Development and validation of an HPLC-DAD method for the simultaneous determination of most common rice pesticides in paddy water systems

Rice crop is mainly cultivated in large river basins which constitute unique ecosystems and their ecological quality is invaluable. However, the high loads of pesticides used in rice cultivation contribute to the contamination of the water resources in such rice-cultivated regions. To regularly monitor the quality of such water resources there is a need for a rapid and sensitive multi-residue analytical method. This study presents the development and validation of a new analytical method for the simultaneous determination of most rice pesticides including penoxsulam, tricyclazole, propanil and its main metabolite 3,4-dichloroaniline, azoxystrobin, molinate, profoxydim and deltamethrin. A solid-phase extraction (SPE) procedure followed by high performance liquid chromatography (HPLC) with diode array detection (DAD) was used. A C-18 RP column operated at 30 degrees C was utilised and the analytes were separated with a mobile phase of acetonitrile/water mixture in a linear gradient. Clean-up of water samples and isolation of pesticides was performed on SPE Bakerbond octadecyl cartridges and an ethyl acetate-dichlomethane mixture (9 : 1 v/v, 2 mL) was used for elution. Method validation was performed by means of intra-day (n = 5) and inter-day accuracy and precision (n 8), sensitivity and linearity. The relative recoveries of the pesticides in paddy water samples were acceptable (80.6-110.2%) and the relative standard deviation (RSD%) ranged from 1.9 to 7.6%. Limits of detection (LOD) and limits of quantification (LOQ) varied from 0.1 to 0.8 ng mL(-1) and 0.25 to 2.0 ng mL(-1) respectively, depending on the analyte. The method was subsequently applied for the determination of pesticide residues in paddy and canal water samples. Tricyclazole was the most frequently detected pesticide at the highest concentrations, while herbicides were less frequently detected and at lower concentrations. The method described could be a valuable tool for regular monitoring of surface water systems in rice-cultivated basins

Laboratory and field dissipation of penoxsulam, tricyclazole and profoxydim in rice paddy systems

Rice cultivation relies on pesticide applications to ensure high yields. However, the regular use of pesticides seriously affects the quality of neighboring surface water systems. Thus complete knowledge of the environmental fate and dissipation of pesticides in the paddy rice environment should become available. So far only a few studies have provided comprehensive assessment of the dissipation of pesticides under the submerged cultivation conditions followed in rice. Thus, laboratory and 2-year field studies were performed to assess the dissipation of two new generation rice herbicides (penoxsulam and profoxydim) and one of the most important rice fungicides (tricyclazole). A good agreement between laboratory and field experiments was observed with a faster dissipation of penoxsulam and tricyclazole under field conditions. Profoxydim was the least persistent chemical (DT50 soil < 1d; DT50 water 0.5-1.2 d), followed by penoxsulam which persisted for longer particularly in the water compartment (DT50water = 3.8-5.9 d). Tricyclazole was the most persistent pesticide, especially in the soil compartment with DT50 values of 44.5-84.6 (field) and 197 d (laboratory). These results could be utilized for the assessment of the environmental risk associated with the use of those pesticides in rice cultivation and the determination of potential mitigation measures for minimizing the risk for contamination of neighboring natural water resources. (C) 2013 Elsevier Ltd. All rights reserved