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

Abstract

The bioavailability of aluminum (Al) to freshwater aquatic organisms varies as a function of several water chemistry parameters, including pH, dissolved organic carbon (DOC), and water hardness. We evaluated the ability of multiple linear regression (MLR) models to predict chronic Al toxicity to a green alga (Pseudokirchneriella subcapitata), a cladoceran (Ceriodaphnia dubia), and a fish (Pimephales promelas) as a function of varying DOC, pH, and hardness conditions. The MLR models predicted toxicity values that were within a factor of 2 of observed values in 100% of the cases for P. subcapitata (10 and 20% effective concentrations [EC10s and EC20s]), 91% of the cases for C. dubia (EC10s and EC20s), and 95% (EC10s) and 91% (EC20s) of the cases for P. promelas. The MLR models were then applied to all species with Al toxicity data to derive species and genus sensitivity distributions that could be adjusted as a function of varying DOC, pH, and hardness conditions (the P. subcapitata model was applied to algae and macrophytes, the C. dubia model was applied to invertebrates, and the P. promelas model was applied to fish). Hazardous concentrations to 5% of the species or genera were then derived in 2 ways: 1) fitting a log-normal distribution to species-mean EC10s for all species (following the European Union methodology), and 2) fitting a triangular distribution to genus-mean EC20s for animals only (following the US Environmental Protection Agency methodology). Overall, MLR-based models provide a viable approach for deriving Al water quality guidelines that vary as a function of DOC, pH, and hardness conditions and are a significant improvement over bioavailability corrections based on single parameters. Environ Toxicol Chem 2018;37:80-90. 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

“…These trends were confirmed by DeForest et al [15], whereas increases in pH, DOC, and hardness were all significantly associated with increasing EC10s for C. dubia exposed to Al. The interactions of DOC and hardness, pH and hardness, and the changes in bioavailability of Al from pH 6 to 8 (termed pH 2 in the MLR) were also found to be significant and retained for the MLR model.…”

“…Pairwise comparisons between ECxx values were considered significantly different statistically if the 95% confidence intervals (CIs) did not overlap [27,28]. Statistical analysis of the multivariate trends between Al toxicity and water quality characteristics were evaluated using data from the present study in the companion multiple linear regression (MLR) study [15], and a summary of those results is presented in the present study.…”

“…Statistical analysis performed by DeForest et al for the MLR [15] showed that increases in pH, DOC, and hardness were significantly associated with increasing EC10s for P. promelas. It is noteworthy that at pH 8, increasing the hardness resulted in greater toxicity and the protective effect of hardness was decreased.…”

“…Only increases in pH and DOC were found to be significantly associated with increased EC10s for P. subcapitata exposed to Al when the interactions of pH, DOC, and hardness were not considered [15]. When accounting for these interactions, all 3 independent variables were significant, as were the interactions of DOC and pH, hardness and pH, and pH 2 , and they were retained for the MLR.…”

“…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.…”