| Pesticides are indispensable agrochemicals to increase the crops production in agriculture practice.However,the intensive pesticides usually could destroy the product quality and endanger the ecosystem safety,and human health.To achieve the high efficiency and low use,the development of the low pollution and environmental friendly new pesticides formulation are one of the main research directions.In recent years,the application of super absorbent polymers(SAP)encapsulated pesticides formulation is the main development direction in the field of pesticidedevelopment and application area.In addition,SAP usually can be used to conserve the water and moisture in arid and semi-arid area.Therefore,the coexistence of SAP and pesticides in environment is a common and noteworthy objective phenomenon.SAP has some functional groups such as-COOH?-OH?-NH2.After entering the soil environment,SAP could interact with pesticide molecules through chemical and biological interactions,and also compete with soil matrix to combine pesticides molecule,which may affect the environment behavior of pesticides in soil,such as adsorption and desorption,degradation and conversion,and biological effects.It is particularly important to study and clarify the environmental behavior of pesticides under the coexistence of SAP and pesticides.Meanwhile,as a fungicide,carbendazim is widely used to control rice,cotton,tobacco and other crop diseases.However,it is noteworthy that there is rare research on the environmental behavior of pesticides under the coexistence of SAP and carbendazim.In this study,we selected carbendazim as the research object,and used the isotope tracer technology,modern instrumental analysis technology and high-throughput sequencing technology to track the transformation kinetics and degradation.From the perspective of mass balance,we focus on the"environmental behavior and fate of Carbendazim when mixed with SAP and Carbendazim,"environmental behavior and fate of Superabsorbent hydrogels(SHs)-encapsulated Carbendazim in aerobic soil","The co-effect of SAP and Carbendazim on soil microbial diversity and community structure" and"Phytoavailability of bound residue of Carbendaizm to Chinese cabbage(Brassica campestris ssp.chinensis)coexisted with Superabsorbent polymers"to elucidate systematically the environmental behavior and transformation of Carbendazim and its influencing factors under SAP coexistence,and to explore the possible mechanism.The main results are as follows:1.Under the coexistence of SAP and '4C labelled Carbendazim(MBC)in aerobic soil(SAP MBC treatment):(1)The extractable residues(ER)of carbendazim.The ER of carbendazim in neutral loamy soil S2 and alkaline saline soil S3 was 6.9-11.4%during 100 d incubation,and there was no significant difference compared with the control group(p>0.05).In acid soil Si,ER were 62.2%and 70.2%of the initial amount in SAP MBC and MBC control group,respectively.The ER was decreased significantly by 11.4%in SAP MBC treatment.The decrease of ER was related to the accelerated degradation of carbendazim.(2)Carbendazim degradation.The half-life of MBC parent compound in the SAP_MBC was 100.5 d,19.4 d and 18.3 d in three test soils(S,,S2 and S3),respectively,while that in MBC control group was 154.0 d,22.5 d and 21.9 d,respectively.Compared with the control group,the half-life of MBC was shortened by 50 days(p<0.5)in acid soil S,.(3)Quality and quantity of degradation products of carbendazim.There was no change of degradation products of carbendazim,which include 2-amino-benzimidazole(2-AB,M1)and 2-hydroxy-benzimidazole(H-AB,M2).Compared with the control group,M1 appeared earlier and the maximum value of M1 content was higher in SAP_MBC treatment.During the incubation of S1,M1 accounted for 0.8-7.5%of the total radioactivity,reaching the maximum value(7.5%)at 45 days.In the control,M1 reached its maximum value at 80 days(4.4%).The percent of M1 in SAP MBC treatment of S2 and S3 was 1.1-8.8%and 1.3-8.6%respectively,which were significantly higher than that in the control(0.3-4.0%and 1.8-6.0%).There was no significant difference in M2(0.2-2.6%)between SAP MBC and MBC control(p>0.05).(4)The mineralization of Carbendazim.In S2 and S3,the mineralization of Carbendazim was 11.3%and 7.7%of the total amount,respectively,after 100 d incubation.However,it has rare mineralization in S1(0.19%).The mineralization of carbendazim in MBC control group was 18.1%,13.1%and 0.18%respectively.Obviously,the addition of SAP could significantly inhibit the mineralization of Carbendazim in neutral and alkaline soils,with the decrease of 37.6%and 41.2%respectively(p<0.05).