Effective dose rate coefficients for exposure to contaminated soil

The Oak Ridge National Laboratory Center for Radiation Protection Knowledge has undertaken calculations related to various environmental exposure scenarios. A previous paper reported the results for submersion in radioactive air and immersion in water using age-specific mathematical phantoms. This paper presents age-specific effective dose rate coefficients derived using stylized mathematical phantoms for exposure to contaminated soils. Dose rate coefficients for photon, electron, and positrons of discrete energies were calculated and folded with emissions of 1252 radionuclides addressed in ICRP Publication 107 to determine equivalent and effective dose rate coefficients. The MCNP6 radiation transport code was used for organ dose rate calculations for photons and the contribution of electrons to skin dose rate was derived using point-kernels. Bremsstrahlung and annihilation photons of positron emission were evaluated as discrete photons. The coefficients calculated in this work compare favorably to those reported in the US Federal Guidance Report 12 as well as by other authors who employed voxel phantoms for similar exposure scenarios.     

Biodegradation of diphenylarsinic acid to arsenic acid by novel soil bacteria isolated from contaminated soil

Microorganisms capable of degrading diphenylarsinic acid (DPAA) were enriched from contaminated soil using the soil-charcoal perfusion method. Two novel bacterial strains, L2406 and L2413, that can degrade DPAA in a mineral salt medium supplemented with DPAA as the sole carbon source were isolated. Based on comparative morphology, physiology, and comparison of the 16S rRNA gene sequences, both were presumed to be species closely related to Ensifer adhaerens. As the metabolites, phenylarsonic acid (PAA) was determined by liquid chromatography-mass spectrometry analysis as well as three unknown peaks all of whose molecular weights were estimated to be 278. The increase of m/z = 16 from DPAA in the unknowns suggests monohydroxylation of DPAA at the 2-, 3- and 4-positions. The ability of strains L2406 and L2413 to degrade DPAA was suppressed in iron insufficient conditions, e.g. less than 7.2 μM iron in the culture medium. These facts strongly suggest the following hypothesis: Monooxygenase works at the initial degradation step of DPAA degradation by the isolates; and direct hydrolysis from DPAA to PAA is not likely to occur. In addition, release of arsenic acid from PAA by strain L2406 was confirmed by liquid chromatography-inductively coupled plasma mass spectrometry. From these results, strain L2406 was considered to be capable of degrading DPAA to arsenic acid via PAA when DPAA was supplied as the sole carbon source.     

External exposure of deciduous tooth enamel to photons: dose conversion coefficients for standard radiation fields

Dose conversion coefficients for teeth of children were computed for external photon sources by means of Monte Carlo methods using a modified MIRD-type mathematical phantom of a 5-year-old child. The tooth region is separated into eight smaller regions that represent incisors, canines, first and second molars. Each of these sub-regions is separated into enamel and dentin parts. Dose conversion coefficients were computed as ratio of absorbed dose in the enamel and air kerma. They are given for unidirectional (AP, PA, RLAT, LLAT), rotational (ROT) and isotropic (ISO) photon sources in the energy range from 10 keV to 10 MeV. All computations were performed with the MCNP4 code including coupled electron-photon transport. The computed coefficients demonstrate a significant non-linearity versus photon energy, which is more pronounced than that observed for adult phantoms. Due to this non-linearity, use of the EPR-measured doses in human teeth requires information on the incident photon fluence spectra. The data presented can be used for assessment of public exposure.     

Tables of dose conversion coefficients for estimating internal and external radiation exposures to terrestrial and aquatic biota

Dose conversion coefficients (DCCs) for assessment of internal and external radiation exposures to terrestrial and aquatic biota are compiled for 75 radionuclides, for 14 terrestrial and 22 aquatic reference organisms. DCC values for internal exposure are calculated based on a homogeneous distribution of the radionuclides in both types of organisms. DCC values for external exposure of aquatic organisms are calculated for complete immersion in water. For external exposure of terrestrial organisms the soil is considered as a planar and homogenously contaminated volume source with a surface roughness of 3 mm and a thickness of 10 cm, respectively. For in-soil-organisms, DCC values for external exposure are given assuming that these organisms live in the middle of a uniformly contaminated 50 cm-thick soil layer. The tables can be used for assessment of exposures of animals and plants living in various habitats. The list of considered organisms covers the Reference Animals and Plants as adopted by the ICRP.     

