Complexation of lead by organic matter in Luanda Bay, Angola Anabela Leitão & Ana Maria Santos & Rui A. R. Boaventura Received: 4 April 2016 /Accepted: 24 August 2016 # Springer International Publishing Switzerland 2016 Abstract Speciation is defined as the distribution of an element among different chemical species. Although the relation between speciation and bioavailability is com- plex, the metal present as free hydrated ion, or as weak complexes able to dissociate, is usually more bioavail- able than the metal incorporated in strong complexes or adsorbed on colloidal or particulate matter. Among the analytical techniques currently available, anodic strip- ping voltammetry (ASV) has been one of the most used in the identification and quantification of several heavy metal species in aquatic systems. This work concerns the speciation study of lead, in original (natural, non- filtered) and filtered water samples and in suspensions of particulate matter and sediments from Luanda Bay (Angola). Complexes of lead with organics were iden- tified and quantified by differential pulse anodic strip- ping voltammetry technique. Each sample was progres- sively titrated with a Pb(II) standard solution until com- plete saturation of the organic ligands. After each addi- tion of Pb(II), the intensity, potential and peak width of the voltammetric signal were measured. The results obtained in this work show that more than 95 % of the lead in the aquatic environment is bound in inert organic complexes, considering all samples from different sam- pling sites. In sediment samples, the lead is totally (100 %) complexed with ligands adsorbed on the parti- cles surface. Two kinds of dominant lead complexes, very strong (logK >11) and strong to moderately strong (8< logK <11), were found, revealing the lead affinity for the stronger ligands. Keywords Lead speciation . Aquatic systems . Voltammetry . ASV . Bioavailability Introduction Coastal areas (estuaries, bays, gulfs, etc.) were, from ancient times, prime locations to fix populations that intensively used the aquatic resources as receiving bod- ies for the discharge of domestic and industrial effluents. These effluents, without previous treatment or without a proper treatment, are a source of pollutants such as biodegradable organic compounds, nutrients (mainly nitrogen and phosphorus), heavy metals, and refractory substances. The metal ions when discharged in an aquatic envi- ronment tend to combine rapidly with ligands at differ- ent types of sites characterized by different binding forces and distributed between the dissolved and partic- ulate phases (Ciffroy et al. 2003). It is usual to consider as dissolved the species present in water that passes through a membrane filter of 0.45 μm porosity and particulate the species retained in the same filter Environ Monit Assess (2016) 188:563 DOI 10.1007/s10661-016-5557-z A. Leitão (*) : A. M. Santos LESRA—Laboratório de Engenharia da Separação, Reacção e Ambiente, Universidade Agostinho Neto, Avenida Ho Chi Min n° 201, Luanda, Angola e-mail: anabela.leitao@yahoo.com R. A. R. Boaventura LSRE—Laboratory of Separation and Reaction Engineering, Associate Laboratory LSRE-LCM, Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal