Environ Earth Sci (2011) 62:953–960 DOI 10.1007/s12665-010-0580-9
ORIGINAL ARTICLE
Levels of organochlorine pesticides in natural water along the Yangtze River, from headstream to estuary, and factors determining these levels Chen Liu • Guo-Li Yuan • Zhong-Fang Yang Tao Yu • Xue-Qi Xia • Qing-Ye Hou • Long Chen
•
Received: 7 September 2009 / Accepted: 5 May 2010 / Published online: 21 May 2010 Ó Springer-Verlag 2010
Abstract Organochlorine pesticides (OCPs), including hexachlorocyclohexane and dichlorodiphenyltrichloroethane, were monitored in 37 samples of water collected along the Yangtze River, the third longest river in the P world (6,300 km). The total concentration of OCPs ( OCPs) in the river water ranged from 0.11 to 27.37 ng/L. It was interesting to discover that, except for some sites near industrial cities, levels of OCPs in the water samples were very similar along the whole river. Significantly, OCPs were detected in Tuotuo River (the origin of Yangtze River) even though OCPs have never been used in this area because of its 4,540 m height above sea level. Furthermore, P it was found that OCPs was related to temperature and altitude along the river. We assume OCPs are transported along the Yangtze River, and the factors affecting this process are discussed. Keywords Organochlorine pesticides Yangtze River Controlling factors Water residues
Introduction The Yangtze River is the longest river in China and the third-longest in the world. It flows through about 6,300 km and covers about 1.8 million km2 from its source in Qinghai Province to the estuary in the east of Shanghai City (according to the website of The Ministry of Water Resources of the People’s Republic of China (2009),
C. Liu G.-L. Yuan (&) Z.-F. Yang T. Yu X.-Q. Xia Q.-Y. Hou L. Chen School of the Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China e-mail:
[email protected] http://www.mwr.gov.cn/, Accessed June 2009). The Yangtze River is the main source of water for the agriculture, industry, and daily life of local people along it. Contaminants in the headstream of the river may affect the quality of water resources, so it is very crucial and meaningful to investigate the status of water pollution along the Yangtze River. Persistent organic pollutant (POPs) are toxic chemicals which can exist in environment for a long time and accumulate in organisms through the food chain (Harner et al. 1999; Zhu et al. 2005). The organochlorine pesticides (OCPs), including hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT), are typical POPs which have been used worldwide (Doong et al. 2008). Although application of OCPs has been prohibited in China since 1983, they are often found in the environment nowadays, because of their persistence and bioaccumulation. Recently, increasing attention has been focused on the harm caused by OCPs to the environment. Thus there have already been several reports about the state of OCPs pollution in different sections of the Yangtze River. In the Wuhan section, HCBs, HCHs, and DDTs has been detected in suspended solids from water samples; it was found that HCB, p,p0 -DDE, and a-HCH are the main pollutants (Yang et al. 2004). In Hangzhou Bay of the Yangtze River estuary the history of pollution by OCPs has been studied on the basis of variations in the OCP content of surface sediments (Gao et al. 2006). It was found that the level of OCPs was rather low in recent surface sediments. However, their impact on the environment of the sea should not be neglected, because of the movement of fine sediments and enrichment by plankton (Gao et al. 2006). Furthermore, health risks caused by semi-volatile organic compounds (SVOCs) in the Yangtze estuary area were assessed by using the health risk assessment method of the USEPA
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Fig. 1 Sketch map of water-sampling sites along the Yangtze River
(US Environmental Protection Agency) (Zhang et al. 2007). Fortunately, the result indicated that, currently, single SVOCs would not cause obvious health hazard to human beings. At the same time, the ecological risks of three typical OCPs in the Wuhan section of the Yangtze River were also studied (Zhi et al. 2008). The results showed that the ecological risks of OCPs to local aquatic organisms were low. Among the three OCPs, the ecological risk of p,p0 -DDT was the highest. As mentioned above, there have been reports referring to OCPs in lake and river environments. Nevertheless, further study is necessary because of insufficient related research data. Because studies of the whole river area are few, a