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Research Project: Integrated Field Scale Management Systems for the Use of Degraded Waters

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Title: Specific surface area effect on adsorption of chlorpyrifos and TCP by soils and modeling

Author
item TURELI, FUNDA - The General Directorate Of Agrarian Reform
item OK, SONAY - Ankara University Of Turkey
item Goldberg, Sabine

Submitted to: Soil and Sediment Contamination: An International Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2014
Publication Date: 10/21/2014
Citation: Tureli, F.C., Ok, S.S., Goldberg, S.R. 2014. Specific surface area effect on adsorption of chlorpyrifos and TCP by soils and modeling. Soil and Sediment Contamination: An International Journal. 24(1):64-75.

Interpretive Summary: Organophosphate pesticides such as chlorpyrifos are extremely toxic to humans and wildlife. Toxic concentrations can occur in agricultural soils. A better understanding of the adsorption behavior of this compound and its degradation product TCP is necessary. Adsorption of chlorpyrifos and TCP by four soil samples belonging to four different soil orders was investigated under changing conditions of solution concentration. The adsorption behavior was evaluated and described using a chemical surface complexation model. Our results will benefit scientists who are developing models of chlorpyrifos and TCP movement in soils. The results can be used to improve predictions of chlorpyrifos and TCP behavior in soils and thus aid action and regulatory agencies in the management of soils which contain elevated concentrations of these compounds.

Technical Abstract: The adsorption of chlorpyrifos and TCP (3,5,6, trichloro-2-pyridinol) was determined in four soils (Mollisol, Inceptisol, Entisol, Alfisol) having different specific surface areas (19–84 m2/g) but rather similar organic matter content (2.4–3.5%). Adsorption isotherms were derived from batch equilibration experiments at 25°C. After liquid-liquid extraction, the chlorpyrifos and TCP concentrations in the solution phase were determined by gas chromatography with an electron capture detector. Adsorption coefficients were calculated using the Freundlich adsorption equation. High KF coefficients for chlorpyrifos (15.78) and TCP (6.54) were determined for the Entisol soil, while low KF coefficients for chlorpyrifos (5.32) and TCP (3.93) were observed in the Alfisol soil. In all four soils, adsorption of chlorpyrifos was higher than that of TCP. A surface complexation model, the constant capacitance model, was well able to fit the adsorption isotherms of both chlorpyrifos and TCP on all four soils. The results showed that specific surface area affected adsorption of both chlorpyrifos and TCP. Among the soil properties, specific surface area could be a better indicator than organic matter content alone for adsorption of chlorpyrifos and TCP by soils that contained low organic matter.