Abstract. The hydrolysis rate of chlorpyrffos (the active ingredient of DURS-BAN @ and LORSBAN | insecticides, registered trademarks of The Dow Chemical Company, Midland, Michigan) in water followed simple first-order kinetics over the concentration range, 3 x 10 -9 to 3 x 10-ZM. In buffered distilled water at 25~ and pH 8. I, 6.9, and 4.7, the haft-life was 22.8, 35.3, and 62.7 days, respectively. Additional data were obtained for rates at 15 ~ and 35~ 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~ Likewise, there was a catalytic effect on the hydrolysis rate in the presence of copper (II) ion.The same information was generated for chlorpyrffos-methyl, the dimethyl analog of chlorpyrifos. In this case, the corresponding "half-life values for hydrolysis at 25~ 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 chlorpyrffos. 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-ethyl O-hydrogen O-(3,5,6-trichloro-2-pyridyl) phosphorothioate (II), and O, O-dihydrogen O-(3,5,6-trichloro-2-pyridyl) phosphorothioate (III). In the case of chlorpyritbs-methyl, the hydrolysis products were compound I and the methyl analog of compound II.Because of the need to evaluate the fate of pesticides in the environment to which they may be applied, a study was carried out to determine the fate of chlorpyrifos in water. The efficacy of this compound has been well demonstrated (Collier and Dieter 1965, Gray 1965, Kenaga et al. 1965. The dimethyl analog, chlorpyrifosmethyl, was included in this study. The investigation reported herein defines the hydrolysis rates at different pH and temperature values, gives the observed activation energy for the reaction, and describes the hydrolysis products.

No abstract

We have shown by means of laboratory experiments with a wide range of soil types that the decomposition rate of picloram (4-amino-3,5,6-trichloropicolinic acid) in soil is dependent on soil temperature and moisture content and to no significant extent on organic matter, sand, silt, clay, pH, or initial concentration. A fractional order rate law (0.8) describes the disappearance rate best. It was not possible to develop a suitably precise equation for prediction of loss rate as affected by the above soil and climatic factors. Application of the Arrhenius equation to the data indicates an activation energy of 5.4 kcal/mol for the decomposition of picloram in soil, thus suggesting that the reaction is biological rather than chemical.

4-Aniino-3,5,6-trichloropicolinic acid was incubated at 70° F in thirteen different soils for periods of up to 2 years at a concentration range of 0-023-24 ppm. Losses varied from complete to non-mrasurable by the bioassay technique employed. The percentage decomposed was generally greater for lower initial concentrations. The results were mathematically analysed in terms of zero-order, half-order, first-order and Michaclis-Menten kinetics. Half-order and Mirhaelis-Menten were found to hv the kinetic expressions that most satisfactorily described the detoxification of the herbicide in soil. Taitx de deloxijication de l'acide 4~amino-3,5,(i-trichloropicolinique dans le solResume. L'acide 4-amino-3,5,B-trichloropifoUnique m61ang^ a 13 sortes de lerres k des concentrations comprises entre 0,023 et 24 ppm a H6 souniis k un s(tjour en ^tuve a 21" C pendant des p^riodes allant jusqu'a 2 ann^es. Los pertcs varierent de la totality a des quantity non mesurables scion la ni^thode d'essai biologique utilise. Le pourceiitage d<^compos^ fut giniralement plus grand pour les concentrations initiale^s Irs plus faibles. Une analyse niatlidmalique a portd sur la coneordance des r^sultats avee des reactions d'ordre z^ro, d'ordre un demi, dc premier ordre, et avec la rin^tique de Michaelis-Menten, 11 a Hi constati que les reactions d'ordre un demi et de Michael is-Mcnlcn t^taient les expressions eint^tiques les plus satisfaisantes pour repr^sentcr la detoxification de l'herbicide dans le sol. Verlauf der Inaktivierung von 4-Amino-3,%6'lrichlorpii:olinsdure im BodenZusammenfassung. 0,023-24 ppm 4-Aniino-3,5,G-trichlorpicolinsaure wurden 13 versthiedenen Boden zugcsetzt und bis zu 2 Jahrc bei 70° F beobachtet. In dieser Zeit wurde das Hrrbizid ciitwcdcr vollkommen abgebaut oder war zumindest mit dem verwendeten Biolcsl nicht mehr nachweisbar. Der prozentualc Abbau war normalerweise bei geringeren Ausgangskonzentrationen am hochsten. Es crfolgtc cine niathematischc Prtilung, ob es sieh um AblSufe folgcnder Ordnungen bandel; 0, 4 (gebrochene), I und Michaelis*Menten. Dabci wurde gefunden, dass der Abbau des Herbizids im Boden am ehesten eincr gebrochcncn und der Michaclis-Mcntcn-Reaktion entspricht.

The 6-hydroxy derivative of picloram (4-amino-3,5,6-trichloropicolinic acid) is not on the main pathway of the soil microbial decomposition sequence for picloram. Rather it may be formed in very small amounts in a competing reaction. Decarboxylation of picloram cannot be the initial reaction in this sequence and, in fact, does not occur.