Organophosphorus Fungicides

Organophosphorus Fungicides. This group comprises pyrazophos (Figure 4.31) and the phosphonic acid amides, triamiphos and ditalimfos (superseded compounds). 

Hudson, H.R., and Pianka, M., An approach to thc development of organophosphorus fungicides, Phosphorus, Sulfur Silicon Relat. Elem., 109, 345, 1996. 

T. Noguer, B. Leca, G. Jeanty, and J.L. Marty, Biosensors based on enzyme inhibition detection of organophosphorus and carbamate insecticides and dithiocarbamate fungicides. Field Anal. Chem. Tech. 3, 171-178 (1999). 

A snpercritical flnid extraction (SEE) method for the determination in strawberries of a number of commonly used organochlorine insecticides, organophosphorus pesticides, and dichloroaniUde fungicides (Pearce et al., 1997). 

Other effective substances for control of house dust mites seem to be fungicides because fungal digestion of skin scales is a prerequisite for mite utilization [237]. Finally, an alternative to organophosphorus pesticide treatment in stored grain has been found in the use of inert substances,... 

A number of organophosphorus esters are fungicidal, but structurally they have little in common. Triamiphos (65) (B-77MI10707), an early systemic fungicide, incorporates the bis(dimethylamino)phosphoryl moiety, but the activity of pyrazophos (66) (B-77MI1708) is almost certainly due to the pyrazolo[l,5-a]pyrimidin-2-one parent. Ditalimfos (67) (65BEP661891) is a foliar fungicide of very low mammalian toxicity. 

Pesticides and Fungicides. Modern pure food regulations require that the food processor be responsible for their finished products. Since so many pesticides and fungicides are used in agriculture, their detection and quantitative analysis are difficult (5, 22). Organophosphorus and chlorinated hydrocarbons are the most common pesticides. When GLC is used for halogens, electron capture or microcoulometric detectors are used for phosphorus, a thermionic flame photometric detector is required. 

Organophosphorus pesticides (OPPs) have been used extensively as insecticides, fungicides, herbicides, and animal pesticides for more than four decades. They have been used instead of organochlorine pesticides because their relatively rapid decomposition makes them less persistent in the environment and because their accumulation in the biological food chain is limited. Basic to the proper assessment of the potential health hazards of OPPs is the knowledge of their fate in biological systems and in the environment (12,13). 

Of the 750 million pounds of pesticides used in 1964, insecticides accounted for nearly half, with herbicides and fungicides comprising most of the balance (23). The markets for fungicides and chlorinated hydrocarbon insecticides have apparently reached a peak while the markets for organophosphorus insecticides and herbicides are increasing. It is predicted that the domestic use of herbicides will far surpass that of insecticides within a few years. 

The carbamates, like the organophosphorus insecticides, are cholinesterase inhibitors. However, the reaction is rapidly reversible. Carbaryl has a half life in the soil of about 8 days and is decomposed by ultraviolet light. The carbamates metabolize rapidly in animals and show little, if any, propensity for storage in animal tissues. Additional properties and reactions of carbamates are discussed in the section on fungicides. 

Table IX shows the dietary levels of some of the organophosphorus insecticides that cause no effect on continued ingestion. These compounds, in general, show no-effect levels of the same order of magnitude as the chlorinated hydrocarbons. Similar data for some of the fungicides (Table X) indicate that the fungicides per se generally have a low order of toxicity. Similar toxicity data are shown in Table XI for a number of the herbicides.

It was not until the late 1960s that effective systemic fungicides appeared on the market, and their development represents an important breakthrough in the field of plant chemotherapy. The major classes of systemic fungicides developed since 1966 are oxathiins, benzimidazoles, thiophanates, and pyrimidines. Other effective systemic fungicides used currently include antibiotics, morpholines, organophosphorus compounds, and most recently, the sterol biosynthesis inhibitors, e.g., triazoles. 

Carbamate anticholinesterases these are reversible in as much as their duration of action is short as compared to organophosphorus anticholinesterases, and are used extensively. An example is carbaryl (carbaril) and several analogues of carbaryl are used as insecticides. However, not all carbamates found in garden formulations are cholinesterase inhibitors the dithiocarbamates are fungicidal. 

Organophosphorus pesticides are another example of nonionic, moderately polar compounds (Fig. 7.13). These pesticides are commonly used today and include compounds such as methyl parathion, parathion, diazinon, and dimethoate. They are used as insecticides on crops such as cotton, as fungicides on fruits, and as nematocides on soil. They are moderately polar... 

Table 10.4 Typical ADI Values and Other Toxicity Data of Three Organophosphorus Insecticides, Two Insecticides Acting on the Sodium Channels, a Fungicide, and an Herbicide...

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