CIESM Congress 2001, Monaco, article 0121

Rapp. Comm. int. Mer Médit., 36,2001

121

During the first weeks after the Chernobyl NPP accident, the

Sr concen-

tration in Black Sea waters increased by 7-20%, and

137

Cs activity doubled due

to atmospheric fallout [1]. Afterwards, the Black Sea was subjected to radioac-

tive contamination mainly through river discharge. The present paper deals with

an assessment and large-scale prognosis of pollution of Black Sea waters, biota

and sediments with

Sr and

137

Cs, using results of measurements and subse-

quent modelling [1-5]. The purpose was to estimate inventories and the time

scale of Black Sea ecosystem response to radioactive contamination, and to

assess time periods during of which the concentrations of

Sr and

137

Cs in

water, marine biota and the upper sediments may decrease to the pre-accidental

levels.

Methods and materials

The study was carried out in 1986-2000 on oceanographic vessels and in the

framework of radioecological monitoring of Sevastopol Bay with support of the

EU programs EROS-2000 and EROS-21, IAEA projects NR 7400 RB and

RER/2/003, and in collaboration with WHOI and EPA (USA). Intercomparison

of the measurements was fulfilled jointly with WHOI, EPA (USA), Riso

National Laboratory (Denmark) and IAEA.

Results and discussion

The study has shown that shortly after radioactive contamination of sea sur-

face with atmospheric fallout, a relatively rapid decrease in

Sr and

137

Cs con-

centrations in the ecosystem compartments was observed during the first year

(Fig. 1). In sediments adjacent to the Danube Delta, the

137

Cs concentration

increased up to 1991. During the following years a decrease in radioactive con-

tamination of waters, biota and sediments was found, and the trends may be suc-

cessfully approximated by exponential equations. This allows calculating

parametersAandpof the exponents:

q = A exp (- p t)(1)where q is in?ow or out?ow ?u

xes of radionuclide

(TBq), or radionuclide concentration in the ecosystem compartment (Bq m

Bq kg

) at time t (year); A and p are parameters. The time periods of decrease

to half of the original levels (half-lives) were calculated as T

= 0.693/p, and the

time for decrease of

Sr and

Cs concentration in wa

r, biota and sediments

to the pre-accidental levels were determined with 95% probability as T = 5 T

The predicted integral components of the Black Sea radioactive balance were

calculated from equation:

Q = A

exp (- p t) dt(2)

whereQis the predicted ?ux (TBq). The results of calculations using equations

(1) and (2) are shown in Tables 1 and 2. They suggest that the time scale of the

Black Sea ecosystem response to the Chernobyl-derived pollution ranges

between 21-73 years for

Sr and 11-77 years for

137

Cs.

References

1. EgorovV.N., Povinec P.P., Polikarpov G.G., Stokozov N.A., Gulin S.B.,

Kulebakina L.G., Osvath I., 1999.

Sr and

137

Cs in the Black Sea After the NPP

Chernobyl Accident: Inventories, Balance and Tracer Applications. J., Environm

Radioact., 43: 137-155.

2. EgorovV.N., Polikarpov G.G., Kulebakina L.G., Stokozov N.A., Yevtushenko

D.B., 1991. Modelling Large-scale Contamination of the Black Sea Caused by

Long-lived Radionuclides of

137

Cs and

Sr Following the Chernobyl Accident. In:

ComperativeAssessment of the Environmental Impact of radionuclides Released

During Three Major Nuclear Accidents Report EUR 13574 Press, pp. 649-664.

3. EgorovV.N., Polikarpov G.G., Mirzoyeva N.Yu., Kulebakina L.G., Artyomov

Yu.G., 2000. The Tendencies of Change of

Sr and

137

Cs Concentration in the

Water and Hydrobionts of the Sevastopol Bays After Chernobyl NPP Accident.

Marine Ecol., 50: 83-87 (In Russian).

4. Gulin S.B., Aarkrog A., Polikarpov G.G., Nelsen S.P., EgorovV.N., 1997.

Chronological Study of

137

Cs Input to the Black Sea Deep and Shelf Sediments.

