Coupling the use of computer chemical speciation models and culture techniques in laboratory investigations of trace metal toxicity

The bioavailability and toxicity of a dissolved metal are closely linked to the metal's chemical speciation In solution A variety of inorganic and org anic ligands are often used in laboratory toxicity tests to control the con centration of labile trace metal in solution. Computerised chemical speciat ion models based on thermodynamic principles can be used to estimate metal speciation under such experimental conditions. However, these models are se nsitive to the quality of their thermodynamic databases. Detailed protocols for the incorporation of reliable equilibrium formation constants into wid ely available computer chemical speciation programs (e.g., MINEQL+ and MINT EQ) are provided. The examples demonstrate both the benefits and the potent ial pitfalls involved in the use of chemical speciation models. The applica tion of chemical speciation modelling to metal toxicity studies is discusse d and guidelines are proposed for its proper use. Both defined media and ch emical speciation programs have co-existed for two decades but the combined use of these techniques has been reserved for those possessing in-depth kn owledge of both chemistry and biology. The techniques presented should enab le an investigator with basic biological, chemical and computing skills to design an aqueous medium and incorporate correct thermodynamic constants in to a computer chemical speciation program, starting from a standardised dat abase, thereby providing a sound framework for critically assessing the bio logical response of a particular test organism to a given metal.