D.C. Aumann

Iodine-129 in the environment of a nuclear fuel reprocessing plant: VII. Concentrations and chemical forms of 129I and 127I in the atmosphere

Gaseous and particulate iodine samples have been collected simultaneously from the atmosphere around the Karlsruhe Reprocessing Plant (WAK) using a three-component sampler which separates the iodine into three fractions, namely: (a) associated with aerosol particles, (b) gaseous inorganic and (c) gaseous organic. These field measurements were conducted at five sampling sites located between 0·7 and 23·0 km from the WAK exhaust air stack in the dominant downwind direction. In 1986 the air samples were collected between October and December and in 1987 between June and September. The aerosol fraction of 129I in 1986 ranged between 5·2 and 30·8% and in 1987 between 1·7 and 9·7%. The corresponding values for 127I were 12·9 and 28·0% (1986) and 16·4 and 9·4% (1987). The gaseous inorganic 129I fraction varied between 26·8 and 35·2% (1986) and between 17·2 and 27·3% (1987). Corresponding 127I data were: 1·6 and 26·2% (1986) and 18·7 and 26·6% (1987). The gaseous organic fraction of 129I accounted for 34·0–65·9% (1986) and 62·9–88·8% (1987). Corresponding 127I values were: 46·1–73·8% (1986) and 59·3–71·9% (1987). A corresponding data set from a ‘control’ site in Bonn gave the following results: aerosol fraction: 129I: (6·0 ± 1·0) × 10−16 g/m3; 127I: (2·0 ± 1·9) × 10−9 g/m3; gaseous inorganic iodine: 129I: (1·1 ± 4·2) × 10−15 g/m3; 127I: (1·5 ± 0·9) × 10−9 g/m3; gaseous organic iodine: 129I: not detectable; 127I: (8·7 ± 3·5) × 10−10 g/m3.

Iodine-129 in the environment of a nuclear fuel reprocessing plant: I. 127I and 127I contents of soils, food crops and animal products

Abstract Concentrations of 129 I and 127 I in soils, food crops and animal products collected in the environment of the small Karlsruhe nuclear fuel reprocessing plant (WAK) were determined by neutron activation analysis. 129 I levels in all samples were found to be elevated by several orders of magnitude above current average biospheric background values. Resultant thyroid doses from consumption of food produced at locations in the vicinity of the Karlsruhe reprocessing plant are, however, small relative to the natural background dose.

Chemical and nuclear interferences in neutron activation of129I and127I in environmental samples

A combination of neutron activation and gamma-ray coincidence counting technique is used to determine the concentration of both long-lived fission produced129I and natural127I in environmental samples. The neutron reactions used for the activation of the iodine isotopes are129I(n, γ)130I and127I(n, 2n)126I. Nuclear interferences in the activation analysis of129I and127I can be caused by production of130I or126I from other constituents of the materials to be irradiated, i.e. Te, Cs and U impurities and from the125I tracer used for chemical yield determination. Chemical interferences can be caused by129I and127I impurities in the reagents used in the pre-irradiation separation of iodine. The activated charcoals used as iodine absorbers were carefully cleaned. Different chemical forms of added125I tracer and129I and127I constituents of the samples can cause different behaviour of125I tracer and sample iodine isotopes during pre-irradiation separation of iodine. The magnitude of the nuclear and chemical interferences has been determined. Procedures have been developed to prevent or control possible interferences in low-level129I and127I activation analysis. For quality control a number of biological and environmental standard samples were analyzed for127I and129I concentrations.

Iodine-129 in the environment of a nuclear fuel reprocessing plant .V: The transfer of 129I and 127I in the soil-pasture-cow-milk/meat pathway, as obtained by field measurements

