Environmental Improvements at Grande Prairie and Ecosystem Response
Table of Contents
In July 1992, the market kraft pulp mill in Grande Prarie, Alberta converted the bleaching process to chlorine dioxide delignification (100% ClO2 substitution). Subsequent environmental improvements have been implemented focusing on reducing BOD5 and TSS.
Bleached pulp quality is excellent with respect to brightness, viscosity, dirt, shives, and strength characteristics. Polychlorinated dioxins and furans, 2,3,7,8-TCDD and 2,3,7,8- TCDF (TCDD/F) are non detectable at an analytical detection limit of < 0.6 ppt.
Final mill effluent parameters have monthly averages of:
The improvements are due to implementation of condensate stripping, enhanced management and operating practices, modifications of the secondary biological treatment system and utilization of chlorine dioxide delignificafion.
Contaminant levels in the receiving environment have declined further. For example, dioxins and furans have declined to levels that are either at or below detection limits in water and suspended sediments. The rapid decline was initially in response to the change to 70% chlorine dioxide substitution. More recently an additional decline has been observed following adoption of 100% chlorine dioxide substitution.
Concentrations of dioxins and furans in fish have also decreased, although at a slower pace. The most recent data show that levels in mountain whitefish (Prosopium williamsoni) fillets are consistently below Health and Welfare Canada's human consumption guideline of 20 ppt toxic equivalents, TEQ (TEQ = [2,3,7,8-TCDD] + 0.1[2,3,7,8-TCDF]). Burbot (Lota lota) fillets and livers are also well below Health and Welfare Canada's human consumption guideline of 20 ppt toxic equivalents.
Chlorinated phenolic concentrations have paralleled the trends seen for dioxins and furans, with a rapid decrease in both water and suspended sediments in response to process changes. For example, concentrations in suspended sediments decreased approximately 200-1000 fold after implementing 100% chlorine dioxide substitution.
The Grande Prairie mill was built in 1972 and is located approximately 500 kilometers northwest of Edmonton, Alberta on the Wapiti River. The mill produces 300,000 air dry metric tonnes (ADMt) annually of fully bleached kraft softwood pulp. This high grade market pulp is used as a carrier fibre for tissue and towel making and is also used for the manufacture of fine writing papers and other specialty products. Important pulp characteristics are the high and uniform refined and unrefined strength as well as a uniform 90% ISO brightness.
In December 1992, a new 5-year operating license was granted to the mill by Alberta Environment. The new license stipulated new monthly average limits for:
The impact of the mill effluent on the receiving environment before and after implementation of these technologies has been measured through monitoring of the Wapiti/Smoky river system. This has included a comprehensive ecosystem study from 1990-1992 (during the period of conversion first to 70% chlorine dioxide substitution and then to 100% chlorine dioxide substitution) . Additional monitoring of water, sediments and aquatic biota began in 1992 and will continue in the future.
The first paper in this series examined the impact of the implementation of chlorine dioxide in the first stage of bleaching on pulp manufacturing and effluent characteristics . This second paper will update the previous paper with particular emphasis on the success of the overall environmental improvement plan on effluent characteristics and the receiving environment.
Environmental Improvement Plan
Chlorine Dioxide in the first Stage of Bleaching
In the fall of 1990, a new 45 t/d R8 chlorine dioxide plant was installed. The low consistency first bleaching stage was converted to medium consistency (MC) and operated with 70% chlorine dioxide substitution. In July 1992, molecular chlorine gas addition was eliminated altogether. The mill has continued to operate ever since with only chlorine dioxide in the first stage of bleaching.
Pulp quality remains excellent and chemical consumption remains at levels reported earlier
Impact of Chlorine Dioxide in the first Stage on Effluent Characteristics
Conversion to chlorine dioxide only in the first stage of bleaching lowered the AOX of the final mill effluent. With only chlorine dioxide in the first stage, the final mill AOX is remarkably stable with a monthly average of 0.5 kg/ADMt for the period 1993-94. AOX Removal across the ASB is normally 18%.
Effluent colour has also been decreased from 140 kg/ADMt at 70% chlorine dioxide substitution to a monthly average in 1993-94 was 80 kg/ADMt at 100% chlorine dioxide substitution.
Utilization of chlorine dioxide only in the first stage of bleaching decreases the formation of chlorinated phenol compounds. As shown in Fig. 1., and in Appendix 1, tri-, tetra-, and penta substituted phenols in the final mill effluent are near detection limits of 0.1 parts per billion (ppb). Mono and di-chlorinated phenols are typically less than 0.5 ppb. The values shown for June are attributed to disturbance of previously deposited sediments in the aeration basin during a routine cell clean-out.
