Comparison of the capacity of two biotic ligand models to predict chronic copper toxicity to two <i>Daphnia magna</i> clones and formulation of a generalized bioavailability model

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Risk assessment in the European Union implements Zn bioavailability models to derive predicted-no-effect concentrations for Zn. These models are validated within certain boundaries (i.e., pH ≤ 8 and Ca concentrations ≥ 5mg/L), but a substantial fraction of the European surface waters falls outside these boundaries. Therefore, we evaluated whether the chronic Zn biotic ligand model (BLM) for Daphnia magna and the chronic bioavailability model for Pseudokirchneriella subcapitata could be extrapolated to pH > 8 and Ca concentrations < 5 mg/L. Results from D. magna experiments suggested that the BLM is not able to reflect the pH effect over a broad pH range (5.5-8.5). In addition, because of Ca deficiency of D. magna in the soft water tests, we cannot conclude whether the BLM is applicable below its Ca boundary. Results for P. subcapitata experiments showed that the bioavailability model can accurately predict Zn toxicity for Ca concentrations down to 0.8 mg/L and pH values up to 8.5. Because the chronic Zn BLM for D. magna could not be extrapolated beyond its validity boundaries for pH, a generalized bioavailability model (gBAM) was developed. Of 4 gBAMs developed, we recommend the use of gBAM-D, which combines a log-linear relation between the 21-d median effective concentrations (expressed as free Zn ion activity) and pH, with more conventional BLM-type competition constants for Na, Ca, and Mg. This model is a first step in further improving the accuracy of chronic toxicity predictions of Zn as a function of water chemistry, which can decrease the uncertainty in implementing the bioavailability-based predicted-no-effect concentration in the risk assessment of high-pH and low-Ca concentration regions in Europe. Environ Toxicol Chem 2017;36:2781-2798. © 2017 SETAC.

{log}_{10} true(EC 50_{{Zn}^{2 +}} true) = {normalQ}_{50} - {normalS}_{pH} \times pH

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Section: Resultsmentioning

confidence: 99%

Analyzing the capacity of the Daphnia magna and Pseudokirchneriella subcapitata bioavailability models to predict chronic zinc toxicity at high pH and low calcium concentrations and formulation of a generalized bioavailability model for D. magna

Regenmortel

Berteloot

Janssen

et al. 2017

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“…The effect of temperature on chronic Ni toxicity significantly differed among clones. A previous study demonstrated an effect of pH on the chronic toxicity of Cu between 2 clones . Therefore, the study of multiple clones is necessary to investigate the effect of environmental variables on chronic metal toxicity to D. magna .…”

Section: Discussionmentioning

confidence: 99%

Effect of temperature on chronic toxicity of copper, zinc, and nickel to Daphnia magna

Pereira

Deruytter

Blust

et al. 2017

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Few studies have considered the effect of temperature on the chronic sensitivity of Daphnia magna to other stressors. The present study investigated the effect of temperature on chronic metal toxicity and whether this effect differed among 4 different D. magna clones. Life table experiments were performed with copper, zinc, and nickel at 15 °C, 20 °C, and 25 °C. General linear modeling indicated that chronic Cu, Zn, and Ni toxicity to D. magna were all significantly affected by temperature. When averaged across clones, our results suggest that chronic metal toxicity to D. magna was higher at 15 °C than at 20 °C, which is the temperature used in standard toxicity tests. At 15 °C, the 21-d median effect concentrations (EC50s) of Cu, Zn, and Ni were 1.4 times, 1.1 times, and 1.3 times lower than at 20 °C, respectively. At 25 °C, chronic Cu and Zn toxicity did not change in comparison with 20 °C, but chronic Ni toxicity was lower (21-d EC50 of nickel at 25 °C was 1.6 times higher than at 20 °C). The same trends were observed for Cu and Ni when the 21-d 10% and 20% effect concentrations were considered as the effect estimator, but not for Zn, which warns against extrapolating temperature effects on chemical toxicity across effect sizes. Overall, however, chronic metal toxicity was generally highest at the lowest temperature investigated (15 °C), which is in contrast with the usually observed higher acute metal toxicity at higher temperatures. Furthermore, the effect of temperature on chronic Ni toxicity depended significantly on the clone. This warns against extrapolating results about effect of temperature on chemical toxicity from single clone studies to the population level. Environ Toxicol Chem 2017;36:1909-1916. © 2016 SETAC.

