LAUSR

Dear Sir, In the recent study ‘Assessment of radiation dose and excessive life-time cancer risk from the Bunair granite, northern Pakistan’, Quereshi et al. performed natural radioactivity measurements for Bunair Granite. The typical indoor effective dose, E ranged from 0.83 to 1.14mSv per year with an average of 1.00mSv. The authors also evaluated excessive life-time cancer risk (ELCR) and the average value was found to be 3.49 × 10 and 0.46 × 10, respectively, for indoor and outdoor exposures. The authors mentioned that risk calculations were performed using fatal risk factor of 0.05 per Sv (5% Sv) as given by the International Commission on Radiological Protection (ICRP) . It was further interpreted that (ELCR)indoor is 1.49 times higher than the world’s average probability of cancer occurrence of 2.41 × 10 while living in dwelling made up of ordinary building materials. In this regard, it may be noted that the calculation of cancer cases using ICRP’s adopted risk factors do not have much significance. ICRP has clearly mentioned that the primary uses of effective dose, E in radiological protection for both occupational workers and the general public are (Para 153): (i) prospective dose assessment for planning and optimisation of protection and (ii) retrospective dose assessment for demonstrating compliance with dose limits, or for comparing with dose constraints or reference levels. ICRP further states that (Para 157) the effective dose is intended for use as a protection quantity on the basis of reference values and therefore is not recommended for epidemiological evaluations, nor should it be used for detailed specific retrospective investigations of individual exposure and risk. The commission further cautions on the misinterpretation of the risk coefficients, effective dose and collective dose and states that—when the collective effective dose is smaller than the reciprocal of the relevant risk detriment, the most likely number of excess health effects is zero. In the ‘Evolution of ICRP recommendations, 1977, 1990 and 2007’, Prof. R.H. Clarke also states that when the detriment figure is 5% Sv and the collective dose is less than 20 man Sv, the most likely number of health effects is zero. Recent UNSCEAR report also supports the view of ICRP on this issue and mentions that the aggregation of very low individual doses over extended time periods is inappropriate for use in risk projections and, in particular, the calculation of numbers of cancer deaths from collective doses based on individual doses that are well within the variation in background exposure, should be avoided . In view of ICRP as well as UNSCEAR recommendations, the risk calculation for trivial dose values is not much meaningful and should be avoided as it not only attracts public concern but also results in numbers which have no statistical and physical significance. In addition, the calculation of risk using ICRP’s adopted risk factors is itself against the recommendations of ICRP.