Abstract niet beschikbaarIn this report the results are given of a preliminary study into the presence of enhanced concentrations of natural radionuclides, notably RA-226, in harbour sludge dumps in polders in the Rijnmond area in the Netherlands. Enhanced concentrations due to human activities are thought to be the result of emissions of phosphogypsum into the River Nieuwe Waterweg. Six polders were sampled at four locations and two depths at each location. The samples were analyzed for the presence of Ra-226 and the element cadmium. The values obtained by measurement were compared with reference values obtained by calculations with a model applicable for many normal Dutch soils. The difference (surplus) between the measured and calculated values was tested for statistical significance. A significant surplus was found only in the uninhabited polders (five of six). The correlation between cadmium and Ra-226 was found to be conspicuous. The calculations allowed a rough estimation of a possibly enhanced radon concentration in houses due to the Ra-226 surplus and also of the related dose level. For the one inhabited polder this estimation amounted to 0.4 mSv/a for persons spending 80% of their time inside the house. Habitation of the polders uninhabited to data might result in an extra dose level of 3.6 mSv/a. Actual measurements of radon concentrations have not been performed in this study. The conclusions of the report are followed by recommendations on further research.DGM/SV
