|2005 Recommendations of the International Commission on Radiological Protection
Response from the Low Level Radiation Campaign.
Contact Richard Bramhall
1. We do not accept the constraints which the Commission has put upon the consultation procedure which apparently limits respondents to typing or pasting text into an email box. We are submitting additional material by post (= references ECRR 2003 and CERRIE 2004b).
2. The Commission's view depends on fundamental assumptions on dose averaging (paragraph 47) and linearity of response (paragraph 48) which many argue are scientifically invalid. We draw ICRP's attention to recent papers showing 40% increases in cancer in large populations in the years following Chernobyl (Okeanov 2004, Tondel 2004). It would be tedious to rehearse all the evidence of this nature since the issues are well known. In brief, there is a very large mismatch between the ICRP's predictions and the emerging reality of disease associated with areas affected by radioactive discharges (e.g. Seascale, Cumbria) and episodes of pollution such as atmospheric weapons tests and Chernobyl. The errors in ICRP's modelling which are implied by such findings are well within the range of uncertainties identified by the Majority Report of the UK's Committee Examining Radiation Risks of Internal Emitters (CERRIE 2004). This points to the serious inadequacy of relying on the concept of dose as a measure of risk from exposure to internal irradiation from many man-made radioactive substances and anthropogenically altered ones.
3. Microdosimetric considerations are fundamental to the understanding of risks from internal emitters. This is because of the anisotropy of ionisation density, which is admitted by ICRP (e.g. paragraph 47 of the ICRP consultation document). In our view and that of CERRIE (see Majority Report Chapter 2.1 paragraph 11) the deployment of the concept of absorbed dose is insufficient to address core concerns associated with the internal paradigm. We recommend that due regard should be paid to ionisation density. The appropriate concept might be track ionisation density per day, or ‘celldose’. Units might be Radiation Absorbed Tracks (Rat). This could be modified to take account of variations in linear energy transfer, giving rise to the concept of ionisation-density-normalised track density per day, or Radiation Effective Tracks (Ret). This is similar to the concept of ‘fluence’, but adjusted for relative energy transfer. For practical purposes this concept needs to be augmented. Accordingly in paragraph 6 below we refer to the recommendations of the European Committee on Radiation Risk.
4. Nowhere is anisotropy greater than for internal radioactive particles, yet it is commonplace to see the risks dismissed as no more hazardous than the same absorbed dose deposited homogeneously. The reasoning is that cell killing in the vicinity of the hot particle predominates. If, however, cell killing does predominate yet the overall effect is the same as for homogeneous dose it follows that some mechanism must be making up for the (supposedly) zero effect in the zero dose zones of the tissue. It seems inevitable that the mechanism involves a considerably enhanced hazard on the edge of the cell killing zone. Such an effect was warned of by Hohenemser et al. (Hohenemser 1986) for beta emitting particles from Chernobyl ("… a substantial zone of cell lethality at short distances followed by an annulus of very high but non lethal dose at larger distances …. "), and Rytomaa and others reviewed for CERRIE by Monty Charles (his review was subsequently published (Charles 2003)). These considerations suggest that warm particles with less or no cell killing would be relatively very effective at causing transformation, which may provide an explanation for the epidemiological observations. Charles et al. suggest that in situations where energy density is highly anisotropic some cell communication effects mediate an increase in transformation. Bridges has pointed out (CERRIE 2004b para. 65) that as a result of the Bragg effect dead cells will tend to be concentrated in a shell at a radial distance equal to the decay range of alpha particles. This zone of dead cells would effectively insulate a community of potentially damaged cells preventing communication with healthy cells outside the range of the decays. These considerations may have significant implications for the development of clonal damage,
Charles et al. remark on the paucity of human data and fail to dispose of experimental results strongly suggestive of enhanced risk.
5. A further consideration is that since it is also accepted that in the high dose region effect is proportional to the square of the dose on account of multiple hits, it is a simple matter to show that for circumstances such as particles immobilised in tissue where multiple hits are likely effect is again proportional to the square of the dose, although the average dose may be low.
6. Thus for circumstances which involve heterogeneous energy density there are reasons to reject the ICRP's assertion (para. 33) that the "dosimetric quantities adopted by the Commission … can be related to quantitative estimates of health risks." Pending experimental resolution of the ICRP's dogmatic difficulties in assessing risk we recommend a pragmatic interim approach using a set of hazard enhancement weighting factors developed by the European Committee on Radiation Risk to modify the present units and quantities. The ECRR takes the view that the weighting factors used by the ICRP to allow for different biological effectiveness of radiations and those allowing for organ sensitivity are not qualitatively different from weighting factors to allow for different fractionations of radiation dose or for the differing abilities of various isotopes, particles or contamination types to cause mutation. Consequently, the ECRR has revived the weighting factor N of an earlier ICRP model. This approach has the great advantage that although the new risks of low level radiation doses from internal or exotic regimes of exposure may be slightly higher than supposed by the ICRP, there is no great need to alter existing legal frameworks in relation to maximum permissible doses and constraints. It is the doses themselves that are be calculated differently. We refer the ICRP to sections 6.5 to 6.9 of the ECRR 2003 Recommendations which describe the system (ECRR 2003).
