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

2.0 General Information

There are currently 134 pulp and paper mills in Canada (Lowell et al., 2003), and the industry employs over one million Canadians. Canada is one of the world leaders in the export of newsprint and market pulp. The industry ranks second to domestic sewage in wastewater output to the Canadian environment. The pulp and paper industry employs a wide range of process types, up to 30 (Lowell et al., 2003).

Pulp is produced from raw wood material and is the basic ingredient in the production of paper. Wood consists of cellulose, hemicellulose, lignin and wood extractives (McLeay & Associates, 1987). The objective of pulping is to separate and recover cellulose fibers from lignin and other wood constituents with maximum yield and minimum fiber degradation. Pulping is carried out by the application of chemical or mechanical energy to wood. Kraft pulping is the most common process employed globally, where wood chips are cooked with sodium hydroxide and sodium sulfide to dissolve lignin. Other pulping processes involving the use of chemicals include soda and sulfite mills. Mechanical pulping involves shredding or grinding wood chips and usually results in high yield pulps; that is, a very high percentage of the original wood components are retained in the final product. Mechanical pulps are most commonly used for newsprint and catalogue paper (Biermann, 1996). Finally, semi-chemical pulping combines chemical and mechanical methods, where wood chips are partially digested in a weak chemical solution followed by mechanical refining for fibre separation (USEPA, 1998). Semi-chemical pulp is commonly used for manufacturing corrugated cardboard. After cooking in the kraft process, the pulp is washed and separated from residual cooking chemicals, known as weak black liquor. At bleached kraft mills, pulp is sent to a bleach plant where residual lignin is removed to achieve a desired brightness in the finished product; this is typically accomplished using a combination of chlorine dioxide and caustic extraction.

Large volumes of water are used in pulp production, which in turn generate significant effluent discharges to aquatic environments. A typical kraft mill discharges between 80,000 and 130,000 m 3 / day of effluent into surface waters. Effluents are a complex combination of waste streams produced in debarking, pulp washing, bleaching, and regeneration of cooking chemicals. Combined effluents are treated prior to release, typically in two stages. In primary treatment, suspended solids are removed in clarifiers and/or settling basins. In secondary treatment, microorganisms break down biodegradable material, which significantly improves effluent quality by reducing biochemical oxygen demand (BOD) and reducing levels of organic compounds associated with toxicity ( Biermann, 1996; McLeay & Associates, 1987).

Environmental effects in the receiving waters downstream of pulp and paper mills, parallels the changes in the level of effluent treatment. From the 1950's to late 1970's, discharge of effluents high in fiber and BOD resulted in habitat degradation ( e.g., smothering of spawning beds due to fiber deposition, reduced oxygen concentration in the water column) and acute lethality to fish in receiving waters (McLeay and Associates, 1987; Folke, 1996; Owens, 1996). In response to these effects, regulators established "end-of-pipe" effluent quality limits for BOD and total suspended solids (TSS), an indication of the fiber concentration in effluents (Owens, 1991; Folke, 1996). Consequently, it was mandated that final effluents not be acutely lethal ( i.e., cause mortality to 50% of a test population) to standard bioassay species prior to release. The pulp and paper industry in North America responded to observations of environmental impact and regulatory concern by significantly improving effluent quality with better process and spill control and installation of effluent treatment systems (Smook, 1994; Folke, 1996).

In the 1970's and early 1980's, the focus of pulp and paper effects assessment was on the identification of the chemicals associated with the acute toxicity of final effluents (Owens, 1991, 1996; Folke, 1996). The toxicity associated with resin and fatty acids and chlorinated phenolics received much attention (Holmbom & Lehtinen, 1980; Kringstad & Lindström, 1984; Owens, 1991). In the late 1980's, pulp and paper production worldwide became an area of increased environmental scrutiny by the public as dioxins and furans were found in effluents and paper products.

In the 1980s discharges from Canadian mills were controlled federally by Pulp and Paper Effluent Regulations (PPER), which had been passed under the Fisheries Act (FA) in 1971. These set daily and monthly mass-based limits for BOD and TSS as well as the requirement that effluents not be acutely lethal to rainbow trout. The regulations did not address dioxin and organochlorine discharges. The regulatory limits were also only legally binding on mills constructed after the promulgation of the legislation in November 1971 which represented fewer than 10 percent of the mills in Canada . In order to address the deficiencies in the 1971 Regulations, the Minister of the Environment announced plans to revise the federal regulatory framework in March 1989.

At the same time, studies conducted in Sweden during the early 1980's 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 (reviewed in Södergren, 1992). The changes in growth, biochemistry and deformities in fish were dose-dependent and the area over which the effluents exerted health effects was considered to be large (> 8-10 km from the pulp mill; dilution of the effluent by more than 1000 times). Additional studies were also conducted at an unbleached kraft mill and relative to the bleached kraft mill, only small effects were demonstrated. Södergren (1989) regarded this as evidence of a relationship between the bleaching process and subsequent effects in the receiving environment. These conclusions were cited as the basis for using adsorbable organic halogens (AOX) to regulate pulp mills in Denmark, Sweden and Finland (Folke et al., 1991). These studies were widely and heavily criticized in several reviews because of the absence of supporting data from North American receiving waters (Sprague & Colody, 1989; Owens, 1991). The reviews suggested that the study site was unique and that such effects would not occur near well-operated mills. This assumption proved to be false, as studies conducted at Jackfish Bay on Lake Superior during the late 1980s found that fish exposed to primary-treated effluent from a bleached kraft pulp mill demonstrated very similar reproductive effects to those documented in Sweden . Fish exposed to effluent exhibited an increased age to sexual maturation, reduced gonadal development, reduced expression of secondary sexual characteristics and corresponding reductions in circulating reproductive steroid hormone levels (McMaster et al., 1991; Munkittrick et al., 1991).

