Geoelectric Evaluation of Aquifer Potential and Vulnerability of Northern Paiko, Niger State, Nigeria
This study was carried out using vertical electrical sounding (VES) to evaluate the groundwater potential and the aquifer protective capacity of Northern Paiko. Sixty vertical electrical soundings were obtained across the study area using Schlumberger electrode configuration. Three to four geoelectric layers were delineated from the interpreted results. The stratigraphy of the subsurface shows: topsoil (62.8–3082 Ωm), weathered layer (15.2–80 368 Ωm), fractured layer (191–236 672 Ωm), and the fresh basement (79.9–308 865 Ωm). The weathered layer was delineated as the major aquiferous horizon. From the results, the resistivity, thickness, and longitudinal conductance maps were drawn. It was observed that groundwater potential is low in about 76.7% of the study area. This study has also shown that the aquifer protective capacity of most parts of the study area is poor (83.3%), thus rendering the aquifer vulnerable to contamination.
Evaluation of groundwater vulnerability and soil corrosivity of the Coastal Plain Sands, case of Delta State, Niger Delta South-South Nigeria
Delta State is one of the oil-producing states in the oil-rich Niger Delta region of Nigeria. Over the past decades, contaminants have been released from oil production and processing processes, domestic and agricultural environments. This study was conducted in order to characterize the subsurface soil corrosivity property and the protective capacity of the overlying geologic layers above the aquifers (APC) against aquifer water contamination. Ninety-two (92) vertical electrical soundings (VES) were used to generate the primary VES data. The results reveal that the state is characterized by diverted geo-electric subsurface layers ranging from 3 to 5 layers. Isoresistivity maps of the state showed that the first and second layers are characterized by very strong variability in layer resistivities. The state is divided into three soil corrosivity zones: non-corrosive (> 180 m), slightly corrosive (60 to 180 m), and moderately corrosive (10 to 60 m). The areas underlain by lithologies of moderately corrosive soils will not be suitable for the burial of utility metallic pipes. The characteristic longitudinal unit conductance delineated three distinct aquifer protective capacity zones as follows: poor (less than 0.10 mhos), moderate (0.2–0.69 mhos), and good (0.7–4.49 mhos). Areas with moderate-to-good APC ratings have good sealing materials for the underlying aquiferous units in the state. The results of this work revealed that some areas characterized by moderate and good APC are also underlain by slightly to moderately corrosive soils. Such areas as these are good for groundwater development, but only nonmetallic pipes as risers must be used.
Human exposure to methylmercury from crayfish (Procambarus clarkii) in China
Methylmercury (MeHg) accumulation in aquatic food raises global concerns about human exposure to MeHg. Crayfish is the world’s third largest farmed crustacean species and a favorite aquatic food in many countries. However, human health hazard due to MeHg exposure via crayfish consumption is unclear, partly because appropriate survey data are lacking. We report on mercury concentrations and speciation in edible tail muscle of crayfish collected from restaurants in 23 Chinese cities. On average, MeHg constituted 99.1 % of mercury in tail muscle, and MeHg concentrations were comparable with those reported for fish in China. Variation in MeHg concentrations was not attributable to broad geographic region (i.e., provinces) or tail length. For different populations, potential health risk (characterized by hazard quotient or HQ) of MeHg exposure through crayfish consumption depended largely on crayfish consumption rates. In particular, a health hazard (HQ > 1) was found for high-rate consumers (i.e., 95 %ile or higher) in some cities in the middle and lower reaches of the Yangtze River (MLYR), during the peak consumption season. Our results suggest that more attention should be paid to dietary MeHg intake via crayfish consumption in China, particularly for communities with high consumption in MLYR.