Radiological Hazard Assessment of High-Level Natural Radionuclides in Surface Sediments Along Red River, Vietnam.

The Red River is one of the largest rivers that plays an important role in the economic development of North Vietnam. There are many radionuclides bearing rare earth, uranium ore mines, mining industrial zones and magma intrusive formations along this river. The contamination and accumulation of radionuclides could exist at high concentration in surface sediments of this river. Thus, the present investigation aims to study the activity concentrations of 226Ra, 232Th (228Ra), 40K, and 137Cs in Red River surface sediments. Thirty sediment samples were collected, and their activity concentration was calculated using high-purity germanium gamma-ray detector. The observed results ranged from 51.0 ± 2.1 to 73.6 ± 3.7 for 226Ra, 71.4 ± 3.6 to 103 ± 5.2 for 232Th, 507 ± 24.0 to 846 ± 42.3 for 40K, and ND (not detected) to 1.33 ± 0.06 Bq/kg for 137Cs, respectively. In general, the natural radionuclides concentration of 226Ra, 232Th (228Ra), and 40K is higher than the average world average values. This indicated that the natural radionuclides could contribute from similar and principal sources surrounding the upstream of Lao Cai where distributed uranium ore mines, radionuclide bearing rare earth mines, mining industrial zones and intrusive formations. Regarding the radiological hazard assessment, results of the indices computed such as absorbed gamma dose rate (D), the excess lifetime cancer risk (ELCR), and the annual effective dose equivalent (AEDE) were nearly two times higher than world average values.

Radiological risk assessment of outdoor222Rn and220Rn around rare earth element and uranium mines from northern Vietnam.

The outdoor222Rn and220Rn concentrations at 320 sampling points at 1 m above the ground in different sites surrounding rare earth element (REE) and uranium mines from northern Vietnam were measured using the RAD7. Results showed that222Rn concentrations were always higher than220Rn concentrations with large variation ranges from 25.7 to 573 Bq m-3and from 18.5 to 385 Bq m-3, respectively. The high correlation between220Rn and228Ra concentrations in surface soil of the studied sites were observed. The highest220Rn and222Rn concentrations are found at the sampling points of the REE NX-Lai Chau site. The220Rn and222Rn activities surrounding the REE mines were found to be higher than those surrounding the uranium mines. The average annual committed effective doses originated from the inhalation of220Rn and222Rn outdoor concentrations is about five times higher than the worldwide average value.

Transfer and bioaccumulation of 210Po from soil to water spinach (Ipomoea aquatica Forrsk.) in Vietnam.

The water spinach (Ipomoea aquatica Forrsk.) is a common vegetable and a part of the staple diet in Vietnam. It has a well-known tendency for the high absorption of lead, including the radioactive isotope 210Pb. 210 Pb day to 210Po, which is one of the most toxic radioactive isotopes when ingested. Currently, there are few data available on the activity concentration or transfer parameters of water spinach grown in Vietnam. To provide this data, in this study, the 210Po activity concentrations in the soil, water and the roots, stems, and leaves of two types of spinach (grown in soil flooded with water and grown in normal soil) in Hanoi, Vietnam were determined by alpha spectrometry. The order of activity concentrations for water spinach grown in unflooded was Cstem < Cleaf < Croot, while for flooded Cstem ≈ Croot < Cleaf. The transfer factors followed a similar pattern.

Distribution and annual committed effective dose assessment of 210Po in popular marine species at the near-shore Binh Thuan province, Vietnam.

210Po concentration in thirty popular marine species (twenty five fishes, four bivalves and one crab) with different habitats, feeding types, and trophic levels at the near-shore Binh Thuan, Vietnam was analyzed using the alpha detectors. The 210Po activities were widely ranged from 3.07 ± 0.18 in a fish species (Bumpnose trevally) to 78.6 ± 5.3 Bq/kg w.w in a bivalve species (Green mussel) with the average value of 16.6 Bq/kg w.w. The results showed that the species with lower trophic level value have higher 210Po concentration. Regarding the feeding types, the 210Po concentration in the omnivorous species is about 2.9 times higher than in the carnivorous species. The species living in demersal zone accumulated a high 210Po in comparison with species living in reef-associated and pelagic-neritic zones. The calculated annual committed effective dose from 210Po due to the ingestion of seafood from demersal zone and bivalve species of the area was significant high.

