Baseline levels of chemical elements in the water of Lake Baikal

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Baseline Levels of Chemical Elements in the Water of Lake Baikal

V. A. Vetrova, A. I. Kuznetsovab and O. A. Sklyarovab

a Institute of Global Climate and Ecology, Rosgidromet and Russian Academy of Sciences, Moscow, Russiab Institute of Geochemistry, Russian Academy of Sciences, Irkutsk, Russia

e-mail: [email protected]: [email protected]

e-mail: [email protected] February 19, 2013

Abstract—Evidence for levels of five major elements (Na, Mg, Si, Ca, and K) and 53 trace elements (Li, Be, B,…, Pb, Th, and U) in the water mass of Lake Baikal is provided. The baseline levels of the elements were obtained from analyzing and summarizing the most reliable data published during the last 15 years, including these authors’ data. Most of the article focuses on an overview of the methodologies as used in the investigations involved (sampling techniques, and sample storage, processing and analysis methods). The summary table provides the most reliable concentration ranges for 58 elements which are recommended by these authors as background (baseline) levels.DOI: 10.1134/S1875372813030062Keywords: Baikal’s water, trace elements, baseline levels of elements, methodology.

INTRODUCTIONDetermination of natural (background) levels of

almost all elements from Mendeleev’s table in surface waters has been and is a currently important goal of investigations in the field of ecological geochemistry. To date the degree of understanding of natural and technogenic geochemical cycles is not sufficiently advanced in order to be able to comprehensively assess today’s state of biosphere and forecast its future changes. Trace element composition of natural waters is a critical indicator of the degree of environmental pollution and contamination [1–4] provided that background content levels of elements are estimated correctly. Such an estimation often presents a serious problem because of the influence of various factors, such as imperfection of sampling, sample preparation and water analysis techniques.

Lake Baikal is a unique object of biosphere. The first short summary of data on the trace element composition of the waters in South Baikal was provided in 1961 in a monograph of K.K. Votintsev, who presented the results from several determinations of Al, Cr, Mn, Fe, Co, Ni, and Cu in South Baikal [5]. Semi-quantitative estimates of the content levels of V, Mn, Fe, Ni, Cu, and Mo in the lake’s water were made by A.A. Matveev abd A.M. Anikanov in 1977 [6].

During the 1970s–1990s, a study of the element composition of Baikal’s waters was undertaken by V.A. Vetrov and collaborators with the participation of research teams from several organizations of the

Academy of Sciences of the USSR (Russian Academy of Sciences), and Goskomgidromet of the USSR [7]. The term “baseline level” was introduced for the first time in the national literature on ecological geochemistry, meaning the concentration of an element obtained by averaging available data over the entire water mass of a water body. The product of the baseline level by the water volume yields the value of total content (reserve) of an element in the water mass. A monograph [7] provides the values of mean concentrations C for 29 elements in the water mass of Baikal which are recommended by the authors as the baseline levels.

In the 1990s, data on the chemical composition on Baikal’s waters were published by American researchers based on results from two expeditions collecting water samples from Baikal: in 1988 [8], and in 1991 [9]. Results obtained by the two expeditions were used to quantify the concentrations of the following elements in the lake’s water: Na, Mg, Si, K, Ca, Li, Ве, Al, V, Cr, Ni, Cu, Zn, Ge, Rb, Sr, Ag, Cd, Cs, Ba, W, Hg, and U. During 1999–2002, the Limnological Institute and the Institute of Geochemistry (Irkutsk), Siberian Branch, Russian Academy of Sciences used the state-of-the-art ICP-MS spectrometers in studying the element composition of Baikal’s water in order to develop and store a standard sample of the composition of Baikal’s water [10–12]. Those investigations resulted in tentative estimates of the composition of about 40 trace elements in Baikal’s water.

ISSN 1875-3728, Geography and Natural Resources, 2013, Vol. 34, No. 3, pp. 228-238. © Pleiades Publishing, Ltd., 2013.Original Russian Text © V.A. Vetrov, A.I. Kuznetsova, O.A. Sklyarova, 2013, published in Geography and Natural Resources, 2013, Vol. 34, No. 3, pp. 41-51.

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GEOGRAPHY AND NATURAL RESOURCES Vol. 34 No. 3 2013

BASELINE LEVELS OF CHEMICAL ELEMENTS IN THE WATER OF LAKE BAIKAL

During 2007–2011, O.A. Sklyarova investigated the trace element composition of the lake’s waters in samples collected from different depths across the entire water body of Baikal. Results of element analysis of samples from Middle Baikal were published in 2011 [13]. This article presents Sklyarova’s summarized results which she obtained for the entire period of investigations.

