Levels of Cs-137, natural radionuclides and heavy metals in soil of Al-Negila area, Northwestern Coast of Egypt: distribution and risk assessment

Abstract

ABSTRACT Radionuclides and heavy metals/metalloids content in soils and shore sediments of Al-Negila area (Matrouh, Egypt) were determined to assess the associated environmental risks. A total of 46 soil and shore sediment samples were collected and analysed for natural and man-made radionuclides (238U series, 232Th series, 40K and 137Cs) and heavy metals/metalloids (Al, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, Mn, Ni, Si, Sr, Zn, and Hg). Within the study area, the soil and shore sediments are mainly calcareous with sandy, sandy clay and silty clay sized textures. The radionuclides and metals/metalloids concentrations in the soil were higher than those in the shore sediments, meanwhile, they are within the safe world average values. The estimated average (±SD) activity concentrations of 226Ra, 228Ra, 40K and 137Cs were 20.3 ± 5.3, 17.8 ± 6.3, 353.1 ± 129.8, and 2.7 ± 2.7 Bq/kg, respectively. The activity concentration of 137Cs is characterised by the greatest variability characterising the fallout deposited radionuclides. The estimated average values of Raeq (72.9 ± 23.7 Bq/kg), air absorbed gamma dose rate (34.9 ± 11.4 nGy/h), annual effective dose (42.8 ± 14.0 µSv/y), and external hazard index (0.2 ± 0.1) are lower than the international averages reported by UNSCEAR 2008. The average concentrations (mg/kg) of heavy metals/metalloids in soil samples decrease in the following order: Mn (129.8) > Sr (95.0) > Si (28.8) > Ba (25.7) > Zn (25.1) > Cr (17.6) > B (10.0) > Ni (3.9) > Cu (3.3) > Co (0.5) > Cd (0.007) > Hg (7.0 µg/kg). According to the classes of pollution load and contamination degree indices, soils and shore sediments of Al-Negila area are generally uncontaminated. However, a few sampling sites were considered moderately contaminated with B, Cd, and Sr. The radionuclides and heavy metal/metalloid contents in the soil and shore sediments of the area should be observed and assessed regularly, especially for 137Cs.