Mechanisms of Toxic Action and Structure-Activity Relationships for Organochlorine and Synthetic Pyrethroid Insecticides

Abstract

The mechanisms and sites of action of organochlorine (DDT-types and chlorinated alicyclics) and synthetic pyrethroid insecticides are presented with discussion of symptoms, physiological effects, and selectivity. The structural requirements for toxicity are assessed, and structure-activity relationships are considered for each subclass. Lipophilicity is important for all the groups because it facilitates delivery of these neurotoxicants to the site of action in the nerve. Steric factors including molecular volume, shape, and isomeric configuration greatly influence toxicity. Electronic parameters also have been demonstrated to affect biological activity in some of the groups of insecticides, e.g., Hammett's a and Taft's a* as indicators of electronegativity. New synthetic pyrethroids continue to be developed, with varied structures and different physicochemical and biological properties.

Chemical composition and insecticidal potential of essential oils from Egyptian plants against Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

“…Monoterpenes act as neurotoxicants against different insect species (Coats et al, 1991;Enan, 1998). They have been shown to inhibit both the GABA receptor in marine algae (Coats, 1990), and acetylcholinesterase (AChE) isolated from different insect species (Grundy and Still, 1985;Ryan and Byrne, 1988); therefore, we suggest that the test oils may cause insecticidal activity via one or more of these modes of action.…”

Structural Requirements for Monoterpenoid Activity against Insects

“…While that non-invasive assay did not allow determination of the exact site or mechanism of action, these studies provide circumstantial evidence that the monoterpenoids act in a manner similar to the cyclodienes. The action of the chlorinated cyclodienes and lindane is acknowledged to occur at the picrotoxinin site of the GABA (γ-amino butyric acid) receptorionophore complex, and as an antagonist of GABA, therefore inhibiting chloride uptake into the neuron through the chloride channel (35,36). Polyhalogenated monoterpenoids have been isolated from a marine alga, and they have been shown to elicit lmdane-like GAB Α-antagonist effects (3 7).…”

Pesticide illness among flight attendants due to aircraft disinsection

“…Pyrethroids are synthetic derivatives of natural pyrethrin compounds and are widely used as broadspectrum insecticides [Ray and Forshaw, 2000;Bradberry et al, 2005]. Both pyrethrins and pyrethroids exert their toxic effects by prolonging the inactivation of sodium channels in the peripheral and central nervous systems [Coats, 1990;Ray, 1991;He, 1994;Bradberry et al, 2005]. Exposure to synthetic pyrethroids can cause abnormal sensations on exposed skin, contact dermatitis, dizziness, nausea, anorexia, fatigue, mild disturbances of consciousness, muscular fasciculations, and, at high doses, pulmonary edema, convulsions, and coma [He et al, 1989;Bradberry et al, 2005;Spencer and O'Malley, 2006].…”