Radiological and mineralogical investigation of accretion and erosion coastal sediments in Nile Delta Region, Egypt

Abstract

The Nile Delta coast is a dynamic sedimentary environment experiencing erosion, transport and re-deposition of sand along the coast. The aim of this study was to investigate the effectiveness of using an integrated approach of natural radioactivity of coastal sediments, heavy mineral distribution and grain size information to differentiate between the eroding and accreting areas of the Nile Delta coast. Also, it is to investigate the relationship between grain size and heavy mineral distributions of these sediments on the spatial distribution of the coastal radioactive materials. The relatively higher profile averages of 226Ra, 214Pb, 214Bi and 210Pb (as 238U series) were 104.37±84.66, 45.60±37.83, 38.43±32.49 and 35.69±24.86 Bq/kg, respectively and228Ra and 212Pb (as 232Th series) were 54.26±56.66 and 42.18±44.66 Bq/kg, respectively. The highest average value of 40K concentration (404.49±125.81 Bq/kg) was detected in the profile located at 2000.1 m west of Rashid estuary. Microscopic study revealed that the more dominant heavy minerals assemblages consisted of Opaques, Hornblende, Augite, Epidote, Biotite and Chlorite. Also, minor amounts of Garnet, Zircon, Rutile, Tourmaline, Kyanite and Monazite have been identified. Relatively high concentrations of 238U and 232Th series members were found in coincident at sites having higher heavy minerals percentages and detected at erosional beach than the accretion one. Coincidence was recognized between the average concentrations of40K and the percentages of the light minerals collected at 100 m distances of the profiles under investigation. Key words: Nile Delta, beach erosion, beach accretion, natural radioactivity, heavy minerals.