Phorate insecticide toxicity

There is, however, one means of achieving the conflicting properties required for apoplastic transport without resort to compromise. This is by using precursors which have characteristics favouring uptake and are then converted within the plant to active toxicants which are more readily translocated. The principle is best illustrated by the long-established organophosphorus insecticides of the systox type such as demeton, disulfoton and phorate which are relatively lipophilic... 

These insecticides range from completely water-miscible compounds to essentially insoluble ones, as indicated in Table VI. Most highly water-soluble insecticides are systemic, that is, they are absorbed into the tissues of the growing crop, either through the leaves or through the roots. But some water-miscible compounds are so unstable that their toxicity is destroyed before systemic activity can be observed (12,18). Tepp, for example, has a half life in water of only 8 hours. While many other compounds in this class have only limited solubility in water, they are still effective systemics. Examples are demeton, methyl demeton, and phorate. 

Phorate is a contact and systemic insecticide. It belongs to the most toxic insecticides known its lDj for rats being 2 mg/kg. Phorate is distinguished by its volatility. Owing to this property, it also exerts its insecticidal action as fumigant. 

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. 

OPs in anti-lice shampoos has recently been qnestioned because of possible absorption through the head, particularly by children. Breakdown prodncts from some insecticides are known to be toxic as, for example, phorate (Table 12.30) which prodnces Et2S2, H2S and HCHO. 

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