AECL6795 ^ 1 ^

ATOMIC ENERGY wBh L'ENERGIE ATOMIQUEOF CANADA UMITED C f i j DU CANADA LIMIT£E

THE ENVIRONMENTAL BEHAVIOUR OF

URANIUM AND THORIUM

LE COMPORTEMENT ECOLOGIQUE DE L'URANIUM ET DU THORIUM

Marsha I. Sheppard

Whiteshell Nuclear Research Etablissement de RecherchesEstablishment Nuclei ires de Whiteshell

Pinawa, Manitoba ROE 1LOAugust 1980 aout

ATOMIC ENERGY OF CANADA LIMITED

THE ENVIRONMENTAL BEHAVIOUR OFURANIUM AND THORIUM

by

Marsha I, Sheppard

Whiteshell Nuclear Research Establishment

Pinawa, Manitoba ROE 1L0

1980 August

AECL-6795

LE COMPORTEMENT ECOLOGIQUE DE L'URANIUM ET DU THORIUM

par

Marsha I. Sheppard

RESUME

Par le passé, l'uranium et le thorium ont eu de nombreusesapplications, et leur emploi présent et possible comme combustiblesnucléaires pour la production de l'énergie est très important. Ces deuxéléments et leurs produits de filiation sont écologiquement intéressantsdu fait qu'ils peuvent avoir des effets à partir du moment où ils sontextraits du sol jusqu'au moment de l'évacuation finale du combustiblenucléaire épuisé. Pour évaluer l'impact sur l'environnement de l'emploiet de l'évacuation par l'homme de l'uranium et du thorium, on doit con-naître le comportement physique, chimique et biologique de ces éléments.

Ce rapport résume la littérature tout en mettant à jour et enétendant les examens antérieurs se rapportant à l'uranium et au thorium.Il examine les propriétés radiologiques, la chimie, les formes sous les-quelles on les trouve dans la nature, les interactions dans le sol, demême que les coefficients de distribution et les modes de déplacementpour ces deux éléments. De plus, il donne un résumé des concentrationsd'uranium et de thorium dans les plantes, des coefficients de transfertdes plantes, des concentrations dans les organismes vivant dans le solet des methods de détection.

L'Energie Atomique du Canada LimitéeEtablissement de Recherches Nucléaires de. Whiteshell

Pinawa, Manitoba ROE 1L01980 août

AECL-6795

THE ENVIRONMENTAL BEHAVIOUR OFURANIUM AND THORIUM

by

Marsha I. Sheppard

ABSTRACT

Uranium and thorium have had many uses in the past, and their

present and potential use as nuclear reactor fuels in energy production

is very significant. Both elements, and their daughter products, are of

environmental interest because they may have effects from the time of

mining to the time of ultimate disposal of used nuclear fuel. To assess

the impact on the environment of man's use and disposal of uranium and

thorium, we must know the physical, chemical and biological behaviour of

these elements.

This report summarizes the literature, updating and extending

earlier reviews pertaining to uranium and thorium. The radiological

properties, chemistry, forms of occurrence in nature, soil interactions,

as well as distribution coefficients and mode of transport are discussed

for both elements. In addition, uranium and thorium concentrations in

plants, plant transfer coefficients, concentrations in soil organisms

and methods of detection are summarized.

Atomic Energy of Canada LimitedWhiteshell Nuclear Research Establishment

Pinawa, Manitoba ROE 1L01980 August

AECL-6795

CONTENTS

1. INTRODUCTION

2. URANIUM

2.1 RADIOLOGICAL PROPERTIES 12.2 URANIUM CHEMISTRY 22.3 URANIUM IN NATURE 32.4 URANIUM IN SOIL 42.5 SOIL-URANIUM INTERACTIONS 62.6 SOIL DISTRIBUTION COEFFICIENT (K^) 82.7 MODE OF TRANSPORT IN SOIL 82.8 URANIUM IN PLANTS 92.9 PLANT TRANSFER COEFFICIENTS 102.10 CHEMICAL TOXICITY VERSUS RADIOLOGICAL INJURY 142.11 URANIUM IN SOIL ORGANISMS 152.12 METHODS OF URANIUM ANALYSIS 152.13 FURTHER RESEARCH 16

3. THORIUM 17

3.1 RADIOLOGICAL PROPERTIES 173.2 THORIUM CHEMISTRY 183.3 THORIUM IN NATURE 183.4 THORIUM IN SOIL 193.5 SOIL-THORIUM INTERACTIONS 213.6 MODE OF TRANSPORT IN SOIL 223.7 SOIL DISTRIBUTION COEFFICIENT (Kd) 223.8 THORIUM IN PLANTS 233-9 PLANT TRANSFER COEFFICIENTS 243.10 THORIUM IN SOIL ORGANISMS 243.11 THORIUM/URANIUM RATIOS IN NATURE 243.12 METHODS OF THORIUM ANALYSIS 253.13 FURTHER RESEARCH 26

4. ACKNOWLEDGEMENTS 26

REFERENCES 27

TABLES 33

FIGURES 38

1. INTROdUCTION

Since Becquerel's discovery of natural radioactivity in 1896,

uranium and later thorium have been of increasing interest, both geo-

logically and geochemically. Uranium has been used for ceramics, abso-

lute dating and military purposes. More recently it has been used to

determine the chemical weathering rates of rocks ' and as a nuclear

reactor fuel for energy production. Thorium has had a number of minor

uses but may become much more important as an alternate reactor fuel.

These elements and their daughter products are of environ-

mental interest because they may affect the environment from the time of

mining (or subsequently from mine wastes) to the time of ultimate dis-

posal of used nuclear fuel. These effects are more serious than those

produced naturally because the elements usually become more concentrated

spatially. To assess the impact of man's use and disposal of uranium

and thorium, we need to know their physical, chemical and biological

behaviour and that of their daughter products in the environment. This

report summarizes the literature pertaining to uranium and thorium in

soil-water-plant systems, and updates or expands previous reviews by

it a].(5)

Adams et al. , Ames et al. , Nishita et al. , and Johnston and

GillhanT

2. URANIUM

2.1 RADIOLOGICAL PROPERTIES

Uranium belongs to the group referred to as primordial radio-

nuclides, which have been present since the earth's formation. All the

isotopes of uranium are radioactive. The uranium isotopes found normally

- 2 -

in nature are U, U and U. These isotopes all decay primarily

by alpha emission, their half-lives are 2.4 x 10 , 7.0 x 10 and 4.5 x 10

years, and their isotopic abundances are 0.0054, 0.720 and 99.2746235 232

percent, respectively. Uranium-238, U and Th are the long-livev'.

parents of the uranium, actinium and thorium series t-hose decay schemes

are shown in Figures 1, 2 and 3 .

238Since U is the most abundant naturally occurring isotope of

238

uranium, further discussion will deal primarily with U unless other-

wise stated but, since the isotopes of uranium behave very similarly

chemically, the discussion will be pertinent to them also. Only in

specific natural locations, referred to as uranium anomalies, could

uranium present a radiological hazard to plants and animals.

2.2 URANIUM CHEMISTRY

Uranium exists in four valence states: U3+, U4+, U 5 + and U6+,

although only the tetra and hexavalent states are commonly found in

naturally occurring groundwater. Hexavalent uranium is invariably found2+

associated with oxygen as the very stable divalent uranyl ion (U0« )

and occurs whenever the electrochemical potential is oxidizing such as

in weathered rock and surficial material. Tetravalent uranium is found

in reducing environments such as in unweathered rock where a reducing

electrochemical potential is maintained.

