The study of adsorption mechanism of mixed pesticides prometryne-acetochlor in the soil–water system
Introduction
Prometryne (2,4-bis(isopropylamino)-6-(methylthio)-s-triazine), as a selective herbicide of the s-Triazimnes chemical family, has been extensively used for a pre- or post-emergence controller of annual grasses and broadleaf weeds in modern agriculture (Zhou et al., 2009). It is well known that prometryne has been widely used in weed control in wheat, cotton, rice, vegetables and many other crops in China, and the half-life in a natural environment was 13 months (Cao et al., 2007, Liang, 2008). Dikić et al. showed that prometryne induced DNA fragmentation, a hallmark of apoptosis in blood leukocytes (Dikić, D. et al., 2009), and it was not permitted to use in Europe. Furthermore, Acetochlor (2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-Methylphenyl)cetamide) was widely used herbicide all over the world for controlling completive grasses and some broadleaf weeds in corn field. The half-life in a natural environment was 45 months (Feng et al., 2007, Yu et al., 2013). Acetochlor could induce metamorphosis in amphibians (Crump et al., 2002, Li et al., 2009), and have been classified as B-2 carcinogen by the U.S. Environmental Protection Agency (USEPA). The single-dose of prometryne and acetochlor were not only widely used, but also, the mixture of prometryne-acetochlor (PA) had many advantages such as high effect, wide weed control spectrum and low resistance for weeds, which was extensively used in China (Fan et al., 2008, Gong, 2012, Li et al., 2013). Therefore, a key question arises, i.e. how to correctly appraise the environmental chemical action and adsorption mechanism of PA in soil has become increasingly important in modern environmental chemistry.
As the repository for pesticide, adsorption-desorption of pesticide in soil have been considered as one of the major factors in soil-water (Liu et al., 1998). It has been suggested that the soil organic carbon content and clay minerals played a major role in the sorption of pesticide (Mader et al., 1997, SPARK and SWIFT, 2002). Based on adsorption mechanism of pesticide in soil, a good understanding of the existence, migration and transformation of pesticides in soil is needed, which could provide a guide for effective utilization of pesticide. Although the adsorption behaviour of single dose of prometryne and acetochlor on soil have been reported (Yang et al., 2002, Guo et al., 2008), the sorption and mechanism of the mixed prometryne-acetochlor (PA) have not been studied yet. Therefore, the aim of this study is to understand the migration and transformation of PA in soil.
Section snippets
Soils
Four soil samples were collected from Yunnan province in China, and taken from the surface layers (0–15 cm) of cultivated fields. The samples were air dried about 20 days (The moisture content was less than 5%), slag stone being removed and sieved (<2 mm).
Materials and instruments
Humic acid (Biochemical Reagents), its total content of acidic groups is 5.74 mmol/g. Carboxyl content was 4.46 mmol/g. Phenolic hydroxyl content is 1.28 mmol/g. Montmorillonite is prepared according to the previous study (Wang et al., 2008).
Physical and chemical characteristics of soil
The organic matter content, particle size distribution, pH, cation exchange capacity and water content are shown here in Table 1 (seeFig. 1).
Adsorption isotherm
Adsorption isotherms of prometryne-acetochlor on the different soils are shown in Fig. 2 and Fig. 3 respectively. The adsorption isotherms on four soils accord with Freundlich equation. The parameters of the Freundlich equation are listed in Table 2.
As is shown in Table 2, the data was found to be best fit the Freundlich sorption isotherm, and R values of
Acknowledgements
This study was supported by International Education Cooperation Base of Yunnan Minzu University (YMU 218-02001001002129), Key Laboratory of Resource Clean Conversion in Ethnic Region, Education Department of Yunnan Province (117-02001001002107), Joint Research Centre for International Cross-border Ethnic Regions Biomass Clean Utilization in Yunnan, National Natural Scientific Fund (No.31460137).
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These two authors contributed equally to this work.