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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PubMed1992

The effect on dose of kilovoltage x-rays backscattered from lead.

Dose enhancement on the backscatter side of a soft tissue/high Z material interface is known to exist for megavoltage x-ray beams. Caused by an increase in backscattered electron fluence, the enhancement persists for short distances upstream of the interface, equal to the range of these electrons. Since photon interaction cross sections are small, there is little photon backscatter at these energies. Consequently, beyond the range of the backscattered electrons, the dose upstream is unaffected by the presence of the interface. A similar dose enhancement has been reported for kilovoltage beams. In this case, due to the very low energy of the backscattered electrons, the enhancement persists for a very short upstream distance. Since photon interaction cross sections at keV energies are relatively large, there is also a substantial backscattered photon fluence. This experimental work investigates the effect of these photons on dose at distances upstream from a water/lead interface beyond the range of the backscattered electrons. Measurements of ionization charge, as a function of interface distance and field size for 60, 100, and 250 kV beams, were made with a parallel plate chamber at a fixed depth. A significant underdose was found upstream of the interface compared to a homogeneous water medium. For example, with the 100 kV beam and a 15 x 15 cm2 field the measured underdose is 23% at 3 mm and 14% at 1.5 cm upstream of the interface. The effect decreases with field size. In fact, for a 2 x 2 cm2 field the upstream dose in unaffected by the interface. Detailed results for this and the other two beams are presented along with backscatter factor measurements for lead. An explanation for the observed underdose is also presented.

Lead↗

PubMed1992

Determination of lead in plant tissues: a pitfall due to wet digestion procedures in the presence of sulfuric acid.

Two wet digestion procedures for the determination of lead in plant materials by electrothermal atomic absorption spectrometry have been evaluated. The combination of HNO3, H2O2 and HF, though leading to incomplete digestion, yielded values corresponding well with the reference or indicative values of the vegetal tissues used. The mixture of H2SO4, HNO3 and HCIO4 gave results that were too low in some instances, owing to the formation of a mixed precipitate (Pb,Ba)SO4.

Lead↗