The uranyl ion has the properties of a large, simple, doubly-

charged metallic ion . It tends to form compounds such as Na.UCL,

U0,(0H)2, UO-CO- and UO.SO,. This large ion is comparable in size to

potassium, rubidium and cesium, which are readily adsorbed by base

exchange on clays and other layer-lattice minerals. Langmuir and

Lemire and Tremaine reviewed uranium chemistry, and Hodge et al.

provided an extensive discussion of the chemical and physical properties

of uranium. In the soil-water-plant environment, we are chiefly con-2- -

cerned with the oxides of uranium and the uranium salts (CO- , F ,

- 3 -

SO^ , Cl , NO, , PO, ). Recently Langmuirv and Tripathiv ' showed

that fluoride complexes increase the solubility of uraninite two orders

of magnitude relative to its solubility in fluoride-free waters. The

phosphate ion also increases the solubility of uraninite . Uranium

has a high degree of mobility in water with low concentrations of calcium

salts, and it can be concentrated from water if the geochemical setting

is suitable<12).

2.3 URANIUM IN MATURE

As a primordial nuclide, uranium is contained within newly

formed rock masses. If the rock mass is not exposed to weathering,

uranium will eventually reach secular equilibrium with all of its radio-(13)

active decay products (Figure 1). Hansen and Stout have statedOIJQ nor

that, in a rock unaffected by weathering for a million years, U, U230

and Th are in secular equilibrium with their decay products (their

activity ratio is equal to one). However, exposure to weathering initi-

ates processes which cause disequilibrium .

(2)Adams et al. indicated that the uranium content of igneous

rocks ranges from 0.001 ug/g in ultrabasic rocks to 30 ug/g in alkaline

rocks. Silicic intrusive, extrusive and pegmatitic igneous rocks contain

1 - 7 ug/g uranium. The average uranium content in igneous rocks is 3 -

4 Ug/f» with the content generally increasing with increasing acidity

or silica content. The variation of uranium content within rock types

is usually larger than the differences among the averages for the various

types of igneous rock. The uranium content in metamorphic rocks varies

from 0.11 ug/g (marble) to 57 ug/g (orthoclase porphyroblast). The mean

uranium content in metamorphic rock is 7.0 Ug/g- The uranium content in

sedimentary rocks varies from 0.1 Ug/g (anhydrite) to 245 yg/g (phosphate

rock). This latter figure alludes to the radiological hazard involved

in handling large quantities of phosphorus fertilizers.

- 4 -

The trs.ce minerals, such as monazite, zircon and xenotime,

tend to contain uhe most uranium (100 - 35 000 ug/g). The major igneous

rock minerals, biotite, hornblende, potassium feldspar, plagioclase,

pyroxene, and quartz, contain 0.1 - 40 ug/g uranium. Thus we would

expect the amount of uranium in soils which have formed from the weather-

ing of igneous rocks to be probably no more and usually considerably

less than 40 Ug/g. One would also expect the amount of uranium in

finer-textured soils, which have developed primarily from the weathering

of sedimentary rocks, to be closer to the mean value for sedimentary

rocks, *v/ 4 ug/g.

A few values for the concentration of uranium in water, air

and plants are given for comparison. Natural waters contain 0.2 to

600 ng/L (0.0002 to 0.6 ug/g) uraniunr , and Adams et al. reported-4

an average amount of uranium in fresh water to be 1.0 x 10 Ug/g;

values as high as 0.46 ug/g have been reported for a mineralized aquifer.(2)

The uranium content of seawater ranges from 0.00036 to 0.0059 Ug/g •

Concentration of uranium in airborne particles at a particular site is

dependent on the concentration of uranium in indigenous soils, rocks and

water. Dust from industrial operations contributes to the uranium

content in airborne materials. Recorded air concentrations are very—12 3

low, varying from 3 x 10 g U/m for air sampled over Antarctica to

4 x 10 g U/m for air sampled over New York City . The amount of

uranium in plant material ranges from 0.1 - 100 ug/g with Astragalus sp.,

Sorbus aueuparia L., and several mosses listed as indicator plants

2.4 URANIUM IN SOIL

Soil consists of unconsolidated weathered rock of varying

mineral content and particle size with some incorporation of organic

material near the soil surface. As this unconsolidated material weathers,

a solum consisting of differentiated horizons, known as the A and B

horizons, develops. These horizons vary characteristically in colour

and structure, and in chemical composition. As weathering and soil

- 5 -

profile development continue and the system sustains plant growth, the

naturally occurring uranium is redistributed. Uranium in solution will

move to the plant root system, or it may be leached Into the groundwater.

Hansen and Stout reported that V is thought to have leached more238

readily than U in the earlier stages of rock weathering, hence the

usefulness of the U/ U ratio to determine weathering rates. The234 238 (13)

occurrence of more U than U in some topsoilsv indicates thatcapillary movement may be prevalent in some areas.

The decaying plant material, or organic mat, at the soil

surface is another Important factor determining the distribution of

uranium in soil. On upland areas, this mat varies from non-existent to

a thin veneer. However, In low-lying areas it can contribute to a

significant accumulation of uranium near the surface. Retention of

uranium by organic matter can also cause an enrichment lower in the

profile such as in a B , horizon, which contains illuviated organic

material. The nature and strength of the uranium-organic matter associ-

ation that is established depends upon the degree of carbonization(13) (12)attained by the humic material . Titaeva postulated that, under

oxidizing conditions, uranium is bound to peat by ion exchange. Peat

readily extracts uranium from natural waters, reducing U to U after

sorption onto the organic fraction . Szalay pointed out that the

sorption of uranium on peat or organic material is by cation exchange,2+ +

identical to the exchange of Ca or K and other cations in soil*.

Uranium content in residual soils is generally highest in the

A or top horizon, second highest in the C-horizon or parent material,(14)and next highest in organically enriched intermediate layers

Megumi and Mamuro reported that uranium content increases with

decreasing particle size below 100 urn, indicating that mineralogy and

The sorption reactions postulated may be precipitation of thereduced uranyl ion.

- 6 -

surface area are important factors in the retention of uranium by soil.

This observation tends to imply that a surface reaction is an important

retention mechanism. If uranium is held by cation exchange, the adsorp-

tion of uranium should be dependent on cation-exchange capacity.

Masuda and Yamamoto found that the adsorption of the uranyl ion was

not dependent on the cation-exchange capacity of the soil. This may

have been affectad by the conditions (pH, solution concentration) of

their experiment.

2.5 SOIL-URANIUM INTERACTIONS

Bird redrew some of the Langmuir Eh-pH diagrams to

describe uranium in groundwaters from a waste disposal point of view.

He pointed out that, in carbonate-free water, oxide and hydroxide com-

plexes predominate at all geologically realistic pH's (4-9). Therefore

most uranium ions will be positively charged. Uranium in a reducing

environment will be in the tetravalent form, which has a high affinity

for organic material* . Grabovnikov and Samsonova showed that

uranium in a carbonate solution could form negatively charged or neutral

carbonate and hydroxide complexes, which would be highly mobile in the(22)

soil-rock system. Yamamoto et al. proposed that uranyl ions are

most likely to be converted to uranyl carbonate complex anions. This(21)

agrees with Grabovnikov and Samsonova and suggests considerable

mobility.

The thermodynamic data for uranium suggest that any uranium

dissolved in natural water will be complexed by carbonate, hydroxide,

phosphate, fluoride, sulfate, and perhaps silicate ions and organic(8 9̂

materials . The fact that uranium forms complexes will greatly

increase its solubility in an oxidizing environment (i.e., the near-

surface layers). To assess the behaviour of uranium under oxidizing

Organic muds, black shales and decaying organic matter concentrateuranium to 350 ug/g.

