Chemistry for Sustainable Development 16 (2008) 383–393 383

Zinc in Environmental Objects of Transbaikalia

V. K. KASHIN

Institute of General and Experimental Biology, Siberian Branch of the Russian Academy of Sciences, Ul. Sakhyanovoy 6, Ulan Ude 670047 (Russia) E-mail: [email protected]

(Received January 24, 2008)

Abstract

The content of zinc in abiotic components (soil-forming rocks, natural waters, soils) and plants of forest-steppe, steppe, arid steppe and floodplain landscapes of Transbaikalia has been studied. A complex character of zinc distribution in environmental objects have been revealed: the content of zinc in soil- forming rocks and the soils of steppe and arid steppe landscapes approximately corresponds to the clarke, being for the rocks and soils of the forest-steppe landscapes equal to 0.4–0.7 of the clarke. It has been established that a deficient content of zinc (20–80 %) in the vegetation of steppe, meadow and agricultural landscapes is inherent in the most part of the territory under investigation. Key words: zinc, distribution, soil-forming rocks, natural waters, soils, plants, landscapes

INTRODUCTION tabolism of proteins, carbohydrates, lipids and nucleic acids. Zinc represents a vitally important micro- The daily demand of an adult human for element for all the taxonomic groups of or- zinc amounts to 15–20 mg. The coefficient of ganisms on condition that its content is normal. its absorption from dietary intakes of vegeta- At the same time it is a hazardous toxicant ble and animal food mixture is as high as 33 %. when superfluously contained in an organism. The symptoms of this element deficiency for Zinc is involved in the structure of about human and animal organisms are exhibited via 300 enzymes those belong to all six classes list- growth inhibition and development delay, dis- ed in the catalogue of enzymes, and in the order of reproductive function, bone forma- structure of hormones (thymulin, prolactin, tion and hemogenesis, cutaneous diseases, de- somatin). This element supports the structure crease in immunity [4–6]. of more than 200 proteins, transcription acti- The deficiency of zinc in soils results in oc- vators those participate in the genetic infor- currence of various diseases of plants, decrease mation transfer [1, 2]. Due to this fact zinc can in their productivity and deterioration of qual- be considered to be a unique microelement: itative composition. At the same time a consid- none microelement forms such a number of erable part of the territories of Russia (75 %), bioinorganic compounds (bioclusters) and ex- the USA (43 States) and other countries are hibits so many various functions. The most im- characterized by the deficiency of zinc in soils portant enzymes containing zinc include car- [7, 8], which represents a serious problem for bonic anhydrase providing the hydration of ÑO 2 the health of population, livestock farming and in biological systems, and superoxide dismu- agriculture. This is especially urgent for the tase catalyzing the disproportionation of su- optimum development of children and teenag- – peroxide ion ( O2 ) and playing an important role ers as the most vulnerable part of population in the protection of cells from free radicals [3]. Zinc-containing fertilizers take a leading place Zinc-containing enzymes take part in the me- in the developed countries abroad among other 384 V. K. KASHIN fertilizers with microelements concerning the rocks, in some plant species as well as in phy- assortment and production volumes [8]. tomass harvested from 1 m2, upon 4- to 6-fold At the same time the increased concentra- repetition. The sampling was carried out dur- tion of zinc exert a toxic effect on living organ- ing the period of a higher biologic efficiency isms. So, the proficiency of zinc in a human or- of dominant plants. Water sampling from the ganism results in nausea, vomiting, respiratory water sources neighbouring to the key plots was embarrassment, pulmonary fibrosis [9]. Under carried out during low-water season (August– the conditions of an increased concentration of September). The destruction of the organic zinc in soils the population morbidity rate value matrix in samples was carried out using a dry with respect to cancer is observed to grow; in ashing technique at 480 îÑ. The content of zinc this connection zinc is referred to priority toxic was determined by atomic absorption spec- elements. However, the toxicity of zinc exhibits troscopy technique, analytical replicated trials be- a restricted distribution being connected mainly ing triple. The detection limit of zinc for soils and to a man-caused environmental contamination plants amounted to 0.5 and 0.1mg/kg, respective- due to corresponding manufactures. ly, for water it was equal to 1.0 µg/L. The relative Thus, the problem of zinc in biosphere is error of determination was about 8–10%. Math- characterized by two practically important as- ematical data processing was carried out using stan- pects biological one, connected with zinc defi- dard techniques described in [14]. ciency, and ecotoxicological one caused by the increased content of zinc. In this connection it is necessary to carry out monitoring of zinc con- RESULTS AND DISCUSSION tent in various parts of biogeochemical food Zinc in soil-forming rocks chain for different regions. The content of zinc is poorly known for the The content of zinc in soil-forming rocks landscapes of Transbaikalia. There are only sep- varied from 23 to 157mg/kg while the aver- arate data concerning zinc content in the some age variation level was equal to 41% (Table 1). soils and fodder plants of the southern areas of The lowest content of zinc (26–30mg/kg) was Buryatia [10, 11], as well as about the accumu- observed in alluvial and diluvium sandy depos- lation of this element by plants growing on ore its of the taiga landscapes, and the highest deposits [12]. The purpose of the present work one (100–140mg/kg) was noted for diluvium consisted in the studies on the features of zinc loamy deposits of the steppe landscapes. For distribution in soil-forming rocks, natural wa- the most part the content of zinc varies within ters, soils and plants of various Transbaikalian the range of 40–100mg/kg (75% of samples) landscapes constituting the major portion of with the average value for all the set of soil- water collecting area of the Baikal Lake basin. forming rocks under investigation amounting to 71mg/kg, which value is corresponding to EXPERIMENTAL the clarke of zinc in the lithosphere. From the geological staindpoint Transbaika- The studies were carried out over the 12 most lia represents rather non-uniform territory populated areas of Buryatia (Western Transbaika- where Pre-Cambrian, Palaeozoic, Mesozoic lia) located within the Selenga River basin that is and Cainozoic igneous, metamorphic, sedimen- the main tributary of the Baikal Lake. The key tary formations are developed. Granitoids pre- sampling sites, plots 100 × 100m in size were cho- vail among the rocks, and there are diorites, sen at the typical areas of the steppe, meadow syenites, gabbro, dunites, basalts, limestones, and agricultural landscapes according to the me- sandstones, clay slates, too [15]. The rocks of- thodical recommendations presented in [13]. Each ten replace spatially each other; this fact ex- plot was treated to obtain a basic soil section hibits a lithologic variety of the territory, and 4 to 6 semi-sections. At all the points a con- which is connected with the variability of the jugate sampling was carried out for the deter- lithogeochemical background. Zinc belongs to mination of zinc content in soil horizons and chalcophilous chemical elements accumulated in ZINC IN ENVIRONMENTAL OBJECTS OF TRANSBAIKALIA 385

