**3. Results and discussions**

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 represented in figures 4 to 9.

400 Pesticides in the Modern World - Risks and Benefits

Geochemical Indicators of Organo-Chloro Pesticides in Lake Sediments 401


p,p'-DDE Diedrin o,p'-DDE Endrin

1+r-chlordane

a-chlordane endosulfan

Table 2. Results of OCPs (concentration in ng/g) (Continue)

Depth (cm)

heptachlor epoxide


Table 1. Results of Organochloro-Pesticides (OCPs) (concentration in ng/g)


Depth (cm) TCMX a-HCH b-HCH d-HCH r-HCH heptachlor Aldrin -3 0.30 0.28 1.42 1.36 0.80 0.09 0.07 -4 0.19 0.11 0.49 1.25 0.11 0.00 0.00 -5 0.12 0.10 0.80 0.45 0.35 0.00 0.00 -6 0.72 0.09 0.33 0.50 0.00 0.00 0.00 -7 0.05 0.08 1.99 0.23 0.10 0.00 0.00 -8 0.06 0.05 0.77 0.20 0.07 0.00 0.16 -9 0.05 0.04 0.29 0.42 0.10 0.00 0.01 -10 0.05 0.02 0.13 0.15 0.09 0.00 0.00 -11 0.05 0.01 0.11 0.12 0.07 0.00 0.00 -12 0.11 0.04 0.07 0.31 0.11 0.04 0.06 -13 0.00 0.01 0.08 0.09 0.08 0.00 0.04 -14 0.28 0.04 0.11 0.27 0.07 0.00 0.00 -15 0.12 0.04 0.10 0.13 0.03 0.00 0.03 -17 0.04 0.01 0.06 0.25 0.15 0.00 0.14 -18 0.08 0.00 0.07 0.18 0.06 0.00 0.03 -19 0.84 0.06 0.11 0.11 0.07 0.05 0.04 -20 0.54 0.07 0.07 0.10 0.08 0.00 0.00 -21 0.33 0.06 0.26 0.22 0.03 0.01 0.08 -22 0.40 0.08 0.10 0.56 0.06 0.01 0.06 -23 0.13 0.05 0.06 0.13 0.05 0.00 0.01 -24 0.28 0.08 0.05 0.26 0.11 0.03 0.00 -25 0.02 0.00 0.00 0.42 0.01 0.02 0.00 -26 0.03 0.01 0.06 0.13 0.07 0.04 0.02 -27 0.08 0.02 0.14 0.31 0.15 0.00 0.06 -28 0.07 0.03 0.06 0.18 0.08 0.00 0.00 -29 0.00 0.01 0.04 0.11 0.08 0.00 0.01 -30 0.05 0.03 0.07 0.54 0.13 0.03 0.00 -31 0.04 0.03 0.13 0.19 0.08 0.03 0.00 -32 0.02 0.02 0.16 0.20 0.18 0.04 0.00 -33 0.06 0.00 0.03 0.07 0.04 0.00 0.01 -34 0.04 0.06 0.08 0.11 0.02 0.00 0.00 -35 0.03 0.06 0.19 0.26 0.04 0.03 0.02 -36 0.04 0.04 0.07 0.10 0.09 0.00 0.00 -37 0.03 0.03 0.16 0.08 0.00 0.09 0.04 -39 0.03 0.02 0.03 0.09 0.05 0.00 0.00 -40 0.02 0.00 0.03 0.23 0.06 0.00 0.01 -41 0.05 0.03 0.09 0.17 0.07 0.00 0.00 -42 0.03 0.00 0.00 0.17 0.02 0.00 0.00 -43 0.03 0.01 0.06 0.06 0.05 0.01 0.00 -44 0.05 0.03 0.06 0.17 0.07 0.00 0.00 -45 0.04 0.03 0.06 0.32 0.07 0.01 0.00 -46 0.06 0.03 0.07 0.23 0.07 0.00 0.00 -47 0.01 0.00 0.00 0.11 0.02 0.00 0.00 -48 0.04 0.03 0.12 0.14 0.05 0.01 0.00 -49 0.03 0.01 0.05 0.14 0.03 0.00 0.00 -50 0.03 0.02 0.06 0.19 0.05 0.01 0.00 -51 0.03 0.02 0.05 0.18 0.05 0.01 0.00 -52 0.04 0.03 0.15 0.12 0.05 0.01 0.00 -53 0.06 0.01 0.05 0.24 0.10 0.02 0.00 -54 0.48 0.03 0.05 0.15 0.03 0.01 0.02 -55 0.00 0.03 0.03 0.14 0.01 0.01 0.01 -56 0.65 0.05 0.11 0.21 0.05 0.03 0.03 -57 0.00 0.04 0.03 0.06 0.00 0.00 0.01 -58 0.02 0.01 0.04 0.08 0.04 0.00 0.00 -59 0.00 0.03 0.00 0.10 0.05 0.01 0.02 -60 0.02 0.02 0.04 0.27 0.02 0.01 0.00

