Acute toxicity pyrethroids

Williamson, E.G., S.F. Long, M.J. Kallman, and M.C. Wilson. 1989. A comparative analysis of the acute toxicity of technical-grade pyrethroid insecticides and their commercial formulations. Ecotoxicol. Environ. Safely 18 27-34. 

As previously mentioned, early in vivo acute toxicity studies indicated that the action of Type II pyrethroids on the nervous system was different from that of the Type I pyrethroids. Deltamethrin decreased the acetylcholine content of the cerebellum, whereas DDT, a well-established voltage-sensitive sodium channel agonist, and cismethrin, caused no significant reduction [2]. 

Neurotoxicity of Pyrethroids 1.1 Acute Toxicity and Clinical Signs... 

Cantalamessa F (1993) Acute toxicity of two pyrethroids, permethrin and cypermethrin in neonatal and adult rats. Arch Toxicol 67 510-513... 

Table 2 Ranges of acute toxicity (pg/L) of SPs to fish, various groups of aquatic invertebrates, and algae (Giddings JM (2006) Compilation and evaluation of toxicity data for synthetic pyrethroids. Unpublished report of Compliance Services International, Rochester)...

Table 6 Oral and contact acute toxicity of pyrethroids to honeybees...

Ion transport is central to nerve impulse transmission both along the axon and at the synapse and many neurotoxicants elicit effects by interfering with the normal transport of these ions (Figure 11.6). The action potential of an axon is maintained by the high concentration of sodium on the outside of the cell as compared to the low concentration inside. Active transporters of sodium (Na+K+ ATPases) that actively transport sodium out of the cell establish this action potential. One action of the insecticide DDT resulting in its acute toxicity is the inhibition of these Na+K+ ATPases resulting in the inability of the nerve to establish an action potential. Pyrethroid insecticides also elicit neurotoxicity through this mechanism. DDT also inhibits Ca2+Mg2+ ATPases, which are important to neuronal repolarization and the cessation of impulse transmission across synapses. 

Some pyrethroids have as many as eight different isomers, and there are several different types. Acute toxicity of a mixture of two isomers depends on the ratio of the amounts of isomers in the formulation. For example, the female rat s acute oral LD50 of permethrin increases from 224 mg/kg to 6,000 mg/kg as the proportion of transisomer increases from 20% to 80%. The route of exposure also is critical in assessing the acute toxicity of a synthetic pyrethroid. Like DDT and many other registered insecticides, naturally occurring pyrethrins and the synthetic pyrethroids are nerve poisons. 

Pyrethroids. Pyrethroids, such as natural pyrethrins and synthetic analogs, allethrin, permethrin, and others, are well known for their neurotoxicity (48-59). However, as a major class of insecticide, they have a remarkable safety margin for mammals, principally because of the rapid metabolic degradation of pyrethroids in mammalian species (48-50). The acute toxicity of pyrethroids involves two distinct syndromes in rats and mice (49-51). The first one, T syndrome or tremor (Type I), is characterized by a rapid onset of tremor, initially in the limbs and gradually extending over the whole body. Death is associated with clonic seizures. The second... 

The high acute toxicity of DDT analogs and most pyrethroids to fish is one of the most significant hazards associated with the widespread use of these compounds. The high toxicity of pyrethroids to fish appears to result in part from high intrinsic sensitivity of the CNS to these compounds (JJ3,J7) Fish are also highly sensitive to some... 

Figure 5, obtained from Wolansky and Harrill (2008), shows the acute toxicity (LD50) values in rats for the parent pyrethroids and one or more of their eruiched isomers. Stmctural information on the compounds tested and their purity was limited to a few of the more commonly used pyrethroids (i.e., allethrin, resmethrin, bifenthrin permethrin, deltamethrin, cypermethrin). The authors recognized the need to standardize test materials, the pyrethroid isomers used in the tests, and their purity for improving the value of information obtained from toxicological studies. 

The utilization of natural insecticides and synthetic insecticides based upon natural insecticides has been an interest of research for more than 50 years. In that period a wide variety of phytochemicals acutely toxic to insects have been identified. This discussion will be limited to three of these plant based insecticides. A review of the literature for the identified natural insecticides, antifeedants and growth regulators found in plants, except for the pyrethroids and insect hormones, has recently appeared (Addor, 1995). 

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