TABLE 1 Content of zinc in soil-forming rocks of Transbaikalia

Soil-forming rock n Content, mg/kg Cc Fluctuation rangeAverage Northern part of the territory under investigation Taiga landscapes Diluvium sandy deposits524–36290.4 Alluvial deposits523–31260.4 Sandy deposits834–45380.6 Forest-steppe landscapes Diluvium deposits, loams1640–60490.7 Diluvium deposits, sandy loams1032–47370.5 Alluvial deposits1627–45330.5 Southern part of the territory under investigation Arid steppe landscapes Diluvium deposits, loams1576–107931.4 Diluvium deposits, sandy loams1564–91791.2 Alluvial deposits1560–96771.1 Ancient lacustrine deposits683–97901.3 Aeolian sands759–71651.0 Steppe landscapes Diluvium deposits, loams590–1571201.8 Diluvium deposits, sandy loams2285–112991.5 Aeolian sands965–87761.1 Alluvial deposits1865–115861.3

Notes. 1. The Earth’s crust clarke amounts to 68 mg/kg [16]. 2. Cc is the clarke of concentration related to Earth’s crust clarke. the base rocks in increased amounts (84mg/kg). basalts of the Dzhida district the content of zinc In the intermediate and acid rocks its content in rocks ranges from 108 to 177mg/kg [17]. is to some extent lower, amounting to 73 and The content of zinc depends on grain-size 58mg/kg, respectively [16]. Zinc is present in composition of rocks, too. So, for sandy loams rocks mainly as zinc sulphide ZnS, as well it and sand this parameter is 1.5–1.9 times lower uses to substitute magnesium in silicates. as compared to that for loamy deposits. It is con- The analysis of spatial distribution of zinc nected with the fact that zinc, as well as many in soil-forming rocks has allowed one to reveal other dispersed chemical elements are concen- the following regional feature. For the rocks trated at the negatively charged surface of su- those compose the southern part of the territo- perfine clay particles due to the sorption via elec- ry under investigation (steppe and arid steppe trostatic interaction and even the incorporation landscapes) the content of zinc is on the aver- into interlamellar space, and formation of stron- age 2.3 times higher as compared to that for the ger inner-sphere complexes [18]. The content of rocks composing the northern part (taiga and clay fraction in various soil-forming rocks of forest-steppe landscapes): 89 and 38mg/kg, re- Transbaikalia varies from 5 up 15%. spectively. This difference is caused mainly by The relationship between silicon oxide and the character of basement rocks: the northern the total of the oxides of other elements is part is mainly combined by acid rocks, whereas considered to be important for estimating the there are also intermediate and base rocks in level of zinc content in rocks and in soils. With the southern part. In particular, for the alkaline the increase in the content of silica the of dis- 386 V. K. KASHIN

