Adsorption of linuron and metamitron on soil and peats at two different decomposition stages

We studied the adsorption of two herbicides of different polarity, linuron and metamitron, by a mineral soil and two peats at different decomposition stages and determined Freundlich and distribution coefficients per unit of organic matter. The Freundlich adsorption constant (K1) was 20‐to 30‐fold higher in the case of linuron and 40‐to 90‐fold higher for metamitron for the organic materials (peats) than for the mineral soil, reflecting adsorption dependence on both organic matter content and type. The well‐decomposed peat showed the highest affinity for both herbicides. Hydro‐phobic bonding is suggested as a possible explanation. For linuron, the variation in K, was reduced to less than a twofold variation in Koc by normalizing adsorption to organic carbon, whereas for metamitron, Koc values were not constant, confirming that this parameter may be of little meaning for polar compounds.