Radioprotection – Colloques, 32, C2: 257-262.

5. Polikarpov G.G., Livingston H.D., Kulebakina L.G., Buesseler K.O., Stokozov

N.A., Casso S.A., 1992. In?ow of Chernobyl Sr-90 to the Black Sea from the

Dnieper River.J. Estuarine, Coastal and Shelf Sciences, 34: 315-320

ASSESSMENT OF THE BLACK SEA RESPONSE TIME-SCALE TO POLLUTION WITH 9

SR AND

137

FOLLOWING THE CHERNOBYL NPP ACCIDENT

EgorovV.N.*, Polikarpov G.G., Stokozov N.A., Gulin S.B. and Mirzoyeva N.Y.

Institute of Biology of the Southern Seas (IBSS), Nat. Ac. Sc. of the Ukraine, Sevastopol, Ukraine - viktor@egorov.sebastopol.ua

Abstract

This assessment summarises studies of

Sr and

137

Cs pollution of the Black Sea Basin carried out during the period 1986-1998 following

the accident at the Chernobyl NPP. Its goal is to assess the temporal evolution of

Sr and

137

Cs mass balance and inventories in some

typical Black Sea ecosystems. It was found that the time scale of the Black Sea ecosystem response to the Chernobyl-derived pollution

ranged between 21-73 years for

Sr and 11-77 years for

137

Cs.

Keywords: Black Sea, pollution,

90S

137

Cs, hydrobionts.

Fig. 1.Temporal variations in radionuclide concentrations in the Black

Sea

a and b – annual average

Sr and

137

Cs ?uxes with the Dnieper and Danube

river run-off; c –

Sr (_) and

137

Cs (+) out?ow through the Bosporus Strait; d

– change of

Sr concentration in front of the Dnieper-Bug estuary; e –

dynamics of

Sr (_) and

137

Cs (+) concentrations in the western mid-gyre; f

and g – change of 90Sr and 137Cs concentrations in Sevastopol Bays; h –

Sr concentration in algae Cystoseira crinita; i –

Sr concentration in mus-

sel Mytilis galloprovincialis (_) and fish Odontogatus merlangus (_); j –

137

Components

137

T0.5TT0.5T

In?ow from the Dnieper River (since 1987)

7.036.02.011.0

In?ow from the Danube River (since 1987)

14.473.06.935.5

Out?ow through the Bosporus Strait (since 1987)13.166.54.423.0

Surface waters near the Dnieper estuary (since 1989 )9.652.0------

Surface waters of the Central Western Black Sea (since 1986)15.6785.4

27.0

Danube Delta marine bottom sediments (since 1991)------14.477.0

Region of the Sevastopol Bay:

Surface waters (since 1987)

6.935.55.930.5

Brown seaweed Cystoseira crinita (since 1987 )4.021.04.423.0

Mollusc Mytilis galloprovincialis (since 1986)6.733.54.321.5

Table 2. Half – lives (T0.5) and complete response times (T) for mass balance

components in some ecosystems of the Black Sea Basin to the pollution

with 90Sr and 137Cs after the Chernobyl NPPaccident (years)Including peri-

od before an exponential decreasing.

90Sr (TBq)

137Cs (TBq)

Components ofInput/OutpuPrognosis ofTotalInput/outputPrognosis ofTotal

balanceAssessmentsconsequentAssessmentsconsequent

input/Output

input/output

Inventory in the

whole volume------

1500------1400

before 26.04.86

± 300

Atmospheric100-300---

1700-2400---

fallout in 05.86

In?ow from the90.2*57.8148.02.0*0.12.1

Dnieper River

In?ow from the24.5*32.857.324.0*13.637.6

Danube River

Out?ow through 94.0*130.2224.2225.0*64.7289.7

Bosporus Strait

Table 1. Mass balance components and prognostic estimations for 90Sr and

137Cs in the Black Sea Basin.Note: * - Estimations for the period 1986-1995