Exposure risk assessment and evaluation of the best management practice for controlling pesticide runoff from paddy fields. Part 2: model simulation for the herbicide pretilachlor.
BACKGROUND
Monitoring studies revealed high concentrations of pesticides in the drainage canal of paddy fields. It is important to have a way to predict these concentrations in different management scenarios as an assessment tool. A simulation model for predicting the pesticide concentration in a paddy block (PCPF-B) was evaluated and then used to assess the effect of water management practices for controlling pesticide runoff from paddy fields.


RESULTS
The PCPF-B model achieved an acceptable performance. The model was applied to a constrained probabilistic approach using the Monte Carlo technique to evaluate the best management practices for reducing runoff of pretilachlor into the canal. The probabilistic model predictions using actual data of pesticide use and hydrological data in the canal showed that the water holding period (WHP) and the excess water storage depth (EWSD) effectively reduced the loss and concentration of pretilachlor from paddy fields to the drainage canal. The WHP also reduced the timespan of pesticide exposure in the drainage canal.


CONCLUSIONS
It is recommended that: (1) the WHP be applied for as long as possible, but for at least 7 days, depending on the pesticide and field conditions; (2) an EWSD greater than 2 cm be maintained to store substantial rainfall in order to prevent paddy runoff, especially during the WHP.
Department of Bioproduction Environmental Sciences, Faculty of Agriculture, Kyushu University, Higashi-ku, Fukuoka, Japan.
Thai Khanh
TK
Phong
Son Hong
SH
Vu
Satoru
S
Ishihara
Kazuaki
K
Hiramatsu
Hirozumi
H
Watanabe
D000083:Acetanilides / Q000032:analysis* / Q000737:chemistry; D057914:Agricultural Irrigation; D004784:Environmental Monitoring; D004785:Environmental Pollutants / Q000032:analysis* / Q000737:chemistry; D004787:Environmental Pollution / Q000032:analysis / Q000517:prevention & control*; D008962:Models, Theoretical; D009010:Monte Carlo Method; D010575:Pesticides / Q000032:analysis* / Q000737:chemistry; D018570:Risk Assessment
D000083:Acetanilides; D004785:Environmental Pollutants; D010575:Pesticides; C118050:pretilachlor