Impact of a “circular” use of sludge from the oil & gas industry: a model for biota radiation protection

Assessing radiological risk for industrial activities that involve the use of Naturally Occurring Radioactive Material is becoming more stringent with the adhesion of these industries to the principles of Circular Economy, that brought the attention to many new exposure scenarios not previously considered. Although there are guidelines for environmental radioprotection, these are not currently integrated into any national or European regulation. The main aim of this study was to propose a new approach to risk assessment that could consider both the already existing dose limits for humans and the Derived Consideration Reference Levels set by the ICRP 108/08 for biota, thereby ensuring a comprehensive protection from exposure to ionizing radiation. The ERICA Tool was used to calculate doses to the terrestrial biota in the scenario of exposure from reuse of sludge from treatment plants of the oil and gas industry. Dose values obtained for unitary activity concentration of each natural radionuclide in the sludge were used to calculate the Operational Levels (OL), maximum activity concentration values below which there is no risk of adverse effects. Comparing OLs for biota (OLB) to those for humans (OLU) showed that in some cases they are lower by up to an order of magnitude, and that the usual approach of only considering OLUs overlooks exposure to the biota. The final result of this study was the proposal of an integrated model for radiological risk management that includes both OLU and OLB values, granting radioprotection for the whole environment.