Natural Background Sources Research Articles

Managing Radioactive Waste: Issues and Misunderstandings

We are all continually exposed to cosmic radiation, and natural radioactive elements are in the air we breath, the earth we walk on, the homes we live in and in the food we eat, as well as in our bones and tissues. In comparison to this ongoing and unavoidable exposure from natural background sources, exposure from artificial sources has a small impact. The artificial radiation exposure is almost totally medically related, with routine nuclear power activities contributing only a very small fraction of one percent to the daily exposure, an addition which can be best characterised as minor (see Figure 1). Natural background exposure, both from external and from internal radiation due to inhaled or ingested radioactive substances, is location dependent. Cosmic radiation varies with altitude and natural radioactive substances in the ground vary significantly by location. Millions of Europeans living in locations with high levels of naturally occurring radioactive radon gas in Austria, Finland, France, Spain, Sweden and the United Kingdom receive some ten and many even 20 times the average world background exposure that is received by residents of New York City, where the radon gas levels are significantly lower. These higher radiation exposures are further exceeded in localised areas, as in parts of Brazil, India and Iran, where individual exposures can be more than one hundred times the world average and more than one million times the average exposure from routine nuclear power activities.

Sentinel node staging of early breast cancer using lymphoscintigraphy and the intraoperative gamma-detecting probe

Sentinel node staging for breast cancer is increasingly used in place of axillary lymph node dissection but is not yet universally accepted. The problems of non-standardized methodologies and lack of consensus on the optimum techniques to identify sentinel nodes are being addressed. Complementary use of radionuclide imaging before surgery, intraoperative probe detection, and blue dye have yielded the best reported sensitivities for finding a sentinel node (94%). The importance of imaging is summarized as identifying sentinel node(s), distinguishing sentinel from secondary nodes, guiding surgical incision planning, and facilitating lower doses. The learning curve phenomenon, which applies to the surgeon and the nuclear medicine physician, has been recognized; measures to minimize it are being implemented. Radiation exposure to operating room and pathology personnel is very low; estimates of exposure to the surgeon's hands are 0.2% of the annual whole body dose received by every human being from natural background and cosmic sources.

Perspective: National Cancer Institute summary report about estimated exposures and thyroid doses received from iodine 131 in fallout after Nevada atmospheric nuclear bomb tests.

Environmental 131I contamination from atmospheric nuclear bomb tests conducted at the NTS from 1951 to 1958 exposed Americans nationwide to a cumulative average dose of 1 to 4 rad to the thyroid gland. By comparison, 10 years of exposure to natural background sources of thyroid radiation results in a cumulative dose of 1 rad. Americans living in certain high-deposition areas received an average cumulative thyroid dose of as much as 16 rad. Individual dose rates vary considerably as a function of age at the time of exposure, site of residence, and dietary habits with respect to milk consumption. The individual cumulative thyroid dose for persons born between 1945 and 1958 may be significantly higher than the reported averages for their locale. The NCI report contains voluminous data tables permitting detailed calculations of individual dose. Additionally, color-coded dose maps allow one to approximate individual dose conveniently. Translation of cumulative thyroid dose attributable to 131I to predictions of increased rates of thyroid cancer appears problematic and is the subject of further study. In contrast to studies of patients receiving external thyroid irradiation, existing studies of patients treated with 131I for diagnostic and therapeutic medical purposes do not document increased rates of thyroid cancer. An Institute of Medicine task force is expected to issue a report on this subject in September 1998. This review also briefly summarizes the evaluation, diagnosis, and treatment of patients with papillary and follicular thyroid cancers. Data from 53,856 patients with thyroid cancer accessioned to the NCDB from 1985 to 1995 document extremely high survival rates for patients in the United States with papillary and follicular thyroid cancer.

Identification of historical lead sources in roof dusts and recent lake sediments from an industrialized area: indications from lead isotopes

