Environment, pesticides metabolic activity

For the last forty years, many reports have emerged on the hormone-like effects of chemical compounds such as pesticides and industrial chemicals upon wildlife and humans. The effects of these materials are believed to be either direct or indirect. Direct effects involve positive or negative interactions with the hormone receptors. Indirect effects may result when the synthesis of hormones or their receptors is altered, or the transport, metabolism, or elimination of hormones is modified in some way. The discovery of hormone-like properties of some compounds was made long after their release into the environment. It was shown soon after their introduction that aviation crop dusters handling DDT had low sperm counts and workers at a plant producing the insecticide kepone were reported to have low libido, sperm counts and to be impotent. Subsequently, experiments conducted in laboratory animals demonstrated unambiguously the oestrogenic activity of these pesticides. 9 refs. 

Over the last decades, large amounts of different man-made chemicals which can act as weak estrogens have been released into the terrestrial and aquatic environment and are distributed world-wide. Classical environmental estrogens are pesticides, such as o,p -DDT, and its metabohtes o,p -DDE and o,p -DDD, methoxychlor and its metabolites, chlordecone (Kepone ), dieldrin, Toxaphene, and endosulfan [126, 135, 136]. It is also known that many chemicals with very weak or no measurable estrogenic activity can be metabolized in organisms especially to hydroxylated compounds which may have much more estrogenic potency than the parent compound. Examples are methoxychlor and its mono- and di-demethylated derivatives [126,127] as well as the alkylphenol... 

Chlorophenols are a class of pesticide substances, e.g. fungicides, used for wood preservation, in pulp production and other miscellaneous applications. The substances were introduced in the 1930s and have been used in very large amounts. Today, the consumption has decreased and the substances are banned in many countries. The main active substance in chlorophenol products is pentachloro-phenol (PCP Figure 3.10). The substance is moderately lipophilic and persistent, yet readily absorbed and accumulated in biota and expresses a rather high acute toxicity. The metabolism and breakdown of this envirotoxicant in biota and in the environment are rather slow, resulting in successively dechlorinated metabolites. 

The specific nature and composition of the substituents which define the class of compounds also determine the intrinsic potency against cholinesterase inhibition, the efficiency of absorption, and the pattern of metabolism seen in both target insects and mammals. It is misleading to talk of anticholinesterase pesticides as a single group since each compound has individual properties and activity against both insect targets and man. The common property is that these pesticides are very unstable in the environment and must be reapplied for effect or formulated in slow-release products. 

Kitamura,, S Suzuki, T Ohta, S and Fujimoto, N. (2003a). Antiandrogenic activity and metabolism of the organophosphorus pesticide fcittltion and related compound.s. Environ. Health Perspect. Ill, 503-508,... 

Degradation and metabolism are the means by which pesticides are removed from the environment. Metabolism of the pesticide is often enhanced by rapid uptake by the target organism and completion of biochemical pathways. The various surfactants in the formulation or adjuvants that are tank mixed to promote uptake can have a significant impact on metabolism. Aids to translocation to the active site or areas of degradation will also have an impact on metabolism of the AI. 

A wide variety of environmental factors have been shown to produce effects -sometimes lethal - on plant lipid metabolism. These factors range from natural influences (such as light) over which Man has little control to xenobiotics which are used deliberately (e.g. pesticides) or which enter the environment accidently. Some factors such as temperature, sulphur dioxide, oxides of nitrogen and ozone can be classed as natural but their levels (and, therefore, their effects on plants) are exacerbated by human activities. 

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