Degradation of the herbicide metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] was used as a model compound to study degradation in aqueous media with different biofilm carriers. Biofilm carriers used were naturally occurring minerals (NOMI), activated carbons (AC), and synthetic minerals combined with activated carbon (MIAC). No transformation was found without biofilm carriers or with NOMI as carriers. Degradation with AC was accompanied by consumption of oxygen but not by release of chloride. On MIAC carriers, release of chloride was observed. Results indicate that abiotic mechanisms play a major role in this type of degradation, which can be the basis for the development of a microbial community with the ability to degrade metolachlor.