Sorption and leaching behavior of hexaconazole as influenced bysoilproperties

Sahid

et al. 2016

Turkish JAF Sci.Tech.

The effect of temperature and pH on adsorption-desorption of fungicide hexaconazole was studied in two Malaysian soil types; namely clay loam and sandy loam. The adsorption-desorption experiment was conducted using the batch equilibration technique and the residues of hexaconazole were analysed using the GC-ECD. The results showed that the adsorption-desorption isotherms of hexaconazole can be described with Freundlich equation. The Freundlich sorption coefficient (K d ) values were positively correlated to the clay and organic matter content in the soils. Hexaconazole attained the equilibrium phase within 24 h in both soil types studied. The adsorption coefficient (Kd) values obtained for clay loam soil and sandy loam soil were 2.54 mL/g and 2.27 mL/g, respectively, indicating that hexaconazole was weakly sorbed onto the soils due to the low organic content of the soils. Regarding thermodynamic parameters, the Gibb's free energy change (ΔG) analysis showed that hexaconazole adsorption onto soil was spontaneous and exothermic, plus it exhibited positive hysteresis. A strong correlation was observed between the adsorption of hexaconazole and pH of the soil solution. However, temperature was found to have no effect on the adsorption of hexaconazole onto the soils; for the range tested. Keywords:Hexaconazole Adsorption Desorption Freundlich Kinetic IntroductionAdsorption and desorption are the main processes that affect the mobility, persistence, degradation, transport, and dissipation of pesticides and contaminants in the soil. Understanding the effects of these processes is important in order to obtain early information for predicting the environmental behaviour of pesticides and contaminants. Adsorption is a process in which the pesticide forms chemical bonds with colloidal materials such as soil organic matter and clay particles (Wauchope et al. 2002). Pesticide soil/solution distribution coefficients (K d values), commonly referred to as pesticide soil sorption values, are used to predict soil mobility of the compounds (Weber et al. 2004).Investigations on adsorption-desorption phenomena of pesticides in soil have been reported for various soil types (Liu et al. 2010, Singh and Singh 2015, Rani and Sud 2015. It has been shown that adsorption and desorption of pesticides in soils depend on soil properties such as pH, organic matter/clay content, chemical properties of the pesticide, and the environment Maznah 2006, Rani andSud 2015). Aside from organic matter and clay content, the adsorption process is influenced by the size, shape, configuration, molecular structure, chemical functions, solubility, polarity, environmental temperature, and acid-base nature of the pesticide molecule itself (Arias-Estevez et al. 2006, Wauchope et al. 2002.The effect of pH on the adsorption of pesticides depends on the soil composition and the characteristics of the compound (Kah and Brown 2006). The pH related dependence of sorption is partly derived from the different proportions of ionic and neutral forms of the pesticide pre...

Section: Adsorption-desorption Studiessupporting

confidence: 82%

Section: Discussionmentioning

confidence: 99%

Section: Adsorption-desorption Studiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Adsorption-Desorption of Hexaconazole in Soils with Respect to Soil Properties, Temperature, and pH

Maznah

Sahid

et al. 2016

Turkish JAF Sci.Tech.

“…However, some work has been published on degradation of hexaconazole in peaches and in model systems (Angioni et al 2003), dissipation in vegetables (Han et al 2013), and effect of bio-compostamendment (Singh and Dureja 2009). Other published works have reported on the persistence of hexaconazole in several soil conditions (Singh and Dureja 2000), sorption and leaching behavior (Sharma et al 2013), photodegradation of hexaconazole in solvent (Santoro et al 2000), and leaching potential and mobility in soil (Fenoll et al 2010;Singh 2005).…”

Section: Introductionmentioning

confidence: 97%

Dissipation of the fungicide hexaconazole in oil palm plantation

Maznah

Sahid

et al. 2015

Environ Sci Pollut Res

Hexaconazole is a potential fungicide to be used in the oil palm plantation for controlling the basal stem root (BSR) disease caused by Ganoderma boninense. Therefore, the dissipation rate of hexaconazole in an oil palm agroecosystem under field conditions was studied. Two experimental plots were treated with hexaconazole at the recommended dosage of 4.5 g a.i. palm(-1) (active ingredient) and at double the recommended dosage (9.0 g a.i. palm(-1)), whilst one plot was untreated as control. The residue of hexaconazole was detected in soil samples in the range of 2.74 to 0.78 and 7.13 to 1.66 mg kg(-1) at the recommended and double recommended dosage plots, respectively. An initial relatively rapid dissipation rate of hexaconazole residues occurred but reduced with time. The dissipation of hexaconazole in soil was described using first-order kinetics with the value of coefficient regression (r (2) > 0.8). The results indicated that hexaconazole has moderate persistence in the soil and the half-life was found to be 69.3 and 86.6 days in the recommended and double recommended dosage plot, respectively. The results obtained highlight that downward movement of hexaconazole was led by preferential flow as shown in image analysis. It can be concluded that varying soil conditions, environmental factors, and pesticide chemical properties of hexaconazole has a significant impact on dissipation of hexaconazole in soil under humid conditions.

Mobility Studies of 14C-Chlorpyrifos in Malaysian Oil Palm Soils

Bull Environ Contam Toxicol

Ismail

Mat

et al. 2015

The mobility of (14)C-chlorpyrifos using soil TLC was investigated in this study. It was found that chlorpyrifos was not mobile in clay, clay loam and peat soil. The mobility of (14)C-chlorpyrifos and non-labelled chlorpyrifos was also tested with silica gel TLC using three types of developing solvent hexane (100%), hexane:ethyl acetate (95:5, v/v); and hexane:ethyl acetate (98:2, v/v). The study showed that both the (14)C-labelled and non-labelled chlorpyrifos have the same Retardation Factor (Rf) for different developing solvent systems. From the soil column study on mobility of chlorpyrifos, it was observed that no chlorpyrifos residue was found below 5 cm depth in three types of soil at simulation rainfall of 20, 50 and 100 mm. Therefore, the soil column and TLC studies have shown similar findings in the mobility of chlorpyrifos.