Sorptive behavior of the phenylamide fungicides, mefenoxam and metalaxyl, and their acid metabolite in typical Cameroonian and German soils

• Published in: Chemosphere (Oxford) Vol. 49; no. 6; pp. 659 - 668
• Main Authors: Monkiedje, Adolphe, Spiteller, Michael
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.11.2002; Elsevier
• Subjects: Absorption; Adsorption; Agronomy. Soil science and plant productions; Alanine - analogs & derivatives; Alanine - chemistry; Alanine - metabolism; Applied sciences; Biological and medical sciences; Biological and physicochemical properties of pollutants. Interaction in the soil; Cameroon; Desorption; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Formulated fungicides; Fundamental and applied biological sciences. Psychology; Fungicides, Industrial - analysis; Fungicides, Industrial - chemistry; Germany; Kinetics; Mathematical Computing; Models, Chemical; Pollution; Pollution, environment geology; Soil and sediments pollution; Soil and water pollution; Soil Pollutants - analysis; Soil science; Soils; Soils; Desorption; Formulated fungicides; Adsorption; Metabolite; Cultivated soil; Tropical zone; Adsorption isotherm; Mobility; Forest soil; Soil pollution; Temperate zone; Metalaxyl; Freundlich isotherm; Lixiviation; Sandy loam soil; Pollutant behavior; Pesticides; Risk analysis; Fungicide; Langmuir isotherm; Sorption; Sandy clay loam soil; Carboxamide; Degradation product
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/S0045-6535(02)00325-9

Laboratory soil sorption experiments were conducted on mefenoxam, formulated metalaxyl (F-metalaxyl), pure metalaxyl (P-metalaxyl) and metalaxyl acid metabolite to elucidate differences in their sorptive behaviour on typical Cameroonian forest soil (sand clay loam, pH 4.8 and 3.01% OC) and German soil (sandy loam, pH 7.2, 1.69% OC) using a batch equilibrium method. The data obtained on all test chemicals conformed to linear and Freundlich adsorption isotherms. The Langmuir equation failed to describe the sorption of the substances tested. All substances were adsorbed to a greater extent by the Cameroonian soil. The average percentage adsorptions for mefenoxam, F-metalaxyl, P-metalaxyl and the acid metabolite on the Cameroonian soil were 27.8%, 28.3%, 31.8% and 46.8% respectively while for the German soil they were 21.7%, 21.5%, 24.7% and 9.8% respectively. The K D and K F parameters and the Freundlich exponential term (1/ n) were low, indicating that the interactions between soil particles and the fungicides were weak. The sorption parameters were lower in the German soil. P-metalaxyl exhibited a higher adsorption capacity than F-metalaxyl in both soils. Mefenoxam and F-metalaxyl exhibited similar sorption parameters in soils, whereas those of P-metalaxyl and acid metabolite differed. Differences observed in the adsorption between the two soils could be attributed to their properties. Desorption studies revealed that the adsorbed fungicides were not firmly retained by soil particles and their adsorption was reversible. Desorption of adsorbed mefenoxam, P-metalaxyl and of the acid metabolite from German soil was almost completely reversible with percentage desorption rates of more than 91.0%, whereas the rate for F-metalaxyl was 74.1%. All compounds exhibited some resistance to desorption from the Cameroonian soil, with percentage desorption rates less than 77.0%. Therefore if degradation in the soil is slow the fungicides described have a potential to leach to lower soil horizons.