An improved understanding of soil Cd risk to humans and low cost methods to phytoextract Cd from contaminated soils to prevent soil Cd risks

We believe greater consideration should be given the agronomic and nutritional/bioavailability factors that influence risk from Cd-contaminated soils. We have argued that the ability of rice to accumulate soil Cd in grain while excluding Fe, Zn and Ca (even though the soil contains 100-times more Zn than Cd) was important in adverse effects of soil Cd is farm families in Asia. Further, polished rice grain is deficient in Fe, Zn and Ca for humans, which promotes Cd absorption into duodenal cells. New kinetic studies clarified that dietary Cd is absorbed into duodenum enterocytes; 109Cd from a single meal remained in the duodenum for up to 16 days; part of the turnover pool 109Cd moved to the liver and kidneys by the end of the 64-day 'chase' period. Thus malnutrition induced by subsistence rice diets caused a higher absorption of dietary Cd and much higher potential risk from soil Cd than other crops. Because rice-induced Fe-Zn-Ca-malnutrition is so important in soil Cd risk, it seems evident that providing nutritional supplements to populations of exposed subsistence rice farmers could protect them against soil Cd during a period of soil remediation. In the long term, high Cd rice soils need to be remediated. Remediation by removal and replacement of contaminated soil is very expensive (on the order of $3 million/ha); while phytoextraction using the high Cd accumulating ecotypes of the Zn-Cd hyperaccumulator, Thlaspi caerulescens, should provide low cost soil Cd remediation.     

Phytoextraction of heavy metals from contaminated soil by co-cropping with chelator application and assessment of associated leaching risk

Phytoextraction using hyperaccumulating plants is generally time-consuming and requires the cessation of agriculture. We coupled chelators and a co-cropping system to enhance phytoextraction rates, while allowing for agricultural production. An experiment on I m3 lysimeter beds was conducted with a co-cropping system consisting of the hyperaccumulator Sedum alfredii and low-accumulating corn (Zea Mays, cv. Huidan-4), with addition ofa mixture of chelators (MC), to assess the efficiency of chelator enhanced co-crop phytoextraction and the leaching risk caused by the chelator. The results showed that the addition of MC promoted the growth of S. alfredii in the first crop (spring-summer season) and significantly increased the metal phytoextraction. The DTPA-extractable and total metal concentrations in the topsoil were also reduced more significantly with the addition of MC compared with the control treatments. However, mono-cropped S. alfredii without MC was more suitable for maximizing S. alfredii growth and therefore phytoextraction of Zn and Cd during the autumn-winter seasons. No adverse impact to groundwater due to MC application was observed during the experiments with three crops and three MC applications. But elevated total Cd and Pb concentrations among subsoils compared to the initial subsoil concentrations were found for the co-crop + MC treatment after the third crop.     

A human health risk assessment of soil and crops contaminated by heavy metals in industrial regions,central Iran

In this study, the concentrations of heavy metal (Cd, Pb, Fe, and Ni) in contaminated soils adjacent to two steel mill companies and in three crops (i.e., wheat, rice, and onion) grown in these regions were compared with a non-industrial site in Isfahan province, central Iran. The results were manifold. The heavy metal concentrations of both the soil and crops within the two industrial regions turned out to be more significant than the nonindustrial counterpart. In addition, the soils surrounding the companies were demonstrated to be contaminated by Cd, Pb, and Ni according to the limits provided by the international standards (i.e., USEPA and European Union standards). As for the crops from the investigated contaminated sites, the mean concentrations of Cd, Ni, and Pb exceeded the maximum permissible levels for human consumption stipulated by FAO/WHO standards. Furthermore, the values gained from the target hazard quotient were above one, meaning that the crops are contaminated. Given the results gained from a comparison made between estimated daily intake and tolerable daily intake, it can be concluded that the inhabitants of the two investigated contaminated sites are at a potentially serious health risk caused by exposure to the crops contaminated with the heavy metal.     

