Pyrethroids toxicity humans

Synthetic pyrethroids are esters of specific acids (chrysantemic acid, halo-substituted chrysantemic acid, 2-[4-chlorophenyl]-3-methylbutyric acid) and alcohols (allethrone, 3-phenoxybenzyl alcohol) (Ray, 1991). They represent a group of insecticides largely used in agriculture and public health because of their relatively low toxicity to humans and mammalian species and their short environmental persistence. 

Toxic Substances and Disease Registry (ATSDR) (2003) Toxicological profile for pyrethrins and pyrethroids. U.S. Department of Health and Human Services, Public Health Service. Atlanta, GA. http //www.atsdr.cdc.gov/ToxProfiles/tpl55.pdf. Accessed 14 Feb 2011... 

The most promising alternatives were synthetic pyrethroids. The pyrethroids, developed as derivatives of naturally occurring pyrethrum, cause hyperexcitation, aggressiveness, incoordination, whole-body tremor, and seizures. Acute exposure in humans, usually resulting from skin exposure due to poor handling procedures, usually resolves within 24 hours. While not particularly toxic to mammals, they can cause an allergic skin response in humans. Some pyrethroids may cause cancer, reproductive or developmental effects, or endocrine system effects. 

Agency for Toxic Substances and Disease Registry, Toxicological Profile for Pyrethrins and Pyrethroids, US Department of Health and Human Services, Atlanta GE, 2003. 

Blood and various organs of humans and other animals contain esterases capable of acetylsalicylic acid hydrolysis. A comparative study has shown that the liver is the most active tissue in all animal species studied except for the guinea pig, in which the kidney is more than twice as active as the liver. Human liver is least active the enzyme in guinea pig liver is the most active. The relatively low toxicity of some of the new synthetic pyrethroid insecticides appears to be related to the ability of mammals to hydrolyze their carboxyester linkages. Thus mouse liver microsomes catalyzing (+)-/runs-resin e 111ri n hydrolysis are more than 30-fold more active than insect microsomal preparations. The relative rates of hydrolysis of this substrate in enzyme preparations from various species are mouse > > milkweed bug > > cockroach > > cabbage looper > housefly. 

Although certain pyrethroids exhibit striking neurotoxicity in laboratory animals whenadminista edby intravenous injection, and some are toxic by the oral route, systemic toxicity by inhalation and dermal absorption is low. There have been very few systemic poisonings of humans by pyrethroids. Although limited absorption may account for the low toxicity of some pyrethroids, rapid biodegradation by mammalian Uver enzymes (ester hydrolysis and oxidation) is probably the major factor responsible. Most pyrethroid metabolites are promptly excreted, at least in part, by the kidney. 

These include amitraz (110), prepared from 54, a member of the form amidine class, active against mites and ticks, that have replaced organophosphorus compounds. Notably, amitraz is active against newer strains of pyrethroid-resistant ticks. The reaction of diphenylamine (8) with sulfur in the presence of iodine as catalyst yields the anthelmintic (worming agent) phenothiazone (phenothiazine) (111) (Scheme 24). It is too toxic for human use, though it is an intermediate in the production of antipsychotic drugs. 

Pyrethrins and Pyrethroids Absorption Eluman toxicity Exposure symptoms Pesticide uses Exemplars Inhalation, ingestion Low human toxicities by themselves Irritating to mouth, nose, throat Insecticides and acaricides Pyrethrin, dimethrin, fenvalerate, permethrin, bifenthrin... 

Pyrethroids, though far less toxic to humans than insects, induce repeated firing of nerve cells and cause incoordination, tremor, salivation, and irritability to sound and touch. El... 

Mixtures of PBO with pyrethroid or carbamate insecticides are often more effective against insect strains resistant to these compounds where oxidative metabolism is responsible for the decreased effect (Davies et at., 1958 Wilkinson, 1968 Glynne-Jones, 1983 MacDonald eta ., 1983 h unaki etai. 1986). There is no evidence to indicate that PBO increases the low toxicity of pyrethrins and pyrethroids l<> mammals. The acceptable daily intake (ADI) of PBO for humans has been established at 0.2 mg per kg body weight (JMPR, 1995),... 

Functionally, pyrethroids are a group of insect growth regulators that act as neurotoxins resisting the development of insect larvae. They are especially effective against insects that are destructive in the adult stage. They are considered non-toxic to animals and humans. Pyrethrum consists of dried flower heads of chrysanthemum. The plant is a native of Dalmatia (Yugoslavia-Balkans) and is now widely cultivated in Kenya, East Central Africa, Japan, Brazil, Ecuador, and India. 

Organophosphorus pesticides have been the insecticides most commonly used by professional pest control bodies and homeowners for the past three decades (Jeannot and Dagnac 2006). Nevertheless, the decision of the US Environmental Protection Agency (EPA) to phase out certain uses of the organophosphate insecticides because of their potentially toxic effects to humans has led to their gradual replacement by other pesticides. Among them, synthetic pyrethroids have been manufactured since 1950 s based upon the structure of natural pyrethrins, which are chemicals with active insecticidal properties in the pyrethrum extract (a mixture of chemicals found in certain chrysanthemum flowers). Pyrethrins are very unstable in the environment, due to oxidation and UV-radiation. 

With the above discussion in mind, it may be assumed that chiral xenobi-otics are likely to be present in various foodstuffs, as human food comprises the meat of fish, birds and terrestrial animals, and of course vegetables. Many chiral pesticides are used to control insects in vegetables and cereals, and hence the presence of these pesticides in the food products is to be expected. Only a few reports are available dealing the presence of chiral pesticides in various foodstuffs. The cholinesterase inhibition activity of chiral organophosphorous pesticides, as well as that of toxic organophosphorous pesticides nerve gases, are enantioselective in nature. Scientists at the Microbiological and Chemical Exposure Assessment Research Division of NERL in Cincinnati, USA, have found the chiral insecticide permethrin, a pyrethroid insecticide, in spinach. Similarly, malathion has been observed in blackberry extract [146]. 

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