Lipid soluble pesticides

The term xenobiotic lipid refers to fat-soluble compounds in the environment that are analogues of naturally occurring lipids and which may be metabolized by animals or plants as if they were natural lipids. Of most practical importance in agriculture are the various types of lipid-soluble pesticides. These may undergo primary metabolic transformations that introduce or expose a carboxylic... 

Air-poUutant effects on neural and sensory functions in humans vary widely. Odorous pollutants cause only minor annoyance yet, if persistent, they can lead to irritation, emotional upset, anorexia, and mental depression. Carbon monoxide can cause death secondary to the depression of the respiratory centers of the central nervous system. Short of death, repeated and prolonged exposure to carbon monoxide can alter sensory protection, temporal perception, and higher mental functions. Lipid-soluble aerosols can enter the body and be absorbed in the lipids of the central nervous system. Once there, their effects may persist long after the initial contact has been removed. Examples of agents of long-term chronic effects are organic phosphate pesticides and aerosols carrying the metals lead, mercury, and cadmium. 

Skin is also important as an occupational exposure route. Lipid-soluble solvents often penetrate the skin, especially as a liquid. Not only solvents, but also many pesticides are, in fact, preferentially absorbed into the body through the skin. The ease of penetration depends on the molecular size of the compound, and the characteristics of the skin, in addition to the lipid solubility and polarity of the compounds. Absorption of chemicals is especially effective in such areas of the skin as the face and scrotum. Even though solid materials do not usually readily penetrate the skin, there are exceptions (e.g., benzo(Lt)pyrene and chlorophenols) to this rule. 

The activity spectrum of a pesticidal compound is often determined by the physical properties of the compound. For example, systemic insecticides usually require both water and lipid solubility since it is necessary for them to pass through... 

The partition coefficient, which will be described in more detail later in this chapter, is the relative solubility of the compound in lipid and water, and the compound s solubility really reflects the ability of the toxicant to move from a relatively aqueous environment across a lipid membrane. It is this factor that is often manipulated in pesticide and drug formulations to create a vehicle. Membrane permeability is therefore strongly correlated to the lipid solubility of the toxicant in the membrane as well as... 

Many pesticides with high lipid solubility tend to accumulate in the tissues of predatory species, including humans. Although most pesticides used today are biodegradable and have lower partition coefficients, not all modern insecticides are unaffected by this problem. Therefore, it is important to understand the principles involved. 

This is undoubtedly the most important factor in bioaccumulation. Pesticides with high lipid solubility have high affinity toward biological constituents. 

Thin-layer radiochromatography (radio-TLC) is widely applied for a variety of environmental studies involving radiolabeled pesticides, such as plant uptake from soil, bioaccumulation in fish, dissipation from soil, metabolism in soil, plants, and fish, and environmental fate. The determination of the lipophiUdty of pesticides is important because their bioaccumulation and tendency for degradation and biotransformation are related to lipid solubility. TLC has advantages for lipohilicity studies compared to traditional partition coefficient measurement in an octanol-water system. 

Gaseous pesticides are evenly dispersed in the air. In the case of inhalation, the anatomy and physiology of the respiratory system diminishes the pesticide concentration in inspired air. As pesticides are mostly lipid-soluble, they are usually not removed in the upper airways but tend to deposit in the distal portion of the lung, the alveoli [83] and may then be absorbed into the blood stream. 

Of the several classes of synthetic insecticides, the chlorinated hydrocarbon (CH) and organophosphate (OP) insecticides have the greatest psychiatric significance [Pesticides and Neurological Diseases 1982 Ecobichon 1996). The CH insecticides, also called organochlorine insecticides, include three chemical classes di-chlorodiphenyltrichloroethane (DDT), cyclodienes (aldrin, dieldrin, heptachlor, chlordane, endosulfan), and chlorinated benzene and cyclohexanes (lindane) (Ecobichon 1996). Their ban in the United States and Europe resulted from their high chemical stability and lipid solubility that allowed environmental persistence and magnification in the food chain (Ecobichon 1996 Kaloyanova and El Batawi 1991). 

Based on oral LDjq values in the rat. Note The likelihood of serious toxicity depends not only on the dose of the pesticide but also on the route or exposure, circumstances of the exposure, and preexisting cholinesterase activity. Moreover, agents that are highly lipid soluble, such as fenthion and sulfoton, may cause prolonged intoxication. 

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