- 7 -

conditions in soil or rock media accurately, the relative stabilities of

the various complexes with the number of ligands present in the system

must be known. The groundwater chemistry must be well defined. Very

little thermodynamic data for temperatures below 20°C are available for

the actinides and, in Canada at least, the groundwater and unconsoli-

dated media near the surface are probably below this temperature for

most of the year.

Since the uranium ion has a very large radius, it would be

expected to adsorb by base exchange onto clays and other lattice miner-(23)

als . Therefore much of the uranium in shales may be in the form of

adsorbed ions and not as discrete minerals. Shales, upon weathering,

form fine-textured soils which could contain adsorbed uranium, especially

those soils with high base exchange capacity. Langmuir , in fact,

suggested that this is a reduction process resulting in a considerably

less soluble uranium complex (PO, , CO., , etc.), which then precipitates

out.

2+The configuration of the uranyl ion (U0_ ), with the oxygen

atoms located colinearly, allows it to form a strong structure when-

adsorbed. This arrangement provides considerable resistance to mobility,(23)

particularly when adsorbed between the layers of carbonaceous material .

Megumi and Mamuro stated that the enrichment or depletion of natural

radionuclides, including uranium in soil, is influenceu by oxides of

iron and manganese. The effect of these oxides is to reduce the uranium

from U to U . Several references in the waste management literature(24) (25)

refer to waste immobilization using manganese oxides . Megumi238

treated soil samples containing U with three extractants: (1) ammo-

nium acetate, (2) ammonium oxalate, and (3) hydrochloric acid, which

removed 90%, 50% and 80% of the soil uranium, respectively. These

fractions may indicate the amount of uranium adsorbed, the fraction

associated with goethite on soil surfaces, and the amount which is

soluble, respectively.

- 8 -

Kovalevsky et al. , extracting uranium-enriched soils with

0.2 mol/L citric, tartaric, oxalic and acetic acids, concluded that 2 -

19% of the total uranium in the soil was mobile. The correlation of

uranium and phosphorus in sediments *" implicates uranium phosphate in

an immobilization process. Sakanoue y and Kuznetsov et al. reported

that phosphate precipitation quickly immobilizes uranium migration.(29)

Yakobenchuk ' analysed the total uranium content in Russian sod-

podzolic soils from the Ukraine, and found ''.hat the total uranium content

correlated with the oxides of silicon, iron and aluminum, suggesting co-

precipitation or inclusion.

2.6 SOIL DISTRIBUTION COEFFICIENT

The distribution coefficient or K, is a convenient method of

quantifying the geochemical reaction of a radionuclide:

„ _ nol U adsorbed/f; soild ~ mol U in solution/mL solution

This concept is restricted to equilibrium conditions. Johnston and

Gillham reviewed the limitations of K.'s and cautioned against their

use in geologic media and unconsolidated materials such as soil. Ames(3)et al. gave K, values for uranium in geologic media (Table 1). These

values were obtained under oxidizing conditions so the data are of

questionable value in a reducing environment, but no K, values for,,,4-furanium (U

literature.

4+uranium (U ) determined under reducing conditions were found in the

2.7 MODE OF TRANSPORT IN SOIL

Solution transport is one mechanism by which soluble uranium

may move vertically or horizontally in a profile. Downward movement

could be in response to the gravitational potential; upward movement

- 9 -

could be in response either to capillary action in fine-textured materials

or to forces exerted by plant roots extracting water from the surrounding

medium. Horizontal migration, often referred to as throughflow, is a

possible mechanism for transport, but is probably significant only when

coupled with gravitational potential in a sloping landscape. Seasonal

runoff-evaporation cycles then lead to a local concentration of uranium

near the surface in either temperate or arid regions.

Another mode of transport which seems to have been neglected

in radioactive solute modelling is transport by the particles themselves.

Particles move in response to gravitational forces, helped along by

turbulent water. The macroscale processes are usually considered

to be runoff and erosion. The microscale process could contribute

significantly to radionuclide movement where finely weathered minerals

such as biotite are loaded with the nuclide because of adsorption. This

mechanism is evident in Luvisolic soils which result from considerable

redistribution of soil particles over long periods of time.

2.8 URANIUM IN PLANTS

The concentration of uranium in plant ash depends on its

concentration and mode of occurrence in rocks, soils and waters, on the

physiology of the plant, and on the character of their adaptation to the

geochemical environment . Other factors include species, time of

year, plant part, soil availability of the element, and chemical composi-

tion of the countryrock • Usually high soil-uranium concentrations

impart high plant-uranium concentrations except in marshy areas, where

the plant-uranium content has been found to be lower than the soil-

uranium content.

In humid areas, primarily under reducing conditions, uranium

is in the tetravalent form and is associated with the organic material

prevalent in these areas. In arid regions, the uranium content in plant

- 10 -

ash exceeds that in soil, perhaps indicating that water stress and

uranium uptake may be related.

The highest uranium content in plants grown in the laboratory

or in the field is in the roots. An early observation^ ' ^ indicates

that uranium is adsorbed by the plant root and stored as a yellow deposit

in the cell nuclei of the meristem. This results in destruction of the

chromatin, and cessation of cell nuclear activity, preventing uranium(3"*)

translocation. Kunasheva postulated that uranium does not enter the

root tissue but is adsorbed onto the root surface. This raises the

question of the selectivity of roots to uranium. Vinogradov pointed

out that the apparent selectivity is attributable to insoluble calcium-

uranyl phosphates which are deposited on the root surface, allowing only

a small portion to enter the root sap.

Primitive plants (mosses, algae and microorganisms) tend to

accumulate more uranium than higher plants, and plant debris (dead

material) accumulates more uranium than living material in contact with

:e of(35)

uranium-enriched water . Sphagnum moss growing on the surface of a

uraniferous peat bog concentrated uranium to a level of 6.5 Pg/g

The uranium concentration in the light brown fibrous peat below the moss

contained 0.9 to 1.6 pg U/g and the more humified peat lower in the

profile contained up to 1290 yg U/g.

2.9 PLAiyr TRANSFER COEFFICIENTS

Plant uptake of elements has been described by the biological

absorption ratio (BAR), the concentration factor (CF) and the transfer

coefficient (TC)„ which are virtually the same and can be expressed as:

__ _ U concentration in plant (ytg/g ash)U concentration in soil or growing medium (yg/g ash)

- 11 -

In the literature, the uranium concentration in plants is

expressed as ng U/g dry plant or yg U/g wet plant. The uranium concen-

tration in soils is expressed as ug U/g dry soil. When plants are grown

in solution culture (often at unrealistically high concentrations), the

units are (pg U/g ash) per (ng U/mL solution). It is important to note

that the plant transfer coefficient is the ratio of the amount of radio-

nuclide (uranium) that is available to the plant (under specific nutrient

conditions of the experiment) to the total uranium in the growing medium.

It is important also from the terrestrial pathways viewpoint to distin-

guish between what is attached to the plant surface (root) as opposed to

what is physically inside the plant. Preparation of vegetables and

fruit for human consumption often involves washing and peeling. If the

transfer coefficient is to be meaningful, this distinction is necessary,

particularly for uranium since it may be associated with a calcified

shell adhering to the root surface and not be in the root itself.

