Environmental Behaviour And Bioavailability Of Cycloxaprid

Degradation, fate and bound residues of pesticides in the soil are important to assess the factors related to the long-term environmental risk. Cycloxaprid (CYC) is a self-dependent candidate neonicotinoid for agricultural pest control in our country. CYC is unique in having two enantiomers. In this thesis, on the basis of isotoping labeling technology, the degradation, fate characteristics, bound residues formation and bioavailability of CYC were systematically investigated, especially in terms of different behavior between its two enantiomers. All results provide theoretical guidance of CYC for safe, reliable, scientific and rational use. This approach also may be similarly applied to other pesticides in improving the understanding of their fate in environmental matrices.1) Investigation on degradation of CYC in soil:The incubation experiment, using 14C-5S8R-CYC, 14C-5R8S-CYC and 14C-racemic-CYC in four flooded and anaerobic soils were performed. Most of CYC had been transformed in four soils at 5 days after treatment. During the incubation period, CYC was found converted to a range of degradation products (TP 1-TP 12). Liquid scintillation counting with LC-MS/MS was used to identify and quantify the major degradation products of CYC enantiomers. Dynamic changes of degradation products identified in four soils were analyzed. However, abiotic or biotic stereoselective persistence of TPs in all soils was not observed from the experimental data. Cleavage of the oxabridged seven-member ring, reductive dechlorination in the chloropyridinyl and cleavage of C-N between the chloropyridinylmethyl and imidazalidine ring are the main degradation pathways of CYC.2) Investigation on fate and mobility of CYC in soil:The soil treated with CYC was incubated under anaerobic and flooded condition. It was observed that CYC intended to move down to the soil layer over time. After 100 day, the ratios between bound residues and extractable residues of CYC were between 1.11 and 4.12. The formation of BR was greatly affected by soil properties. The high radioactivity of 14C-CYC in the water phase (> 60% of total extractable residues) suggested that CYC residues under the experimental condition were readily available for leaching or offsite transport. Stereoselective behaviors between CYC enantiomers under flooded and anaerobic condition were not observed. The fraction of bound residues of 14C-C YC individual enantiomers in yellow loamy soil exceeded the risk assessment threshold of 70%. However, it is still unclear whether the BR of the single CYC enantiomer could be subsequently released, and if so what its availability and phytotoxic effects would be.3) Investigation on bioavailability of CYC bound residues in soil:Earthworms, model organisms for bioaccumulation in the food chain, lived in the soil-bound residues for 28 d. All earthworms survived the exposure to the treatments. And there were no differences in the weights of the earthworms between the CYC exposure group and blank control groups. This indicated that the risk of expose of CYC bound residues to earthworms was limited. In addition, 11-25% of the previously bound radioactivity in soil was extractable by solvent, mineralized to CO2. In addition,14C radioactivity was observed in the earthworms. This indicated that, under the environmental conditions, the CYC bound residues were released and bioavailable. The bound radioactivity in the earthworms increased rapidly and almost achieved stable states after 10 d of exposure, accounting for 32% of the total radioactivity. In contrast, the extractable radioactivity in the earthworms accounted for 70% of the total radioactivity. The biota-sediment accumulation factor (BSAF) was fitted well to the two-compartment accumulation model. The BSAF values ranged from 0.59 to 0.97. Compared to the BSAFs of some toxic pollutants in soil, the calculated BSAFs of CYC were rather low. This indicated that the bioavailability of CYC was rather low, and the influence of CYC bound residues on terrestrial organisms was limited. The elimination of CYC from earthworms was dominated by bound radioactivity and extractable radioactivity. The elimination of CYC individual enantiomers from M. guillelmi was fitted to an availability-adjusted decay model with a half-life of eight d. Stereoselective release or bioavailability between CYC enantiomers was not observed.4) Investigation on synthesis and insecticidal evaluation of fused heterocyclic cis-nitromethylene neonicotinoids derivatives:Through the activated intermediate containing oxazolone moiety prepared by PerKin reaction, a series of novel tetrahydroimidazo[1,2-a]pyridin-5(1H)-one derivatives were synthesized. All these compounds were comfirmed by NMR and HRMS specctroscpy. Some compounds exhibited moderate activity against brown planthopper (Nilaparvata lugens) at 500 mg L-1.