Radium in baggerspecie van 1994 en 1995 uit het Rijnmondgebied - Metingen en dosisberekeningen

Dredgings from the harbours and waterways of the Rhine delta show elevated levels of natural radionuclides. The pathways to be used for calculations of the dose to the population have been the subject of debate lately. Part of this report deals with this subject and describes the results of discussions among research institutes, industrial companies and the Dutch government. Apart from that, this report gives the results of measurements of the Ra-226 content of harbour sludge samples taken during the 1994 and 1995 sampling campaigns of Public Works and the city of Rotterdam. In reporting the results, the natural radium contents and enhancement due to industrial dumpings are distinguished. The range of the natural radium contents of the 1994 en 1995 samples was 8-25 Bq kg-1, of the actually measured radium contents 13-264 Bq kg exp.-1 and of the enhancements 0-240 Bq kg exp.-1. Repeated sampling of the same locations shows that the radium content in 1995 was on the average 16 plusminus 2 (1 sigma) percent higher than in 1994. The natural radium contents in 1995 showed no difference with 1994. The enhancements were on the average 39 plusminus 7 percent higher in 1995. The radium contents compare well with previous occasional measurements. Exposure to radon when living on sites where harbour sludge with enhanced levels of radium has been used as landfill, is considered as the dominant potential exposure pathway. According to this model, the highest enhancements found correspond to a potential individual dose of approximately 6 mSv a exp.-1. Approximately 15% of the dredged material may cause an additional individual dose of 1 mSv a exp. -1 or more