The present work describes a procedure for the sequential determination of Pd(II), Pt(II), Rh(III), by square wave adsorption stripping voltammetry (SWAdSV) and Pb(II) by square wave anodic stripping voltammetry (SWASV) in environmental matrices (sediments, soils and superficial water) in the presence of possible metal interferences, including high concentration ratios. The supporting electrolytes were 0.1 mol/L HCI, 0.1 mol/L HCI + 1.8 x 10(-4) mol/L dimethylglyoxime (DMG) and 0.6 mmol/L formaldehyde + 1.2 mmol/L hydrazine (formazone complex) in 0.1 mol/L HCI. The voltammetric measurements were carried out using, as working electrode, a stationary hanging mercury drop electrode (HMDE), a platinum wire as auxiliary and an Ag vertical bar AgCl vertical bar KClsat as reference electrode. The analytical procedure was verified by the analysis of standard reference materials (CCRMP-CANMET-TDB-1 and CCRMP-CANMET-UMT-1 (rock soils), Sea Water BCR-CRM 403 and Fresh Water NIST-SRM 1643d). In the case of water standard reference materials, the solutions were spiked with known element concentrations, successively verifying the percentage recovery. In the presence of reciprocal interference, the standard addition method considerably improved the resolution of the voltammetric technique, even in the case of very high element concentration ratios. Once set up on the standard reference materials, the analytical procedure was transferred and applied to sediments, soils and superficial waters sampled in proximity of superhighway and in the Po River mouth area. A critical comparison with spectroscopic measurements is also discussed. (c) 2006 Elsevier Ltd. All rights reserved.