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ISSN 1064-2293, Eurasian Soil Science, 2006, Vol. 39, Suppl. 1, pp. S63–S68. © Pleiades Publishing, Inc., 2006.

INTRODUCTION

Soil is an important natural resource supporting theecological equilibrium on the planet. Soil fertility,which is partly formed due to the activity of microor-ganisms, is one of the primary soil characteristics. Soilcontamination with industrial pollutants leads tochanges in the microbiological activity of soils and to adecrease in their fertility.

Ions of heavy metals, being important micronutri-ents up to certain concentrations, become contaminantsin heavily polluted soils of industrial regions. Ions ofZn

2+

, Cu

2+

, Mn

2+

, Fe

2+

, and Co

2+

are the most wide-spread soil contaminants. In this relation, the study ofthe effect of increased concentrations of heavy metal(HM) ions on the chemical and physicochemical prop-erties and fertility of soils is an important task.

It is known that chemical elements are accumulatedin the biomass of organisms differently; for instance,the accumulation of Fe

2+

and Mn

2+

ions in the biomassexceeds the accumulation of Cu

2+

, Zn

2+

, Co

2+

, and Mo

2+

ions by many times. As follows from Table 1, the Fe :Mn ratio in sedimentary rocks and in ocean water isapproximately (8–9) : 1, whereas it is approximately1 : 1 in vegetation and 18.8 : 1 in soils. A significantaccumulation of Fe in the pedosphere points to the greatrole of soil microorganisms in this process.

A predominant accumulation of Fe in the pedo-sphere makes it possible to suggest that iron electrodesinstalled in the soil may be indicative of the soil micro-biological activity. It is known that iron is present insoils in the forms of Fe

2

O

3

and Fe(OH)

3

that are dif-ficultly available to organisms in contrast to Fe

2+

ionsthat may participate in the biochemical processes.These ions are formed on the surface of iron elec-trode in the outer layer of the double electric layer[2]:

M

–

ne

M

n

+

. Many microorganisms (bacteria,bacilli, microscopic algae, and fungi) can transformHM ions into complex organic compounds. This trans-

formation proceeds in the course of metabolism in par-allel with the metabolic transformation of macronutri-ents P, N, K, S, and Ca that are present in the substrate.Therefore, microorganisms and plants are used for soilpurification purposes [3].

In 1988, Japanese scientist Teruo Higa studied about3000 microorganisms and found that their regenerativeand degenerative functions are interrelated. He alsofound that only about 5% of pathogenic microorgan-isms are leaders. Other microorganisms can changetheir orientation towards leaders. Teruo Higa selected86 leading regenerative strains, which perform all thefunctions related to the nutrition of plants, their protec-tion from diseases, and improving soil conditions.

Soil Contamination with Heavy Metals and Possibility for Its Remediation

N. I. Melekhova, S. V. Semashko, E. A. Gorskaya, and A. V. Troshina

Tula State University, pr. Lenina 92, Tula, 300600 Russia

Received March 15, 2003

Abstract

—The problems of changes in soil fertility under the impact of industrial contaminants and of reme-diation of soils polluted with heavy metals are discussed. It is shown that Fe(II) ions may serve as soil remedi-ators. It is also shown that changes in the soil microbiological activity can be estimated by the electrochemicalmethod from data on the potential of the biologically active iron electrode.

DOI:

10.1134/S1064229306130114

Table 1.

Distribution of heavy metals between the sedimen-tary mantle of the lithosphere (Tt—10

12

t), vegetation of con-tinents, oceanosphere (Mt—10

6

t), and pedosphere (Dobro-vol’skii, 1998)

Metal Sedimentarymantle, Tt

Oceanospher,Mt

Vegetation,Mt

Pedosphere,Mt

Fe 60721 4658 500 1550

Mn 7520 548 600 93

V 171 – 3.75 9.3

Cr 132 274 4.5 12.4

Zn 129 6850 75 76

Ni 92 685 5.0 12.4

Cu 56 1233 20 9.3

Pb 32 41.1 3.13 6.2

Co 22 41.1 1.3 3.1

Mo 3.3 – 1.2 1.5

Cd 0.4 151 0.09 0.9

Hg 0.6 206 0.03 0.3

SOILCHEMISTRY

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MELEKHOVA et al.