Hence, over the last 15 years, new data have been obtained on the elemental composition of the lake’s water by using state-of-the-art high sensitivity methods of analysis [8–14]. This paper considers the results from relevant investigations with the purpose of gaining a more penetrating insight into the content levels of chemical elements in the water of Lake Baikal.

METHODOLOGYThe Methods Used

The main requirement to the methodology involves meeting the conditions ensuring the absence of losses and contaminations in all stages: from sampling to analytical completion. Another important condition implies using a set of analytical methods with a possibility of comparing results from analyzing a single element obtained by different methods. Furthermore, preference is given to multielement instrumental methods of analysis in which the use of chemical agents is minimized.

The following methods of analysis were mostly used in [7–14] considered here: atomic emission with arc and plasma (inductively coupled plasma) excitation (AE, and ICP-AE); instrumental neutron-activation (INA); inductively coupled plasma mass spectrometry (ICP-MS), and atomic absorption with plasma and electrothermal atomization (AA-PA, and AA-ETA).

Sampling and Sample Preparation for Analysis A general recommendation for minimizing the

pollution risk and losses in all stages of investigation involves a reduction (to a minimum) of any manipulations with the sample. Thus, when developing the scheme for collection and storage of water samples from Lake Baikal, the analytical procedures as used in [7] excluded the operations of acidification and filtration because of their almost inevitable contamination by Zn, Ag, Cu, Pb, and other elements; concentration was carried out by evaporation to a dry residual.

In [8, 9], samples were collected into 500-millimeter polyethylene reservoirs which were preliminarily flushed with 0.2N HCl and deionized water (DDW). In determining most of trace elements, samples were filtrated through acid-treated 0.45-μm nuclear filters, acidified to pH = 2 three times with purified HNO3, and were stored in preliminarily cleaned reservoirs. The methods of preconcenration included evaporation to dryness, extraction, coprecipitation, and ion-exchange concentration.

In the direct determination of trace elements, using

the “standard” of Baikal’s water, by the ICP-MS method [10–12], the sample preparation procedure used a stepped water filtration and sterilization system. The water taken from a great depth was passed through the 5, 1 and 0.45 μm filters, ozonizated and exposed to ultraviolet radiation.

For determining the distribution of trace elements in the water column of Middle Baikal [13], water samples for analysis were collected by means of expendable medical syringes which were flushed with the analyte twice, and put into polyethylene (preliminarily rinsed with 2% nitric acid) 15 mL containers. On the sampling site, samples were filtrated using expendable sterile Minisart filters (Sartorius, cellulose-acetate membrane filters) with 0.45 μm pores, and were immediately thereafter acidified with ultrapure nitric acid (“Merk”, Germany) to рН = 1–2.

Methods of Analyzing Samples In the investigations made during the 1970s–1990s

by Vetrov, Kuznetsova and collaborators [7], the scheme of multielement analysis for samples of a different origin included three methods of analysis: AE, INA, and AA, with results of INA analysis being monitored through comparison with direct (without concentration) methods of analysis, i.e. AA, and ICP-MS.

A wide variety of analytical methods were used by American researchers in the 1900s: АА-PА, АА-ETA, and АА with hydride generation (GFAAS); ICP-MS with isotopic dilution (ID-TIMS), with hydride generation (HG-ICP-MS), and with thermal atomization; gas chromatography and potentiometry [8, 9].

Atomic emission analysis. AEA with arc excitation was used in quantifying trace elements in the natural environments of Lake Baikal [7]. Special-purpose procedural investigations showed a possibility of quantifying in the dry residual of the water of the lake and its tributaries as many as 16 elements: B, Al, Ti, V, Mn, Fe, Со, Ni, Cu, Zn, Sr, Mo, Ag, Sn, Ba, and Pb [15].

Atomic absorption analysis. In the natural waters in the area of Lake Baikal, the variant of the AA method with electrothermal atomization can be used to quantify Ni, Cu, Zn, Sr, Ag, Ba, and Pb with their levels 0,n−n μg/L in natural waters [7]. In investigating the aquatic ecosystems of the Baikal Natural territory, the AA method was used to quantify Hg by decreasing the detection limit (DL) to 0.0005 μg/L/dm3 by trapping fumes of recovered Hg with an absorbing solution [14].