In 1989-1990 the Canadian Federal government responded to the presence of dioxins and furans in effluents by conducting an assessment of effluents from mills using chlorine bleaching under the Canadian Environmental Protection Act (CEPA). The assessment concluded that bleached kraft mill effluent met the toxicity criteria used under CEPA. The assessment also concluded that the quality of the underlying science was insufficient to design regulations curtailing organochlorine discharges beyond what would be attained with the proposed dioxin-furan measures and new Fisheries Act regulations. Information deficiencies included knowledge of the make up of the organochlorine content of effluents and at that time it was not known which compounds were responsible for the observed environmental effects.

Federally, new regulations were passed under CEPA in 1992 to control releases of dioxins and furans. The existing PPER under the FA was updated and set stricter limits for BOD and TSS, while maintaining a similar non-acute lethality requirement as in the 1971 regulations. The limits in these new regulations became legally binding on all mills, unlike the earlier requirements. 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 man's use of fisheries resources to be assessed. Compliance with the CEPA regulations entailed a capital investment of approximately $600 million for the affected 42 mills. The regulatory limits came into effect on passage in 1992, although mills which needed time for process modifications were allowed to defer compliance to January 1, 1994 . The CEPA regulations on dioxins and furans were achieved by reducing the amount of dioxin precursors introduced to the process, as well as reducing the opportunity for the precursors to become chlorinated (Haliburton & Maddison, 2003).

Compliance with the new FA regulations entailed major changes in the way effluents were treated by the industry, requiring in most cases the installation of secondary treatment. In 1992, total capital costs of $2.3 billion were estimated for the 124 mills subject to these provisions (Haliburton & Maddison, 2003). For many mills, the prompt installation of controls was impeded by the poor market conditions of the time. The regulations therefore included provisions to allow eligible mills to defer compliance with limits to dates up to January 1, 1996 , as justified by applications. Of the 124 mills subject to the regulations in 1996, 79 mills deferred compliance to then.

A retrospective report on the impact of the 1992 Federal Pulp and Paper Regulatory Framework on effluent quality was prepared. It demonstrates that dioxin and furan discharges have decreased more than 99%, biological oxygen demand of the effluents have decreased by 94% and total suspended solids by 70% (Halliburton & Maddison, 2003). Compliance rates with the new limits set under the 1992 regulations were also very high with mills meeting the BOD and TSS limits 99.8 % of the time and the rainbow trout acute lethality test 94.9% of the time (Halliburton & Maddison, 2003).

Under the FA regulations mills were also required to conduct EEM on a cyclical basis. EEM is a continuous, site-specific oriented program, aimed at providing a more complete and comprehensive understanding of the long-term impact of effluents on the Canadian aquatic environment. Research was a key activity to ensure continuous improvement in the scientific aspects of EEM. The constant evolution of the program was designed to allow mills to identify and differentiate causes of the observed effects, and to evaluate their significance, so that they may implement the necessary mitigation measures. To date, two cycles of studies have been completed and interpretive reports submitted to the National EEM office. Studies evaluate four areas:

  • Sub-lethal toxicity testing, on 6-month intervals, to assess effluent quality;
  • A benthic invertebrate community survey assessing fish habitat;
  • A fish population survey to assess the health of fish; and
  • A study of dioxin and furan levels in edible fish tissue for mills using chlorine bleaching, and a tainting study evaluating the usability of fisheries resources.

The cycle 1 reports were submitted in 1996, and covered sampling years from 1992 to 1996. Since about two-thirds of the mills sampled had yet to complete and bring on line secondary treatment plants in this period, sampling results in most cases represented the condition of biota exposed to primary treated effluents. The cycle 2 reports were submitted in April 2000 and covered sampling in the years 1997 to 1999. The cycle 2 results represented the biota's post-regulatory condition. The National EEM Office of Environment Canada and research scientists from the National Water Research Institute of Environment Canada have recently completed an assessment of the cycle 2 data (Lowell et al., 2003).

The CEPA assessment of bleached kraft mill effluents in the early 1990's observed that the quality of the underlying science was insufficient to design regulations curtailing organochlorine discharges beyond what would be attained with the new regulations. In order to fill the information gaps, in 1992 the Minister of the Environment launched an intensive government, industry and university research program. The original objectives of the research program were to 1) identify the causative organochlorine compounds, 2) determine how to eliminate them from the process, and 3) determine the short-term and long-term environmental effects of these compounds. Results from this research program along with feedback from the Environmental Effects Monitoring program would then be used to define what additional control actions may be necessary. The following document describes the research conducted from 1992-2002, following the implementation of the 1992 regulatory package. It is separated into three specific sections of research, 1) Field Studies and Mechanistic Research, 2) Development and Application of Bioassays, and 3) Characterization of Bioactive Chemicals.