Table 1. Results of Organochloro-Pesticides (OCPs) (concentration in ng/g)


Table 2. Results of OCPs (concentration in ng/g) (Continue)

Geochemical Indicators of Organo-Chloro Pesticides in Lake Sediments 403


Table 4. Results of OCPs (concentration in ng/g) (Continue)

methyoxychlor PCB209 Totals without ISTD

Depth (cm))


Table 3. Results of OCPs (concentration in ng/g) (Continue)



sulfate

p,p'-DDT Endrin ketone

(cm) Endulsufan 2 p,p'-DDD o,p'-DDT Endrin aldehyde endosulfan

Table 3. Results of OCPs (concentration in ng/g) (Continue)


Table 4. Results of OCPs (concentration in ng/g) (Continue)

Geochemical Indicators of Organo-Chloro Pesticides in Lake Sediments 405

ß -HCH

Aldrin

p,p'-DDE

Concentration (ng/g) Concentration (ng/g) Concentration (ng/g) Concentration (ng/g)


Depth (cm)

Depth (cm)

Concentration (ng/g) Concentration (ng/g) Concentration (ng/g) Concentration (ng/g)

Endusulfan ?

Endosulfan sulfate

Total OCP


Depth (cm)

Depth (cm)




Depth (cm)

Concentration (ng/g) Concentration (ng/g) Concentration (ng/g)

0.00 0.05 0.10 0.15 0.20 0.25

0.00 0.05 0.10 0.15 0.20 0.25 0.30

0 2 Concentration (ng/g)

0.0 0.2 0.4 0.6 0.8 1.0 Concentration (ng/g)

0 2

d -HCH

Heptachlor epoxide

Diedrin

p'p'-DDD

p,p'-DDT


Depth (cm)

Depth (cm)

Depth (cm)



Depth (cm)


Depth (cm)


0.00 0.05 0.10 0.15 0.20 0.25 0.30

0 2

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Concentration (ng/g)

0.0 0.1 0.2 0.3 0.4 Concentration (ng/g)

? -HCH

a -chlordane

o'p'-DDE

o,p'-DDT

Endrin ketone



Depth (cm)

Depth (cm)



Depth (cm)

Depth (cm) -60 -50 -40 -30 -20 -10 0

Depth (cm)


Depth (cm)

0.00 0.05 0.10 0.15 0.20 0.25 0.30 Concentration (ng/g)

0.00 0.02 0.04 0.06 0.08 0.10

0.0 0.1 0.2 0.3 0.4

0.0 0.2 0.4 0.6 0.8 Concentration (ng/g)


Concentration (ng/g)

0.0 0.2 0.4 0.6 0.8 1.0 Concentration (ng/g)

Fig. 4. Graphs of OCPs

a -HCH

Heptachlor

Indosulfan? + ? -chlordane

Endrin

Endrin aldehyde

Methyloxychlor


Depth (cm)

Depth (cm)

Depth (cm)



Depth (cm)


Depth (cm)


Depth (cm)


0.00 0.04 0.08 0.12 0.16

0 2 4 6 8 10


> 0.0 0.1 0.2 0.3 0.4 Concentration (ng/g)


A critical appraisal of the data indicated that concentration values were higher at the lake bed surface and near surface for all detected organic compounds. The shape of the graphs of concentration with depth as well as age-concentration values conformed to this general trend.

