The use of slude as fertilizer: radiological impact to the members of the public and agricultural workers of sludge related to norm involving industries

At European level the general obligation to recycle drives for increased reuse of residues containing Naturally Occurring Radioactive Material (NORM). This includes the reuse in agriculture of sludge produced by groundwater filtration facilities (GFF) and by waste water treatment plants (WWTP) that receive sewage from NORM involving industries. In the frame of the European project RadoNORM, a study has been conducted in order to evaluate the annual effective dose of agricultural workers and members of the public living near agricultural fields where sludges containing NORM are spread. Both for GFF and WWTP sludge exposure scenarios are developed considering the annual sludge spreading based on the European Directive 86/278/EEC and the annual application of sludge over many years, thus accounting for accumulation of radionuclides in arable lands. Exposure scenarios have been modeled in a generic and conservative way by means of RESRAD (ONSITE) software using dose coefficients for external and internal exposure pathways taken from the most recent ICRP publications for relevant segments of the U-238 and Th-232 decay chains. For GFF, a generic methodology to quantify exposure and to obtain screening values – so-called Operational Levels (OLs) - was developed. OLs can be used as screening tools by an authority/operator, even non-experts in the field of radiation protection, to decide on further eventual necessary analysis in the context of a graded approach. These OLs pertain to the activity concentration of natural radionuclides (in terms of kBq kg -1) present in sludge that is reused in agriculture, for which dose criterion of 1 mSv per year is complied with. For WWTP, two main aspects have been considered to develop screening values related to the total discharged annual activity by relevant NORM involving industries, namely the size of the waterworks in terms of population equivalent (PE) and the distribution of radionuclides between solid and liquid phase in the sludge. In this presentation, the main results of the modelling exercises and considerations about the possible use of this methodology to support decision makers will be discussed. The methodology and results of this study could contribute to the update of the Clearance Levels and discharge levels reported in the European guidelines RP 122 Part II and RP 135, respectively.