**1. Introduction**

The study area, Lake Liangzi is regarded as one of the least polluted lakes in Central China. This is because the local people have made great efforts to protect the lake from the use of all forms of chemicals for crop and fish farming activities. Besides this measure, other uses such as recreation, water supply and electricity production are also not permitted. In fact, it is noteworthy to mention that the lake supplies one of the most popular and delicious types of fish in Central China. It is called "Wuchang fish" and is very popular in most leading restaurants in Central China and quite expensive for its delicacy.

However, since modern technology has revealed that organic compounds such as Organo chloro-pesticides (OCPs) could be deposited into lakes and other water bodies from remote areas, far from the point of application, it will be worthwhile to undertake investigation to ascertain whether the lake is free from these contaminants. The path of investigation used dated sediment core since according to Venkatesan, et al, (1998), the history of chlorinated hydrocarbon contamination can be followed using contaminants from dated sediment cores, since sediments integrate and retain records of influx of recalcitrant organic contaminants. It should be mentioned that this volume of work is part of the author's PhD research and also one of the pioneering research works on pesticides in the lake.

OCPs are a group of common pollutants belonging to the class of pollutants called Persistent Organic Pollutants (POPs). One of the most important families of Persistent Organic Pollutants (POPs) that has a significant impact upon the environment are pesticides.

According to Sierra Club of Canada, (1998), pesticides are the only man-made toxic chemicals deliberately released over large areas. They are poisonous almost by definition. Pesticides poison the food chain, contaminate water supplies and are implicated in the declining populations of many biotic species.

In this study, a single drilled undisturbed sedimentary core extracted from Lake Liangzi in Central China was analyzed for target compounds using highly sophisticated instruments. Even though other organic compounds (such as Polycyclic Hydrocarbons; PAHs, Aliphatic Hydrocarbons; Ahs and heavy metals) were detected, they are not discussed in this article.. The focus of discussion are the organocgloro-pesticides, including DDT, DDD and DDE and the geochemical relationship between them.

#### **1.1 Brief background to DDT, DDD and DDE**

According to Environmental Protection Agency (EPA) of USA, (1989), the term DDT refers to the collection of all forms of DDT, DDE, and DDD.

Geochemical Indicators of Organo-Chloro Pesticides in Lake Sediments 395

**N**

Fig. 1. Map of Wuhan and other major cities in Hubei Province (including the study area)

The limnology according to Donyinah et al. (2007), is based on the information supplied by J. Xiangtan (1995). The lake which lies within the southeast area of the heavily industrialized city of Wuhan is the 13th largest freshwater lake in China and the second largest shallow lake of Hubei Province. It is a low-lying lake, which is located not far from the southern bank of the Yangtze River. In the 1950s, the actual surface area of the lake was 458.5km.2 (177.0 mi²), but in the 1980s and 1990s, the area of the lake shrank to 227.15km2 (87.70 mi²) because of reclamation of the lake for agricultural purposes. Also in the 1950s the lake was 2.25-2.8 m (7.38-9.18 ft) deep and the deepest area was 1.5 m (4.9 ft) during winter, when the water was lowest. In 1997 and 1998, the lake measured between 1.2 and 4.2 m (3.9 and 13.7 ft) and the average depth was 2.8 m (9.2 ft). The circumference of the lake totals more than 470 km (292 mi) and the shoreline is irregular. The vegetation around the lake is grass with a few trees. Except in the east, there are many small uplands and hills around the lake; the hills are, however, some distance away. Few croplands near the small hamlets around the extended edges of the lake. Rainfall is abundant, with the average rainfall range over several years being 1263.4mm/yr (49.7 in./yr). The average air temperature area the lake is about 17ºC. The highest monthly air temperature is 28.6ºC and the lowest is 3.3ºC. The wind circulation pattern consists of cold winds from the north blowing in the winter and spring and northeast and east winds blowing in the summer and fall, respectively. The temperature

