The role of organic colloids in herbicide transfer to rivers: a quantitative study of triazine and phenylurea interactions with colloids.

For moderately hydrophobic compounds such as most pesticides adsorption on colloids (<0.2 microm) may play a key role in pesticide mobility as well as in their degradation by chemical and microbiological processes. However, until now, pesticide-organic colloid interactions are poorly understood. Quantitative data for sorption equilibria on colloids of two series of herbicides including triazines (atrazine, simazine, terbutylazine, prometryne, desethylatrazine, and desisopropylatrazine) and phenylureas (isoproturon, linuron, neburon, and diuron) sampled in the Seine river (urban zone) and the Marne river (agricultural zone) are presented. Partition coefficient of herbicides on colloids (K(com)), were evaluated by solid-phase extraction coupled with high-performance liquid chromatography-UV diode-array detection (SPE-HPLC-UV/DAD). In the case of triazines a satisfactory log-log correlation was found between K(com) and octanol-water coefficient (K(ow)) values. Phenylureas did not obey this correlation, with K(com) values being about two times higher than those of triazines. The existence of two distinct types of adsorption behaviour on colloids partly explains the different occurrence of triazines and phenylureas in surface waters.