study of river water pollution along the whole river would be a significant research project. It has been proved that OCPs can reach everywhere in the world, even high latitudes (Pacyna and Oehme 1988; Gregor and Gummer 1989; Bailey et al. 2000; Chen et al. 2008) and high-altitude areas (Blais et al. 1998; Grimalt et al. 2001; Ribes et al. 2002) because of their transport in the atmosphere and precipitation by ‘‘cold condensation’’. Because of continuous volatilization in warmer regions and condensation in cooler locations, concentrations of OCPs are gradually increasing at high latitudes. So, OCPs can be ubiquitously detected throughout the world, even in pristine polar and near-polar locations (Welch et al. 1991; Wania and Mackay 1993; Simonich and Hites 1995). Daly and Wania considered that transportation of OCPs could be controlled by mountain cold-trapping, i.e. relative enrichment of some SVOCs at higher altitudes as a result of temperature-controlled environmental partitioning processes (Davidson et al. 2003; Daly and Wania 2005; Wania and Westgate 2008). Weather conditions (i.e., yearly mean temperature and precipitation) and geographic character (for example altitude, longitude, and latitude) were also regarded as the factors affecting the distribution of OCPs (Shen et al. 2009).
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Along the Yangtze River, the altitude changes greatly from west to east. In the Tuotuo River area, where the Yangtze River originates, the altitude reaches about 4,540 m. On the other hand, the river also includes the rather lower Yangtze Valley and the lowest estuary plain area near sea level. The temperature along the Yangtze River decreases gradually from east to west. Furthermore, the population and industry are focused in the east. In the Tuotuo River area, there is almost no industry and population. In order to characterize the distribution of OCPs from its origin (Tuotuo River) to its estuary, altitude, longitude, and local temperature were considered as controlling factors. Also, transport of OCPs from their source areas to the Tuotuo River is presumed in this work.
Materials and methods Sample collection The 37 water samples were collected along the Yangtze River from the headstream to the estuary in July to August of 2007. The sample sites were located in Tibet, Qinghai, Sichuan, Yunnan, Hubei, Hunan, Jiangxi, Anhui and Jiangsu Provinces, and Chongqing and Shanghai Cities (Fig. 1). In order to avoid differences between the surface and deeper water body, the water samples were collected 30 cm below the surface in pre-cleaned brown glass bottles then immediately sealed and stored under refrigeration until extraction. The samples were carried to the laboratory as soon as possible, and were processed immediately. Sample extraction and instrument analysis The samples were extracted with 20 ml dichloromethane (pesticide grade) in a separation funnel. After 5 min shaking, the organic phase was collected. The procedure
Environ Earth Sci (2011) 62:953–960
was repeated three times. After separation, purification was performed by concentrating the extract to 2–3 ml by evaporation, purification on silica gel (analytical grade) and alumina (Chromato-Graphic) columns, and elution with 25 ml hexane (pesticide grade) for further cleaning. Finally, the solution was evaporated to 1 ml by use of clean, dry nitrogen. Levels of the OCPs were measured by gas chromatography (GC)–lECD (Agilent 6890N equipped with a Ni63 electron capture detector). An Agilent capillary column coated with a 0.25-lm film of DB-5 was used to separate the target compounds. Helium (99.999%) was used as carrier gas, at 1 ml min-1. The GC was operated conventionally (splitless mode), and 1 ll of the sample was injected into the GC system. The oven temperature was programmed at 30° min-1 from 80 to 185°C, then at 3° min-1 to 215°C, and finally at 1° min-1 to 225°C which was held for 2 min. Finally, the temperature was raised to 290°C and held for 4 min to clean the column. Quality assurance and quality control OCP peaks were identified by accurate comparison of retention times with those of standard. The peaks of eight OCP compounds, a-HCH, b-HCH, c-HCH, d-HCH, p,p0 DDE, p,p0 -DDD, o,p0 -DDT, and p,p0 -DDT, appeared in succession. These eight OCP compounds were quantified by use of eight calibration curves prepared for the individual compounds. Field blanks and laboratory blanks were processed and analyzed by the same method. The minimum detection limits of the methods were 0.01–1.03 ng/L and the recoveries of DDT and HCH were 88–102%.