X-ray fluorescence and stable lead (Pb) isotopic analyses have been undertaken on dusts, known from microscopic investigation to contain significant quantities of industrially- and urban-derived particulate matter, present in the roof cavities of houses in the Illawarra region (N.S.W., Australia), with the objective of examining the historic record of Pb pollution. All investigated houses contained in excess of 250 μg g −1 Pb, with dwellings close to a copper smelter, in a large industrial complex including a major steelworks, containing higher (> 2500 μg g −1) Pb concentrations. The isotopic composition in the dusts, expressed here as 206Pb 204Pb , is relatively constant at 17.0, irrespective of dwelling age or distance from the industrial complex. Contamination of the dusts by Pb sourced from paint cannot explain the isotopic uniformity of the dust samples. Isotopic modelling indicates that the dusts contain Pb derived from the copper smelter, gasoline-air Pb and a minor contribution from coal-utilising sources. Lead loading was also investigated in the adjacent lagoon, which acts as a natural sink for particulate matter in the Illawarra region. Isotopic data and modelling indicate that one natural and four anthropogenic sources contribute to the Pb burden of this lagoon. The natural source consists of Permian rocks cropping out in the catchment area which have a 206Pb 204Pb of ∼ 18.7. The suggested anthropogenic sources are an old disbanded base-metal (Pb) smelter ( 206Pb 204Pb ∼ 16.2–16.3 ), the copper smelter ( 206Pb 204Pb ∼ 17.9 ), gasoline-air derived Pb ( 206Pb 204Pb ∼ 16.4–16.5 ) and industries utilising coal, for example the recently closed thermal coal-fired power station ( 206Pb 204Pb ∼ 18.9 ). The relative contributions of the base-metal (mainly lead) smelter and gasoline-air Pb in the sediment can only be partly assessed due to the isotopic similarity of these sources. Likewise the natural background and coal source (e.g. power station) contributions can only be estimated from historical data. Age estimations for sediment cores, using 137Cs, provide some control on these assessments. Near surface sediments in the lagoon have a relatively constant 206Pb 204Pb of 17.6–17.7, irrespective of sample location. Isotopic calculations, together with records of particulate matter pollution emissions, indicate a link between the Pb in roof dusts ( 206Pb 204Pb ∼ 17.0 ) and Pb contamination of the near surface (upper 20 cm) lagoonal sediments via a homogeneous, non-unique source of lead whose isotopic composition closely matches that of the dusts. Over the last 5 decades, atmospheric fallout of Pb-bearing particulate matter appears to have been the dominant pathway for addition of Pb to the lagoon and dwellings in the Illawarra region.

Lipid geochemistry of surficial sediments from the coastal environment of Egypt I. Aliphatic hydrocarbons — characterization and sources

Samples of surficial bottom sediments collected from six main zones along the Alexandria coast (Egypt) have been analyzed and characterized in terms of their contents of biogenic and anthropogenic hydrocarbon biomarkers. The distributions, structures, and applicability of these compounds in determining sample sources are discussed using the biomarker multi-tracer approach. By means of multivariate statistical analyses (Q-mode cluster analysis, extended Q-mode factor analysis, and linear programming technique), the hydrocarbon tracers were grouped according to their probable input sources and the sampling stations according to the relative importance of each source contribution. Homologous long chain n-alkanes (C15C38), CPI, UCM, and biomarkers such as pristane, phytane, tricyclic (C19C29) and tetracyclic (C24, C28 and C29) terpanes, 17α(H),21β(H)-hopanes (C27C35), 5α(H),14β(H),17β(H)-steranes (C27C29) with minor amounts of 5α(H),14α(H),17α(H)-steranes and 13α(H),17β(H)-diasteranes were found to be the most suitable indicators to differentiate between sewage/industrial pollution and natural background sources. Several ratios of the terrestrial and anthropogenic biomarkers were calculated for every station in each zone. These ratios, the aliphatic hydrocarbon concentrations (relative to TOC), and the statistical findings from the multivariate techniques indicate strong signals of petroleum/industrial and biogenic/terrestrial aliphatic hydrocarbons in the Alexandria coastal region.

Metals in Estuarine Sediments: Factor Analysis and Its Environmental Significance

Q-mode factor analysis has been used to partition the variability of environmentally active metals in Delaware Bay sediments. Three factors, identified as a natural background source, an oceanic or seawater source, and an estuarine source, account for 96 percent of the metal variability.

Radiation Hazards of Primary Concern to Public Health—Present Status and Outlook

The radiation hazards currently of primary concern to public health are fallout of radioiodine from testing nuclear weapons and excessive x-ray exposures performed by careless and sometimes poorly trained physicians. Because of the relatively short half life of I/sup 131/(8 days), it might be expected to be of little consequence as a public health hazard following nuclear weapons testing. However, the yield of I/sup 131/ from a nuclear weapon is sufficiently high that considerable contamination of the environment takes place, and the hazard to the general population becomes greatest when the weapon is detonated at low altitude. The ground contamination problem increases as the altitude of detonation decreases. After the USSR tests of 1961, levels of I/sup 131/ contamination rose rapidly-in a few communities to a level which, if continued over a period of several months, would cause a dose in excess of the Federal Radiation Council's (FRC) radiation protection guide of 0.5 rem. The meteorologic aspect is of interest to public health authorities because it clearly indicates the manner in which variation in the weather pattern may cause fallout to occur from time to time in quite unexpected places. As a result of later detonations, estimates indicate that inmore » some regions of the United States the radiation dose received by the thyroid glands of children may reach a level of 1.5 rem/yr, which represents the ingestion of 100,000 mu mu C of radioiodine. This amount is 3 times the quantity of radioiodine recommended by the FRC as a maximum limit. The FRC has announced that its radiation standards, applicable to the peacetime uses of radionuclides, do not apply to environmental contamination from fallout. The political implications of this decision, as well as the confusion it has introduced among public health authorities, are discussed. Reduction of the I/ sup 131/ hazard by the use of dried or stored fresh milk by infants and lactating mothers, and addition of stable iodide to the diet, are also discussed. Problems of medical overexposure to radiation are, in general, the result of the use of unsafe x-ray equipment or careless use of x-ray equipment. It is recommended that exposure dose values to such tissues as the reproductive organs be reduced to 15 mr/yr or about 15% of the exposure dose from natural background sources, as an The duties and experiences encountered during the 4-yr operation of a radiation control agency are recounted. The most important part of a comprehensive radiation control program, in terms of overall exposure of the population, is the effort to minimize the radiatlon exposure from the medical and dental use of x-rays. The fact that much of the equipment is installed in apartmert houses, other multiple dwelling structures, and office buildings means that a more critical evaluation of the structural shielding is necessary. An inspection of existing x-ray installations showed that much equipment had been installed in multiple dwellings without having the basic structural shielding considered standard practice for many years. Public health considerations relating to siting nuclear reactors in cities are discussed, particularly with respect to nuclear-powered vessels entening the harbors of large cities. The problem of safeguarding the public from hazards associated with the transportation of radioactive materials in a large city is also discussed. Dosimetry tests showed that many watches being sold with luminous dials exceeded permisnible dose rates, and many jewelry and department stores have been restrained from selling such watches. Other tests showed that, under normal use, television equipment does not emit a sufficiently hlgh dose rate of x-rays to constitute a health hazard. (BBB)« less