The important assumption which underlies the use of transfer

coefficients is that there is a linear relationship between the concen-

tration of the element in the plant and the concentration of the element

in the soil or rock. Data extracted from the literature^ have been

plotted to test this assumption. Figure 4 illustrates this relationship

for peat-forming plants using the results of analysis for the exposed

parts (twigs and leaves) of plants growing on hydromorphic soil (soil

samples were taken from the 0.5 m depth). The plants consisted of

Betula (birch), Ericaceae (ledum), Alnus (alder), Saliaaoeae (willow),

Lavix (larch), sedge and herbs. There is no apparent linear relation-

ship for these plants, however the authors did find a linear rela-

tionship between the uranium concentration in moss ash and in the dry

residue of water, suggesting that the linearity assumption may only hold

for more primitive plant forms.

(

Data from Prister for the aboveground parts of oats,

wheat, millet, peas, potatoes, carrots, cabbage, radish and natural

- 12 -

grasses (Figure 5) do not indicate any relationship between the uranium

concentration in the plant and the soil. However data extracted from

Morishima et al. for radish leaves (Figure 6) do suggest that a

relationship exists and that there may be a minimum soil concentration

below which uptake does not occur. Figure 7, illustrating data from

Cannon , shows that there may be a linear relationship between the

plant uranium concentration and the uranium concentration of the under-

lying rock.

The data from Figures 4 to 6 have been combined in Figure 8,

illustrating that, over a large concentration range, the linearity

assumption may not present too serious a problem when used as an input

parameter in the dose assessment models.

The transfer coefficients for herbs, shrubs and trees range

from 0.0001 to 0.02, whereas those for mosses and peat range from 0.6 to

325 . The uranium contents of organs and tissues have been listed in

the order branches > bark > leaves (needles) > wood based on Pioea

obovata Ledeb., Sovbus auouparia L. and a birch referred to as "fluffy"

birch<38).

An acropetal gradient generally describes the distribution of(39)uranium. Kovalevskiy included cones in his analyses of the uranium

distribution in natural plants, and his order is cones > branches >

leaves (needles). Table 2 shows the average uranium content for these

different organs in six species of trees and shrubs. The data on cones

must be used with caution, however his order, branches > leaves (needles),(38)

was subsequently confirmed by Verkovskaja

Cannon stated that there is considerably more uranium

absorbed by plants from deposits of calcium-uranium carbonate and lime-

stone than from deposits of calcium-poor sandstone and shale. This(34)conflicts with the point made by Vinogradov that calcium-uranyl

- 13 -

phosphates prevent uranium migration into the root tap. The mosses,

Sorbus auauparia L. and Asvralagus sp., are indicator plants for uranium,

and have been used as prospecting aids by the United States Geological

Survey since 1943. Cannon' reported that the leaves of plants rooted

in an ore body contained 2 - 100 yg/g uranium. She also stated that,

through the growing season, the uranium content tends to increase in

evergreens but decreases in most deciduous species.

Although most of the early studies on uranium uptake were

conducted on species growing in uranium-rich areas, some recent studies

have included cereal grains, forage species and vegetables. For these

crops the effect of artificial fertilization on uranium uptake is impor-(37)

tant. Morishima et al. reported that the transfer coefficients of

uranium in cotyledons and the upper leaves of radish, pimento rid cucumbei

were higher than in the other parts (Table 3), and that the absorption

of uranium by radish plants under cultivation with an incomplete ferti-

lizer (nitrogen-potassium) is higher than that with a complete fertilizer

(nitrogen-phosphorus-potassium). He used nitric acid as an extractant,

which indicates mobile uranium only. He also indicated that the uranium

content in radish leaves increases with growth, as opposed to the decreas

shown in the roots. This is predominantly due to a greater biological

dilution factor, since the roots tend to grow faster than the leaves.

He also found that root crops and leafy vegetables contain a higher

level of uranium than other crops and, in agreement with Prister and

Prister and Drobkov , found that a growing organism is high in(42)

uranium content. Mordberg et al. reported a significant increase in

the uranium transfer coefficient for vegetables growing on contaminated(43)soil when the crop was irrigated. Morishima et al. showed that

uranium-rich irrigation water results in much higher transfer coefficient

than does contaminated soil (1 - 100 and 10 - 10 respectively).

Plants high in potassium and calcium have the lowest concen-

tration of uranium in their ash . However, Morishima et al.

obtained a better correlation between uranium and phosporous contents in

- 14 -

leafy vegetables than between the uranium and calcium contents. Further,

the availability of uranium to the plant is extremely important, varying

from 0 to 43% (extractable with HNOj) *• , and 1.5 to 3% of the total

uranium in the soil is mobile . Garner reported that the ratio

of uranium in plant material to that of mobile uranium in soil (based on

Hg U/kg dry wt.) differed by a factor of 10 between individual plants

examined. For grains and legumes, tubers, roots and hay, the factor was

only a little above one. Starchy root vegetables are said to constitutefl4)

the most important source of ingested uranium in United Kingdom diets .

Prister and Prister stated that the uranium content in the dry

matter is three times greater for vegetative than for reproductive

organs.

From an environmental viewpoint, the stabilization of uranium

tailings is important, and several grasses have been chosen by Moffett(44)

and Tellier for this purpose. These authors reported that the

uranium content of dry matter grown on tailings was 0.041, 0.019, 0.044

and 0.017 yg/g for creeping red fescue, reed canary grass, redtop and

Climax timothy, respectively. The mean uranium content was approximately

16 pg/g in tailing material most of which was sand size. Uranium content

in the plants was slightly higher in the finer-textured tailing material.

This may be the result of a different moisture and/or chemical regime.( 26)

Kovalevsky et al. found the uranium content in plants growing on a

uranium anomaly (5.3 x 10~ to 1.5 x 10~ % U dry wt.) to be 5 to 85

times greater than in plants from a control zone (1.3 x 10 % U dry

wt.). They indicated that uranium uptake is accomplished by ion exchange,

or by formation of a complex with the organic acids given off as root

exudates.

2.10 CHEMICAL TOXICITY VERSUS RADIOLOGICAL INJURY

Uranium may be a micronutrient for the higher plants

However the amount required must be extremely small since concentrations

- 15 -

above a very low level retard root growth or are toxic. In the 1930's,

chemical toxicity was observed in roots of plants growing in solutions

containing more than 50 pg U/g root. Jacobson and Overstreet demon-

strated that radiation injury to the roots is severe when the mean

activity of uranium in soil at the region of contact is 0.1 uCi*/g.

Thus 0.1 uCi/g soil would be equivalent to 1.4 x 10 yg U/g soil. This

concentration would cause chemical toxicity. There appears to be little

information in the literature to indicate what levels of uranium are

toxic to various plant species. It is difficult to determine whether

reduced growth, or death, of the plant was due to chemical toxicity or

radiation injury. This problem appears to plague most studies on plant

uptake involving relatively high concentrations of radionuclides.

Radiation damage at naturally occurring uranium levels is usually ex-

pressed as morphological variability (double flowering, leaf splitting,

etc.) and can be observed in 10 to 20% of the plants of a particular

sPecieS<26>.

