Influence Of Black Carbon On The Adsorption And Phytotoxicity Of Two Ionizable Herbicides

Burning of straw in the field is a common phenomenon in Hunan province and even the whole country of rice-growing area. The black carbon from burning straw could affect the environmental behavior and the bioavailability of pesticides. Herbicide is the most widely used pesticide and most of the herbicide with acidic or alkaline functional groups is ionizable. The influence of black carbon from burning straw on the bioavailability of ionizable herbicides in soil is still unclear.The influence of black carbon on the adsorption charaeteristies of two kinds of weak acid herbicides sulfentrazone and quinclorac was studied, and then the phytotoxicity of sulfentrazone to Oryza sativa L was observed in the amended black carbon soil. To understand the mechanism of black carbon alleviating phytotoxicity of sulfentrazone to O. sativa L, the sulfentrazone concentrations in soil solution was determined by hollow fiber liquid phase microextraction-HPLC. The main results for this study are as follows:1. The Linear equation and the Freundlich equation can be used to fit the adsorption isotherm of two kinds of herbicides in the soil, with R2 more than 0.976. The adsorption of sulfentrazone and quinclorac in Xiaoshan, Zhejiang province, Changsha, Hunan province and Yichun Heilongjiang three typical soil was low adsorption, adsorption coefficient (Kd) of sulfentrazone in three kinds of soil ranged from 0.817 to 2.85L/kg, the Kd of quinclorac ranged from 0.167-1.34 L/kg.2. After amending the black carbon, the adsorption of sulfentrazone and quinclorac in Changsha soil increased significantly. When 1% of black carbon was added in the soil, the Kd of sulfentrazone increased from 1.06 to 6.87 L/kg, Kd of quinclorac increased from 0.382 to 2.63 L/kg.3. The adsorption of sulfentrazone and quinclorac by black carbon and the effect of pH on the adsorption was studied, found Friendrich equation could better fit the adsorption isotherm of sulfentrazone, R2 increases to 0.987 from 0.976, Kfads was133.4 mg1-1/n kg-1 L1/n. Linear equation and Friendrich equation can well fitting adsorption isotherm, Kd was 218.6 L/kg. The Linear equation and Friendrich equation can well fit adsorption isotherm of quinclorac, Kd was 218.6 L/kg. The adsorption of two kinds of herbicides by black carbon decreased with increasing pH.4. After black carbon being added in the aqueous solution and soil, the phytotoxicity of sulfentrazone to O. sativa L alleviated. When 1% of the black carbon was amended in the soil, the phytotoxicity of sulfentrazone to O. sativa L alleviated in all soil. However, the influence of black carbon on the phytotoxicity of sulfentrazone to O. sativa depend on the soil. When 1% black carbon was amended in Xiaoshan, the concentration that inhibits growth by 50% (IC50) increased from 0.22 mg/kg to 1.67 mg/kg, about 6 times was increased. The IC50just increased from 1.85 mg/kg to 2.66 mg/kg, less than a third was increased.5. In order to understand the mechanism of amending black carbon alleviating phytotoxicity of sulfentrazone to O. sativa L depend on the soil, the sulfentrazone concentrations in soil solution was determined by hollow fiber liquid phase microextraction-HPLC. We found that after amending the black carbon in soil, the sulfentrazone concentrations in soil solution reduced differently in different soil, suggesting that the decrease of sulfentrazone concentrations in soil solution resulted in amending black carbon alleviating phytotoxicity of sulfentrazone to O. sativa L depend on the soil.