Results and discussion The levels and distribution of OCPs The concentration of OCPs in water samples from the Yangtze River are shown in Table 1. The total concentraP tion of OCPs ( OCPs, i.e. the sum of HCHs and DDTs) ranged from 0.11 to 27.37 ng/L with an average value of 3.30 ng/L. The total HCHs (sum of a-HCH, b-HCH, c-HCH and d-HCH) were in the range 0.11–13.68 ng/L with a mean value of 3.36 ng/L and the DDTs (sum of p, p0 -DDE, p,p0 -DDD, o,p0 -DDT and p,p0 -DDT) ranged from not detected (ND) to 21.31 ng/L with a mean value of 3.72 ng/L. The distribution of HCHs and DDTs will be discussed later in detail. The results showed that the detection rate of a-HCH and b-HCH were high whereas the isomers c-HCH and d-HCH were hardly detected in the upriver samples. Furthermore, b-HCH was the dominant isomer. As shown in Fig. 2, the
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P total concentration of HCHs ( HCHs) generally tends to increase along the Yangtze River from west to east, with several peak values at some sites. The highest value of P HCHs reached 13.68 ng/L which occurred in Wuhan of Hubei Province. The DDTs were hardly appeared in the headstream of the river. The total DDT isomer content P ( DDT) increased from the middle river, and in Jiangsu Province the value reached 21.31 ng/L. Because OCPs were widely used in these areas in the 1960s and 1970s, they remained in the soil and are partly carried by water. In addition, Wuhan and Nanjing are traditional industrial cities, and the high levels of HCHs are at least partially attributable to industrial production in this area. The widespread use of OCPs in large quantities in industry also can increase accumulation of HCHs. The input sources of OCPs HCHs HCH and lindane were two typical manufactured products which have been widely used in China. Technical HCH contains 55–80% a-HCH, 5–14% b-HCH, 12–14% c-HCH, 2–10% d-HCH, and 3–5% of other compounds (Gao et al. 2006; Qiu et al. 2005) whereas lindane contains 99% c-HCH. Among the four isomers, b-HCH seems more stable in organisms than the other isomers, because of its rather stable structure, lower vapor pressure, and higher bioenrichment factor (Willet et al. 1998). In addition, b-HCH can be formed from other isomers in the environment because of isomer conversion. Therefore, the environmental concentration of b-HCH is often higher than that of other isomers, despite its low relative amount (5–14%) in commercial mixtures (Middeldorp et al. 1996). In Yangtze River water, b-HCH is almost always the dominant component whether in the upriver samples or in the lower reach of the river; exceptions are samples 18–25 (Fig. 3). This result indicates lack of recent HCH input in most areas. c-HCH is the effective component of commercial HCHs among the four isomers and it comes from both commercial HCH and lindane in the environment, whereas the a-HCH isomer only comes from use of commercial HCH. So the ratio a-HCH/c-HCH has been used to determine whether c-HCH in the environment originates from commercial HCH or from lindane. Furthermore, the value of a-HCH/c-HCH also can indicate changes in the environment. If the ratio is between 4 and 7, the pollution can be attributed to use of commercial HCH. If the ratio is higher, the original pollution may have come from atmospheric transfer over long distances (Li et al. 1998; Munn and Gruber 1997; Walker et al. 1999) or new input of HCH. As shown in Fig. 4, a-HCH/c-HCH values at sites 19, 22, and
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Table 1 The sample sites and concentration of OCPs (ng/L) Sample Site
Longitude
Latitude
Location
b-HCH/
P HCHs
a-HCH/c-HCH
P HCHs
P DDT
P OCPs
01
92.38
34.23
Qinghai
0.95
ND
1.945
0.260
2.21
02
97.25
32.99
Qinghai
1.00
ND
2.010
ND
2.01
03
98.59
31.63
Sichuan
1.00
ND
0.820
ND
0.82
04
99.04
29.88
Sichuan
0.85
ND
0.730
ND
0.73
05
99.39
28.17
Yunnan
0.86
ND
2.155
ND
2.16
06
101.50
26.59
Sichuan
1.00
ND
0.745
ND
0.75
07
101.75
26.57
Sichuan
0.95
ND
1.815
ND
1.82
08
101.88
25.96
Yunnan
0.55
1.174
1.100
ND
1.10
09
102.90
26.91
Sichuan
0.84
ND
0.560
ND
0.56
10
103.39
27.04
Yunnan
0.69
0.767
2.910
0.125
3.04
11 12
104.52 105.25
28.69 28.74
Sichuan Sichuan
1.00 0.92
ND ND
1.300 1.485
ND ND
