33 ND

0.0001/0.14 ND 0.004/0.71 ND 0.009/0.14

0.001/0.67

0.0003/0.33

0.0003/0.33

0.023/0.29

4.808/3.33

0.024/0.33

0.182/l

0.006/2.29

0.26912 0.505/1.33 0.277/1.33

0.024/1.71 0.350/2 0.001/0.14

0.299/1.67 2.115/3.33 5.82011.33

0.001/0.33 0.063/1.33 0.001/0.17

0.018/1.67 0.126/1.67 0.167/1.33

0.002/0.71 0.195/2.14 0.007/1.14

0.022/1.23

0.67411.67

0.002/1.57

0.041/1.67

0.064/l

0.067/0.33

0.001/1.14

1.446/11.3

5.845121.3

2.725112.6

17.77/21.3

7.786120.7

0.307/11.0

Wulihu 1.128/2.11 0.353/l

Taihu 0.470/2.30 0.634/l. 18

Wulihu 1.094/1.33 0.149/l

Taihu 0.72112.28 1.46711.86

0.002/0.56 2.74614.22 0.41212.22 0.456ll.22 0.172/0.56

0.008/0.20 0.031/0.62 0.008/0.53 0.027/0.40 0.003/O. 16

0.005/1.33 1.521/3.67 0.42912 0.173/l 0.516/1.67

0.020/0.43 0.028/0.86 0.015/0.57 0.074/0.57 0.0001/0.33

0.018jO.67

0.009/0.49

0.053/l

1.722/2.11

0.018/0.97

0.180/2

0.195/1.78 0.915/2.11 2.088/1.33

0.009/0.92 0.203/1.82 0.003/0.48

0.261/1.22 10.47/21.1

1.30/10.3

0.026/l. 14

*The data in the table are the average concentration (flg/l)/number of organic contaminants of different classes. tND means that the contaminants were identified bv GC-MS but have an average concentration below the detection limit of GC. ITotal = the sum of data in the column.

Water exchange between the lakes

The water level in Lake Taihu is largely controlled by the tributaries of the lake. In spite of the complicated hydrological conditions in Lake Taihu, water flow in Lake Taihu follows a certain pattern. Water flows preferentially into Lake Taihu from the tributaries on the west, southwest, and northwest side of the lake, and flows out of the lake via both Lake Wulihu and the tributaries on the east side during the rainy season. Water flow in Lake Taihu takes the reverse direction during the dry season due to the low water level of Lake Taihu and its tributaries on the west side. Water contamination in Lake Taihu during the rainy season is caused mainly by the contaminants from the tributaries on the west side of the lake due to the direction of the water flow. The reverse water flow in Lake Taihu during the dry season minimizes the concentration of those contaminants from the tributaries on the west side of the lake. As a result, the concentration of contaminants in Lake Taihu is higher during the rainy season than during the dry season. By comparison, a dilution effect by Lake Taihu water during the rainy season lowers the concentration of contaminants in Lake Wulihu. Conversely, the concentration of contaminants in

Lake Wulihu during the dry season remains high due to the lack of the dilution effect by Lake Wulihu water. Transport and transformation

Lake Taihu receives contaminants of all types from many different sources. Our results showed that 39 of the 49 priority organic contaminants in Lake Taihu were found in Lake Wulihu, which suggests that Lake Wulihu provides Lake Taihu with a most important source of contaminants that are transported into Lake Taihu mainly during the dry season. Organic contaminants from Lake Wulihu are not only greatly diluted in Lake Taihu, but also significantly degraded during their slow transport. With a hydraulic residence time of about 300 days in Lake Taihu, it would take many days (depending on the time of year) to move contaminants from Lake Wulihu to sampling site 6 in the middle of Lake Taihu ( N 20 km). Volatilization, sorption onto sediments, and chemical/biological degradation during movement of contaminants greatly lower the concentration of contaminants in Lake Taihu. Table 3 lists aquatic fate process data for some typical contaminants found in Lake Taihu (Mabey et al., 1981). The calculated pseudo first-order coefficients

