The present study considers the environmental consequences of fibre sediments contaminated with mercury and PCBs. Release rates of contaminants from fibre sediments, before and after remedial actions involving dredging and land disposal, are compared. The mechanisms for the release of contaminants have been identified and quantified for both situations. Mathematical models are formulated and solved analytically or numerically. Calculations show the impact of sorption effects, diffusion, advection, erosion, sedimentation and release to the atmosphere. Chemical conditions, degradation and production are also studied. The relative importance of the different mechanisms is hard to determine due to lack of reliable input data. However, sorption, erosion, advection and probably also release to the atmosphere will be the most important mechanisms in the case without any remedial actions. In the case of dredging and land disposal, sorption, advection and possibly also release of volatile compounds to the atmosphere will determine the release rate. The study is focused on two contaminants, mercury and PCB. For mercury the most important parameters are: sorption into the fibre material, chemical form, volatility and biomethylation and demethylation. For PCB the most important parameters are: sorption onto the fibre material, chemical form and possible microbial degradation. The release rate from the fibre sediment has been estimated to be up to about 4 mg/m(sup 2),yr for PCB and 5 mg/m(sup 2),yr for mercury, depending on the higher volatility. The release rate from the land disposal has been estimated to 0.3 mg/m(sup 2),yr for PCB and 1.6 mg/m(sup 2),yr for mercury, where 1.3 mg/m(sup 2),yr is released to the atmosphere. (99 refs., 14 figs., 13 tabs.) (au).