7. Linearity. The assumption of a continuous linear dose response relationship is biologically implausible. For example, increasing dose to the foetus will ultimately result in its death. As a consequence, if an analysis of any end point in infants were expressed in terms of increasing dose it would show a maximum followed by a reduction. Also, if there were sub populations of cells or people of different sensitivity there could then be a subsequent increase (a biphasic dose response). A range of studies of radiation and leukaemia show such effects. These include the Hiroshima studies, several studies of nuclear workers and their children (e.g. Muirhead 1999, Roman et al.1999, Draper et al. 1997) and the Chernobyl infant leukaemia studies summarised by Busby and Scott-Cato (Busby and Scott-Cato 2000). A number of biological studies (e.g. Burlakova 2000, Ohtaki et al. 2004) provide support for the existence of a biphasic response in response to either radiation or biochemical insult. We are sending a copy of the CERRIE Minority Report (CERRIE 2004b) as part of this consultation response and draw the ICRP's attention in particular to the summaries of studies from the Chernobyl affected territories, many of which show non-linear responses.
Busby C and Scott Cato M (2000) Increases in leukaemia in infants in Wales and Scotland following Chernobyl: evidence for errors in statutory risk estimates. Energy and Environment, 11, 127-39.
Burlakova EB (2000) Low doses of radiation, are they dangerous? New York: Nova publishers
CERRIE 2004 Majority Report of the Committee Examining Radiation Risks of Internal Emitters, London ISBN 0-85951-545-1 October 2004
CERRIE 2004b Minority Report of the UK Department of Health / Department of Environment (DEFRA) Committee Examining Radiation Risks of Internal Emitters; Richard Bramhall Chris Busby Paul Dorfman. Sosiumi Press Aberystwyth. ISBN 0-9543081-1-5
Charles M.W.; Mill A.J.; Darley P.J. Carcinogenic risk of hot-particle exposures Journal of Radiological Protection, 2003, vol. 23, no. 1, pp. 5-28(24)
Draper GJ, Little MP, Sorahan T et al (1997) Cancer in the offspring of radiation workers- a record linkage study. NRPB R298 Chilton: NRPB
ECRR 2003 Recommendations of the ECRR The Health Effects of Ionising Radiation Exposure at Low Doses and Low Dose Rates for Radiation Protection Purposes: Regulators’ Edition. Eds. Chris Busby with Rosalie Bertell, Inge Schmitz-Feuerhake, Molly Scott Cato and Alexei Yablokov Published on Behalf of the European Committee on Radiation Risk Comité Européen sur le Risque de l’Irradiation, Brussels by Green Audit, 2003. ISBN: 1 897761 24 4.
Hohenemser C. et al. Agricultural impact of Chernobyl: a warning: Nature vol. 32 p 817 June 1986
Muirhead CR, Goodill AA, Haylock RG, Vokes J, Little MP, Jackson DA, O'Hagan JA, Thomas JM, Kendall GM, Silk TJ, Bingham D and Berridge GL (1999) Occupational radiation exposure and mortality: second analysis of the National Registry for Radiation Workers. J Radiol Prot; 19: 3-26.
Ohtaki K, Kodama Y, Nakano M, Itoh M, Awa AA, Cologne J, Nakamura N. 2004 Radiat Res. 2004 Apr;161(4):373-9 Human fetuses do not register chromosome damage inflicted by radiation exposure in lymphoid precursor cells except for a small but significant effect at low doses.
Okeanov 2004 A national cancer registry to assess trends after the Chernobyl accident
A. E. Okeanov, E. Y. Sosnovskaya, O. P. Priatkina; Clinical Institute of Radiation Medicine and Endocrinology Research, Minsk, Belarus Swiss Medical Weekly 2004;134:645–649 Issue 43/44
Roman E, Doyle P, Maconochie N, Davies G, Smith PG, Beral V (1999) Cancer in children of nuclear industry employees: report on children aged under 25 years from nuclear industry family study. BMJ 318 1443-1450.
Tondel M et al 2004 Increase of regional total cancer incidence in north Sweden due to the Chernobyl accident? Journal of Epidemiology and Community Health 2004;58:1011-1016
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