Evaluation of a field scale agricultural nonpoint source simulation model against field experiment data is an important step that must be considered before a model can be used as a management tool. Field soil water content and metribuzin residue adsorbed in soil profile were intensively monitored and measured by the gravimetric method and the LC-MS/MS method, respectively, for a soybean field plot located at the Asian Institute of Technology, Thailand. The Root Zone Water Quality Model (RZWQM) was evaluated based on laboratory-measured soil hydraulic properties and pesticide residue in Bangkok clay soil. Reasonable agreement exists between the soil water content measured and predicted by RZWQM for 10–20 and 30–40 cm soil depths. The model slightly overestimated the pesticide residue at 0–10 cm soil depth 1 day after application at surface, whereas pesticide residue at 10–20 and 30–40 cm soil depths was in agreement with model acceptance. These results indicate that RZWQM can be used when properly calibrated to predict the movement of water and metribuzin through the soil profile in the tropical zone.

The present work describes the application of an analytical procedure, utilizing ultra performance liquid chromatography (UPLC) coupled with mass spectrometry instrumentation, for the determination of 253 multiclass pesticides, classified in six different groups. Solid phase extraction was applied for the isolation and pre-concentration of target compounds in water samples. Surface waters of the lakes located in Northern Greece (Volvi, Doirani, and Kerkini), were collected in two time periods (fall/winter 2010 and spring/summer 2011) and analyzed, applying the developed analytical methods. Spatial distribution of detected pesticides was visualized using interpolation methods and geographical information systems (GIS). Pesticides with maximum concentrations were amitrole, propoxur, simazine, chlorpyrifos, carbendazim, triazophos, disulfoton-sulfone, pyridaben, sebuthylazine, terbuthylazine, atrazine, atrazine-desethyl, bensulfuron-methyl, metobromuron, metribuzin, rotenone, pyriproxyfen, and rimsulfuron. In Lake Kerkini, mainly carbamates and triazines were determined at elevated concentrations, near the coastal point of the NW side of the lake. Seasonal variations were strong among the applied pesticide classes and determined concentrations, indicating the contribution of pesticide application patterns and rainfall. Lake Doirani exhibited organophosphate pesticides at higher concentrations mainly at coastal points, while triazines emerged as the main pollutant during spring sampling. Lake Volvi exhibited the highest pesticide concentrations, mostly triazines and ureas at the central part of the lake. The occurrence of extreme values and nonconstant seasonal variations indicated that the concentrations were increased disproportionately during the second sampling, as a result of the varying contribution of pollution sources right after the application period. In all cases, the total concentration of pesticides increased during the second sampling period.