Sediment Concentrations of Trace Metals in the Berre Lagoon (France): An Assessment of Contamination

This paper reports the concentrations of eight trace metals (Cr, Zn, Cu, Pb, Ni, As, Cd, and Hg) in the surficial sediments of the Berre lagoon. This is a typical Mediterranean lagoon, seriously affected by human activities since the 1930s, when it became one of the most important industrial sites in France. The overall range of concentrations is 38–428 mg kg−1 for chromium, 50–151 mg kg−1 for zinc, 11–48 mg kg−1 for copper, 18–82 mg kg−1 for lead, 18–56 mg kg−1 for nickel, 4–10 mg kg−1 for arsenic, 0.2–1.6 mg kg−1 for cadmium, and 0.15–0.40 mg kg−1 for mercury. The spatial distribution of concentrations largely mirrors the localization of major impact sources, with the most affected area restricted to a radius of a few kilometers from point sources, due to the environmental conditions of the outfall zone (fine sediments, low hydrodynamic regime, confinement), which favor the in situ accumulation of pollutants. The extent of contamination from trace metals in the lagoon sediments is evaluated through a three-pronged approach: (i) by comparison with other areas (see Table 3 for an up-to-date review of trace metal concentrations in lagoon systems and coastal regions of the world ocean); (ii) by evaluating the metal enrichment in the sediments through the calculation of concentration factors (CF) for each trace metal and by combining the CFs to estimate a Metal Pollution Index (MPI) taking into account the differences in toxicity of trace metals; and (iii) by defining a potential level of biological risk by the use of quality criteria such as the Threshold Effect Level (TEL) and Effects Range–Low (ER-L) benchmarks. On the basis of the calculated CFs, sediments appear as particularly enriched with Pb and Cd throughout the lagoon and with Cr and Zn at some sites. Although no site can be classified as “unpolluted” when looking at the calculated MPIs, two regions—the Vaïne pond and the southwestern area—have been identified as critical points of contamination. Trace metal inputs to the lagoon need to be kept under strict control in the future, with particular regard to Ni, Cr, Pb, and Cu that, on the basis of TEL and ER-L benchmarks, already appear associated with a potential biological risk.