These microorganisms were referred to as effectivemicroorganisms.

A considerable part of soil microorganisms belongsto the group of effective microorganisms, which con-sume iron ions together with other microelements. Thenecessary microelements can be recovered from min-eral crystals and other difficultly soluble compounds bycell enzymes. This fact suggests that the microbiologi-cal activity of soil can be controlled electrochemically(by ionometry), via measuring changes in the stationarypotential of a biologically active iron electrode

E

st

,additionally to direct methods of cell counting and thestudy of decomposition of substrates (e.g., cotton fab-ric) applied into the soil (known as the applicationmethod in Russian literature). Earlier observationsdemonstrated the agreement between the resultsobtained by the method of ionometry and by Mishus-tin’s application method [4]. The principle of ionome-try is based on a thermodynamic equation describingchanges in the electrode potential depending on theproperties of the electrode material, enclosing medium,and potential-determining components. The equilib-rium potential of the double electric layer on a metal(

E

e

) is described by the following equation [1]:

E

e

=

E

0

+ (

RT

/

nF

)ln

a

i

, (1)

where

E

0

is the standard electrode potential,

R

is theuniversal gas constant,

T

is temperature,

F

is Faraday’sconstant,

n

is the valence of metal ions, and

a

i

is theactivity of metal ions.

Equation (1) can be used for calculating the equilib-rium potential

E

e

of the double electric layer and fordetermining the concentration of the potential-formingcomponent by the change in the electrode potential.

The stationary potential

E

st

is formed in the soil onthe metal surface at the expense of stationaryquasiequilibrium processes running on the surface ofthe electrode in the double electric layer:

Fe – 2

e

Fe

2+

, (2)

Fe

2+

+ [L] [FeL]

2+

, (3)

where [L] is the concentration of ligands or microor-ganisms in the soils near the electrode surface,mmol/kg.

According to Eqs. (2) and (3), changes in the con-centration of electro active Fe

2+

ions in the near-elec-trode layer result in the formation of the electrodepotential

E

st

.Changes in the concentration of Fe

2+

ions on themetal surface in the soil may be due to the microbiolog-ical activity and various complexing reactions.

The value of the stationary potential of iron elec-trode in the contaminated soil can be calculated as fol-lows:

= + (0.059/2) , (4)Estex Est

0 aFe2+log

where and are the values of the electrodepotential under experimental conditions and in the con-trol, and is the activity of iron ions in the near-

electrode layer.If the complex-forming processes in the studied

soils have the same intensity (soils of the same type),then changes in the electrode potential are only due tochanges in the activity of microorganisms upon the soilpollution:

∆

E

st

= ( – ). (5)

When the biological activity of soil is low or absent,the stationary electrode potential

E

st

is formed on thesurface of the electrode only under the impact of com-plexing reactions. The microbiological activity of soilincreases the expenditure of iron ions, which shifts theequilibria in reactions (2) and (3). The released elec-trons should displace the potential of the iron electrodetoward the zone of negative values [6].

The aim of this work was to study the effects ofstress doses (up to 10 MPCs) of industrial contaminants(including HM ions) on the physicochemical and bio-logical properties of soils and soil fertility and the influ-ence of Fe (II) ions as remediators of contaminatedsoils.

OBJECTS AND METHODS

The soils of the reserved zone of Bogoroditskii dis-trict, arable chernozems of Kireevskii district, gray for-est soils of Arsen’evskii district, and soddy-podzolicsoils of Belevskii district of Tula oblast were the objectsof the study.

The changes in soil acidity (pH), redox potential(Eh), microbiological activity (

E

st

), and fertility (

K

sr

)were measured in model laboratory experiments anddirectly in the field [6, 7].

Measurements of E

st

Heavy metal ions in doses corresponding to tenfoldmaximum permissible concentrations (MPCs) wereadded to the soils in the form of water solutions of salts.The contaminated soil samples were carefully mixedand incubated for 7 days, and then plant seeds weresown. The measurements of Eh,

E

st

, and pH in the soilsand in the rhizosphere were performed on the 14th dayafter germination, and the degree of plant developmentwas recorded; the experiment was performed in tripli-cate. Average values are presented in the tables. Thedifference between the electrode potentials in parallelsoil samples did not exceed 10–15 mV. The values of

−

E

st

(mV) in the control plowed gray forest soil and inthe same soil contaminated with Cu

2+

and Zn

2+

and inthe rhizosphere of barley seedlings developing in thecontrol and contaminated soils are presented in Table 2.