Table 3. Degradation coefficients for tvoical contaminants

Sediment/water partition coefficent (l/kg) Henry’s law constant (atm’ml/mol) Photolysis rate constant (l/h) Peroxide oxidation rate constant (mol/l’h) Hydrolysis rate constant (l/h) Biodegradation rate constant (ml/cell’h) Pseudo first-order rate constant (l/h) Half-life (h)

in Lake Taihu

Toluene

Phenol

300 6.66 X 10-1 N/A 144 0 1 X IO-’ 1.022 0.678

142 4.45 X IO-’ N/A

330 3.58 x IO-’ N/A

0 3 X 10-e 3.01 0.230

0 3 X 10-q 0.052 13.3

I x 10’

Chlorobenzene

N/A

Bis(Z-chloroethyl)ether 13.9 1.3 X IO-’ N/A 24 4 x IO-6 3 X 10-q 0.034 20.4

Anthracene 1.4 X 104 1.25 x lo-’ 0.15 2.2 X 10’ 0 3 X IO-’ 0.197 3.52

H. Zou et al.

2008

and half-lives using typical water environmental data in Lake Taihu are also given in Table 3. The application of such a calculation in the area under study has been justified (Xu and Sheng, 1987). The longest half-life is only around 20 h, which indicates that those contaminants are quickly removed from Lake Taihu. Table 1 shows that the concentration of most of the contaminants (alkylaromatics, anilines, phenols, halo- and nitrobenzenes, halogenated aliphatic ethers, polynuclear aromatics, etc.) in sampling site 6 is lower than that in Lake Wulihu by, typically, 2-3 orders of magnitude. Those contaminants are even not able to reach sampling sites 5, 8, and 9, as indicated in Table 1 by either ND (not detectable) or very low concentration. Chemical

property-dependent

concentration

distri-

bution

Although oil and fuel contamination from water craft may enhance the concentration of some contaminants, the concentration distribution is largely dependent on the chemical properties and uses for those contaminants present in relatively high concentrations in Lake Taihu (alkanes, halogenated aliphatic compounds, and phthalates). Phthalates, which are plasticizers, are mostly used in industry, manufacture, agriculture, and the home. They show little degradation and are widely distributed. Such non-point contamination provides Lake Taihu with a rich source of phthalates. Halogenated aliphatic hydrocarbons, important as solvents, are also widely used in industry, and are found mostly in water environments. Their volatility, high sorption, and resistance to degradation also make them widely distributed. As shown in Table 1, the concentration of phthalates and halogenated aliphatic hydrocarbons in Lake Taihu is very similar to that in Lake Wulihu. High concentrations of n-alkanes are expected from the degradation of natural polymers in eutrophicated Lake Taihu. Temperature plays an important role in degradation reactions. As shown in Table 1, the high concentration of alkanes during the rainy season and the normal season is largely due to the degradation of natural polymers. The low concentration of alkanes during the dry season is mainly due to the suppression of degradation reactions by the cold temperature in winter. The concentration of alkanes in Lake Wulihu remains high during the dry (cold) season due to the fact that the lake is contaminated mainly by industrial pollutants.

In summary, the distribution of contaminants in Lake Taihu and Lake Wulihu is controlled by several factors. These factors include point versus non-point sources, water flow patterns in the lakes, conditions of the water environment, and the physico-chemical properties of the contaminants. The information presented in this study was of great value to local decision-makers. However, many problems still remain unsolved. Further study will be needed to provide more information about the sources and sinks of contaminants, transport and transformation in the lakes, and exchange between sediment and water, for example. Acknowledgements-We thank Jianquing Ding, Institute of Wuxi Environmental Science and Technology, for his assistance in sample collection and GC-MS analyses. This research was supported by the Chinese Environmental Protection Agency. REFERENCES

Center for the Biology of Natural Systems, Carcinogen Information Program (1985) CIP Bulletin. Washington University, St. Louis. Gibs J., Najar B. and Suffet I. H. (1984) Broad-spectrum analysis of organics in drinking water using macroreticular resins-a quality assurance evaluation in water chlorination. In 5th Chem. Enviro. Impact Health Effect Conference (Edited by Jolley R. L. et a/.), pp. 1099-I 114. Institute of Wuxi Environmental Science and Technology (1988) Investigation of Contaminant Sources Surround Lake Taihu (Report). Wuxi, Jiangsu. Lee M. L., Yang F. J. and Bartle K. D. (1984) Open Tubular Column

Gas Chromatography:

Theory

and Practice,

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