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201.
Mehdi Razzaghi 《Environmental and Ecological Statistics》2009,16(1):25-36
To establish allowable daily intakes for humans from animal bioassay experiments, benchmark doses corresponding to low levels
of risk have been proposed to replace the no-observed-adverse-effect level for non-cancer endpoints. When the experimental
outcomes are quantal, each animal can be classified with or without the disease. The proportion of affected animals is observed
as a function of dose and calculation of the benchmark dose is relatively simple. For quantitative responses, on the other
hand, one method is to convert the continuous data to quantal data and proceed with benchmark dose estimation. Another method
which has found more popularity (Crump, Risk Anal 15:79–89; 1995) is to fit an appropriate dose–response model to the continuous
data, and directly estimate the risk and benchmark doses. The normal distribution has often been used in the past as a dose–response
model. However, for non-symmetric data, the normal distribution can lead to erroneous results. Here, we propose the use of
the class of beta-normal distribution and demonstrate its application in risk assessment for quantitative responses. The most
important feature of this class of distributions is its generality, encompassing a wide range of distributional shapes including
the normal distribution as a special case. The properties of the model are briefly discussed and risk estimates are derived
based on the asymptotic properties of the maximum likelihood estimates. An example is used for illustration.
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Mehdi RazzaghiEmail: |
202.
Radon and gamma dose rate measurements were performed in 512 schools in 8 of the 13 regions of Greece. The distribution of radon concentration was well described by a lognormal distribution. Most (86%) of the radon concentrations were between 60 and 250 Bq m−3 with a most probable value of 135 Bq m−3. The arithmetic and geometric means of the radon concentration are 149 Bq m−3 and 126 Bq m−3 respectively. The maximum measured radon gas concentration was 958 Bq m−3. As expected, no correlation between radon gas concentration and indoor gamma dose rate was observed. However, if only mean values for each region are considered, a linear correlation between radon gas concentration and gamma dose rate is apparent. Despite the fact that the results of radon concentration in schools cannot be applied directly for the estimation of radon concentration in homes, the results of the present survey indicate that it is desirable to perform an extended survey of indoor radon in homes for at least one region in Northern Greece. 相似文献
203.
204.
Towell MG Bellarby J Paton GI Coulon F Pollard SJ Semple KT 《Environmental pollution (Barking, Essex : 1987)》2011,159(2):515-523
This study investigated the microbial degradation of 14C-labelled hexadecane, octacosane, phenanthrene and pyrene and considered how degradation might be optimised in three genuinely hydrocarbon-contaminated soils from former petroleum refinery sites. Hydrocarbon mineralisation by the indigenous microbial community was monitored over 23 d. Hydrocarbon mineralisation enhancement by nutrient amendment (biostimulation), hydrocarbon degrader addition (bioaugmentation) and combined nutrient and degrader amendment, was also explored. The ability of indigenous soil microflora to mineralise 14C-target hydrocarbons was appreciable; ≥16% mineralised in all soils. Generally, addition of nutrients or degraders increased the rates and extents of mineralisation of 14C-hydrocarbons. However, the addition of nutrients and degraders in combination had a negative effect upon 14C-octacosane mineralisation and resulted in lower extents of mineralisation in the three soils. In general, the rates and extents of mineralisation will be dependent upon treatment type, nature of the contamination and adaptation of the ingenious microbial community. 相似文献
205.
The use of building materials containing naturally occurring radionuclides as 40K, 232Th, and 238U and their progeny results in external exposures of the residents of such buildings. In the present study, indoor dose rates for a typical Jordan concrete room are calculated using Monte Carlo method. Uniform chemical composition of the walls, floor and ceiling as well as uniform mass concentrations of the radionuclides in walls, floor and ceiling are assumed.Using activity concentrations of natural radionuclides typical for the Jordan houses and assuming them to be in secular equilibrium with their progeny, the maximum annual effective doses are estimated to be 0.16, 0.12 and 0.22 mSv a−1 for 40K, 232Th- and 238U-series, respectively. In a total, the maximum annual effective indoor dose due to external γ-radiation is 0.50 mSv a−1. Additionally, organ dose coefficients are calculated for all organs considered in ICRP Publication 74. Breast, skin and eye lenses have the maximum equivalent dose rate values due to indoor exposures caused by the natural radionuclides, while equivalent dose rates for uterus, colon (LLI) and small intestine are found to be the smallest. More specifically, organ dose rates (nSv a−1 per Bq kg−1) vary from 0.044 to 0.060 for 40K, from 0.44 to 0.60 for radionuclides from 238U-series and from 0.60 to 0.81 for radionuclides from 232Th-series.The obtained organ and effective dose conversion coefficients can be conveniently used in practical dose assessment tasks for the rooms of similar geometry and varying activity concentrations and local-specific occupancy factors. 相似文献
206.
