New recommendations from the International Commission on Radiological Protection--a review.

For almost half a century, the International Commission on Radiological Protection (ICRP) has revised its recommendations on radiological protection with an average frequency of about 10 years, building on the experience gained in their implementation. This has ensured that the recommendations remain up to date and fit for purpose and it is this that has led in turn to their wide acceptance internationally. Indeed, the 1990 version of the recommendations forms the basis of the international radiological protection standards and the systems of control of exposure to ionizing radiation in many countries throughout the world. This version introduced new concepts and a more holistic approach to radiological protection but marrying the different exposure situations into one coherent framework has proved not to be straightforward and further reflection seemed necessary in order to satisfy both those who are responsible for the development of the control systems as well as a broader audience. Review of the 1990 recommendations started around 1998 and, since then, many ideas have been explored and avenues followed. Eventually, new recommendations were agreed by the Commission at its meeting in Essen in March 2007. This paper provides a review of these new recommendations and their possible implications.

Scope of radiological protection control measures.

In this report, the Commission recommends approaches to national authorities for their definition of the scope of radiological protection control measures through regulations, by using its principles of justification and optimisation. The report provides advice for deciding the radiation exposure situations that should be covered by the relevant regulations because their regulatory control can be justified, and, conversely, those that may be considered for exclusion from the regulations because their regulatory control is deemed to be unamenable and unjustified. It also provides advice on the situations resulting from regulated circumstances but which may be considered by regulators for exemption from complying with specific requirements because the application of these requirements is unwarranted and exemption is the optimum option. Thus, the report describes exclusion criteria for defining the scope of radiological protection regulations, exemption criteria for planned exposure situations, and the application of these concepts in emergency exposure situations and in existing exposure situations. The report also addresses specific exposure situations such as exposure to low-energy or low-intensity adventitious radiation, cosmic radiation, naturally occurring radioactive materials, radon, commodities, and low-level radioactive waste. The quantitative criteria in the report are intended only as generic suggestions to regulators for defining the regulatory scope, in the understanding that the definitive boundaries for establishing the situations that can be or need to be regulated will depend on national approaches.

The control of indoor radiation exposure.

Surveys of natural radiation indoors permit improved estimates to be made of exposures nationally and of regional variations. In the UK, there are clear indications that individual doses from radon decay products can be more than two orders of magnitude above the national average. A reliable risk factor for lung cancer allows the risks to individuals to be determined, and some members of the public are seen to be exposed to relatively high risks. The feasibility of reducing such risks requires a knowledge of the costs and effectiveness of remedial and preventive measures. There are also social and administrative considerations. The form of standards and the means of implementating them require careful consideration. A systematic approach to these issues is discussed in this paper.

Surveys of natural radiation exposure in UK dwellings with passive and active measurement techniques.

A representative sample of over 2,000 UK dwellings was monitored for a year using thermoluminescent and etchable plastic dosemeters to measure gamma-ray dose rates and radon concentrations. The survey was carried out by post. Each householder completed a questionnaire on the type of dwelling and its characteristics. These data will be used in the assessment of the factors affecting indoor exposure. The mean gamma-ray dose rates were 0.062 and 0.057 microGy h-1 in air and the mean radon concentrations were 25 and 18 Bq m-3 for living areas and bedrooms respectively. Other results of the preliminary data analysis are given. More detailed surveys were conducted in areas where the local geology indicated that elevated exposures to natural radiation might occur. Over 800 dwellings were visited and measurements made of several parameters. The mean gamma-ray dose rates varied from 0.05 to 0.10 microGy h-1 in air. The mean radon concentrations varied from 14 Bq m-3 to 520 Bq m-3. Other findings related to equilibrium factors and regional differences are discussed.

Radon daughter exposures in the U.K.

Exposure due to the inhalation of the short-lived daughters of 222Rn is the single largest contributor to the exposure of the U.K. population. A survey of dwellings situated largely in the centers of population indicates an annual exposure of 0.16 WLM, on the average. On the basis of current knowledge this is equivalent to an annual effective dose equivalent of 800 mu Sv. This compares with the overall average of the effective dose equivalent from natural radiation of almost 1900 mu Sv in a year. The distribution of exposures to the short-lived daughters of 222Rn is markedly skew and indicates that some dwellings support concentrations of these daughters leading to exposures in excess of 1 WLM in a year. The areas of the U.K. in which exposures above this level are most likely to occur are regions with enhanced uranium mineralisation. These areas are sparsely populated and high exposures here do not significantly affect the overall average exposure of the population to radon daughters. An intensive survey of radon and radon daughters concentrations in one predominantly igneous region is reported. The average exposure for the 250 dwellings in this region surveyed so far was estimated to be 1.3 WLM in a year, a factor of 8 greater than the national value. About 5% of the homes exceed 5 WLM in a year. Measurements of equilibrium factor indicate that plate-out contributes to the removal of radon daughters from room air. In general, the equilibrium factor measured indicates an unattached fraction of 218Po of less than 10%.

