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This article is a review of research efforts over the last decade on the sources and characteristics of substances in Canadian pulp mill effluents associated with two responses in fish: (1) induction of detoxification enzymes and (2) reproductive effects. The initial uncertainty regarding the role of chlorine bleaching and dioxins in these responses was resolved by the mid 1990s, when it was determined that effects were not correlated with effluent adsorbable organic halogen (AOX) levels and that releases of dioxins had decreased substantially. In the mid 1990s researchers were able to partially attribute enzyme activity induction in fish to wood components, while other studies showed individual wood extractives had the potential to affect fish reproduction. A lack of correlation between threshold reproductive responses and effluent concentrations indicated additional unidentified compounds and mechanisms were involved. In the late 1990s, source identification approaches in concert with the development of mechanistically linked in vitro and in vivo bioassays showed multiple compounds are affecting production and signaling of sex steroids in fish. These substances are bioavailable and accumulated rapidly, consistent with the body of evidence that has shown a sustained exposure is required to produce both elevated enzyme activity and depressions in sex steroid levels. The patterns of these substances in effluents and fish tissues are not correlated with production type or effluent treatment. Collectively, these findings show that bioactive substances originate from wood and are derived from lignin and/or terpenoids, they are liberated during pulp digestion, and in kraft mills they are present in black liquor and chemical recovery condensates. Additional bioactive substances are also present in bleachery effluents containing residual lignin. The lack of a definitive identification of the responsible compounds has prevented an evaluation of the effectiveness of industry-wide process changes. Continued research into the identities, origins, and environmental fate of these substances and the efficacy of effluent treatment is required to determine their significance and relationship to the existing impacts of effluents from pulp and paper mills in Canadian aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Studies conducted in Sweden in the early 1980s provided some of the first evidence that effluents from some pulp mills were capable of inducing toxic responses in fish at very low concentrations in the receiving environment. In response to these findings, studies were initated in Canada and impacts of primary treated bleached kraft mill effluent on reproductive function in fish were found. Reproductive impacts in fish were not limited to mills that used chlorine in the bleaching process and were also evident at some mills that employed secondary effluent treatment. In 1992, new federal regulations were passed under the Canadian Environmental Protection Act to control releases of dioxins and furans, and a new Pulp and Paper Effluent Regulation under the Fisheries Act set stricter limits for biological oxygen demand and total suspended solids. Very importantly, the new regulations included requirements for environmental effects monitoring (EEM) at all mill sites. This allowed the effectiveness of the control limits in protecting fish, fish habitat, and human use of fisheries resources to be assessed. At the same time, the Minister of the Environment launched an intensive government, industry, and university research program. Results from this research program along with feedback from the EEM program would then be used to define what additional control actions might be necessary. This article reviews the field studies and mechanistic research conducted in Canada following the implementation of the new federal regulations. Great progress has been made in this area, first demonstrating reproductive effects at various locations, then determining the mechanisms responsible for the reproductive effects at specific sites, followed by the demonstration of partial recovery in reproductive function following process and treatment changes in response to the new regulations. However, it is clear from the results of the first two cycles of the EEM program that mill effluents still affect the local receiving environments at a number of locations across Canada, and that continued research combining field studies, bioassay application, and chemical identification is required. [ABSTRACT FROM AUTHOR]