Assessing trace-element mobility in Algeciras Bay (Spain) sediments by acid and complexing screening

Acetic acid (HOAc) and diethylenetriaminepentaacetic acid (DTPA) single extraction agents were evaluated as screening methods to estimate the mobility of some trace elements in coastal sediments from Algeciras Bay. Sediments’ total metal concentrations of most heavy metals were found to be high around the areas impacted by anthropogenic activities such a sewage, atmospheric deposition and industrial activities, with notable values for As, Ni, Cr, Pb and Cd. The order of significant extraction efficiencies obtained with DTPA, were as follows: Pb (25.65%), Cu (19.78%), Cd (14.80%) and Zn (11.25%), while those obtained with HOAc were: Mn (33.00%), Tl (24.88%), Pb (18.99%), Cd (13.59%) and Co (11.78%). The comparison between the risk assessment codes (RAC) and the percent metal extractable fractions provided results of serious concern. Very high risk values of Cu, Zn, Cd and Pb extracts in DTPA were observed near the metallurgical industry, with Mn and Tl in HOAc extracts showing high risk values near the same industrial area and harbour activities. Sediments’ total metal concentrations were compared with the Low Alert-Level (LAL) sediment quality guidelines, where Co, Pb, Zn and Ni in both extractants and Cd and Cu in DTPA as well as Tl extracted in HOAc exceeded the LAL values respectively. The Spearman Rank test showed positive correlations between Co, Cu, Ni and Zn in DTPA extracts and their corresponding total metal concentrations, with Co, Cr, Fe, Ni, Tl and Zn in HOAc and total concentrations showing positive correlations. Furthermore, higher positive correlations were found between both extraction methods for Co (ρ = 0.797), Cu (ρ = 0.777), Ni (ρ = 0.789) and Zn (ρ = 0.942), indicating comparable potential extraction efficiencies between these extractants for these metals in the sediment studied. Keywords: Acetic acid, DTPA, Coastal sediment, Single extraction, Trace-element mobility