Regardless of the method of bleaching, the effluent may have certain other characteristics that can damage the environment, such as suspended solids and the capacity to deplete oxygen from the receiving waters.
The chemical composition of bleached pulp mill effluents is variable and not well characterized. Approximately 250 compounds have been identified in pulp-mill effluents but many more remain unidentified.
Bleaching mechanical pulps with hydrogen peroxide produces additional salts in the effluent. If the effluent is discharged in inland rivers and lakes, salinity levels can be raised. High salt levels can make the water unsuitable for a variety of human and animal uses.
Chelating agents bind trace metal ions in the pulp to prevent them from degrading the peroxide. This increases the metal load in effluents and is an issue of concern; however, the environmental impact of the process so far is largely unknown.
Other materials commonly found in bleached pulp mill effluents include resin and fatty acids.