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PubMed1993

Environmental monitoring and dose assessment following the December 1991 K-reactor aqueous tritium release.

Between 22 December and 25 December 1991, approximately 570 L of tritiated water was released from the K Reactor at the Savannah River Site. Analyses of river flow rates and measured tritium concentrations showed that approximately 210 TBq of tritium had been released from the reactor and was being transported down the Savannah River. Elevated tritium concentrations in the Savannah River were first detected on 26 December 1991. The maximum measured tritium concentration at Highway 301 (a major sampling point 37 km downstream of the Savannah River Site) was 2.5 Bq mL-1. A hypothetical maximum individual located at Highway 301 would have received a drinking water dose of approximately 0.35 microSv, less than 1% of the Environmental Protection Agency's 40 microSv y-1 drinking water standard. Concentrations at the intake canals to two water treatment facilities, approximately 160 km downstream, began to rise above normal on 28 December. The population dose to users of the downstream domestic water supplies and consumers of Savannah River biota was estimated to be 4.7 x 10(-3) person-Sv.

Environmental Monitoring↗

PubMed1993

Uncertainties in predicted radionuclide body burdens and doses from discrete stochastic source terms.

Expressions are derived in three cases for the expectation and uncertainty of body burdens and doses calculated from a linear model of environmental transport and human metabolism in terms of expectation and uncertainty in inputs of discrete, stochastic random variables. Three cases are compared to determine the relationship of the expectations and uncertainties under varying assumptions. In the constant input case, the input is selected randomly at the outset of the simulation period [O,T] from the distribution to which the population is exposed and then is held constant throughout [O,T]. In the two time-varying cases, random and autoregressive, it was assumed that N discrete stochastic exposures to the input were made uncorrelated and partially correlated, respectively. Each exposure was constant during each time interval of length T/N. The expectation values of the body burdens and doses in the constant input case were identical to those in the random case and the autoregressive cases for stationary inputs. The uncertainties of the body burdens and the doses in the constant input case were identical in the limit of rapid metabolism to those of the random case and the autoregressive cases for stationary inputs. In the limit of slow metabolism, the uncertainties of the body burdens and the doses in the constant input case were N1/2 and (3N/4)1/2, respectively, greater than those in the random case and were ((1 + alpha)/[(1 - alpha)N])1/2 and (4(1 + alpha)/[3(1 - alpha)N])1/2, respectively, greater than those in the autoregressive case for stationary inputs and autocorrelation coefficient alpha. That is, increasing the number of sampling periods decreases the uncertainty and increasing the autocorrelation increases the uncertainty. In an example application for ingestion of 137Cs at Bikini Island, a weak form of both slow and rapid metabolism limits apply and give the result that the uncertainty of the body burden in the constant input case is 18 times greater than the random case. For alpha = 0.5, the uncertainty of the body burden in the autoregressive case is 1.7 times greater than the random case. The smooth transition of the autoregressive case from the random case to the constant input case is shown as alpha increases from 0 (random) to 1 (constant).

Adolescent↗

PubMed1993

137Cs transfer after Chernobyl from fodder into chicken meat and eggs.

The distribution and the biological half-lives of 137Cs in poultry after continuous intake of foodstuffs contaminated by the Chernobyl fallout were studied in order to determine transfer coefficients to yolk, albumen, and shell of eggs as well as transfer coefficients to chicken meat. Mean values for laying hens were found to be 0.2 d kg-1 (whole consumable egg), 1.2 d kg-1 (leg meat), and 1.6 d kg-1 (breast meat) when radiocesium was fed in contaminated grass pellets, and about twice as large [i.e., 0.4 d kg-1 (whole consumable egg), 2.8 d kg-1 (leg meat), and 3.0 d kg-1 (breast meat)] when radiocesium was fed in contaminated wheat. Reducing effects of the feed additive ammonium-ferric-cyano-ferrate in concentrations of 0.66 g kg-1 of feed mixture on the contamination of hen products were quantified to be a factor of 3 to 4 (whole consumable egg and meat after grass pellet feeding) and 8 to 14 (whole consumable egg and meat after wheat feeding). A drastically higher reduction with an ammonium-ferric-cyano-ferrate dose twice as large (1.33 g kg-1) was achieved. For broiler chickens, activity concentration ratios of meat to feed were derived for various fattening periods, with mean values of about 0.3 (leg), 0.4 (breast), and 0.2 (liver). The addition of ammonium-ferric-cyano-ferrate reduced the activity concentrations in meat by factors of more than 6.