Abstract A field investigation of the transfer of 129 I and of natural 127 I in the soil-pasture-cow-milk/meat pathway has been carried out at a dairy farm situated 5400 m to the north of the small Karlsruhe nuclear fuel reprocessing plant. Soil and herbage samples were collected during the period between April 1986 and April 1987. Milk samples were collected during the 1986 grazing season (28 April to 30 December) and again at the beginning of the 1987 grazing season. The concentrations of 129 I and 127 I were determined in all soil, herbage and milk samples. The concentrations of 129 I and 127 I in the soil samples (dry weight) were found to be: for 129 I, between 1·4 × 10 −13 and 7·1 × 10 −13 g/g (geometric mean 3·5 × 10 −13 g/g and for 127 I, between 2·2 × 10 −6 and 1·8 × 10 −5 g/g (geometric mean 6·3 × 10 −6 g/g). The concentrations of 129 I and 127 I in the samples of pasture vegetation (wet weight) were: for 129 I, between 8·2 × 10 −15 and 2·4 × 10 −13 g/g (geometric mean 4·1 × 10 −14 g/g) and for 127 I, between 1·2 × 10 −8 and 4·1 × 10 −7 g/g (geometric mean 5·0 × 10 −8 g/g). Those in the milk samples (wet weight) were: for 129 I, between 1·1 × 10 −12 and 1·1 × 10 −11 g/litre (geometric mean 3·4 × 10 −12 g/litre) and for 127 I, between 4·8 × 10 −6 and 3·1 × 10 −5 g/litre (geometric mean 1·4 × 10 −5 g/litre). From the concentrations of 129 I and 127 I in soil and pasture vegetation, soil-to-plant concentration factors for 129 I and 127 I in pasture vegetation could be calculated. Geometric means for the concentration factors for 129 I and 127 I for pasture vegetation of B v = 9·9 × 10 −2 and 7·9 × 10 −3 , respectively, were obtained. For the grazing season, the transfer coefficients for 129 I and 127 I from feed to milk could be determined. The F M values found were: for 129 I, between 2·6 × 10 −4 and 1·1 × 10 −2 d/litre (geometric mean 1·1 × 10 −3 d/litre) and for 127 I, between 3·5 × 10 −4 and 9·3 × 10 −3 d/litre (geometric mean 2·6 × 10 −3 d/litre). Since one cow and one calf were slaughtered during this field investigation, the transfer coefficients F f for 129 I and 127 I from feed to beef and veal could be determined. These were F f = (11±6) × 10 −3 d kg −1 and F f = (3·9±2) × 10 −3 d kg −1 for 129 I and 127 I, respectively, in beef, and F f = (3±1) × 10 −3 d kg −1 and F f = (0·2±0·06) × 10 −3 for 129 I and 127 I, respectively, in veal.

Iodine-129 in the environment of a nuclear fuel reprocessing plant: II. Iodine-129 and iodine-127 contents of soils, forage plants and deer thyroids

Abstract Concentrations of 129 I and 127 I in soils, forage plants and deer thyroids collected in the environment of the small Karlsruhe nuclear fuel reprocessing plant (WAK) were determined by neutron activation analysis. Levels of 129 I in all samples were found to be elevated by several orders of magnitude above current average biospheric background values. In particular, deer thyroids were found to have very high 129 I levels and corresponding high 129 I/ 127 I ratios. Using all the analytical data for 129 I and 127 I concentrations in plants it seems probable that there is a correlation between the 129 I and the natural 127 I concentrations in plants.

A study on the association of two iodine isotopes, of natural127I and of the fission product129I, with soil components using a sequential extraction procedure

Sequential extraction techniques have been utilized in order to investigate the degree of binding or association of natural iodine127I and the radioactive iodine isotope129I with soil components. The results indicate that only a small fraction of natural iodine (2.5–4%) but a large fraction of the recently added radioactive129I (38–49%) is water-soluble. The other forms of iodine which were determined for both iodine isotopes were exchangeable iodine, iodine bound to metal-oxides and iodine bound to organic matter.

Iodine-129 in the environment of a nuclear fuel reprocessing plant: IV. 129I and 127I in undisturbed surface soils

Abstract Concentration profiles of 129 I and 127 I in soils from the environment of the small Karlsruhe reprocessing plant have been measured at sites in the predominant downwind direction between 1100 m and 18 000m from the exhaust stack. The 129 I concentration profiles were analysed using a compartment model to estimate residence half-times in surface soils. Effective mean residence half-times in the top 30 cm of soil (the time required for half of a single deposition to pass through this layer) have been found to average 28·4±7·7 years, while the residence half-time within the uppermost 5 cm of soil average 9·0±3 years. Half-depths of 129 I in soil were also determined; they ranged from 4·2 to 10·9 cm with a mean of 7·6 cm.