Radiation biology.

The Symposium on Radiation Biology presented at the Forty-fourth Annual Meeting of the Radiological Society of North America provided a broad and eclectic review of this rapidly evolving field for members of the radiological profession. The Symposium comprised two papers on radiation carcinogenesis and on late somatic effects of radiation, respectively, and four papers dealing with cell renewal and radiation injury, with possible additive or synergistic effects of combining chemotherapeutic agents with radiotherapy, and with the possible amelioration of radiation damage by one of the newer hormonal agents. The latter four papers appear in this issue of Radiology. A second symposium dealt with the hazards of radiation exposure in diagnostic roentgenology and the methods by which such exposure might be reduced.1 Such symposia can serve a most useful purpose by helping the radiologist keep abreast of developments in this sometimes bewildering field. Three different lines of investigation are generally subsumed under the heading “Radiation Biology”: (1) the possible hazards of diagnostic and other medical uses of radiation; (2) the mechanism by which radiation kills normal and malignant cells, and the modification of these effects; (3) the assessment, treatment, and prevention of somatic and genetic injury to whole populations due to radiation from nuclear weapons testing, civilian medical applications, and natural background sources. The first of these areas, to which the public at large has now been alerted by a number of reports (1, 2, 3), is of particular interest to the diagnostic radiologist; the second is obviously the concern of the therapeutic radiologist; and it is clearly the responsibility of all radiologists to be conversant with the third, inasmuch as the public and our medical colleagues look to members of our specialty for authoritative opinions on all questions in this area. The evaluation of possible hazards of small radiation doses in large populations is a tricky and difficult subject for investigation (4, 5, 6), and the radiologist must be alert to the statistical, dosimetric, and epidemiologic pitfalls with which it is beset. Our training has given us little preparation for dealing with these topics, and yet we are better prepared than the rest of our medical colleagues, who therefore look to us for help. Symposia which provide us with the timely, carefully considered views of experts in this branch of radiation biology may help us to fulfill this obligation. The enhancement of awareness, per se, among members of our profession regarding sources of unnecessary and possibly excessive radiation exposure in the course of diagnostic x-ray examinations has done much to provide solutions to the problem.

THYROID RADIATION DOSES FROM FALLOUT

Absorbed doses of radiation from fallout, when averaged over yearly periods and over large numbers of individuals, have usually been assumed to be well below the corresponding doses from natural background sources. Although this assumption may be valid for most body organs, it is unlikely to have been valid for the thyroid glands of the average infant and child in the U.S. The purpose of this note is to point out that for the last few years such thyroids probably have received an annual radiation dose (chiefly, from the beta-rays of radioiodine) that is approximately equal to the annual dose which they receive from natural background radiations.

Leukemia and ionizing radiation.

Leukemia in man can be induced by ionizing radiations and also occurs spontaneously. For the "average" individual in a population, the probability of developing radiation-induced leukemia is estimated to be 2 x 10(-6) per rad (unit of absorbed dose of radiation) per year. The available data from four independent sources make it likely that this estimate is valid within a factor of about 3, giving a range from 0.7 x 10(-6) to 6 x 10(-6) per rad per year. It is pointed out that 10 to 20 percent of the spontaneous incidence of leukemia (Brooklyn, 1943-52) may result from radiation from natural background sources. It is estimated that a 5- to 10-percent increase in the current spontaneous incidence of leukemia would occur if the population were to reach and maintain a body level of Sr(90) amounting to one-tenth of the "maximum permissible concentration."