persed elements decreases. The content of SiO2 TABLE 2 in soil-forming rocks of Transbaikalia ranges Content of zinc in naturally occurring waters of Transbaikalia from 61 to 73%, and the fraction of the ox- Water source,Content, µg/L ides of other elements varies within the range from 27 to 39% [19]. The differences in the sampling siteFluctuationAverage content of clay minerals and the relationship range Rivers between SiO2 and the oxides of other elements are responsible for the content of zinc in rocks Kizhinga, Kizhinga village55–6965 as well as for the heterogeneous character of Selenga, Shigayevo village48–6356 its spatial distribution. Dzhida, Dzhida station44–5852

Zheltura, Zheltura village46–5750 Zinc in natural waters Burgultayka, Nizhniy

The content of zinc in water of the rivers Burgultay village42 –5348 of the Selenga River basin ranges from 3 to Irkilik, Zyryansk village36–4440 69 µg/L (Table 2). The average concentration of zinc in river waters is equal to its clarke Tugnuy, Tugnuy village34–4038 amounting to 20 µg/L [20]. A higher content of Angyr, Zyryansk village32–3936 zinc was revealed in water of large rivers (the Bichura, Bichura village27–3632 Selenga, the Dzhida), which could be caused by a relatively increased salinity (150mg/L) as Orongoy, Orongoy village25–3630 compared to small mountain rivers and rivu- Il’ka, Novoil’insk village13–1916 lets (10–30mg/L), as well as by the element Kurba, Novaya Kurba village15–2318 entering with atmospheric precipitation. The Zagustay, Yagodnoye village 8–1511 contribution of the latter to large rivers run- ning over vast territories could be as much as Chikoy, Povorot village 5–11 8 50% of the total content [21]. Ubukun, Ardatsan village 3–9 5

