Toxicity, bioavailability, and mobility of a metal depend on its speciation rather than its total concentration. In this discussion, we emphasize the need for field-based metal speciation analysis methods, given the flaws of traditional techniques. We express a science-based opinion that the diffusive gradients in thin-films (DGT) is a promising and powerful technique for performing in-situ measurement of metal species or speciation in different environmental samples. Several limitations and challenges in further application of DGT are also highlighted in this discussion.