English Abstract In 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.
