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

8.1 Sublethal Toxicity Testing - Monitoring Changes in Effluent Quality Among Cycles

Sublethal toxicity endpoints can be used to compare the quality of effluent at different times. Comparisons among results for Cycles 1, 2 and 3 were made for the distributions of endpoints from all Canadian mills for each freshwater and estuarine/marine test species (Figs. 12 and 13). For each test, all IC25s were compiled, and the percentage of tests falling into each defined category range of effluent concentration (i.e., =100% v/v, =60% to <100% v/v, =36% to <60% v/v, etc.) was calculated. For example, Figure 12A illustrates the results of sublethal toxicity tests conducted on Ceriodaphnia dubia during Cycles 1, 2 and 3 of the EEM program. The vertical bars indicate the percentage of tests conducted in each cycle in which C. dubia exhibited a 25% decrease in function at that threshold of concentration. A high proportion of tests carried out in Cycle 1 showed this effect at concentrations of effluent below 1%; however, during Cycles 2 and 3, between 25% and 30% of mills did not show this effect at concentrations equal to or greater than 100% effluent.

The Cycle 3 sublethal data sets were similar to the Cycle 2 results for the freshwater test species (C. dubia, fathead minnow and Selenastrum capricornutum), confirming the improvement in effluent quality from Cycle 1 (Fig. 12; note that S. capricornutum is now classified as Raphidocelis subcapitata). This improvement in effluent quality was attributed in the national assessment of Cycle 2 EEM data to the installation of advanced effluent treatment after Cycle 1. The results of the rainbow trout toxicity test, which is used only in British Columbia, however, indicated an increase in moderate toxicity of effluent (i.e., >36% v/v to >60% v/v) in comparison with Cycles 1 and 2 (Fig. 12C). The reason for this will remain unknown without an in-depth analysis of the individual mills. Problems with egg viability, however, were reported. To resolve this issue, the testing period was moved from January to May, which may have altered the degree of effluent toxicity that was measured.

For the marine toxicity test results, in particular the toxicity tests with Champia parvula, topsmelt and inland silversides, Cycle 3 results were similar to the Cycle 2 results. The inland silverside growth assay results for Cycle 3 confirmed the Cycle 2 improvement in effluent quality in comparison with Cycle 1 (Fig. 13). The Cycle 3 results for the topsmelt growth inhibition test, which showed no toxicity to effluent at full concentration, were similar to the Cycle 2 results, but no comparison could be made with Cycle 1, as this test was not used at that time (Fig. 13). Although there is a wide spread in the distribution of the toxicity data for the Champia reproduction assay, the data for both Cycles 2 and 3 generally indicate an improvement in effluent quality compared with the Cycle 1 test results (Fig. 13).

Comparison of sublethal toxicity to freshwater species in Cycles 1, 2 and 3. Note that for the rainbow trout test, the EC25 is the effective concentration for 25% of the embryos

Figure 12: Comparison of sublethal toxicity to freshwater species in Cycles 1, 2 and 3. Note that for the rainbow trout test, the EC25 is the effective concentration for 25% of the embryos.

Comparison of sublethal toxicity to marine species in Cycles 1, 2 and 3.

Figure 13: Comparison of sublethal toxicity to marine species in Cycles 1, 2 and 3.

For the echinoderm fertilization test, there was a slight shift in the data spread from no toxicity in Cycle 2 to a moderately toxic effect (i.e., in the range of <22% v/v to =7.8% v/v) in Cycle 3. The reason for this shift will not be known without further analysis of the individual mill data. There may be higher variability in the echinoderm toxicity data because of the different species that were used for this test between cycles. For Cycle 3, 85% of test species were sea urchins, including Lytechinus pictus, Arbacia puctulata and Strongylocentrotus purpuratus, and 15% of test species were sand dollars (Dendraster excentricus). In contrast, Arbacia was not used in Cycle 2.

Looking at both the freshwater and marine histograms over all three cycles (Figs. 12 and 13), the tests measuring reproductive endpoints (C. dubia, echinoderms, C. parvula) were shifted the farthest to the right, indicating the higher sensitivity of those tests.

In Figure 14, the percentages of tests with IC25s showing no sublethal response in the highest test concentration are compared for Cycles 1, 2 and 3. For most of the tests, the percentages of tests reporting no sublethal response increased from Cycle 1 to 2 and showed little further change in Cycle 3 (as discussed above, methodological difficulties were encountered with the rainbow trout test).

Percentages of sublethal tests showing no effect at highest concentration

Figure 14: Percentages of sublethal tests showing no effect at highest concentration.