DDT and its analogues

Ability to release hydrogen chloride when adsorbed at the site of 

Muller himself and other entomologists tested a wide array of compounds similar to DDT in order to reveal the relationship between structure and activity. The most important outcome besides DDT was methoxychlor having p,p -methoxy groups instead of p,p -chloro groups. The methoxy groups have approximately the same size and shape as the chloro groups. 

Methoxychlor is much less stable and became popular when the environmental contamination caused by DDT was recognized. The methoxy groups are easily attacked by oxidative enzymes (CYP enzymes). Ethyl groups in the para position are also possible, as in Perthane. Another DDT analogue, more active as a miticide, is dicofol. The structures of DDT and some of the more important derivatives are shown. 

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Mode of Action. DDT and its analogues specifically affect the peripheral sense organs of insects and produce violent trains of afferent impulses that result in hyperactivity, convulsions, and paralysis. Death results from metaboHc exhaustion and the production of an endogenous neurotoxin. The very high lipophilic nature of these compounds faciUtates absorption through the insect cuticle and penetration to the nerve tissue. The specific site of action is thought to be the sodium channels of the axon, through inhibition of Ca " ATPase. 

Beezhold and Stout [68] studied the effect of using mixed standards on the determination of PCBs. Mixtures of Arochlors 1254 and 1260 were used as comparison standards and gas chromatograms of these mixtures were compared with those obtained from a hexane extract of the sample after clean-up on a Florasil column. Polychlorinated biphenyls were separated from DDT and its analogues on a silica gel column activated for 17h and with 2% (w/w) of water added. The extracts were analysed on a silanised glass column packed with 5% DC-200 and 7.5% QF-1 on Gas Chrom Q (80-100 mesh) operated at 195°C with nitrogen as carrier gas (50-60mL min-1) and a tritium detector. 

These may be classified into four chemical groups Chlorinated hydrocarbons which include dico-phane (DDT) and its analogues (e.g. dicofol and methoxychlor), hexachlorocyclohexMie isomers (e.g. lindane), and bridged polycyclic chlorinated compounds (e.g. chlordane) ... 

Figure 6.2 Toxicity of halocyclopropane analogues of DDT. LD50 values for DDT and DCC as functions of the temperature. Note that DDT and its analogues and pyre-throids do not depend on chemical reactivity to be toxic. They can therefore be quite stable, as is the case with DDT. (Data from Holan, G. 1969. Nature, 221, 1025-1029.)...

Similar examination of models of DDT and its analogues (including the related, more stable diphenylo c/opropanes, e.g. (7.50), which produce identical symptoms in the housefly), indicated that activity was lost if the distance between the insertion points of the electron-releasing groups (halo-, alkyl-, alkoxy-) in the benzene rings exceeded ii A other limiting dimensions were specified (Holan, 1969,1971). 

The pyrethroids and DDT are by far the most important insecticides in this category. According to their modes of action, they are sometimes classified into two types. Type 1 includes DDT, its analogues, and pyrethroids without a cyano group, whereas type 2 compounds include the pyrethroids with an a-cyano-3-phenoxybenzyl alcohol. In mammals, they give slightly different symptoms by poisoning. Type 1 causes whole-body tremors, whereas type 2 causes salivation and choreoathetosis. Insects also show different symptoms, but not so distinct. 

The metabolism of DDT 355), and presumably its analogues 356, 357, 393), involves a series of reductive dechlorinations and dehydrochlorina-tions/ Buselmaier et have reported that DDD is mutagenic with Ser-ratia marcescens but not with Salmonella strain G46 in the host-mediated assay DDT, DDE, and DDA [di(4-chlorophenyl)acetic acid] were not positive in similar testing. 

Beasley, H.L., T. Phongkham, M.H. Daunt, et al. 1998. Development of a panel of immunoassays for monitoring DDT, its metabolites, and analogues in food and environmental matrices. J. Agric. Food Chem. 46 3339-3352. 

Table 8.4 Vapor Density and Vapor Pressure of DDT, Its Metabolites, and Analogues...

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