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

Abstract

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.

Updated Chronic Copper Bioavailability Models for Invertebrates and Algae

“…In the present study, we demonstrated the cross‐species application of the updated models to nonmodel cladocerans, rotifers, algae, and plants (Table 2). Recently, Nys et al (2020) proved that the updated chronic Cu fish bioavailability model developed based on juvenile rainbow trout ( O. mykiss ) can be extrapolated to other life stages of the same species as well of other fish species (i.e., P. promelas ). For a few taxonomic groups there remains some uncertainty related to the cross‐species applicability of the updated chronic Cu invertebrate bioavailability model.…”

“…The updated models developed in this manuscript, together with the recently published chronic Cu fish bioavailability model (Nys et al, 2020), constitute a complete, consistent, and updated Cu bioavailability model set. It uses the most recent version of the WHAM VII, and all models are of the gBAM type, which has an improved estimation of the effect of pH on Cu toxicity compared with the classic BLM-type model (Nys et al, 2020;Van Regenmortel et al, 2015). The gBAM structure has the advantage that it avoids the need to consider the potential toxicity of CuOH and CuCO 3 , thereby reducing the number of model parameters without losing predictive power.…”

Statement of the PPR Panel on a framework for conducting the environmental exposure and risk assessment for transition metals when used as active substances in plant protection products (PPP)

“…This complexity has been addressed by the development of BLM or alternatives such as the so‐called generalised bioavailability model (gBAM; e.g. Nys et al., 2020). The toxic effect depends on the metal speciation under different environmental conditions (spatial and temporal) and on the aquatic organism.…”

“…This complexity has been addressed by the development of BLM or alternatives such as the so-called generalised bioavailability model (gBAM; e.g. Nys et al, 2020).The toxic effect depends on the metal speciation under different environmental conditions (spatial and temporal) and on the aquatic organism. BLMs have been developed to predict acute and chronic toxicity to algae, invertebrates and fish for a range of physicochemical water parameters.…”

Integrating Bioavailability of Metals in Fish Population Models

“…In that regard, different bioavailability models such as biotic ligand models (BLMs) or generalized bioavailability models (gBAMs) have been developed over the years to account for differences in bioavailability and toxicity of metals in different water chemistries. Examples of this for fish are the chronic zinc (Zn; De Schamphelaere and Janssen 2004) and copper (Cu) BLM (Crémazy et al 2017) for Oncorhynchus mykiss and the recently published Cu gBAM for O. mykiss (Nys et al 2020). However, these bioavailability models were developed specifically to correct effect concentrations, obtained with concentration–effect models from individual‐level toxicity tests, measured after a certain test period.…”