Transfer of radionuclides from soil to Acacia auriculiformis trees in high radioactive background areas in North Vietnam.

The Acacia auriculiformis is a tree common in tropical Asian countries, capable of growing in many different soil types, so it could be used for biomonitoring for high natural radionuclide areas in tropical and subtropical climates. The transfer factor (TF) of radionuclides from soil to A. auriculiformis in eight uranium and rare earth element (REE) mining areas of North Vietnam was investigated. The activity concentrations 226Ra, 238U, 137Cs, 228Ra, and 40K in both soil and A. auriculiformis showed considerable variation. The TFs of these radionuclides also varied in a wide range. In most of the eight areas, the highest TF was observed for 137Cs and 228Ra. While the TFs for 226Ra and 238U were smallest. In addition, the TFs for radionuclides near REE mines were similar to those observed near uranium mines. The TFs for A. auriculiformis were within the ranges of TF reported for other plants, except for 137Cs.

Study of Well Waters from High-Level Natural Radiation Areas in Northern Vietnam.

The determination of natural radionuclide concentrations plays an important role for assuring public health and in the estimation of the radiological hazards. This is especially true for high level radiation areas. In this study, 226Ra, 228Ra and 238U concentrations were measured in well waters surrounding eight of the high-level natural radiation areas in northern Vietnam. The 226Ra, 228Ra and 238U activity concentrations vary from <1.2 × 10-3-2.7 (0.46), <2.6 × 10-3-0.43 (0.07) and <38 × 10-3-5.32 Bq/L (0.50 of median), respectively. 226Ra and 238U isotopes in most areas are in equilibrium, except for the DT-Thai Nguyen area. The calculated radiological hazard indices are generally higher than WHO (World Health Organization) recommendations. Average annual effective dose and excess lifetime cancer risk values due to drinking well water range from to 130 to 540 µSv/year and 7.4 × 10-6 to 3.1 × 10-5, respectively.

Study of soil to plant transfer factors of 226Ra, 232Th, 40K and 137Cs in Vietnamese crops.

The study of staple food products is crucial to assure public safety and provides input for predictive dose assessment models. To further this goal, the activity concentrations, transfer factors, and radiological hazards of 226Ra, 232Th, 40K, and 137Cs were studied for ten pairs of selected vegetables and soils in Tien Le near Hanoi in Vietnam. This is the first study in this area for Vietnamese vegetable samples. The ten most popular vegetables in Vietnamese diet were selected, namely choy sum, crown daisy, lettuce, cabbage, Malabar spinach, beans, sweet potato, potato, kohlrabi and carrot. The research results showed that the activity concentrations observed in vegetable crops did not present the previously reported strong correlation to those in soil. The ranges of TFs of 226Ra, 232Th, and 40K were 4 × 10-2 - 6.9 × 10-1, 8 × 10-2 - 9.7 × 10-1; and 1.0 × 100-1.6 × 101, respectively. Values for leafy vegetables and tubers exceed previous world range figures for Th and K. The soil has been evaluated for radiological hazard indices, which predict almost no risk to human health in the study area.

Gross alpha and gross beta activities in selected marine species in Vietnam.

The measured gross alpha and gross beta activities in the edible muscle tissues of eleven selected marine species along the coast of North Vietnam varied from 10.2 ± 1.5 to 73.2 ± 8.1 Bq/kg (wwt) and from 10.6 ± 0.4 to 68.8 ± 2.8 Bq/kg (wwt), respectively. The lowest gross alpha activity was recorded for bigfin reef squid (Sepioteuthis lessoniana) as a result of its carnivorous diet, and the highest alpha activity was noted for blood cockle (Anadara granosa) as a result of its omnivorous diet. However, the gross beta activities in both carnivorous and omnivorous species were similar. The highest and lowest gross beta activities were observed for narrow-barred Spanish mackerel (Scomberomorus commerson) and for bigfin reef squid and squid (Teuthida), respectively. All three aforementioned species have carnivorous diets. The calculated annual committed effective dose resulting from the consumption of 25 kg of muscle tissue per year varied from 192 to 1375 µS with an average of 689 µS.

