Organophosphorus Pesticides - Mechanisms Of Their Toxicity

In this rapidly developing, capitalist world, people are continually exposed to numerous environmental pollutants such as industrial waste, polluted air and pesticides. These invariably comprise complex mixtures of chemicals. The effects of the mixtures and their mode of action in humans are insufficiently well studied. The majority of pollutants are potentially toxic for organisms, some being connected to disease development. In this context, the increase of chronic degenerative disease including cancer in humans, is of considerable concern (Gupta, 2006). Pesticides are a very important group of environmental pollutants used in intensive agriculture for protection against diseases and pests. The estimated annual application is more than 4 million tons, but only 1% of this reaches the target pests (Gavrilescu, 2005). Functionwise they are divided into herbicides (protection against weeds), insecticides (against insects), fungicides (against fungi), and others. While their use improves the quantity of agricultural products it potentially affects their quality, as pesticides may enter human diet (Grlić, 1988). This is a matter of major current concern. Organophosphorus compounds or organophosphates (OPs) form a large group of chemicals used over the past 60 years for protecting crops, livestock, human health and as warfare agents. On the basis of structural characteristics they are divided into at least 13 types, including phosphates, phosphonates, phosphinates, phosphorothioates (S=), phosphonothioates (S=), phosphorothioates (S substituted), phosphonothioates (S substituted), phosphorodithioates, phosphorotrithioates, phosphoramidothioates (Gupta, 2006). OPs are the most widely used pesticides worldwide and their metabolites are widespread across different populations (Aprea, 2000; Barr, 2004; Curl, 2003). The adverse short-term effects of exposure to these chemicals have been studied mostly in the nervous system, which is their primary target (Gupta at al., 2001), but there is a growing concern about their possible toxic effects in non-target tissues and (long-term) chronic effects that have not been studied in such detail. The majority of people are continually exposed to low OP concentrations, and long-term epidemiologic studies reveal linkage to higher risk of cancer development (Brown et al., 1990; Waddell at al., 2001). The World Health Organization estimates that every year 3 million people experience acute poisoning by OPs, 200.000 people terminally (WHO, 1990). The main routes of OP exposure are shown in Figure 1. Humans are exposed to OPs via ingested food and drink and by breathing polluted air (WHO, 2001). The exposure of workers in closed areas and of agricultural workers or people living near farms, is also very important (Gupta, 2006).