Development and application of a biotic ligand model for predicting the chronic toxicity of dissolved and precipitated aluminum to aquatic organisms

Abstract

Aluminum (Al) toxicity to aquatic organisms is strongly affected by water chemistry. Toxicity-modifying factors such as pH, dissolved organic carbon (DOC), hardness, and temperature have a large impact on the bioavailability and toxicity of Al to aquatic organisms. The importance of water chemistry on the bioavailability and toxicity of Al suggests that interactions between Al and chemical constituents in exposures to aquatic organisms can affect the form and reactivity of Al, thereby altering the extent to which it interacts with biological membranes. These types of interactions have previously been observed in the toxicity data for other metals, which have been well described by the biotic ligand model (BLM) framework. In BLM applications to other metals (including cadmium, cobalt, copper, lead, nickel, silver, and zinc), these interactions have focused on dissolved metal. A review of Al toxicity data shows that concentrations of Al that cause toxicity are frequently in excess of solubility limitations. Aluminum solubility is strongly pH dependent, with a solubility minimum near pH 6 and increasing at both lower and higher pH values. For the Al BLM, the mechanistic framework has been extended to consider toxicity resulting from a combination of dissolved and precipitated Al to recognize the solubility limitation. The resulting model can effectively predict toxicity to fish, invertebrates, and algae over a wide range of conditions. Environ Toxicol Chem 2018;37:70-79. C 2017 SETAC

Evaluating the effects of pH, hardness, and dissolved organic carbon on the toxicity of aluminum to freshwater aquatic organisms under circumneutral conditions

“…It is possible that hardness may affect membrane permeability because Ca 2þ ions are known to have this effect in fish [5,7], which may also protect against negative respiratory effects of Al hydroxides. The DOC and pH likely influence toxicity owing to controls over the formation of colloidal Al precipitates or via direct control over Al bioavailability [16]. The DOC effects evaluated in the present study were based on laboratory exposures to Suwannee River NOM, which is a commonly used natural form of DOC for metal toxicity studies.…”

“…Specifically, these tests were used in the development of an Al biotic ligand model (BLM), which, based on the water quality parameters that drive Al speciation, can predict the toxicity of both dissolved and precipitated forms of Al to aquatic organisms [16]. Unlike BLMs for other metals (e.g., copper and zinc [4,36]), which are based exclusively on dissolved metal concentrations and chemical speciation, the BLM for Al incorporates the effects of both dissolved and precipitated forms of Al.…”

“…Although hardness may be a reliable predictor of acute Al toxicity, future regulatory frameworks should focus instead on the effects of additional water quality factors such as DOC and pH. Ultimately, the best regulatory solution would involve the use of a BLM [16] or MLR [15] framework, because this would offer a much more robust and accurate explanation of toxicity on the basis of bioavailability based on exposure to both dissolved and precipitated forms of Al.…”

“…Therefore, the present study presents the results from new aquatic toxicity studies that empirically evaluated the influences of pH, hardness, and DOC on Al toxicity to freshwater fish, invertebrates, and algae under circumneutral conditions. These data, along with the data from 2 companion studies [13,14], will be used to establish empirical relationships between Al toxicity and water quality conditions, and to assist in the development of bioavailability models for derivation of aquatic life protection criteria [13,15,16]. To ensure that these data take into account the effects of insoluble forms of Al under circumneutral conditions, we also conducted studies to develop Al solution aging protocols to ensure adequate representation of chronic environmental exposure conditions, as well as studies that would help us to better understand the relative importance of dissolved versus precipitated Al toxicity to the test organisms.…”

Multiple linear regression models for predicting chronic aluminum toxicity to freshwater aquatic organisms and developing water quality guidelines

“…This is not an early-life stage test as defined in USEPA guidelines [12], but testing demonstrated that this test had a comparable sensitivity to Al as an early-life stage test (Supplemental Data, Table S1). All Al toxicity data used in the present evaluation are expressed as total Al because this includes both dissolved and precipitated forms of Al that contribute to potential toxicity in laboratory waters [9,11,13].…”