For water of the freshwater lakes under in- Lakes vestigation the content of zinc ranges from 5 to 34 µg/L (14 µg/L on the average). A low content Shchuch’ye, Yagodnoye village12–2518 of zinc is inherent in water the Baikal Lake rang- Gusinoye, Gusinoozersk city19–3426 ing from 5 to 12 µg/L (7 µg/L on the average). Kamyshovoye, Yagodnoye village12–1915 This fact could be explained by its ultrafresh Baikal, Istomino village 5–12 9 type (the mean salinity amounting to 97mg/L) and a high level of oxidation processes occur- Underground waters ring. High concentrations of zinc (27–93 µg/L) Artesian well, Kyakhta city69–8275 are observed for waters of closed saline lakes Artesian well, Zyryansk village64–7670 (with the salinity of 35000mg/L) attached to arid steppe landscapes. However, these values Artesian well, Nizniy Torey village47–5652 do not exceed the background values for zinc Spring, Dzida road45–5350 content in superficial waters (5–300 µg/L). Artesian well, Turuntayevo village42–5046 For the subsoil well-waters the content of zinc is demonstrated to vary within the range Artesian well, Ust-Kyakhta village19–3324 from 4 to 32 µg/L (15 µg/L on the average). For Artesian well, Kizhinga village14–3022 the majority of underground potable deep-well Artesian well, Mukhorshibir village21–2620 water from boreholes the content of zinc Artesian well, Kulskiy Stanok village13–2117 amounts 15–24 µg/L (average value being at 20 µg/L), whereas for the underground waters Artesian well, Yagodnoye village11–1915 of an arid steppe landscape this value is 2.4 times Artesian well, Gusinoozersk city5–12 8 higher than the abovementioned amounting to Artesian well, Novoselenginsk village3–8 5 45–82 µg/L (48 µg/L on the average). At the same ZINC IN ENVIRONMENTAL OBJECTS OF TRANSBAIKALIA 387 time, the clarke of zinc for underground waters 8.7 (within the horizon A the ðÍ value being at of the hypergenesis zone is equal 41.4 µg/L [20]. about 7.0–7.2) and, consequently, the sedimen- The analysis of zinc spatial distribution for tation of zinc in the form of zinc hydroxide, various water sources of the Selenga River and its fixation in a non-exchangeable form via basin has allowed one to establish that for the the chemisorption by iron oxides. It is experi- waters of the southern part of arid steppe mentally established that iron hydroxides use to landscape (42–58 µg/L, Dzida district) zinc con- absorb heavy metals more actively, than clay centration is higher as compared to the forest- minerals and organic matter, being able to bind steppe landscape of the northern part of the up to 50% of the total amount of metals [18]. territory under investigation (4–21 µg/L, Zaig- In particular, for farinaceous carbonate cher- raevo distrrict). This fact could be to a consid- nozem soils the content of Fe2O3 within the ho- erable extent caused by a different level of zinc rizon Âc amounted to 10.8–15.4%, whereas within content in rocks, the basic sources of this chem- the horizon this value ranged within 5.1–6.8%. ical element for natural waters. In the soils where the carbonate horizon is not Thus, the content of zinc in natural waters present, zinc is distributed in the profile with a is characterized by a significant contrast rang- considerable homogeneity: the difference in its ing from 3 to 82 µg/L (27-fold). For the most content in separate horizons is statistically non- part, the content of zinc in superficial waters significant amounting to ±1.2 times. The main is close to the clarke of zinc for river waters, types of Transbaikalian soils are characterized whereas for the underground potable deep-well by a low content of humus, therefore no corre- water from boreholes this value is twice lower lation in the humus–zinc system is observed than the clarke of zinc for underground wa- (r =0.10). The biogenic accumulation of zinc is ters of the hypergenesis zone. noted only for the soils with an increased content of organic matter such as meadow chernozem permafrost soils and bottomland-meadow soils. Zinc in soils In the arid steppe landscapes the soils of A geographical heterogeneity of zinc distri- chestnut type are prevailing those are charac- terized by neutral or alkalescent pH value of bution in soils, caused by the differences in its the medium within the humus horizon. The con- content in rocks is inherent in the region under tent of zinc in such soils ranged from 57 p to study [22, 23]. The close contingency of these 101mg/kg (78mg/kg on the average) (Table3). parameters is reflected by the linear correla- With the close ðÍ values and humus content, tion coefficient value: r =0.84. This is connect- such a considerable difference in the content ed with the fact that the bulk of the soils un- of zinc could be mainly caused by different der our investigation include 94.5–98.8% of a concentration level of this element in soil-form- mineral substance (the content of humus rang- ing rocks ranging from 64 to 107mg/kg (1.7- ing within 1.2–5.5%). fold difference) as well as by the variety of The differentiation of microelements within grain-size composition of soils, from sandy soil the soil profile is determined by the content of up to medium-loamy soil. the organic matter, sludgy fraction, the presence Farinaceous carbonate chernozem soils are of sorption geochemical barriers and ðÍ value in the most distributed within steppe landscapes the medium. For the conditions of Transbaikalia on the slopes of intermountain declines of the one should distinguish the two most characteris- northern exposition; they are characterized by tic types of the vertical zinc distribution. neutral pH value of the soil medium. The grain- For the chestnut soils and farinaceous car- size composition varies from sandy soil up to bonate chernozem soils of steppe and arid loamy soil (the content of the fraction <0.01mm steppe landscapes in the presence of an alka- ranging within 13–35%). The content of zinc line sorption barrier in the carbonate horizon in the chernozem soils of steppe landscapes one can observe an increased (1.6–1.8-fold) zinc ranges from 96 to 115mg/kg (the average val- accumulation level as compared to a soil-form- ue amounting to 107mg/kg). ing rock. This fact is caused both by the ðÍ Grey woodland soils (ðÍ 6.2–7.7) are formed value increase within the horizon Âc up to 7.6– on the northern slopes of the intermountain de- clines of taiga, forest-steppe and steppe land- 388 V. K. KASHIN

TABLE 3 Content of zinc in Transbaikalian soils (within the layer of 0–20 cm)

