BLM: A Model for Predicting Metal Toxicities

Metals are found everywhere in the environment. As such, in practical terms, the ecological risk from metals will never be zero. We are faced, then, with the problem of what level of risk to accept in this case, and this is one of the most difficult problems to solve in risk assessment. In order to carry out a risk assessment, we need to know the hazards. Metal toxicity varies with water chemistry, and it used to be difficult to predict such toxicity; however, this difficulty was overcome by the biotic ligand model (BLM) revolution, and currently, risk assessment involving metals is not conducted without use of the model. In the first part of this chapter, the model is described in detail. Risk assessment is often carried out on a substance-by-substance basis, and therefore the model parameters of the BLM are estimated for each metal individually. These parameters and the metal toxicity values, which are individually estimated, are plotted on a graph in the search for a pattern, and model analysis focused on the source of this pattern provides insight into the toxic effects of the given metal(s). In the second half of the chapter, we explain how the relationship between the parameters and estimated toxicity values for individual metals can give us such insights.