Influence of point sources on trace metal contamination and distribution in a semi-enclosed industrial embayment: the Ferrol Ria (NW Spain)

Abstract

Concentrations of heavy metals (Co, Cr, Cu, Fe, Ni, Pb and Zn), particulate organic (POC) and nitrogen (PON), particulate inorganic carbon (PIC) and opal content were measured in 35 surface sediment samples taken in the Ferrol Ria (Galicia, NW Spain). This ria is a semi-enclosed embayment receiving inputs from industrial and urban effluents. The restricted water exchange between the ria and the shelf has led to a significant accumulation of contaminants within the embayment. Two main factors controlled the metal distribution and concentrations in the bay: (1) contamination point sources and (2) distribution of the organic-rich sediments. Zn, Cu and, to a lesser extent Pb, were the metals most contaminated in the bay, with average enrichment factors (AEF)—defined as the mean metal concentration in the bay divided by the background value reported for this ria—of 4.7, 5.5 and 2.7, respectively. The highest concentrations for these metals were observed in the vicinity of the point sources. Values found for Zn, Cu and Pb are comparable to other industrialized coastal areas in the world. For Ni, Fe, Cr and Co a negligible to low contamination was found (AEF = 1–2), with the highest concentrations found in the organic-rich sediments.