Soil type n HumusAqueousZinc content, Cc content, %pHmg/kg Fluctuation rangeAverage* Northern part of the territory under investigation Taiga landscapes Peaty swamp (peat bog) soils 5– 5.231–42 370.4 Grey woodland soils132.3–2.66.2–6.444–59 520.6 Alluvial sod soils 41.4–1.8 6.439–47 440.5 Forest-steppe landscapes Chestnut soils212.0–2.36.8–7.835–57 460.5 Farinaceous carbonate chernozem soils102.9–3.76.8–7.035–48 420.5 Grey woodland soils 8 2.2 7.041–52 450.5 Alluvial meadow soils152.8–5.56.9–7.538–55 470.5 Southern part of the territory under investigation Arid steppe landscapes Chestnut soils311.4–3.26.9–7.957–101 780.9 Farinaceous carbonate chernozem soils 5 3.4 7.189–103 951.1 Grey woodland soils102.2–3.87.1–7.397–1191131.3 Alluvial meadow soils282.7–4.77.3–8.070–93 820.9 Alluvial sod soils 81.2–1.57.8–8.188–107 921.0 Steppe landscapes Chestnut soils141.2–1.86.9–7.875–136 971.1 Farinaceous carbonate chernozem soils112.4–2.86.9–7.296–1151071.2 Grey woodland soils212.4–2.96.8–7.791–108 971.1 Alluvial meadow soils 7 2.8 8.089–1161001.1 Alluvial sod soils121.4–2.17.3–7.784–100 901.0

* The average zinc content in soil all over the world amounts to 90 mg/kg [16]. scapes. According to the grain-size composition alluvial soils is quite different: for alluvial mead- there are light loamy and medium loamy vari- ow soils its value amounts to 2.7–5.5 %, where- eties (the content of the fraction <0.01mm rang- as for alluvial sod soils it is equal to 1.2–2.1%. ing within 18–38%). Depending on the composi- The content of zinc in alluvial soils ranges from tion of soil-forming rocks, on the grain-size com- 38 to 116mg/kg (76mg/kg on the average). position and on ðÍ value the content of zinc in A distinct correlation between the content the soils ranges from 44 to 108mg/kg. of zinc in soil-forming rocks and the soils formed Meadow soils are formed on alluvial depos- on them is observed upon the analysis of sep- its in the valleys of the rivers of the Baikal arate sections (S). So, for example, the content Lake basin for all the Transbaikalia landscapes of zinc in grey woodland soil and soil-forming under our investigation. These soils are charac- rocks for the forest-steppe landscape amounts terized by a wide range of ðÍ values (6.4–8.4). to 48 and 43mg/kg, respectively (S51Kzh), for The grain-size composition varies from sandy the arid steppe landscape these values are equal soil up to medium loamy soil (the fraction to 100 and 113, respectively (S38K), whereas <0.01mm amounting to 12–35%). Depending on for the steppe landscape they are 95 and 91mg/kg, moistening conditions the content of humus in respectively (S22Ò). The content of zinc in allu- ZINC IN ENVIRONMENTAL OBJECTS OF TRANSBAIKALIA 389 vial soils and alluvial sediments for the taiga land- of the element ranging within 20–60% of the scape amounts to 44 and 40mg kg, respectively standard value for the plants with a low zinc (S104Pb), for the forest-steppe landscape the withdrawal. The investigated soils of the region corresponding values are 38 and 30, respective- are mainly (82% of the area) characterized by ly (S52Kzh), for arid steppe landscape they are 40–80% deficiency of mobile zinc. A higher con- 87 and 84 (S59D), for the landscape steppe land- tent of zing was revealed in peaty swamp soils scape being at 87 and 80mg/kg, respectively (2.9 times higher as compared to the standard). (S20Ò). Similar dependence of zinc content in The mobile zinc reserves in the soils of the taiga soils on the content of zinc in soil-forming rocks and forest-steppe landscapes amounting to about was observed for chestnut and chernozem soils 16% of the area of agricultural lands are in a formed on diluvium deposits of the forest- good correspondence with the standard. steppe, steppe and arid steppe landscapes. One of the major factors determining the There are considerable lands of peaty low content of mobile zinc species in the soils swamp soils in Transbaikalia. A vast tract of of steppe and arid steppe landscapes is their lowland peaty soils (20000 ha) is located within saturation with calcium. For the absorbing soil the delta of the Selenga River. The content of complex of chernozem, chestnut, grey wood- zinc in soils of this land ranged from 31 to land and bottomland soils the content of calci- 42mg/kg, which is in a good correspondence um was as high as 20–26 mg-eq, which is with zinc concentration in the peaty swamp soils 4 times higher as compared to the content of of the European part of Russia [24]. magnesium. The mechanism of zinc mobility Thus, the background content of zinc in the regulation effected by calcium consists in the main types of soils in the region varies within fact that such stable compounds as zinc hydrox- the range of 31–136mg/kg at the average vari- ide and carbonate are formed in neutral and ation level of 37%. The average content of zinc alkalescent media [25]. The low mobility of zinc in soils amounts to 76mg/kg and almost corre- in soils results in the deficiency of its accumu- sponds to its content in soil-forming rocks. Thus, lation in plants and, hence, in the organisms it is just the composition of soil-forming rocks of humans and animals. that is a primary factor determining the con- tent of zinc in soils not subjected to man-caused Zinc in plants impact. No statistically significant difference was revealed in the average content of zinc for var- Different species of plants exhibit a selec- ious types of soils. However, the increase in zinc tive ability to accumulate zinc even when grow- content in the soils from the north to the south ing within the same ecotope. In order to esti- of the territory under investigation is traced as mate specific features of the accumulation of distinctly, as it is for soil-forming rocks: for the chemical elements by plants one should consid- soils of the northern part this value varies within er not absolute, but the relative content of the the range of 35–59mg/kg (45mg/kg on the element under investigation in the species of average), whereas for the southern part it ranges plants (RCSP) under comparable conditions [12]. within 57–136mg/kg (the average value The use of this parameter for the compari- amounting to 91mg/kg). The zinc reserves in soils son of 12 basic species growing within the same as compared with the clarke for the northern ecotope, has allowed us to distinguish the part amounts to 0.5–0.6, whereas for the south- groups of plants with the increased (1.4–1.8 ern part it is equal to 0.9–1.3. times), medium (0.8–1.2 times) and low (0.4– The biological activity of zinc in soils and 0.7 times) zinc accumulation level. The largest its ability to enter plants depend on the pres- group (seven species) was characterized by a ence of biologically accessible species of this medium zinc accumulation level. The maximum element. The results of the determination of difference in the content of zinc in such con- the mobile zinc extracted with the use of am- trast plant species as Potentilla lanacetifolia Willd. monium acetate buffer solution (ðÍ 4.8) indicate and Agrostis mongolensis was as high as 4.7-fold a low reserve in the soils of steppe and arid (28 and 6mg/kg, respectively). These features steppe landscapes with respect to such species of plants are caused by a long-term evolution 390 V. K. KASHIN