1.30 1.49
13
106.52
29.39
Chongqing
0.85
1.605
3.380
0.530
3.91
14
106.78
29.61
Chongqing
0.94
ND
2.075
0.175
2.25
15
107.29
29.73
Chongqing
0.78
1.682
2.690
0.550
3.24
16
108.42
30.75
Chongqing
1.00
ND
1.310
ND
1.31
17
109.81
31.05
Chongqing
0.69
1.361
1.380
0.070
1.45
18
110.99
30.85
Hubei
ND
0.129
5.400
ND
5.40
19
110.12
30.85
Hubei
ND
10.667
0.350
ND
0.35
20
111.41
30.52
Hubei
ND
0.116
5.605
ND
5.61
21
112.28
30.07
Hubei
ND
0.110
7.440
0.315
7.76
22
113.83
29.94
Hubei
0.05
30.133
8.795
12.085
20.88
23
114.19
30.46
Hubei
0.04
0.648
13.680
9.265
22.95
24
115.07
30.31
Hubei
0.14
1.945
8.400
4.500
12.90
25
113.07
29.43
Hunan
ND
ND
0.110
ND
0.11
26
113.22
29.53
Hunan
ND
ND
0.130
0.100
0.23
27 28
115.92 116.55
29.71 29.91
Jiangxi Jiangxi
0.47 0.68
1.121 4.407
1.160 2.270
ND 9.730
1.16 12.00
29
116.89
30.36
Anhui
0.76
1.783
2.675
0.465
3.14
30
117.65
30.69
Anhui
0.81
2.121
2.670
0.370
3.04
31
118.19
31.29
Anhui
0.74
1.708
2.540
0.370
2.91
32
118.39
31.65
Anhui
0.67
2.324
1.850
0.655
2.51
33
118.52
31.88
Jiangsu
0.66
2.605
6.060
21.305
27.37
34
119.47
32.27
Jiangsu
0.67
2.541
6.365
7.485
13.85
35
120.18
31.94
Jiangsu
0.78
2.069
6.380
1.450
7.83
36
120.68
32.06
Jiangsu
0.80
2.643
6.085
1.260
7.35
37
121.31
31.53
Jiangsu
0.74
1.972
5.600
0.480
6.08
28 are higher than 7, which may indicate a new input source of commercial HCH in these areas rather than atmospheric transfer over long distances. Sampling sites 19 and 22 are both in Hubei Province near Wuhan, a classic industrial city. Industrial influence in Wuhan shows that discussion about the HCH input source on the basis of a-HCH/c-HCH is reasonable. Sample 28 was obtained at Jiujiang of Jiangxi Province. Jiujiang is an economically developed area, including a large petroleum corporation and electric power bases. So the new input source of HCHs
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may be attributed to the production of several pesticides. In most samples, values of a-HCH/c-HCH are \4, so it is presumed that HCHs pollution may originate partly from accumulation. DDTs Levels of DDTs in the Yangtze River were much lower than those of HCHs. The DDTs were almost not detected in upriver samples along the Yangtze River. The distribution
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P P P Fig. 2 HCHs, DDTs, and OCPs content of water samples along the Yangtze River
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Fig. 5 Correlations between
P OCPs and longitude
of DDTs is shown in Fig. 2. The highest value for DDT, 21.31 ng/L, was in sample 33 which was obtained at Nanjing, the important comprehensive industrial production base of China. The developed industry and the huge population may affect the accumulation of DDTs in the soil, and transportation by the river. From Table 1 it is apparent that DDT was detected at the origin of the river even though OCPs have not been used in that area. Why does it appear there? The influencing factors and mechanism will be discussed later in this work. The correlation between
Fig. 3 b-HCH and Yangtze River
P HCHs content of water samples along the
Fig. 4 Value of a-HCH/c-HCH for water samples along the Yangtze River
P
OCPs and longitude
In order to discover potential factors affecting the concentration of OCPs along the Yangtze River, correlations P of OCPs with longitude, temperature, and altitude are discussed herein. P The correlation between longitude and OCPs has seldom been mentioned in previous reports. In China, it is well known that the Yangtze River flows across an extended span from west to east and longitude increases from upstream to estuary. For such a special geographical feature, longitude was regarded as an important factor affecting the level of OCPs. Figure 5 shows the correlation P between the concentration of OCPs and longitude along the Yangtze River. On the basis of the trend curve, the P OCPs has a positive tendency with longitude. That is, P the concentration of OCPs increases with increasing of longitude along the Yangtze River from west to east generally. This result can be attributed to special geographical conditions in China with high altitude in the west and low altitude in the east. This characteristic altitude change along Yangtze River, from west upriver to east estuary, is clearly shown in Fig. 6. The possible environmental process affecting the concentration of OCPs in water samples will be discussed in detail later.
