| Application of pesticides has greatly improved the quality and quantity of agricultural production for world growing population. However, with increasing utility of pesticldes, great concerns about their adverse effects on non-target organisms, including human beings, have arised. Extensive use of chemicals in conventional agricultural practices has resulted in continuous environmental pollution. In fact, the contamination of herbicides (or their residues) in ecosystems has become one of the serious environmental problems, which is linked to the crop production, quality, and human health. Since the majority of pesticides occur in the soil medium, the residues of pesticides constitute the major sources that not only contaminate the groundwater by downward movement but are adsorbed by crops as well. Soil organic matter (SOM) is recognized as the key factor affecting the behavior and fate of organic pollutants in soils. Addition of organic amendments to soils changes the SOM content and thus may greatly affect pesticide adsorption/desorption processes. In this dissertation, the influence and its mechanisms of exogenous DOMs and organic amendments on behaviors of prometryne in soils were investigated. Main original conclusions are shown as follows:Batch experiments, soil columns and soil plate were conducted to study the effect of DOM on the sorption/desorption and mobility of prometryne in soils. Basic physicochemical properties of two dissolved organic matter were also determined. The results showed that sorption capacity in one soil type for prometryne was significantly reduced by application of DOM, whereas desorption and migration of prometryne was notably promoted by DOM treatments. Compared to the control, the addition of DOMs at 160 mg DOC L-1 (SL2, ST2) decreased the prometryne adsorption by71.0% and 71.8% respectively. Whereas, the application of DOMs at 160 mg DOC L-1 (SL2, ST2) increased the recoveries of prometryne from 22.5%(control) to 36.9%(SL2) and 52.5%(ST2), also increased the Rf values for prometryne mobility in soils from 0.1823 (control) to 0.2147 (SL2) and 0.2376 (ST2). As compared to DOM extracted from sludge, DOM from straw had a stronger effect on behavior of prometryne in soils. This effect could be intensified when high concentration of DOM was added. The results of C, H, N and ash contents analysis indicated that that DOM (ST) contained more organic matters and unsaturated structures than DOM (SL). That suggested DOM could activate prometryne in agriculture soils and increase its activity.Batch experiments and soil columns were also conducted to clarify the effect of pig manure compost (PMC) and lakebed sludge (SL) on sorption/desorption and mobility of prometryne in soils. Elemental analysis and FT-IR spectra techniques were applied to determine the physicochemical properties and group components of the two organic amendments. They were also used to monitor the effect of the organic amendments on the basic physicochemical properties of soils. Sorption capacity in soils for prometryne was significantly promoted by application of organic amendments, whereas desorption and migration of prometryne was drastically reduced by organic amendments. Compared to the control, the addition of SL increased the Kf values by 49.6%(SL-1) and 95.2%(SL-2). Similarly, the Kf values for treatments with the addition of PMC were 3.1-3.3 times compared with the control. Whereas, the application of organic amendments (SL and PMC) decreased the recoveries of prometryne from 85.8%(control) to 62.9%(SL-1),57.9% (SL-2),35.2%(PMC-1) and 29.2%(PMC-2). Organic amendments could decrease the activity of prometryne in agriculture soils. As compared to sludge, pig manure compost had a stronger effect on behavior of prometryne in soils. Analysis of C, H, N and ash contents revealed that PMC contained more organic matter and unsaturated structures than SL.The soil pot experiment was employed to investigate prometryne-induced biological toxicity in wheat (Triticum aestivum). Wheat plants were grown in soils with prometryne at 0-24 mg kg-1 soil. The growth of wheat treated with prometryne was inhibited. Chlorophyll content significantly was decreased even at the low level of prometryne (4 mg kg-1 soil). Accumulation of thiobarbituric acid reactive substances (TBARS), an indicator of cellular peroxidation was increased, suggesting oxidative damage to the plants. The prometryne-induced oxidative stress triggered significant changes in activities of a variety of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) and glutathione S-transferase (GST). Activities of the enzymes showed a general increase at low prometryne concentrations, but decrease at high levels. Analysis of non-denaturing polyacrylamide gel electrophoresis (PAGE) confirmed the results. To get an insight into the molecular response, a qRT-PCR-based assay was performed to analyze the transcript abundance of Cu/Zn-SOD and GST with prometryne exposure. Our analysis showed that both genes were up-regulated in expression with a pattern similar to the activities of the enzymes. Therefore, we concluded that that prometryne-induced biological toxicity was responsible for the disturbance of the growth and antioxidant defensive systems in wheat plants.Accumulation of prometryne and biological responses of wheat plants as affected by pig manure compost (PMC) was investigated. Compared to prometryne toxicity in the absence of PMC, treament of prometryne at 5% PMC reduced prometryne.and thiobarbituric acid reactive substances (TBARS) accumulation in plants, O2- and H2O2 accumulation in leaves, but increased chlorophyll content in leaves. To further understand the putative role of PMC in alleviating prometryne-induced oxidative injury, we measured the activities of several antioxidant enzymes and observed that PMC application decreased the prometryne-induced activities of ascorbate peroxidases, glutathione reductases, glutathione-S-transferases, peroxidase and superoxide dismutase in prometryne-treated seedlings. However, an increased catalase activity was observed in seedling root under the same condition. In this case, PMC probably reduced the oxidative injury by enhanced CAT activities for removal of H2O2. Because excessively accumulated prometryne triggers oxidative damage to plants, the biochemical and molecular responses of several major enzymes and its gene expression were determined. Analysis of SOD, GST and HO-1 using RT-PCR revealed that PMC might mediate detoxification of prometryne at molecular as well as physiological levels in wheat plants. DNA degradation was assayed to confirm the effect of PMC on prometryne-initiated programmed cell death (PCD). Our result indicated that PMC delivers protection against prometrnye injury and prevents DNA fragmentation. Although the mechanism is not fully understood, it is convincingly illustrated by our current study that, PMC amendment is able to mitigate the prometryne-induced toxicity, providing a sound strategy in both agronomic and environmental aspects. |
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