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Long-term toxicity to aquatic invertebrates

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Literature Review: Six long-term chronic toxicity studies to two species of aquatic invertebrates(Ceriodaphnia dubia and Daphnia magna) were identified as acceptable studies. See Table # "Overview of long-term effect on aquatic invertebrates" (below). ECr10s were calculated using raw data provided from each study using the statistical program Toxicity Relationship Analysis Program (TRAP) version 1.10 from the US EPA National Health an Environmental Effects Research Laboratory (NHEERL). All other endpoints were as reported in each study. NOECs and EC10s ranged from 0.076 to 4.9 mg Al/L and 0.021 to 0.997 mg Al/L, respectively. Water quality data for these studies suggest a direct relationship between toxicity and pH, hardness, and DOC. For studies that experimentally manipulated water quality (e.g., CIMM 2009 and 2010a ), toxicity decreased with increasing pH, hardness, and DOC.

Recent studies conducted by the Chilean Mining and Metallurgy Research Center (CIMM) tested aluminium toxicity to C. dubia and D. magna (one data point) across a range of pH, DOC, and hardness values. These results demonstrated that increasing DOC concentration has a protective effect on aluminium LC50s for invertebrates. Increasing water hardness also had a protective effect. Aluminium toxicity was reduced at high pH, but a larger reduction was observed when changing pH from 6 to 7 than from 7 to 8. 

The acute fish BLM developed for S. salar was applied to the chronic invertebrate data (CIMM 2009, CIMM 2010; Figure 7.1.1.2.2.-1) by developing a critical accumulation value appropriate for this organism. In addition, the chronic invertebrate data suggested that overall fit would be improved with a small increase in the Ca binding parameter (i.e. the log K for Ca binding at the biotic ligand was increased from 4.2 to 4.8), which is the same adjusted value used in the chronic fish model. After application of the modified Al BLM, the variability in the response curve data substantially decreased (Figure 7.1.1.2.2.-2). These data were subsequently used to establish the CA10 (i.e. the critical accumulation level that results in a 10% reduction in reproduction), and likewise, the CA50. The CA10 and CA50 values can then be used to predict EC10 values and EC50 values in various water types.  

Figures 7.1.1.2.2.-3 and 7.1.1.2.2.-4 provide an evaluation of the ability of the chronic invertebrate Al BLM to predict EC50 and EC10 values. All of the EC50 values are predicted within 2-fold of the reported EC50 values. Most of the EC10 values are predicted within 2-fold of the reported EC10 values, and all of the predicted EC10 values are within 4-fold of the reported values. These results indicate that the chronic Al BLM performs reasonably well for predicting sublethal effects of Al on invertebrates. It should be noted that in both the fish and the invertebrate tests, saturation index calculations suggested that the majority of the toxicity values exceed Al(OH)3solubility. However, bioavailability factors (i. e. pH, DOC, and hardness) still are consistent with the trends predicted by the Al BLM.

Two additional LC50 values that are not included in this comparison were reported for pH 7 and pH 8 in filtered test media (i. e., filtered before organisms were exposed). The filtered test media were approximately 5-fold less toxic, meaning that their LC50s were approximately 5-fold higher than the results from exposure to unfiltered media. Therefore, toxicity was largely a function of exposure to aluminium hydroxides, which are removed by filtration through these types of filters.