Source: LandingChina.com; "The Professional Travelling guide to China", 2004

**1.2.1 The limnological data of the Lake Liangzi** 

**1.2 Study area** 

The primary forms or isomers of DDT, DDE, and DDD are (namely *p,p'*-DDT, *p,p'*-DDE, and *p,p'*-DDD) (US EPA,1989). US EPA, (1989), also indicate that DDT (1,1,1-trichloro-2,2-bis(*p*chlorophenyl) ethane) is a pesticide that was once widely used to control insects on agricultural crops and insects that carry diseases like malaria but is now used in only a few countries to control malaria. Technical-grade DDT is a mixture of three forms, *p,p'*-DDT (85%), *o,p*'-DDT (15%), and *o,o*'-DDT (trace amounts). All of these are white, crystalline, tasteless, and almost odorless solids. Technical grade DDT may also contain DDE (1,1 dichloro-2,2-bis(*p*-chlorophenyl)ethylene) and DDD (1,1-dichloro-2,2-bis(*p*-chlorophenyl) ethane) as contaminants. US EPA (1989), further indicate that both DDE and DDD are breakdown metabolites of DDT and that DDT does not occur naturally in the environment. They may occur in the atmosphere as a vapor or be attached to solids in air. Vapor phase DDT, DDE, and DDD may break down in the atmosphere due to reactions caused by the sun. DDT, DDE, and DDD last in the soil for a very long time, potentially for hundreds of years. Most DDT breaks down slowly into DDE and DDD, generally by the action of microorganisms. These chemicals may also evaporate into the air and be deposited in other places (EPA, 1989). These organic compounds, according to Agency for Toxic Substances and Disease Registry (ATSDR 2002), are easily broken down in air with a half-life of two days. Also according to ATSDR (2002), DDT and especially DDE build up in plants and in fatty tissues of fish, birds, and other animals.

#### **DDT**

Chemical formula: (C14H9Cl5). Structure:

#### **DDD**

Chemical formula, (C14H10Cl4). Structure:

**DDE** 

Chemical formula (C14H8Cl4) Structure:

#### **1.2 Study area**

394 Pesticides in the Modern World - Risks and Benefits

The primary forms or isomers of DDT, DDE, and DDD are (namely *p,p'*-DDT, *p,p'*-DDE, and *p,p'*-DDD) (US EPA,1989). US EPA, (1989), also indicate that DDT (1,1,1-trichloro-2,2-bis(*p*chlorophenyl) ethane) is a pesticide that was once widely used to control insects on agricultural crops and insects that carry diseases like malaria but is now used in only a few countries to control malaria. Technical-grade DDT is a mixture of three forms, *p,p'*-DDT (85%), *o,p*'-DDT (15%), and *o,o*'-DDT (trace amounts). All of these are white, crystalline, tasteless, and almost odorless solids. Technical grade DDT may also contain DDE (1,1 dichloro-2,2-bis(*p*-chlorophenyl)ethylene) and DDD (1,1-dichloro-2,2-bis(*p*-chlorophenyl) ethane) as contaminants. US EPA (1989), further indicate that both DDE and DDD are breakdown metabolites of DDT and that DDT does not occur naturally in the environment. They may occur in the atmosphere as a vapor or be attached to solids in air. Vapor phase DDT, DDE, and DDD may break down in the atmosphere due to reactions caused by the sun. DDT, DDE, and DDD last in the soil for a very long time, potentially for hundreds of years. Most DDT breaks down slowly into DDE and DDD, generally by the action of microorganisms. These chemicals may also evaporate into the air and be deposited in other places (EPA, 1989). These organic compounds, according to Agency for Toxic Substances and Disease Registry (ATSDR 2002), are easily broken down in air with a half-life of two days. Also according to ATSDR (2002), DDT and especially DDE build up in plants and in

fatty tissues of fish, birds, and other animals.

Chemical formula: (C14H9Cl5).

Chemical formula, (C14H10Cl4).

