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Surface deposits and sediment cores were collected from the Upper Bonny Estuary, located in Southwest Nigeria, and analyzed to determine spatio-temporal and vertical distributions of radio-nuclide activities expressed in Bq·kg−1 dry weight. The results of activities of naturally occurring radionuclides of 226Ra (15 ± 2–34 ± 3 Bq·kg−1), 228Ra (32 ± 5–48 ± 6 Bq·kg−1), 40K (264 ± 29–462 ± 36 Bq·kg−1) were found to be all within the range of typical values reported for coastal regions. Ratios of 226Ra to 228Ra suggested accretion for all samples with low sediment accumulation registered during rainy months. In addition, vertical distributions at the three sampling sites were also studied with the initial aim of establishing chronologies from the decay of excess 210Pb. In two cores, excess 210Pb, estimated by subtracting 226Ra from total 210Pb on a layer-by-layer basis, exhibit relatively constant activity with discrete minima and maxima. Therefore, these cores were excluded from radiometric dating. Only the third core could be dated by the constant rate of supply model, and 137Cs was utilized to validate the 210Pb chronology.

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The research evaluated temporal trends of naturally occurring radionuclides and their vertical distributions in sediment cores collected from three sites of diverse sedimentation regimes in Bonny Estuary, and developed and implemented sediment dating with unsupported lead-210. Radium (Ra) isotopes exhibited a very similar distribution throughout all sampled cores in each month, with 228Ra, while 226Ra displayed some variability with generally lower specific activities in dry months than in wet months. The values found in the study were all less than unity ranging from 0.3 to 0.8, which suggested sediment accretion and that the study area corresponded to zones with different sedimentation regimes. Temporal distribution of total 210Pb in the sampled cores determined via its daughter 210Po by alpha spectrometry assumed that the secular equilibrium between both radionuclides was achieved. However, the activities in Station 3 were found to be lower than those in Station 1, with Station 2 having the lowest activity registered in the samples collected in December month. The specific activities of 228Ac (228Ra), 212Pb (228Th) and 40K against depth in the sampled cores were observed to be almost equal to one another at each stratigraphic interval. The average sedimentation rate throughout the core obtained from Constant Rate of Supply model (0.068 ± 0.015g.cm-2.y-1) was nearly the same as that obtained from the Constant Initial Concentration model (0.065 ± 0.004). However, the estimated ages were quite variable with depths of various stratigraphic layers. The age of the sediment core was dated approximately 80 years, which was qualitatively validated using 137CS whose activity was definitely undetected in the basal part of the core. The sedimentation rates calculated suggested low sedimentation characterized by low energy environment dominated by weak tidal currents.

Sediment and biota samples were collected biannually from the Bonny/New Calabar River Estuary in Niger Delta, Nigeria and analysed for poisonous metals of interest to the International Atomic Energy Agency (Pb, Cd, and Hg) using atomic absorption spectrophotometer A-500 and Direct Mercury analyser (DMA-80). Results for biota showed that Cd ranged from 0.003 to 0.558 ± 0.01mg/kg, Hg ranged from 0.014 ± 0.004 to 0.021± 0.010 mg/kg, Sediment: Cd ranged from 0.022 ± 0.001 – 0.82 ± 0.0002 mg/kg; Hg 0.010 ± 0.005 to 0.027 ± 0.009 mg/kg. Lead was below the detection limit of the instrument   both in biota and sediment. The concentrations of the respective poisonous metals were within the permissible limit of the World health organization. The study showed high concentration of Cd in Crayfish compared to other seafood.  The bioaccumulation factor showed higher level of Hg compared Cd while the Analysis of variance for the three stations did not show any significant variation among the three stations. Regular monitoring and comparison of level of contamination with regulatory bodies are advocated to prevent the concentration of the metal contaminants from getting to an alarming level.