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Fig. 7 The level of Yangtze River Fig. 6 Correlations between longitude and altitude
The correlation between
P
OCPs and temperature
Besides longitude, several studies have focused on the P effect of temperature on the concentration of OCPs. Wania and Mackay (1995) even made a model to study the fate of organic contaminants in relation to temperate change. They confirmed that contaminant concentrations in the polar region were increased by condensation at low temperatures. Other researchers (Pham et al. 1996) also reached a similar conclusion. This means that the temperature could affect the environmental partitioning processes of OCPs and then affect their distribution. The Yangtze River extends more than 6,300 km, and over several different climate areas from semi-tropical to frigid zones. For this reason, average temperature should be regarded as an important factor in the distribution of OCPs along this sampling site. As shown in Fig. 7, the average temperature range along the Yangtze River in summer could be divided into two sections. One is a hightemperature area, ca. 25°C, and the other is a low-temperature area, below 25°C. The average temperature in the Tuotuo River area, the origin of Yangtze River ca. 4,540 m altitude, is just 8°C in summer. From the middle section to the estuary, the temperature is almost always above 25°C in summer (average temperature data were supplied by the China Meteorological Administration). It is clearly apparent that the basic concentration of P OCPs in the high-temperature section is almost the same as that in low-temperature section even though OCPs have not been used in the latter area. The concentrations of OCPs in the low-temperature area are not lower as expected. This may be explained by the ‘‘grasshopper-
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P OCPs and temperature change along the
effect’’, i.e. the geochemical process by which some chemicals, most notably POPs, are transported from warm to cold regions of the Earth, particularly the poles and mountain tops (Gouin et al. 2004). Nevertheless, concenP trations of OCPs in some sites, near Wuhan and Nanjing City, are much higher than the base-line. This could be attributed to artificial activity at present as mentioned above. Effect of altitude on the OCPs distribution To reduce the potential damage of OCPs to the environment and to humans, it is very important to identify their possible sources and to understand the model with which OCPs are subject to long-range transport. Besides longitude and temperature, some studies have focused on the effect of altitude on the distribution of OCPs (Shen et al. 2009). Blais et al. (1998) has reported that the concentrations of semi-volatile organochlorine compounds in snow increased gradually over a 1000 meters altitudinal height in the mountains of western Canada. Wania and Westgate (2008) provide a reasonable explanation of this phenomenon. First, OCPs are transported into the atmosphere in warm low-altitude regions. They are then precipitated by ‘‘cold condensation’’ in cold high-altitude regions. As a result, OCP concentrations gradually increase in highaltitude, rather cold regions. Such a geochemical process is similar to the ‘‘grasshopper-effect’’. In the Tuotuo River area, the upstream region of the Yangtze River with 4,540 m altitude, pesticides have hardly been used because of the low population. However, levels of OCPs in water samples are not lower than expected (Fig. 8). Generally, the altitude in China is high in the west and low in the east. The main rivers almost all flow from the
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Fig. 8 Level of River
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P OCPs and altitude-change along the Yangtze