Accidents↗

PubMed1993

Monitoring 90Sr contamination in terms of 131I contamination in imported food.

This paper describes a method for monitoring 90Sr contamination in terms of 131I contamination in food imported from a country with a recent nuclear power plant accident. For imported food, the guideline levels set by the Codex Alimentarius Commission will be applied, which requires that the contamination in food by beta emitters (typically strontium) be monitored. However, the measurement of strontium contamination cannot be made within a reasonably short time as it requires rather time-consuming chemical extraction and sample preparation procedures in advance. We propose here to use the contamination level of 131I in these foodstuffs as indicators of 90Sr contamination levels. Possible accident scenarios are employed to estimate the abundance ratio of 131I and 90Sr deposited on soil and intercepted by plants. Using a dynamic food chain model, we can calculate their relative activities in the food products which, when combined with the 131I levels present, give the theoretical 90Sr levels present.

Accidents↗

PubMed1993

Plutonium in daily diet in Poland after the Chernobyl accident.

The content of 239,240Pu was determined in the daily diet collected in northeastern Poland (Bialystok) from March 1987 to May 1992. The estimated annual intake of plutonium decreased from 774 mBq y-1 in the first year after the Chernobyl accident down to approximately 90 mBq y-1 in the sixth year. Large fluctuations of daily intake in the first 2 y suggested that a large fraction of plutonium in the daily diet originated from the external contamination. Assuming the fractional absorption factor of 10(-5) for externally contaminated foodstuffs and 10(-3) for root uptake, the assimilated 239,240Pu would be in the range from approximately 0.02 mBq up to approximately 2 mBq for the period studied.

Accidents↗

PubMed1994

Transfer kinetics and coefficients of 90Sr, 134Cs, and 137Cs from forage contaminated by Chernobyl fallout to milk of cows.

A experiment was conducted to study kinetics, transfer coefficients, and biological half-lives of 90Sr, 134Cs, and 137Cs from feed to milk. A cow was fed a diet containing alfalfa hay contaminated by Chernobyl fallout for 14.5 wk. The time-dependent activity in milk was approximated by a two-compartment model with fast biological half-lives of 2, 0.9, and 1 d and slow biological half-lives of 36.9, 8.7, and 12.4 d for 90Sr, 134Cs, and 137Cs, respectively. The transfer coefficients determined in the experiment were 0.0008 d L-1 for 90Sr, 0.0029 d L-1 for 134Cs, and 0.0031 d L-1 for 137Cs. The biological elimination phases of 134Cs and 137Cs were described by a two-compartment model while a one-compartment model was proposed for 90Sr.

Accidents↗

PubMed1994

Sensitivity analysis of ECOSYS-87: an emphasis on the ingestion pathway as a function of radionuclide and type of deposition.

A sensitivity analysis of parameters associated with the ingestion pathway was conducted for the computer model ECOSYS-87. The model is currently being used extensively throughout Europe for accident consequence analysis following a nuclear release. Individual parameter perturbation was used to develop sensitivity indices. The sensitivity indices identified parameters whose uncertainties had a large impact on model results. The relative ranking of the sensitive parameters depended on the radionuclide (137Cs, 90Sr, 131I, or 239Pu), whether dose 1 y or 50 y postaccident was being considered, and whether the deposition event was dry or mixed. The most influential parameter for 239Pu was resuspension. Parameters to which human dose was sensitive following exposure to 137Cs, 90Sr, and 131I, were as follows: yield (biomass) of vegetation, transfer of radionuclides from plants to animals, deposition velocity, changes in radionuclide concentrations due to food processing, livestock feeding rates, and weathering of radionuclides from plant surfaces. The ranking of 131I's parameters was governed by its 8-d physical half-life. Parameters that affected the initial deposition, parameters that could rapidly affect the transfer of 131I from the biota to humans, or parameters that allowed 131I to decay prior to consumption were important. Important parameters specific to 90Sr and 137Cs included transfer of radionuclides from soil to plant, leaching from the plant rooting zone, and resuspension. Parameters associated with the movement of radionuclides within the soil were not as important for 137Cs as they were for 90Sr. With the exception of the deposition velocity, if a parameter proved to be sensitive for dry deposition, it was as sensitive, or even more so, for a mixed deposition event. Extending the model end point from 1 y to 50 y postaccident also caused a shift in the relative ranking of sensitive parameters for 137Cs and 90Sr. Parameters that were not important for any of the radionuclides considered under this scenario were those related to timing and length of crop harvest, transfer of radionuclides from leaf surfaces to edible portions of plants, rate at which radionuclide concentrations in plants decrease due to growth dilution, and time for animals to reach marketable size.