Chemical formula (C14H8Cl4)

**DDT** 

**DDD** 

**DDE** 

Structure:

Structure:

Structure:

Fig. 1. Map of Wuhan and other major cities in Hubei Province (including the study area) Source: LandingChina.com; "The Professional Travelling guide to China", 2004

#### **1.2.1 The limnological data of the Lake Liangzi**

The limnology according to Donyinah et al. (2007), is based on the information supplied by J. Xiangtan (1995). The lake which lies within the southeast area of the heavily industrialized city of Wuhan is the 13th largest freshwater lake in China and the second largest shallow lake of Hubei Province. It is a low-lying lake, which is located not far from the southern bank of the Yangtze River. In the 1950s, the actual surface area of the lake was 458.5km.2 (177.0 mi²), but in the 1980s and 1990s, the area of the lake shrank to 227.15km2 (87.70 mi²) because of reclamation of the lake for agricultural purposes. Also in the 1950s the lake was 2.25-2.8 m (7.38-9.18 ft) deep and the deepest area was 1.5 m (4.9 ft) during winter, when the water was lowest. In 1997 and 1998, the lake measured between 1.2 and 4.2 m (3.9 and 13.7 ft) and the average depth was 2.8 m (9.2 ft). The circumference of the lake totals more than 470 km (292 mi) and the shoreline is irregular. The vegetation around the lake is grass with a few trees. Except in the east, there are many small uplands and hills around the lake; the hills are, however, some distance away. Few croplands near the small hamlets around the extended edges of the lake. Rainfall is abundant, with the average rainfall range over several years being 1263.4mm/yr (49.7 in./yr). The average air temperature area the lake is about 17ºC. The highest monthly air temperature is 28.6ºC and the lowest is 3.3ºC. The wind circulation pattern consists of cold winds from the north blowing in the winter and spring and northeast and east winds blowing in the summer and fall, respectively. The temperature

Geochemical Indicators of Organo-Chloro Pesticides in Lake Sediments 397

sediment cutter. The sliced samples were immediately put into fresh plastic sample bags and serially well labeled, using coloured felt pens. Maximum precaution was taken to avoid any contamination, such as skin exposure, especially the bare hands (since the touching with the bare hands could contaminate the samples from the possible lipids of the hands by touching with the bare hands) and thus sampling was carried out by wearing fresh plastic disposable gloves. In order to preserve the freshness of the samples, they were immediately stored in a freezer at -20°C until the time for the laboratory analysis. The handling and the transportation of the samples from the lake to the laboratory were carefully and cautiously

For the purpose of instrumental analyses, the target compounds were extracted from the solid samples and transferred into liquid form. This initial extraction process is called the pretreatment of samples. The pre-treatment was performed at the Environmental Laboratory of the School of Environmental Studies, China University of Geosciences,

The reagents used for the pretreatment were hexanes, dichloromethane, surrogate standards, silica gel, aluminum oxide and distilled water (for washing and rinsing of the

A total of seventy-seven (77) samples were analyzed. One hundred milliliters of the initial solvent, dichloromethane, was poured into the sample for the extraction process. The surrogate standard was introduced into one selected sample in each set of batch samples. A set of six batches of samples were kept on hot water bath (Model HHS-6; temperature range 37ºC-100ºC) and Soxhlet extractor at fixed temperature of 50ºC and left for 48 hrs. The temperature fluctuation during the period was within an accuracy of ±1ºC. The extractor was then filtered into another round-bottomed flask and concentrated by rotation evaporation using a rotary evaporator (ZFQ-85A; speed range 0-200 rpm) and Auto Science vacuum and pressure (model AP-01; pressure range = 0- 30 mm Hg [0-4 kPa]). The pressure used for the evaporation was fixed at 20 mm Hg (2.6 kPa) for all the samples. The concentrate was carefully transferred into special 5 mL sample bottles using special pipettes and immediately stored in a freezer. After the transfer of each concentrate, the roundbottomed flask was thoroughly rinsed with dichloromethane. The process was repeated for all the 77 samples. The extracts were then left to evaporate naturally at room (ambient) temperature and then mixed with hexanes until all the dichloromethane totally evaporated. These extracts were then column fractionated into the target compound (OCPs) using silica and aluminium oxide. The particle size of the aluminium oxide and the silica gel was 100- 200 mesh. Care was taken to label each extracted solution. The column extraction was conducted through columns of aluminium oxide, and silica gel was placed in 100 mL burettes. The aluminium oxide formed the top column (5 mL), whereas the silica gel was the bottom column (15 mL). Prior to passing the samples through the columns; 30 mL of dichloromethane was initially passed through the columns to wash any possible contaminants in the column. Another 30 mL of the dichloromethane was passed through the columns after each sample was introduced into the column for the extraction of target organic compounds. These fractionated solutions were again concentrated by rotation evaporation using the Rotary evaporator (ZFQ-85A), and bottled in 8 milliliter cell bottles. They were then evaporated again, using a Nitrogen manifold setup with a gentle stream of nitrogen gas (99.9% purity) to about 5mL. The final extracted samples of analysis were

Wuhan. Standard laboratory procedures were followed throughout the process.

analyzed by gas chromatography (GC) and GC-mass spectrometry (GC-MS).

handled to avoid any possible contamination.

