Byline: KHURAM SHAHZAD AHMAD, NAGHMANA RASHID, MUHAMMAD FAIZAN NAZAR AND SAADIA TAZAIYEN
Summary: A versatile cost-effective Benzimidazole based fungicide, Carbendazim (methyl 1H- benzimidazole-2 carboxylate ) has been utilized to investigate its sorption-desorption behaviour on physicochemical properties of geographical soils, ranging from hilly to desert areas of Pakistan, via batch equilibrium method. The data obtained in all tests showed that adsorption co-efficient isotherm for Carbendazim in four tested soil were well fitted the freundlich equation. Distribution co-efficient (Kd ) parameters are low (3.59 to 11.60 ml ug-1) indicating low adsorption. It was observed that Carbendazim showed a relatively greater degree of adsorption on soil samples (Soil 4) that were collected from northern hilly areas Ayubia, Khyber Pakhton khaw (KPK) (Silt loam) i.e.11.60 ml ug-1 and least adsorption on sandy Soil of Multan Punjab(Soil 2). While other two soils 1 were collected from Murree region, a boarder of Punjab and KPK mountain area and Soil 3 from Tarnol, Islamabad.
Desorption studies reveal that the adsorbed fungicide is firmly retained by soil particles and their adsorption are almost irreversible. The results indicate that soil organic matter (SOM) and appropriate pH also play key role in sorption capacity.
Keywords: Carbendazim, sorption, desorption, physicochemical properties, soil organic matter.
Owing to dynamic agricultural applications, pesticides are playing central role in the challenges to increase food production and control vegetation growth phenomena but over recent years the contaminations of soils and ground water by pesticides have been recognized as an important environmental issue . To avoid hazardous effects and to preserve the environment, it now becomes important to know the fate of individual pesticides in the natural environment . Understanding about the sorption behavior of pesticides in soils, to predict their bio-efficacy and persistence, is an important factor to govern the migratory behavior of these pesticides in soils and ground water which may also influence their uptake and metabolism by plants or microorganisms or other organisms present in the soil . The phase distribution of pesticides in soil is determined by the nature and amount of adsorptive soil components and the physiochemical characteristics of the pesticides .
The pesticides have a number of physicochemical properties, however the most important for adsorption- desorption studies are the electronic structure and their water solubility. It is known that the sorption of pesticides by soil is governed by various intermolecular interactions including Vander-Waals forces, hydrogen bonding, charge transfer, ligand exchange, direct and induced ion-dipole and dipole- dipole interaction and chemisorptions . The soil components that control adsorption are the clay particles, amorphous mineral matter and the soil organic matter.
The sorption mechanism to explain the binding of non ionic pesticides to the soil components exclusively depended on the chemistry of pesticides and the nature and properties of the soil components [6, 7]. Generally, binding by physical sorption is reversible whereas binding by chemisorption is irreversible. However, an apparent irreversibility or "hysteresis" in desorption of a solute from a sorbent may be caused by failure to reach equilibrium during desorption and...
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