Comparison between Polar Organic Chemical Integrative Sampler (POCIS) and Grab Samples to Estimate Time-Weighted Average Concentrations of Paddy-Use Pesticide Residue in Stream Water

In this study, the application of the polar organic chemical integrative sampler (POCIS) for the time-weighted average concentration (TWAC) of paddy-use pesticides in environmental water was evaluated. Two herbicides and one fungicide were selected and investigated by deploying POCIS and high-frequency grab sampling (more than two times per day) in three paddy drainage canals (2.8–70 ha) and one river in the Lake Biwa basin for 7–21 day periods. TWACs determined by POCIS and by high-frequency grab samples showed good agreement, and 11 of 14 datasets (79% of all datasets) were within the range of 0.5–2.0-fold difference. To generate estimates of TWAC at different sampling intervals, the high-frequency grab sampling data were subsampled at intervals of 1, 2, 3, 4, and 7days. On the basis of the comparison of TWACs between POCIS and different grab sampling intervals, it is considered that the sampling interval that yields equivalent TWACs to those of POCIS was more than once a week in datasets with low CVs of pesticide concentration (CV ≦ 100%),but more than three day intervals in databases with high CVs.