Inductively coupled plasma atomic emission spectrometry. In interlaboratory experiments to analyze a candidate standard water sample from Baikal, some laboratories in other countries used the ICP-AES method to determine the major component composition of the water [10].

Instrumental neutron-activation analysis. An analysis of Baikal’s water by the INAA method was


230 VETROV et al.

made for the first time in 1974 [7]. Solids were analyzed after evaporation to dryness. The DL for the elements Sc, Co, Sb, Cs, and Eu ~ 0.001 μg/L, and for Na, Fe, Zn – 1–10 μg/L. Comparison with other methods of analysis showed the reliability of the determination of the elements Sc, Zn, Se, Br, Rb, Sr, and U in Baikal’s water using the INAA method [7].

The analytical technique of inductively coupled plasma mass spectrometry. The ICP-MS technique began to be used in determining trace elements in Baikal’s water by national laboratories in 2000 [10–12]. Low concentrations of most elements in blank tests were instrumental in quantifying the content levels of 42 elements in the water of Baikal. In the DL region, Al, Ti, Zn, Ga, Tl, and Th were analyzed [13].

The photometric method should be added to the aforementioned analysis techniques; it was used to determine fluorine with DL = 0.05 μg/dm3 in the aquatic ecosystem of the Baikal Natural Territory [14].

TRACE ELEMENTS IN THE WATER MASS

OF LAKE BAIKALNew data. Water samples were collected by O.A.

Sklyarova from three hollows across two transverse cross-sections (profiles) of Lake Baikal at each of the sampling points (stations) at an equal distance from the shore during the summer months of 2007–2011

by means of a five-liter plastic deep-water “Niskin” bathometer (Fig. 1). Each of the profiles in the northern and southern hollows incorporated three stations, with five stations corresponding to each of the profiles in the middle hollow, totaling 22 sampling stations. At each station in the southern hollow, samples were taken from depths ranging from 200 to 1200 m, amounting to a total of 76 samples. At each of the 10 stations in the middle hollow, three samples were collected from a depth of 100 m, totaling 30 samples. Samples in the northern hollow were collected in 2007 and 2011 at six stations (profiles A and B) from depths of 200–625 m, totaling 32 samples. Thus 138 samples were taken from the entire water mass of the lake.

The sampling, sample preparation and analysis methods were the same as used in investigating the trace element composition of the waters of Middle Baikal [13] (see the “Methodology” section”).

Table 1 provides summarized data obtained by analyzing, by the ICP-MS method, all samples collected between 2007 and 201 in the form of mean values and parameters of statistical distributions of element concentrations for the entire set of analysis results obtained. We divided all the analyte elements into five groups.

The elements of group I show an even distribution throughout the column of Baikal’s water, and their DL (according to the 3σ-criterion for blank test) is vastly below the determined concentrations. We included in group II the elements with concentrations in the lake’s water similar to or below the respective DL. Group III includes the hydrolyzant elements Al and Fe that form colloids of hydroxides differing in size and showing an uneven distribution in Baikal’s water. This group also incorporated the biogenic elements Mn and P whose content levels in the lake’s water can depend on plankton content and vary markedly with sampling depth, place and time. Group IV includes the elements Zn and Cd, characterized by a wide range of concentrations because of unmonitored pollution at the stages of sampling and sample preparation.

Table 1 provides minimum and maximum values of element concentrations for groups III and IV, because statistical distributions of concentrations of these elements have no stable regularities. Group V includes rare-earth elements in Middle Baikal [13]; the confidence range of concentrations is characterized by the interval of percentiles (15–85%) corresponding to the interval [(С – σ) – (С + σ)].

Fig. 2 shows the forms of statistical distributions for representatives of four out of the aforementioned groups of elements: Sc – first group, normal distribution; Ga – second group, asymmetric distribution; Fe – third group, uneven distribution, and Cd – fourth group, bimodal distribution.

Summary of data. The summary of the most representative data on element contents in the lake’s water thus far published is provided in Table 2 together with our data (see Table 1). Column 2 of Table 2 shows

Fig. 1. Schematic map of water sampling from Lake Baikal.

(1) sampling station. (2) А−F – profiles.

