This dataset presents metal concentrations in transitional and coastal waters measured in Diffusive Gradients in Thin-films (DGT) passive samplers by Inductively Coupled Plasma Mass Spectrometry (ICP-MS: Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn) and in concurrently collected spot samples by ICP-MS (Al, Cd, Co, Cu, Mn, Ni, Pb, Zn) and Anodic/Cathodic Stripping Voltammetry (ASV/CSV: Cd, Ni, Pb) and obtained in the framework of the MONITOOL Project. Data on seawater physico-chemical parameters is also provided (salinity, temperature, dissolved oxygen, pH, turbidity, total suspended solids, dissolved organic carbon, total organic carbon). Sampling sites include the following ecoregions: Canary Islands, Iberian Coast, Bay of Biscay and English Channel, Celtic Sea North Sea and Western Mediterranean Sea (for detailed description of sampling sites see Caetano et al., Marine Pollution Bulletin 179 (2022) 113715). ICP-MS and voltammetry analysis (Anodic Stripping Coltammetry: Cd and Pb; Cathodic Stripping Voltammetry: Ni) were carried out in filtered seawater (see Bersuder et al., MethodsX 8 (2021) 101462; Rodríguez et al., Science of the Total Environment 783 (2021) 147001; Amouroux et al., Environmental Sciences Europe (2023) 35:29). Detailed description of the DGT technique and a user-friendly guidance can be found in Millán et al. (2021. A Good Practice Guide for the Use of DGTs. ITC. ISBN: 978-84-09-30846-0) and Gonzalez et al. (Science of the Total Environment 847 (2022) 157499). More info: https://www.monitoolproject.eu.