TABLE 4 Statistical and variation parameters for the content of zinc in soils, in the vegetation of different phytocenoses and the coefficient of biological absorption (Kb)

Parameter nM±m VariationConfidence V, % r rangeinterval Steppe phytocenoses In soil, mg/kg16 81±7 42–136 67–96330.57 In plant incineration ash16414±46200–800315–51245

Kb 16 5.1±0.41 2.5–8.2 4.3–6.131 Meadow phytocenoses In soil, mg/kg14 70±6 38–100 55–84350.65 In plant incineration ash14276±33100–500204–34745

Kb 14 3.9±0.392.0–6.3 3.2–4.936 Agricultural phytocenoses In soil, mg/kg27 79±5 40–136 68–91360.59 In plant incineration ash27224±17100–375189–25939

Kb 27 2.8±0.19 1.5–4.7 –33 of the organism–geochemical environment in- phytic vegetation of steppes as compared to tegrated system resulted in developing a certain that for mesophytic vegetation of meadows and biogeochemical specialization in plants. cultivated phytocenoses. As against the majori- In order to estimate the intensity of the ty of microelements, zinc it characterized a absorption of chemical elements by plants from valid positive average correlation between its a soil it is conventional to use the ratio Kb be- accumulation level in plants (for incineration ash) tween the content of elements in plant ashes and the total content of this element in soils: to the content in soil or in the Earth’s crust at tfact =2.6, 3.0, 3.6 and ttheor =2.2, for steppe [12]. According to this parameter one can judge vegetation r=0.57, for meadow vegetation the degree of bioavailability of the elements r =0.65, for cultivated vegetation r =0.59. and their behaviour in the soil–plant system. The accumulation level of zinc in aerial parts As it is seen from data presented in Table 4, of the vegetation biomass of steppe, meadow zinc belongs to chemical elements of rich accu- and cultural cenoses depending on zinc content mulation. It should be noted that there is an in soils is expressed as sinusoidal curves with increased Kb value for zinc in the vegetation of several rises and decays (Fig. 1). steppe landscapes as compared to meadow and The same plant species under different en- cultivated phytocenoses (1.3- and 1.8-fold, re- vironmental conditions within the same vege- spectively). This fact could be caused by a more tation stage (flowering) exhibit a considerable vigorous activity of the root system of xero- difference in the content of zinc. So, for the 48 plant species under our investigation the dif- ference could range from 1.5-fold value (for crested grass Agropyron cristatum (L.)) to 8.4- fold one (for wormwood sage Artemisia frigi- da), 8.0-fold difference for yellow bedstraw Galium verum L., 7.9-fold one for sickle alfalfa Medicago falcata L. and 7.8-fold value for loco- wed (Astragalus Adsugens Pallas) [26]. The plants specified are characterized by wide ecological amplitude of growth. The data obtained indicate a barrier-free Fig. 1. Zinc accumulation within aerial biomass of steppe (1), meadow (2) and cultivated (3) phytocenoses (for type of zinc accumulation for these species and incineration ash) depending on Zn content in soils. their possible use as indicators of soil contami- ZINC IN ENVIRONMENTAL OBJECTS OF TRANSBAIKALIA 391

