Closure of water circuits in papermaking is of vital importance for achieving a more sustainable and economic manufacturing of paper. The most important limiting factor for a further closure is the accumulation of dissolved and colloidal materials (DCM). The extent to which DCM can become enriched in the water depends not only on how many times water is reused but also on the degree to which this matter becomes reattached to the fibers and other solid components of the paper furnish. This study analyzes the accumulation of the most typical contaminants in newsprint (NP) and light weight coated (LWC) paper production. Results show that the release of DCM depends on the present contaminant load in the waters: higher at low contaminant load and lower at high contaminant load. A simulation was carried out to analyze the differences between assuming a constant and a variable release of contaminants to waters. Important differences were observed, especially at low fresh water consumption for those species with a major affinity for the fibers. (C) 2008 Elsevier B.V. All rights reserved.