In the previous study, testing of influent to secondary treatment showed the tri-, tetra, and penta chlorinated phenols to be below detection limits of 0.1 ppb . This is 25-50 times lower than the US EPA's proposed minimum levels for bleach plant effluent .
The mill is currently complying with the Canadian Environmental Protection Act (CEPA) requirements for 2,3,7,8-TCDD and 2,3,7,8-TCDF as shown in Table 2. The CEPA requirement for 2,3,7,8-TCDD in final effluent is "non-measurable" i.e. < 15 ± 5 parts per quadrillion (ppq) and for 2,3,7,8-TCDF, "non measurable" i.e. < 50 ppq.
Foul condensates from digesting and evaporation are contaminated with odorous compounds such as hydrogen sulfide, and methyl mercaptans. In addition, organic material, primarily methanol, is also present and if not removed, contributes to the BOD5 discharged into the secondary treatment system.
In September 1993, a new foul condensate steam stripping and non-condensable gas (NCG) system, designed to substantially reduce odour at the mill site and to decrease the BOD5 load to secondary treatment, was started up.
Contaminated condensates are collected from the turpentine underflow system, the 5th effect evaporator and evaporator seal tank. Condensate segregation concentrates the total flow to the stripper to 600 US gpm. The foul condensates are preheated and then stripped in a 22 tray column. Vapour from the high solids concentrator is used as the stripping medium. Steam at 55 psig. is available as back-up.
As shown in Fig. 2, water vapour is condensed from the stripped gases leaving the column. The volatile gases are then transported to the power boiler for combustion. The lime kiln can be used as a back-up incinerator. Cleaned condensate from the stripping column is used as hot process water for brown stock washing.
The design basis for the condensate stripping system was specified at 98% Total Reduced Sulfur (TRS) and 95% methanol removal efficiencies. Preliminary testing indicates that these values will be easily met. The reductions in methanol and TRS have decreased the influent BOD5 from an average of 34 kg/ADMt to 24 kg/ADMt. Influent sulphide concentration has decreased from 5.0 mg/L to 0.02 mg/L as shown in Fig. 3.
Aerated Stabilization Basin Upgrade
Secondary effluent treatment, shown in Fig. 4, consists of an 11.5 million US gallon (43 thousand m3) settling pond followed by two 113 million US gallon (428 thousand m3) aerated cells in series and a 21 million US gallon (80 thousand m3) quiescent zone. The system retention time is 13-14 days.
Primary clarified alkaline effluent is mixed with the bleach plant acid sewer in a mix tank. The total effluent then flows to the ASB. The average effluent volume is 60,000 m3/d (66 m3/ADMt).
Options to upgrade the system were evaluated using the National Council for Air and Stream Improvement (NCASI) ASB model. The electrical system was upgraded to allow for 9 additional floating aerators to be added. There are now eighteen 75-HP aerators in the first cell and nine in second for a total of 2025 HP. Polyethylene curtains were added in the Spring of 1993 to the second cell to provide more plug flow and minimize short circuiting.
To maintain a high ASB operating efficiency, it is imperative that the appropriate amount of nutrients, phosphoric acid and anhydrous ammonia, are added initially. Other critical parameters must also be managed. To that end, a profile across the ASB is monitored daily. Conventional parameters such as flow, temperature, pH, BOD5, dissolved oxygen and nutrient concentrations are measured in the influent, midpoint and effluent. Other parameters such as oxygen uptake rate, soluble BOD5 removal, microbial characteristics and toxicity are carefully analyzed for trends and indications of changes in performance.
Extraordinary measures are used for early warning signals. For example, routinely samples are taken at the mid-point in the ASB for rainbow trout 96-hr. LC50 toxicity testing. Typically this effluent passes the test at 100% effluent concentration.
Effluent Monitoring and Management
The objective of the effluent monitoring and management program is to provide the operators with the necessary training and tools to optimize the quality of effluents. The variability of influent parameters such as BOD5 and toxicity have significant impact on the operation of the ASB and final effluent quality. Instrumentation was installed in the appropriate processes to measure flow, temperature and conductivity. Other parameters such as colour and pH are monitored in the bleach plant alkaline and acid sewers. Process effluents are characterized with Microtox assays and analyzers such as the Arthur respirometer.
