As low as reasonably achievable (ALARA): is it appropriate for low level exposures?

Through various researches and investigations it has been established that high doses of ionizing radiation are harmful to health and there is a linear relationship between dose and the effect. There is substantial controversy regarding the biological and health effects of low doses of ionizing radiation in humans and the biota, in vitro and in vivo despite the large amount of work carried out (both laboratory and epidemiological). By low-level exposure, we mean the exposure to radiation levels comparable to those encountered in the natural environment (ambient radiation level). The proponents of the ALARA policy are the believers of LNT hypothesis adopted by major scientific, official and governmental organizations such as ICRP, NCRP, the NAS-NRC etc. for risk assessment, according to which exposure to any amount of radiation, no matter howsoever small is potentially harmful. The idea that the dose to radiation worker should be As Low As Reasonably Achievable (ALARA) is only appropriate if small doses have a risk. Current radiation risk estimates, drawn by linear extrapolation, from high dose and dose rate of radiation to zero dose, clearly ignore the effects of the repair of DNA- the target of radiation damage. If the hormetic effect is added to the effect predicted by the LNT hypothesis, the resultant effect will be somewhat different from that predicted by the LNT hypothesis alone. Excellent human data show that a moderate increase in background radiation decreases the risk of cancer and significantly increases longevity. There are strong arguments, both experimental and epidemiological, which support the radiation hormesis (beneficial effects of low-level ionizing radiation). In the present paper, we propose to highlight the results of a comprehensive study of the available literature, data and reports of various radiation exposure and protection studies carried out in India and abroad. In conclusion, we find that the radiation hormesis contradicts the predictions made by the LNT hypothesis and the policy of ALARA needs revision as regards health effects of ionizing radiation in the low dose region. (author)