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National Assessment of Pulp and Paper Environmental Effects Monitoring Data: Findings from Cycles 1 through 3

9.0 Summary and Conclusions

Having completed its third cycle of data collection and reporting, the EEM program has provided an extensive database and a fairly robust picture of the nature of the effects of pulp and paper mill effluents on receiving water biota across the country.

The response patterns observed for effluent-exposed fish and benthic invertebrates during Cycle 3 were, for the most part, similar to those measured during Cycle 2. The national average response pattern measured for fish in both Cycles 2 and 3 was consistent with one of nutrient enrichment overlaid by metabolic disruption. That is, exposed fish have consistently shown evidence of increased food availability or increased food absorption (fatter, faster growing, with larger livers) together with disruption of allocation of resources to reproduction (smaller gonads). This latter metabolic disruption may include some aspect of endocrine disruption associated with problems in producing sufficient sex steroid hormones. Other observed response patterns for fish have included nutrient enrichment without measurable metabolic disruption, nutrient limitation and chemical toxicity. These findings agree with a number of research studies that have been carried out at mills across the country (reviewed by Munkittrick et al. 1991, 1994, 2000, Lowell et al. 2003, 2004).

The national average response for benthic invertebrate communities in both Cycles 2 and 3 was consistent with one of eutrophication, ranging from mild to more pronounced, partly depending on habitat type. More specifically, benthic invertebrate communities exposed to pulp mill effluent have commonly exhibited increases in abundance, together with some combination of increases, decreases or no change in taxon richness, depending on the degree of eutrophication. Other observed benthic invertebrate response patterns have included toxicity or smothering effects. These response patterns and the mechanisms leading to them have been confirmed by a number of experimental studies conducted at mills across Canada (reviewed by Culp et al. 2000, Lowell et al. 2000, 2003).

The sublethal toxicity data showed clear improvements in effluent quality from Cycle 1 to Cycle 2, with, for the most part, no further changes in effluent quality in Cycle 3. It should be noted, however, that the sublethal toxicity reporting methodology and selection of tests do not track all aspects of effluent quality. In particular, they do not currently measure nutrient enrichment effects of the effluent (the most commonly observed effect in the field surveys), although the tests could be modified to provide some information on nutrient enrichment effects. Also of note, and consistent with the reductions in gonad size measured in the fish field survey, the most sensitive sublethal toxicity tests were those that measured a reproductive endpoint (although these did not include fish tests).

Some possible shifts in the patterns of effects measured in the fish and benthic invertebrate field surveys between Cycles 2 and 3 were also observed. The fish data have suggested some overall lessening of nutrient enrichment effects. On a habitat-specific basis, the benthic invertebrate data have shown evidence of a possible lessening of toxicity/smothering effects in marine-type habitats, as well as more pronounced eutrophication in freshwater depositional habitats. These shifts for fish and invertebrates may be due to a variety of possible causes. For example, the average reduction in number of invertebrate taxa observed in Cycle 3 may have led to a reduction in food availability for sentinel fish at some mills (resulting in reduced nutrient enrichment in fish), if the taxa that were lost were also taxa that the fish would normally use as a food source. Alternatively, the shifts in fish and invertebrate responses may have been influenced by changes between cycles in study designs and selection of study areas. It is also possible that the fish and benthic invertebrate response patterns will continue to show slight shifts from cycle to cycle due to natural variability in the receiving environment or to anthropogenic changes through time that are unrelated to exposure to pulp and paper mill effluent. Under this extrinsic variability scenario, these shifts may include either increases or decreases in individual endpoints, sometimes changing direction from cycle to cycle. In this situation, the underlying, time-averaged response pattern may remain approximately the same, unless these extrinsic factors show a long-term, unidirectional trend.

The sublethal toxicity data suggest that effluent quality has not changed between Cycle 2 and Cycle 3. However, as noted above, not all aspects of effluent quality are currently measured by the sublethal toxicity tests (particularly nutrient enrichment), so it is possible that changes in effluent quality may have contributed to the field survey shifts outlined above. It should also be noted that some of these shifts may have resulted from gradual recovery from (or, in some cases, added accumulation of) historical effluent deposits in the receiving environment. Further, some of the shifts may have resulted from lag effects. That is, recovery from (or worsening of) some effluent effects may not be evident until some time after release of the effluent causing the effects, as effects are gradually transmitted through complex trophic food webs. Additional information is required to fully address these issues. The results obtained in Cycle 4 and beyond, together with more focused studies at some mills, will help to answer these questions.

In the meantime, the national analyses have identified a subset of mills and kinds of effects toward which more extensive monitoring should be directed. Finer-resolution evaluations will be made at the regional level, but initial estimates are that approximately 20% of the monitored mills are expected to conduct only sublethal toxicity testing in Cycle 4, while roughly another 20% are would be expected to progress to determinations of the extent and magnitude of effects or, for some mills, investigations of the causes of the effects.

Despite the mainly small shifts in response patterns noted above, the effects measured in the fish and benthic invertebrate field surveys were, for the most part, quite similar between Cycles 2 and 3. Most notably, both cycles have shown 1) evidence of overall nutrient enrichment or eutrophication (with the degree of response partly linked to habitat type) and 2) a reduction in fish gonad size that has remained virtually unchanged over two cycles of data collection.