Rare earth elements determination and distribution patterns in sediments of a polluted marine environment by instrumental neutron activation analysis

Results obtained from the analysis of sediment core samples taken from a fairly polluted marine environment were analyzed for the REE contents to determine the concentrations of La, Ce, Sm, Eu, Th, Dy and Yb using instrumental neutron activation analysis. Core samples were divided into strata of between 2 to 3 cm intervals and prepared in the powdered form before irradiating them in a neutron flux of about 5.0 . 10(12) n . cm-(2).s(-1) in a Triga Mark II reactor. Down-core concentration profiles of La, Ce, Sm, Eu, Th, Dy and Yb in 3 core sediments from three sites are obtained. The shale-normalized REE pattern from each site was examined and later used to explain the history of sedimentation by natural processes such as shoreline erosion and weathering products deposited on the seabed and furnishing some baseline data and/or pollution trend occurring within the study area. The shale-normalized REE patterns also showed that LREE in the sediment samples exhibit enrichment relative to HREE particularly, La and Sin showing enrichment compared to the ratios in shale. REE concentrations of 124 mug/g at the surface of sediment collected at two of the three sites were found to decrease to 58 and 95 mug/g, respectively. This was of particular interest when it is used to explain the anomalies occurring in the marine sediment as a result of geochemical processes over a long period of time. Changes in concentrations from surface to bottom of the sediments ratioed to Sm concentrations and the correlation between concentrations of Sm and these elements were also investigated and correlation coefficients were calculated for all REEs and sites. Validation of the method used was done using a Soil-7 SRM.