Dose pathways

NTKi (l-trt96 defined two EPZ at radii of 10 miles to provide protection from direct niduiion hy evacuating or sheltering the public and at 50 miles within which food and water interdiction would prole,a from this dose pathway. 

Because there are so many factors involved in establishing dose pathways and which may be the critical pathway, various dose assessment computer based models have been developed. These models are also used to calculate the dose per unit release of a specified radionuclide for various pathways. The Release Upper Bound, RUB can be evaluated using a dose assessment model. This is done by varying the source term used such that the resulting dose equals the dose constraint or limit. The various exposure scenarios and pathways are also chosen for importance. 

The basic analytical models of MACCS2 provide atmospheric transport, dispersion, deposition, and dose calculation for the released inventory. A Gaussian dispersion model based on the Tador-Gur parameterization is used for this SAR to provide consistency with previous safety studies on the HCF. Radioactive isotopes are allowed to decay and build up daughter activity during transport and deposition. The decay is based on an input file of half-lives and decay schemes for hundreds of isotopes. Dose pathways modeled were radioactive plume inhalation and immersion, groundshine from deposited radiation, and resuspension inhalation dose. Groundshine and resuspension inhalation pathways are very minor contributors to dose. 

For materials where internal exposure is a possibility, steps must be taken to reduce or eliminate that dose pathway. To limit internal dose below regulatory limits and in accordance... 

Nicardipine is almost completely absorbed after po adrninistration. Administration of food decreases absorption. It undergoes extensive first-pass metaboHsm in the Hver. Systemic availabiHty is dose-dependent because of saturation of hepatic metaboHc pathways. A 30 mg dose is - 35% bioavailable. Nicardipine is highly protein bound (>95%). Peak plasma concentrations are achieved in 0.5—2.0 h. The principal path of elimination is by hepatic metaboHsm by hydrolysis and oxidation. The metaboHtes are relatively inactive and exert no pharmacological activity. The elimination half-life is 8.6 h. About 60% of the dose is excreted in the urine as metaboHtes (<1% as intact dmg) and 35% as metaboHtes in the feces (1,2,98,99). 

MESOREM Jr. Impell Corporation Becky Cropper 300 Tristate Internat l Suite 400 Lincolnshire, IL 60069 (312) 940-2090 Atmospheric release analysis system that includes back calculations of source release rates from field readings, terrain modeling, meteorological conditions modeling of multipoint dose and deposition exposures. Also provides ingestion exposure reports for atmospheric effluent pathways. 

For example, given a BWR-1 release (Table 8,2-1), typical weather conditions, no rain and less than one mile from the accident immersion, inhalation, and ground produce about the same magnitude doses for exposure times of several hours or less. The exposure from a cloud ceases once the cloud has passed, but exposure may continue from the ground until the area is decontaminated or evacuated. If the exposure time is long, the ground dose can eventually dominate. Tables 9-6 and 9-7 in NUREG/CR-2300 show examples of the relative importance of these pathways. 

The ingestion dose contributes very little to the dose from a severe reactor accident and is usually not computed. However, the food pathway is a major determinant of bow the exposed area must be treated in the months and years following the accident. If the ground concentration is high, the land may be interdicted from agricultural u.se or grazing. 

The biotransformation of a given chemical compound in experimental animals and in humans may differ. Furthermore, high doses of chemical compounds are used in studies with experimental animals, and this may cause alterations in biotransformation of the tested chemicals that do not occur at the lower doses relevant to the human exposure situation. For example, a metabolic pathway dominating at low doses may become saturated, and a salvage metabolic pathway, e.g., one that produces reactive intermediates of the compound, may become involved in the biotransformation of the chemical. Since this intermediate could never be produced at the exposure levels encountered in humans, the overall result... 

Fluorid ions stimulate bone formation by a direct mitogenic effect on osteoblasts mediated via protein kinase activation and other pathways. Further to these cellular effects, fluorides alter hydroxyapatite crystals in the bone matrix. In low doses, fluorides induce lamellar bone, while at higher doses abnormal woven bone with inferior quality is formed. The effect of fluorides on normal and abnormal (e.g. osteoporotic) bone therefore depends on the dose administered. 

Additionally, mechanisms of immunosuppression by organotins have also focused on the role of apoptosis versus proliferation arrest. The apoptotic pathway followed by organotin compormds such as dibutyltin dichloride and tributyltin chloride at high doses is... 

Seth RB, Sun L, Chen ZJ (2006) Antiviral innate immunity pathways. Cell research 16 141-147 Shapiro RL, Thior I, Gilbert PB, Lockman S, Wester C, Smeaton LM, Stevens L, Heymann SJ, Ndung u T, Gaseitsiwe S et al. (2006) Maternal single-dose nevirapine versus placebo as part of an antiretroviral strategy to prevent mother-to-chUd HIV transmission in Botswana. Aids 20 1281-1288... 

IFN-)il exhibits dose- and time-dependent inhibition of HCV rephcation in various models, independently of type I and IIIFN receptors and induced pathways (Marcello et al. 2006). A pegylated form of IFN-A, will soon enter clinical evaluation. 

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