Parathion safe levels

This paper establishes toxicologically-safe levels for total residues of parathion, azinphosmethyl, methidathion and their oxons on tree foliage and reports these levels in terms of absorbance units as determined by the rapid field method. Safe levels for a new insecticide, chlorthiophos, are also proposed based on preliminary residue data. Chemical structures of the four insecticides mentioned above are shown in figures 1, 2, 3 and 6. 

Figures 1A, 2A and 3A give representative dissipation curves for parathion, azinphosmethyl and methidathion on orange trees in California (6). Parathion dissipates with the formation of considerable amounts of paraoxon. Low volume application (100 gal/acre) of these insecticides results in high levels of OP residues and thus longer dissipation times to safe levels. Azinphosmethyl does not dissipate as rapidly as parathion under field conditions. Azinphosmethyl oxon is formed during the process and dissipates slowly with time. Azinphosmethyl oxon levels were determined only for azinphosmethyl at 6.0 lb AI per 100 gal/acre. Methidathion dissipates on citrus also with the formation of its oxon.

Safe Levels for Parathion, Azinphosmethyl, Methidathion and Their Oxons on Tree Foliage... 

Table I was constructed according to the procedure of Knaak et al. (3) using the dermal dose-ChE response curves in Figures 4 and 5. Paraoxon was used as the pesticide standard for methidathion and chlorthiophos, while azinphosmethyl oxon was used as a standard for chlorthiophos oxon sulfoxide and methidathion oxon. The groupings are based upon similar slope values for the dose-response curves. Parathion and azinphosmethyl acted as their own standard. A standard is a pesticide for which safety information is available. In this Table, safe levels are given for the thions and their respective oxons. The safe level for total residues (thion + oxon) lies between the safe levels for the thion and its oxon if the oxon level is at or below its safe level.

The procedure involves converting oxon to thion toxicity equivalents by multiplying the oxon value by its relative toxicity (ED of thion r ED,.q of oxon) in Table I. The ED. value is the aermal dose in ug/cnr of total body surface which produces 50% inhibition of red cell ChE activity 72 hours after application. The total thion and oxon level is then divided by the thion toxicity equivalents and the factor is multiplied by the safe level established for thion in Table I. This procedure was conducted for the dislodgeable residues of parathion-paraoxon, methidathion-methidathion oxon, and azinphosmethyl-azinphosmethyl oxon. The safe levels for the total disloggeable residues were determined to be 0.06, 0.2 and 1.6 ug/cm, respectively, for... 

The safe levels established for parathion + paraoxon, azinphosmethyl + azinphosmethyl oxon and methidathion + methi-dation oxon on foliage have absorbance values determined by the rapid field method (4 ) equal to those given in Table III. Absorbance values greater than those listed in Table III signal an unsafe working condition. Field testing can also be conducted by standard gas chromatographic analysis of the leaf disk samples by state-approved laboratories. 

The California Department of Food and Agriculture recently established toxicologically safe levels for total residues of parathion to,0-diethyl 0-(4-nitrophenyl) phosphorothioate], ... 

Figure 5 shows the degradation of diazinon in soil at 2000 ppm by parathion hydrolase. It is easy to see that degradation is very rapid and effective - reaching safe environmental levels by 24 hours. 

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