Gas‐phase reaction of dichlorvos, carbaryl, chlordimeform, and 2,4‐D butyl ester with OH radicals

Abstract

Widespread use of pesticides has caused serious environmental concern. In order to evaluate the fate of organic pesticides in the atmosphere, rate constants for gas phase reactions of OH radicals with dichlorvos, carbaryl, chlordimeform, and 2,4-D butyl ester were measured using the relative rate method at ambient temperature and 101 kPa total pressure. On-line FTIR spectroscopy was used to monitor the concentrations of pesticides as a function of time. The reaction rate constants with OH radicals (in units of cm 3 molecule −1 s −1 ) have been determined as (2.0 ± 0.4) × 10 −11 for dichlorvos, (3.3 ± 0.5) × 10 −11 for carbaryl, (3.0 ± 0.7) × 10 −10 for chlordimeform, and (1.5 ± 0.2) × 10 −11 for 2,4-D butyl ester. These rate constants agree well with those estimated based on the structure-activity relationship. The group rate constant for N C group (k (N C) ) was estimated as 2.7 × 10 −10 cm 3 molecule −1 s −1 . Dimethyl phosphite has been tentatively identified as a product of the reaction of dichlorvos with OH radicals. Atmospheric lifetimes due to the reactions with OH radicals were also estimated (in units of h): 14 ± 3 for dichlorvos, 8 ± 1 for carbaryl, 1.0 ± 0.3 for chlordimeform, and 19 ± 3 for 2,4-D butyl ester. These short atmospheric lifetimes indicate that the four organic pesticides degrade rapidly in the atmosphere, and they themselves are unlikely to cause persistent pollution. Further studies are needed to identify the potential hazard of their degradation products. C 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: [755][756][757][758][759][760][761][762] 2005

Environmental Fate and Toxicology of Carbaryl

“…However, it was also noted that all detections decayed to relatively low concentrations within 2 hr after application (< 2 ug/m 3 ; Currier et al 1982) . Airborne carbaryl degrades after reaction with photochemically produced hydroxyl radicals in the atmosphere (Kao 1994) , with a reaction rate constant of 3.3 × 10 −11 cm 3 /sec (Sun et al 2005) . Low drift concentrations were reported in a California study, with concentrations of up to 1.12 µg/m 3 in the air after ground spraying to control the glassywinged sharpshooter, Homalodisca coagulate (Walters et al 2003) .…”

Theoretical study on the reaction mechanism of chlordimeform with OH radicals

“…4 along with the available experimental results [17]. The measured value in [17] is the consumption of reactant, so we discuss here only the first step reaction process, in which the consumption of the reactant chlordimeform occurred. Steps 1c-8c are the follow-up reaction, i.e., not included in the consumption of the reactant, so are not discussed in detail, and the rate constants of 1c-8c…”

“…The ICVT/SCT rate constants of the major channels are plotted against the reciprocal of temperature in Fig. 4 along with the available experimental results [17]. The measured value in [17] is the consumption of reactant, so we discuss here only the first step reaction process, in which the consumption of the reactant chlordimeform occurred.…”

“…In 2005, the total rate constant for the gas-phase reaction of the volatile chlordimeform with the hydroxyl was measured, giving a value of (3.0±0.7)×10 −10 cm 3 molecule −1 s −1 at 296 K using a relative rate method [17]. No experimental information about the branching ratios is available for these reactions.…”

“…Chlordimeform has been listed in Priority Pollutants prescribed by China. The degradation mechanisms of chlordimeform have attracted research interest [17][18][19][20][21]. The chemical conversions of chlordimeform in the atmosphere are mainly the reactions with oxidants (such as hydroxyl, O 3 , and NO 3 ) and photolysis.…”