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Federal Register / Vol. 86, No. 52 / Friday, March 19, 2021 / Rules and Regulations
criteria. These taxa are intended to be representative of a wide spectrum of aquatic life, such that the representative taxa serve as surrogates for untested species. Therefore, the representative test organism species do not need to be present in the waters where the criteria will apply. A state is not precluded from relying on toxicity data using resident species to develop site-specific criteria to apply at a localized site. In developing site-specific criteria, EPA
recommends that the state maintain similar broad taxonomic representation in calculating the site-specific criteria to ensure protection of the most sensitive species at the site. If a state chooses to carry out the deletion of data portion of the species re-calculation process, the state should consider how to demonstrate that the species included in the derivation of EPAs national recommended criteria are not present and would not serve as surrogates for other species that occur at the site.3
III. Freshwater Aluminum Aquatic Life Criteria A. EPAs National CWA Section 304a Recommended Freshwater Aluminum Criteria
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EPAs 2018 national CWA Section 304a recommended freshwater aquatic life criteria for aluminum Final Aquatic Life Ambient Water Quality Criteria for Aluminum 2018, EPA 822R18001, as cited in the Federal Register at 83 FR
65663, December 21, 2018, referred to in this action as the 2018 national recommended criteria, were developed following the Aquatic Life Guidelines.
These recommended criteria update and replace EPAs 1988 national CWA
Section 304a recommended freshwater aquatic life criteria for aluminum. The 2018 national recommended criteria apply to fresh waters and include a calculator that takes into account three water chemistry characteristics that affect aluminum toxicity. The 2018
national recommended criteria reflect the latest scientific knowledge and understanding of the interaction between water chemistry and aluminum toxicity, and represent a scientifically defensible method upon which EPA is basing this CWA action to establish WQS for fresh waters in Oregon 83 FR
65663, December 21, 2018.
3 USEPA. 2013. Revised Deletion Process for the Site-Specific Recalculation Procedure for Aquatic Life Criteria. U.S. Environmental Protection Agency, Office of Water, Washington, DC. EPA
823R13001. https www.epa.gov/sites/
production/files/2015-08/documents/revised_
deletion_process_for_the_site-specific_
recalculation_procedure_for_aquatic_life_
criteria.pdf.

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The 2018 national recommended criteria are based upon Multiple Linear Regression MLR models for fish and invertebrate species that use sitespecific pH, dissolved organic carbon DOC, and total hardness inputs to quantify the effects of these water chemistry parameters on the toxicity of aluminum to aquatic organisms. The MLR models normalize the available toxicity data to accurately reflect the effects of the site-specific water chemistry pH, DOC, total hardness on the toxicity of aluminum to tested species. The normalized toxicity test data are then used in a criteria calculator to generate criteria for specific ambient water chemistry conditions. The numeric outputs of the 2018 national recommended criteria calculator for a given set of conditions vary depending on the site-specific pH, DOC, and total hardness entered into the calculator. The calculator outputs CMC and CCC for a given set of input conditions are numeric values that would be protective for that set of input conditions i.e., water-chemistrycondition-specific CMC and CCC
outputs.
Users of the 2018 national recommended criteria can generate criteria magnitude values in two ways:
1 Use the lookup tables provided in the criteria document to find the numeric aluminum CMC and CCC most closely corresponding to the local conditions for pH, DOC, and total hardness; or 2 use the provided Aluminum Criteria Calculator V2.0
Excel spreadsheet to enter the pH, DOC, and total hardness conditions at a specific site to calculate the numeric aluminum CMC and CCC corresponding to the local input conditions.
In its 2018 national recommended criteria, EPA expressed the aluminum criteria as total recoverable metal concentrations. The primary reason for the expression of the criteria as total recoverable aluminum concentrations is because the laboratory toxicity tests used in the effects assessment in the development of the aluminum criteria reported the aluminum concentrations as total recoverable aluminum. The use of total aluminum concentrations is justified for laboratory toxicity test data where the total aluminum concentration is in either a dissolved monomeric form or precipitated forms e.g., aluminum hydroxides of aluminum. The laboratory dilution waters in tests used for EPAs criteria development did not contain suspended solids, clays, or particulate matter where aluminum could be bound. However, total recoverable aluminum concentrations measured in natural waters may
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overestimate the potential risks of toxicity to aquatic organisms if suspended solids, clays, or particulate matter to which aluminum may be bound are present, because total recoverable methods measure bioavailable and non-bioavailable forms of aluminum.
As discussed in Section 2.6.2 of EPAs 2018 national recommended criteria document, the different forms of aluminum vary in toxicity. The criteria document discusses differences between aluminum toxicity in a controlled laboratory setting and the toxicity of aluminum in natural waters that contain suspended particles, clays, and aluminosilicate minerals not present in lab waters. Dissolved and particulate e.g., aluminum hydroxides aluminum, as well as small sized colloids containing aluminum, exhibit toxic effects on aquatic life depending on the pH, DOC, and total hardness of the waters. Total recoverable aluminum methods determine the total concentration of monomeric both organic and inorganic forms of aluminum, polymeric and colloidal forms, as well as particulate forms and aluminum sorbed to clays present in a sample. Total recoverable methods use a strong acid pH <2 digestion step to prepare the sample for measurement. In contrast, methods to determine dissolved concentrations of aluminum involve filtering test samples prior to digestion, which excludes particulate forms of aluminum from the test sample. Methods to determine dissolved concentrations of aluminum, therefore, may underestimate the toxicity of the aluminum in a sample if the particulate forms including aluminum hydroxide precipitates that contribute to toxicity are not measured. In conclusion, dissolved aluminum measurements are not appropriate for comparison to the aluminum criteria that EPA is promulgating for Oregon. EPA
acknowledges, as several commenters noted during the comment periods for both EPAs 2017 draft national CWA
Section 304a recommended criteria for aluminum and EPAs proposed criteria for Oregon, that not all forms of aluminum that may be present in ambient waters are biologically available or bioavailable to aquatic species. Bioavailable aluminum or the bioavailable fraction of aluminum is defined as the amount of aluminum that is available to cause a biological response in an aquatic organism. The best measures of bioavailability involve interactions of aluminum with a membrane e.g., aluminum binding to proteins of gill membranes, diffusion
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