Trichlorfon toxicity

Official Soviet science considered that OPPs did not remain in the soil for very long, and the products resulting from its decay were of low toxicity [21, 30]. In fact trichlotfon, for example, decays slowly in acid soils. It more actively dehydrochlorinates in alkaline media, but it then forms highly toxic dichloifos [33]. Parathion may remain in soil for up to 16 years [34]. Cases are known when phosalone and chlorpyrifos remain in soil for up to two years [3, 20]. Methyl parathion and trichlorfon were detected in the Kilmez region of the Kirov Oblast in an underground chemical repository 20 years later [3]. 

Brecken-Folse.l.A.. Mayer. F.L.. Pedigo. L.E.. and Marking. L.L. Acute toxicity of 4-nitrophenol. 2.4-dinitrophenol.terbufos and trichlorfon to grass shrimp (Palaemonetes spp.) and sheepshead minnows (Cyprinodon variegatosf as affected by salinity and temperature. Environ. ScL Technol, 13(l) 67-77.1994. 

Howe, G.E., Marking, L.L., Bills, T D., Rach, J.J., Mayer, Jr., F.L. (1994) Effects of water temperature and pH on toxicity of terbufos, trichlorfon, 4-nitrophenol and 2,4-dinitrophenol to the amphipod Gammarus pseudolimnaeus and rainbow trout (Oncorhyn-chus mykiss). Environ. Toxicol. Chem. 13, 51-66. 

Trichlorfon is widely used in agriculture to protect plants, in sanitation and veterinary medicine. More information about trichlorfon applications can be found in Part 6. Trichlorfon is toxic however, it is less toxic than DDT, hexachlorane, thiophos and other pesticides. 

Trichlorfon is mostly used to kill mangold fly larvae it is also very efficient against the dangerous rice weevil, which can destroy whole harvests. Trichlorfon is successfully used in viticulture (to kill grapevine moths) and pomiculture (to kill apple, pear and plum sawflies, apple ermine moths and gooseberry sawflies). Trichlorfon is very efficient in cot-ton-growing (to kill cotton worms). The low toxicity of trichlorfon for warm-blooded animals accounts for its use in veterinary medicine to combat parasites on large animals. 

This substance is less toxic for warm-blooded animals than trichlorfon and is meant for pest control in gardens and on farmlands. 

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. 

As mentioned earlier, atrazine induces various detoxification enzymes in insects. Table 9.18 shows that the induction by atrazine was associated with decreased toxicity of carbaryl, permethrin, and indoxacarb but increased toxicity of methyl parathion, phorate, and trichlorfon in fall armyworm larvae. The increased toxicity of methyl parathion and phorate was likely due to enhanced microsomal desulfuration and sulfoxidation, respectively, by atrazine (see the following text for explanation). 

Since 1917, only 11 new endoparasiticides have been developed for use in the horse. Many of the early compounds had very narrow spectra of activity and/or high potential for toxicity such that they have become obsolete. Febantel, levamisole, trichlorfon, dichlorvos, phenothiazine and carbon disulfide are no longer used routinely in the horse (Lyons et al 1999). 

Trichlorfon is moderately toxic for laboratory animals by ingestion or dermal absorption. The oral LD50 for trichlorfon in rats is 150-649 mg kg 300-1370 mg kg in mice, 97mgkg in cats, 400 mg kg in dogs, 420 mg kg in guinea pigs,... 

Trichlorfon is highly toxic to birds, as the oral LD50 is 37 mg kg in wild birds, 36.8 mg kg in mallards. 

Trichlorfon is also highly toxic to both cold and warm water fish, and its acute toxicity is between 1.67 and 180 ppm. The 24 h LC50 for striped bass is... 

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. 

Little is known about the long term effects of the biocides. The assortment of these compounds is changing fairly rapidly, with research trying to catch up. For example, Atlantic salmon were treated for sea lice infection by DDVP (di-chlorvos, 2,2-dichloroethenyl dimethyl phosphate), trichlorfon (dimethyl (2,2,2-trichloro-l-hydroxyethyl)phosphonate), hydrogen peroxide, ivermectin, azamethiphos (S-[(6-chloro-2-oxooxazolo[4,5-h]pyridin3(2H)-yl)methyl] 0,0-dimethyl phosphorothioate), and cypermethrin (cyano(3-phenoxyphenyl)me-thyl 3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylate). The last three compounds in particular are highly toxic to aquatic invertebrates in laboratory tests, but their fate and effects in field situations has not been studied in detail. 

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. 

Acephate and monocrotophos produced mutagenic effects in typhimurium> an increase in mitotic recombination in cerevisiae D3 and unscheduled DNA synthesis (UDS) in WI-38 cells. Acephate and monocrotophos produced no effects in E coli or subtiIis relative toxicity assays. The negative findings for acephate, monocrotophos, and trichlorfon in bacterial relative toxicity assays may mean that these pesticides did not diffuse into the agar. Both acephate and trichlorfon were tested for oncogenic transformation in C3HI0T1/2 CL8 cells only the latter was positive. 

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