**2.1 Laboratory methods** 

apparatuses before usage).

of the water in the lake is higher than the surrounding air. Whereas the average temperature of the surrounding air over several years is 17.5ºC, the highest monthly average temperature of the lake is about 30ºC and lowest is 4.7ºC. Annually, there are 243 days when the temperature of the lake water is higher than 10ºC. No significant difference exists between the temperatures of each layer of water in the lake; the difference between the upper layer and the bottom layer is not more than 1ºC. The lake water is very clear, but the shallow water near the edges becomes turbid when there are stormy waves. The transparency changes between 0.3 and 1.4 m (1 and 4.5 ft) and the average is 0.8 m (2.6ft). Generally, the transparency in spring and winter is high, and the lake's water appears light green. The water is alkaline, and the pH is commonly about 8.1, with no distinct differences between the upper layer and the bottom layer. The main ions in the water are bicarbonate class. The iron content of the lake water is fairly high, and the average is 7 mg.

Fig. 2. A Map Showing the Location of Lake Liangzi

#### **2. Sampling and sampling techhniques**

The location chosen for sampling was at the middle and the deepest part of the Lake, the sediment core samples will thus assumed to be a true representative of the Lake's sediments and therefore, reliable for all analyses.

Sampling was carried out from a small local motorized fishing boat, using a soft manual hand-driven core-drill (KC Kajak Sediment Core Sampler). Core samples were taking from a depth of 70~80cm in the lake's bed and each core sample was immediately sliced (from top to bottom) into fractions of (1cm thick), using a well polished and treated metallic soft-core sediment cutter. The sliced samples were immediately put into fresh plastic sample bags and serially well labeled, using coloured felt pens. Maximum precaution was taken to avoid any contamination, such as skin exposure, especially the bare hands (since the touching with the bare hands could contaminate the samples from the possible lipids of the hands by touching with the bare hands) and thus sampling was carried out by wearing fresh plastic disposable gloves. In order to preserve the freshness of the samples, they were immediately stored in a freezer at -20°C until the time for the laboratory analysis. The handling and the transportation of the samples from the lake to the laboratory were carefully and cautiously handled to avoid any possible contamination.

#### **2.1 Laboratory methods**

396 Pesticides in the Modern World - Risks and Benefits

of the water in the lake is higher than the surrounding air. Whereas the average temperature of the surrounding air over several years is 17.5ºC, the highest monthly average temperature of the lake is about 30ºC and lowest is 4.7ºC. Annually, there are 243 days when the temperature of the lake water is higher than 10ºC. No significant difference exists between the temperatures of each layer of water in the lake; the difference between the upper layer and the bottom layer is not more than 1ºC. The lake water is very clear, but the shallow water near the edges becomes turbid when there are stormy waves. The transparency changes between 0.3 and 1.4 m (1 and 4.5 ft) and the average is 0.8 m (2.6ft). Generally, the transparency in spring and winter is high, and the lake's water appears light green. The water is alkaline, and the pH is commonly about 8.1, with no distinct differences between the upper layer and the bottom layer. The main ions in the water are bicarbonate class. The

**N**

iron content of the lake water is fairly high, and the average is 7 mg.

Fig. 2. A Map Showing the Location of Lake Liangzi

The location chosen for sampling was at the middle and the deepest part of the Lake, the sediment core samples will thus assumed to be a true representative of the Lake's sediments

Sampling was carried out from a small local motorized fishing boat, using a soft manual hand-driven core-drill (KC Kajak Sediment Core Sampler). Core samples were taking from a depth of 70~80cm in the lake's bed and each core sample was immediately sliced (from top to bottom) into fractions of (1cm thick), using a well polished and treated metallic soft-core

**2. Sampling and sampling techhniques** 

and therefore, reliable for all analyses.