Accidents↗

PubMed1994

Transport of iodine and cesium via the grass-cow-milk pathway after the Chernobyl accident.

More than 150 data sets giving time-dependent concentrations of 131I and 137Cs in feed and milk of cows after the Chernobyl accident are evaluated using a minimal compartmental modeling approach. Transfer of cesium via the grass-cow-milk pathway is adequately described by a three-compartmental model. No unique model results for 131I, as a compartment with slow secretion of 131I into milk, are identified for some datasets only. Frequency distributions of weathering half-lives on grass and of equilibrium feed-to-milk transfer coefficients are approximately lognormal. Mean values of weathering half-lives on plants are 9.1 +/- 0.6 d for iodine and 11.1 +/- 0.8 d for cesium, in good agreement with means established from experiments performed before 1986. Mean values of equilibrium feed-to-milk transfer coefficients are 3.4 +/- 0.4 10(-3) d L-1 for 131I and 5.4 +/- 0.5 10(-3) d L-1 for 137 Cs. Both are lower than means calculated from the pre-Chernobyl data base. Plausible explanations of the differences include (1) reduced availability of fallout compared to soluble tracer; (2) underestimation of post-Chernobyl transfer coefficients by some experiments concluded too early to record slow transport processes; and (3) reduced transfer of 131I compared to long-lived iodine isotopes due to decay during fixation in the thyroid. Feed-to-milk transfer of 131I is related to milk yield, but no influence of milk yield and type of feed on transfer is apparent for cesium.

Accidents↗

PubMed1994

Transfer of 210Po and 210Pb through the lichen-caribou-wolf food chain of northern Canada.

Natural background activity and food chain transfer of the uranium decay products, 210Po and 210Pb, were examined in the lichen-caribou-wolf food chain at two locations in the Northwest Territories of Canada. 210Po and 210Pb activities in lichens differed with species and location. Both 210Po and 210Pb were markedly higher in caribou bone than in wolf bone. 210Po activities in liver, kidney, and muscle were similar in both species. Caribou fetuses had lower activities of 210Po but higher activities of 210Pb than maternal muscle and placenta, suggesting greater placental transport of 210Pb than 210Po. Concentration ratios (CR = Bq kg-1 in consumer/Bq kg-1 in its food source) and ff values (ff in d kg-1 = Bq kg-1 in muscle/Bq d-1 ingested) showed that wolves retain more 210Po and less 210Pb from their diet than do caribou. 210Po CRs averaged 0.38 for caribou/lichens, 0.26 for caribou/rumen contents, and 0.40 for wolves/caribou. 210Pb CRs averaged 0.36 for caribou/lichens, 0.57 for caribou/rumen contents, and 0.13 for wolves/caribou.

Animals↗

PubMed1994

Dosimetry of 210Po in humans, caribou, and wolves in northern Canada.

Effective doses from 210Po intake with caribou meat were determined for human residents in Baker Lake and Snowdrift in the Northwest Territories of Canada and compared to doses calculated from reported 210Po tissue activities in Alaskan and British residents (Hill 1966; Blanchard and Moore 1971). Effective doses were calculated to separate body tissues, using ICRP 60 human weighting factors and the ICRP 30 metabolic model for 210Po. Baker Lake and Alaskan effective doses were similar at 0.4 mSv y-1 and slightly higher than Snowdrift doses (0.3 mSv y-1). Alaskan tissue activities indicated higher effective doses to liver, bone surfaces and red marrow and lower doses to spleen than the 210Po metabolic model (ICRP 1979a) predicts. Effective doses to Baker Lake and Snowdrift caribou and wolves, calculated from tissue activities, ranged from 7-20 mSv y-1, using human weighting factors for comparison to human doses only. Effective doses to northern Canadians and wildlife were, respectively, 7-11% and 1.8-5 times an estimated human background of 4 mSv y-1 from all sources.