From activities around the lake, there was no indication of direct sources of supply of pesticide entry into the lake. This is due to a concerted effort by the local people who avoid the use and application of pesticides in and around the lake due to the importance of the local fishing industry. According to ATSDR (2002), one of the modes of transmission of these pesticides is through the atmosphere and therefore, it could be inferred that the only possible source of deposition into the lake is through atmospheric transfer.

The mode of transfer for pesticides into water bodies such as rivers, streams, lakes and estuaries can be either by direct point source or non-direct point source. The situation in Lake Liangzi involves non-point source, as there is no evidence of a direct point source within the lake's environs. The catchment area does not have any rivers or streams inflow into the lake (fig 2) and since the use of any pesticides for farming activities around the lake is prohibited, run-offs could not be a source of deposition.

According to Sierra Club, (1998), properties attributed to pesticides show that upon their release into the atmosphere they can travel far from the point of application. In view of this, it could be inferred that the possible source of these pesticides could only be from remote areas and through atmospheric transfer. A significant indication presented by the sediment core analysis and the presence of the organochloro-pesticides was that their concentration levels conform to the time of usage for chemical application in agriculture in China. According to Chiras (2000), the traditional Chinese pest control methods were the practice for farming until very recent times, when modern chemical application became popular. This practice was when the people dug trenches and directly confronted the pests by catching them. Furthermore, the correlation of the concentrations to the sediment dating is not a surprise as China only adopted modern chemical pesticides after 1949. Chen et al. (1996), mentioned the use of DDT in the 1960's, a peak period of use occurring during the 1970's and the chemical banned in the early 80's due to its toxic effect. It should therefore, be noted that the indication of DDT in the sediment core is from the residue of previous usage. Again, this should not be a surprise as these pesticides belong to POPs and can persist for years post deposition.

#### **3.1 Geochemical degradation of DDT**

The geochemical degradation of DDT was observed from the variable concentrations of its derivative compounds, DDD and DDE. According to ATSDR (2002), DDD and DDE enter the atmosphere as contaminants of toxic breakdown products of DDT. A critical examination of these three organochloro-pesticides reflects the organic processional relationships that exist between them. These organic compounds, according to ASTDR, are easily broken down in the atmosphere with a half-life of two days. DDT in soils breaks down slowly to DDD and DDE through micro-organism activity at a half-life of between two and fifteen days. This partially explains the presence of these compounds at variable concentrations at different levels of the sediment core, which did not conform to the trend indicated by the other pesticides (Compare figures 4 to 9).

A critical appraisal of the data indicated that concentration values were higher at the lake bed surface and near surface for all detected organic compounds. The shape of the graphs of concentration with depth as well as age-concentration values conformed to this general

From activities around the lake, there was no indication of direct sources of supply of pesticide entry into the lake. This is due to a concerted effort by the local people who avoid the use and application of pesticides in and around the lake due to the importance of the local fishing industry. According to ATSDR (2002), one of the modes of transmission of these pesticides is through the atmosphere and therefore, it could be inferred that the only possible source of deposition into the lake is through atmospheric

The mode of transfer for pesticides into water bodies such as rivers, streams, lakes and estuaries can be either by direct point source or non-direct point source. The situation in Lake Liangzi involves non-point source, as there is no evidence of a direct point source within the lake's environs. The catchment area does not have any rivers or streams inflow into the lake (fig 2) and since the use of any pesticides for farming activities around the lake

According to Sierra Club, (1998), properties attributed to pesticides show that upon their release into the atmosphere they can travel far from the point of application. In view of this, it could be inferred that the possible source of these pesticides could only be from remote areas and through atmospheric transfer. A significant indication presented by the sediment core analysis and the presence of the organochloro-pesticides was that their concentration levels conform to the time of usage for chemical application in agriculture in China. According to Chiras (2000), the traditional Chinese pest control methods were the practice for farming until very recent times, when modern chemical application became popular. This practice was when the people dug trenches and directly confronted the pests by catching them. Furthermore, the correlation of the concentrations to the sediment dating is not a surprise as China only adopted modern chemical pesticides after 1949. Chen et al. (1996), mentioned the use of DDT in the 1960's, a peak period of use occurring during the 1970's and the chemical banned in the early 80's due to its toxic effect. It should therefore, be noted that the indication of DDT in the sediment core is from the residue of previous usage. Again, this should not be a surprise as these pesticides belong to POPs and can persist for

