Assessment of the metal pollution, potential toxicity and speciation of sediment from Algeciras bay (South of Spain) using chemometric tools

Resumen

Surface sediments from Algeciras Bay were analysed for total and mobile metals. A preliminary study of total metals (V,Cr,Co,Ni,Cu,Zn,As,Cd,Ba,Pb,Mn,Fe) was carried out to assess status of metal pollution, with 17 sampling points (spring 2007). The results showed potential hotspots, with Ni and Cr surpassing the ERM (toxic effects). To predict the potential bioavailability of metals studied, the averages of mobile concentrations were compared with low alert-level sediment quality guidelines. Co (extracted by acetic acid) and Cu, Zn and Pb (extracted by DTPA) were above low alert guideline. Further investigations were then recommended and the BCR speciation methods were done. For that, 5 points were studied during autumn 2007-2008 and spring 2008-2009. The results showed that sediments acted as sink since most of metals were found in the residual fraction, principally for Ba, As, Ba, Tl and Pb. However, some quantities were founded in exchangeable (Co,Zn,Cd), reducible (V,Zn,Cd) and oxidisable fractions (Ni,Co,Zn,Cd,Pb,Cr,Cu). Contamination source assessments were performed using PCA, ANOVA and agglomerative hierarchical cluster, studying the influence of seasonality and anthropogenic activities on the quality of the sediments. The PCA found two groups of behaviours: group 1 for Mn and As, while group 2 included the rest of the metals. The analysis further identified the city of Algeciras and the industrial zones as the major sources of metal pollutants in the bay.