Interaction

of Radionuclides with Organic Dissolved in Seawater

•\Interaction

•\

Department

of

Yuichiro

Radiocobalt

KIMURA

of Nuclear

Reactor

with

and

Amino

Yoshihide

Kinki

Higashi-Osaka,

Faculty

of Science

University,

Osaka, June

Acids

HONDA

Engineering,

and Technology,

Received

Some

Matter

Japan

14, 1976

The interaction of radiocobalt with glycine, alanine or aspartic acid dissolved in seawater was investigated by means of adsorption on Chelex 100, solvent extraction with dithizone or gel filtration chromatography. Although the distribution coefficients of Co on Chelex 100 decreased gradually with ageing even in the absence of organic matter, much more decreases were observed in the presence of the amino acids. The distribution coefficients on the resin reached equilibrium states in about 20 days. The extraction of cobalt with dithizone in carbon tetrachloride was also inhibited in the presence of the amino acids. Alanine and aspartic acid showed a similar interfering tendency in both adsorption on Chelex 100 and dithizone extraction, while glycine inhibited dithiz one extraction more than adsorption on Chelex 100. From the fractionation of Co by Sephadex G-10 gel filtration chromatography, the higher molecular species of Co associated with the amino acids occurred after several days ageing and then increased together with decreasing in the lower molecular species.

1.

Introduction It is known

that

radiocobalt

such as 58Co

zovic,

et al.2),3) and

gested cation

that most of cobalt occurs as a simple within few days ageing in seawater

Honda,

et al.4),5) sug-

by means of electrodialysis and paper electrophoresis. Fukai, et al.6) showed that divalent cations of cobalt are stable at the pH of seawater, unless the seawater contains sufficient adsorbents. Although these considerations and experimental facts are not sufficient to determine the chemical form of

and 60Co are among the major neutroninduced radionuclides occurred in the cooling water from nuclear power reactors. Although the levels of radiocobalt are quite low in areas contaminated by reactor effluents, through the accumulation by aquatic biota, 60Co which has relatively long halflife of 5.3 years might possibly become critical in radioactive waste disposal operations. The physico-chemical states of radionuclides in seawater is of fundamental importance to redistribution and the uptakes by organisms. Some inf ormations on the

cobalt in seawater that divalent cation

medium, and/or

form may be present. On the other hand,

they indicate its hydrolyzed

it was

pointed

out

that the considerable part of cobalt in the marine environment was associated with the sediments and the transport of cobalt might be influenced by organic matter in seawater7). Duursma8) reported the interfering effect of leucine on the adsorption of cobalt on marine sediments. Suzuki and Ikeda9) also

physico-chemical characteristics of cobalt in seawater have been obtained. Sillen1) assumed the co-existence of Co2+ and solid CoOOH in equilibrium on the basis of the solubility equilibrium in seawater. Mara(7)

528

RADIOISOTOPES

reported acids

that such

partic

acid

tion

of

and

usual

by

the

inhibitive

on

cation chelate

with

as

and

the

the and

involved of

their

not

tion

with

usually

adsorption

in

on

traction

with

All

the

of

the

following

organic

constructed. of

(1) (2)

seawater, resin,

dithizone

and

such which

means

of

solvent gel

Two

ex-

filtration

Materials

,

seawater

content

300

in

1.5

specific

mCi/ml,

as

tope

supplied

100

ml/min final

95 the

acid

mCi/mg,

Japan

5.6

the

at

appropriate

ing

to

the

receipt

of

The

chlorinity

of

The

seawater

was

membrane the

filters

seawater N

sodium

The mesh ries

of

change Co2+ was

and

then

is

to

carbonate

19.00%.

using use.

0.45

The to

pH

8.1•}0.2

One

gm

efficient

solution.

(0.32

about

1

of

the

dry

hour,

and

supernate

(Ku).

terms The

of Kd

100:

used.

To

added

then

the is

assay ageing.

Chelex

The

in

aliquot for

weight)

counting. in

An

were

sample.

for

15•}2•Ž.

during on

about

carrier

taken

was

of

and

of

was

(the

of

cobalt

intervals

tube

men-

capped

rate

10-7M.

cobalt

g

above

seawater

flow

of

technique

gamma

expressed

100,

sodium from

Richmond,

form,

100-200

Bio-Rad

a 1 ml

and

5 ml

mixture

was

centrifuged.

was

analyzed

The

results

by are

distribution represented

50 of

coby

the

California. was

1 g

washed equilibrated

of

estimated oven

3 times

The to

dried with with

/ G Kd=C0-C/C•~V

Laborato-

be

meq

resin. distilled the

where C0 is the activity in the seawater solution before equilibrium (cpm), C is the activity in the supernate after equilibrium

ex-

3.0

The

(cpm), V is the volume of the seawater solution (ml). G is the dry weight of the resin introduced into the system (g). The percentage adsorption is given by

water artificial

seawater. Dextran

temperature

centrifuge

5.61 X 10-4

was

of

the

of

50 mg/l

formulation,

obtained

per

ml

gross

of with

were

4 flasks

flask

a

samples

seawater

the into

Each

time

100

the

stirred

resin:

capacity

resin

Fleming11)

seawater

adjusted

of

of

at

was

batch

Chelex

accord-

and

filtered

prior

Chelex was

Lyman the

was

Chelating

prepared

systems

evaporation

seawater

glass

each poured

aerated

Adsorption

Radioiso-

: was

experiments

acid 50 mg/1, 3.76x

each).

at

system

ml seawater

the

50 mg/l,

concentration

of

Association.

