Heavy metals detection in sediments using PGNAA method

Shielding design in neutron activation experiment system based on D-T neutron tube

The deuterium-tritium neutron generator should be fully shielded for the safety of the operators participating in the experiments since the D-T neutron generator is commonly used in activation experiments. In this study, MCNP5 code was used to simulate the shielding effect of the neutron thermalization device previously designed by our group with Pb and boron-containing polyethylene as the shielding material. The neutron dose rate outside of the previous thermalization device can not meet the requirement, so a concrete wall is needed between the device and the operators. Two models are designed with concrete walls. One model is that the device and the experimental operators are not in the same room, another one is that the device and the experimental operators are in the same room, and there is an L-shaped concrete wall between them. In both models, the dose rate to the operators was less than 5 ?Svh-1.

Integrated bioinformatics analysis of As, Au, Cd, Pb and Cu heavy metal responsive marker genes through Arabidopsis thaliana GEO datasets

BACKGROUND

Current environmental pollution factors, particularly the distribution and diffusion of heavy metals in soil and water, are a high risk to local environments and humans. Despite striking advances in methods to detect contaminants by a variety of chemical and physical solutions, these methods have inherent limitations such as small dimensions and very low coverage. Therefore, identifying novel contaminant biomarkers are urgently needed.

METHODS

To better track heavy metal contaminations in soil and water, integrated bioinformatics analysis to identify biomarkers of relevant heavy metal, such as As, Cd, Pb and Cu, is a suitable method for long-term and large-scale surveys of such heavy metal pollutants. Subsequently, the accuracy and stability of the results screened were experimentally validated by quantitative PCR experiment.

RESULTS

We obtained 168 differentially expressed genes (DEGs) which contained 59 up-regulated genes and 109 down-regulated genes through comparative bioinformatics analyses. Subsequently, the gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichments of these DEGs were performed, respectively. GO analyses found that these DEGs were mainly related to responses to chemicals, responses to stimulus, responses to stress, responses to abiotic stimulus, and so on. KEGG pathway analyses of DEGs were mainly involved in the protein degradation process and other biologic process, such as the phenylpropanoid biosynthesis pathways and nitrogen metabolism. Moreover, we also speculated that nine candidate core biomarker genes (namely, NILR1, PGPS1, WRKY33, BCS1, AR781, CYP81D8, NR1, EAP1 and MYB15) might be tightly correlated with the response or transport of heavy metals. Finally, experimental results displayed that these genes had the same expression trend response to different stresses as mentioned above (Cd, Pb and Cu) and no mentioned above (Zn and Cr).

CONCLUSION

In general, the identified biomarker genes could help us understand the potential molecular mechanisms or signaling pathways responsive to heavy metal stress in plants, and could be applied as marker genes to track heavy metal pollution in soil and water through detecting their expression in plants growing in those environments.

Efficiency calibration of HPGe detector in a PGNAA system for the measurement of aqueous samples

In this work, a method was proposed for efficiency calibration of HPGe detector employed in a prompt gamma-ray neutron activation analysis (PGNAA) system for large aqueous sample analysis. Experimental measurements of a reference surface gamma-ray source were combined with efficiency transfer method to obtain efficiency of a volumetric source. Then efficiency curve over the energy range 0.5-8.5 MeV were determined with prompt gamma-rays of chlorine. To evaluate the performance of the calibration curve, an internal standard method was used to determine the aqueous sample containing manganese based on the calibration curve. The 7.058 MeV and 7.243 MeV manganese gamma-ray peaks were used to calculate the mass of manganese. The relative deviations of calculated values and actual value were 5.0% and 6.5%, respectively.