Bleaching of pulp has been a major issue for environmentalists since the detrimental effects of bleaching with chlorine gas became obvious in the 80s. Bleaching with elemental chlorine has almost been totally replaced by chlorine dioxide as a main bleaching agent.
The ECF (Elemental Chlorine-Free) bleaching process, dominant today, is an environmentally compatible method, as is TCF (Totally Chlorine-Free) bleaching. The ECF process generates not highly chlorinated organic compounds, but residues that are biodegradable in effluent treatment or in the natural recipient.
Read more at Alliance for Environmental Technology