(5)Bound residues(BR)formation of carbendazim.After 100 days of incubation,BR accounted for 40.5%,77.7%and 82.3%in three soils(S,,S2 and S3),while BR in the control group was 34.0%,69.8%and 74.1%respectively.SAP significantly increased the BR of Carbendazim in soil,with a relative increase of 11.1-19.1%.(6)Bioavailability of Carbendazim bound residues.In S2,addition of BR from SAP MBC treatment promoted Chinese cabbage growth.When cultured for 35 days,the dry weight of edible part of Chinese cabbage in SAP_MBC treatment(398.27 mg/plant.d.w)was significantly higher than that in control group(365.23 mg/plant.d.w)(p<0.05),while in S3,there was an opposite result.The absorption and distribution of 14C-bound residue test showed that BR from soil was absorbed by 4.09 ug/g after 21 days in S3,which was significantly higher than that of control group(2.67 ug/g)(p<0.05);the contents of edible parts(2.24 ug/g)and roots(21.21 ug/g)were significantly higher than those of control group(1.03 ug/g for edible parts and 14.59 ug/g for roots)(p<0.05).Compared with the control,the same result was observed.The absorption level in whole plant was 4.19 ug/g,the edible part was 2.03 ug/g and the root part was 11.02 ug/g in SAP MBC treatment,which were higher than those in the control group(whole plant for 2.90 ug/g,the edible part for 1.57 ug/g and the root part for 21.51 ug/g(p<0.05).The bound residue in soil was 38.57%and 61.76%respectively,in SAP_MBC treatment and the control group after 35 days,which infers that the bound residue in SAP MBC treatment was easier to be released and transformed,and the release rate was 1.6 folds as much as that of the latter.Similar results were also found in S3.The results showed that the combination of SAP and carbendazim was easier to form bound residues in soil and had more bioavailability.(7)Soil microbial diversity and community structure.Compared with the control group,SAP significantly increased soil microbial diversity and richness,and the Shannon index was significantly increased,and the richness and evenness were increased by 2 to 3 folds.At the phylogenetic level,the relative abundance of Proteobacteria and Cleroflexi involved in carbendazim degradation was increased by 2 to 3 folds when SAP was added to S,.In S2,the relative abundance of Firmicutes was doubled.In S3,Proieobacteria and Actinoacteria did not be changed significantly,while the relative abundance of Firmicutes,Chlorooflexi and Acinoobacteria was increased by 1 to 3 folds.At the species level,the relative abundance of some major bacterial Proteobacteria,Bradyrhizobium,Sphingomonas and Methylobacterium in SAP MBC treatment were increased by more than two folds when compared with the control group,while the relative abundance of Lactococcus,Marmoricola,bacillus and Firmicutes was decreased by 30-100%.In S2,Bacillus was increased by 2 folds,subgroup 6 norank was decreased by 45%and the total amount of Nitrosomonadaceae uncultured was increased but the relative amount was decreased by 30%.In S3,bacillus,subgroup 6 norank and blastocatella were increased by 1 to 4 folds,while Sphingomonas and Comamonadacea were decreased by 35-70%.Obviously,SAP could be the edible nutrition source for soil microorganism,and change the microbial diversity and community structure,which could influence the environmental behavior and transformation fate of carbendaizm.2.Treatment of Superabsorbent hydrogels(SHs)-encapsulated 14C labelled Carbendazim formulation(HMBC)in aerobic soil:(1)The extractable residue(ER)of HMBC.At 100 days,ER accounted for 8.5%and 16.9%respectively in neutral S2 and alkaline S3,and 8.5%and 11.4%in MBC control group,respectively.No significant difference was detected between HMBC and MBC(p>0.05).However,there was opposite result in acidic S1.The ER of HMBC was decreased by 18.6%compared with MBC control.(2)Degradation of Carbendazim in superabsorbent hydrogels(SHs)-encapsulated formulation(HMBC).In three soils,the half-life of MBC were 70.7 d,14.8 d and 13.5 d,respectively.In the control group,the degradation rates in the corresponding soils were 154.0 d,22.5 d and 21.9 d,and the degradation were increased by 54.1%,34.2%and 38.4%,respectively.(3)Quality and quantity of HMBC.The degradation products of encapsulated Carbendazim were changed significantly.There were 6 intermediates were detected by HPLC-Q-TOF-MS/MS,which includes M1,M2,2-amino-3-((aminomethyl)-amino)-phenol(M3),2-amino-3-((hydroxymethyl)-amino-phenol(M4),3-(2-((methoxycarbonyl)amino)-1H-benzo[d]imidazole-1-propionic acid(M5),1-vinyl-2,3-dihydro-1 H-benzo[d]imidazole(M6).M1 and M2 are the main degradation products in HMBC treatment.During the whole incubation period,M1 and M2 accounted for 0.9-9.8%and 0.6-5.8%of the initial amount,respectively,which were significantly higher than those of the control at corresponding time points(p<0.05).M5 and M6 only appeared in the HMBC treatment,and the contents were 0.3-4.2%and 0.9-1.7%,respectively.M3 was detected only in S2 and S3,the content was 0.5-1.6%,while M4 was detected only in Si,and the highest value was 5.8%.