Isolation of Penicillium citrinum from Roots of Clerodendron cyrtophyllum and Application in Biosynthesis of Aglycone Isoflavones from Soybean Waste Fermentation.

Soybeans offer an abundant source of isoflavones, which confer useful bioactivities when existing in aglycone forms. The conversion of isoflavones into aglycones via fermentation of soybean products is often realized by ß-glucosidase, an enzyme produced by fungi. In this study, a filamentous fungus, Clerodendron cyrtophyllum, was isolated from root of Clerodendron cyrtophyllum Turcz, which was able to produce the highest activity of ß-glucosidase up to 33.72 U/mL at 144 h during fermentation on Potato Dextrose Broth (PDB). The obtained fungus was grown on isoflavones-rich soybean extract to produce genistein and daidzein, achieving the conversion rate of 98.7%. Genistein and daidzein were isolated and purified by column chromatography using hexane/acetone (29:1/1:1), reaching purities of over 90% of total isoflavones, as identified and determined by TLC, LC-MS/MS, and 1H and 13C NMR spectroscopy. These results imply that the isolated P. citrinum is a potential fungal strain for industrial-scale production of genistein and daidzein from isoflavones-containing soybean extracts. These products may serve as potential raw materials for manufacture of functional foods that are based on aglycones.

Insights into the Kinetics of the Resistance Formation of Bacteria against Ciprofloxacin Poly(2-methyl-2-oxazoline) Conjugates.

The influence on the resistance formation of polymers attached to antibiotics has rarely been investigated. In this study, ciprofloxacin (CIP) was conjugated to poly(2-methyl-2-oxazoline)s with an ethylene diamine end group (Me-PMOx28-EDA) via two different spacers (CIP modified with α,α'-dichloro- p-xylene-xCIP, CIP modified with chloroacetyl chloride-eCIP). The antibacterial activity of the conjugates against a number of bacterial strains shows a great dependence on the nature of the spacer. The Me-PMOx39-EDA-eCIP, containing a potentially cleavable linker, does not exhibit a molecular weight dependence on antibacterial activity in contrast to Me-PMOx27-EDA-xCIP. The resistance formation of both conjugates against Staphylococcus aureus and Escherichia coli was investigated. Both conjugates showed the potential to significantly delay the formation of resistant bacteria compared to the unmodified CIP. Closer inspection of a possible resistance mechanism by genome sequencing of the topoisomerase IV region of resistant S. aureus revealed that this bacterium mutates at the same position when building up resistance to CIP and to Me-PMOx27-EDA-xCIP. However, the S. aureus cells that became resistant against the polymer conjugate are fully susceptible to CIP. Thus, conjugation of CIP with PMOx seems to alter the resistance mechanism.

Estimation of seabed shear-wave velocity profiles using shear-wave source data.

This paper estimates seabed shear-wave velocity profiles and their uncertainties using interface-wave dispersion curves extracted from data generated by a shear-wave source. The shear-wave source generated a seismic signature over a frequency range between 2 and 60 Hz and was polarized in both in-line and cross-line orientations. Low-frequency Scholte- and Love-waves were recorded. Dispersion curves of the Scholte- and Love-waves for the fundamental mode and higher-order modes are extracted by three time-frequency analysis methods. Both the vertically and horizontally polarized shear-wave velocity profiles in the sediment are estimated by the Scholte- and Love-wave dispersion curves, respectively. A Bayesian approach is utilized for the inversion. Differential evolution, a global search algorithm is applied to estimate the most-probable shear-velocity models. Marginal posterior probability profiles are computed by Metropolis-Hastings sampling. The estimated vertically and horizontally polarized shear-wave velocity profiles fit well with the core and in situ measurements.