<P> Enzymes like xylanase have been used in pulp bleaching to increase the efficiency of other bleaching chemicals . It is believed that xylanase does this by cleaving lignin - xylan bonds to make lignin more accessible to other reagents . It is possible that other enzymes such as those found in fungi that degrade lignin may be useful in pulp bleaching . </P> <P> The bleaching of chemical pulps has the potential to cause significant environmental damage, primarily through the release of organic materials into waterways . Pulp mills are almost always located near large bodies of water because they require substantial quantities of water for their processes . An increased public awareness of environmental issues from the 1970s and 1980s, as evidenced by the formation of organizations like Greenpeace, influenced the pulping industry and governments to address the release of these materials into the environment . </P> <P> Conventional bleaching using elemental chlorine produces and releases into the environment large amounts of chlorinated organic compounds, including chlorinated dioxins . Dioxins are recognized as a persistent environmental pollutant, regulated internationally by the Stockholm Convention on Persistent Organic Pollutants . </P> <P> Dioxins are highly toxic, and health effects on humans include reproductive, developmental, immune and hormonal problems . They are known to be carcinogenic . Over 90% of human exposure is through food, primarily meat, dairy, fish and shellfish, as dioxins accumulate in the food chain in the fatty tissue of animals . </P>

Which one of the following is commonly used for pulp bleaching in the paper industry