Geographical distribution of metals and metalloids along the estuary of the Oka River in the biosphere reserve of Urdaibai, Spain.

Sediments sampled at the estuary of the Oka River in the biosphere reserve of Urdaibai, Spain were analyzed for trace elements. Sediments were collected at 45 points of the estuary and the concentration of 14 elements was measured. The geoaccumulation indexes (Igeo), Normalized Average Weighted Concentrations (NAWC) and mean Effect Range-Median quotients (mERMq) were calculated. The results obtained were complementary and allowed intra- and inter-estuary comparison. According to the present findings, the estuary was classified as healthy, since the anthropogenic contribution of metals and metalloids was generally small. However, shipping and fishing activities at the ports of Bermeo and Mundaka and urban and industrial wastes from Gernika were regarded as the major pollution sources. Nevertheless, only slightly contaminated and toxic sediments, especially related to Ni and Cu, were found in the towns of Gernika and Mundaka.

Is there a direct relationship between stress biomarkers in oysters and the amount of metals in the sediments where they inhabit?

The effects exerted by metals in oysters are still a matter of debate and require more detailed studies. In this work we have investigated whether the health status of oysters are affected by the amount of metals present in the sediments of their habitat. Sediments and oysters were collected in the tidal part of the estuary of the Oka River (Basque Country), representative of other mesotidal, well mixed and short estuaries of the European Atlantic coast. The concentrations of 14 elements were determined in all the samples. Several biomarkers were also measured in the soft tissues of oysters. According to the concentrations found, the sediments were classified as non-toxic or slightly toxic. In good agreement, the histological alterations observed in oysters were not severe. Interestingly, in those sampling sites where the sediments showed relatively high metal concentrations, the metallic content in oysters was lower, and vice versa.