2.11 URANIUM IN SOIL ORGANISMS

There are few references to uranium accumulation in soil

organisms, although organisms such as earthworms are important in soil

mixing. Anaerobic bacteria are suspected of accumulating uranium, since

they create the best environment for its precipitation . Asotobaater

axe. apparently stimulated at concentrations up to 4.7 ug/g uranium and

inhibited at higher concentrations . Millot et al.s confirmed

from laboratory studies that microorganisms actively participate in(41)

remobilization of uranium in natural deposits

2.12 METHODS OF URANIUM ANALYSIS

A suitable method for field analysis of total uranium has been

given by Chamberlain '. Tewhey indicated that an estimate of the

1 Ci = 37 GBq

- 16 -

proportion of leachable and non-leachable uranium In samples can be made

on the basis of certain geochemical Indicators obtainable by multi-

element, neutron activation analysis. This is possible because of a

correlation between thorium and uranium ratios, and zirconium and lan-

thanum values. This procedure can replace acid-leaching experiments to(49)

estimate leachable uranium. Mateiciuc et al. discussed the use of238

neutron activation, to determine total U. The technique is based on

measurement of the delayed neutrons emitted by the decay of fission

products. It is important to distinguish between the activation products

and those naturally occurring in the sample.

Laboratories without reactor facilities utilize fluorimetric,

colorimetric, and radiological counting methods of analysis. James

indicated that wavelength-dispersive X-ray emission spectrometry appears

to be an excellent alternate method to neutron activation. All of these

techniques require the sample to be dry ashed and ground. It is particu-

larly important for the analysis of environmental samples (especially

plants) that only a small amount of dry ash be required, and that the

method be sensitive at very low levels of radioactivity (nano-pico Ci)•

It is also important to choose the correct procedure if leachable or

plant-available elemental contents are desired, as opposed to the total

amount.

2.13 FURTHER RESEARCH

To understand the movement of uranium in the environment

thoroughly, work should be carried out on the following objectives:

1. Determination of the K,'s (soil) and sorption mechanisms under

reducing conditions.

2. Clarification of the role of carbonates and phosphates in

uranium complexing and resultant mobility.

- 17 -

3. Definition of the role of the soil organisms in uranium migra-

tion and plant uptake.

4. Determination of what soil extractants indicate the amount of

soil uranium that is available to plants.

5. Determination of the root selectivity mechanism for uranium,

as well as its dependence on concentration, species, time of

year, soil pH, etc.

6. Determination of a capability to predict the chemical form of

uranium '- the soil-plant system given groundwater - soil

water composition, pH, Eh, rock-soil mineralogy, etc.

7. Determination of the effect of the nutrient status of the soil

on the uptake of uranium by leafy vegetables.

8. Assessment of the chemical toxicity limits versus radiological

injury levels for various plant species.

3. THORIUM

3.1 RADIOLOGICAL PROPERTIES

232The thorium isotopes normally found in nature are Th and

230

Th. Thorium-232 is the parent nuclide of the thorium decay series

(Figure 3), and thorium-230 is the short-lived isotope, commonly called

ionium, created by the alpha decay of uranium-234 in the uranium decay

series (Figure 1). These isotopes both decay by emitting an alpha10 4

particle. Their half-lives are 1.4 x 10 and 8.0 x 10 years respec-230 ?̂ ft

tively. More Th than U is found in the earth's crust. Thorium-232230

is significantly more abundant than Th, therefore, discussion will be232

limited to Th unless otherwise stated.

- 18 -

3.2 THORIUM CHEMISTRY

Thorium has generally been considered to be a lithophiiic4+ 4+

element of low geochemical mobility. Like U , Th is relatively

immobile since it is adsorbed tenaciously on cation-exchange resins and

is one of the last elements to be eluted when cation-exchange columns

are leached with 3 mol/L HC1 . Thorium forms metal complexes with

substances such as citric acid, oxalic acid and acetyl acetone, which

render it more mobile . In a similar manner, thorium can be leached

from soils and soil-clay fractions by various solutions.

Thorium occurs in nature as tetravalent ions. It cannot be

oxidized under geologic conditions to a hexavalent state to form an(2)

analogue of the uranyl ion . In solution it is quickly adsorbed or

precipitated as an hydrolysate, because of the very high ionic potential(2)

of the tetravalent ion . This is the reason for the low thorium/uranium(2)

ratio observed in natural waters. Adams et al. stated that, like

uranium, thorium is concentrated largely in accessory minerals such as

zircon, monazite and xenotime. Because it can be hydrated, thorium is

easily precipitated and adsorbed on or held by surfaces. Thorium also

forms radiocolloids which attach to other particles and are transported

in this manner

3.3 THORIUM IN NATURE

Because zirconium interferes with the micro-determination of

thorium, the average thorium content in various rock types (Table A) is( 52)

derived from very limited data. The Th/U ratio, given by Gera ,

varies from 3.2 to 6.2 for igneous rocks and from 0.5 to 30 for sedi-

mentary rocks. The Th/U ratio may be lower in metamorphic rocks (0.2 to(52)

13.5) . Thorium is found dissolved or suspended in very small quan-

tities in ocean water (5 x 10~ ng/g), although the uranium content is—3 (53)

3 x 10 yg/g • The reported range of concentrations of thorium in

- 19 -

seawater Is 4 x 10~ to < 5 x 10 Vg/g . Because of the affinity of

thorium for solid-phase material, Th produced by U decay settles(13)

on the ocean floor . Thorium is usually found in low concentration(14)in water, since it is readily precipitated and adsorbed . The thorium

—12 3content of air varies from 7.1 x 10 g Th/m for Algonquin Park,

—12 3Ontario, Canada, to 570 x .10 g Th/m over the industrialized area of

(52)northwest Indiana, U.S.A. .

In soils of the Russian plains, the thorium content ranges

from 2.3-14 ug/g with an average of 4 - 6 ug/g . Niuhita et al. '

listed thorium contents in soil ranging from 2.3 to 10 Vij/g. Tyury-(54)ukanova and Kalugina reported that thorium was distributed non-

uniformly in the soil profile. The lowest thorium concentration is

detected in the surface organic horizons, and the highest concentration

is found in the unconsolidated material close to bedrock. Accumulations

of thorium are often associated with a gleyed horizon, suggesting that

thorium accumulates under reducing conditions. The low thorium content

in peaty soils is apparently due to a low biogenesis and weak assimila-

uenc:(17)

(54)tion by bog plants . Surface area is a factor influencing thorium

content in soil particles less than 100 ym in diameter

3.4 THORIUM IN SOIL

(54)Tyuryukanova and Kalugina listed thorium content for

various soil types, forest floors, and forest vegetation. The values

range from 0.2 ug Th/g dry soil for the A-horizon of a peaty-gley soil

to 9.5 lag Th/g dry soil at 50-60 cm depth in a gleyed clay soil, with(52)

the average thorium content being 4 yg/g dry soil. Gerav ' and Vino-

gradov both reported an average thorium content of 6.0 yg/g in soil.

The thorium content of podzolic sandy soils is approximately

twice that in rock. In the eluviated horizon of a podzolic soil, the

thorium content is one-half that of an alluvial soil, and in sandy

- 20 -

ferruginized soils the thorium accumulates in the ferruginous-enriched

humus horizonv . There appears to be an association between the

distribution 01 thorium in the soil profile and the podzolic and hydrato-

genous accumulation processes.

Uranium and thorium redistributions in soil are complicated by

the intra-nuclear conversions which transmute one element into another.234 234

As soil profiles develop, Th disintegrates to U and eventually to230

Th. Thorium-230 frequently deviates from secular equilibrium withits parent IT . In a soil studied by Hansen and Stout^ , there

234 230was more U than Th present in the topsoil. In the deeper horizons230 234

the activity of Th exceeded that of U, demonstrating a separation

of uranium and thorium in the soil-forming process. Thorium-230 anom-

alies appeared more often in the alluvial soils than in the residual

soils.

Hansen and Stout* ' have shown that thorium leached from

organic layers reprecipitates in zones containing less organic matter.

