Radiological risks and excess lifetime cancer risk of the topsoil around the coal-fired Plomin thermal power plant (Istria, Croatia) and long-term effects after ceasing use of the coal with elevated radionuclides activities

Abstract

Radiological and health risks arising from 226Ra, 232Th, and 40K in topsoil due to coal combustion in Plomin thermal power plant were assessed: outdoor absorbed dose rate in air (D), annual outdoor effective dose rate (Def), external hazard index (Hex), internal hazard index (Hin), and excess lifetime cancer risk outdoors (ELCRout). Spatial distribution of risks around the plant was studied and relative contributions of 226Ra, 232Th, and 40K to D (applies to Def and ELCRout as well), Hex, and Hin were determined. The risks were studied at two soil depths (A: 0–10 cm, B: 10–25 cm), radially around the plant at 1 km, 5 km, and 10 km distances from the plant, and in a downwind (SW) profile at 0.1–1 km distance from the plant. Elevated D, Def, Hin, and ELCRout were determined, while Hex was not elevated. Almost all D, Def, and ELCRout values were above the world average for soils (58 nGy/h, 0.07 mSv/y, and 0.29 × 10−3, respectively). D, Def, and ELCRout were: 32–338 nGy/h (mean value: 116 nGy/h), 0.039–0.414 mSv/y (mean value: 0.142 mSv/y), and 0.17 × 10−3–1.79 × 10−3 (mean value: 0.61 × 10−3), respectively. Hex was in the 0.18–1.98 range (mean value: 0.69), with only two extreme values above the recommended limit of 1. Hin was in the 0.22–3.67 range (mean value: 1.02), with most of the values above the recommended limit of 1 in the downwind profile and at one station with extremes (1 km from the plant). A “hot spot” was determined for all risks at 1 km distance from the plant in the wind direction (SW from the plant). The next highest, elevated, risks were observed in the downwind profile stations. The most important parameters influencing spatial distribution of risks are 226Ra activities in soil, wind direction, and distance from the plant. 226Ra is generally the most important contributor to risks in soils, while 40K is the least important. 226Ra and 232Th were found to be the most significant and comparable contributors to D, Def, Hex, and ELCRout. Only 226Ra was found as the most significant contributor to Hin in the studied area. Elevated risks are partially from the natural source (carbonate bedrock) and partially from the power plant (coal combustion and handling, ash deposition on soil).