Estex Est

0

aFe2+log

Estex Est

0

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SOIL CONTAMINATION WITH HEAVY METALS AND POSSIBILITY S65

As seen from Table 2, copper and zinc ions had toxiceffects on the soil microorganisms, because they dis-placed

E

st

to the region of more positive values. Theaddition of Cu

2+

ions at the rate of 5 MPC increased the

E

st

value by 55 mV (up to –606 mV) in comparisonwith the control (–661 mV) on the 60th second. The

E

st

value under the influence of Zn

2+

ions added in thesame concentration increased by 26 mV (in comparisonwith the control) during the same time interval. Thetoxic effects of copper and zinc were also observed inthe rhizosphere of barley seedlings, but to a lesserextent, which may be explained by the additional com-plex formation between iron ions and root exudates; thecorresponding changes in the electrode potential com-prised 33 mV for copper and 16 mV for zinc (on the60th second). With an increase in the time (duration) ofmeasurements, the values of the iron electrode potentialin the contaminated soils gradually approached those inthe control soils. This fact attests to the activating effectof iron ions from the double electric layer on the soilmicrobiological activity. It can be supposed that theaddition of iron ions into the contaminated soils (in theform of chemical ameliorants) should result in the res-toration of the soil microbiological activity. It is obvi-ous that a positive effect of ameliorants produced fromthe powdered metallurgic slag on the soil fertility was

caused by several factors, including the bioremediationof the soil by Fe (II) ions in the blast furnace slag [8, 9].

Measurements of Eh and pH

The values of redox potential (Eh) and soil acidity(pH) were measured by routine methods [7]. Theresults of the measurements at the depths of 3 and10 cm in two pits with stable parameters of the micro-biological activity are presented in Table 3 and in thefigure.

Table 2.

Changes in the stationary potential (–

E

st

, mV) in the plowed gray forest soil, in the soil samples contaminated withCu

2+

(5 MPC) and Zn

2+

(5 MPC) ions, and the in rhizosphere of barley seedlings

Variant

τ

= 15 30 60 90 120 180 s

Control 635

±

5 650

±

5 661

±

2 669

±

4 675

±

9 683

±

7

MPC Cu

2+

540

±

5 582

±

9 606

±

4 622

±

8 634

±

8 651

±

4

MPC Zn

2+

522

±

4 615

±

7 635

±

7 648

±

7 669

±

6 675

±

4

Rhizosphere of barley seedlings

Variant τ = 15 30 60 90 120 180 s

Control 640 ± 5 679 ± 6 701 ± 3 713 ± 7 723 ± 6 730 ± 4

MPC Cu2+ 635 ± 9 653 ± 7 668 ± 9 680 ± 9 691 ± 7 701 ± 8

MPC Zn2+ 638 ± 6 667 ± 5 685 ± 4 698 ± 7 709 ± 9 717 ± 5

Table 3. Est and Eh (mV) values as dependent on time in the chernozem and gray forest soil of the reserve zone at the depthsof 3 and 10 cm

τ, s Eh, 3 cm Eh, 10 cm –Est, 3 cm –Est, 10 cm Eh, 3 cm Eh, 10 cm –Est, 3 cm –Est, 10 cm

Chernozem Gray forest soil

0 272 250 800 785 210 120 700 685

15 275 251 800 787 197 120 710 710

30 277 252 803 790 191 115 740 750

45 279 252 804 790 189 110 750 770

60 280 253 805 795 182 108 760 778

120 280 255 805 797 179 105 760 780

16 18 20 22 24 1 2 3 4 5%

A(0–15)A1(15–27)

AB(27–42)BA(45–64)

A(0–12)A1(15–27)

AB(27–42)BA(45–64)

(a) (b)

Fig. 1. Changes in the microbiological activity MBA in thesoil profile as judged from the weight loss (%) of cotton fab-ric 10 × 10 cm2 applied into (a) typical chernozem and(b) gray forest medium loamy soil.

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MELEKHOVA et al.