Environmental control limits are established for each process operating station in the mill to alarm out-of-limit conditions. Overview graphics provide a preview of plant environmental performance. Historical data bases are trended to predict expected performance. Operations teams review environmental performance daily and develop strategies to respond to potential problems. Monthly management reviews assess performance and provide recommendations for changes in operating and control parameters.
Operating stability and plant reliability are key to meeting stringent environmental requirements. Process parameters such as pulp washing and chemical addition are optimized for environmental performance. Reclamation systems are in place to recover process spills. The equalization basin, formerly used to buffer the impact of process spills on the ASB, has been converted to a dedicated spill recovery system. Black liquor spills from mill upsets are now contained and reprocessed through the evaporator system. Make-up to the liquor cycle has been reduced from 16 to 5.5 kg/ADMt Na (50 to 17 kg/ADMt as Na2SO4)
Effect of Environmental Improvements on Effluent Quality
As a result of these improvements to the ASB and implementation of steam stripping, BOD5 removal efficiency has increased from 85% to 94%. The high removal efficiency has been maintained while the influent BOD5 has been decreased by the steam stripping system.
Final effluent BOD5 and TSS have averaged 1.4 and 1.2 kg/ADMt respectively over the past sixteen months since the improvements. These values are below the currently proposed US EPA effluent guidelines of 2.19 and 3.89 kg/kkg of product for bleached paper grade kraft . Final effluent COD averages 40 kg/ADMt since the start-up of the condensate stripping system.
Final mill effluent consistently passes acute toxicity tests for rainbow trout (96-hr LC50) and Daphnia magna (48-hr LC50) with zero mortality of test species in 100% effluent concentration. Chronic toxicity testing of final mill effluent has recently begun using Ceriodaphnia and fathead minnows. The No Observable Effect Concentration (NOEC) is typically > 25% for Ceriodaphnia and 100% for fathead minnows. These tests would indicate that no benthic or fish population degradation would be expected at the current ratios of mill effluent to receiving water, even in winter when the volume/volume % can be as high as 6-10%. Investigations of the receiving environment have focused extensively on fish reproduction; no impacts are observed (see below.)
Impact of Enviromnental Improvement Plan on the Receiving Environment
The 1990-1992 Wapiti/Smoky Ecosystem Study investigated a set of fish population and biomarker endpoints at a site where benthic disruptions due to organic enrichment and fibre deposits were absent . In the latter phases of the study efforts concentrated on hepatic enzyme induction and a complete reproductive assessment. In addition, individual body burdens of chlorinated materials were analyzed such as (TCDD/F) in fillet, specific chlorophenols in bile and fillet, and EOC1 in bile and fillet. Thus, there were concurrent data on exposure, biomarkers and population-level effects.
These chemical data were used to search for any association between chemical doses and biological effects or trends to test for cause and effect linkages between bleaching and environmental effects. This study was conducted using sampling stations up to 230 km downstream of the mill. Multiple samplings have taken place during several seasons between 1990 and 1993 as well as at a reference site in a separate river system that does not receive effluent from any pulp mills.
Fish Population Responses
At sites receiving untreated or poorly-treated effluent in Sweden and Canada, exposure to bleached kraft pulp mill effluent (BKME) has been linked with degradation of fish habitat, changes in species distribution and abundance, and effect on growth, and reproduction [4,5,6,7,8]. These effects were related to a combination of nutrient enrichment, low dissolved oxygen, fibre mats and chemical toxicity [9,10]. Other studies at sites with primary and secondary-treated BKME have found older, slower-growing fish with reduced reproductive capacity, or, faster-growing fish with delayed maturity [11, 12].
The results from the 1990-1992 Wapiti/Smoky Ecosystem Study showed that the mill effluent had not eliminated spawning, overwintering, or rearing habitat in the Wapiti/Smoky River system, although it had altered some habitats in the near-field (2-30 km from mill site). Nutrient enrichment from both the City of Grande Prairie sewage treatment plant and the mill had somewhat altered habitat through an increase in periphyton growth (attached algae) and benthic invertebrate (bottom insects) abundance . Pollution sensitive species such as mayfly larvae were present. There was no avoidance by fish species of the near-field areas; species distribution data showed that this area was actually preferred, especially in the fall and winter, presumably because of the abundant food source.
Seasonal distribution patterns of fish species were largely the result of natural phenomena such as river flows and the quality of the habitat. Fish movement (as measured through tag/recapture and radiotelemetry) could be both extensive and rapid and involved large portions of the river system, both upstream and downstream of the mill.
