Soil-to-plant transfer factor (TF) is a parameter utilized in predicting the accumulation of radionuclides in the plant system. Virgin soil from an uncultivated area and tailings from an abandoned tin mining site were used to formulate three soil groups. Group A (virgin soil only), group B (tailings only) and group C (equal mixture by mass of the virgin soil and tailings). Pot experiments were performed using the soil groups to determine the transfer factors of 40K, 238U and 232Th in maize (Zea mays L.) plants for the tropical ecosystem of Nigeria. The activity concentrations of 40K, 238U and 232Th in the soil groups and the maize plant compartments (seed, stem, leaf and root) were determined using NaI(Tl) gamma-detector. The geometric mean (GM) of the TF values for 40K, 238U and 232Th respectively ranged from 0.02 to 0.27, below detectable limit (BDL) to 0.008 and 0.01 to 0.09 in the in the seeds; 0.04 to 1.74, BDL to BDL and 0.01 to 0.29 in the stems; 0.03 to 0.93, BDL to 0.33 and 0.02 to 0.08 in the leaves and 0.03 to 1.29, 0.05 to 0.38 and 0.08 to 0.41 in the roots.. Potassium-40 had the highest TF values and exhibited the plant accumulation strategy for all the plant compartments. The stem samples had the highest TF for 40K and BDL values for 238U for all the soil groups. Significance differences were observed only in the accumulation of 40K and 232Th across the soil group. Keywords: Radioactivity, potassium, mining, Gamma-ray detectors, calibration

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Microbial fuel cell (MFC) is a device that coverts the chemical energy contents of organic matter to electrical energy by the catalytic action of microorganisms. Cow dungs as organic substrates were used in three sets of dual chambered MFCs to study the effects ofelectrodes on the open circuit voltage (OCV) generation of MFC. The anode and cathode compartments were connected using a protonexchange membrane, 1 kg of the cow dung diluted with 500 ml of water was introduced in the anode compartment of each of the setups. The electrode configurations for set-up 1, 2 and 3 respectively were Carbon-Carbon(C-C), carbon-copper(C-Cu) and carbon- zinc(C-Zn). Samples  for microbial load count were collected every two days from the anode compartment of the MFC and analyzed using standard microbiological methods. The OCV of the three setups were measured daily for two weeks using a digital multimeter. The microbial load ranged from 4.2 × 104 to 8.5 × 104 CFU/ml for bacteria and 2.1 × 102 to 2.3 × 103 CFU/ml for fungi. The range (average) of the OCV obtained from the set-ups were 0.06 to 0.72 V (0.42 V) for the C–C; 0.02 to 0.67 V (0.26 V) for C-Cu and 0.11 to 0.78 V (0.39 V) for the C-Zn. The OCV for the C-C electrode combination showed an increasing trend while the OCV of C-Cu and C-Zn showed decreasing trends with increasing number of days. The C-C electrode combination gave the best OCV. Keywords: microbial fuel cell, open circuit voltage, electrodes, organic substrate

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