For the purpose of instrumental analyses, the target compounds were extracted from the solid samples and transferred into liquid form. This initial extraction process is called the pretreatment of samples. The pre-treatment was performed at the Environmental Laboratory of the School of Environmental Studies, China University of Geosciences, Wuhan. Standard laboratory procedures were followed throughout the process.

The reagents used for the pretreatment were hexanes, dichloromethane, surrogate standards, silica gel, aluminum oxide and distilled water (for washing and rinsing of the apparatuses before usage).

A total of seventy-seven (77) samples were analyzed. One hundred milliliters of the initial solvent, dichloromethane, was poured into the sample for the extraction process. The surrogate standard was introduced into one selected sample in each set of batch samples. A set of six batches of samples were kept on hot water bath (Model HHS-6; temperature range 37ºC-100ºC) and Soxhlet extractor at fixed temperature of 50ºC and left for 48 hrs. The temperature fluctuation during the period was within an accuracy of ±1ºC. The extractor was then filtered into another round-bottomed flask and concentrated by rotation evaporation using a rotary evaporator (ZFQ-85A; speed range 0-200 rpm) and Auto Science vacuum and pressure (model AP-01; pressure range = 0- 30 mm Hg [0-4 kPa]). The pressure used for the evaporation was fixed at 20 mm Hg (2.6 kPa) for all the samples. The concentrate was carefully transferred into special 5 mL sample bottles using special pipettes and immediately stored in a freezer. After the transfer of each concentrate, the roundbottomed flask was thoroughly rinsed with dichloromethane. The process was repeated for all the 77 samples. The extracts were then left to evaporate naturally at room (ambient) temperature and then mixed with hexanes until all the dichloromethane totally evaporated.

These extracts were then column fractionated into the target compound (OCPs) using silica and aluminium oxide. The particle size of the aluminium oxide and the silica gel was 100- 200 mesh. Care was taken to label each extracted solution. The column extraction was conducted through columns of aluminium oxide, and silica gel was placed in 100 mL burettes. The aluminium oxide formed the top column (5 mL), whereas the silica gel was the bottom column (15 mL). Prior to passing the samples through the columns; 30 mL of dichloromethane was initially passed through the columns to wash any possible contaminants in the column. Another 30 mL of the dichloromethane was passed through the columns after each sample was introduced into the column for the extraction of target organic compounds. These fractionated solutions were again concentrated by rotation evaporation using the Rotary evaporator (ZFQ-85A), and bottled in 8 milliliter cell bottles. They were then evaporated again, using a Nitrogen manifold setup with a gentle stream of nitrogen gas (99.9% purity) to about 5mL. The final extracted samples of analysis were analyzed by gas chromatography (GC) and GC-mass spectrometry (GC-MS).

Geochemical Indicators of Organo-Chloro Pesticides in Lake Sediments 399

The dating of the samples was carried out at the State Key Lab of Organic Geochemistry

Lead isotope 210 (210Pb) was used for dating the samples and the results obtained showed that at a depth of 18 cm from the surface of the lake's bed, the age of the samples was a little over 100 years, (precisely 101 years). A graph of depth age was plotted and indication showed that the age of the lake sediment at any depth could be found by simple

A regression graph was also plotted to indicate the accuracy of the technique of analysis.

0 2 4 6 8 10 12 14 16 18 20

depth(cm)

0.1 1 10

The results derived from the instrumental analysis were processed using Excel and Original (Version b) and presented in a tabular form (tables 1 to 4 refer). Graphical illustrations are

ln(deviation210Pb) /dpm/g

y = -5.56ln(x) + 12.29 R² = 0.992

Fig. 3b. Regression Diagram of accuracy of Results of Dating by (210Pb)

(SKLOG), Guangzhou Institute of Geochemistry, and Chinese Academy of Sciences.

**2.3 Dating of sediments** 

extrapolation from the graph.

0

Fig. 3a. Graph of Dating ( years) verses depth (cm)

0.0

4.0

8.0

depth /cm

**3. Results and discussions** 

represented in figures 4 to 9.

12.0

16.0

20

40

60

years

80

100

120

Both graphs are presented below.
