Parathion curves

The final optically clear solution is evaluated as to intensity of color at 555 m/x, and with slit width at 0.02 to 0.04 mm., on a Beckman spectrophotometer adjusted to 100% transmittance with an untreated sample freshly processed in parallel with the unknown sample. From a standard calibration curve (see Figure 3), the concentration of parathion may readily be ascertained, and an appropriate factor converts this value to micrograms of parathion present in the original field sample. 

Typical standard curves for a technical grade of parathion are shown in Figure 3. Beer s law is followed within the range 10 to 400 micrograms of parathion per milliliter of dyed solution. Deviation becomes apparent outside this range, under the conditions of test. 

These curves also demonstrate the incidental 50% loss of parathion after the additional 4 days in the field for the second sample. 

Figure 9. Transmittance-Wave-Length Curves for Dyed Parathion in 20% Ethyl Alcohol...

Tautomerism of the Dye. The complete visible absorption spectra were secured for dyed parathion at several pH values in both 20 and 60% ethyl alcohol. These curves are plotted in Figures 9 and 10. The appearance of an isobestic point in both instances indicates that tautomeric forms of the dye are involved (8). 

Figure 2. Transmission-Wave-Length Curves for Dyed Benzene Extractives from Peel of Parathion-Treated Navel Oranges...

With the duplicate parathion-treated samples and one untreated sample, the benzene extracts were processed in the usual manner and subjected to the dyeing procedure. Their transmission-wave-length curves are shown in Figure 2 with a companion curve for dyed parathion. 

With reference to the curve for dyed parathion, shifts toward longer wave lengths in all maxima and minima are apparent with the greatest displacement in the region 400 to 440 m/z. 

The intensities of absorption change proportions between sample and reference curves. The fact that the transmission-wave-length curve of dyed parathion is composite precludes the possibility of interpreting these observations at the present time. 

The 0,0-diethyl O-p-nitrophenyl thiophosphate used in the preparation of the standard curves was obtained by isolation from a high-purity technical parathion according to the method devised by Edwards and Hall (2). It was a crystalline material that melted sharply at 6° C. The physical constants were in agreement with those published by Fletcher et al. (4)-... 

Figure 1. Standard Curves for Parathion Determination Sensitivity, microampere per millimeter, A, 0.020 fi, 0.030 C, 0.040...

Fig. 12.8 Distributions of parathion in (A) biologically-inert (sterile) Gilat soil (20% moisture content, 1.4 g cm bulk density) after 3.03 days, and (B) biologically-active Gilat soil (34% soil moisture content, 1.4 g cm bulk density) after 2, 4 and 7 days. The solid curves were calculated using D= 1.67x 10 cm s the points represent experimental measurements (Gerstl et al. 1979a)...

Fig. 16.36 Change in bacteria populations in remoistened Gilat soil after application of 10-160 pg parathion per g dry soil. Plotted points are means of three replicates standard error. Continuous curves represent model simulations. Values obtained in control soils to which hexane alone was added have been subtracted. Reprinted from Nelson LM, Yaron B, Nye PH (1982) Biologically-induced hydrolysis of parathion in soil. Soil Biol Biochem 14 223-227. Copyright 1982 with permission of Elsevier...

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.

Figures IB, 2B and 3B, drawn using the data from Figures 1A, 2A and 3A, give the dissipation curves for the total residues (thion + oxon) of parathion, azinphosmethyl and methidathion. These dissipation curves are similar to the curves obtained when OP residues are determined by the rapid field method as shown by the extensive studies conducted by Gunther et al. (5) which compare gas chromatographic values for thion + oxon with RFM values for total OP residues.

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.

Figure IB. Dissipation of parathion (closed symbols) and paraoxon (open symbols) on orange trees by total OP method. Curves are drawn from Figure 1A. Key see Figure I A.

Figure 6.4. Sorption rate curves of (a) carbaryl and (b) parathion on Ca-saturated soil humic material as a function of (time)1/2. [From Leenheer and Ahlrichs (1971), with permission.]...

To illustrate this distribution, Figure 1 shows the result of an actual aerial application of a typical pesticide spray to a broadleafed tree species (3). The "application level" (A) simply assumes that all the spray leaving the aircraft becomes uniformly distributed over the target area (1.12 kg/ha), and the curve shows the parathion levels analytically detected on a statistical sampling of leaves. A major part of the applied pesticide (B) fails to reach the canopy, as corroborated by Barry (2) with conifers, and is assumed to represent airborne drift, volatilization, and, to a lesser extent, penetration to the ground. Once on the... 

Figure 1 shows the isothermal separation of parathion and paraoxon. The insecticide concentration was calculated in each sample in the hydrolysis series from standard curve of peak area vs. concentration. Each experiment was repeated three times. 

Figure 4.1. General classes of adsorption isotherms. 5 turve, data courtesy of C. S. LeVesque L curve, data from I.C.R. Holford et al. H curve, data from J. Garda-Mirayagaya and A. L. Page, Sorption of trace quantities of cadmium by soils with different chemical and mineralogical composition Water, Air, and Soil Pollution 9 289 (1978) C curve, data from B. Yaron and S. Saltzntan, Influence of water and temperature on adsorption of parathion by soils Soil Sci. Soc. Am, J, 36 583 (1972).

