ADSORPTION OF LINURON AND METAMITRON ON SOIL AND PEATS AT 2 DIFFERENTDECOMPOSITION STAGES

We studied the adsorption of two herbicides of different polarity, lin uron and metamitron, by a mineral soil and two peats at different deco mposition stages and determined Freundlich and distribution coefficien ts per unit of organic matter. The Freundlich adsorption constant (K-f ) was 20 to 30-fold higher in the case of linuron and 40- to 90-fold h igher for metamitron for the organic materials (peats) than for the mi neral soil, reflecting adsorption dependence on both organic matter co ntent and type. The well-decomposed peat showed the highest affinity f or both herbicides. Hydrophobic bonding is suggested as a possible exp lanation. For linuron, the variation in K-oc was reduced to less than a twofold variation in K-oc by normalizing adsorption to organic carbo n, whereas for metamitron, K-oc values were not constant, confirming t hat this parameter may be of little meaning for polar compounds.