Kinetics and mechanism of dimethoate chlorination during drinking water treatment

Abstract

h i g h l i g h t sThe reaction of DMT with chlorine was of first-order in each reactant. The observed rate constant of DMT degradation was strongly pH dependent. Both bromide and humic acid promoted but ammonium inhibited the degradation of DMT. Three organic byproducts were detected in DMT degradation by chlorine. The toxicity of DMT solution obviously increased after chlorination. a r t i c l e i n f o a b s t r a c t Dimethoate (DMT), a commonly used organophosphorus pesticide, is of great concern because of its toxicity and potentially harmful effects on water sources. The elimination of DMT as well as the toxicity and persistence of the byproducts formed during DMT degradation is most important for the safety of drinking water. This study first determined the reaction kinetics of DMT with free chlorine (FC) under typical water treatment conditions. The reaction between DMT and FC proceeded rapidly, exhibiting first-order with respect to each reactant. The degradation of DMT by FC was highly pH dependent, and the pseudofirst-order rate constant decreased obviously from 0.13 to 0.02 s À1 with an increase in pH from 7.0 to 8.3. Bromide ion accelerated the reaction by acting as a catalyst, and the accelerated reaction rate was linearly proportional to the bromide concentration. As a ubiquitous component in natural waters, humic acid also increased the reaction rate. However, the presence of ammonium inhibited the degradation of DMT due to its rapid converting FC to chloramines. Omethoate (OMT) was identified as an important byproduct of DMT chlorination, but only accounted for ca. 28% of the DMT degraded; and other two organic byproducts were also identified. The acute toxicity of DMT solution increased after treatment with FC due to the formation of more toxic byproducts (e.g. OMT).

Greenhouse and field‐based studies on the distribution of dimethoate in cotton and its effect on Tetranychus urticae by drip irrigation

“…Some organophosphorus and carbamate insecticides are more easily hydrolyzed under alkaline conditions. Tian reported that the degradation rate of dimethoate by free chlorine was highly pH dependent, and methiocarb degradation pathways also exhibit a strong pH dependence . According to our results, soil pH could have a substantial impact on the control efficacy of dimethoate on mites, and soil pH values of 6.70 or 5.70 with a low amount of 1.50 kg ha –1 dimethoate caused mite mortalities >60% 7 days after the treatment.…”

“…Tian reported that the degradation rate of dimethoate by free chlorine was highly pH dependent, and methiocarb degradation pathways also exhibit a strong pH dependence. 21,22 According to our results, soil pH could have a substantial impact on the control efficacy of dimethoate on mites, and soil pH values of 6.70 or 5.70 with a low amount of 1.50 kg ha -1 dimethoate caused mite mortalities >60% 7 days after the treatment. Obviously, soil pH should be given full consideration before practical drip irrigation of an insecticide in different Table 9.…”

Ternary Layered Double Hydroxides (LDHs) Based on Co‐, Cu‐Substituted ZnAl for the Design of Efficient Photocatalysts

“…To evaluate the catalytic ability of the designed LDH materials, the photocatalytic degradation of a model dye, orange II, was investigated under UV light irradiation. Indeed, catalytic degradation reactions have been proposed as highly advanced oxidation processes (AOPs), and widely used for the remediation of the wastewater in lieu of traditional methods such as chlorination or filtration . Generally, the hydroxyl and superoxide radicals that are catalytically generated by photoactive materials are responsible for the degradation of organic pollutants , .…”

Degradation of nitro-based pharmaceuticals by UV photolysis: Kinetics and simultaneous reduction on halonitromethanes formation potential

“…There are no obvious differences among the HNM yields at pH 5.0e7.0, while the HNM formation amounts decreased in alkaline circumstance with the minimum value of 9.2 and 4.0 mg L À1 at pH 9.0 for RNTD and NZTD, respectively. The pK a of RNTD, NZTD and HOCl were 8.7, 6.8, and 7.5, respectively (Degim et al, 2001;Tian et al, 2014). As RNTD and NZTD are prone precursors of HNMs during chlorination, it is speculated that the both the neutral and anionic species of RNTD and NZTD contributed to the HNMs formation.…”