The pulp and paper manufacturing industry generates large quantities of wastewater and has been described as a significant pollutant of the aquatic environment for many decades. The majority of pulp mills are located in the U.S. and Canada, and these countries are therefore subject to the greatest environmental impact. Some form of toxicity following exposure to mill effluent has been documented in numerous species, both aquatic and terrestrial, and the compounds present in effluents can affect multiple physiological processes, including hepatic mechanisms, reproduction and development, and endocrine function. Although the effects of PME on wildlife have been known for some time, the detection of chlorinated organic compounds generated substantial concern to humans because of the potential risk of exposure to these highly toxic compounds through environmental persistence and bioaccumulation. Government regulations were imposed on the pulping industry in an effort to prevent further contamination and reduce the toxic potential of pulp mill effluent to both humans and wildlife. Included among these regulations was the elimination of bleaching processes that utilized organic chlorine in favor of elemental chlorine free (ECF) and totally chlorine free (TCF) bleaching processes. There is little in the peer-reviewed literature describing the advantages of TCF over ECF, and many Internet sources claim that the differences between the two are small, although ECF is better economically. The USEPA has listed ECF as one of the best available technologies (BAT) within the Cluster Rule. However, because the mechanisms of MFO activity are unclear and reproductive effects have been observed following effluent exposure, and because some of these same effects have been reported in areas minimally compromised by PME, it is difficult to assess the true improvements that these processes are attaining. Other methods of bleaching continue to be tested and each has its own beneficial aspects. However, negative elements still seem to arise, either through chemical persistence, the formation of previously undetected compounds, or the conversion from one toxicant to another. Certainly, the elimination of elemental chlorine in pulping and bleaching processes will improve the quality of effluents with respect to chlorinated organics, but further research is necessary to determine the actual benefits of all processes and to determine how the toxicity that remains can be eliminated. © 2006 Springer Science+Business Media, Inc.