الفهرس 
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Abstract
1.1. Pyrethroids
1.1.1 Types and structure
The widespread use of pesticides in public health protection and agricultural
programs has caused severe environmental pollution and health hazard, particularly in
developing countries including cases of severe acute and chronic human and animal
poisoning as well as damage to other non-target organisms (Assayed, et al., 2010).
Humans are potentially exposed to pesticides either directly, as workers in greenhouse
and in agriculture, or indirectly, via food consumption. In addition, it is likely that a
significant amount of these pesticides and their metabolites reach rivers and estuaries via
run-off from farmland that are potentially toxic to wildlife (EL-Shenawy, 2010).
The pesticides featured belong to two major different classes of insecticides, namely
organophosphate and pyrethroids.Synthetic pyrethroids a unique group of insecticides
having pyrethrin-like structure with better performance characteristics and globally
account for over 30% of insecticides use (Shulka, et al., 2002). Pyrethroids are modified
derivates of pyrethrin, natural substance from the flowers of pyrethrum species (Luty, et
al., 2000).
Various classes of insecticides include organophosphate, organochlorine, carbamate and
pyrethroid. Pyrethroids use has increased much for the last 10 years (Wolansky, et al., 2006).
The incidence of major outcomes and fatalities attributable to pyrethroids are considerably less
than organophosphates (Sudakin, 2006). However, their pathological effects have been
encountered in experimental studies in different animals (Manna, et al., 2004 and Khan, et al.,
2009).
Initially, pyrethroids were extracted from the dried and powdered flower heads of
Chrysanthemum cinerariaefolium. The extract contains chrysanthemic (pyrethrin I) and
pyrethric acid esters (pyrethrin II) in about equal quantities. Natural pyrethrin is a mixture
(1:1) of pyrethrin I and pyrethrin II (Davies, 1985).
The toxicity of pyrethroids insecticides to mammals has received much attention in
recent years because animals exposed to these insecticides showed change in their
physiological activities besides other pathological features (Glass, 2008).
Good solubility of pyrethroids in fats facilitates their absorption, spread in an
organism and penetration to the nervous tissue. Pyrethroid insecticides show neurotoxic
effect which is manifested by an increased excitatory effect of central and peripheral
nervous systems (Crafton, et al., 1995).
Pyrethroids, the synthetic analogues of pyrethrin, fall into two distinct categories (Type I
and Type II) based on the symptoms in experimental animals receiving acute toxic doses
(Verschoyle and Aldridge 1980). Type I pyrethroids, e.g. pyrethrin and permethrin, do not have
an alpha cyano group while Type II pyrethroids such as cypermethrin and fenvalerate, contain an
alpha cyano group. It is generally agreed that Type II pyrethroids are more potent insecticides
Introduction
2
due to the alpha cyano group in their structure (Vijverberg.