Dissipation Of Pretilachlor In Soil And Field Water Analysis

Dissipation of pretilachlor in soil and field water
The dissipation behaviour of pretilachlor from ready mix formulation in paddy grown field soil at all three different doses of application was studied. The mean pretilachlor recovered from the soil and field water at different time intervals from various doses applied treatments are presented in table 4. The amount of herbicide recovered on 0th day (2 hrs after application) was ranged from 104 – 247 µg / kg in soil and 12.2 -13.1 µg / mL in field water at different doses of ready mix application. The pretilachlor residue concentration at different time intervals was influenced by the dose of application and increased with increase in dose of ready mix application. More than 50 % of the initial
This showed that the dissipation of pretilachlor was fast in field water than soil. The dissipation rate was slow at higher rate of 20 kg ha-1 specifically during the later period (on day 15 for soil and 5 for field water) in field water and vice versa in soil. On day 30 after application of ready mix formulation, more than 90 % of the initial concentration of pretilachlor recovered on day 0 in all three treatments, dissipated from soil and then degraded to below the quantification limit on 45th day. However in field water, 68.5 to 73.8 % of pretilachlor residue dissipation occurs on 5th day across different doses of application and then degraded to below the quantification limit of 0.01 µg/g. The rate of pretilachlor dissipation in soil and filed water followed first order degradation kinetics at all the three doses of application and observed a good linear fit of pretilachlor concentration at different intervals against time (Fig 2). The calculated values of degradation rate constant, coefficient of determination (R2) for first order dissipation kinetics and half-lives of pretilachlor in soil and field water at three
Similarly, the residues of both pyrazosulfuron ethyl and pretilachlor were below the detection limits of 0.01 and 0.005 µg / g respectively, in rice grain and straw samples collected from different treatments of 10.0, 12.5 and 20.0 kg ha-1. The high temperature, clayey soil texture and high rain fall and even distribution during the crop growing period (Fig 3) might have enhanced the chemical and microbial degradation of pretilachlor to below 0.01 µg/g. Kaur et al. (2015) reported that the soil physico-chemistry, management practices and climatic conditions largely influenced the pretilachlor dissipation in paddy soil and water. The maximum residue limits (MRL) of both pyrazosulfuorn ethyl and pretilachlor residues in rice grain have not been set by European Union (EU), USDA, WHO / FAO, FFCR, Japan and PMRA, Canada, however the MRL of 0.01 and 0.05 mg/kg respectively in rice grain was set by FSSAI (2011). Similar results were reported by Kaur et al. (2015) for pretilachlor where the residue was below 0.01 mg/kg in rice grain. The major pathway of pretilachlor degradation in rice plant is its conjugation with reduced glutathione by the action of glutathione-S-transferase enzymes which transform the parent molecule into an inactive derivative