Evolution of lead concentrations in the Nervión Estuary, southeastern Bay of Biscay

Abstract

Over many years the Nervión estuary has received an intense lead input from various sources in relation to different human activities. This input has produced lead accumulation in some compartments of the estuarine system, which is mainly reflected in the sediments. In recent years, the closure and/or transformation of some contaminating industries, in addition to the implementation of a sewerage scheme, have considerably reduced these inputs into the system. The lead concentration in the sediments has shown a general decreasing trend since 1995. Although this trend is neither progressive nor statistically significant for all the studied stations, lead concentrations in surficial sediment are significantly lower in recent years than at the beginning of the study period. Regarding potential adverse effects on biota, although one third of the values measured during the study period are above concentrations associated with toxicity, in recent years very few values exceed these references. Time series of lead concentrations in biomonitors (mussels) do not show statistically significant temporal trends, and most of the values fulfil the quality objective proposed for this region.