New ICRP recommendations.

This paper provides a review of the 2007 recommendations of the International Commission on Radiological Protection (ICRP). These new recommendations take account of the latest biological and physical information and consolidate the additional guidance provided by ICRP since 1990. The changes to the scientific data are not substantial. ICRP has retained its fundamental hypothesis for the induction of stochastic effects of linearity of dose and effect without threshold and a dose and dose-rate effectiveness factor (DDREF) of 2 to derive nominal risk coefficients for low doses and low dose rates. While the overall detriment from low radiation doses has remained unchanged, ICRP has made adjustments to the values of the radiation and tissue weighting factors. In particular, the tissue weighting factor for breast has increased while that for gonads has decreased. There are some presentational changes to the system of protection. While ICRP has maintained the three fundamental principles--justification, optimisation of protection, and dose limitation-it has attempted to develop a more holistic approach to radiological protection covering all exposure situations--planned, existing and emergency--and all radiation sources, whether of natural or artificial origin. This approach should ensure that attention is focused on those exposures that can reasonably be controlled. It has also strengthened the principle of optimisation of protection with a particular emphasis on the use of constraints for planned exposure situations and reference levels for existing and emergency exposure situations. Dose constraints and reference levels are categorised into three bands which should assist in rationalising the many values of dose restrictions given in earlier ICRP publications. There are no changes to the dose limits. ICRP also indicates its intentions with respect to the development of further guidance on the protection of the environment. The fact that these new recommendations are more a matter of consolidation of previous ICRP recommendations and guidance should provide confidence that the system of protection established by and large in its present form several decades ago has reached a certain level of maturity. As such, no major changes to radiological protection regulations based on the 1990 recommendations should be necessary.

5-Methylnicotinamide-adenine dinucleotide. Kinetic investigation with major and minor isoenzymes of liver alcohol dehydrogenase and structural determination of its binary complex with alcohol dehydrogenase.

5-Methylnicotinamide-adenine dinucleotide and 3-cyano-5-methylpyridine-adenine dinucleotide was prepared from 5-methylthionicotinamide-adenine dinucleotide by chemical conversion. The 5-methylthionicotinamide-adenine dinucleotide was obtained by enzymic transglucosidation. Model compounds ascertained the structure. None of the dinucleotides methylated at C-5 was active with the major isoenzyme EE of horse liver alcohol dehydrogenase, but activity with 5-methylnicotinamide-adenine dinucleotide was measured with the minor isoenzymes. The binding of 5-methylnicotinamide-adenine dinucleotide to liver alcohol dehydrogenase, investigated by X-ray diffraction methods to 0.37-nm resolution, occurs with the pyridinium ring away from the active site as previously described for 3-iodopyridine-adenine and pyridine-adenine dinucleotides. A general conclusion on the use of inhibitors as tools for exploration of the active site is drawn.

Preparation and properties of 3-halopyridine--adenine dinucleotides, NAD+ analogues and model compounds.

The preparation of model compounds 1-(2',6'-dichlorobenzyl)-3-halogenopyridinium and the study of their properties were achieved. Their chemical reduction to the corresponding 1,4-dihydropyridines is proved by spectroscopic analysis. 3-Iodopyridine--adenine dinucleotide was prepared by enzymic transglycosidation while the 3-chloro, 3-bromo and 3-iodo pyridine--adenine dinucleotides were synthesized from 3-amino-pyridine--adenine dinucleotide. The 3-halogenopyridine--adenine dinucleotides were proved to be active as hydrogen acceptors with alcohol as a substrate. The absorption band at 290 nm of cinnamaldehyde appeared to be a very sensitive tool for studying the enzymic reaction. With the alcohol dehydrogenase from yeast, only slight activity was detected. 3-Halogenopyridine--adenine dinucleotides are competitive inhibitors with respect to nicotinamide--adenine dinucleotide with alcohol dehydrogenase from yeast, lactate dehydrogenase and malate dehydrogenase. The use of 3-iodopyridine--adenine dinucleotide as a heavy-atom derivative for X-ray structure determination is proposed.