Evaluation Methods Of Thiacloprid Bioavailability In Soil And The Influence Of Biochar

The environmental risk assessment of pesticides has long been mostly based on their total concentration, but ignored the correlation between the total concentration in environmental and the uptake portion by the cretures in siol, which leads to the overestimating of the pesticides’ environmental risks based on the pesticides total concentration determined by those methods. However, the traditional biological method to evaluate the bioavailability wastes time and energy. Therefore, it is very important to develop the chemical evaluation method. Take thiacloprid for example, this thesis applied different chemical evaluation methods to evaluate its bioavailability to earthworm, and explores the effects of biochar on bioavailability through adding different kinds and levels biochar into the soil. Here are the main research results:1. The effect of soil type on toxicity of thiacloprid to earthworms (Eisenia fetida) was observed by fortifying thiacloprid into different types of soils. The result indicated that the soil type has a great influence on the thiaclopris’s toxicity. The median lethal concentrations (LC50) values of thiacloprid to earthworm in different kind of soil ranges from3.39mg/kg to23.06mg/kg, and the variation coefficient is71.58%. The soil organic matter contents were the main factors governing the toxicity of thiacloprid.2. When calculating the LC50in different soil with the concentration obtained by different chemical methods, it showed that the differences of LC50among different soil became smaller as it calculated with ex situ pore water concentrations (CEPW) and in situ pore water concentrations (CIPW) and concentrations extracted by Tenax (OTenax).And, when LC50was calculated with CIPW and CTenax, the variation coefficients were24.15%and27.79%separately, which indicated that the two methods could predict the bioavailability of thiacloprid to earthworm.3. It showed that the adding of biochar has a great influence on the adsorption capacity and linear of thiacloprid in the soil when different kinds and levels biochar were added into the soil. The greatest influence was observed when adding1%BC001to the soil:the Kf value increased from3.26L/kg (no biochar added) to65.53L/kg and1/n decreased from0.90to0.74. What’s more, this effect becomes greater with biochar addition level growing.4. It studied the effect of adding different levels of biochar on the degradation of thiacloprid in soil and found that with the growing of the adding level, the degradation half-life (T1/2) also became longger correspondingly. The T1/2values of the soil containing BC500of0,0.1%,0.5%,1%,2%are14.44,28.88,36.48,53.32,86.64d separately. At the same time, in the soil with little biochar (0.1%), the thiacloprid on the contrary degrades faster than in the soil without biochar at the beginning of the experiment.5. It showed that the adding of biochar has a great influence on the bioaviliablity of thiacloprid when different kinds and levels biochar were added into the soil, and resulting in reducing bioconcentration factor and the uptake concentration of thiacloprid by earthwarm effectively. It also found that it had different rules under different aging time. For example, in the case of60d, the concentration (2.51-3.09mg/kg) of thiacloprid in earthworm in the soil with biochar was higher than that without biochar (0.51mg/kg).