(4)The mineralization of HMBC.The amount of HMBC in aerobic soil is closely related to soil type.After 100 days of incubation,the mineralization was 30.4%and 19.2%in S2 and S3 with high organic matter,respectively.However,it was more difficult to open the imidazole ring to mineralize in S1(0.42%).The mineralization in control group was 18.1%,13.1%and 0.19%:in corresponding three soils,respectively.Compared with the control,the mineralization of HMBC was increased by 68%and 46.6%,respectively,in S2 and S3.(5)The bound residue(BR)of HMBC.BR decreased significantly in S2 and S3,and the relative reduction was 15.2%and 14.2%respectively.Superabsorbent hydrogels(SHs)-encapsulated formulations could significantly reduce the formation of carbendazim BR in S2 and S3.However,BR was increased by 35%in acid S1.(6)Bioavailability of HMBC bound residues.In S2,the dry weight of whole plant and edible parts of Chinese cabbage in HMBC treatment were 930.10 mg/plant.d.w and 571.97 mg/plant.d.w,respectively.Both of them were all significantly higher than those of the control(544 mg/plant.dw,edible part 365.23 mg/plant.d.w)(p<0.05)at 35 d.Similar results were found in S3.The absorption and distribution of 14C-bound residue test in plant showed that the total absorption of 14C-bound residue from soil was 1.30 ug/g,and the coontent of edible part was 0.54 ug/g in HMBC treatment after 21 d incubation,which was significantly lower than that in the control(2.67 ug/g and 1.03 ug/g)(p<0.05).In addition,the release of BR rate after encapsulated treatment was 46.56%.No significant different was detected when compared with the control(38.24%)(p>0.05).Compared with the control,the same result was observed at 21 d.In HMBC treatment,the absorption level of the whole plant was 1.05 ug/g,and the edible part was 0.56 ug/g,which was significantly lower than that of the control grup(whole plant for 2.90 ug/g and edible part for 1.57 ug/g)(p<0.05).Overall,compared with the control group,the HMBC treatment had low bioaccumulation concentration,and was related to the release rate of BR.The release rate of BR was 51.66%and 51.57%respectively in the control group and the HMBC.And there was no significant difference between two treatments(p>0.05).The results showed that the bound residue of HMBC treatment was low in soil and had no adverse effect on the growth of cabbage(7)Soil microbial diversity and community structure.In S,-S3,compared with the control,the Shannon index of HMBC was increased significantly,and the richness and evenness were increased by 1 to 3 folds.Microbial community structure analysis showed that the relative abundance of Firmicute.s and Proteobacteria in HMBC treatment was significantly increased by 0.5 to 1 folds in S,.In S2 and S3,the relative abundance of Actinobacteria,Acidobacteria and Clero'lexi were increased significantly by 1 fold.At species level,in S1,the relative abundance of Lactococcus,Bacillus and Sphingomonas in HMBC treatment were increased by 2 to 3 folds compared with that in control,while Methylobacterium and Sinomonas was decreased by 25-99%.In S2 and S3,compared with the control,the relative content of Bacillus and Marmoricola were increased by 1.5 to 3 folds in HMBC,while Comamonadaceae uncultured was decreased by 70-90%.Superabsorbent hydrogels(SHs)-encapsulated MBC formulations could enrich the microbial diversity and change microbial community structure,thereby affecting the environmental behavior and fate of carbendazim in the tested soilsIn this study,we found that amendment of SAP could changed the environmental behavior of Carbendazim in soil,including extractable residues,bound residues,mineralization and parent compound degradation.These results suggest that the evaluation of the environmental safety and toxicology of carbendazim will be biased when SAP coexist with Carbendazim.Meanwhile,the Superabsorbent hydrogels(SHs)-encapsulated MBC formulations has low total residue in neutral and alkaline soil by reducing the formation of BR,and is more easily detoxified by opening the imidazolium ring for mineralization.In acidic soils,however,the behavior and fate of encapsulated carbendazim showed different characteristics,such as accelerated parent degradation and increased bound residues.The results show that Superabsorbent hydrogels(SHs)-encapsulated formulation could reduce the carbendazim residue in soil and has a good potential application prospect in future.The results imply that the behavior and fate of Superabsorbent hydrogels(SHs)-encapsulated MBC formulation can not be characterized in the case of carbendazim alone. |
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