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A Decade of Research on the Environmental Impacts of Pulp and Paper Mill Effluents in Canada (1992-2002)

5.1 Characterization of Bioactive Chemicals - Summary

A large body of work has been completed in the last decade on investigating the sources and identities of bioactive substances present in final effluents from pulp and paper mills in Canada . Canadian research has focused on chemicals causing induction of detoxification enzymes and chemicals causing changes in the levels of reproductive hormones. Several things became apparent from the studies conducted during the early 1990s, including that i) it would be more difficult than originally assumed to identify the responsible chemicals, ii) there may be more than one chemical or group of chemicals responsible for impacts, and iii) the responsible chemicals were likely previously unidentified. Initial speculation about the role of chlorine bleaching and dioxins in the responses were addressed in the early 1990s, which determined that historical effects could only be partially attributed to dioxins and furans and that effects were not correlated with organochlorine discharges or AOX. By the mid 1990s, interest increased in trying to identify the characteristics of the chemicals responsible for induction of detoxification enzymes and the changes in steroid hormone levels. Research also expanded into the identification of individual waste stream sources of chemicals. The advent of suitable bioassays to drive investigative studies has afforded new opportunities to investigate chemicals affecting fish reproduction in the late 1990s to the present day.

From the work conducted to date it is apparent that the sources of bioactive substances originate from lignin degradation. This has the form of original digestion of wood furnish (black liquor, condensates derived from black liquor, black liquor carryover to bleach plant), and bleach plant effluents, which contain residual lignin removed during bleaching. There are indications that active substances can be recovered from wood directly. The best evidence now indicates that multiple compounds are functioning in multiple mechanisms affecting fish reproduction. Several compounds have been identified that cause elevated activity of detoxification enzymes but there remain multiple unidentified chemicals causing induction in final effluents. Evidence also indicates that continuous exposures are required to maintain the responses, suggesting the active substances are not persistent nor do they appreciably bioaccumulate. The releases of bioactive substances are not correlated with production or treatment processes.