bomb dosimetry unlikely to change risk estimates

Sir — After 11 September 2001, the UnitedStates adopted precautionary measures toprotect its people and institutions. Manyinstitutions have slammed their doors toMuslim scientists. As a scientist and writerinterested in science and society, I amconcerned that the current political andemotional upheavals will severely handicapthe growth of science in the Islamic world.

Discriminatory US policies discourageUS institutions from recruiting Muslimscientists. These policies include the USDepartment of Agriculture’s ban onscientists from several countries includingtraditional Islamic areas; extensive back-ground checks on Muslims; and the recentlaw requiring men from Islamic countriesto report to immigration offices.

These exclusion policies cover a broadrange of science, from agriculture to IT,and will severely inhibit the growth ofscience in the Islamic world. To avertcatastrophe, all groups — Muslims,

Americans and Europeans — must act.Muslims must recognize the need to

spend petrochemical wealth in establishingcentres of scientific excellence and creatingan environment conducive to scientificgrowth in all Islamic countries (not justArab ones). Muslim nations must formulaterelevant R&D programmes, restructureinstitutions to end corruption and dynasticpractices, and collaborate with both Westernand newly industrialized states to nurture astrong science base. Finally, Muslims mustdemand more from their leaders, so thatthey can become equal to other societies.

US organizations and individualscientists must lobby hard to change post-11 September policies that are detrimentalto scientific endeavour. US scientists couldcollaborate, mentor and otherwise assistMuslim scientists. American Muslimscientists must take the lead in Islamicscience, as they live in a progressive country.

Europeans can take an active role in

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bridging the rift between the US andMuslim worlds, filling the vacuum createdby US precautionary policies. Europeansare already taking small steps to collaboratewith the Arab countries (Nature 423, 906;2003). This process should be encouraged.

There is an urgent need to reinvigoratethe rusted scientific sector of the Muslimworld beyond rhetoric, marathon confer-ences and establishment of skeletoninstitutions. It requires the concerted effortof politicians, scientists, philanthropists,entrepreneurs and ordinary citizens. Thereis definitely room for reform and businessopportunities in the Islamic world.

The United States was brutally hurt by a few ruthless terrorists, and faces furtherthreats. However, blanket repressivepolicies in response will cause more harmthan good to the world as a whole.Ahmed M. DirieCalifornia, USAadirie2001@yahoo.com

Bomb dosimetry unlikelyto change risk estimatesSir — In his News and Views article “A doseof the bomb” (Nature 424, 495–496; 2003)about the impact of the new A-bomb dosi-metry on radiation-risk estimates, MarkLittle argues that the risks of �-ray exposureshould become more reliable. Two otherfactors suggest that the new dosimetry islikely to have little or no impact on riskestimates for doses that are occupationallyor environmentally relevant.

The US National Council on RadiationProtection and Measurements (NCRPReport No. 126, NCRP, Bethesda, 1997) hasdetermined the dose-rate effectiveness factorto be the main source of uncertainty in riskestimates, accounting for about 40% of totaluncertainty. Overall, dosimetry uncertaintiesaccount for less than 10% of the total.

Dose-rate effectiveness factors must beapplied to A-bomb-derived risk estimatesto account for differences in temporal dosedelivery. The bomb exposed people to veryhigh dose rates (essentially instantaneousexposure), whereas risk estimates areusually applied to occupational orenvironmental situations where the dose isdelivered at a significantly lower rate andrisks are assumed to be lower because ofbiological repair mechanisms.

The second source of uncertainty isdose extrapolation. A-bomb risks are basedon excess cancer deaths in people exposedto doses greater than 200 mSv (D. A. Pierce

et al. Radiat. Res. 146, 1–27; 1996). Belowthis dose the total excess number of cancerdeaths is too small to be used reliably inrisk estimation. Accordingly, risks calculatedfrom high-dose data are extrapolated usingthe linear non-threshold theory to predictrisks at small doses. Assuming thatoccupational and environmental doses arearound 2 mSv per year, dose extrapolationis significant and the theoretically derivedrisks are highly uncertain.Kenneth L. Mossman School of Life Sciences, University Office ofRadiation Safety, Arizona State University,Tempe, Arizona 85287-3501, USA

Mark Little replies — I am grateful for DrMossman’s comments on my article. As I stated in the penultimate paragraph,sources of uncertainty other than thedosimetry have to be taken into account inderiving risk estimates from the A-bombdata. Constraints of space did not allow meto go into these in detail. I would concurwith Dr Mossman that extrapolation ofrisks to low doses and low dose rates is oneof the more substantial of these, othersbeing the extrapolation of risks to the endof life and across populations, for examplefrom a Japanese to a UK population (NCRPReport No. 126, NCRP, Bethesda, 1997).

The various sorts of bias (selection,ascertainment and so on) to whichepidemiological studies are prone shouldalso be considered. As discussed in myarticle, selection bias in A-bomb survivorsmay be significant, and as with the problems

of extrapolation of dose and dose rate, maylargely invalidate the A-bomb risk estimates.However, as noted previously, cancer risksderived from A-bomb survivor data arestatistically consistent with those observedin groups exposed at moderate-to-low dosesand dose rates (M. P. Little et al. Radiat. Res.151, 218–224; 1999; R. Wakeford et al. Int.J. Radiat. Biol. 79, 293–309; 2003).

Nothing new under the Sun?Sir — J. M. Gordon and colleagues, in theirBrief Communication “Surgery by sunlighton living animals” (Nature 424, 510; 2003),describe the use of a solar photocoagulatorto necrose a rat liver lesion in what theybelieve to be “the first time that intenseincoherent light has been applied success-fully in an interstitial medical procedure”.They may be surprised to learn that such atechnique played a significant role in thedevelopment of a modern clinical ophthal-mic practice: retinal photocoagulation. TheGerman ophthalmologist Gerhard Meyer-Schwickerath (G. Meyer-Schwickerath Ber.Dtsch. Ophthalmol. Ges. 55, 256–259; 1949)not only undertook the repair of retinalbreaks by focused sunlight, but also designedthe optical instrumentation that bears hisname: the Meyer-Schwickerath coagulator.Merrick Moseley Department of Ophthalmology, Imperial College,St Dunstan’s Road, London W6 8RP, UK

It’s time for the US and Muslims to work togetherEach side has problems to solve and much to gain from contact with the wider world.

© 2003 Nature Publishing Group