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Bioavailability assessment of metals in aquatic environments: A historical review
Citation:
Adams, W., R. Blust, R. Dwyer, Dave Mount, E. Nordheim, P. Rodriguez, AND D. Spry. Bioavailability assessment of metals in aquatic environments: A historical review. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 39(1):48-59, (2020).
Impact/Purpose:
The manuscript presents a historical review of research developments building the understanding of the aquatic toxicity of metals as it relates to metal bioavailability. Important research contributions from the initial studies indicating that water quality characteristics such as pH and hardness can affect the aquatic toxicity of metals, through the development of detailed mechanistic models to predict metal toxicity in any water composition, are presented. Also discussed is the history of advances in the application of these bioavailability principles in the derivation and implementation of water quality criteria issued by U.S. Environmental Protection Agency, and in similar regulatory approaches from other countries. This paper also serves as an introduction to other papers being published simultaneously, which describe in greater detail the state of the science in approaches to evaluate and predict metal bioavailability in fresh waters.
Description:
Metals are widely studied environmental contaminants for several reasons, including their ubiquity, potential toxicity to aquatic life, and tendency for their aquatic toxicity to vary widely with the chemistry of the surface water in which they occur. These interactions between metal and underlying water chemistry are described as influencing metal bioavailability, an index of the rate and extent to which the metal reaches the site of toxic action within an exposed organism. The implications of metal bioavailability for ecological risk assessment is large, as it can produce differences in toxicity of as much as 100-fold across a range of water chemistries in surface waters. Beginning as early as the 1930s, considerable research effort has been expended in an attempt to document and understand metal bioavailability, as a function of total and dissolved metal, water hardness, natural organic matter (NOM), pH, and other characteristics of natural waters. The growing understanding of these factors, and improvements in both analytical and computational chemistry, led in turn to a series of modeling approaches intended to describe and predict the relationship between water chemistry and metal toxicity, including the Free Ion Activity Model, the Gill Surface Interaction Model (GSIM), the Biotic Ligand Model, and additional derivatives and regression models that arose from similar knowledge. The arc of these scientific advances can also be traced through the evolution of U.S. EPA Ambient Water Quality Criteria over the last 50 years, from guidance in the “Green Book” published in 1968, to metal-specific criteria produced in the last decade. Through time, these criteria have incorporated increasingly sophisticated means of addressing metal bioavailability, as has regulatory guidance developed by other jurisdictions across the globe. These actions have shifted the debate toward identifying harmonized approaches for determining when knowledge is adequate to establish bioavailability-based approaches and how best to implement them. This Focus Article presents and discusses the history of scientific understanding of metal bioavailability, and the development and application of models to incorporate this knowledge into regulatory practice.