Concerns on the health effects of low-dose ionizing radiations from naturally occurring radioactive materials (NORM)

摘要

It is a widely known feet that man evolved in a naturally radioactive environment. Even today life exists in an atmosphere of cosmic and terrestrial radiation. Radionuclides are found naturally in air, water and soil. They are even found in us, we being the products of our environment. Every day, we ingest and inhale radionuclides in our air and food and the water. Natural radioactivity is common in the rocks and soil that makes up our planet, in water and oceans, and in our building materials and homes. There is nowhere on earth that one cannot find natural radioactivity. Radioactive materials which occur naturally and expose people to radiation occur widely, and are known by the acronym 'NORM' (Naturally Occurring Radioactive Materials). Besides, around the globe there are some areas with an elevated background radiation. These areas include parts of Brazil, Iran, India and China. The sources of radiation in these areas include monazite containing beach sands and radium from hot springs. On the southwest coast of India, there are large deposits of thorium bearing monazite sands that contribute to an external radiation dose of about 5-6 mGy/yr, but in some parts doses up to 32.6 mGy/yr have been reported. Nevertheless, most general public associate ionising radiations only with the nuclear industry. Antinuclear activists often fail to accept the fact that coal-fired power stations and the oil and gas exploration operations may emit more radioactivity than an operating nuclear reactor. Another NORM issue relates to radon exposure in homes, particularly those built on granite grounds. The solid airborne Rn-222 progeny, particularly Po-218, Pb-214 and Bi-214 are of health importance because they can be inspired and retained in the lung causing cancer. Man-made operations like oil and gas production and processing operations result in technologically enhanced naturally occurring radioactive materials (TENORM) to accumulate at elevated concentrations in byproduct waste streams. The concern arises because of the very large amounts of TENORM needing recycling or disposal from many sources. The largest TENORM waste stream is coal ash. In India and Australia mining of beach minerals is a profitable industry. The beach sands along the south Indian coast are rich sources of minerals such as ilmenite, rutile, zircon, silimanite and garnet. The tailings obtained after the extraction of the above minerals get enriched with monazite, a thorium bearing mineral that is radioactive. Recent studies show that the activities in the tailings are somewhat more than the natural background levels in some parts of south India. Studies on health effects (cancer) from doses arising from these levels of natural radiation exposure are contradictory, some reporting adverse effects, others null and a few others beneficial hermetic effects. Systematic and large-scale epidemiological studies and laboratory investigations are called for in order to resolve this issue. Concerns on biological effects of radiations from NORM are growing and efforts are on to implement radiation protection standards in TENORM industries in the same way as in the nuclear industry.