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Organizations & People
Pure Appl. Chem. Vol. 68, No. 9, pp. 1721-1730 (1996)
Chlorine in the Bleaching
of Pulp and Paper
(Centre for Toxicology, University of Guelph, Guelph ON, N1G 2W1, Canada)
The pulp and paper industry in Canada
contributes significant effluent discharges to surface and marine waters.
Chlorine and chlorine compounds are used in the bleaching of pulp. A
large number of organochlorine chemicals of widely differing properties
are, or have been, produced from this bleaching. These range from the
highly hydrophobic, persistent and bioaccumulative toxic substances,
such as 2,3,7,8-TCDD, to the higher molecular weight, non-hydrophobic
material usually characterized by absorbable organic halogen. Chlorine
dioxide and chlorine react with lignin by different chemical processes
and produce different organochlorine products. Use of molecular chlorine
as a bleaching agent results in the formation and release of chlorinated
organic compounds, sometimes at concentrations that present an unacceptable
risk to the receiving environment and the food chain. Alternatives to
the use of molecular chlorine, such as chlorine dioxide, result in reductions
in the quantities of organochlorines produced, and the degree of chlorine
substitution in the organochlorines formed. This, in turn, leads to
reduced persistence, reduced potential for bioaccumulation and food
chain transfer, reduced toxicity and reductions in adverse ecological
effects. However, sufficient evidence exists from responses observed
at non-bleached mills to show that other (probably non-halogenated)
compounds are released or formed during the production of pulp and cause
responses such as induction of MFOs, changes in hormone levels, and
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