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Enormous quantities of organic and inorganic compounds are released

into the environment each year as a result of human activities. Every

year hundreds of chemicals are manufactured and the use of these

chemicals pollutes the environment. They can be mutagenic and/or

carcinogenic as well as toxic to a broad range of organisms. A wide

range of contaminants can reach the river either via groundwater or

through drainage ditches, including artificial fertilizer residues,

insecticides, herbicides, pesticides, etc all of which are potentially very

harmful. So, it is the aquatic environment that is of serious concern.

[22] Considering of the use of some rivers and lakes as water supplies,

threaten are thus posed on human health via drinking water, polluted

vegetable and foodstuff etc. besides the disruption of the natural

environment.

Pesticides used in agriculture are the most widespread method for pest

control all over the world. However, the irrational use of pesticides has

led to serious problems to environment and human health by means of

water pollution.

Each year an estimated 2.5 million tons of pesticides are applied to

agricultural crops worldwide. The amount of pesticide coming in direct

contact with or consumed by target pests is an extremely small

percentage of the amount applied. In most studies the proportion of

pesticides applied reaching the target pest has been found to be less
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than 0.3%, so 99.7% went 'somewhere else' in the environment

(Pimentel, 1995). Where they pose undesirable effects, as the target

species selectivity of pesticides is not as well developed as might be

hoped for, non-target species are frequently affected because they

possess similar characteristics to those of the target organisms

(Cantelli-Forti et al., 1993).

Despite the large increases in food production brought about by these

chemical inputs the agricultural, environmental and health costs

arising from pesticide use are high (Wilson, 2000).

The pesticides currently in use include a wide variety of compounds

belonging to different chemical classes. Pesticides have been

considered potential chemical mutagens. Experimental data revealed

that various agro-chemical ingredients possess mutagenic properties

inducing gene mutation, chromosomal alteration or DNA damage. The

genotoxic potential for agrochemical ingredients is generally low: they

give positive results in few genotoxicity tests. In human biomonitoring

studies genetic damage associated with pesticides has been detected

for high exposure levels and intensive use. The genetic effects depend

on quantity and variety of chemical formulations consumed (Bolognesi

and Morasso. 2000). Studies have shown chromosomal aberrations and

chromatid aberrations in association with pesticide exposure (Amer et

al., 1996).
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According to IENES, 100000 chemicals are presently in use and some

of them-or their metabolites-have the potential to react with DNA and

increase genotoxic stress on humans and the ecosystem. DNA

damaging agents are of particular concern because their effects can

give rise to mutations, deformities, degenerative diseases, and/or

cancers. Over 200 animal carcinogens have been reported (Claxton,

1988), 73 pesticides still in use are classified under categories Bl and

B2 (probable human) and C (possible human) of carcinogenicity by the

EPA (National Research Council, 1987), and defined as ‘potentially

oncogenic compounds’.

Because exposure to determined chemicals or complex mixtures can

lead to cancer in later life (Bonassi et al., 2008), and can also induce

heritable changes in man. Such changes can arise following damage to

DNA and resulting mutations. Therefore, it has become necessary to

determine whether commonly used pesticides possess the ability to

damage DNA.

Furthermore, bioassays are essential for the evaluation of integrated

toxic effects, including mutagenic and genotoxic effects. Mutagenesis

is defined as the induction of a heritable change on the genetic

material of an organism by altering the base sequence of DNA.

Genotoxicity, in addition to mutagenesis, involves change in the

chromosome structure, number, shape or position (Bulich, 1993).

Biomarker can be defined as ‘the measurements of body fluids, cells,

or tissues that indicate in biochemical or cellular terms the presence of

contaminants or the magnitude of the host response’ (Bodin et al.

2004).

Among the molecular components of the cell, DNA is an important

target for the evaluation of environmental toxicity both in aquatic and

land organisms. The integrity of DNA can be greatly affected by

genotoxic agents due to DNA strand breaks, loss of methylation and

formation of DNA adducts (Pisoni et al. 2004). The loss of DNA integrity

can cause the induction of mutations, chromosome aberrations, birth

defects, and long-term effects such as cancer and other irreversible

toxic effects like the ‘‘genotoxic disease syndrome’’ in vertebrates

(Kurelec, 1992). Consequently, there is great interest in evaluating the

impact of the genotoxins released into aquatic environment. Therefore,

the levels of DNA molecular damage have been proposed as a

sensitive indicator of genotoxicity and an efficacious biomarker in

environmental monitoring (Shugart, 1990).

This has led to the development of several mutagenicity assays such

as chromosome aberration, micronucleus test and sister chromatid

exchanges (SCE) to study genotoxicity of the chemicals in the

environment. SCE and chromosome aberration analysis as dependable

and sensitive indicators of DNA damage caused by environmental

pollutants have been demonstrated by several authors using aquatic

models (Al-Sabti, 1985; Harrison, 1986; Lobillo et al., 1991; Wrisberg

and Van Der Gagg, 1992; Albertini et al, 2000; Bonassi et al, 2004;

Campana et al., 1999; Das and John, 1999; Farah et al., 2003;

Velmurugan et al., 2006).

It has been shown that fish are suitable sentinel organisms for

monitoring genotoxic pollutants in the aquatic environment because

they play an important role in the food web, they are bio-concentrators

and are responsive to mutagens at low concentrations such as

environmental pollutants. Fish also metabolize many carcinogens in a

manner analogous to that of mammalian organisms (Stegeman and

Lech, 1991).

Fish are good indicators for assessing the genotoxic and mutagenic

effects of xenobiotics and physical agents (Al-Sabti, 1986). Sister

chromatid exchange (SCE) tests have been applied to various fish

species (Kligerman, 1979; Vigfusson et al., 1983) and the clastogenic

effects of carcinogenic-mutagenic chemicals on kidney cells of

Cyprinius carpio have been described (Al-Sabti, 1986). The

development of in vivo genotoxicity assays using fish as model

systems (Powers, 1989) is being enhanced by their easy handling in

the laboratory.
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Cytogenetic damage in circulating lymphocytes has been widely used

as a biomarker of exposure (and perhaps of effect) in those exposed to

pesticides. This has resulted in a number of reports in which pesticide

exposure has been associated with increases in chromosome

aberrations (CA), micronuclei (MN) and sister chromatid exchanges

(SCE) in cultured lymphocytes isolated from peripheral blood taken

from exposed individuals (Bolognesi 2003). It has been suggested that

the assessment of cytogenetic effects in exposed subjects can serve as

an early indicator of increased risk of cancer (2–4) although the

evidence is somewhat contradictory (5).