Artificial

for

hydrochloric

by

in

procedures

ml

the

The

The

Seawater

0.1

N

activity

is

quality.

was ml

prevent

each CoC12

material

experimental

hundred

tioned

to

Radiocobalt: 60Co

this

seawter+l-a-alanine M+60Co, (4) seawater+l-aspartic 10-4 M+60Co.

interac-

acid by

chelating

,

molecular

seawater+60Co, (control), seawater+glycine hydrochloride , 4.48x 10-4 M+00Co,

have

Experimental

solution,

used

Experimental

continuously

2•E1

for

reagent

The

acids

aspartic

Chemicals

nominal

limit

chemicals

were

chromatography.

2.

The

(3)

with

40-120

Fine

Chemicals:

compounds

amino

and

exclusion

2.2

features

some

alanine

used.

waters.

the mechanisms

deals

weight

Mur-

understood.

paper

cobalt

glycine,

occur

and

was

size

particle

Pharmacia

as well

of

organic-metal

clearly

present

of

as

nature

G-10, by

Uppsala

well-known

in natural

physico-chemical

yet been The

is

Sephadex produced

No.9

700.

of some

in seawater

which

chemical

formation

and

occurrences

cobalt

on

m,

of amino

Fukai

compound

the

compounds

constant

ions.

ƒÊ

adsorp-

dominated

formation

cobalt

on the was

organic

However,

acid

The

as-

sediments

cyanocobalamin

organic

amino

marine

cobaltous

of

of leucine,

exchanger

ray10) demonstrated forms

effect

alanine,

glutamic

cobalt

an

acid

the

as glycine,

Vol.25,

gel:

(8)

Kd

Sept.

Y. Kimura,

1976

et al.:

Interaction

of radionuclides

with

Hitachi %

Adsorption=C0-C/C0•~100

Extraction carbon a

the

separatory

Cobalt

carbon

tetrachloride for 3

The

minutes.

A0

before the

The

changes

of

cobalt

of

the

(Kd)

of

cobalt

of

ageing

function

seawater

Discussion of

are

on

values on

time

shown

in

Chelex

of

Chelex

of

Fig.

100

distribution 100

cobalt

as

in

the

1.

dithi-

extraction

extraction

was

is

is

given

by

A0-A/A0•~100

the

activity

extraction

tion

in

the

(cpm),

aqueous

aqueous

A

phase

is

after

3

phase

the

activity

times

extrac-

(cpm). Gel

filtration

The was

at

the

sample

with

the

with

room

(15ƒÓ•~830

filtered

temperature.

seawater

the

column

equilibrated

seawater of

chromatography:

chromatography

mm)

sample was

was

eluted

filtered

artificial One

applied

by

seawater

ml

each

and

then

downward at

a

flow

flow

rate

of

ml/h. Each

5 ml

using

of

the

fraction by

aliquot

of

gross

gamma

metry

for

which

were Kd

represented

=Vs-VB.D./

effluent

was

collector

manufactured

The

The

a

ml

Adsoption

times.

Extraction=

where

10 0.05%

and

3•E1

coefficient

the

distilled

into

containing

percentage %

extracted

5.88%

then

with

Results

5 ml

of

and

15 ml

Spectrophotometer

used.

in

added

1 ml

solution to

was

30

repeated

and

citrate diluted

water.

zone

were

sample

was

dithizone

529

matter

Perkin-Elmer

139 was

3.

funnel

sodium

mixture

20

with :

seawater

(w/v)

in

cobalt

tetrachloride12)

To of

of

Model

organic

Toyo

each

Sangyo

effluent

was

counting amino

acids

used

values

for for

by

the

Fig.

collected

Model

1

Co.

Ltd.

analyzed

An by

Although

and

spectrophoto-

ageing

and

Blue

much

Dextran

column

calibration.

fractionated

cobalt

Changes Chelex time.

SF-160K

time more

observed is

such

formulation,

VTHO-VB.D.

of

Kd

100 as

the

Kd

even

in

values the

decreases in

the

as glycine,

values

decreased

in the

alanine

seawater.

These

ally

toward

equilibrium

and

decreases

amino

aspartic

with

were acids acid

trended about

ageing

seawater,

Kd values of

in

60Co on of

control

presence

the

of

a function

in

gradu-

20 days.

