40K, 226Ra, 232Th, 238U and 137Cs relationships and behaviour in sedimentary rocks and sediments of a karstic coastal area (Kaštela Bay, Croatia) and related rocks and sediments' differentiation

Relationships between radionuclides, metals, and sediment properties in sediment of a bay exposed to anthropogenic pressure and mixed sediment sources (Kaštela Bay, Adriatic Sea, Croatia)

Natural and anthropogenic radionuclides, metals, organic matter, sediment grain size, mineral composition, and sediment sources were studied in marine sediment of Kaštela Bay up to a depth of 0.5 m. Deposition of man-modified material into the sea was evidenced in sediment mineral composition. Presence of pyrite and hematite in this sediment may pose an environmental concern. Metals, radionuclides, and organic matter were grouped in three groups: (i) variables under no anthropogenic influence and preferentially associated with carbonates (Ca, Sr); (ii) variables under no or weak anthropogenic influence and preferentially associated with aluminosilicates (Al, K, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Rb, Y, 40K, 232Th); (iii) variables under notable anthropogenic influence and/or natural processes of separation (Cu, Zn, Pb, As, 226Ra, 238U, 137Cs, organic matter). Predominant influencing parameters change with sediment depth for some variables. Anthropogenic influence was the most emphasised for Cu, Zn, and Pb, followed by 137Cs.

Geochemical distributions of natural radionuclides in surface soils and sediments impacted by lead-zinc mining activity

This study investigated the distribution features of uranium-238 (238U), radium-226 (226Ra), thorium-232 (232Th), and potassium-40 (40K) and evaluated the associated environmental radiological hazards of the topsoil and river sediments in the Jinding lead-zinc (Pb-Zn) mine catchment from Southwest China. The activity concentrations of 238U, 226Ra, 232Th, and 40K ranged from 24.0 ± 2.29-60.3 ± 5.26 Bq.kg-1, from 32.5 ± 3.95-69.8 ± 3.39 Bq.kg-1, from 15.3 ± 2.24-58.3 ± 4.92 Bq.kg-1, and from 203 ± 10.2-1140 ± 27.4 Bq.kg-1, respectively. The highest activity concentrations for all these radionuclides were primarily found in the mining areas and decreased with increasing distance from the mining sites. The radiological hazard indices, including radium equivalent activity, absorbed gamma dose rate in the air, outdoor annual effective dose equivalent, annual gonadal dose equivalent, and excess lifetime cancer, revealed that the highest values were observed in the mining area and downstream, specifically in the vicinity of the ore body. These elevated values exceeded the global mean value but remained below the threshold value, suggesting that routine protection measures for Pb-Zn miners during production activities are sufficient. The correlation analysis and cluster analysis revealed strong associations between radionuclides such as 238U, 226Ra, and 232Th, indicating a common source of these radionuclides. The activity ratios of 226Ra/238U, 226Ra/232Th, and 238U/40K varied with distance, suggesting the influence of geological processes and lithological composition on their transport and accumulation. In the mining catchment areas, the variations in these activity ratios increased indicated the impact of limestone material dilution on the levels of 232Th, 40K, and 238U in the upstream region. Moreover, the presence of sulfide minerals in the mining soils contributed to the enrichment of 226Ra and the removal of 238U caused those activity ratios decreased in the mining areas. Therefore, in the Jinding PbZn deposit, the patterns of mining activities and surface runoff processes in the catchment area favored the accumulation of 232Th and 226Ra over 40K and 238U. This study provides the first case study on the geochemical distributions of natural radionuclides in a typical Mississippi Valley-type PbZn mining area and offers fundamental information on radionuclide migration and baseline radiometric data for PbZn deposits worldwide.

Natural and anthropogenic radionuclides in karstic coastal area (Kaštela Bay, Adriatic Sea, Croatia) exposed to anthropogenic activities: distribution, sources, and influencing factors

40K, 226Ra, 232Th, 238U, and 137Cs massic activities were determined by gamma-spectrometry in limestones, marls, stream sediments, and soils of Kaštela Bay (Adriatic Sea, Croatia) coastal area. Their distribution, sources and potential influencing factors were studied. The lowest 40K, 226Ra, 232Th, and 238U massic activities were determined in limestones and the highest in soils, with the following median values, respectively: 7.2, 14, 0.8, and 5.3 Bq/kg in limestones and 518, 72, 71, and 31 Bq/kg in soils. All four radionuclides were of natural origin and reflected background values of the karstic area influenced by flysch/marl and terra rossa soil. Local TENORM disposal site did not influence the study area, but it will be needed to study its potential influence on marine sediments. Strong disequilibrium between 226Ra and 238U was found in limestones s.l. and soils, but not in marls and only moderately in stream sediments. This implies that limestones are more susceptible to selective 238U leaching than marls, and soils more than stream sediments. 137Cs was the only radionuclide of anthropogenic origin, with a global source only. It was detected in stream sediments and soils with median values of 5.4 and 31 Bq/kg, respectively. 137Cs distribution was more heterogeneous in stream sediments than in soils, but soils generally presented higher activities. Soil is considered the most important reservoir of 137Cs and its potential source.

Radiological risks from 40 K, 226Ra and 232Th in urbanised and industrialised karstic coastal area (Kaštela Bay, Croatia)

Radiological risks associated with ⁴⁰ K, ²²⁶Ra and ²³²Th massic activities in limestones, marls, stream sediments and soils of the Kaštela Bay (Croatia) coastal area were assessed by calculating outdoor absorbed dose rates in air (D), annual outdoor effective dose rates (D_ef), radium equivalent activities (Ra_eq) and external hazard indices (H_ex). Radionuclides relative contributions to D and H_ex were determined for all four types of samples as well as their total contribution to H_ex in all samples. D, D_ef, Ra_eq and H_ex were the lowest in limestones and the highest in soils. Maximum Ra_eq and H_ex in soil were below the recommended values of 370 Bq/kg and 1.0. No adverse radiological effects were determined in the researched area. The most important contribution to D and H_ex in limestones was almost exclusively from ²²⁶Ra, in marls from ⁴⁰ K, in stream sediments from ²²⁶Ra and in soils from ²³²Th. The most significant total contribution to H_ex in all samples came from ²²⁶Ra and ²³²Th, and the lowest came from ⁴⁰ K. ²²⁶Ra showed the largest variability of its total contribution to H_ex, with tendency to higher values. Special attention should be given to ²²⁶Ra when studying radiological risks in typical karstic areas, irrespectively of other possible influences of geological background.