“…Both existing fish BLMs formulate the effect of pH on free Cu 2+ ion toxicity as a linear single‐site competition effect of H + at the Cu 2+ uptake site (i.e., the biotic ligands). An alternative formulation of the pH effect in the chronic Cu Daphnia bioavailability model has recently been proposed through the use of gBAMs (Van Regenmortel et al 2015).…”

Section: Introductionmentioning

confidence: 99%

“…The gBAMs are an alternative to the existing BLMs to predict chronic effect concentrations for Cu (and other metals) in freshwater organisms (Mebane et al 2020), such as fish (e.g., nickel [Ni]; Deleebeeck et al 2007), D. magna (e.g., for Cu and zinc [Zn]; Van Regenmortel et al 2015, 2017), and algae (e.g., for Cu; De Schamphelaere and Janssen 2006). The chronic Cu Daphnia gBAM combines a log‐linear pH effect on free Cu 2+ ion toxicity with conventional linear protective effects of major cations.…”

Section: Introductionmentioning

confidence: 99%

“…Due to its log‐linear model structure, gBAMs may account for other factors that determine the effect of pH on bivalent metal cation (Me 2+ ) toxicity besides the competitive effect of H + at the biotic ligand site (discussed in more detail in the Discussion section). For D. magna , the gBAM provided a better prediction of the effect of pH on Cu 2+ ion toxicity than the chronic Daphnia Cu BLM and required 2 parameters less to be calibrated (Van Regenmortel et al 2015).…”

Section: Introductionmentioning

confidence: 99%

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A Generalized Bioavailability Model (gBAM) for Predicting Chronic Copper Toxicity to Freshwater Fish

Nys¹,

Vlaeminck

Sprang³

et al. 2020

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The generalized bioavailability model (gBAM) has been proposed as an alternative to the biotic ligand model (BLM) for modeling bioavailability and chronic toxicity of copper (Cu). The gBAM combines a log-linear effect of pH on free Cu 2+ ion toxicity with BLM-type parameters for describing the protective effects of major cations (calcium [Ca] 2+ , magnesium [Mg] 2+ , and sodium [Na] +). In the present study, a Windermere Humic Aqueous Model (WHAM) VII-based gBAM for fish was parametrized based on an existing chronic (30-d) dataset of juvenile rainbow trout (Oncorhynchus mykiss). The model, with defined parameters (pH slope parameter [S pH ] = 0.4449 and biotic ligand competition constants [log K CaBL = 4.0, log K MgBL = 3.4, and log K NaBL = 3.0]), was shown to accurately predict the effects of pH, dissolved organic carbon, Ca, and Mg on chronic Cu toxicity to juvenile rainbow trout at the effect levels relevant for environmental risk assessment (i.e., median prediction error of 1.3-fold for 10 and 20% lethal concentrations). The gBAM predicted the effect of pH more accurately than a previously published Cu BLM for juvenile rainbow trout, especially at pH > 8. We also evaluated the cross-species and cross-life stage applicability of the newly developed juvenile rainbow trout gBAM using existing chronic Cu toxicity data with early life stages of fathead minnow (Pimephales promelas) and rainbow trout. We did this because using a single bioavailability model for all fish species and life stages is practical from a regulatory point of view. Although the early life stage datasets exhibit considerable uncertainties, 91% of the considered toxicity values at the effect levels most relevant in European environmental regulations (10% effect on survival or growth) were predicted within a 2-fold error. Overall, the chronic Cu gBAM we developed is a valuable alternative for the existing chronic Cu BLM for rainbow trout and performs sufficiently well to be used in risk assessment according to currently accepted standards of bioavailability model performance (from the current European regulatory point of view). However, our analysis also suggests that bioavailability relations differ between different fish life stages and between endpoints (e.g., mortality vs growth), which is currently not accounted for in environmental risk assessments.