Baranov et al. showed that soils high in organic matter have the

lowest Th/Ra ratio. Thorium is solubilized by humic acids in an ammonia

solution, by the formation of an anionic thorium-humic acid complex

Rancon identified four types of soil-thorium adsorption reactions:

(1) Th(OH), precipitation caused by calcareous soil buffering, (2)

strong adsorption on clay soils from dilute solutions (< 1 g Th/L solu-

tion, pH > 2 ) , (3) strong adsorption on organic soils under neutral and

acidic conditions, and (4) reduced adsorption in basic solutions causedby humic acid dissolution. By use of calcium-saturated reference clays

( 58"i(montmorillonite and kaolinite) and calcium humate, Bondietti studied

thorium adsorption from waters at pH ^ 6.5, and found 95% and 99.9%

adsorption, respectively. Calcium citrate desorbed 10-30% of the thorium

from the clays, but only 1% from the humate, indicating thorium is

strongly adsorbed to organic materials.

- 21 -

Hansen and Huntington reported that thorium may be subject

to cheluviation (complexation with organic substances and transported in

solution), but it may have a different pattern of translocation and

different conditions for reprecipitation than iron, which is commonly

cheluviated. Assuming similar initial concentrations, this could be

reflected in a more diffuse profile distribution for thorium than for

iron. The thorium distribution in the soil profile is apparently less

affected by change in pH than is the iron distribution. Vinogradov

was unable to detect thorium in soil solutions.

3.5 SOIL-THORIUM INTERACTIONS

Because thorium dees not crystallize out of basic magmas, it

is enriched in silicic magmas such as granites. It may be present in

simple isomorphous substitution for tetravalent zirconium, or as optically(59)

continuous inclusions of the isomorphic thorite (ThSiO,) . In well

crystallized, coarse-grained rocks, much of the thorium as well as the

uranium may be occluded, adsorbed on crystal imperfections, or fixed in

other dispersed sites before being concentrated enough to enter into the

stable mineral species^ . Picciotto^ indicated that thorium and

uranium occur in very small mineral or liquid inclusions in quartz.

Analysis of quartz in beach sands indicates that about 5% of the thorium

and uranium in granite can be expected to be similarly fixed

In addition to isomorphous substitution, the thorium as well

as uranium content of quartz, feldspar and ferromagnesian minerals may

be attributed to one or more of the following:

1. entrapment in lattice imperfections

2. entrapment in liquid inclusions

3. deposition along fracturesC2)

4. adsorption on crystal structures .

- 22 -

Iron and manganese hydrous oxides play an important role in immobilizing(25)

thorium through precipitation. Megumi stated that 90% of thorium is

surface adsorbed, 80% coexists with goethite and 80% is soluble in HC1,

when extractions are carried out on separate soil samples.

3.6 MODE Ot TRANSPORT IN SOIL

Evidence indicates that the transport of thorium in solution

is a very unimportant process. Since a significant amount of the thorium

in the environment is adsorbed onto clay-sized particles, or precipi-

tated, the major means of transport are by wind and water erosion, and

by mineral and/or organic particles moving through the soil system.

Baranov et al. stated that, unlike uranium, thorium in the natural

environment is transported primarily in the colloidal form. Dementyev

and Syromyatnikov concluded that thorium migrated in groundwater as

colloidal particles and as anionic complexes, the latter probably with

organic acids.

3.7 SOIL DISTRIBUTION COEFFICIENT (K.)a

Rancon* ' measured KjTh for both a clay soil and pure illite

at 0.1 g Th/L solution over a range of pH. Above pH 6, sorption is

complete and the KjTh > 10 mL/g. At pH < 2, the K,Th is less than

2 mL/g. In an organic-rich soil, the K, is very low above pH 7.6 due to

dissolution of humic acids which complex thorium. Calcareous soils

neutralize even concentrated thorium wastes and precipitate Th(OH),. In

soils of low calcium carbonate and low organic matter, the K.Th decreases

as the initial thorium concentration increases. The drop in K, is(57)

caused by sorption site saturation. Rancon y also showed that the

K.Th is concentration dependent to concentrations as low as 1 mg Th/L

(1 Pg/g).

- 23 -

3.8 THORIUM IN PLANTS

(34)Vinogradov stated that the thorium concentration in plants

is not known. Tyuryukanova and Kalugina cited researchers who

claimed that very little is known about the levels of thorium in plants,

but they suggested that, as a rule, the thorium concentration in plant

ash does not exceed its concentration in the soil. Thorium concentra-

tions in forest floor materials, mosses, lichens and grasses vary from

0.3 to 12 (Jg/g ash . The lower value is associated with green moss

and pine forest floor material; the higher value is associated with

CZadonia (a lichen). Bog plants are poor assimilators of thorium

Thorium is an essential plant micronutrient . It is

logical that thorium incorporation into plants depends on the solubility

of the thorium compounds in the soil. Hansen and Stout believe that

thorium accumulated by the plant comes from the secondary thorium mineral

fraction. They also stated that most of the thorium accumulates in aged

tissues such as the bark, branches and wood, and the least is observed

in annual organs such as the leaves. Table 5 shows the distribution of

thorium isotopes in the various parts of several plant species. The

variability in this data is apparently due to a highly uneven distribu-(62)

tion of nuclides in the soil or rock where the plants were growing

These data show that the location of the largest concentration of thorium

in a plant depends on the species. Siberian Larch (Larix siberiaa232

Ledeb.) has a higher concentration of Th in its needles and the

lowest in the xylem. Scots pine (Pinus silvestris L.), however, has the232

highest concentration of Th in the branches and the lowest in the

needles.

These data show that the ratios of thorium isotope concentra-

tions in plants of the same species growing in the same area vary consid-

erably . This is attributed to the fact that the ratio of thorium

isotope concentrations, depending on the depth in the rhizosphere layer

of the soil, varies within greater limits than the uranium isotope

ratios<62>.

- 24 -

3.9 PLANT TRANSFER COEFFICIENTS

D'Souza and Mistry carried out Th uptake studies with

red kidney beans (Phaseolus vulgaris L.) in solution culture, using a230

carrier-free solution with an activity of 0.25 uCi Th/L. Most of the

thorium added to the culture was taken up by the roots (76% of added)

and virtually none (0.09% of added) by the shoots. The transfer coeffi-

cient was 0.91 for shoots and 4185 for the roots. The transport index

(TI), defined as:

TI = Shoot ContentTotal Plant Content

was only 0.12,, illustrating that, in this experiment, virtually no

thorium is transported from the root to the shoot. As with uranium,

this raises the questions - is the root selective, is there a chemical

or biological mechanism involving a calcium phosphate complex, or is

there an organic complex formed by root exudates which ties up the

thorium at the soil solution - root interface? Data from Ng et al.(52)

and Gera suggest a transfer coefficient for waste management assess-—3

ments of 4.2 x 10 (resulting from a plant concentration of 2.5 x

10 ug/g and a soil concentration of 6.0 ug/g). This value is within232

the range (0.0001 to 0.007) found for Th for snap beans, millet,

soybeans and tomatoes by Bondietti and Sweeton . Titaeva et al.

reported a higher range (0.001 to 0.42) for uncultivated plants.

3.10 THORIUM IN SOIL ORGANISMS

Nothing has been found in the literature on this subject.

3.11 THORIUM/URANIUM RATIOS IN NATURE

The thorium/uranium ratio varies from 3 to 5 in granites and

ocks(34)

(2)other acid rocks . This ratio changes sharply in sedimentary rocks

because of the different behaviour of these elements. Vinogradov

- 25 -

showed the thorium/uranium ratio in carbonate rock varies widely (3 to(2)

80). Adams et al. reported a much lower thorium/uranium ratio in

metamorphic rocks (0.2 to 13.5). The average value for common shales is

3.8 ± 1.1, with a range from 0.01 for chert to 22 for some residual

bauxites .