Evaluation of the use of resonant frequencies to characterize physical properties of human long bones

Human tibiae were subjected to steady state vibration over a frequency range to evaluate the use of clinical measurements of resonant frequency to characterize osteoporosis. Displacement and force transmitted to the bone were monitored and used to obtain measures of dynamic mass, stiffness, damping and resonant frequency. Initial results indicate that resonant frequency F is a less sensitive indicator of change in state than either generalized mass M or generalized stiffness K due to the functional relationship of these three parameters.     

Organ and detriment-weighted dose rate coefficients for exposure to radionuclide-contaminated soil considering body morphometries that differ from reference conditions: adults and children

Radiation and Environmental Biophysics - The system of protection established by the International Commission on Radiological Protection (ICRP) provides a robust framework for ionizing radiation...     

Chemically enhanced phytoextraction of risk elements from a contaminated agricultural soil using Zea mays and Triticum aestivum: performance and metal mobilization over a three year period

Enhanced phytoextraction using EDTA for the remediation of an agricultural soil contaminated with less mobile risk elements Cd and Pb originating from smelting activities in Príbram (Czech Republic) was assessed on the laboratory and the field scale. EDTA was applied to the first years crop Zea mays. Metal mobilization and metal uptake by the plants in the soil were monitored for two additional years when Triticum aestivum was planted. The application ofEDTA effectively increased water-soluble Cd and Pb concentrations in the soil. These concentrations decreased over time. Anyhow, increased concentrations could be still observed in the third experimental year indicating a low possibility of groundwater pollution after the addition of EDTA during and also after the enhanced phytoextraction process under prevailing climatic conditions. EDTA-applications caused phytotoxicity and thereby decreased biomass production and increased Cd and Pb uptake by the plants. Phytoextraction efficiency and phytoextraction potential were too low for Cd and Pb phytoextraction in the field in a reasonable time frame (as less than one-tenth of a percent of total Cd and Pb could be removed). This strongly indicates that EDTA-enhanced phytoextraction as implemented in this study is not a suitable remediation technique for risk metal contaminated soils.     

Structural conversion from non-native to native form of recombinant human epidermal growth factor by Brevibacillus choshinensis

Brevibacillus choshinensis (Bacillus brevis) HPD31 is a very efficient producer of recombinant human epidermal growth factor (EGF). The produced EGF is secreted into the medium with high efficiency. However part of the EGF that accumulates in the medium, exists as multimeric forms which are biologically inactive. We found the bacterium has the activity to structurally convert multimeric forms to the monomeric, native ones. Optimal temperature and pH for the conversion were 40 degrees C and pH 9, respectively. The reaction was promoted in the presence of reduced glutathione or cysteine. But the cells which had been sonicated or exposed to moderate heat treatment completely lost the activity. Thus, it was presumed that the activity might be due to the enzyme(s) that catalyze the protein disulfide exchanging reaction, and that they resides on the surface of viable cells.     

Evidence for conversion of human salivary alpha-amylase family A to family B by an enzyme action.

SDS-PAGE showed that human salivary alpha-amylase family A (HSA-A) was converted to family B (HSA-B) in human saliva. This conversion did not occur in the supernatant of saliva which had been centrifuged at 105,000 x g for 60 min. An enzyme which catalyzed the conversion existed in the insoluble fraction of human saliva. The enzyme was solubilized with nonionic or zwitterionic detergents, and showed the maximum activity around pH 6. It was stable between pH 4 and 10, and at a temperature lower than 40 degrees C. The enzyme reduced the molecular weight of HSA-A (62,000) to the same molecular weight (58,000) as that of HSA-B without forming any intermediate. It also changed the PAGE pattern of multiple forms of HSA-A to the same pattern as that of HSA-B. It was not inhibited by protease inhibitors, and it did not destroy the reactivity of HSA-A with anti-human salivary alpha-amylase antiserum. The enzyme diminished the reactivity of HSA-A with concanavalin A. These results indicate that HSA-A was converted to HSA-B through the release of sugar chains by the action of the enzyme in the insoluble fraction of human saliva.     