Animals↗

PubMed1994

Radiocesium in diet and humans in northeastern Poland after the Chernobyl accident.

137Cs and 134Cs concentrations were determined in the daily diet and foodstuffs in northeastern Poland in the fourth through sixth years after the Chernobyl accident. Intakes, body burdens, and dose equivalents were evaluated in the consecutive years. The data from this and previous work were used for the calculation of the effective half-time of radiocesium in humans. The effective half-time for 137Cs (1.94 y) was similar to that observed after nuclear weapons tests. The effective half-time for 134Cs was 0.98 y. Taking these half-times into account, the whole-body committed dose equivalent for the adult population was estimated to be 256 microSv; it was about 50% higher than that after the nuclear weapons tests.

Accidents↗

PubMed1995

Fractional absorption of ingested uranium in humans.

This paper provides a review and reanalysis of data relating to gastrointestinal (GI) uptake of uranium in humans. Estimates of GI uptake of uranium in adult humans have been derived from results of three controlled experimental studies involving short-term oral intake of an elevated quantity of uranium in fluids, from a controlled balance study conducted in a metabolic research ward of a hospital, and from a variety of environmental studies in which urinary uranium could be related to total intake or total excretion of this element in the same population. For controlled studies, uptake values range from less than 0.1% to about 6% for individual subjects, with central values for different studies falling in the range 1-2.4%. Environmental studies yield central estimates in the range 0.3-3.2%. Expressed as a percentage of total intake of uranium in food and fluids, average GI uptake of uranium in adult humans appears to be about 1-1.5%. Limited intake and excretion data for environmentally exposed human subjects > or = 5 y of age do not reveal important differences with age in uranium uptake, but more definitive information is needed for children. More information is also needed to determine whether fractional uptake of uranium increases with decreasing levels of intake and whether uptake from drinking water is substantially higher than uptake from food. Data for laboratory animals indicate that fractional uptake of uranium depends strongly on the chemical form ingested and the length of time since the last intake of food.

Animals↗

PubMed1995

Prevalence of lens changes in Ukrainian children residing around Chernobyl.

The objective of this study is to determine the prevalence and characteristics of lens changes in the eyes of a pediatric population, 5-17 y old, living in the permanent control zone around the Chernobyl nuclear reactor and to compare these findings with those from an unexposed control population. A total of 1,787 children are reported on (996 exposed and 791 unexposed). Over three-quarters of the subjects examined in this study show a form of minor change, termed focal lens defect, in the cortical and/or nuclear portions of the lens of the eye. The exposed group shows a small (3.6%), but statistically significant excess (p = 0.0005) of subclinical posterior subcapsular lens changes similar in form to changes identified in atomic bomb survivors. These posterior subcapsular changes tend to occur in boys 12-17 y old and in exposed children who report consuming locally grown mushrooms on a regular basis.

Adolescent↗

PubMed1995

Uptake of 137Cs in vegetable crops grown on a contaminated lakebed.

Mean concentrations and plant:soil concentration ratios of 137Cs were determined for six vegetable crops grown on an exposed, contaminated lakebed of a former reactor cooling reservoir in South Carolina. Each crop species was grown with or without potassium fertilizer. Selected crops were also irrigated with either reservoir water or groundwater. Subsamples of crops were prepared for human consumption before analysis to determine the extent of any loss. Plant:soil concentration ratios (dry basis) ranged from 0.22 to 6.82, values which were substantially higher than those used in generic assessment models. While there was no statistically significant effect of irrigation source or culinary preparation, the effect of potassium-fertilizer was dramatic. In many cases, concentrations of 137Cs in those plants receiving potassium were less than half of the concentrations in plants that did not receive potassium. Significant differences among species and plant parts for 137Cs concentrations were observed. Dose/risk calculations for the ingestion of these vegetables by a hypothetical 30-y resident indicates the possibility of a lifetime fatal cancer risk well-above the U.S. Environmental Protection Agency's regulatory guideline of 10(-4).

Biological Transport, Active↗

PubMed1996

Internal exposure from the ingestion of foods contaminated by 137Cs after the Chernobyl accident. Report 1. General model: ingestion doses and countermeasure effectiveness for the adults of Rovno Oblast of Ukraine.

