When dissolved is not truly dissolved-The importance of colloids in studies of metal sorption on organic matter

► Biosorbents may release organic colloids that interact strongly with trace metals. ► Ignoring colloid-bound metals may bias distribution coefficient calculations. ► Distribution coefficients can be corrected with a multi-site Langmuir isotherm. ► Ultra-filtration should become routine practice in all metal biosorption studies. ► Colloid release may cause premature break-through of packed-bed biosorbent columns.