The two main study species, mountain whitefish (Prosopium williamsoni) and longnose sucker (Catostomus catostomus) were both growing at rates that were similar to those observed in nearby Northern Alberta rivers [14, 15], with no evidence of either the slower or more rapid growth seen at other BKME sites [5, 12]. The fish had higher condition factors (were deeper-bodied) with greater fat storage than in reference fish; however, this was not accompanied by any disruption in allocation of energy to reproduction (e.g. there was no difference in mean age of mature fish, or relative gonad sizes). The age structure of the populations showed that there had been no losses of age classes through reproductive or recruitment failures. Observations of the young-of-the-year confirmed that successful reproduction had taken place in both longnose suckers and mountain whitefish and that rearing habitats were being successfully utilized (including areas within 1 km of the effluent discharge).
There were no significant correlations between indicators of exposure (e.g. tissue dioxin/furan burdens, induction of P4501A enzyme) and population-level effects. The only relationships appeared to be with habitat; the data indicated that there may be population parameter gradients of response to habitats (e.g. in condition factors and gonad size).
In summary there was no evidence of deleterious effects on fish species composition, distribution or relative abundance among exposed fish in the Wapiti/Smoky River system. Longnose sucker and mountain whitefish populations reproduced successfully throughout the study and grew at comparable rates to those of reference fish.
Contaminant Concentrations in the Receiving Environment
During the 1990-1992 Ecosystem Study and from 1992 to the present, contaminants have been monitored in key fish species and in selected compartments of the river system (such as water and suspended sediments). The primary contaminants that have been monitored are the dioxin/furan congeners. More limited data are available for chlorinated phenols and for extractable organic chlorine.
Dioxin/furan congener concentrations in water declined to below detection limits during the Ecosystem Study in 1990-1991. After 70% chlorine dioxide substitution, no congeners were detected.
Concentrations of (TCDD/F) in suspended sediments declined during the Ecosystem Study for 1990-1991 (during the period when 70% chlorine dioxide substitution was implemented). Monitoring since complete substitution of chlorine dioxide has shown that (TCDD/F) on suspended material, is at or near the analytical detection limit as shown in Fig.5
Monitoring of two fish species, mountain whitefish and burbot (Lota lota), has shown declines in concentration of (TCDD/F) since chlorine dioxide substitution was increased. In mountain whitefish fillets, the levels have declined from above Health and Welfare Canada's limit for human consumption (20 ppt TEQ) to levels that are consistently well below the limit as shown in Fig. 6.
Concentrations of (TCDD/F) in burbot liver (which has a very high lipid content) have declined more slowly; however, the most recent data from 1993 and the spring of 1994 (after incorporation of complete chlorine dioxide substitution), have shown significant decreases as shown in Fig. 7. Other congeners are still detectable in both mountain whitefish fillets and burbot livers, with concentrations declining concomitantly with (TCDD/F).
Chlorinated Phenol Compounds
Concentrations of chlorinated phenolic compounds in river water have declined dramatically since the implementation of 70% and then subsequent complete substitution of chlorine dioxide. The environmental data parallel the results seen in the effluent.
In 1990, 26 chlorinated phenolic compounds were detected at the near-field water quality site, with several present at greater than 1 ppb. In the spring of 1991, only three chlorinated phenolic compounds were detected at the near-field site; all concentrations were below 0.1 ppb. By the fall of 1991 only one compound, 6-chlorovanillin was detected. These results were seen after 70% chlorine dioxide substitution. Recent data for complete chlorine dioxide substitution have shown that concentrations remain below detection limits with the exception of 6-chlorovanillin, which was present at a concentration of 2 ppb at the near-field site in the spring of 1994.
Suspended sediments carried a variety of chlorinated phenolic compounds (including the more highly substituted compounds) during the period just before and after 70% chlorine dioxide substitution (1990-1991). Concentrations were generally at or marginally above detection limits (which were 0.5 ppb in 1991), although some were present well above detection limits during periods of low flow (e.g. 15 compounds were detected in the fall of 1991, ranging from 0.8 to 230 ppb). After complete substitution with chlorine dioxide, fewer compounds were detected. For example, in the fall of 1993, only 4 compounds were detected ranging from 1.1 to 13 ppb.