The Chernobyl accident, which occurred in April 1986, resulted in the atmospheric release of about 70--100 PBq of 137Cs. This paper examines the doses to the adult population of the northern part of Rovno Oblast, Ukraine, from ingestion of 137Cs. Fallout of 137Cs in these regions was lower than in other regions of Ukraine. However, the transfer of 137Cs from soil to milk in the region considered is high (up to 20 Bq L-1 per kBq m-2) and results in the predominance of internal doses compared to those from external exposure. Numerous measurements of 137Cs soil deposition, 137Cs milk contamination, and 137Cs body burden have been made in the area and form the basis of a general model of internal exposure from the ingestion of foods contaminated by 137Cs. This paper has two main purposes. The first is to develop the general phenomenological description of the process leading to internal exposure from the ingestion of 137Cs contaminated foods in the situation where different countermeasures are realized. The second is to apply the model for the adult population of the northern part of the Rovno Oblast (first report) for the limited time period of up to six years after the accident. The doses actually received by the adults are estimated to be four to eight times smaller than the doses calculated for the situation without countermeasures.

Adult↗

PubMed1996

Countermeasures for radiocesium in animal products in Norway after the Chernobyl accident--techniques, effectiveness, and costs.

Nine years after the reactor accident in Chernobyl contamination by radiocesium is still a significant problem in sheep and reindeer production in Norway. To reduce the impact of the accident, effective countermeasures had to be developed and implemented. The levels of radiocesium in meat were reduced by a combination of countermeasures such as special feeding, use of cesium binders (bentonite and Prussian blue), and changing of slaughtering time. The countermeasures were labor intensive and expensive. Costs per averted dose per person-Sv were calculated to range from NOK 1,000 to 100,000 (7 NOK = $1 U.S.), with the use of cesium binders being the least expensive and condemnation of meat the most costly. Dietary advice, which did not include any compensation costs, had a cost of NOK 40 per person-Sv. Apart from the rejection of meat in 1986, countermeasures were deemed to be justified on a cost-benefit basis (less than NOK 600,000 per person-Sv).

Animals↗

PubMed1996

Long-term behavior of radiocesium in dairy herds in the years following the Chernobyl accident.

The longterm behavior of 137Cs in milk of a Bavarian farm (farm A) deposited as a consequence of the Chernobyl accident has been followed from April 1986 until August 1994. On the basis of activity measurements in milk and feed, transfer coefficients for the different seasons have been estimated in order to see any changes in transfer behavior (aging effect) of 137Cs with time. The influence of different grazing regimes has been tested by comparison of activity concentrations in milk and pasture grass in one farm (farm A with rotational grazing regime) with that of a nearby farm (farm B with continuous grazing regime) over a complete grazing season by frequent measurements in 1993. Though the farms are located only 4 km apart, have similar soils, and were contaminated to the same extent by the Chernobyl fallout, tenfold lower 137Cs activity concentrations in milk have been observed in farm B. This finding seems to be partly due to the influence of a different grazing intensity.

Animals↗

PubMed1996

A review of countermeasures to reduce radioiodine in milk of dairy animals.

The most effective countermeasure for radioiodine contamination of milk is to provide dairy animals with uncontaminated feed, with the added advantage that it will be effective for other radionuclides in the fallout. Another effective response is to process the milk into storable dairy products for an appropriate length of time to allow for physical decay. The use of additives given to ruminants to reduce radioiodine in milk is an alternative countermeasure which could be effective. Stable iodine administration is a practically feasible option which has the potential to reduce radioiodine levels in milk by at most a factor of three. Stable iodine supplementation should be at sufficiently high rates to be effective (and at least 1 g d-1 for dairy cows), particularly for ruminants already receiving high amounts of iodine in the diet. Currently available data are inadequate to recommend a suitable stable iodine administration rate for different species of ruminants. Other compounds, such as perchlorate and thiocyanate, also reduce the transfer to radioiodine to milk (and thyroid). Some of these compounds seem to be potentially equally as effective as stable iodine. However, currently there is inadequate information on their effectiveness and possible toxicity to both ruminants and humans for these compounds to be considered as suitable countermeasure additives.

Animals↗