Exposure risk assessment and evaluation of the best management practice for controlling pesticide runoff from paddy fields. Part 1: Paddy watershed monitoring.
Rice pesticide concentrations in surface water along with hydrological balance and water management conditions were investigated in a paddy watershed of about 100 ha at the Sakura river basin in Tsukuba, Japan, for 3 years from April 2002. Monitoring on different hydrological scales ranging from a paddy plot up to a watershed determined the importance of water management associated with rainfall events and the cyclic irrigation for reducing pesticide discharge into aquatic environments. Surface drainage significantly increased as a response to rainfall events greater than about 1.5 cm day(-1). A total of 16 herbicides were detected in the stream water and their peak concentrations mostly occurred from early to mid-May following the pesticide application period. Two water management factors influencing the pesticide runoff from paddy fields were defined: excess water storage capacity (EWSC) and water holding period (WHP). Uncertainty analyses of pesticide discharge from a paddy plot for dymron (daimuron) and imazosulfuron (IMS) were performed using Monte Carlo simulation (MCS) with prescribed probability of rainfall and water management practice from observations over a period of 3 years. Application of an intermittent irrigation scheme with shallow water depth practice and high drainage gate to maintain the EWSC > 2 cm and increasing WHP from the current Japanese Agricultural Chemicals Regulation law of 3-4 days to at least 10 days were recommended for reducing the pesticide runoff from paddy fields in a monsoon region such as in Japan. The combination of good water management in field plots and small-scale water cycling is the best management practice for controlling pesticide discharge from paddy watersheds.
Vu
Son Hong
SH
Tokyo University of Agriculture and Technology, Graduate School of Agriculture, 3-5-8 Saiwaicho, Fuchu, Tokyo 183-8509, Japan.
Ishihara
Satoru
S
Watanabe
Hirozumi
H
D000383:Agriculture / Q000379:methods*; D004784:Environmental Monitoring; D005618:Fresh Water / Q000032:analysis*; D006540:Herbicides / Q000032:analysis; D009010:Monte Carlo Method; D012275:Oryza / Q000254:growth & development; D010575:Pesticides / Q000032:analysis*; D018570:Risk Assessment; D014877:Water Pollution, Chemical / Q000032:analysis / Q000517:prevention & control*
D006540:Herbicides; D010575:Pesticides