The geochemical degradation of DDT was observed from the variable concentrations of its derivative compounds, DDD and DDE. According to ATSDR (2002), DDD and DDE enter the atmosphere as contaminants of toxic breakdown products of DDT. A critical examination of these three organochloro-pesticides reflects the organic processional relationships that exist between them. These organic compounds, according to ASTDR, are easily broken down in the atmosphere with a half-life of two days. DDT in soils breaks down slowly to DDD and DDE through micro-organism activity at a half-life of between two and fifteen days. This partially explains the presence of these compounds at variable concentrations at different levels of the sediment core, which did not conform to the trend

is prohibited, run-offs could not be a source of deposition.

trend.

transfer.

years post deposition.

**3.1 Geochemical degradation of DDT** 

indicated by the other pesticides (Compare figures 4 to 9).

Fig. 4. Graphs of OCPs

Geochemical Indicators of Organo-Chloro Pesticides in Lake Sediments 407

0.0 .2 .4 .6 .8 1.0 1.2 1.4

0 2 4 6 8 10 12

DDD

DDD+DDE

Fig. 8. Graph of Concentration (ng/g) of ∑ DDD and DDE

Depth(cm)

Fig. 7. Graph of Concentration (ng/g) of DDD verses Depth (cm)

Depth(cm)

0







0







Fig. 5. Graph of Concentration (ng/g) of DDT verses Depth (cm)

Fig. 6. Graph of Concentration (ng/g) of DDE verses Depth (cm)

Depth(cm)

0







0







Depth(cm)

DDT

DDE

0 2 4 6 8 10 12

Fig. 5. Graph of Concentration (ng/g) of DDT verses Depth (cm)

Fig. 6. Graph of Concentration (ng/g) of DDE verses Depth (cm)

0.0 .2 .4 .6 .8 1.0 1.2 1.4 1.6 1.8

Fig. 7. Graph of Concentration (ng/g) of DDD verses Depth (cm)

Fig. 8. Graph of Concentration (ng/g) of ∑ DDD and DDE

Geochemical Indicators of Organo-Chloro Pesticides in Lake Sediments 409

water body that is exposed to natural conditions such as the geochemical cycle, solar energy, atmospheric and aquatic effects. From the combination of these processes, and in view of the fact that these organochloro- pesticides are all of recent deposition into the lake, the equilibrium between deposition and maturity is yet to be reached. It should also be noted that the concentration levels of the pesticides detected are as a result of the recalcitrant nature of all the pesticides detected. It is suggested that the variability and distribution of the concentrations from high to low for most of the compounds detected throughout the sediment column could be attributed to these processes. Also sediment trap studies by Sanders (1993), suggest that fractions of organic pollutants entering the water column becomes incorporated into the bottom sediment and that large proportions of remainder is returned to the atmosphere, following outgassing across the water/air surface. Sanders indicate that it is important to acknowledge that historical sediment records do not quantifiably reflect inputs to a water body, but rather provide an over all qualitative time-

Twenty one (21) different organo-chloro pesticides were detected from the single drilled sedimentary core from the bed of Lake Liangzi. All the 21 organochloro-pesticides detected indicated high values at the surface and decreased down in the sediment column. They all fall within the second generation of pesticides and the class of the organocholoro-pesticides or organo-chlorines, commonly called OCPs. The organochloro-pesticides detected in the sediment core analysis included the most dangerous types; Dichloro Diphenyl Trichloro Ethane (DDT), Dichloro Diphenyl Dichloro Ethane (DDD) and Dichloro Diphenyl Dichloro Ethylene (DDE), which are among the ecological high risk class of organochloro-pesticides. The Organochoro detected were: Hexachlorocyclohexane (HCH, a,b,c), Heptachlor,Aldrin, Heptachlor Epoxide, Chlordane, Endosulfane 1 + r-Chlordane, Dieldrin, Endrin, Endolsufane II, Endrin Aldehyde, Endosulfane Sulfate, Endrin Ketone, Methyoxychlor, p,p'

