Research On The Occurrence Characteristics Of Pesticides And High-efficiency Purification Technology In The Water Bodies Of The Huangpu River Basin

In order to reveal the distribution and risk of pesticides in the Huangpu River basin,the spatial and temporal variations of 29 pesticides concentration in water samples and their risk quotient?RQ?values for three different trophic organisms?fish,daphnia,green algae?from 16 sampling sites in four seasons were analyzed.These 29pesticides include 4 carbamates,2 benzimidazoles,6 nicotine and amides,2organophosphates,9 triazoles and 6 others.Notably,the detection frequencies of 18pesticides were 100%,reflecting the widespread use of pesticides in this region.The detection concentration level of target pesticides in water samples was<LOQ–607.3ng L^-1,with carbendazim being the highest(607.3 ng L^-1 in spring)and buprofezin being the lowest?<LOQ in summer,autumn and winter?.The concentrations of pesticides from Taihu Lake to the estuary generally increased first and then decreased,reaching a peak in the rural or urban areas,which was closely related to the use of pesticides and the import of tributaries in these regions.At the same time,the consumption of pesticides in urban areas was huge,and the contribution to the concentration of pesticides in surface water cannot be ignored.The total summed concentrations of 29 pesticides in winter(1037.6 ng L^-1)was higher than summer(788.82 ng L^-1)in rural and urban areas,indicating that low flow flux and low temperature might induce the higher concentration in winter.The spatial and temporal trends of RQ values were basically consistent with the trends in pesticide concentrations.For different organisms,there was no necessary relationship between the pesticide concentration and the RQ value.For fish,daphnia and green algae,the triazoles,carbamates,nicotine and amides were at highest risk,respectively.On the basis of river sampling,the concentration changes of 29 pesticides in four waterworks?A,B,C and D?and the human exposure risk levels of three groups of people?adult,children,infant?were further analyzed and evaluated.The concentration of pesticides in raw water was lowest in summer or autumn,and highest in spring or winter.The concentration of pesticides in the raw water ranged from<LOQ to 2391.3 ng L^-1,while decreased to<LOQ to 269 ng L^-1 in the effluent.After the different treatments in the water plant,the pesticides concentration decreased significantly.The average concentration of pesticides in the effluent was about 4.7 ng L^-1,and the removals of benzimidazoles,organophosphorus and others were>85%.The average removal of nicotine and amides was relatively low?51.4%?.The contribution of the advanced treatment process was much higher than that of the conventional treatment process,and the low temperature affected the removal efficiency of the biological activated carbon?BAC?process.The average removal of D water plant with ultrafiltration process was higher than that of A,B and C water plants,indicating that the ultrafiltration process can improve the removal of pesticides to some extent.There was a significant positive correlation between total organic carbon?TOC?and pesticides concentration.Among the seven pesticides with higher detection frequency and concentration,R² reached a maximum of 0.98?isoprothiolane?and the lowest was 0.87?isocarbophos?,indicating that TOC may be an important factor affecting the concentration distribution of pesticides.The human exposure risk assessment results indicated that the estimated daily intake?EDI?value of a single pesticide was much lower than the allowable daily intake?ADI?,indicating that there was no chronic toxicity risk for a single pesticide,but synergism may be occurred among the multiple pesticides in the water and this remains to be studied.The EDI value of the effluent was 67%lower than the raw water and 3 to 9 orders of magnitude lower than the ADI value.In order to further improve the removal of pesticides in the water treatment process,the organic and inorganic activations of permanganate?PM?were thoroughly studied at the laboratory level.PM is a widely-used oxidant in water treatment.However,the oxidation rate of micro-pollutants by PM is highly variable,dependent on the electron density of certain moieties of micro-pollutants.Using a pesticide?carbendazim,CBZ?as a target micro-pollutant,this study compared the organic and inorganic activations of PM by benzoquinone?PM/BQ?and bisulfite?PM/BS?,respectively.It was found that both the PM/BQ and PM/BS systems could accelerate the degradation of CBZ with different degradation rates.The PM/BS system completed the degradation of CBZ?96.6%?within 15 s,while the PM/BQ system took 2 h to achieve a 95.7%removal.The optimal molar ratios of[PM]_?:[BS]_?and[PM]_?:[BQ]_?were determined to be 1:5 and 1:0.1,respectively.Interestingly,both the degradation of CBZ in the PM/BQ and PM/BS systems were dependent on dissolved oxygen?DO?concentration.When DO was around 0.5 mg L^-1,the removals of CBZ by the PM/BQ and PM/BS systems were just 3.6%and 36.8%,respectively after 2 h,significantly lower than those under 9.1-mg L^-1 DO?95.7%and 96.6%,respectively?.Based on the quenching experiments,the enhanced degradation in the PM/BQ system was mainly ascribed to the formations of Mn?III?and ¹O₂,while the formations of SO₅^·-and SO₄^·-mainly contributed to the accelerated degradation in the PM/BS system.The effect of Mn?III?was limited in the PM/BS system.The transformation products of CBZ in both the PM/BQ and PM/BS systems were identified and the degradation pathways including dehydrogenation,alkylation,carboxylation and hydroxylation were proposed.The inorganic activation of PM by BS exhibits a higher degradation rate and stability under different water matrices,indicating its potential engineering application in water treatment.