No evidence for genotoxic effects from 24 h exposure of human leukocytes to 1.9 GHz radiofrequency fields

The current study extends our previous investigations of 2-h radiofrequency (RF)-field exposures on genotoxicity in human blood cell cultures by examining the effect of 24-h continuous-wave (CW) and pulsed-wave (PW) 1.9 GHz RF-field exposures on both primary DNA damage and micronucleus induction in human leukocyte cultures. Mean specific absorption rates (SARs) ranged from 0 to 10 W/kg, and the temperature within the cultures was maintained at 37.0 +/- 1.0 degrees C for the duration of the 24-h exposure period. No significant differences in primary DNA damage were observed between the sham-treated controls and any of the CW or PW 1.9 GHz RF-field-exposed cultures when processed immediately after the exposure period by the alkaline comet assay. Similarly, no significant differences were observed in the incidence of micronuclei, incidence of micronucleated binucleated cells, frequency of binucleated cells, or proliferation index between the sham-treated controls and any of the CW or PW 1.9 GHz RF-field-exposed cultures. In conclusion, the current study found no evidence of 1.9 GHz RF-field-induced genotoxicity in human blood cell cultures after a 24-h exposure period.     

Enzymatic conversion of prostaglandin H2 to prostaglandin F2 alpha by aldehyde reductase from human liver: comparison to the prostaglandin F synthetase from bovine lung

The primary structure of prostaglandin (PG) F synthetase from bovine lung shows 62% similarity with that of human liver aldehyde reductase (EC 1.1.1.2) (Watanabe, K., Fujii, Y., Nakayama, K., Ohkubo, H., Kuramitsu, S., Kagamiyama, H., Nakanishi, S., and Hayaishi, O. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 11-15). We therefore purified human liver aldehyde reductase to homogeneity and compared the immunological and catalytic properties of aldehyde reductase and PGF synthetase. Although both enzymes belong to a group of aldoketoreductases and their molecular weights are essentially identical, aldehyde reductase had no cross-reactivity to anti-PGF synthetase antiserum. Furthermore, there was a difference in the substrate specificity for reduction of PGs between the two enzymes. Aldehyde reductase catalyzed the reduction of PGJ2, delta 12-PGJ2, PGH2, or PGA2, but not that of PGB2, PGD2, or PGE2, whereas PGF synthetase reduced PGD2. The optimum pH, Km value for PGH2, and the turnover number were 6.5, 100 microM, and 3.1 min-1, respectively. The PGH2 9,11-endoperoxide reductase activity of aldehyde reductase was not affected in the presence of a substrate such as p-nitrobenzaldehyde, DL-glyceraldehyde, or 9,10-phenanthrenequinone, suggesting that PGH2 9,11-endoperoxide and other substrates are reduced at different active site(s). The reaction product formed from PGH2 by this enzyme was identified as PGF2 alpha by gas chromatography/mass spectrometry. These results suggest that aldehyde reductase is not exactly identical to PGF synthetase in terms of its immunological property and substrate specificity for PGs, but that this enzyme is also involved in the direct conversion of PGH2 to PGF2 alpha similar to PGF synthetase.     