west mountains to the east ocean, from low to high longitude. As shown in Fig. 8, the Yangtze River flows across a big drop of altitude. In the Tuotuo River area, industrialization is low and the effect of human activities is minor. Except for some sites near industrial cities, the level of P OCPs at high altitude is almost no lower than those in the low-altitude area. It is well known that usage and industrial sources of OCPs were focused in Yangtze River delta, and they have been never used and produced in the Tuotuo River area. However, the level of OCPs in water samples is almost same as that at 250 m height. Such a result can also be well understood by the model of ‘‘grasshopper-effect’’. Figure 9 shows there is a good negative correlation of temperature with altitude. It was mentioned above that the average temperature in summer was just 8°C at the origin of river. Such a low-temperature environment provides an ideal location for ‘‘cold condensation’’ and precipitation of OCPs after long-distance transport. The temperature in the Yangtze River delta area is high and it decreases gradually along the Yangtze River to the Tuotuo River. On the other hand, the Yangtze River delta area is the main source of OCPs. So the transport process of OCPs along the Yangtze River could be presumed as following geochemical process. First, the OCPs in the Yangtze River delta are evaporated because of high temperature. Subsequently, they are transported in the atmosphere from east to west. The gradual altitude increase from east to west results in a gradual decrease in temperature, so OCPs in the atmosphere undergo ‘‘cold condensation’’ because of the decreasing temperature. OCPs tend to partition into the condensed phase and precipitate along the Yangtze River from the east to west. Simultaneously, these OCPs from other sources are also partially evaporated and precipitated.
Fig. 9 Correlation between temperature and altitude
By repeated evaporation and precipitation, OCPs are transported from the Yangtze River delta to the Tuotuo River, from low to high altitude areas, and from warm to cold areas. Consequently, OCPs are transported into the Tuotuo River area, and the concentration in this area gradually increases. As a result, the level of OCPs in Tuotuo River, which is 4,540 m altitude and several kilometers from the source, is similar to that in the 250 m altitude area of the Yangtze River delta.
Conclusions Levels of OCPs in natural water from headstream to estuary along the Yangtze River, and the factors determining these levels, were studied in this work. The results P show that concentrations of OCPs range from 0.11 to 27.37 ng/L. Levels of OCPs were very similar along the Yangtze River except at some sites near industrial cities. The high level of OCPs at these sites may be attributed to new inputs. It was found that the distribution of OCPs along the river was determined by major factors such as longitude, temperature, and altitude. Generally, the conP centration of OCPs increases with increasing longitude along the Yangtze River from west to east, because of the special geographical feature of China. At the origin of the Yangtze River, the Tuotuo River area with high altitude and low temperature, OCPs have not been used but are P detectable. The concentration of OCPs in these lowtemperature sections is almost the same as that in the hightemperature section along the Yangtze River. Transport of OCPs from warm to cold areas could be well explained by ‘‘cold condensation’’ and the ‘‘grasshopper-effect’’. In conclusion, OCPs were transported from the rather warm
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Yangtze River delta area, the main source area of the OCPs, to the Tuotuo River area which is far away from the source with high latitude and low temperature. This cold environment provided an ideal location for ‘‘cold condensation’’ and precipitation of transported OCPs in this highaltitude area. The high temperature in the Yangtze River delta accelerates evaporation of the OCPs. As a result, the level of OCPs in water samples from the Tuotuo River area at an altitude of 4,540 m is similar to that in the source area at lower than 250 m altitude. Acknowledgments This research was financially supported by the Specialized Research Fund for the Doctoral Program of Higher Education in China (20090022120001) and China Geological Survey (GZTR02-01, 2008).
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