CHAPTER ONE

1.0     INTRODUCTION

There has been a global increase in pesticides usage due to the compelling need to feed the

ever-increasing human and animal populations, and to reduce the incidence of food and

vector-borne diseases (Ambali, et al., 2012). These health and economic benefits of

pesticide usage are achieved not without simultaneous potential health risks and adverse

health outcomes in non-target species, including man (Abdollahi et al., 2004).

The adverse effect of some pesticides has necessitated legislation in most developed

countries against potentially damaging ones (Czarniewska et al., 2003). However, in most

developing nations, regulatory laws governing pesticide production and utilization are

almost completely lacking or where available these laws are poorly implemented thereby

having a far-reaching effect on the ecosystem (Otitoju and Onwurah, 2005).

Organophosphate (OP) compounds are one of the most widely used pesticides accounting

for about 50% of the global pesticide use (Ambali, et al., 2012). This may be of particular

concern given the widespread use of OP pesticide in household, agricultural, and

commercial environments worldwide (Terry et al., 2007). Human studies in agricultural

communities in developing countries have shown that cumulative exposure to OP is

associated with cognitive and psychomotor impairments (Kamel and Hoppin, 2004; Kamel

et al., 2007).

Chlorpyrifos (CPF) is a chlorinated OP insecticide that has enjoyed widespread use in

agricultural and domestic pest control (Steenland et al., 2000; Ambali et al., 2009). It is of

public health importance as CPF residues have been detected in poultry egg, meat, cow milk

and milk products (Rawat et al., 2003). CPF is thought to cause oxidative stress in both

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humans and animals via the formation of free radicals (Terry et al., 2007). Exposure to CPF

at doses that did not result in overt clinical symptoms has been reported among pesticide

applicators and other farm workers (Farahat et al., 2010) thereby constituting an important

source of occupational hazards to these groups of individuals (Ray and Richards, 2001).

However, the body is endowed with enzymatic and non-enzymatic antioxidant systems to

counter the lipid peroxidative changes induced by reactive oxygen and nitrogen species. In

condition of enhanced free radicals formation (Ambali et al., 2010c, 2012), which can also

be referred to oxidative insult or stress by CPF     these antioxidant systems could be

overwhelmed resulting in tissue damage. The brain, due to its biochemical and

physiological properties is especially sensitive to reactive oxygen species (ROS), which

disrupt its functions and structure (Drewa et al., 1998). This is witness in neurological

disorders such as Alzheimer’s dementia, affecting learning and memory aspect of brain

functions.

Learning is the acquisition of new information by the nervous system, resulting in changes

in behavior. While memory is the ability to store, process and recall learnt information

(Mangina and Sokolov, 2006).

Cognition is the ability to consciously carry out functions utilizing the human brain and

includes: visual perception, selective attention, logical reasoning, construction (sentences

for example) calculation, attention information processing), planning, problem-solving,

comprehension and memory (Warburton, 1995; Claxton, 2002).