Adsorption Of Diazinon Research Articles

COUPLING DIAZINON VOLATILIZATION AND WATER EVAPORATION IN UNSATURATED SOILS: I. WATER TRANSPORT

Volatilization of pesticides from soil is one of the key processes causing transport of chemicals to non-target areas. This study focuses on how water transport in the surface soil affects volatilization of pesticides. Volatilization of soil-incorporated diazinon [O, O diethyl O-(2-isopropyl-4-methyl-6-pyrimidinyl) phosphorothioate] was measured under different initial soil-water contents and soil-water evaporation conditions. These conditions were varied by passing wet air and dry N2 alternately across the soil surface. When dry sweep gas (N2) was used in high initial water content columns, diazinon volatilization was accelerated as a result of appreciable upward water flow. When upward water flow was insufficient to meet evaporative demand, soil-water content at the soil surface was quickly reduced below a threshold, and diazinon volatilization started to decrease exponentially because of diazinon adsorption on the dry soil surfaces. When the sweep gas was switched to humidified air, the soil surface adsorbed water and diazinon volatilization increased dramatically. A numerical model was developed to simulate pesticide transport in soil for isothermal conditions. The calculated and measured diazinon volatilization fluxes agreed well, but the model overestimated diazinon concentrations in the deeper depths of the soil significantly.

Diazinon leaching through a sandy soil amended with different humic materials

The water leaching of diazinon (O,O‐diethyl‐O‐2‐isopropyl‐6‐methylpyrirnidin‐4‐yl phosphoroth‐ioate) through soil columns, was studied after column amendments with two well characterized humic acids (HA), in both liquid and solid state, and with the original raw organic materials, an oxidized coal and a leonardite, from which the HA were extracted. The percolation curves and the pesticide distribution over the soil columns showed that the addition of the raw organic materials and the solid HAs reduced significantly the mobility of the pesticide along the soil column. The oxidized coal was more effective than the leonardite original material; the different origin of the two carbon‐rich materials had an influence on the diazinon movement along the soil columns and such difference was enhanced with increasing addition rates. Moreover, incubation at field capacity for two months of the soil columns treated with raw oxidized coal and leonardite, largely enhanced the described effects on pesticide behaviour. A complete adsorption of diazinon on columns and a practical absence of leaching was observed when the HA from both materials were added in dissolved form. These results were explained with the swelling of the humic micelles in water and the enhanced availability of inner hydrophobic surfaces for the strong adsorption of diazinon. The water diffusion into the solid humic materials after two months incubation, also explains their high pesticide retention capacity. This work indicates the usefulness of either solid o dissolved humic substances, with the proper hydrophobic character, in preventing the vertical leaching of non‐polar organic pesticides in soils.

Adsorption Kinetics of Diazinon at the Air−Water Interface

The adsorption kinetics of diazinon is studied by using pendant bubble tensiometry enhanced by video digitization. The relaxations in surface tension for two types of processes were measured: the adsorption onto an initially clean air−water interface and the desorption out of a suddenly compressed interface that is originally at equilibrium. The adsorption of diazinon onto a clean air−water interface is verified to be a diffusion-controlled process. A diffusion coefficient was computed by comparing these adsorption profiles with numerical solutions of the bulk surfactant diffusion equation and the Langmuir equilibrium adsorption isotherm. The reequilibration of a compressed interface agrees well with a diffusion-controlled process. Lower bounds on the kinetic constants for the sorption process are inferred for diazinon by comparing numerical solutions of mixed diffusion and surface kinetic transfer with the desorption relaxation data. Problems of decomposition of diazinon and the sudden shrinkage of the ...

Effect of organic cosolvents on adsorption of organophosphorus pesticides by soils

A study was conducted to describe the adsorption and mobility of diazinon and acephate in soils from aqueous medium and mixtures of methanol-water and hexane-water. Pesticide adsorption from aqueous system was related to organic matter content ( viz. diazinon), and to content and composition of clay mineral fraction ( viz. acephate). In the methanol-water systems, the adsorption of diazinon and acephate by soils decreases. In the hexane-water mixtures the adsorption of diazinon decreases, whereas the adsorption of acephate increases.

In vitro and in vivo adsorption studies of diazinon.

The in vitro and in vivo adsorption of diazinon to two brands of activated charcoal and locally produced carbon black (N220) has been studied. Solutions of diazinon 10, 20 and 40 micrograms ml-1 were prepared in distilled water and different quantities of adsorbent added. Diazinon-adsorbent slurries were vortex mixed, centrifuged and analysed for free diazinon spectrophotometrically at 241 nm. Small quantities of activated charcoal (AC) and carbon black (CB) showed little or no adsorption of diazinon, while 1000 mg of either AC or CB was able to take up more than 70% at all concentrations of diazinon tested. In acute toxicity tests in mice the optimal adsorbent: diazinon ratio was 8:1 when the animals were treated with 45 mg kg-1 diazinon after immediate, 1, and 3 h post administration of the adsorbent.