Extractable Organic Chlorine Compounds, (EOCI)
EOCI was not detected in water in 1991 (detection limit of 10 ppb); however, with an improvement in detection limits in 1992, a concentration of 6.2 ppb was reported for a site just downstream of the mill. EOCI upstream of the mill was 4.5 ppb, indicating other sources of extractable organic chlorine compounds in the watershed.
In the Fall of 1993, EOCI was not detected in river water.
Trends in suspended sediment concentrations of EOCI are difficult to discern. In 1991, the highest concentrations were upstream of the mill (1.6 ppm); concentrations downstream of the mill were from 0.89 ppm to the detection limit (0.5 ppm). In 1992, EOCI was not detectable. In the fall of 1993, a concentration of 12 ppm was reported at the site just downstream of the mill. Decant from a holding pond containing dredged sludge from the effluent ponds (dredging was done in June, 1993) may have resulted in elevated EOCI concentrations during this sampling period.
EOCI concentrations in mountain whitefish fillets have shown a steady decline since 1990. Concentrations in 1990 ranged from 13-43 ppm. In 1991, concentrations had declined an order of magnitude to 3-7 ppm. In the fall of 1993, concentrations had declined further to 1-2 ppm. The steady decline in EOCl concentrations in fish fillets indicates that exposures are low with metabolism and excretion exceeding any intake.
EOCI concentrations in mountain whitefish bile have also declined. In 1991, concentrations just downstream of the mill ranged from 24-192 ppm. In the fall of 1993, EOCI was not detected in mountain whitefish bile. The absence of detectable EOCI in fish bile indicates very low or no recent exposure (either via food or water).
Resin and Fatty Acids
Resin and fatty acid compounds were not detected in Wapiti/Smoky waters upstream and downstream of the mill in 1990-1991. In 1992, certain compounds were present at higher concentrations downstream of the mill, including myristic, palmitic, linoelic, stearic and arachidic acids, with concentrations ranging from 0.01-49 ppb. Two chlorodehydroabietic (mono, di) acid compounds were present downstream, but not upstream. Concentrations of these two compounds were 0.025-0.038 ppb. Recent data from the fall of 1993 and in the spring of 1994 show all resin and fatty acids were non detectable (< 0.0 1 ppb) with the exception of palmitic acid which was detected at 0.02 ppb.
Resin and fatty acids were detected in both longnose sucker and mountain whitefish bile in 1991. Thus, these compounds were being taken up by fish and then metabolized and excreted via the bile. The source of exposure may have been the bottom sediments, where resin and fatty acids were present in detectable quantities in 1991.
In the fall of 1993, resin and fatty acids were not detected in fish bile samples. This indicates that exposure to these compounds has been reduced, perhaps in response to improved efficiency of the effluent treatment system.
Biomarkers are anatomical, physiological, and biochemical responses of an organism which indicate exposure to and/or effects of natural or anthropogenic (man-made) stressors . A wide suite of biomarkers have been used in attempts to assess the environmental impact of pulp mill effluents on organisms in receiving waters. Initial studies in Sweden associated biomarker changes with organic eutrophication and chemical toxicity, including chlorinated organic compounds . Subsequent Canadian biomarker investigations have shown inconsistent changes with two exceptions, the induction of one mixed function oxidase enzyme (EROD or P4501A) and indications of potential decreases in sex steroid hormones. These changes have been found at both bleached and unbleached mill sites [6-7, 18-24].
In this study, most biomarkers showed no statistically significant changes between exposed and reference populations or trends associated with body burdens. Histopathology showed no tumors or pre-neoplastic lesions, even in the oldest fish. Tissue lesions that were observed occurred at similar low rates in both exposed and reference populations and were attributed to parasites .
Hematology and blood chemistry showed no statistical differences between exposed and reference mountain whitefish, the species with the highest body burden. In longnose sucker, statistical differences were seen at various sites and times in red blood cell hemoglobin content and serum chloride, potassium, gamma globulin, total protein and albumin levels. However, the patterns were inconsistent over time, and many differences occurred between Smoky and Wapiti fish rather than between exposed and reference fish, perhaps due to habitat differences. It is noteworthy that the reference site more closely matched the Wapiti habitat than the Smoky habitat .
The reproductive assessment based on relative gonad size and the egg number and the size was extended by analyzing the serum levels of steroid hormones. In the more highly exposed whitefish, no differences were observed in hormone levels or patterns between exposed and reference sites. The results in this study for mountain whitefish are not inconsistent with recent observations in a ten mill survey in Eastern Canada. Hormone decreases were observed at both bleached and unbleached mill sites while hormone levels were similar between mill effluent exposed fish and local reference fish at other sites .