The general trend observed from the analysis indicated variable concentrations of the compounds throughout the column. Concentrations were relatively higher at the surface and near-surface of the column which is in conformity with dates during which pesticide use was prevalent in China. The geochemical degradation of DDT to DDD and DDE was also observed. The relatively higher concentration of DDE is due to the process of bioaccumulation. Most of the pesticides detected are from the residue of previous chemical composition, since DDT and other pesticides have been banned in China. The sources of deposition into the lake was atmospheric transfer, and their point source may be remote as there is no evidence of direct contamination for these organic compounds. The general trend observed indicated that the levels of concentration correlated with recent depositions for

 It could therefore, be inferred that Lake Liangzi has not been spared the menace of pollution, despite the attempts by the people to avoid the use and applications of any

Agency for Toxic Substances and Disease Registry (ATSDR) Toxicological profile of DDT,

trend assessment of the remaining resistant component.

DDE, o,p'DDE, p,p'DDD, o,p'DDT, and p,p'DDT.

DDE, DDD, September, 2002, pg2

these organochloro- pesticides.

chemicals for farming activities.

**5. References** 

**4. Conclusion** 

Fig. 9. Graph of ratio of DDT to ∑ DDD and DDD

The most remarkable indication is the relatively higher concentrations of DDE over DDD. This is because DDE accumulates in plant and animal tissues. The extremely high concentration value for DDE at different levels is thus indicative of this phenomenon. It has been assumed that after the transformation from DDT or DDD the resultant DDE compound bio-accumulated in the fatty tissue of aquatic species (including micro-organisms) then decomposed and re-deposited in the lake sediments. The "apparent anomalous" indication of DDE and its predominance over other compounds detected is thus explained through this phenomenon of bioturbation. Also, according to Wedemeyer (1967), and Baxtor (1990), DDT undergoes slow degradation in comparison to DDD and DDE by chemical and biological processes in the natural environment. The degradation rate and degradation products are controlled by the parameters of environment conditions such as pH, redox condition and microbial activity. The ratio of various degradation products may, therefore, reflect some of the localized environmental conditions attributing to the degradation process.

An analysis of the general trend of the other detected organochloro-pesticides in the sediment core indicate that the variable concentrations may be attributed to leaching or post depositional geochemical processes within the sediment. In the analysis of sediment core, consideration will have to be given to the physical processes continually at work within sediments. This according to Sanders et al. (1992), could lead to a gradual alteration and possible disturbance of accumulating stratigraphy. Such mechanisms according to Sanders et al, eventually result in partial loss of temporal resolution within the core. Another issue to be considered according to Sanders et al. (1992), is the fate of a compound following deposition to a water surface, and the potential losses incurred during its passage through the water column and after incorporation into the sediment profile. They further indicate that biotic and abiotic degradation may serve to deplete certain susceptible compounds, and enhance levels of more recalcitrant components. It should be noted that a lake is an open water body that is exposed to natural conditions such as the geochemical cycle, solar energy, atmospheric and aquatic effects. From the combination of these processes, and in view of the fact that these organochloro- pesticides are all of recent deposition into the lake, the equilibrium between deposition and maturity is yet to be reached. It should also be noted that the concentration levels of the pesticides detected are as a result of the recalcitrant nature of all the pesticides detected. It is suggested that the variability and distribution of the concentrations from high to low for most of the compounds detected throughout the sediment column could be attributed to these processes. Also sediment trap studies by Sanders (1993), suggest that fractions of organic pollutants entering the water column becomes incorporated into the bottom sediment and that large proportions of remainder is returned to the atmosphere, following outgassing across the water/air surface. Sanders indicate that it is important to acknowledge that historical sediment records do not quantifiably reflect inputs to a water body, but rather provide an over all qualitative timetrend assessment of the remaining resistant component.