It is seen from Table 3 that chernozems have higherEh values than gray forest soils; in the latter, the Eh val-ues at the depth of 10 cm are by 22–25 mV lower thanthose as the depth of 3 cm. In chernozems, the Ehremain relatively stable during the time of measure-ments. In the gray forest soils, they somewhat decreasefrom the beginning to the end of measurements. Cher-nozems are characterized by more negative Est in com-parison with gray forest soils. In the latter, the distribu-tion of both Eh and Est values in the soil profile and intime is more contrasting than that in chernozems.

Microbiological Activity as Assessedby the Decomposition of Cotton Fabric in Soil

Cellulolytic microorganisms were selected as indi-cators of soil microbiological activity [5]. The degree ofdecomposition of uncolored cotton fabric of 10 ×10 cm2 with known weight placed for 14 days into theA (0–20 cm), AB (20–45 cm), and BA (45–64 cm) hori-zons of chernozems and gray forest soils in the reservedzone of Bogoroditskii district was studied. Overall,more than 50 samples were analyzed. Data on themicrobiological activity (as expressed in percent of theweight loss of cotton fabric) are presented in the figure.

It is seen from the figure that the microbiologicalactivity slightly varies in the profile of chernozems andcomprises 20–25%. In the gray forest soils, someincrease in the microbiological activity is seen at thedepth of 15–27 cm. In general, the microbiological(cellulolytic) activity is the gray forest soils does notexceed 5%.

DISCUSSION

A comparison of the activity of cellulolytic microor-ganisms with the electrochemical parameters (redoxpotential) of the soils points to correlative relationshipsbetween them.

High Eh values in chernozems (270–280 mV) incomparison with gray forest soils (120–210 mV) corre-late with the high microbiological activity (20–25% inthe entire profile of chernozems). The differencebetween Eh values in chernozems and gray forest soilsaverages 100 mV (∆E = Ehchern – Ehgray soil ≈ 100 mV,τ = 120 s).

Therefore, the increase in the microbiological activ-ity per unit of the redox potential (Eh) comprises (25 –5) % : 100 mV = 20 : 100 = 0.2% per 1 mV.

The increased microbiological activity in cher-nozems also corresponds to the lower values of –Est thatcomprise –(800–805) mV in chernozems (for the upper3 cm) and –(700–760) mV in gray forest soils. The dif-ference in –Est values between the two soils decreasesdown the soil profile. For example, –Est values on the120th second at a depth of 10 cm are equal to –780 mVin chernozems and to –797 mV in gray forest soils. Thechange in the –Est value with time in the gray forestsoils indicates the potential capacity of these soils forincreasing the microbiological activity under the influ-ence of Fe (II) ions.

The effect of Remediators on Est

The effects of Fe2+ ions as remediators were studiedby adding the solution of potassium ferrocyanideK4[Fe[CN)6] in concentration of 1 MPC to the soil.

Changes in the –Est values with time in the cher-nozem contaminated with Cu2+, Zn2+, Cr3+, and Cr6+

ions in concentration of 10 MPC and with the remedia-tor (Fe2+) introduced are shown in Table 4.

The application of potassium ferrocyanidedecreased the toxicity of contaminated soils in all thecases: the –Est values were shifted toward negative val-ues. However, the level of the control was reached innone of the variants.

Table 4. Changes in the –Est (mV) values in the chernozem contaminated with Cu2+, Zn2+, Cr2+, and Cr6+ and after the addi-tion of Fe2+ as a remediating agent

No. Variant E30 E90 E120 ∆E(120–30)

