Persistence cyclodienes

The cyclodiene insecticides aldrin, dieldrin, endrin, heptachlor, endosulfan, and others were introduced in the early 1950s. They were used to control a variety of pests, parasites, and, in developing countries, certain vectors of disease such as the tsetse fly. However, some of them (e.g., dieldrin) combined high toxicity to vertebrates with marked persistence and were soon found to have serious side effects in the field, notably in Western European countries where they were extensively used. During the 1960s, severe restrictions were placed on cyclodienes so that few uses remained by the 1980s. 

Apart from the oxidations just mentioned, cyclodienes are rather stable chemically. It should, however, be noted that dieldrin can undergo photochemical rearrangement under the influence of sunlight to the persistent and toxic molecule photo dieldrin, which occurs as a residue following the application of this insecticide in the field. 

Cyclodienes A group of organochlorine (OC) insecticides, some of which are highly toxic and persistent (e.g., aldrin, dieldrin, and heptachlor). 

The most serious toxicological effect of endrin is central neurotoxicity (Klaasen et al. 1986). Organo-chlorines interfere with the normal flux of cations across the axon, disrupting central nervous system homeostasis (Finkel 1983 Klaasen et al. 1986). Endrin is one of the most toxic cyclodienes, and seizure activity may develop rapidly after exposure (Proctor et al. 1988). In most cases, recovery is rapid. However, headaches, dizziness, weakness, and anorexia may persist for 2-4 weeks. 

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. 

Poisonings resulting in convulsions have occurred in manufacturing workers. Recovery after occupational exposures is usually complete within 24 hours. Unlike dieldrin, which persists in the body, endrin is rapidly eliminated from the body and apparently does not accumulate, even in fatty tissue. However, endrin is the most acutely toxic of the cyclodiene compounds, which also include chlordane, heptachlor, dieldrin, and aldrin. ... 

Chlordane was introduced as an insecticide in 1945 and was the first cyclodiene insecticide that was used in agriculture (Eisler, 1990). It was the second most important organochlorine pesticide after toxaphene from 1976 to 1977 (Stansley Roscoe, 1999). It has been used on agricultural crops and extensively in the control of termites (Smith, 1991). Chlordane and heptachlor can be metabolized into two persistent (oxygenated) epoxides—oxychlordane and heptachlor epoxide—in mammals (Nomeir Hajjar, 1987) such that the two compounds are always measured together with chlordane and heptachlor. 

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. 

Several investigations (38-40) between i960 and 1965 finally dispelled the myth of dieldrin s metabolic inertness in mammals and since then numerous laboratories have shown that cyclodienes conform to the established principles of drug metabolism (4l). Molecular structure has a profound influence on the exposure of the non-chlorinated portions of these molecules to enzymatic attack and the low persistence of endrin, as compared to dieldrin, in mammalian tissues appears largely due to the stereochemical difference (42). The biotransformations of dieldrin are summarised in Figure 5 ... 

Lindane is relatively non-persistent, especially under anaerobic conditions, and although its more highly chlorinated residues may present the same problems as those of polychlorophenols, the less chlorinated residues should follow pathways similar to those established for the microbial degradation of the chlorinated phenoxyalkanoic acid herbicides. Recent evidence (46) indicates that certain microbes can dechlorinate DDT anaerobically, thereby making available intermediates which may undergo further aerobic attack, leading in principle to total degradation. The ultimate fate of the hexachloronorbornene nucleus of cyclodienes is still uncertain and this question continues to attract attention. 

Photolysis of 2-bromo-4,4-dimethyl-2-cyclohexenone only affords reduction, even in a nucleophilic medium343,344. Apparently, this substrate is structurally not suitable to form a vinyl cation. Formation of vinyl radical-derived products is also the main process for all vinylic halides, if their irradiation is performed in an apolar medium. Such photochemical reductive dehalogenation and especially dechlorination reactions have been extensively studied in the past, not in the least because of their importance as abiotic transformation of persistent polychlorinated environmental pollutants. Examples are the cyclodiene insecticides aldrin and dieldrin, which contain a vicinal dichloroethene chromophore. In recent... 

Epoxidation Epoxidation is an important microsomal reaction. For example, the cyclodiene insecticide aldrin can be oxidized to its epoxide dieldrin (as shown in Chapter 4, Figure 4.4), and heptachlor is oxidized to heptachlor epoxide. There is no great increase in toxicity in this case, but the epoxides are more environmentally persistent than their precursors. Moreover, some of the epoxides produced in the microsomal oxidation are highly reactive and can form adducts with cellular macromolecules such as proteins, RNA, and DNA, often resulting in chemical carcinogenesis. 

DDT and the cyclodiene pesticides are only a few components of a large soup of persistent environmental contaminants consisting of halogenated organics - that is, molecules with a carbon skeleton (usually aromatic) deriving some or all of their toxicological activity through the insertion of chlorine. 

Cyclodiene insecticide resistance is found in more species than any other type of resistance 291 species are able to resist this class of insecticide, compared to smaller numbers for DDT, OPs, carbamates or pyrethroids (Table II). The preponderance of resistance to the cyclodienes is almost certainly due to the long persistence of these chemicals in the environment. 

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). 

The perspective that "The persistent chlorinated hydrocarbons appear to be uniquely well adapted for soil use" (3) rather quickly collided with the reality of insect microevolution. The first evidence of rootworm control failures occurred in Nebraska in 1959, and by 1962 resistance of rootworms to the cyclodienes had been conclusively documented (4). The spread of this resistance during the 1960 s, along with environmental scrutiny of the ecological impacts of these persistent compounds, created a demand for more environmentally sound insecticides. 

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. 

Considerable research effort has been paid to the problems of the persistence of chemical means for the plant protection. Many of the studies have been aimed at the persistence of pesticides in the soil. Insecticides based on chlorinated hydrocarbons are particularly persistent, for instance DDT, BHC isomers and so-called polychlorinated cyclodiene compounds, aldrin, dieldrin, andrin, heptachlor. In many countries the use of these pesticides has been either restricted or even prohibited on account of their persistence in the environment. For chemical protection of plants they are gradually being replaced by organophosphate and carbamate substances, which are more toxic, but are less stable in the environment (e.g. parathion, dichlor-vos, carbaryl, propoxur). 

Traditional analysis for cyclodiene insecticides involves their extraction from rendered adipose fat followed by gas or thin layer chromatography and detection by electron capture or mass spectrometry (6z. 1). These methods are time consuming, require sophisticated equipment and highly trained personnel. Because of the persistence of cyclodiene insecti-... 

There is considerable, but variable, cross resistance from DDT to other chlorinated hydrocarbons such as benzene hexachloride and the cyclodiene insecticides. However, when one substitutes a para-methoxy group for para-chlorine in the DDT molecule, a far less persistent—and somewhat less active—but... 

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