The use of diffusive gradients in thin films (DGT) for predicting metal bioavailability was investigated by exposing the bivalve Tellina deltoidalis to an identical series of metal-contaminated sediments deployed simultaneously in the field and laboratory. To understand the differences in metal exposure occurring between laboratory and field-based bioassays, changes in metal fluxes to DGT probes in sediments, and metal concentrations and partitioning to porewaters and overlying waters were investigated. DGT-metal fluxes (Cu, Pb and Zn) were lower in the overlying waters of most field-bioassays compared to the laboratory, causing differences in Pb and Zn bioaccumulation between bivalves exposed to laboratory and field conditions. Overall, DGT-metal fluxes provided predictions of metal bioaccumulation similar to those obtained using dilute-acid extractable metal measurements. This study demonstrates that, irrespective of the physicochemical properties of the sediment and type of exposure (laboratory or field), sediments pose a significant risk of bioaccumulation by T. deltoidalis when the Cu, Pb and Zn DGT flux exceeds 3.5, 1.3 and 156 µg/h/m2, respectively. The results presented here support the use of the DGT technique for sediment quality assessment and the hypothesis that DGT-metal fluxes may potentially be useful surrogates for the lability of metals for all exposure routes.