1 Control 755 ± 9 771 ± 8 774 ± 9 20

2 C + Cu2+, 10 MPC 440 ± 10 540 ± 7 575 ± 10 135

3 C + Zn2+, 10 MPC 476 ± 15 547 ± 7 567 ± 9 87

4 C + Cr3+, 10 MPC 374 ± 13 405 ± 11 418 ± 13 44

5 C + Cr6+, 10 MPC 250 ± 5 250 ± 4 253 ± 3 ±4

With application of a remediating agent

6 C + (Zn2+ + Fe2+) 526 ± 7 562 ± 8 574 ± 9 50 ± 4

7 C + (Cu2+ + Fe2+) 513 ± 4 557 ± 9 609 ± 7 52 ± 8

8 C + (Cu2+ + Zn) + Fe2+ 469 ± 5 606 ± 9 627 ± 8 60 ± 5

9 C + (Cr3+ + Fe2+) 590 ± 5 618 ± 7 623 ± 7 33 ± 7

10 C + (Cr6+ + Fe2+) 530 ± 7 565 ± 6 573 ± 7 42 ± 6

EURASIAN SOIL SCIENCE Vol. 39 Suppl. 1 2006

SOIL CONTAMINATION WITH HEAVY METALS AND POSSIBILITY S67

Changes in Soil Fertility as Dependenton the Nature of Contaminants

The effect of contaminants on soil fertility wasdetermined in chernozems of Shchekinskii district andgray forest soils of Arsen’evskii district in Tula oblastfrom data on changes in the coefficient of soil responseKsr calculated as follows:

Ksr = ,

where BISc is the biological index of the control soil,and BISex is the biological index of the experimentalsoil.

In our work, we used the mass m (g) of the above-ground biomass of barley plants grown in the control(mc) and experimental (contaminated) soils (mex) dur-ing the growing season as the biological index of soilfertility. Thus, the Ksr was calculated as follows:

Ksr = .

The experimental values of m, pHKCl, and Ksr for the

two soil types contaminated with Zn, Cu, Fe, Pb, N ,and CaCO3 in stress concentrations of 10 MPC andwith humic acid HA obtained from brown coal of Mos-cow coal basin are presented in Table 5. It is seen fromthese data that changes in the soil fertility depend on thesoil type and on the contaminant nature.

Chernozems proved to be more sensitive to theintroduced contaminants in comparison with gray for-est soils. In chernozems, the loss of soil fertility underthe impact of contaminants was no less than 35% in allthe cases. In some cases (variants 6, 8, and 12 with the

BISc BISex–BISc

-------------------------------

mc mex–mc

--------------------.

H4+

addition of lead acetate Pb(Ac)2 lime and alkali), barleyplants did not grow at all. Thus, chernozems have alower homeostatic natural potential and a lower buffer-ing capacity in comparison with gray forest soils.

Gray forest soils have a lower absolute fertility incomparison with chernozems (28.6 and 51.3 g per potin the control variants, respectively), but are better pro-tected and have a higher buffering capacity for indus-trial contaminants and acidity in comparison with cher-nozems. In two variants (5 and 10), the addition of cop-per nitrate and NH4NO3 to the gray forest soil resultedin the rise of the Ksr value. Only in the case of alkali, thefertility of gray forest soil was completely lost.

Zinc introduced to the soils in the form of chloridewas a more dangerous contaminant than copper andzinc in the sulfate form. Excess of Zn in the soilsresulted in a decrease in fertility of gray forest soils andchernozems by 66.7 and 85%, respectively.

Gray forest soil demonstrated a positive response(an increase in fertility) to the application of copperand ammonium nitrates (variants 5 and 10). Onlynegative response was observed in chernozems in allthe cases, including the addition of ammoniumnitrate (variant 10).

Thus, gray forest soil demonstrated a more effectivemechanism of self-regulation with respect to some con-taminants, particularly to nitrates, ammonium, copper,and increased acidity. Unlike chernozem, it did not loseits fertility even after the addition of the stress amountof sulfuric acid. In the latter case, the fertility of cher-nozem dropped by 62%. Chlorides were the most dan-gerous among anionic contaminants.

A particular emphasis should be placed on the vari-ants with the addition of humic acid obtained from thebrown coal of Moscow coal basin and added in concen-

Table 5. Changes in the weight of the aboveground parts of barley (m, g), in the coefficients of soil response (Ksr), and inthe pH of chernozems from Shchekino district and of gray forest soils from Arsen’evo district after the addition of differentcontaminants at concentrations of 10 MPC

No. VariantChernozem Gray forest soil

m, g Ksr pH m, g Ksr pH

1 Control 51.3 0.00 4.9 28.6 0.00 4.42 ZnSO4 33.7 –0.343 4.1 17.9 –0.374 4.03 ZnCl2 7.7 –0.850 4.6 9.5 –0.668 4.14 Cu(SO4)2 21.3 –0.585 4.7 22.9 –0.199 4.05 Cu(NO3)2 31.1 –0.394 4.7 32.1 +0.122 4.26 Pb(Ac Not –1.00 4.6 22.6 0.210 4.47 H2SO4 19.5 –0.620 4.3 28.6 0.000 3.88 NaOH Not –1.00 5.1 Not –1.000 –9 FeNH4(SO4)2 12.7 –0.752 2.8 21.3 0.255 2.4

