Imidacloprid concentrations in paddy rice fields in northern Vietnam: measurement and probabilistic modeling

摘要

Uncertainties associated with pesticide exposure forecasts arise from many sources such as spatial and temporal variability of factors influencing pesticide behavior, inaccuracies in the measurement or estimation of input parameters and deficiencies in model structure. It is well acknowledged that, at least to some extent, simulation uncertainties should be accounted for when technical and political strategies are developed to mitigate pesticide exposure. We monitored the fate of the insecticide imidacloprid in a paddy rice field in Chieng Khoi watershed, Northern Vietnam. Pesticide fate was modeled using a new dynamic model together with the General Likelihood Uncertainty Estimation (GLUE) approach. A 95 % prediction uncertainty (PU) band was computed accounting for uncertainties in pesticide parameters, management practices, and weather conditions. As assessment criterion we used the Nash and Sutcliffe modeling efficiency (NSE). Measured paddy water concentrations of imidacloprid reached up to 53 mu g L-1, paddy soil concentrations up to 9 mu g kg(-1). Calculated PU bands were in good agreement with field measurements. The field-scale model was extended to simulate pesticide fate in connected paddies. Imidacloprid concentrations in the afflux of the stream were estimated to be up to 83 mu g L-1 under the current management practice in the research area. The loss of imidacloprid to the stream was assessed to range between 21 and 68 % of applied mass. Future studies, however, should focus on assessing loads of pesticides further widely used in connected paddies to help decision makers and farmers to adjust management strategies of protecting the environment.