Fate and transport of bensulfuron-methyl and imazosulfuron in paddy fields: experiments and model simulation

Abstract

Experiments were conducted to determine the fate of bensulfuron-methyl (BSM) and imazosulfuron (IMS) under paddy conditions. Initially, laboratory experiments were conducted and the photolysis half-lives of the two herbicides were found to be much shorter than their hydrolysis half-lives in aqueous solutions. In the aerobic water-soil system, dissipation followed first-order kinetics with water half-lives of 9.1 and 11.0 days and soil halflives of 12.4 and 18.5 days (first phase) and 35.0 and 44.1 days (second phase) for bensulfuron-methyl and imazosulfuron, respectively. However, the anaerobic soil halflives were only 12.7 and 9.8 days for BSM and IMS, respectively. The values of K d were determined to be 16.0 and 13.8 for BSM and IMS, respectively. Subsequent field measurements for the two herbicides revealed that dissipation of both herbicides in paddy water involved biphasic first-order kinetics, with the dissipation rates in the first phase being much faster than those in the second phase. The dissipation of bensulfuron-methyl and imazosulfuron in the paddy surface soil were also followed biphasic firstorder kinetics. These results were then used as input parameters for the PCPF-1 model to simulate the fate and transport of BSM and IMS in the paddy environment (water and 1-cm surface soil layer). The measured and simulated values agreed well and the mass balance error during the simulation period was -1.2 and 2.8% of applied pesticide, respectively, for BSM and IMS.

Analysis of parameter uncertainty and sensitivity in PCPF-1 modeling for predicting concentrations of rice herbicides

“…Since the results of sensitivity analyses depend on the base-case scenarios, 30) four di erent scenarios consisting of the case of four herbicides, mefenacet, 5) pretilachlor, 6) bensulfuron-methyl and imazosulfuron 7) were used in this study. PCPF-1 was previously validated with these four compounds with the actual data sets of water balance and chemical parameters taken from monitoring and experimental studies at the National Institute for Agro-Environmental Sciences (NIAES) in 1998, in Tsukuba, Japan.…”

“…e parameter median values of the four pesticides were extracted from previous validation studies using the PCPF-1 model. [5][6][7]43) Normal distributions were attributed to the bulk density 38) as well as the 1st-order dissolution rate and the 1st-order desorption rate constants.…”

“…3a, c) resulting from high equilibrium partitioning coe cient values, 24.07 L/kg and 34.8 L/kg, respectively. 5,7) When studies focus on the PSL concentrations which are calculated several DAHA, parameters that require careful determinations are primarily those related to mass partitioning (Oc, θ Sat-PSL , ρ b-PSL ) and, secondarily k BIOCHEM-PSL .…”

“…3,4) PCPF-1 is a mathematical model which calculates the pesticide concentrations in paddy water and paddy-surface soil at a depth of 1 cm. It has been validated with four rice herbicides, mefenacet, 5) pretilachlor, 6) bensulfuron-methyl and imazosulfuron, 7) (MF, PTC, BSM, and IMS) with monitoring data under the typical paddy conditions used in Japanese rice elds. e PCPF-1 model has been mainly used to evaluate the best management practices in controlling pesticide discharges from paddy elds.…”

Herbicide discharge from rice paddy fields by surface runoff and percolation flow: A case study in paddy fields in the Lake Biwa basin, Japan

“…Previous reports [31][32][33][34] showed that the elimination rate constant of herbicide concentrations in paddy water was assumed to follow biphasic first-order kinetics; an initial rapid-elimination phase followed by a second, slow-elimination phase. In the current study, the turning points between the two phases for herbicides were set to 10 days after application.…”