Occupational dose from natural radionuclides in phosphate fertilizers

In this investigation the occupational exposure of single persons due to the gamma radiation of the natural radionuclides in rock phosphates and phosphate fertilizers and their contribution to the population dose in the FRG has been determined. The exposure rates in the working fields production, transport, loading and storage or rock phosphates and phosphate fertilizers and due to their application in agriculture have been measured by means of scintillation dose rate meters or LiF-thermoluminescence dosemeters or have been estimated from specific activities. Mean additional exposure rates of 2--26 muR/h, with local maximum values up to 190 muR/h, were observed. From these values, together with statistical data for the number of occupied persons and annual working times in the various working fields, the mean and maximum annual dose of individuals and the contribution to the mean population dose have been estimated. The results show that a maximum annual dose to individuals from 0.4 mrem/y (agriculture) up to 45 mrem/y (production plants or storehouses) can occur. The corresponding mean annual doses are 0.05--20 mrem/y. The contribution of the occupational radiation exposure due to rock phosphates and phosphate fertilizers to the mean population dose is 174 man . rem/y related to whole body. To this, fertilizer production contributes 40 man . rem/y, transport and loading 45 man . rem/y, agricultural storehouses 31 man . rem/y, and agriculture 58 man . rem/y. Altogether, this investigation shows that an occupational radiation exposure of individuals may occur which corresponds to the mean terrestrial radiation exposure in the FRG. The contribution of the occupational collective doses due to phosphates to the population dose, however, is negligibly small.