Critical group

Thenumber of people who might be exposed is not well defined. The critical group considered in the National Academy study (NASNRC 1995) was expected to be less than 100. 

Crowley, M., P.I. Mitchell, J. O Grady, J. Vires, J.A. Sanchez-Cabeza, A. Vidal-Quadras, and T.P. Ryan. 1990. Radiocaesium and plutonium concentrations in Mytilus edulis (L.) and potential dose implications for Irish critical groups. Ocean Shoreline Manage. 13 149-161. 

A report by a scientific advisory panel to Health Canada is one of the most extensive to analyse the possible health risks from di-2-ethylhexyl phthalate (DEHP), a plasticiser used to soften PVC medical products such as bags and tubing. This article gives details of the report, which has concluded that DEHP does pose health risks for some critical groups. 

Edible mushrooms are a significant element of the diet of the local population, and therefore represent a serious source of internal exposure to irradiation. Between 30% and 60% of the local population of Ukrainian Polissya regularly consume forest food products (Strand et al., 1996a), and a close correlation has been established between their consumption and i Cs load (Jacob and Likhtarev, 1996 Strand et al. 1996b). The contribution of forest food products to the internal exposure dose of the population in the forested region varies widely - from 12%-40% of the entire population to 50%-95% in some critical groups (Balonov et al., 1996 ... 

Binding of protons to critical groups on hemoglobin stabilizes deoxy-bemoglobin and thereby decreases the O2 binding affinity of hemoglobin. 

Generally, it is rarely possible to satisfy all of the various similarity criteria in scale-up, especially those related to chemical and thermal dimensionless groups. An alternative solution is to determine the effect of each group and perform intermediate scale experiments to determine the effect of the critical groups. 

Critical groups of the population should be taken into account when these groups are disproportionately affected by the chemical. 

To ensure that any radioactivity in food and the environment due to authorised radioactive releases and discharges do not compromise public health or the environment, undertaken by assessing critical group doses and comparing them to legal limits. 

A prospective upper bound on the individual dose which is used in the optimisation of protection and safety for sources. For occupational exposures, dose constraint is a source-related value of individual dose used to limit the range of options considered in the process of optimisation. For public exposure, the dose constraint is an upper bound on the annual doses that members of the public should receive from the planned operation of any controlled source. The exposure, to which the dose constraint applied is the annual dose to any critical group, summed over all exposure pathways, arising from the predicted operation of the controlled source. The constraint for each source should ensure that the sum of doses to the critical group from all controlled sources remains within the dose limit. For medical exposure the dose constraint levels should be interpreted as guidance levels, except when used in optimising the protection of persons exposed for medical research purposes or of persons, other than workers, who assist in the care, support or comfort of exposed patients. 

Exposure of members of the public attributable to practices shall not exceed the following limits which shall apply to the estimated average doses to the relevant critical groups ... 

The concept of the critical group was formulated by the ICRP in Publication 26. The local population will normally include the critical group and is geographically close to the point of release or will include consumers of locally harvested foods. In selecting a critical group two requirements must be met ... 

The critical group must be representative of those expected to receive the highest doses. 

The critical group should be homogeneous with respect to those factors that affect the doses received. 

Exposure of man occurs at step 1 above via inhalation of diluted/dispersed release. At step 2, there is direct contamination and direction radiation from cloud of activity or from layer on ground step 2 can also deposit on water or from run-off of soil into water bodies and further food chain steps. Step 3 is an interim step where reconcentration can occur. In Step 4 intake depends on the habits of the critical group, i.e. what food is eaten, how it is eaten, how much is eaten. Steps 2 and 4 also depend on population habits. 

It is important to determine eating and drinking habits of the population as a whole and identify the critical group. 

The approach used is that outlined by Dodd B. and Humphries L.L., (1988) although significant input was also obtained from IAEA Safety Series No. 57, Generic Models and Parameters for Assessing the Environmental Transfer of Radionuclides from Routine Releases Exposures of Critical Groups (1982). 

The upper bound for annual release can then be derived from the dose upper bound by using the overall transfer factors (. ., ) where j represents population group, k represents release mode and / represents the radionuclide. If the dose commitment to the critical group / per unit release of a radionuclide is given by fj,, then the release upper bound, Ri i, is given by... 

Haxton J, Lindsay DG, Hilsop JS, et al. 1979. Duplicate diet study on fishing communities in the United Kingdom Mercury exposure in a "critical group.6 Environ Res 18 351-368. 

Premature infants are another critical group they often require to be kept on parenteral nutrition for up to three months until they have matured sufficiently to be able to suckle and take in more normal nutrition. 

Nowadays, food producers trade worldwide and there is a massive normalization process occurring on our supermarket shelves such that, by and large, we can expect that food high in heavy metals will be eaten only rarely and that other foods from other sources will be used in between these doses. Estimation of extreme intakes of such heavy metals can lead to consideration of the worst possible cases or, if radionuclides are concerned, of critical groups. Not unsurprisingly, the press occasion-... 

Haxton, J., D.G. Lindsay, J.S. Hislop, L. Salmon, E.J. Dixon, W.H. Evans, J.R. Reid, C.J. Hewitt, and D.F. Jeffries. 1979. Duplicate diet study on fishing communities in the United Kingdom Mercury exposure in a critical group . Environ. Res. 18(2) 351-368. 

Nuclear power plant to critical group (Sweden) X-ray investigation barium meal (intestine) intravenous urography abdomen and lung mean gonadal dose (abdomen), genetically significant dose dental... 

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