Trichlorfon insecticide toxicity

Another group of organophosphoms insecticides consists of preparations with the so-called systemic (inside the plant) effect. They are absorbed by plant tissue, making the plant poisonous for insects feeding on it. These insecticides are mercaptophos (systox) and M-74 (pisyston), derivatives of mono- and dithiophosphoric acid. However, both substances are very toxic for people and cattle and are even more dangerous than thiophos that is why they are not used in Russia. Other systemic preparations, such as methylmercaptophos (metasystox) synthesised by G.Schrader, and M-81 (intrathion) obtained in the laboratory of Academician M.I.Kabachnik, are less toxic than methaphos but more toxic than trichlorfon. 

Trichlorfon has a low mammalian toxicity. Dichlorvos is more toxic, but the difference in toxicity between insects and vertebrates is very high. It evaporates easily and may be formulated in plastic strips that slowly release the insecticide, killing the insects, but it is apparently harmless to humans. The two compounds have also been widely used to kill salmon ectoparasites, as well as parasites encountered in veterinary medicine. However, they are strong teratogens in some species, disturbing brain development (Mehl et al., 2000), and should therefore be used with care. 

OP insecticide-induced intermediate syndrome (IMS) was reported for the first time in human patients in Sri Lanka in 1987 (Senanayake and Karalliede, 1987). Since then, this syndrome has been diagnosed in OP-poisoned patients in South Africa (1989), Turkey (1990), Belgium (1992), the United States (1992), Venezuela (1998), France (2000), and elsewhere. IMS is usually observed in individuals who have ingested a massive dose of an OP insecticide either accidentally or in a suicide attempt. IMS is clearly a separate clinical entity from acute toxicity and delayed neuropathy. A similar syndrome has also been observed in dogs and cats poisoned maliciously or accidentally with massive dosc.s of certain OPs. OPs that are known to cause IMS include bromophos, chlorpyrifos, diazinon, dicrotophos, dimethoatc, fenthion, malathion, merphos, methamidophos, methyl parathion, monocrotophos, omethoate, parathion, phosmet, and trichlorfon. These compounds and IMS are discussed further in Chapter 26. 

Of the 19 pesticides grouped in Table II, all were negative in five Phase I bioassays and the Phase 2 bioassays performed. These compounds included insecticides (I), fungicides (F), and herbicides (H). Malath ion, parathion, pentachloronitrobenzene (PCNB), and phorate were also negative for heritable chromosomal effects in the mouse dominant lethal test. The six compounds grouped in Table III that were positive in three or more bioassays were acephate, captan, demeton, folpet, monocrotophos, and trichlorfon. Positive results were seen for demeton in all in vitro tests in Phase 1 and Phase 2. Folpet and captan were positive in all Phase 1 and all Phase 2 in vitro assays except the test for unscheduled DNA synthesis in WI-38 cells. Trichlorfon was positive in all Phase 1 and Phase 2 in vitro tests, with the exclusion of relative toxicity tests with E coli and subtiI is. 

Diazinon and trichlorfon (Dylox 50% WP or Proxol 80 SP) are two insecticides frequently used by the commercial lawn industry because of their relatively low level of acute toxicity. Recommended rates for insect control may vary. Diazinon may be applied at 1 to 3 oz. active ingredient per 1,000 sq. ft. Trichlorfon is also used for control of insects at 2 to 3 oz. active ingredient per 1,000 sq. ft. Lawn insects controlled include chinch bugs, sod webworms, cut worms, army worms, and grubs. 

Another approach is to attempt to chemically modify the toxicants to yield nontoxic products which are returned to their active state by digestive or metabolic processes. The pesticide trichlotfon, which is toxic to fire ants, is not effective as an agent for control of the species due to its rapid action. Polymeric insecticides of the ester of trichlorfon with PAA have been prepared with hydrolytically unstable covalent linkages [225]. The preparation of polymeric esters of trichlorfon with spacer groups between the insecticide and the polymer backbone 2 have been prepared to eliminate the limited toxicity of the polymeric insecticide 1, which is a reflection of the limited loading and slow hydrolysis of the insecticide due to the steric hindrance of the polymer backbone (Scheme 3.18). 

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