Geospatial analysis and assessment of 226Ra, 235U, 232Th, 137Cs, and 40K at Anzali wetland, north of Iran

Achieving better monitoring and radiation risk assessment is among the main issues in environmental studies. In this regard, natural radioactivity measurements in sediments can provide useful information about the environmental transport mechanism and about the sources of radionuclides. Anzali wetland, as the study area of this research, is located on the southwestern shore of the Caspian Sea with rapidly changing ecosystems. Because of its strategic location, increasing pollution levels, decreasing water table, and increasing sediment discharge from rivers, Anzali wetland has a unique significance in terms of studying its radioactivity from sediment and soil samples. The average Ra-226, U-235, Th-232, Cs-137, and K-40 values for 33 sediment and soil samples were 24.66, 3.72, 31.94, 11.66, and 506.38 Bq kg(-1), respectively. Variography analyses revealed a spatial structure with minimum/maximum variance equal to 3/8 from 135 degrees/45 degrees azimuth direction. In addition, the fractal geometry indicates values higher than 3.7, 24.5, 30, 25, and 475 Bq kg(-1) as anomalous values for U-235, Ra-226, Th-232, Cs-137, and K-40 using Kriging estimated data with a search radius of 5000 m, respectively. Compared with the average values published by UNSCEAR (2008) for earth's crust average and compared with the values for the southern areas of Iran (Oman Sea), the estimated average and anomalous data for a pollutant at Anzali wetland do not exceed the reference data. The higher values in the samples of this study could be related to specific environmental problems such as industrial wastewater from about 30 polluted factories transported by 10 major rivers. Agricultural wastes, such as herbicides, pesticides, and fertilizers from rice fields, and being a tourist attraction zone at sea beach are the other most possible pollution sources in the study area.