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At least 631 records · Page 35Linked to original sources
PubMed2005

Parameterization of a dynamic specific activity model of 14C transfer from surface water-to-humans.

Carbon-14 is a particularly interesting radionuclide from the perspective of dose estimation because it mixes readily with stable CO2, and hence enters the food-chain as fundamental biomolecules. A model was developed for the situation of 14C releases to surface waters, where there are distinct changes in the water 14C activity concentrations throughout the year. The model computes the specific activity in water, phytoplankton, fish, crops, meat, milk and air, following a typical irrigation-based food-chain scenario. This paper describes the derivation of the required 14C-specific parameter values. Many of the key parameters are not commonly measured, at least not in the context of dose assessment. Thus, inference from other sources of data was required, and this is the scientific contribution described in this paper. The best estimates and appropriate measures of statistical dispersion are provided. This required consideration of both the temporal and spatial averaging domains to ensure they were correct for parameters as defined in the model. The model coupled with these parameter values represents several new developments for modelling 14C transfers.

Air Pollution, Radioactive↗
PubMed2005

Conceptual approaches for the development of dynamic specific activity models of 14C transfer from surface water to humans.

Carbon-14 is a particularly interesting radionuclide from the perspective of dose estimation. Many nuclear facilities, including power reactors, release 14C into the environment, and much of this is as 14CO2. This mixes readily with stable CO2, and hence enters the food chain as fundamental biomolecules. This isotopic mixing is often used as the basis for dose assessment models. The present model was developed for the situation of 14C releases to surface waters, where there are distinct changes in the water 14C activity concentrations throughout the year. Complete isotopic mixing (equilibrium) cannot be assumed. The model computes the specific activity (activity of 14C per mass of total C) in water, phytoplankton, fish, crops, meat, milk and air, following a typical irrigation-based food-chain scenario. For most of the biotic compartments, the specific activity is a function of the specific activity in the previous time step, the specific activity of the substrate media, and the C turnover rate in the tissue. The turnover rate is taken to include biochemical turnover, growth dilution and mortality, recognizing that it is turnover of C in the population, not a tissue or an individual, that is relevant. Attention is paid to the incorporation of 14C into the surface water biota and the loss of any remaining 14CO2 from the surface water-air interface under its own activity concentration gradient. For certain pathways, variants in the conceptual model are presented, in order to fully discuss the possibilities. As an example, a new model of the soil-to-plant specific activity relationship is proposed, where the degassing of both 14C and stable C from the soil is considered. Selection of parameter values to represent the turnover rates as modeled is important, and is dealt with in a companion paper.

Air Pollution, Radioactive↗
PubMed2003

Cancers among residents downwind of the Hanford, Washington, plutonium production site.

A community-based health survey for the time period between 1944 and 1995 was collected from 801 individuals who had lived downwind of the U.S. plutonium production facility located in Hanford, Washington. The results of the survey revealed high incidences of all cancers, including thyroid cancer. There were greater than expected numbers of central nervous system tumors and cancers that invaded the female reproductive system (e.g., cancers of the uterus, ovary, cervix, and breast). The authors argue that the greater-than-expected numbers found cannot be accounted for by selection bias alone. Comparisons of crude incidence rates, as well as of occurrence ratios between pairs of cancer types among Downwinders and reasonably similar populations, suggested that the excess neoplasms may be associated with radioactive contamination of food, water, soil, and/or air. In addition, a synergistic effect may exist with agricultural toxins. Previously neglected biophysical and physiological properties of internally lodged, long-lived 129I may be a significant etiological factor in the development of thyroid diseases, including cancer, and other malignancies in exposed populations.

Adolescent↗
PubMedDate not supplied

Radionuclides in domestic and imported foods in the United States, 1987-1992.

Findings from the U.S. Food and Drug Administration's Radionuclides in Foods program are summarized for foods collected between October 1, 1986, and September 30, 1992. Concentrations of radionuclide activity in the Total Diet Study and reactor-survey foods were in Range 1 or low in Range II of the surveillance and control recommendations of the Federal Radiation Council; no control actions were suggested. Dietary intake of 90Sr continued the general decline observed since 1961. Approximately 2600 test portions of imported foods were analyzed for contamination associated with the Chernobyl nuclear accident. Concentrations of radionuclide activity were below limits of detection for the vast majority of the imported food test portions but were above the levels of concern for 23 portions. Since 1986, the fraction of imported food test portions having measurable amounts of contamination has steadily declined, as have the average concentrations of radionuclide activity; however, contamination is still occasionally found. Continued monitoring of both domestic and imported foods is planned.

Adolescent↗
PubMedDate not supplied

FDA Total Diet Study, July 1986-April 1991, dietary intakes of pesticides, selected elements, and other chemicals.

The U.S. Food and Drug Administration conducts the Total Diet Study to determine dietary intakes of selected pesticides, industrial chemicals, and elements (including radionuclides). This paper reports results for the sampling period July 1986 to April 1991. The study involves retail purchase of foods representative of the ¿total diet¿ of the U.S. population, preparation for ¿table-ready¿ consumption, and individual analyses of 234 items making up the diets of 8 population groups. The diets were based on 2 nationwide food consumption surveys. The data presented represent 21 food collections (also termed ¿market baskets¿) in regional metropolitan areas during the 5-year period. Dietary intakes of nearly 120 analytes are presented for 8 population groups, which range from infants to elderly adults. Intakes of selected population groups are compared with representative findings from earlier Total Diet Study sampling periods. As reported previously, average daily intakes are well below acceptable limits.

Adolescent↗
PubMed1989

Influence of husbandry on the transfer of radiocaesium from feed to milk during the winter that followed the Chernobyl reactor accident.

The release of activity from the Chernobyl nuclear reactor resulted in deposition of radionuclides throughout the UK in early May 1986. Since that time, the transfer of radiocaesium from feed to milk has been followed at two farms that differ in both location and husbandry practice. This paper concerns the winter of 1986/87, when activity concentrations in milk increased because of the consumption of silage prepared earlier in the year. Silage-to-milk transfer coefficients have been estimated which suggest that, when incorporated into prepared silage, radiocaesium from Chernobyl is less available for transfer to cows' milk than soluble caesium-134 applied directly onto pasture. The measured activity concentrations in milk have been compared with those predicted by the NRPB model FARMLAND; despite differences between the husbandry practice assumed in the model and those observed in practice, the model provides an adequate radiological assessment of the feed-cow-milk pathway after an accidental release of radioactivity.

Accidents↗
PubMed1992

Caesium contamination in human milk and transfer factor from diet.

A study on caesium contamination in human milk, as a consequence of the Chernobyl fallout, was conducted in 1989 on a group of women from one of the areas of northern Italy most heavily affected by the radioactive fallout. Their diet was studied, and the caesium intake was calculated by using the mean food activity concentration in that area. The caesium transfer factor was evaluated both as the ratio of caesium concentration in mother's milk to the daily intake, and by using a simplified milk compartment model.

Accidents↗