Food chains cyclodienes

The formation of polar metabolites from nonpolar materials may actually facilitate monitoring programs—in many cases the polar chemicals are highly concentrated in certain body fluids such as bile and urine. On the other hand, materials such as certain cyclodienes and polychlorinated biphenyls, which are very lipid soluble and resistant to metabolism, may accumulate and these chemicals may persist in the environment and may be transferred via the food chain to man. There is also interest in these biotransformation processes in lower organisms since the simplicity of these systems may lead to a better understanding of the phylogenetic development of xenobiotic metabolism. 

However several POPs, particularly the OCPs and dioxins, remain at low levels in the Australian environment and several remain persistent at low levels in body fats and fluids of Australians. The levels reflect the past use and persistence of OCPs in the Australian environment, contamination of the food chain and the capacity of the body to metabolise and store in body fats. The dioxins remain due to the ubiquitous nature of their sources with combustion as a major source and their persistence. Future trends are likely to mean very low-level residues in human fats of DDE, cyclodienes, HCB, HCHs and dioxins in the long term. Their rate of decline will probably depend on removing HCB from chlorinated industrial chemicals and OCPs from the environment (e.g. remediation of contaminated soils) by hazardous waste treatment methods (e.g. physical, chemical and biological degradation or fixation) or secure landfill. 

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). 

Cyclodienes (chlordane, aldrin, dieldrin, heptachlor, endrin, mirex, endosulfan, chlordecone). This new class of pesticides appeared on the scene following World War II. Most of them are very stable to sunlight and persistent in soil and they were used to control termites and other insects. Their effectiveness leads to insect resistance and bioaccumulation in the food chain and for these reasons their use was banned between 1984 and 1988. These compounds affect the CNS in the same way, causing tremors, convulsions, and prostration to the maximum extent, depending on the rate and time of exposure. 

The cyclodienes, particularly aldrin, dieldrin, and endrin, are considered unsafe for any kind of use. Lindane, on the other hand, has high selectivity in favour of Man. It is included in the World s principal pharmacopoeias as an insecticide, acaricide, and larvicide. A 0.2% alcoholic solution is applied topically for head lice and a 1 % emulsion is employed in the treatment of scabies, in humans. The use of DDT in human medicine, for similar purposes, has greatly diminished in the last decade. It must, however, be pointed out that it has a high safety record in Man, and that government bans on its use are concerned with its accumulation in the food chains of birds and fish where it interferes with the calcium metabolism of shells and bones, respectively (see p. 96). In 1956, Hayes, Durham and Cueto, of the USA Public Health Service, fed 35 mg of DDT per man per day (i.e. 200 times the highest average dietary intake of that time in the USA) to human volunteers for 18 months. None of the subjects developed any symptom related to this chemical. 

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