TABLE 5 Content and accumulation of zinc in the aerial biomass of Transbaikalian vegetation

Vegetation type (sampling site) n Zinc content,Biological productivity,Zinc accumulation mg/kgcentners/halevel, g/ha Steppe (overall) 5420.0 6.0 15.4 Motley grass (forb) steppe (Belozersk village) 541.3 6.7 27.7 Wormwood sage steppe (Yagodnoye village) 418.2 6.2 11.3 Wild rye sedge steppe (Borgoy village) 616.8 3.2 5.4 Cereal steppe (Tokhoy village) 5 7.8 5.6 4.4 Cereal wormwood sage steppe (Ivolginsk village) 515.4 9.8 15.1 Natural meadow (overall)11718.347.3 86.6 Motley grass (forb) meadow (Ust-Kyakhta village) 536.050.4181.4 Cereal-forb meadow (Kizhinga village) 619.844.0 87.1 Cereal meadow (Verkhniye Taltsy village) 4 7.425.0 18.5 Cereal meadow (Petropavlovka village) 515.638.0 59.3 Motley grass (forb) meadow (Tugnuy village) 531.054.0167.4 Cereal meadow (Kokorino village) 510.788.4 94.6 Cereal meadow (Kalenovo village) 6 8.437.6 31.6 Forb-cereal meadow (Unegetey village) 515.642.0 65.5 Swamp meadow (overall) 2527.644.4122.5 Cultivated vegetation (overall)13315.946.4 73.7 Cultivated cereals (Ivolginsk village) 6 8.341.0 34.0 Cultivated cereals (Oshurkovo village) 513.464.0 85.8 Cultivated cereals (Bolshaya Kudara village) 517.124.0 41.0 Standard [4]40 Excess amount [4] 500 nation with this chemical element. The majori- munities: the withdrawal of zinc with steppe ty of the species (39 or 81%) exhibit an insig- vegetation is insignificant (5.4–27.7g/ha). nificant difference in the content of zinc de- The content of zinc in the vegetation of the pending on growing within in different boitopes meadow landscapes ranges from 6.1 to 51.4mg/kg (up to 3 times), i.e. these species demonstrate with the maximal values for sedge of the bog the accumulation of the element according to meadows and minimal ones for cereal vegeta- a background barrier type. tion of the natural meadows. Meadow phyto- The content of zinc in hay crops of the aerial cenoses are formed within the flood-lands of biomass harvested from steppe, meadow and the rivers the Baikal Lake basin under the con- cultivated vegetation was characterized by a ditions of normal (natural meadows) and su- significant heterogeneity and varied within the perfluous (bog meadows) moistening; thee are range of 6.1–51.4mg/kg (Table 5). characterized by a high bioproductivity of the The content of zinc in steppe vegetation aerial mass and high zinc withdrawal with aerial changed from 6.4 to 48.6 mg/kg. The minimal parts of plants ranging within 19–181g/hà content is inherent in cereal phytocenoses, (97g/ha on the average). whereas the maximal content is typical for mis- The aerial mass of the plants of cultivated cellaneous herbs. The extreme environmental crops for the fodder purposes is characterized conditions with respect to moistening supply by the content of zinc ranging from 6.6 to (200–250mm of atmospheric precipitation dur- 31.2mg/kg. The basis of the agronomical phy- ing the vegetative season) determine a low bio- tocenoses is formed by cereals (mainly oats), logical productivity of the steppe plant com- therefore these cenoses are to the least extent 392 V. K. KASHIN provided with zinc (40% with respect to the cereals, the dominant vegetation of the steppe, standard). The productivity of the phytomass meadow and agricultural landscapes. within agrocenoses on the average amounts to It is revealed, that the content of zinc in 46.4centners/ha, whereas zinc withdrawal due grain of the main cereal crops (wheat and oats) to the phytomass is as high as 74g/ha. can vary over a wide range. So, for the grain The optimum zinc content in fodder plants of wheat the difference between the maximal according to contemporary requirements must content of zinc (58mg/kg) and minimal one be equal to 30–50 mg/kg (40mg/kg on the aver- (24mg/kg) amounts to 1.6 times, exhibiting 2.1- age), the deficient content is less than 20mg/kg, fold value for the grain of oats (the maximum whereas the maximum permissible zinc content and minimum being of 45 and 21mg/kg, re- amounts to 500mg/kg [5]. The zinc deficiency spectively). The content of zinc in the grain of based diseases of animals are observed within wheat and