[en] In this study, the influence of sample matrix on the relative bioavailability of arsenic (As), cadmium (Cd) and lead (Pb) was assessed following exposure of C57BL/6 mice to spiked aged (12 years) soils. AIN93G mouse chow was amended with individual and tertiary As, Cd and Pb soil combinations which were administered to mice over a 9 day exposure period. Contaminant relative bioavailability was calculated by comparing As urinary excretion and Cd-kidney/Pb-liver accumulation to corresponding values for compounds used to derive the respective toxicity reference value. Strong linear dose-responses were observed for mice exposed to AIN93G mouse chow augmented with individually spiked soil with As, Cd and Pb. When mice were exposed to co-contaminants, As relative bioavailability (RBA) decreased similar to results from previous co-contaminant salt experiments presumably due to the influence of Cd on phosphate transport proteins, which are utilized for As absorption. However, a decrease in Cd-kidney and Pb-liver accumulation was also observed following co-co-exposure. It was postulated that this resulted from interactions with other (essential) metals (e.g. iron, aluminium, manganese, magnesium) within the soil matrix and their influence on absorption via divalent metal transporters. - Highlights: • Spiked soil was assessed using an in vivo mouse model to determine co-contaminant interaction. • Cd co-exposure with As decreased the relative bioavailability of As in urine. • Cd co-exposure with Pb decreased the relative bioavailability of Pb in the liver. • As and Pb co-exposure with Cd decreased the relative bioavailability of Cd in the kidneys.