Distribution and seasonal changes of lead in an estuarine system affected by agricultural practices: The Penzé estuary, NW France

Over this one-year study, we examined the variations of lead along the salinity gradient of the Penzé estuary (Brittany, Western Channel, France). Concentrations of total dissolved and total particulate lead ranged from 0.04 to 0.62 nM and from 29 to 61 μg g−1, respectively. These values, though being higher than contamination-free systems, remain lower than those found in heavily industrialised systems indicating a limited effect of agricultural practices. Our field data showed, for most seasons (i.e. spring, summer and autumn), a metal removal in the salinity range 0–10, effected mainly by co-precipitation with iron and manganese oxides. On the other hand, after a strong winter ascending flood, an addition of dissolved lead occurred in the estuary following resuspension of particles and desorption mechanisms. This metal addition along with the high water discharge were responsible for the particularly high Pb output flux reported for winter (67 g day−1) compared to the ones estimated for other seasons (1–18 g day−1).