oats grown on soils of the forest- biogeochemical provinces and spots whose soils steppe landscapes is 1.4–1.6 times and 1.3–1.4 contain less than 3.0mg/kg of exchangeable times, respectively, higher as compared to its zinc, with fodder containing less than 20mg/kg. content in grains of these crops cultivated un- Basing on the standards presented, one could der the conditions of the steppe and arid steppe note mainly low zinc content in the vegetation landscapes (Fig. 2). The level of zinc content in of the region. The content of zinc in the vege- grain is much higher than that in straw. The tation taken from the 61 key sampling sites grain/straw zinc content ratio value ranges from (91%) of the 67 ones under investigation, ap- 2.3 to 5.0 for wheat and from 2.8 up to 4.5 for peared lower than the standard value, and the oats. This fact indicates the absence of a barri- deficiency of zinc for 45 of them ranged with- er at the boundary between vegetative and gen- in 50–80%, for 16 of them amounting to 20– erative organs with respect to the element un- 50%. The content of zinc in the vegetation, der consideration and the fundamental differ- which meets the standard (34–46mg/kg), was ence in the character of zinc accumulation in revealed only for six (9%) key sampling sites. grain as compared to other microelements. The low content of zinc in the vegetation of natural and agronomical cenoses (except for CONCLUSIONS the vegetation of swamp meadows) could be caused by the two factors such as a low con- The variety and complexity of the geochemi- tent of mobile zinc in the main types of soils cal processes occurring within natural landscapes and a barrier nature of zinc accumulation in attached to either lithogeochemical background cause spatial heterogeneity of zinc content in soil- forming rocks, natural waters, soils and plants. It has been established that the content of zinc in soil-forming rocks for steppe and arid steppe landscapes of the southern part of the territory studied (65–120mg/kg) is higher as compared to that for taiga and forest-steppe landscapes of the northern part (33–49mg/kg). The content of zinc in soil-forming rocks of the southern part amounts to 1.0–1.8, and for the northern part ranges within 0.4–0.7 with respect to its clarke in the lithosphere. Fig. 2. Zn content in wheat grain (1, 3) and in straw (2, 4), The content of zinc in natural waters of growing in forest-steppe (1–8) and steppe (9–16) landscapes the region is characterized by a maximum con- of the Western Transbaikalia: 1 – Korymsk, 2 – Stepnoy Dvorets, 3 – Kabansk, 4 – Selenginsk, trast ranging from 3 to 69 µg/L that is 23-fold. 5 – Zyryansk, 6 – Turuntayevo, 7 – Nyuki, 8 – Il’inka, Zinc concentration in superficial water is on the 9 – Shibertuy, 10 – Tarbagatay, 11 – Kharashibir, average equal to the clarke in river waters, 12 – Tugnuy, 13 – Maly Kunaley, 14 – Sharalday, whereas the concentration in underground wa- 15 – Bichura, 16 – Pesterevo. ZINC IN ENVIRONMENTAL OBJECTS OF TRANSBAIKALIA 393 ter is twice lower than its clarke in underground within the forest-steppe landscapes is higher as waters within the hypergenesis zone. compared to those for the steppe landscapes. It The differentiation of zinc in the soil profile is established that there is a barrier-free accu- occurs in accordance with two types. In the first mulation of zinc in grain with respect to straw. case in the presence of the alkaline sorption barrier the maximal content of zinc is inherent in carbonate horizons of chestnut and cher- REFERENCES nozem soils. The second type is characterized 1 T. M. Udelnova, B. A. Yagodin, Usp. Sovrem. Biotekhnol., by relatively uniform distribution of zinc in grey 113, 2 (1993) 176. woodland and alluvial soils (0.9- to 1.2-fold dif- 2 M. A. Rish, Tekhnogenez i Biogeokhimicheskaya ference in zinc content). It is revealed that there Evolyutsiya Taksonov Biosfery (Treatises), Nauka, is a close contingency between zinc content in Moscow, 2003, vol. 24, pp. 301–348. 3 Yu. A. Ershov, V. A. Popkov, A. S. Berland, A. Z. Knizh- soils and its content in soil-forming rocks and nik, Obshchaya Khimiya. 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