**4. Conclusion**

408 Pesticides in the Modern World - Risks and Benefits


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

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

the localized environmental conditions attributing to the degradation process.

DDD+DDE

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

DDT

1.8

1.6

1.4

1.2

1.0

.8

.6

.4

.2

0.0

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

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 these organochloro- pesticides.

 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 chemicals for farming activities.

## **5. References**

Agency for Toxic Substances and Disease Registry (ATSDR) Toxicological profile of DDT, DDE, DDD, September, 2002, pg2

**22** 

Feza Geyikçi

*Turkey* 

**Pesticides and Their Movement** 

**Surface Water and Ground Water** 

*Ondokuz Mays University, Chemical Engineering Department,* 

Pesticides are poisons designed to kill pests such as rodents, insects, weeds and fungi. Pesticides are, by their nature, toxic chemicals; since many pesticides may potentially leave residues on foods available for human consumption, there is much concern regarding the potential health risks of pesticides in the human diet. Pesticides used in agriculture to control pests, such as insects, weeds, and plant diseases, have been subject to considerable legislative, regulatory, and consumer scrutiny over the past few decades. Pesticides, with their high degree of toxicity, constitute a very important group of target compounds in environmental samples. Those presentnin waters may have an agricultural, domestic or industrial origin, the most harmful effect being their inclusion in the so-called "nutritionchain" (Vinas et al., 2002). Many common pesticides contain potent neurotoxic chemicals that attack and disable portions of the nervous system and brain. The use of pesticides in commercial agriculture has led to an increase in farm productivity (Guler et al., 2010). Pesticides also present environmental concerns including water and soil contamination, air pollution, destruction of natural vegetation, reductions in natural pest populations, effects upon non-target organisms including fish, wildlife, and livestock, creation of secondary pest problems, and the evolution of pesticide resistance (Winter, 2004). Many pesticides were used on a global scale from the 1950s to the mid-80s, most of which are stable and persistent

The use of pesticides in agriculture is necessary to combat a variety of pests that could destroy crops and to improve the quality of the food produced. The advantages and disadvantages of pesticide pollution controlling technique are determined by many factors, which require a comprehensive evaluation method adopted in the evaluation of pesticide pollution controlling techniques. Exposure to high levels of pesticides can cause a range of acute, flu- and malaria-like symptoms including headaches, weakness, nausea, respiratory distress, convulsions, coma, and death, accounting for an estimated 20,000 fatalities per year

In a recent USEPA summary report defined vulnerability applied to risk assessment as a four component system: (1) susceptibility or sensitivity of the human or ecological receptors; (2) differential exposures of the receptors; (3) differential preparedness of the receptor to withstand the insult from exposure; (4) differential ability to recover from these effects. All of these components are pertinent to systems undergoing development from the fetus

**1. Introduction** 

in the environment (Barra et al., 2001).

(Jiang and Wan, 2009; Guler et al., 2010).