The thorium/uranium ratio for soils ranges from 2.5 to 5.0 .

The higher ratio is associated with soils undergoing podzolization where

thorium is static and uranium is leached downward. Soils in areas of

uranium mineralization have the lowest thorium/uranium ratios. The

thorium/uranium ratio varies from 0.3 to 4.8 in Russian soils (assuming

radium is in secular equilibrium with uranium) • Megumi and Mamuro

reported a thorium/uranium ratio of 4.5 to 6 in soil particles of 0 -

100 nm in size and of 3.0 for particles > 100 um for soil of igneous

origin. Under certain conditions this ratio serves as an indicator of

weathering-intensity.

Vinogradov reported the thorium/uranium ratio in seawater

to be about 0.2, and Koczy et al. reported a value of < 10~ .

3.12 METHODS OF THORIUM ANALYSIS

( 68}Lieberman and Moghissi measured thorium by alpha-

spectrometry by co-precipitating thorium with a stable thorium carrier.

An average yield of 80% was achieved using this method. The sensitivity

of the technique was = 1 fCi/g. Samples as small as 1 g can be used.

D'Souza and Mistry co-precipitated Th fluoride with a

neodymium carrier, and measured its alpha activity in a low-background

ZnS(Ag) scintillation counter. Thorium has been measured with a colori-

metric method using arserazo III . James analyzed for thorium by

neutron activation or wavelength-dispersive X-ray emission spectrometry.

- 26 -

3.13 FURTHER RESEARCH

To elucidate thoroughly the redistribution of thorium in the

environment, more information is needed in the following areas:

1. Determination of the K.'s (soil) and sorption mechanisms under

reducing conditions.

2. Clarification of the role of carbonates and phosphates in

thorium complexing and resultant mobility.

3. Thorium content and assimilation mechanisms in soil organisms,

particularly since humus plays such a large role in thorium

immobilization.

4. Characterization of the mechanisms of translocation and repreci-

pitation.

5. Investigation of the possible existence of a selective mecha-

nism at the plant-root interface for thorium as is the case

for uranium.

6. Assessment of the chemical toxicity limits versus radiological

injury levels for various plant species.

4. ACKNOWLEDGEMENTS

I wish to thank Bruce Goodwin for his helpful discussions on

uranium chemistry and his comments on the manuscript. I would also like

to acknowledge the assistance of Keith Mayoh in preparing the computer

plots.

- 27 -

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44. D. Moffett and M. Tellier, "Uptake of Radioisotopes by Vege-tation Growing on Uranium Tailings", Can. J. Soil Science 57,417 (1977).

45. L. Jacobson and R. Overstreet, "The Uptake by Plants of Pluto-nium and Some Products of Nuclear Fission Adsorbed on SoilColloids", Soil Science 6^, 129 (1948).

46. M.G. Millot, G. Capus and C. Munier, "Mise en Evidence deFortes Concentrations d'Uranium dans les Corps Microbiens deMicro-organisms Actuel", C.R. Hebd. Seances Acad. Sci. Ser. D.Sci. Nat. 287, 191 (1978).

- 31 -

47. J.A. Chamberlain, "A Field Method for Determining Uranium inNatural Waters", Geological Survey of Canada, Paper 64-14(1964).

48. J.D. Tewhey, "The Distribution of Uranium in Sediment Samplesas Determined by Multi-element Analysis", U.S.G.S. Uranium-Thorium Symposium, 1977. pp. 43-45.

49. V. Mateiciuc, H. Constantinescu, T. Stadnicov and T. Burtic,"Analysis of Uranium in Geological Samples by the Method ofDelayed Neutrons", Stud. Cercet. Fiz. .31(3), 247 (1979).

50. G.W. James, "Low-level Determinations of Uranium and Thoriumby X-ray Spectrometry", U.S.G.S. Uranium-Thorium Symposium,1977. pp. 47-48.

51. R.O. Hansen and G.L. Huntington, "Thorium Movements in MorainalSoils of the High Sierra, California", Soil Sci. 108(5), 257(1969).

52. F. Gera, "Geochemical Behavior of Long-lived RadioactiveWastes", Oak Ridge National Laboratories Report, ORNL-TM-4481(1975).

53. E.D. Goldberg and M. Koide, "Geochronological Studies of Deep-Sea Sediments by the Ionium/Thorium Method", Geochim. Cosmochin.Acta 26, 417 (1962) .

54. E.B. Tyuryukanova and V.A. Kalugina, "Behaviour of Thorium inSoils", Soviet J. of Ecology 2, 467 (1971).

55. V.I. Baranov, N.G. Morozova, K.G. Kunasheva and G.I. Grigor'ev,"Geochemistry of Some Natural Radioactive Elements in Soil",Soviet Soil Science J3, 733 (1964).

56. V.A. Dementyev and N.G. Syromyatnikov, "The Form of ThoriumIsotopes in Ground Waters", Geokhimiya _2> 211 (1965).

57. D. Rancon, "The Behaviour in Underground Environments ofUranium and Thorium Discharged by the Nuclear Industry", inEnvironmental Behaviour of Radionuclides Released in theNuclear Industry. Proc. Symp. in Aix-en-Provence, May 13-18,paper IAEA-SM-172/55. IAEA Vienna, STl/PUB/345 (1973). pp.333-346.

58. E.A. Bondietti, "Adsorption of Pu(IV) and Th(IV) by SoilColloids", Agronomy Abstracts (1974).

59. H. von Buttlar and F.G. Houtermans, "Photographic Measurementof Uranium and Thorium Contents by Film Techniques", Geochim.Cosmochim. Acta 2^ *3 (1957).

- 32 -

60. E.E. Picciotto, "Distribution of Radioactivity in IgneousRocks", Bull. soc. beige g^ol. pal£ontol. hydrol. 5£, 170(1951).

61. E.G. Murray and J.A.S. Adams, "Amount and Distribution ofThorium, Uranium, and Potassium in Some Sandstones", Geochim.Cosmochim. Acta 13, 260 (1958).

62. N.A. Titaeva, A.I. Xaskaev, V. Ya Ovchenkov, R.M. Aleksakhinand I.I. Shuktomova, "Contents and Characteristics of Uranium,Thorium, Radium and Radon Uptake in Plants Growing UnderDifferent Radioecological Conditions", Soviet J. of Ecology 9_,328 (1978).

63. • T.J. D'Souza and K.B. Mistry, "Comparative Uptake oi Thorium-230,Radium-226, Lead-210, and Polonium-210 by Plants", Radiat.Bot. 10, 293 (1970).

64. Y.C. Ng, C.A. Burton, S.E. Thompson, R.K. Tandy, H.K. Kretnerand M.W. Pratt, "Prediction of the Maximum Dosage to Man fromthe Fallout of Nuclear Devices. IV. Handbook for Estimatingthe Maximum Internal Dose from Radionuclides Released to theBiosphere". USAEC Report URCL-50106 (Pt. 4) 1968.

65. E.A. Bondietti and F.H. Sweeton, "Transuranic Speciation inthe Environment", in Transuranics in Natural Environments,M.G. White and P.B. Dunaway (editors), Nevada Applied EcologyGroup, U.S. ERDA Report NVO-178 (1977). pp. 449-476.