Loureiro S Amorim MJ Campos B Rodrigues SM Soares AM 《Environmental pollution (Barking, Essex : 1987)》2009,157(2):625-636
Contamination problems are often characterized by complex mixtures of chemicals. There are two conceptual models usually used to evaluate patterns of mixture toxicity: Concentration Addition (CA) and Independent Action (IA). Deviations from these models as synergism, antagonism and dose dependency also occur. In the present study, single and mixture toxicity of atrazine, dimethoate, lindane, zinc and cadmium were tested in Porcellionides pruinosus and Enchytraeus albidus, using avoidance as test parameter. For both species patterns of antagonism were found when exposed to dimethoate and atrazine, synergism for lindane and dimethoate exposures (with the exception of lower doses in the isopod case study) and concentration addition for cadmium and zinc occurred, while the exposure to cadmium and dimethoate showed dissimilar patterns.This study highlights the importance of dose dependencies when testing chemical mixtures and that avoidance tests can also be used to asses the effects of mixture toxicity. 相似文献
207.
Long-term safety assessments for geological disposal of radioactive waste in Switzerland involve the demonstration that the annual radiation dose to humans due to the potential release of radionuclides from the waste repository into the biosphere will not exceed the regulatory limit of 0.1 mSv. Here, we describe the simple but robust approach used by Nagra (Swiss National Cooperative for the Disposal of Radioactive Waste) to quantify the dose to humans as a result to time-dependent release of radionuclides from the geosphere into the biosphere. The model calculates the concentrations of radionuclides in different terrestrial and aquatic compartments of the surface environment. The fluxes of water and solids within the environment are the drivers for the exchange of radionuclides between these compartments. The calculated radionuclide concentrations in the biosphere are then used to estimate the radiation doses to humans due to various exposure paths (e.g. ingestion of radionuclides via drinking water and food, inhalation of radionuclides, external irradiation from radionuclides in soils). In this paper we also discuss recent new achievements and planned future work. 相似文献
208.
In case of an accidental release of radioactive substances into the environment, it is important to quickly and reliably estimate the radiation dose received by people in the affected area, and to determine the extent of the contamination. Measurements of the extent of the release and the subsequent contamination can be facilitated if there are predetermined reference sampling sites with known background radiation and inventory of radionuclides. Since 1996, 34 reference sites for soil sampling, field gamma, and intensimeter measurements have been established in western Sweden. Time series data for dose rates and radioisotope inventory have been collected at these sites, allowing for the investigation of changes in these parameters over time. The mass activity densities for the uranium and thorium series elements varied approximately between 10 and 50 Bq/kg and between 10 and 40 Bq/kg, respectively. The mass activity density of 40K was approximately in the range 300–800 Bq/kg. The radiation exposure due to 137Cs was rather small in this area. The dose rates calculated from in situ measurement data showed that the contribution to the total dose rate was almost entirely due to naturally occurring radionuclides. The measured dose rate was about twice as high as the calculated rate, even after subtracting the contribution from cosmic radiation. This may be explained by the fact that intensimeters generally are calibrated to measure the quantity ambient dose equivalent, which should not underestimate the effective dose. 相似文献
209.
The overall survey on indoor radon concentration was conducted at all subway stations in a major city, Daejeon in the central part of Korea. It was quarterly performed from September 2007 to August 2008. The annual arithmetic mean of indoor radon concentration of all the stations was 34.1 ± 14.7 Bq m−3, and the range of values was from 9.4 to 98.2 Bq m−3. The radon concentrations in groundwater (average 31.0 ± 0.8 Bq m−3) were not significantly high in most stations, but the concentration (177.9 ± 2.3 Bq L−1) of one station was over the level of 148 Bq L−1 in drinking water proposed by U.S. EPA. Based on indoor survey results, the approximate average of the annual effective dose by radon inhalation to the employees and passengers were 0.24 mSv y−1, and 0.02 mSv y−1, respectively. Although the effective dose based on the UNSCEAR report was potentially estimated, for more accurate assessment, the additional survey on the influence by indoor radon will be necessary. 相似文献
210.
The evaluation and assessment of monitoring data generated over a period of 1983-2007 (25 years) of a nuclear facility is presented. Time trends of particulate radioactivity, correlation between 137Cs in discharge canal seawater and station discharged activity and correlation of 137Cs, 60Co, and 131I in marine species such as sponge and Nerita (gastropod) and corresponding discharged activity are discussed. The concentration of 137Cs and 131I in seawater versus biota are discussed. A good correlation between 137Cs in seawater and 137Cs in liquid waste discharged was observed (R2 = 0.8, p < 0.001). Similarly, correlation was good for Nerita and discharged concentration of 137Cs, 131I and 60Co (R2 = 0.55-0.73 and p < 0.001). The measurements over the years indicated that there is no accumulation of radionuclides in either the terrestrial or aquatic environments. The mean 137Cs decreased from the pre-operational levels: 7.0-3.6 Bq kg−1 in soil, 0.91-0.016 Bq L−1 in milk and 0.28-0.036 Bq kg−1 in vegetation. Similarly, the mean 90Sr in these matrixes decreased from 3.9 to 0.26 Bq kg−1; 0.37-0.011 Bq L−1 and 0.34-0.022 Bq kg−1 respectively. Cesium-137 of about 700 μBq m−3 was measured in the air filter disks during 1986 and there was a decrease of three orders of magnitude in concentration over the 25 years. The evaluation of environmental data indicated that the radionuclide concentrations and potential impacts, in terms of effective dose to the members of public, have significantly reduced since 1969. 相似文献