title: Factors affecting metribuzin retention in Algerian soils and assessment of the risks of contamination.
abstract: Metribuzin is a widely used herbicide around the world but it could lead to soil and water contamination. Metribuzin retention on a silty-clay agricultural soil of Algeria was studied in laboratory batch experiments to assess the contamination risk of the groundwater. Factors conditioning the fate of metribuzin were investigated: soil nature, metribuzin formulation, NPK fertilizer, and soil pH. Freundlich sorption isotherms gave the coefficients K F between 1.2 and 4.9 and 1/n a between 0.52 and 0.93. The adsorption is directly dependent on organic and clay soil contents. Formulated metribuzin (Metriphar) reduces the adsorption (K F = 1.25) compared to pure metribuzin (K F = 2.81). The addition of an NPK fertilizer decreases the soil pH (6.67 for the soil without fertilizer and 5.86 for 2 % of fertilizer) and increases metribuzin adsorption (K F is 4.83 for 2 % of fertilizer). The pH effect on the adsorption is corroborated in experiments changing the soil pH between 5 (K F is 4.17) and 8 (K F is 1.57) under controlled conditions. Desorption isotherms show a hysteresis and only 30 to 40 % of the initially adsorbed metribuzin is released. The estimated GUS index is ≥ 2.8 for a DT50 ≥ 30 days. K F values and the hysteresis show that metribuzin is little but strongly retained on the soil. Formulated metribuzin and addition of fertilizer affect the retention. However, the GUS index indicates a high mobility and a significant risk of leaching. The most appropriate risk management measure would be an important increase in organic matter content of the soil by addition of organic amendments.
authors.affiliation: Ecole Nationale Polytechnique, Laboratory of Environmental Sciences and Technology, 10 Avenue Hassen Badi, BP 182, 16200 Algiers, Algeria. ouznahaouchine@yahoo.fr
authors.forename: Ouzna
authors.initials: O
authors.lastname: Oukali-Haouchine
authors.forename: Enrique
authors.initials: E
authors.lastname: Barriuso
authors.forename: Yamina
authors.initials: Y
authors.lastname: Mayata
authors.forename: Khadija M
authors.initials: KM
authors.lastname: Moussaoui
mesh_terms: D000327:Adsorption; D000383:Agriculture; D000462:Algeria; D004784:Environmental Monitoring; D005308:Fertilizers; D006540:Herbicides / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D018570:Risk Assessment; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*; D014227:Triazines / Q000032:analysis*
chemical_list: D005308:Fertilizers; D006540:Herbicides; D012987:Soil; D012989:Soil Pollutants; D014227:Triazines; C009235:metribuzin