| Worldwild pesticide extensive usage has resulted in the environmental pollution, which is receiving increasing public concern. Pesticides are primarily used in the agricultural soil, but only 30% of the pesticides applied in soil are ultilized by plants while others become pesiticide residues in the soil. Pesiticide residues can reach the surface water and groundwater through direct run-off and leaching. Large usage of pesiticides can thus cause the pollution of soil and water circumstances. Although many studies addressing pesiticides degradation in the soil and aquatic system are available, the detailed insight into their fate in the environment, esipecially in the water-sediment system, is still missing. Therefore, the two widely used pesticides-glyphosate and metamitron-were chosen as targeted compunds to investigate their detailed fate including their mineralization, degradation kinetics, degradatation pathway and the formation of non-extractable residues (NER)with a particular on the biogenic reisudes in soil and water-sediment systems by using stable isotope (13C and 15N) and biomarkers (fatty acids and amino acids). Based on the distribution of 13C and 15N with time during the degradation process, the following conclusions have been drawn:(1) In soil, the mineraliztion of glyphosate reached 72.6%. Its half life was 3.4 days, and it was completelty removed at the end of the experiment. In water-sediment systems, the mineralization of glyphosate was 55.7%. Its half life was 15 days.4.9% of the initially applied glyphosate finally remained. In comparsion to water-sediment systems, the mineralization in the water system was only 2.4%, and the final removal efficiency of glyphosate was 9.9%. In soil, the mineraliztion of metamitron was 59.7%. Its half life was 5.6 days, and it was totally degraded at the end of the experiment. In water-sediment systems, the mineralization reached eventually 49.2%. Its half life was 13 days. And no metamitron was detected at the end. Compared with water-sediment systems, the water system showed 8.7% of mineralization,and final removal efficiency of metamitron was 12.7%.(2)Aminomethyl phosphonic acid (AMPA) is the main metabolite of glyphosate degradation in soil and water-sediment systems. In soil, glyphosate was biodegraded by the AMPA pathway, and microorganism started ultilizing the AMPA after 20 days. While glyphosate was first degraded via sarcosine pathway related to microbial growth. Later, its degradation via AMPA pathway dominated, no degradation of AMPA was found during the experiment. In soil and water-sediment systems, metamitron was degraded by different pathways. In soil, three different metabolites were found, their molecular formulars are C10H9N3O, C10H8N4O5 and C4H6N4O, respectively,while two metabolites were detected in water-sediment systems, and their molecular formulars are C10H9N3O and C13H14N4O, respectively.(3) In soil and water-sediment systems, the microbial community changed during the biodegradation process of glyphosate and metamitron according to the distribution of 13C in the fatty acids in the time course. During the degradation of glyphosate in soil, 9.89% of the initial applied 13C and 24.38% of the initially applied 15N were finally incorporated into total amino acids, while 10.06% of the label 13C and 12.17% of the label 15N were eventually detected in total amino acids in water-sediment systems. During the metamitron degradation in soil,14.85% of the initially applied 13C were finally incorporated in total amino acids, while 11.88% was eventually found in total amino acids in water-sediment systems. Microbial componnents became biogenic residues after the cell death remaining in soil. Biogenic resiudes accounted for 89.5%and 98.3% of NER formed during the biodegradation of glyphosate and metamitron in soil, respectively, while 89.4% and 66.0%, respectively, in water-sediment systems, indicating that biogenic residues are the main components of NER during the biodegradation of glyphosate and metamitron. |
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