Indicators for elevated risk of human exposure to host-seeking adults of the Rocky Mountain wood tick (Dermacentor andersoni) in Colorado

The human-biting adult stage of the Rocky Mountain wood tick (Dermacentor andersoni) can cause tick paralysis in humans and domestic animals and is the primary tick vector in the intermountain west of the pathogens causing Colorado tick fever, Rocky Mountain spotted fever, and tularemia. We conducted drag sampling studies in Poudre Canyon and Rocky Mountain National Park of Larimer County, CO, to determine microhabitat use patterns by host-seeking D. andersoni adults and find environmental factors signaling elevated risk of tick exposure. Big sagebrush (Artemisia tridentata) was found to serve as a general indicator of areas with elevated risk of exposure to host-seeking D. andersoni adults; this likely results from a shared climate tolerance of big sagebrush and D. andersoni. Grass was the favored substrate for host-seeking ticks. Drag sampling of open grass or grass bordering rock or shrub produced abundances of D. andersoni adults significantly higher than sampling of brush. Sampling sites in Rocky Mountain National Park, relative to Poudre Canyon, were characterized by more intense usage by elk (Cervus elaphus) but decreased brush coverage, smaller brush size, and lower abundances of host-seeking D. andersoni adults. There has been a tremendous increase in the population of elk in Rocky Mountain National Park over the last decades and we speculate that this has resulted in an ecological cascade where overgrazing of vegetation by elk is followed by suppression of rodent populations, decreased tick abundance, and, ultimately, reduced risk of human exposure to D. andersoni and its associated pathogens.     

Loss of ecto-5'nucleotidase from porcine endothelial cells after exposure to human blood: Implications for xenotransplantation

The endothelial cell surface expression of ecto-5'-nucleotidase (E5'N, CD73) is thought to be essential for the extracellular formation of cytoprotective, anti-thrombotic and immunosuppressive adenosine. Decreased E5'N activity may play a role in xenograft acute vascular rejection, preventing accommodation and tolerance mechanisms. We investigated the extent of changes in E5'N activity and other enzymes of purine metabolism in porcine hearts or endothelial cells when exposed to human blood or plasma and studied the role of humoral immunity in this context. Pig hearts, wild type (WT, n = 6) and transgenic (T, n = 5) for human decay accelerating factor (hDAF), were perfused ex vivo with fresh human blood for 4 h. Pig aortic endothelial cells (PAEC) were exposed for 3 h to autologous porcine plasma (PP), normal (NHP) or heat inactivated human plasma (HHP), with and without C1-inhibitor. Enzyme activities were measured in heart or endothelial cell homogenates with an HPLC based procedure. The baseline activity of E5'N in WT and T porcine hearts were 6.60 +/- 0.33 nmol/min/mg protein and 8.54 +/- 2.10 nmol/min/mg protein respectively (P < 0.01). Ex vivo perfusion of pig hearts with fresh human blood for 4 h resulted in a decrease in E5'N activity to 4.01 +/- 0.32 and 4.52 +/- 0.52 nmol/min/mg protein (P < 0.001) in WT and T hearts respectively, despite attenuation of hyperacute rejection in transgenic pigs. The initial PAEC activity of E5'N was 9.10 +/- 1.40 nmol/min/mg protein. Activity decreased to 6.76 +/- 0.57 and 4.58 +/- 0.47 nmol/min/mg protein (P < 0.01) after 3 h exposure of HHP and NHP respectively (P < 0.05), whereas it remained unchanged at 9.62 +/- 0.88 nmol/min/mg protein when incubated with PP controls. C1-inhibitor partially preserved E5'N activity, similar to the effect of HHP. Adenosine deaminase, adenosine kinase and AMP deaminase (other enzymes of purine metabolism) showed a downward trend in activity, but none were statistically significant. We demonstrate a specific decrease in E5'N activity in pig hearts following exposure to human blood which impairs adenosine production resulting in a loss of a cytoprotective phenotype, contributing to xenograft rejection. This effect is triggered by human humoral immune responses, and complement contributes but does not fully mediate E5'N depletion.     