10 NH4NO3 20.5 –0.600 3.8 30.3 +0.06 4.311 HA** 14.3 –0.712 4.5 20.1 –0.298 4.1

** Ac—acetate ion.** HA—humic acid obtained from brown coal of the Moscow coal mining region.

)2*

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MELEKHOVA et al.

tration of 1%; its application decreased Ksr by 29.8% inthe gray forest soil and by 71.2% in the chernozem.

Negative effect of humic acids extracted frombrown coal on the fertility of chernozems and gray for-est soils that was registered in our study, as well as inthe field surveys of the Institute of Liquid fertilizers(1996), casts doubt on the expediency of application ofhumic substances obtained from the brown coal ofMoscow coal mining region as fertilizers.

CONCLUSIONS

(1) It is shown experimentally that changes in thesoil microbiological activity can be controlled by theelectrochemical method via measuring the stationarypotential of the biologically active iron electrode. Thismethod is only applicable to those microorganisms thatactively utilize Fe (II) ions.

(2) Ions of Cu2+ and Cr6+ are more toxic for the soilsof Kireevskii district of Tula oblast in comparison withZn2+ and Cr3+ ions. The toxic effect registered in therhizosphere of barley seedlings is less pronounced thanthat in the soil due to the additional complex formationbetween iron ions and root exudates.

(3) The activity of cellulolytic microorganisms isseveral times (no less than four times) higher in thechernozems than in the gray forest soils.

(4) Ions of Fe (II) can serve as remediators of thesoils polluted with heavy metal ions.

(5) Chernozems are genetically less protected fromthe industrial contaminants in comparison with grayforest soils.

REFERENCES1. V. P. Vasil’ev, Analytical Chemistry, Vol. 2: Physico-

chemical Methods of Analysis (Vysshaya Shkola, Mos-cow, 1989) [in Russian].

2. O. A. Ezerskaya, “Features of Metal Dissolution,” inProceedings of the VII International Frumkin Sympo-sium on Basic Electrochemistry for Science and Tech-nology, Moscow, Russia, 2000 (Moscow, 2000), Part 2[in Russian].

3. A. Zh. Barne and A. A. Rakhleeva, “Mesofauna of Tech-nogenically Disturbed Soils,” in Proceedings of the FirstScientific Youth School and Conference “Creation ofBiodiversity and the Rational Use of BiologicalResources,” Moscow, Russia, 2000 (Moscow, 2000),p. 10 [in Russian].

4. E. N. Mishustin, Microorganisms and Agricultural Pro-ductivity (Nauka, Moscow, 1972) [in Russian].

5. L. M. Polyanskaya, V. V. Geidebrekht, A. L. Stepanov,and D. G. Zvyagintsev, “Distribution of Microbial Pop-ulation and Biomass in the Profiles of Zonal Soils,”Pochvovedenie, No. 3, 332–335 (1995).

6. I. S. Kaurichev and D. S. Orlov, Redox Processes andTheir Role in Soil Genesis and Fertility (Kolos, Moscow,1982) [in Russian].

7. N. I. Melekhova, “Acquisition of Information on theHeavy-Metal Contamination and Fertility of Soils on theBasis of Microbiological Activity,” in Proceedings of theAll-Russian Scientific and Technical Conference “Infor-mation Technologies and Models in the Solution of Cur-rent Ecological Problems,” Tula, Russia, 2002 (Tula,2002), pp. 29–30 [in Russian].

8. N. I. Melekhova, E. A. Gorskaya, A. V. Zaitsev, andO. V. Dukhnovskaya, “Possible Solutions of EcologicalProblems Related to Soils Contaminated with HeavyMetals,” in Proceedings of the Conference “EcologicalProblems and the Effective Use of Resources,” Tula,Russia, 2003 (Tula, 2003).

9. N. I. Melekhova, S. I. Voronin, A. Ya. Litvinov, et al.,Patent RF no. 97119031…125(020292), 1997.