2.2. Field Experiment Design

Field experiments including the degradation dynamics and final residues in supervised field trials were conducted in Chongqing municipality in 2017 (Table 1). All the experiments were designed based on the “Guidelines on pesticide residue trials (NY/T 788-2004)” published by the Institute for the Control of Agrochemicals, Ministry of Agriculture and Rural Affairs of the People’s Republic of China [36]. The area of the field experiment plot was 30 m² and each treatment had three replicated plots. Furthermore, a buffer area was designed to isolate the experiment plots.

The location of experimental plots.

The degradation dynamics experiments were conducted with two dosage levels, pyrazosulfuron-ethyl (22.5 g a.i.ha⁻¹, the recommended dosage and 45 g a.i.ha⁻¹, double of the recommended dosage), bensulfuron-methyl (26.2 g a.i.ha⁻¹, the recommended dosage and 52.4 g a.i.ha⁻¹, double of the recommended dosage), acetochlor (52.5 g a.i.ha⁻¹, the recommended dosage and 105 g a.i.ha⁻¹, double of the recommended dosage) and butachlor (112.4 g a.i.ha⁻¹, the recommended dosage and 224.8 g a.i.ha⁻¹, double of the recommended dosage), respectively. All the four herbicides were sprayed one time after rice transplanting. Representative 2 kg paddy soil and 500 mL water samples were collected randomly in each plot at 0 (2 h post-treatment), 5, 10, 20, 30, 40, 80 days and pre-harvest interval (PHI) of 7 days after herbicides application. The representative 2 kg rice samples were randomly collected at pre-harvest interval (PHI) of 7 days. All the collected paddy soil, water, and rice samples were stored at −20 °C, respectively.