環境および分析毒性学

Present study on the sustainable use of saline land and saline groundwater for agricultural production has been conducted in the pre-Saharian area of Ain El Atti through the application of environmental isotopes supported by the hydrochemistry. In the study area, a network of 20 water points has been the focus of the isotope analysis (δ18O, δ2H, 3H and 14C) and physical chemistry. The samples were collected once every 3 months from artesian groundwater of “the Infracenomanian” (4), the Turonian (4), the Senonian (1) and the Quaternary aquifer (5) and from the precipitation of the years 2001, 2002 and 2003. The results show that (i) the stable isotope from the Infracenomanian is very poor and they are without tritium, confirming the fact that this aquifer is confined and it is not evaporated. Its strong salinity is due to the dissolution and the lixiviation of the geological formation; (ii) the Turonian, the Senonian and the Quaternary aquifers are not confined, and their stable isotope contents more or less as important as the tritium, signifying that they receive recent recharge. The first one is affected by the artesian well and it is not evaporated and it has high salinity. The second and the third one are not affected by the artesian well, but the influence of the precipitation and the flood is clear. Their groundwater is not evaporated and their salinity is moderate; (iii) however, the Ziz surface water isotopic elements are rich, signifying an actual recharge. Its water is highly evaporated and its salinity is variable.

Silver pollution in the marine environment is of concern, particularly, with the rapid increasing use of silver nanoparticles in consumer products providing additional sources of silver emissions. Silver is highly toxic and known to bioaccumulate in aquatic organisms; however, the risk silver poses to the marine ecosystem is poorly understood. The sperm whale (Physeter macrocephalus), a toothed whale having a wide global distribution and high trophic level, is a sentinel of ocean health. The aim of this study was to provide a global baseline for silver as a marine pollutant using the sperm whale as an indicator species. Skin biopsies were collected in free-ranging sperm whales around the globe during the voyage of the research vessel, Odyssey, during 2000 and 2005. Total silver levels were measured in 298 sperm whales from 16 regions. Detectable levels were found in 176 whales and ranged from 0.1 to 4,179.0 μg/g ww with a global mean level of 16.9 ± 14.1 μg/g ww. The highest mean level was found in whales sampled in waters near Seychelles with 123.3 μg/g ww, and the lowest mean in whales near Chagos with 0.1 μg/g ww. These data provide an important global baseline for silver pollution that precedes the recent emergence of silver nanoparticles.

The study examined the spatial characteristics of boreholes of ten selected locations with the opinion of appraising the sustainability of groundwater resource in the Deltaic formation, Niger Delta Nigeria. Data on Borehole Parameters (Depth of Hole, Screen Length, Yield of Well and Drawdown) were obtained from the Rivers State Ministry of Water Resources, Port Harcourt, and Rivers State. Both Descriptive and Inferential Statistical methods were employed in the analyses of the data while the relationship between the well yield and other borehole parameters was also modelled. The result showed that the aquifers of the study area are very thick, deeply located, and highly porous and saturated; emphasizing high yield potentials. It was also revealed that the basin contains adequate water to sustain her population as indicated by the high mean yield (30,056 lit/m) recorded for the study area. Finally, the result of the correlation statistics showed that the yield of well increases with depth of hole (r=0.82), rate of drawdown (r=0.62) and length of screen (r=0.63); and that the rate of drawdown increases as the length of screen increases (r=0.99). The study concluded by emphasizing the indispensability of adequate knowledge of hydrogeology in groundwater exploration and development particularly in regions of complex geological heterogeneity such as that of the Deltaic formation.

A pot experiment was conducted to study the extractability of cadmium and zinc by CaCl2 and rhizon extraction methods after the application of organic matter and chloride as soil amendments. Two methods, Rhizon and CaCl2 extraction methods were concurrently employed to study the effects of the various amendments on the mobility of Cd and Zn. Both CaCl2 and Rhizon extraction methods generally extracted appreciable amounts of the heavy metals after the application of the amendments. However, the results from the experiment shows that the Rhizon samplers extracted higher concentrations of both Cd and Zn as compared to the CaCl2 extraction method. The use of Rhizon soil moisture sampler is also non destructive to the soil and makes it possible to ascertain levels of heavy metals at equilibrium in the soil solution without changing the compisition of the soil solution in the process of extracting it. Assessment of the soil pH in the soil samples and the Rhizon extracts after the application of the amendments showed no significant difference with the control. Comparatively, application of CaCl2 had a significant mobilizing effect on the mobility of both Cd and Zn as a result of the combined effect of complexation of Cd and Zn by the chloride anion, and by the fact that Cd and Zn are preferentially absorbed in cation exchange positions. Therefore the Ca2+ ion can displace these metals into the soil solution.

Rapid industrialization, urbanization and increase in population have led to increasing the pollution levels. Heavy metal pollution of water is of major concern now-a-days as water is the basic need for mankind. The present investigation is removal of lead from aqueous solutions using a new biosorbent Casuarina leaf powder. The cumulative effects of operating parameters such as initial metal ion concentration, pH of the aqueous solution, biosorbent dosage and temperature on the lead biosorption were analyzed using Response Surface Methodology (RSM). For obtaining the mutual interaction between the variables and optimizing these variables, a 24 full factorial central composite design was employed. According to ANOVA results, the proposed quadratic model for CCD fitted very well to the experimental data. The optimal set of conditions for maximum percentage biosorption of lead is found to be pH=4.988, biosorption dosage (w) =35.37 g/L, initial lead concentration (Co)=18.0555 mg/L and temperature=306.47 K and the % of biosorption calculated at these values found to be 95.73%. The Langmuir isotherm fitted well with a correlation factor of 0.9944, followed by Freundlich and Temkin. The entire biosorption process followed pseudo second order kinetics. By applying the Van’t Hoff equation the thermodynamic parameters such as enthalpy (ΔH°), entropy (ΔS°) and free energy (ΔG°) were evaluated which described the biosorption process as spontaneous, irreversible and endothermic in nature. The optimized values obtained through central composite design and one factor at a time process is in good agreement.