Complexation of lead by organic matter in Luanda Bay, Angola.
Speciation is defined as the distribution of an element among different chemical species. Although the relation between speciation and bioavailability is complex, the metal present as free hydrated ion, or as weak complexes able to dissociate, is usually more bioavailable than the metal incorporated in strong complexes or adsorbed on colloidal or particulate matter. Among the analytical techniques currently available, anodic stripping 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 identified and quantified by differential pulse anodic stripping voltammetry technique. Each sample was progressively titrated with a Pb(II) standard solution until complete saturation of the organic ligands. After each addition 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 sampling sites. In sediment samples, the lead is totally (100 %) complexed with ligands adsorbed on the particles 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.
LESRA-Laboratório de Engenharia da Separação, Reacção e Ambiente, Universidade Agostinho Neto, Avenida Ho Chi Min n° 201, Luanda, Angola. anabela.leitao@yahoo.com.
Anabela
A
Leitão
LESRA-Laboratório de Engenharia da Separação, Reacção e Ambiente, Universidade Agostinho Neto, Avenida Ho Chi Min n° 201, Luanda, Angola.
Ana Maria
AM
Santos
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.
Rui A R
RA
Boaventura
D000327:Adsorption; D000810:Angola; D061006:Bays / Q000737:chemistry*; D001682:Biological Availability; D004784:Environmental Monitoring; D063366:Estuaries; D019015:Geologic Sediments / Q000032:analysis*; D007854:Lead / Q000032:analysis* / Q000737:chemistry*; D008024:Ligands; D014874:Water Pollutants, Chemical / Q000032:analysis*; D060753:Water Quality
D008024:Ligands; D014874:Water Pollutants, Chemical; D007854:Lead
ASV; Aquatic systems; Bioavailability; Lead speciation; Voltammetry