Richard W. Meikle

The hydrolysis rate of chlorpyrifos,O-O-diethylO-(3,5,6-trichloro-2-pyridyl) phosphorothioate, and its dimethyl analog, chlorpyrifos-methyl, in dilute aqueous solution

The hydrolysis rate of chlorpyrifos (the active ingredient of DURSBAN® and LORSBAN® insecticides, registered trademarks of The Dow Chemical Company, Midland, Michigan) in water followed simple first-order kinetics over the concentration range, 3×10−9 to 3×10−7M. In buffered distilled water at 25°C and pH 8.1, 6.9, and 4.7, the half-life was 22.8, 35.3, and 62.7 days, respectively. Additional data were obtained for rates at 15° and 35°C. The activation energy for the reaction under these conditions was 21.2 kcal/mole. A 16-fold rate enhancement was demonstrated in canal and pond water at 25°C. Likewise, there was a catalytic effect on the hydrolysis rate in the presence of copper (II) ion.The same information was generated for chlorpyrifos-methyl, the dimethyl analog of chlorpyrifos. In this case, the corresponding half-life values for hydrolysis at 25°C and pH 7.8, 6.7, and 4.2 were 12.7, 17.4, and 22.8 days, respectively. The activation energy was 20.8 kcal/mole, not significantly different from that for chlorpyrifos. A hydrolysis rate enhancement also occurred for chlorpyrifos-methyl in canal water.Qualitatively, the products of chlorpyrifos hydrolysis were 3,5,6-trichloro-2-pyridinol (I),O-ethylO-hydrogenO-(3,5,6-trichloro-2-pyridyl) phosphorothioate (II), andO, O-dihydrogenO-(3,5,6-trichloro-2-pyridyl) phosphorothioate (III). In the case of chlorpyrifos-methyl, the hydrolysis products were compound I and the methyl analog of compound II.

Principles of Pesticide Degradation in Soil

History will record that eventually there was a relatively simple accommodation to the extraordinarily complex problem of defining and using principles of degradation to predict this aspect of the behavior of pesticides in soil. So it is with many scientific endeavors.

Chlorpyrifos: The Photodecomposition Rates in Dilute Aqueous Solution and on a Surface, and the Volatilization Rate from a Surface

The combined photolysis-hydrolysis rate of chlorpyrifos in water at 25†C followed simple first-order kinetics at 9 × 10−7M concentration. In buffered, distilled water at pH 5.0, 6.9, and 8.0, the half-life was 11.0, 12.2, and 7.8 days, respectively. The half-life of the isolated photolysis reaction was 13.9, 21.7 and 13.1 days, respectively. Qualitatively, the products of the combined photolysis-hydrolysis reactions with chlorpyrifos wereO-ethylO-(3,5,6-trichloro-2-pyridyl)-phosphorothioate, 3,5,6-trichloro-2-pyridinol, and five radioactive unknowns, one of which was thought to contain H14CO3−.Loss rates of chlorpyrifos due to photodecomposition on and volatilization from an inert surface at 25†C were best represented by first-order processes. The half-life for disappearance of chlorpyrifos was 3.2 and 0.3 days, respectively. The results reported herein suggest that on those occasions when chlorpyrifos shows reduced efficacy in the field, volatility loss may be the primary cause.The rates of photolysis and hydrolysis reactions are sufficiently fast that the compound will not persist in bodies of water, nor will the compound present any problems relative to field reentry safety intervals.

The inhibition of several enzyme systems by 2,2-dichloropropionate

Abstract The effect of 2,2-dichloropropionate on three enzyme systems involving pyruvic acid as a substrate has been studied. Pyruvate oxidase from Streptococcus faecalis is inhibited in a complex manner somewhat resembling uncompetitive inhibition. Yeast carboxylase and pyruvate oxidase from Proteus vulgaris X-19 both appear to be competitively as well as uncompetitively inhibited.

The Hydrolysis and Photolysis Rates of Nitrapyrin in Dilute Aqueous Solution

The hydrolysis rate of nitrapyrin (2-chloro-6-(trichloromethyl)pyridine), the active ingredient of N-SERVE® nitrogen stabilizer (a registered trademark of The Dow Chemical Company, Midland, Michigan), in buffered, distilled water followed simple first-order kinetics over the concentration range, 6.2×10−7 to 8.7×10−5M. The only product of the reaction was 6-chloropicolinic acid. The rate of the reaction decreased with increasing buffer concentration at 35°C (M buffer concentration-half-life): 0.005M − 1.7 days, 0.02M−2.0 days, 0.067M−4.0 days. The ramifications of this negative salt effect are discussed. The hydrolysis rate was independent of pH over the range, 3.2 to 8.4. Additional data were obtained for rates at 25° and 45°C. The activation energy for the reaction under these conditions was 25.0 kcal/mole.Photolysis of nitrapyrin at 25°C in 0.005M phosphate buffers at pH 5.1, 7.1, 8.0, and in a natural water also followed simple first-order kinetics over the nitrapyrin concentration range, 7.1×10−6 to 7.5×10−6M. Again, there was no observable pH effect on the rate over the pH range investigated, nor was there a rate enhancement in the natural water. The half-life of the reaction under these conditions was 0.5 day. The products of this reaction were 6-chloropicolinic acid (6-C1PA), 6-hydroxypicolinic acid (6-OHPA), and unidentified polar material formed in that order in a series of sequential reactions. Simulation of the set of sequential reactions using determined first-order rate constants at 25°C and a starting concentration of 1.7 ppm predicts that nitrapyrin will be half gone in 0.5 day, that the concentration of 6-ClPA will peak at 1.3 ppm in 1.8 days, and that the concentration of 6-OHPA will peak at 0.2 ppm in 3.7 days.

Automatic Calculation of Color Differences

Punched-card operated computing machines have been used to translate from C.I.E. space to the equal visual stimulus space of Adams. Differences in terms of Judd units are calculated by the machines as are the original colorimetric integrations. These methods have been used to process several thousand routine reductions of spectrophotometric data and their conversion to Adams space.

A mathematical method for estimation of soil temperatures in England and Scotland

Abstract A mathematical expression (fourth-degree polynomial) is derived to calculate the maximum and minimum soil temperatures at a 10-cm depth for any day of the year at 18 locations in England and Scotland. Coefficients for the equations are tabulated.

Measurement and prediction of the disappearance rates from soil of 6-chloropicolinic acid

Abstract6-Chloropicolinic acid is the sole detectable metabolite, other than carbon dioxide, arising from decomposition of 2-chloro-6-(trichloromethyl) pyridine in soil. The pyridine compound is a potent inhibitor of nitrification now in use with ammonium fertilizers. The purpose of this study was to evaluate the relative influence of various soil and climatic factors on rates of degradation of 6-chloropicolinic acid in soil.Experiments with a wide range of soil types (23 soils) demonstrate that the most important factor influencing the decomposition rate of 6-chloropicolinic acid is soil temperature. When temperature is not a variable, the quantity of organic matter (0.9 to 6.9% by weight) and pH (4.8 to 8.1) significantly affect the rate of decomposition, but sand, silt, and clay percentages do not. Moisture content was without apparent effect because the range of values investigated was too narrow.A fractional-order rate law (0.7) describes the disappearance rate best.Application of the Arrhenius equation to the data for the decomposition of 6-chloropicolinic acid in soil indicates an activation energy of 6.57 kcal per mole, suggesting that the chemical is biologically rather than chemically degraded.It was not possible to develop a suitably precise equation for prediction of loss rate as affected by the above soil and climatic factors because undefined biological factors in the soils override the effect of measurable properties of soil and climate.