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DOI: http://dx.doi.org/10.1065/jss2001.04.008 - - - (1)Background, Aims and Scope: Bioavailability of toxic compounds in soil can be defined as the fraction able to come into contact with biota and to cause toxic effects. The contact toxicity tests may detect the total toxic response of all bioavailable contaminants present in a sample. The objectives of this study were to evaluate the use of microbial contact toxicity tests for cadmium bioavailability assessment and to evaluate the relationship between sorption, soil characteristics and cadmium bioavailability. - - (2) Methods: A test soil bacterium, Bacillus cereus, was put in direct contact with the solid sample. Four unpolluted soils were selected to provide solid samples with a variety of physicochemical characteristics. The toxicity and sorption behaviour of cadmium spiked to the soil samples were determined. - - (3) Results, Discussion and Conclusions: A significant correlation between contact toxicity test results and partitioning of cadmium in the soil samples (r2 = 0.79, p smaller than 0.05; n = 26) was found. The results confirm that the bioavailability of cadmium in soil depends on its sorption behaviour. Cadmium sorbed to the cation exchange sites associated with fulvic acids is non-bioavailable in the toxicity test employed in this study. It is concluded that the microbial contact toxicity test is a suitable tool for detecting cadmium bioavailablity in the soils used in this study. - - (4) Outlook: The application of microbial contact toxicity tests for bioavailability assessment can be very useful for the risk identification and remediation of soil-associated contaminants.