Optimized collimators for scintillation cameras.

In this study, the potential genotoxic effects and phytoremediation capacity of Ludwigia repens J.R. Forst. were evaluated under lead (Pb) stress in contaminated aquatic environments. To achieve this, clonal L. repens plants were used to investigate their ability to remove Pb from freshwater systems and the experimental setup was established in controlled aquarium conditions. The plants were exposed to 0, 10, 25, 50 and 100 micromolar (μM) concentrations of Pb(NO3)2 in a 0.2% Hoagland nutrient solution for a period of ten days. Experimental results showed that Pb accumulated in both stems and leaves of L. repens. Although Pb levels did not meet hyperaccumulator criteria, the bioaccumulation index (BAI), bioconcentration factor (BCF) and translocation factor (TF) values revealed that the plant was capable of accumulating noteworthy amounts of Pb. In parallel, band profile analysis revealed new band appearances only with the UBC 812 primer, while no band loss or new band formation was detected with the other primers (UBC 808, UBC 826, UBC 833 and UBC 834). Instead, only changes in band intensities were observed, indicating a low polymorphism rate and a high level of genomic template stability (GTS). The findings also indicate that L. repens exhibits notable tolerance to Pb stress, as supported by high BAI, BCF and TF values in the absence of visible phytotoxic symptoms. Additionally, the consistent and progressive decline in mineral nutrient levels across Pb treatments, together with the moderate decline in total chlorophyll content, further supports the existence of a coordinated physiological adjustment, potentially reflecting a tolerance mechanism aimed at maintaining ionic balance under heavy metal stress. Moreover, low polymorphism rates and high genomic template stability (GTS) values derived from molecular analyses suggest that this species may serve as a genetically stable and physiologically resilient aquatic plant. These combined traits highlight its potential to contribute effectively to phytoremediation applications, particularly when co-cultivated with established Pb hyperaccumulator species.

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PubMed2006

Long-term reactive transport modelling of stabilized/solidified waste: from dynamic leaching tests to disposal scenarios.

Environmental impact assessment of hazardous waste disposal relies, among others, on standardized leaching tests characterized by a strong coupling between diffusion and chemical processes. In that respect, this study shows that reactive transport modelling is a useful tool to extrapolate laboratory results to site conditions characterized by lower solution/solid (L/S) ratios, site specific geometry, infiltration, etc. A cement solidified/stabilized (S/S) waste containing lead is investigated as a typical example. The reactive transport model developed in a previous study to simulate the initial state of the waste as well as laboratory batch and dynamic tests is first summarized. Using the same numerical code (HYTEC), this model is then integrated to a simplified waste disposal scenario assuming a defective cover and rain water infiltration. The coupled evolution of the S/S waste chemistry and the pollutant plume migration are modelled assessing the importance of the cracking state of the monolithic waste. The studied configurations correspond to an undamaged and fully sealed system, a few main fractures between undamaged monoliths and, finally, a dense crack-network in the monoliths. The model considers the potential effects of cracking, first the increase of rain water and carbon dioxide infiltration and, secondly, the increase of L/S ratio and reactive surfaces, using either explicit fracture representation or dual porosity approaches.

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PubMed2006

Pb speciation versus TCLP release in army firing range soils.

A series of soil parameter and mineralogical investigative techniques were applied to assess the Pb speciation in four US Army firing range soils that presented significantly different Pb leaching regimes and soil characteristics. Soil gradation tests were complemented by total chemical analyses, X-ray powder diffraction (XRPD), Rietveld quantification, optical microscopy and scanning electron microscopy (SEM) analyses. The bulk geotechnical, mineralogical and chemical analyses pointed to two possible Pb retention mechanisms: precipitation as lead carbonate and sorption in the case of fine-grained soils. Lead speciation and mobility was further investigated by the toxicity characteristic leaching procedure (TCLP) and sequential extraction test (SET). As the TCLP Pb concentrations did not necessarily reflect the total Pb analysis of the soils, the Pb leachability ratio (TCLP/total) was found to be controlled by soil mineralogy and its response to changes in system pH. Geochemical modeling, using Visual MINTEQ, was employed to evaluate the mechanisms that controlled the observed TCLP Pb leaching behavior. It was found that lead carbonate precipitation/dissolution reactions controlled Pb TCLP leachability in all soils, while sorptive phenomena did not seem to play a role even in the case of fine-grained soils. More specifically, TCLP Pb leachability was controlled by the pH, the available Pb and the available carbonate in solution. This indicates that geochemical modeling strongly complimented TCLP Pb analyses. Thus, geochemical modeling is an important assessment tool to evaluate the magnitude of site-specific Pb-related environmental problems in firing range soils. Carbonation reactions, involving metallic Pb, that occur during the SET obscure its ability to reliably ascertain Pb speciation. More specifically, SET lumps the extractable Pb into predetermined phase categories that may not be truly representative of the actual soil mineralogy or dominant forms of Pb in the soil. A thorough geotechnical, mineralogical and chemical investigation of firing range soils, complemented by geochemical modeling, was therefore found to be a more reliable approach to evaluate Pb speciation and TCLP release in firing range soils.

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