66. V.I. Baranov, A.B. Ronov and K.G. Kunasheva, "The Geochemistryof Thorium and Uranium Disseminated in Clays and CarbonateRocks of the Russian Platform", Geokhimiya J3, 3 (1956).

67. F.F. Koczy, E. Picciotto, G. Poulaert and S. Wilgain, "Determi-nation of Thorium Isotopes in Sea Water", Geochim. Cosmochim.Acta 11, 103 (1957).

68. R. Lieberman and A.A. Moghissi, "Co-precipitation Techniquefor Alpha Spectroscopic Determination of Uranium, Thorium andPlutonium", Health Physics 15_, 359 (1968).

- 33 -

TABLE 1

DISTRIBUTION COEFFICIENTS FOR URANIUM*

Absorbing Material

river sediment

organic peat

low organic sediment

altered schist

pure quartz

pure calcite

illlte

Kd (mL/g)

39

33

16

270

0

7

139

from reference 57

TABLE 2

AVERAGE URANIUM CONTENT IN THE ASH OF DIFFERENT ORGANS OF PLANTS*

Genus

Betula

Populus

Loniaeva

Ribes

Larix

Pinus

Observations

20

21

9

5

5

2

Average U Content 10 %

Branches

14

18

18

25

22

5

Leaves(Needles)

8.5

17

12

22

11

5

Cones

85**

45**

Relative U Content

Branches

1.0

1.0

1.0

1.0

1.0

1.0

Leaves(Needles)

0.6

0.9

0.7

0.9

0.5

1.0

Cones

4

9

* from reference 39

** one determination

- 35 -

TABLE 3

URANIUM DISTRIBUTION IN PARTS OF

CUCUMBER, RADISH AND PIMENTO*

Vegetable

Cucumber

Radish

Pimento

Part

Leaves and StemsFruits

LeavesRoots

Leaves and StemsFruits

Uranium Distribution

GO

71.128.9

62.337.7

82.517.5

from reference 40

TABLE 4

MEAN THORIUM CONTENT AND RANGE IN IGNEOUS, SEDIMENTARY AND METAMORPHIC ROCKS*

Rock Type

Igneous

Sedimentary

Metamorphic

Mean Thorium Content(UB/S)

10

18

15

Content Range(yg/g)

3 - 18

1.1 - 60

0.03 - 67.7

Rock Type Associated with Range

basalts - granites

limestone - placers enriched inheavy minerals

marble - orthoclaseporphyroblasts

to

I

from reference 52

- 37 -

TABLE 5

THOR; !M ISOTOPE CONTENT (nCi/g OF ASH) AMD ISOTOPE RATIO

IN THE ABOVEGROUHD PARTS OF DOMINANT PLANT SPECIES*

Plant Species

Vicia oraooaDesohampsia caespitosaBromopeis inermisCar ex aquatilisAahillea millefoliwnChamenerion angustifoliumCirsium setosumSalia phyliaifolia (leaves)

Vicia avaaaaTri folium pratenseTrigloahin palustreCares aquatilisCalamagrostis epigeiousDeeahampsia aaespitosaTuBsilago farfaraAnthrisous silvestrisEquisetum arvenseRhinanthus majorGeranium pratenseHordeum vulgare (leaves)

Trifolium pratenseAnthrisous silvestris

Larùc sibirioaNeedlesBarkXylem

Pinus silvestrisNeedlesBarkBranches

Salix oapreaBarkBranchesXylem

Populus tremulaBranchesXylem

Betula pube8oens (leaves)

2

0-00-000

000000000002

00.0

0.0.0.

0.0.0.

1.0.0.

0.0.0.

=»2Th

.37

.09

.10

.04

.53

.51

.20

.5519682330637584561575

140465

341209

071723

401413

071113

230Th

Area

0-02--61

Area

391558140

1371-113

Area

100

00.0.

0.0.1.

3.0.0.

5.0.0.

1

.68

.15

.22

.60

.05

2

.2

60825212

65

547591

3

469287

592062

205817

434838

185548

22 8 T h

28.00.851.670.3221.81.973.7921.5

2.1715.00.639.420.5128.36.731.2875.80.870.26

129

0.920.310.88

0.540.273.08

4.6211.17.59

17.512.90.35

0.753.30

12.9

227Th

0.52--0.150.500.060.720.75

---0.94-26.4---0.116.50

0.75-0.81

0.330.17-

0.05__

-__

-_

230Th

TTTZxh

1-122--122

196282452190

2172-2111

10231

116

2.3.5.

2.3.2.

30.5.4.

.84

.67

.2

.4

.06

.3

.68

.7

.40

20

75742

4034

746789

864109

454392

50036

228ThTrreïh

75.7-18.63.20-49.37.15

42.1

10.827.33.8213.92.22

94.310.71.7190.21.551.7346.9

6.577.751.35

1.592.2534.2

66.065.333.0

12.592.12.69

10.730.099.2

from reference 62

234mPa(UXII)

238U(U

218.Th(Io)

214

210.22 a

Pb(Rad)

00

FIGURE 1: Uranium Series Decay Scheme (reference 6)

235'U(AcU) 231

7.13 x 108 aTh(UY)- 227

24.6 h

215Po(AcAr*" 3.9 s2"Rn(An)^_4.

211Pb(AcB) 21136.1 min Bi(AcC)

18.4 day

Po211(AcC)

FIGURE 2: Actinium Series Decay Scheme (reference 6)

232Th(Th)1.41 x 1010 a

»228Ra(M8Th.1 6.7 a

212

10.6 h

212Bi(ThC)

0.158 s

60.5 min

-228Ac(MsTh.) — £ — • • 228Th(RdTh)*• 6.13 n

1.91 a

216Po(ThA)-*-

220

52 s

2243.64 day

Ra(ThX)

212Fo(ThC')

0.3 us^TUDPb(ThD) (Stable)

l(ThC')

FIGURE 3: Thorium Series Decay Scheme (reference 6)

- 41 -

33.11

7.76

3.

04

1.82

0.43

10. I02

U in soil (pg/g)

FIGURE A: Uranium Concentration in Plant Ash/Soil (ug/g)for Betula, Ledum, Alnus, Larix and SedgeGrowing in Soil Derived from Granitic ParentMaterial. Reference 30.

- 42 -

(Jib

0-08

0.04

0.02

0.01

l

-

-

i

1 i

• -

•

-

0

I i

0.027 0.029 0.030 0.032

V in soil (yg/g)

0.033

FIGURE 5: Uranium Concentration in Plant Ash/Soil (yg/g)in Grain, Potato, Carrot, Cabbage, Radish andan Annual Grass Growing in a Mineral Soil.Reference 36.

- 43 -

3.16

63.1 79.4

U in soil (vg/g)

100. 125.9

FIGURE 6: Uranium Concentration in Plant Ash/Soil (pg/g)for Radish Leaves Growing in Sandy Soil Con-taining High Natural Concentration of Uranium.Reference 37.

- 44 -

O.I0.32 3.16 31.62

U in rock (yg/g)

3.I6XI02 316XI03

FIGURE 7: Uranium Concentration in Plant Ash/Rock (ug/g)for Several Plant Genera Growing in MineralizedRock. Reference 15.

- 45 -

3.98XI02

OS3 .

28.16

1.99

0.14

<

0.01

B

BB B B

• B B BBa

1 1

1

» /

fl B• • • B a

B a

t

-

0.027 0.479 8.32 I.44XI02 2.51 XIO3

U in soil (pg/g)

FIGURE 8: Uranium Concentration in Plant Ash/Soil (pg/g)as a Combination of Figures 4, 5 and 6.

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