In longnose suckers, hormone results were inconclusive because of highly variable data and small sample sizes. Research is continuing.
Planar hydrophobic compounds, both chlorinated and unchlorinated, can induce the specific mixed function oxidase enzyme P4501A in several fish tissues, including liver. The enzyme can be measured directly using immuoblotting techniques (P4501A) and can be measured enzymatically by the de-ethylation of ethoxyresorufin (EROD). EROD or P4501A induction has been observed in exposed fish to pulp mill effluent in previous studies at both bleached and unbleached sites [6-7, 18-20, 22, 24, 27-29]. However, the consequences of induction are not known. EROD induction is best used as a marker of exposure and an indication that other, effects-related, parameters should be understood.
At Grande Prairie in 1991, induction was highest in mountain whitefish, (30 fold on average; 90 fold maximum in one individual), with levels highest near the discharge and diminishing downstream of the mill. The biological gradient coincided with an observed gradient with mountain whitefish muscle tissue TEQ. The relationship was statistically significant with an r2 value of 0.73 . A systematic analysis with other measured endpoints indicated that induction did not correlate with any adverse trends, including postulated associations such as increased liver size or reduced gonad size.
An association was observed between the degree of induction and fillet levels of 2,3,7,8-TCDD-TCDF expressed as toxic equivalents [24, 29]. Mountain whitefish have been subsequently monitored in 1992 and 1993 for hepatic EROD/P4501A induction. These results show a steady fall in EROD/P4501A induction which appears to parallel fillet TCDD,-TCDF TEQ levels (Figure 8 A and 8 B). As the half-life of induction and TCDD,-TCDF toxic equivalents has been calculated to be approximately one year, these findings are consistent for other feral fish species for TCDD.
These data indicate that exposure to (TCDD/F) has been drastically reduced or eliminated and that levels will continue to decline over time as fish eliminate the present body burdens.
Grande Prairie is committed to continuous environmental improvement. An ambitious environmental improvement plan began in 1992 when Procter & Gamble implemented 100% chlorine dioxide substitution in the first stage of bleaching. In 1993, the mill, now operating as Weyerhaeuser Canada, continued the program by starting-up a condensate stripping system, installing curtains and expanding the aeration capacity in the secondary waste treatment plant and implementing enhanced environmental monitoring and management practices.
These actions have further improved the quality and the stability of the final mill effluent:
These improvements in effluent quality are only one aspect of environmental protection. True environmental impact or the lack of impacts (the vision of a minimum impact mill) can only be assessed in the receiving ecosystem. The Grande Prairie mill has over the period 1990 through 1993 systematically evaluated the impact of the mill effluent on the Wapiti/Smoky River Ecosystem. The results of that analysis show there was no evidence of deleterious effects on fish species composition, distribution or relative abundance among exposed fish. Populations reproduce successfully and grow at comparable rates to those of reference fish.
Furthermore, receiving water quality continues to improve. For example, dioxins and furies have declined to levels that are either at or below detection limits in water and suspended sediments.
Concentrations of dioxins and furans in fish have also decreased, although at a slower pace. The most recent data show that levels in mountain whitefish fillets are consistently below Health and Welfare Canada's human consumption guideline of 20 ppt toxic equivalents (TEQ). Concentrations in burbot livers have also decreased significantly.
Chlorinated phenol concentrations have paralleled the trends seen for dioxins and furans, with a rapid decrease in both water and suspended sediments in response to process changes. For example, concentrations of tri-, tetra- and penta chlorinated phenols in water decreased approximately 200-1000 fold after implementing 100% chlorine dioxide substitution.
Investigations of subtle parameters, biomarkers have shown that the induction of the mixed function oxidase, EROD or P450A1, continues to decline. This coincident with declining fish body burdens of 2,3,7,8-TCDD and 2,3,7,8-TCDF. Investigations of the impact of mill effluent on circulating sex steroids in spawning fish show no difference between exposed and reference mountain whitefish.
The results of the environmental improvement plan, coupled with the most comprehensive assessment of fish reproduction undertaken at a pulp mill, shows that exposed fish species are not affected by this pulp mill effluent.
The authors gratefully acknowledge the hard work, commitment and dedication to excellence of Weyerhaeuser Canada Ltd. Grande Prairie operations. The authors also wish to thank EMA/Golder Associates, the Procter & Gamble Co. and ERCO Worldwide for their support.