The C-curve isotherm is characterized by an initial slope that remains independent of the concentration of a substance in the soil solution until the maximum possible adsorption. This kind of isotherm can be produced either by a constant partitioning of a substance between the interfacial region and an external solution or by a proportional increase in the amount of adsorbing surface as the surface excess of an absorbate increases. The example of parathion (diethyl p-nitrophenyl monothiophosphate) adsorption in Fig. 4.1 shows constant partitioning of this compound between hexane and the layers of water on a soil at 50 per cent relative humidity. The adsorption of amino acids by Ca-montmorillonite also exhibits a... 

Dermal Dose-Response Studies. The dermal dose red cell ChE-response curves for parathion and thiodicarb are given in Figure 2. Para-thion, the most toxic pesticide used, inhibited 50Z of the red cell ChE activity at a dose level ot 31 t%/cm (3.2 mg/kg) of treated skin in 72 hr, tdiile 322 ug/cm of thiodicarb (33.3 mg/kg) gave 50 ChE inhibition in 24 hr. Carbaryl at dose levels up to 4,000 ng/cn of treated skin (417 sig/kg) did not produce detectable ChE inhibition 24 hr after application of the dose. Thiodicarb was dermally more toxic than carbaryl, but substantially less toxic (1/10) than parathion. 2... 

Figure 2. Dermal dose-ChE response curves for thiodicarb (top) and parathion (bottom). Male Sprague-Dawley rats weighing 220-240 g were used. A 25 cm area of skin was treated.

Simultaneous Absorption and Elimination in Plasma. The ty e-concen-tration curves for the absorption and elimination of [ C]labeled parathion, carbaryl, and thiodicarb equivalents in plasma of adult rats are giv in Figure 8 and the pharmacokinetic constants in Table III. The [ C]equivalents were found in blood shortly after the application of the dose and reached maximum concentrations in plasma in 2.5 to 12 hr. Carbaryl and paraty on [ C]equivalents were eliminated during the study, while [ C]thiodicarb equivalents... 

Knaak et al. ( ) detected parathion equivalents in low concentrations in blood soon after topical application. The parathion equivalents reached a maximum concentration within 12 hr as shown by the blood plasma absorption-elimination curve. These blood levels most likely occur in workers exposed to foliar residues of parathion and are responsible for illnesses reported in workers several hr... 

Thiodicarb was initially lost from skin at a rate similar to that of parathion and carbaryl. After 24 hr, the rate of loss decreased by a factor of 1/6. The initial loss of thiodicarb appears to be due to a combination of events which may include evaporative or other losses, the initial penetration of the dose into skin and rapid distribution to blood and other tissues. Absorption was slow after 24 hr as indicated by the t 1/2 for skin loss of 254 hr. Parathion and carbaryl, on the other hand, penetrated the skin and were absorbed at a more uniform rate after 24 hr according to the skin loss data. The plasma absorption-elimination curve for thiodicarb plateaued after 24 hr. The dose remaining on the surface of the skin acted as an infinite dose supplying the rat with a low but uniform amount of thiodicarb. 

Organophosphate pesticides studied in this work were the model low-toxic OPC trichlorfon, and some common organophosphate pesticides malathion, parathion, dichlorvos, and diazinon (Table I). Calibration curves for these pesticides (dependences of the sensor inhibition response on the analyte concentration) were obtained for all of these OPCs. These calibration curves were obtained under conditions (time of inhibition, pH and temperature) optimize with the model analyte trichlorfon. All of the pesticide calibration curves are similar and Fig. 4 illustrate the method by the example of malathion. The lowest concentration of pesticide samples assayed with 10 min. of incubation of the electrode in inhibitor containing solution was 5 ppb. This resulted in approximately 10 % of the relative inhibition signal. Fig. 4 predicts much better performance of our system compared with the literature data. For example, trichlorfon detection by means of ISFET had a reported limit of detection of ca 250 ppb (5), while conductometric sensor assay registered trichlorfon at ca. 25 ppb (5), still an order of magnitude higher than the described sensor. An amperometric sensor was used to detect dichlorvos with a limit of detection of 350 ppb (2J) and a potentiometric (pH-sensitive) sensor was shown to detect parathion at 39 ppm and diazinon at 35 ppb (9). 

A mixture of equimolar concentrations of chlorpyrifos, diazinon, dichlorvos, malathion and parathion (which sum to the plotted concentrations) was analyzed by this assay using the bromine oxidation protocol. Shown in Figure 7 are the inhibition profiles for paraoxon and the previously described mixture. Over a limited concentration range (i.e., 0.1 nM and above), the inhibition profile of the mixture is similar in shape to the paraoxon curve with paraoxon showing greater inhibition than the mixture. At concentrations below 0.1 nM, the curve deviates from its typical shape and the mixture appears to inhibit to a greater extent than paraoxon. This feature in the inhibition profile (i.e., the plateau in the activity at about 80% of maximum at low compound concentrations) was also observed with chlorpyrifos-oxon (see Figure 5). 

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