On the other hand, the percentage adsorption of cobalt in the control was more than 97% during 36 days ageing, while those of cobalt in the presence of glycine, alanine and aspartic acid were 85.5%, 54.1% and 72.0

where Vs is the effluent volume of 60Co (ml), VB,D, is the effluent volume of Blue Dextran (ml), VTHO is the effluent volume of tritiated water (ml). Measurement of activity: The activity of each sample was measured using Auto-well gamma system Model JDC-752 manufactured by Aloka Co. Ltd. The standard deviation of each measurement was less than 10%. Spectrophotometry:

% in 36 days, respectively (Table 1). The Chelex 100 has an unusually preference for copper, cobalt heavy metals over such rations potassium, are major dium form (9)

high

and other as sodium,

magnesium and calcium which cations in seawater13). The soof Chelex 100 is represented by

530

RADIOISOTOPES

Table

1

Vol.25,

Interfering effects of amino acids on the adsorbtion in seawater

and extraction

formulation,

eospecificity

< CH2-COO-Na+

enter

R-N

As

of

the

its

resin,

as

discussed

36 days ageing)

complexes, did

will

IDAA

above,

9

of radiccobalt

(After

the

No.

or

some

not

glycine16).

organic

cobalt

CH2-COO-Na+ complexes, where

R

represents

the

co-polymer

especially

takes

carboxyl

groups

cobalt

ions

are

in

contact

pounds and

Ting14)

Chelex

al.15)

of

also

up

as

for

an

tend

Loewenschuss,

et

chelating

resin acid

as

a

chelating

metal-resin

the

3•E2 in

hydrolytic

cobalt negative

form

charged

is be

products

medium, might

might

since

the

electroneuproducts17).

Extraction

of

carbon

tetrachloride

cobalt

with

dithizone

The

cobalt. that

the

has

an

to

could

following

matter,

seawater

fraction which

(7.8-8.2)

Chelex

form

complexes

complexes. by

unsorbed

As

of

which

group

cobalt

resin.

alkaline

similar

metal-ligand-resin

represented

an

demonstrated

(IDAA)

possible

of

the

seawater

organic

the

and/or

the

control

dissolved

in

by

whereas in

A-1

of

towards

oxidation

Dowex

iminodiacetic

mixed

al.16)

tied

resin.

seawater

the

tral

retained

hand,

the

to

cobalt

hydrolysis

available

unstable

Co3+

of

favor

case

et is

not

environment,

pH

to

is

is

to

The

would

organi-

Co(III)

chelating

acid

of

Callahan,

the

Co3+

air-oxidized

medium.

as

the

the

from

be

other in

attributed

resin,

cyanocobalamin

and

them15),

in is

100

that

by by

of

forms.

complex

exchange

reduction

as

ionic

strong

indicated

0.6%

such

the

suggested

a

Co2+

only

the

cobalt

free

Lowman

chelating

might

On of

com-

100.

the

two Thus

chelate

Chelex that

cobalt

91%

to

with

the

nitrogen.

converted

retained

bound

and

between

tertiary

reported

100

cally

place

and

the

matrix. glycinate

Coordination

in

the

as

well

reactions

are

formulas,

M+L•¬ML ML+R•¬MLR where

M

ligands

is in

complexes, mixed ever, tate because

metal the

ions

R

is

metal

ions

its

bound as

bulky

solution, is

L

MLR

complexes. to

EDTA molecules

the

is How-

a large or

is

metal-ligand

resin,

resin

such of

the

ML

chelating

metal-ligand

ligand,

in

solution,

polydenlike, and

which, the

Fig. 2

Extraction carbon

ster-

(10)

of 60Co with

tetrachloride.

dithizone

in

Sept.

Y. Kimura,

1976

et al.:

Interaction

of radionuclides

The results of the extraction of cobalt from the seawater with dithizone in carbon tetrachloride are shown in Fig. 2. From these results, more than 97% of

with

organic

matter

531

cobalt (II) complexes with the amino acids and dithizone (logK1K2: aspartic acid > glycine > alanine > dithizone)18), complexes with the amino acids

the cobalt are more

cobalt in the control seawater was extracted in 36 days ageing, while the percentages of extraction of cobalt in the presence of the amino acids decreased with ageing time and gradually trended toward equilibrium. Lowman and Ting14) reported that the extraction of cobalt into dithizone in organic solvent removed only 1.3% of the cyanocobalamin from seawater, but extracted 970 of the ionic cobalt. Compared the results from the solvent extraction with those from the adsorption on the chelating resin, a similar interfering tendency was observed in both alanine and aspartic acid, while in the case of glycine, somewhat different result was obtained. Namely, the interfering effect of glycine on the extraction of cobalt with dithizone was greater than that on the adsorption on the chelating resin (Table 1). This fact might be attributed to the possibility of the formation of cobalt-glycine-resin complexes. Taking account of the stability constants of Table

2

Fractionation

of radiocobalt

Fig. 3

Fractionation

in seawater

by Sephadex

G-10 gel chromatography ( Column Flow

Standard

deviation

of

Kd

Standard

deviation

of

recovery:

of 60Co by gel filtration

chromatography.

value: •}0.1