3D simulations for evaluation of location factors in an urban environment: application of a novel methodology to calculate external exposure doses for evacuees from Pripyat

This article presents a methodology for assessing the radiation doses in an urban environment due to external irradiation from radionuclides deposited on the ground and other surfaces as well as from a passing radioactive cloud. The approach was developed and applied to assess individual doses of residents of the town of Pripyat who were evacuated shortly after the Chernobyl accident. Typically, the so-called location factor is defined as the ratio of the dose rate at a point of exposure and the dose rate at an undisturbed lawn far from any buildings. The present study used a new definition of the location factor as a regular four-dimensional grid of ratios of air kerma rates indoors and outdoors distributed in space and time. The location factors were calculated for two scenarios: outdoor and indoor values for typical apartments and buildings in Pripyat. Indoor location factors varied within two orders of magnitude depending on the floor of residence and place of staying inside the apartment. Values of the indoor location factor differed during the daytime and night by a factor of 30–40 depending on the behaviour of an individual within the apartment. Both, outdoor and indoor location factors decreased with decreasing distances between buildings. It was shown that during the first 4 days after the accident, air kerma rates in Pripyat were governed by the radionuclides deposited on the ground surface, and not by radionuclides in the cloud. Specifically, the contribution of the radioactive cloud to air kerma rate was maximal (i.e., 2.3%) on the morning of 28 April 1986. The methodology and results of this study are currently being used to reconstruct the radiation gonadal dose for the subjects of the American–Ukrainian study of parental irradiation in Chernobyl cleanup workers and evacuees for investigating germline mutations in their offspring.

     

Use of DNA adducts to identify human health risk from exposure to hazardous environmental pollutants: the increasing role of mass spectrometry in assessing biologically effective doses of genotoxic carcinogens

The carcinogens to which humans are exposed are normally in the form of complex mixtures, and much effort has gone into determining the nature of the most significant carcinogenic components in these mixtures and their mechanisms of action. Essential to achieving this aim in exposed populations is the use of biomarkers, which can characterize the chemical nature of the carcinogens involved and identify key biological effects that result from the exposure. DNA adducts are particularly appropriate as biomarkers in the case of genotoxic carcinogens as they indicate the biologically effective dose of the genotoxin in the target tissue under study. This review considers in particular the use of mass spectrometry (MS), which is having an increasing role in the determination of DNA adducts. Compared to other existing DNA damage detection methods, such as 32P-postlabeling, HPLC-fluorescence or electrochemical detection, immunoassay-based techniques and modified Comet assays, MS provides improved structural characterization of adducts. Greater selectivity in the analyses is achieved by the use of tandem MS with selected reaction monitoring or constant neutral loss of ions. Use of capillary/nano liquid chromatography and micro/nano electrospray ionization improves the analytical sensitivity and higher throughput may be obtained by the use of online-column switching. The application of microfluidics technology offers exciting new possibilities for interfacing sample preparation to the mass spectrometer. Despite these improvements in the use of MS for adduct detection, the main current requirement is to validate these methods both analytically and in molecular epidemiology studies. More knowledge of the stability of stored samples is required. Development of sensitive mass spectrometric DNA adductomic screening systems, and of long-term biomarkers (e.g., phosphotriester adducts that are not repaired efficiently) seems important areas for the future assessment of the effects of human exposure to environmental genotoxins, together with studies of dose-response relationships at low doses.     

Formation of albumin dimers induced by exposure to peroxides in human plasma: a possible biomarker for oxidative stress

Human serum albumin (HSA) has one free thiol residue at Cys-34 that is likely oxidized by various reactive oxygen species (ROS). We attempted to identify the oxidation product of Cys-34 of HSA following exposure of plasma to ROS. Oxidation induced by tert-butyl hydroperoxide (t-BuOOH) of this free cysteine residue in HSA was observed in detail. Analysis of oxidized albumin in a partially purified fraction obtained by affinity column chromatography clearly revealed the formation of albumin disulfide dimers following t-BuOOH exposure. Albumin disulfide dimer formation was observed in normal plasma following treatment with various peroxides, as well as in untreated plasma from patients on hemodialysis using SDS-PAGE and Western blot analysis. The present results indicate that albumin dimers are oxidative products derived from peroxides, and that their presence in plasma might be a marker of oxidative stress as secondary metabolites of peroxidation.