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Richard Bramhall, Low Level Radiation Campaign (bramhall@llrc.org)
In this essay we argue that there is such uncertainty about the scientific basis of radiation protection standards that no valid standard for delicensing land exists. Resolving the scientific debate inherent in the uncertainties may well be beyond the capacity of Stakeholders in the present Dialogue, but proceeding towards guidelines for managing contaminated land without taking due account of it would be unethical.
Our case in brief:
In the short term (i.e. pending research results) the 400 becquerels/kg Substances of Low Activity (SoLA) level is scientifically and legally insecure as a de minimis level for land; the interpretation of SoLA as meaning 400 Bq/kg in addition to the legacy of man-made contamination on any given site is legally insecure; sites should be retained under present ownership, and access to them should be controlled, with measures to assess and prevent off-site migration of radioactivity.
The flaws in the NRPB / ICRP model are becoming widely known. The present model depends on studies [NRPB says they are "pivotal"] of the survivors of the Hiroshima A-bomb. The group considered to be "exposed" consisted of those who were in the open at the time of the explosion. Their exposure was therefore
The control group consisted of people who were elsewhere at the time or were shielded. The problem is that both groups, by definition, lived in the bombed cities, and were therefore exposed to ingesting, inhaling and absorbing fallout. This means the studies are silent on internal radiation and the very different types of exposure involved:
The ICRP/NRPB model is essentially a physics based one. As far as the epidemiology is concerned all that has been done is to extrapolate the exposed group's high dose data points in a straight line down to the low dose region. This assumption that risk is directly proportional to dose has been widely criticised on various grounds. For example, Goodhead calls the extrapolation "a large region of uncertainty"(1), while others question the validity (2) and relevance (3)of bomb survivors' data. A further shortcoming is that doses are averaged over large volumes of tissue, although it is well known that radiation damage to body cells is caused by discrete tracks which either hit vital structures or miss them altogether. It is for this reason that concepts such as average energy transfer, absorbed dose, and relative biological effectiveness are useless at the low doses relevant to land delicensing.(4)
The fact that cancers are monoclonal (i.e. they start with mutations to one cell) ought to alert us to the inadequacy of the averaging approach.
Chris Busby's Second Event theory describes the hazard from isotopes which decay more than once, where there is an enhanced probability [relative to the yardstick of Natural Background] that a first decay damages a cell, initiating its repair process, and a second or subsequent decay disrupts the repair. NRPB's Cox and Edwards discuss this in the International Journal of Radiation Biology(5). Responding, Busby observes that by NRPB's own calculation the existence of one atom of radioactive Strontium within an individual cell is, as far as that cell is concerned, equivalent to doubling the external natural background exposure. The great instability of many man-made isotopes makes them "second event" hazards by virtue of their rapid decay. This does not apply to the natural nuclides. However, Busby points out [also in IJRB] that where natural nuclides exist in the form of hot particles they confer "second event" hazards on any tissue in which they lodge; insoluble Uranium oxides are an example.
The recent furore over the effects of depleted Uranium weapons amply illustrates the crisis of confidence in the conventional modeling of low dose radiation risk. Ministers, NATO officials and MoD spokesmen have insistently referred to the hazards of Uranium in terms of its soluble forms, including battlefield debris and internal contamination with shrapnel. This is to overlook the largely novel type of exposure consequent upon the creation of large amounts of ceramic Uranium Oxide particles. Following inhalation such particles are known to be retained long-term in tracheobronchial lymph nodes (TBLNs) at potentially very high concentrations. LLRC has been issuing warnings about the risk of chronic irradiation of lymph tissue for several years (6). These have now been echoed by Britain's most senior radiation biologists; Professor Dudley Goodhead and Professor Eric Wright, are quoted in New Scientist (13 January, p. 5, and 20 Jan. ) and the Daily Telegraph (23 February 2001) drawing attention to the potential for damage to haemopoetic stem cells, possibly leading to leukaemia. It should be noted that the exposures Goodhead, Wright and LLRC refer to confer very little radiation as conventionally estimated on the basis of whole body doses. Nevertheless, the lymph nodes have such a remarkable capacity to concentrate and retain insoluble actinides that NRPB and COMARE were constrained to consider lymph doses from Plutonium for the COMARE 4th Report. LLRC has drawn attention to the inadequacy of their calculations of doses.(7) This is of considerable relevance to land re-use, especially as attention begins to be directed to the impact of dust. [Note: a DG11/ WHO Symposium in September 2000 concluded by consensus that environmental pollution with radioactivity and chemicals is a major factor in the world-wide increase in cancer; a paper on the role of radioactive dust presented to the Conference is soon to be published.]
There is no essential difference between the nuclides present on contaminated sites and those from Chernobyl and weapons test fallout in the 1950s and '60s. Epidemiological studies of "downwinders" (including Chernobyl), of populations exposed to weapons fallout, and of nuclear workers and their children provide ample evidence that radiation hazard at low dose has been severely underestimated.
There is too much such evidence to discuss here. There is a Compendium on the Web (www.llrc.org/compendium.htm) which LLRC has submitted to a number of consultations. It includes commentary and is divided into categories of:
Arguably the most important paper in the Compendium is one recently published (8) whose authors calculate that official risk estimates are in error by a factor of at least 100. This is the first time a calculation showing an error of this magnitude has been published in the peer reviewed literature.
From the findings of distinct peaks in infant leukaemia in 1987 - 88 [a phenomenon observed in Wales, Scotland, Greece, Germany, and the USA] the authors suggest a range of values, depending on which exposure route is responsible for the disease;
An error of even the smallest of these values is easily enough to account for phenomena such as the leukaemia clusters found near reprocessing plants, elevated incidence of childhood leukaemia in the Nordic countries at the time of weapons testing (9) and high rates of cancer in people living near plutonium-laced mudflats along the Irish Sea coasts of north Wales and the Republic of Eire (10).
At LLRC's request Dr Colin Muirhead, NRPB's head of epidemiology, has responded to the publication of the post-Chernobyl infants leukaemia paper. His paper and LLRC's critique are (or soon will be) on LLRC's website. (11)
It is generally assumed that the standard for deregulation of contaminated land is 400 becquerels/kg. - the SoLA Exemption Order benchmark which has long stood as a definition of what is regarded as "radioactive" in the sense of requiring regulation under the RSA. It was never intended to apply to large volumes of material, having been adopted before the concept of "clearance" was defined by the new BSS Directive, but it has been extended to encompass Clearance of contaminated material in the UK. This may be subject to legal challenge.
The application of SoLA to delicensing land is even more questionable. Stephen Kaiser of the European Commission has recently written to Dr Caroline Lucas MEP that Clearance was never intended to apply to delicensing land. However, it is clear that NRPB and the industry regard even 400 Bq/kg as unnecessarily restrictive, and clean-up targets at Harwell interpret it as meaning "400 in addition to what's already there" (12). This again, is open to challenge, since Dr. Kaiser's letter also states that "it is ... appropriate not to include "background" ... in any exemption values or clearance levels." In considering the question of who is responsible for contamination Dr Kaiser adds that "If the residues are the undertaking's own (historical) responsibility, it would in general not be appropriate to include this in the background."
Finally, we should point out that the assessment of "the actual health effects of specific nuclides and specific physical and chemical forms of them" which we have referred to in this essay is distinct from the modelling used by IAEA, NRPB, ICRP, the Article 31 group of "experts", and recently endorsed by RWMAC.(13) These bodies base their assessments on the physical characteristics of radioactive substances and on concepts such as average energy transfer, absorbed dose, and relative biological effectiveness which have been called into question.
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