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Federal Register / Vol. 86, No. 52 / Friday, March 19, 2021 / Rules and Regulations through the cell membrane, and flocculation of precipitated aluminum on the gill. Bioavailable aluminum is the toxicologically relevant fraction of aluminum which results from a combination of dissolved and precipitated aluminum, in contrast to mineralized non-toxic forms of aluminum.4 The non-bioavailable fraction of aluminum includes large suspended particles, clays, and aluminosilicate minerals.
EPAs 2018 national recommended criteria document Section 2.6.2 from pp. 2225 explains the science behind this understanding of aluminum chemistry and toxicity in more detail.
There is also relevant discussion of aluminum chemistry Section 2.2 from pp. 710 and mode of action and toxicity Section 2.3 from pp. 1016
that help explain the factors affecting bioavailability and toxicity.

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B. Final Acute and Chronic Aluminum Criteria for Oregons Fresh Waters EPA is promulgating aluminum criteria for Oregon that incorporate by reference the calculation of CMC and CCC freshwater aluminum criteria values for a site using the 2018 national recommended criteria.5 Doing so means that the CMC and CCC freshwater aluminum criteria values for a site shall be calculated using the 2018 Aluminum Criteria Calculator V.2.0 Aluminum Criteria Calculator V.2.0.xlsx or a calculator in R or other software package using the same 1985 Guidelines calculation procedure and underlying model equations as in the Aluminum Criteria Calculator V.2.0 Excel spreadsheet, as established in the 2018
national recommended criteria.
Consistent with the 2018 national recommended criteria, the final water quality criteria for aluminum in Oregon fresh waters are expressed as the CMC
as a one-hour average total recoverable aluminum concentration in mg/L and the CCC as a four-day average total recoverable aluminum concentration in 4 Per Rodriguez et al. 2019: To properly characterize the Al concentrations in the toxicity studies, a method was needed that could discriminate bioavailable Al from mineral forms of Al. An extraction method at pH 4 for bioavailable Al was developed and evaluated using C. dubia chronic toxicity studies in the presence of TSS. It is concluded that the proposed method is better able to discriminate chronic toxicity effects attributable to bioavailable Al from mineralized nontoxic forms of Al compared with existing methods using total or total recoverable Al i.e., extraction at pH 1.5.
5 USEPA. 2018. Final Aquatic Life Ambient Water Quality Criteria for Aluminum. U.S. Environmental Protection Agency, Office of Water, Washington, DC. EPA822R18001. https www.epa.gov/
sites/production/files/2018-12/documents/
aluminum-final-national-recommended-awqc.pdf.

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mg/L. The CMC and CCC are not to be exceeded more than once every three years.
EPA is promulgating multiple footnotes to the criteria statement to provide clarification on the criterias intended application, and highlights two in this paragraph. The first footnote specifies that to apply the aluminum criteria for CWA purposes, criteria values based on ambient water chemistry conditions must protect the water body over the full range of water chemistry conditions, including during conditions when aluminum is most toxic. The second footnote states that 1
these criteria are based on aluminum toxicity studies where aluminum was analyzed using total recoverable analytical methods; 2 Oregon may utilize total recoverable analytical methods to implement the criteria; 3
for characterizing ambient waters, Oregon may also utilize, as scientifically appropriate and as allowable by State and Federal regulations, analytical methods that measure the bioavailable fraction of aluminum, as described above, e.g., utilizing a less aggressive initial acid digestion, such as to a pH of approximately 4 or lower, that includes the measurement of amorphous aluminum hydroxide yet minimizes the measurement of mineralized forms of aluminum such as aluminum silicates associated with suspended sediment particles or clays; and 4 Oregon shall use measurements of total recoverable aluminum where required by Federal regulations.
Commenters were generally supportive of EPAs proposal to base its promulgation for Oregon on EPAs 2018
national recommended criteria for aluminum. EPA acknowledged in the preamble to the proposal that the Agency may consider future modifications to the criteria if warranted based on, among other things, further public input, tribal consultation, new data, or evaluations of listed species completed during Endangered Species Act ESA consultation, or the results of ESA consultation. On February 13, 2020
and July 1, 2020, EPA completed consultation with the U.S. Fish and Wildlife Service USFWS and NOAA
Fisheries, respectively. After evaluating potential effects of the Agencys action on federally-listed species during ESA
Section 7a2 consultation with USFWS and NOAA Fisheries, in addition to consideration of comments received during the public comment period associated with the proposed rulemaking, EPA is promulgating aluminum criteria consistent with the 2018 national recommended criteria.

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The 2018 national recommended criteria represent the latest scientific knowledge on aluminum speciation, bioavailability, and toxicity, and provide predictable and repeatable outcomes. Consistent with the Aquatic Life Guidelines, the 2018 national recommended criteria protect aquatic life for acute effects survival and immobility, as well as chronic effects survival, growth, and reproduction at a level of 20% chronic Effects Concentration EC20 for the 95th percentile of sensitive genera. The docket for the 2018 national recommended criteria document contains detailed information on the science underlying that recommendation Docket ID: EPAHQ
OW20170260.
Comments Regarding Total Recoverable Aluminum and Use of an Emerging Analytical Method As mentioned above, commenters pointed out that, as EPA had acknowledged in its 2018 national recommended criteria document, the current test methods for total recoverable aluminum may, in some waters, overestimate the amount of aluminum that will be toxic to aquatic life in ambient waters in Oregon.
Commenters suggested that in order to better approximate the toxic fraction of aluminum, EPA should allow use of an emerging analytical method that measures bioavailable aluminum by using an initial digestion at pH 4.
Commenters urged use of such an analytical method to characterize aluminum concentrations in ambient waters, particularly in waters with high levels of total suspended solids suggesting the presence of colloidal, particulate, and clay-bound aluminum.
Some commenters requested that the final criteria for Oregon be expressed as bioavailable or total recoverable aluminum to confirm availability for use of an alternative analytical method.
EPA acknowledges in the final rule that the promulgated criteria are based on aluminum toxicity laboratory studies where aluminum was analyzed using total recoverable analytical methods.
However, EPA also acknowledges that under natural conditions not all of these forms of aluminum would be biologically available to aquatic species.
All of the approved total recoverable methods require that samples be preserved in the field by acidifying to pH <2 and digested in the laboratory with strong acid solution that dissolves the monomeric and polymeric forms of aluminum, in addition to colloidal, particulate, and clay-bound aluminum.
Over the last three decades, the
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