Transformation And Mechanism Of Methyl Parathion In Drinking Water Disinfection Processes

Objective:Organophosphorus pesticides are widely used in agricultural pest control due to their broadly spectrum, its efficiency, and their production accounts for more than half of the total pesticides. However, some of organophosphorus pesticides threaten human health and environment due to their highly toxicity. Methyl parathion is a typical organophosphorus pesticide, which was detected in water sources in many reports.Organophosphorus pesticides are listed in the “Standards for drinking water quality”(GB5749-2006) as unconventional detection index. Meanwhile, the standard also underline the “drinking water should be disinfected”, as a result, some small central water supply take the simple disinfection measure, which virtually increase the risk of disinfection of drinking water on human health. Therefore, it is necessary to identify the mechanism and transformation of organophosphorus pesticide residues in drinking water disinfection processes to provide theoretical support to control the health-risk of organophosphorus pesticides.Contents:1 Transformation of methyl parathion in drinking water disinfection processes.2 Neurotoxicity evaluation of degradation byproducts of methyl parathion in drinking water disinfection processes.3 Transformation mechanism of methyl parathion in drinking water disinfection processes.Methods:Methyl parathion transformation by chlorine dioxide, chlorine, ozone was studied by a static sterilization experiments. Solid phase extraction was taken for the recovery of methyl parathion, and methyl parathion was determined by gas chromatography. Byproducts were identified by Gas chromatatography-massspectrometry and ion chromatography. C.elegans was used to evaluate neurotoxicity of byproducts of methyl parathion.Innovations:The pollution of organophosphorus pesticides in water sources has been reported.Current practical problems of drinking water disinfection and the pollution of pesticides are considered together to study the transformation and mechanism of organophsphorus in drinking water disinfection processes.Results:1. Conditions for Methyl parathion test.Methyl parathion was analyzed with capillary column gas chromatography(GC:Agilent 7890 N, Detector: FPD detector, Column: J&M123-3832(30m×320μm×0.25μm), Conditions: gasification chamber temperature:250℃, the detector temperature: 250℃, temperature program:100℃ keeps 1 min, 15℃/min speed rose to 250℃, keep 9 min. Carrier gas flow rate: the flow rate of hydrogen(75m L/min), air flow(100m L/min), make up nitrogen flow(15m L/min), splitless.Methyl parathion testing standard curve y=7069.94x+9.63, x is the concentration(μg /m L), y is the peak area, the correlation coefficient r=0.99974.The enrich and recovery of methyl parathion was measured with C18 solid phase extraction in water samples, SPE(solid phase extraction) twice with 5m L of methanol were added, 10 m L water cleaning, 100 m L water samples were added to extraction column with 2m L/min flow rate, followed by 10 m L water cleaning, 10 min drying;with 5m L dichloromethane, a flow rate of 2m L/min, respectively eluted twice eluate anhydrous sodium sulfate(120℃ oven drying) dehydration, nitrogen blow concentrated to 1m L, sealed at 4℃ to be detected.2. Transformation of methyl parathion in drinking water disinfection processes.Methyl parathion was degraded in the process of chlorine dioxide disinfection in water. The higher the concentration of chlorine dioxide, methyl parathion degradation effect was more obvious. After 20mg/L of chlorine dioxide in 6h, methyl parathion had 54.68% degradated. With the initial concentration of methyl parathion increased,the degradation effect was reduced. As the solution p H increased from 6.0 to 9.0, the p H had no obvious influence on the methyl parathion hydrolysis reaction, thetemperature also had no significant effect on the process. The mode is Ct1.52=kt+b,r(0.05,4)> 0.729, is methyl parathion concentration in different times(ug/L), t is time(h),k is rate constant, b is a constant.Methyl parathion was also degraded during the process of chlorine disinfection of drinking water. The higher the concentration of chlorine, methyl parathion degradation effect was more obvious. 12mg/L chlorine was treated 2h, 20ug/L methyl parathion were degraded completely. With the initial concentration of methyl parathion increased, its degradation effect was reduced. With the increasing of p H, the effect of degradation was more obvious. When the temperature was 4℃ ~ 30℃,methyl parathion degradation effect was more obvious with the increasing of temperature. The dynamic model is Ct1.58=kt+b, r(0.05,4)> 0.729, Ct is methyl parathion concentration in different times(ug/L), t is time(min), k is rate constant, b is a constant.Ozone disinfection made a certain methyl parathion degraded in drinking water.The higher the concentration of ozone, methyl parathion degradation effect was more obvious. 3mg/L ozone acted 30 min, 20ug/L methyl parathion was 93.69% degraded.With the initial concentration of methyl parathion improved, its degradation effect was reduced. p H effect on ozone and methyl parathion was no significant difference.In the range of 4℃-30℃, ozone had no significant effect on the role of methyl parathion. The model is Ct1.45=kt+b, r(0.05,4)> 0.729, Ct is methyl parathion concentration in different times(ug/L), t is time(min), k is rate constant, b is a constant.3. Biological effect evaluation of transformed products in drinking water disinfection process.Drinking water with methyl parathion after routine water disinfection process has some neurotoxicity, C.elegans acetylcholinesterase activity was inhibited. With increasing concentration of the disinfectant and the contact time, the post-disinfection water had neurotoxicity gradually. Within chlorine dioxide disinfection, the byproducts can make Ach E activity of decrease. The time-response relationship is Y=-0.0142X+0.2801, r(0.05,4)=0.924,(X is time, Y is Ach E acitivity), the concentration of chlorine dioxide was meaningless to Ach E activity. Within chlorine disinfection,the time-response relationship is Y=-0.0008X+0.3055,r(0.05,4)=0.928,(X is time, Y is Ach E activity), the concentration of chlorine had a vital effect on Ach E activity.Within ozone disinfection, the time-response relationship is Y=-0.0066X+0.3201,r(0.05,4)=0.952,(X is time, Y is Ach E activity),the concentration of ozone on Ach E activity is meaningful.4. Mechanism of methyl parathion in drinking water disinfection processes.Gas chromatography-mass spectrometry, ion chromatography for methyl parathion degradation products analysis showed: methyl paraoxon will appear in chlorine dioxide, chlorine, ozone disinfection process.Conclusion:1. With the increasing of disinfectants concentration, methyl parathion degraded obviously. The alkaline condition promoted the hydrolyzation of methyl parathion.During the disinfection of chlorine dioxide and ozone, the effects of p H and temperature on degradation of methyl parathion were not obvious. Alkaline condition and high temperature enhanced the degradation of methyl parathion in the chlorine disinfection.2.The transformed products obviously inhibited activity of Ach E during the disinfection.And with the increase of disinfectant concention and the extension of exposure time,the activity of Ach E was inhibited more obviously.There were a time-depentant manner between the exposure time and activity of Ach E.3. Methyl paraoxon was a common product produced during drinking water disinfection processes.