The Effects Of Interaction Between Cadmium And Bensulfuron-methyl On Their Environmental Behavior

The herbicide bensulfuron-methy (BSM) were widly used in rice field and the typical heavy metal Cd was selected as materials in the present study. The effects and mechanism of interaction between cadmium and bensulfuron-methyl on their environmental behavior were studied, including effects of interaction between cadmium and bensulfuron-methyl on the adsorption and desorption for each other on soil and clay minerals; effects of bensulfuron-methyl on Cd forms transformation in soil; degradation characteristic of bensulfuron-methyl in soil with applying bensulfuron-methyl for several years and biological characteristic of in such soil; differences of degradation characteristic of bensulfuron-methyl in distilled water and lake water; effects of Cd on degradation characteristic of bensulfuron-methyl in water and biological degradation characteristic of bensulfuron-methyl in soil; effects of combination of cadmium and bensulfuron-methyl on the ecological toxicity to soil microbial biomass phospholipd content, soil phosphatase activity, soil urease activity, soil dehydrogenase activity, soil protein content and soil phenol content under different environmental condition(the soil temperature, pH, the moisture content). The results were shown as follows:1. Cd or BSM would enhance the affinity and isotherm adsorbed amount of BSM or Cd on soil and soil claymiaerals. Cd's isotherm adsorption data on soil and soil claymiaerals, with or without the presence of BSM, was well fitted to Freundlich equation with coefficient r~2>0.98. At the same time, BSM's isotherm adsorption data on soil and soil claymiaerals, with or without the presence of Cd, was also well fitted to Freundlich equation with coefficient r2>0.95.2. With the increase of pH, Cd adsorption ratio on soil and soil claymiaerals increased with or without the presence of BSM, but the desorption ratio of corresponding adsorbed Cd decreased. At lower pH (pH<5.4 for soil, pH<5.4 for kaolinite, pH<5.5 for goethite, pH<6.4 for montmorillonite), BSM promoted Cd's adsorption on soil and soil claymiaerals and reduced the desorption ratio of corresponding adsorbed Cd. While at higher pH (pH>5.4 for soil, pH>5.4 for kaolinite, pH>5.5 for goethite, pH>6.4 for montmorillonite), BSM reduced the adsorption of Cd on soil and soil claymiaerals and increased the desorption ratio of corresponding adsorbed Cd. The strength of corresponding effects increased with the increas of BSM's concentration..3. With or without the presence of Cd, with the increasing of pH, BSM's adsorption ratio on soil and soil claymiaerals decreased, as well as the desorption ratio of corresponding adsorbed BSM increased. Cd promoted BSM's adsorption on soil and soil claymiaerals in all pH range and reduced the desorption ratio of corresponding adsorbed BSM. The strength of corresponding effects increased with the increase of Cd concentration.4. The change of IR characteristic of kaolinite adsorbed BSM with or without the presence of Cd proved that Cd2+ could promote BSM's adsorption on kaolinite. The mechanism was that N-H group of BSM could come into being hydrogen bound with Si-O-Si and O-H group of kaolinite or chelate with Cd2+ adsorbed on kaolinite.5. Soluble Cd and exchangeable Cd content would decrease with BSM's concentration increasing, while organic Cd, Cd that be bounded to clays and oxides and residual Cd content would increase with BSM's concentration increasing. This result indicated adding BSM would promote the adsorption of Cd on soil and promote Cd to transform into relatively stable form, i.e. tighten bound form (organic Cd, Cd that be bounded to clays and oxides and residual Cd).6. BSM degradation were well fitted to first order reaction dynamics equation in paddy soil previously treated with this same herbicide under 3 years, 1 year or 0 year, all the coefficient r2 were higher than 0.98. BSM's degradation speed was accelerating with the length of treated previously, and the DT50 (time taken for 50% of the applied pesticide to degrade) of BSM were 6.57. 9.43. 16.01 d in p...