Soil-to-vegetation transfer of natural 127I, and of 129I from global fallout, as revealed by field measurements on permanent pastures

Abstract Concentrations of natural 127 I and of 129 I which has been introduced into the environment as fallout from nuclear weapons testing were determined by neutron activation analysis in pasture vegetation and associated soils. The range of concentrations of 129 I ( 127 I) in the soils was between 2·0 × 10 −14 g / g and 1·9 × 10 −13 g / g (dry wt) (3·0 × 10 −8 g / g and 2·8 × 10 −6 g / g (dry wt) and in the pasture samples between 4 sd 3 × 10 −16 g / g and 6·9 × 10 −14 g / g (wet wt) (4·2 × 10 −9 g / g and 4·9 × 10 −7 g / g (wet wt)). The soil-to-plant transfer factors (concentration in vegetation (wet wt)/ concentration in soil (dry wt)) for vegetation of permanent pastures for 129 I ( 127 I) were between B v = 0·01 and B v = 1·05 and ( B v = 0·006 and B v = 0·27). Geometric means for the transfer factors for 129 I ( 127 I) for pasture vegetation of B v = 0·086 (0·024) were obtained.

Why are the soil-to-pasture transfer factors, as determined by field measurements, for 127I lower than for 129I?

Abstract Measurements of soil-to-pasture transfer factors of natural 127I and of 129I, which has been released to the environment through the exhaust air stack of the small Karlsruhe Nuclear Fuel Reprocessing Plant (WAK), and of 129I, which has been introduced into the environment as fallout from nuclear weapons testing, were performed between 1985 and 1989. The soil-to-pasture transfer factors for natural 127I are consistently lower than those determined for 129I. The mean of all the soil-to-pasture transfer factors presented in this work is Bν = (1·4 ± 0·4) × 10−1 for 127I and Bν = (9·0 ± 2·8) × 10−1 for 129I. An aqueous extraction has been utilized in order to determine the fractions of both iodine isotopes in soil which are leachable by water and thus available for plant-root uptake. The water-soluble fractions of 127I are between 2·5 and 9·7% and for 129I between 21·7 and 48·7%, respectively, indicating that most of the natural 127I is strongly bound to soil components. If different bioavailabilities of the two iodine isotopes are taken into account, effective transfer factors can be calculated. These effective soil-to-pasture transfer factors are similar for both iodine isotopes. (Bνeff = (2·2 ± 1·1) for 127I and Bνeff = (2·3 ± 0·9) for 129I).

Environmental transfer parameters and radiological impact of the Chernobyl fallout in and around Bonn (FRG)

Abstract Concentrations of 103 Ru, 131 I, 134 Cs and 137 Cs deposited in the fallout from the Chernobyl reactor accident in the environs of Bonn (FRG) and of the natural radionuclide 40 K were measured in soils, food crops, milk and pasture vegetation between May 1986 and September 1987. Soil-to-plant concentration factors and transfer coefficients from feed to milk were determined. Geometric means for the soil-to-plant concentration factors for 40 K and 137 Cs into pasture vegetation were obtained as B v = 0·54 and 4·2 × 10 −2 , respectively. The geometric means for the soil-to-plant concentration factors for 134 Cs, 137 Cs and 40 K for field-grown food crops were found to be 9·0 × 10 −2 , 2·5 × 10 −2 and 0·17, respectively. For the 1986 and 1987 grazing seasons, the transfer coefficients for 134 Cs, 137 Cs and 40 K from feed to milk, F M , could be determined. The F M values (geometric means) obtained were: for 134 Cs, 3·7 × 10 −3 (d/litre) and, for 40 K, 2·2 × 10 −3 (d/litre). For the 1986 grazing season, and F M value of 4·2 × 10 −3 (d/litre) for 131 I could also be measured. Concentration-depth profiles of 137 Cs have been measured in soil cores at two sites, a permanent pasture and an undisturbed area without vegetation. Using a diffusion-like model for the transport of 137 Cs in the soil core, a root mean square displacement of x ≅ 2 cm could be derived for the 3 year period following the Chernobyl accident. Resultant whole body doses from consumption of food containing 134 Cs and 137 Cs and produced at locations in the environs of Bonn were estimated at 14·7 μSv for 1986 and 0·56 μSv for 1987.