Organophosphorus absorption

Oral absorption and bioavailability, prediction of, 41 (2003) 1 Organophosphorus pesticides, pharmacology of, 8 (1971) 1 Oxopyranoazines and oxopyranoazoles,... 

In two cases of moderate intoxication from mevinphos, urinary excretion of dimethylphos-phate (a metabolite of mevinphos) was almost complete 50 hours after exposure/ Although a number of other organophosphorus pesticides also yield dimethyl phosphate, the presence of significant amounts of this metabolite in the urine may be useful in estimating the absorption of mevinphos. 

Absorption. Absorption of foreign compounds from various sites is dependent on the physiological and physical conditions at these sites. These, of course, may be subject to species variations. Absorption of compounds through the skin shows considerable species variation. Table 5.2 gives an example of this and shows the species differences in toxicity of an organophosphorus compound absorbed percutaneously. Human skin is generally less permeable to chemicals than that of rabbits, mice, and rats, although there is variation. For some compounds, rat skin has similar permeability to human skin and seems to be less permeable than that of the rabbit. 

A number of instrumental analytical techniques can be used to measure the total phosphorus content of organophosphorus compounds, regardless of the chemical bonding of phosphorus within the molecules, as opposed to the determination of phosphate in mineralized samples. If the substances are soluble, there is no need for their destruction and for the conversion of phosphorus into phosphate, a considerable advantage over chemical procedures. The most important methods are flame photometry and inductively coupled plasma atomic emission spectrometry the previously described atomic absorption spectrometry is sometimes useful. 

L.C. Thomas and R.A. Chittenden, Characteristic infra-red absorption frequencies of organophosphorus compounds-II. P-O-(X) bonds, Spectrochim. Acta, 20, 489-502 (1964). 

Since PM-IRRAS is insensitive to the strong IR absorption of water vapor, it has proved to be an efficient way to study the conformation and orientation of protein molecules because only important bands arising from the monolayer are observed [72,97-103], The first in situ study of the protein conformation by PM-IRRAS technique was reported by Dziri et al. [97]. The vibrational spectrum of acetylcholinesterase (AChE) at the air-water interface in its free form and bound to either its substrate or organophosphorus (OP) inhibitor was measured. PM-IRRAS spectra collected during compression of the AChE... 

Infrared spectroscopy can also be of diagnostic use for the identification of organophosphorus compounds and comprehensive data is available from several sources.18 Diagnostic absorptions include the P—H stretch, which typically occurs in the region 2460-2450 cm-1, the P=0 stretch at 1320-1200 cm-1 and the P=N at 1440-1120 cm-1. Other useful absorptions include the P—O—(C) stretch at 870-730 cm-1 and the P—O—P stretch at 800-650 cm-1 found in phosphate esters. 

The other factor in Beer s Law aflFecting sensitivity is the absorptivity of the sample. The analyst, of course, has no control over this factor, but he certainly should be aware of it. He should know that a larger sample of the low-absorptivity cyclodiene pesticides, for example, will be required to achieve a satisfactory spectrum than for the more strongly-absorbing organophosphorus pesticides. 

Boutsiouki, P., Thompson, J.P., and Clough, G.F., Effects of local Wood Uow on the percutaneous absorption of the organophosphorus compound malathion a microdialysis study in man. Arch. Toxicol., 75, 321-328, 2001. 

Certain organophosphorus compounds are used, infrequently, in the treatment of glaucoma, where they are administered as eyedrops to reduce intraocular pressure. There may be a markedly depressed level of serum cholinesterase activity in such patients, demonstrating significant systemic absorption of the compound. 

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