T Wang

Comprehensive Screening Study of Pesticide Degradation via Oxidation and Hydrolysis

This comprehensive study focused on the reactivity of a set of 62 pesticides via oxidization by free chlorine, monochloramine, chlorine dioxide, hydrogen peroxide, ozone, and permanganate; photodegradation with UV(254); and hydrolysis at pH 2, 7, and 12. Samples were analyzed using direct injection liquid chromatography-mass spectrometry detection or gas chromatography-electron capture detection after liquid-liquid extraction. Many pesticides were reactive via hydrolysis and/or chlorination and ozonation mechanisms under typical drinking water treatment conditions, with less reactivity exhibited on average for chlorine dioxide, monochloramine, hydrogen peroxide, and UV(254). The pyrazole and organophosphorous pesticides were most reactive in general, whereas carbamates and others were less reactive. The screening study provides guidance for the pesticide/oxidation systems that are most likely to lead to degradates in water treatment and the environment.

Identification of hydrolytic metabolites of dyfonate in alkaline aqueous solutions by using high performance liquid chromatography – UV detection and gas chromatography-mass spectrometry

Organophosphorus compounds, becoming the most commonly used pesticides in agriculture, are garnering more interest to be environment and health issues associated with their usage. These compounds run-off into surface water and leach into groundwater supplies where they have been detected. Dyfonate is commonly applied to the soil as an insecticide for the control of variety of insects. However, critical information on the transformation of dyfonate into its hydrolytic byproducts during water treatment is lacking, even though they have been used in the field for a long time. In this study, dyfonate hydrolysis at elevated pH levels, simulating a water treatment operation or similar process, was investigated. Dyfonate, an organophosphorus insecticide used to treat infestations primarily on corn, was investigated due to its greater rate of hydrolysis observed during our screening studies. The hydrolysis of dyfonate was investigated at pH 10, 11, and 12 in phosphate buffered water over the course of 7 days. Two hydrolysis products, thiophenol and phenyl disulfide, were detected. Dyfonate and thiophenol were analysed using high pressure liquid chromatography/UV detection (HPLC/UV), while phenyl disulfide was detected using gas chromatography/mass spectrometry (GC/MS). The relative concentration profiles of dyfonate and its hydrolysis products, as well as their transformation pathways, were also reported. The data from this study will help environmental researchers understanding the hydrolytic pathways of dyfonate and its metabolites at different pHs in a water treatment system.

Comprehensive studies of aldicarb degradation in various oxidant systems using high performance liquid chromatography coupled with UV detection and quadrupole ion trap mass spectrometry

Aldicarb, a carbamate pesticide, is commonly used in agriculture and can be naturally degraded to metabolites, resulting in their occurrence in drinking water supplies. The disinfection process using different oxidants for the treatment of drinking water provides the opportunity to degrade aldicarb and its metabolites to byproducts that may pose more human health risk than the parent compounds. A comprehensive study of aldicarb and its metabolites involving treatment with free chlorine (FC), monochloramine (MCA), ozone (O3), chlorine dioxide (ClO2), hydrogen peroxide, permanganate ( ) and UV radiation was performed to identify the degradation products. Free chlorine, high-dosage UV radiation and permanganate exhibited stronger oxidation capacity than the other oxidants studied, with chlorine dioxide showing the weakest oxidation ability among them. Aldicarb sulfoxide was formed as the degradation product of aldicarb by oxidation with free chlorine, MCA, ozone, and hydrogen peroxide. Aldicarb sulfone was identified as an oxidation byproduct of both aldicarb and aldicarb sulfoxide by permanganate. N-chloro-aldicarb sulfone was formed as an oxidation byproduct of aldicarb sulfone by free chlorine. The comprehensive information is very valuable for water treatment facilities and environmental researchers.

Analysis of Oxidation Byproducts of Dyfonate in Various Oxidant Systems Using High Performance Liquid Chromatography Coupled with Quadrupole Ion Trap Mass Spectrometry

Dyfonate is a dithiophosphonate pesticide used to control lepidopterous insects in corn, potatoes, and peanuts. It may be transferred to the surface water and underground water system and can be degraded by free chlorine and other oxidants, which are used by water treatment plants during the disinfection process, to produce oxidation byproducts. These byproducts may be more toxic than their parent compounds. Therefore, it is crucially important to identify these byproducts during the water treatment for full scale removal of them. In this article, a high pressure liquid chromatography/mass spectrometry (HPLC/MS) method was developed to investigate the oxidation byproducts of dyfonate by free chlorine (Cl2), hydrogen peroxide (H2O2), monochloroamine (MCA), chlorine dioxide (ClO2), Ozone (O3), and permanganate in an aqueous buffer (pH 7). Thin layer chromatography (TLC) and nuclear magnetic resonance (NMR) were also used for structure confirmation of the byproduct that was identified through HPLC/MS. One byproduct, dyfonate oxygen analog (phosphonothioic acid) was identified as the primary oxidation byproduct for free chlorine, ozone, MCA, and the H2O2 system, while no oxidation byproduct was detected in the ClO2 and permanganate system. The results of this study can serve as a valuable reference for water treatment plants.