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Table 1. Content of trace elements in the water of Lake Baikal according to these authors’ research results

Element DL, μg/L N C , μg/L М, μg/LPercentiles, μg/L

σ, μg/LР10 Р90

Group ILi 0.14 138 2.02 2.01 1.99 2.09 0.04B 0.3 87 5.0 4.9 4.4 5.6 0.4Sc 0.0006 138 0.0017 0.0017 0.0011 0.0025 0.0006V 0.01 138 0.37 0.37 0.35 0.38 0.02Cr 0.01 138 0.07 0.07 0.06 0.08 0.01Ni 0.01 138 0.15 0.14 0.13 0.16 0.01Cu 0.01 138 0.21 0.21 0.18 0.25 0.03As 0.02 138 0.40 0.40 0.34 0.47 0.05Se 0.01 138 0.04 0.04 0.03 0.06 0.01Br 1.0 48 7.9 7.8 7.2 8.8 0.6Rb 0.01 138 0.55 0.55 0.53 0.57 0.02Sr 0.1 138 101 100 96 106 4.3Y 0.0006 138 0.0033 0.0033 0.0027 0.0039 0.0006

Mo 0.03 138 1.34 1.34 1.30 1.39 0.04Sb 0.013 138 0.031 0.032 0.028 0.034 0.002Ba 0.1 138 9.9 9.9 9.5 10.4 0.4W 0.01 138 0.05 0.05 0.05 0.06 0.005U 0.01 138 0.55 0.54 0.51 0.58 0.03

Group IIBe 0.0014 138 < 0.0014 – – – –Ti 0.03 87 0.04 0.04 0.03 0.05 0.01Co 0.0020 138 0.0030 0.0030 0.0023 0.0045 0.0009Ga 0.0008 96 0.0009 0.0008 < 0.0008 0.0013 0.0003Ge 0.0015 96 0.0017 0.0016 < 0.0015 0.0028 0.0008Zr 0.0010 138 0.0017 0.0016 < 0.0010 0.0028 0.0008Ag 0.002 138 < 0.002 – – – –Sn 0.01 138 < 0.01 – – – –Cs 0.0010 138 0.0013 0.0013 <0.0010 0.0016 0.0003Tl 0.0005 138 ≤ 0.0005 – – – –Pb 0.02 138 < 0.02 – – – –Th 0.0004 138 0.004 – 0.002 0.006 –

Group III

Element DL, μg/L N C , μg/L М, μg/LConcentration limits

σ, μg/Lmin max

Al 0.15 138 0.38 0.33 < 0.15 0.92 0.19P 0.2 87 15.7 15.6 11.2 23.5 –

Mn 0.01 138 0.13 0.04 0.01 0.53 –Fe 0.04 138 0.38 0.34 0.09 1.64 0.22

Group IVZn 0.3 87 3.2 1.2 < 0.3 14.0 –Cd 0.005 138 0.008 0.008 < 0.005 0.017 –


232 VETROV et al.

Fig. 2. Statistical distribution of results from analyzing the elements, the representatives of the four groups (see Table 1).Distribution: gr. I (Sc) – normal, gr. II (Ga) – asymmetric, gr. III (Fe) – uneven, gr. IV (Cd) – bimodal.

Table 1 (Contd.).

Element DL, μg/L N C , μg/L М, μg/LPercentiles, μg/L

σ, μg/LР15 Р85

Group VLa 0.0013 30 0.0024 – 0.0018 0.0030 0.0006Ce 0.0005 30 0.0034 – 0.0027 0.0041 0.0007Pr 0.0001 30 0.0004 – 0.0003 0.0005 0.0001Nd 0.0007 30 0.0017 – 0.0011 0.0023 0.0006Sm 0.0002 30 0.0004 – 0.0003 0.0005 0.0001Eu 0.0007 30 < 0.0007 – – – –Gd 0.0001 30 0.0005 – 0.0004 0.0006 0.0001Tb 0.0001 30 < 0.0001 – – – –Dy 0.0001 30 0.0004 – 0.0003 0.0005 0.0001Ho 0.0001 30 < 0.0001 – – – –Er 0.0001 30 0.0003 – 0.0002 0.0004 0.0001Tm 0.00007 30 < 0.00007 – – – –Yb 0.0001 30 0.0003 – 0.0002 0.0004 0.0001Lu 0.0001 30 < 0.0001 – – – –

Note. DL – detection limit; N – number of samples; C − mean value; М – median; Р10 – 10% percentile: the concentration below which there are 10% of the values of the sample; Р90 – 90% percentile: the concentration above which there are 10% of the values of the sample; σ – standard deviation of statistical distribution.

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Table 2. Content of chemical elements in the water of Lake Baikal according to research data after 1991

ElementVetrov and Kuznetsova

[7]Falkner et al.

[8, 9]Suturin et al.

[10] Paradina et al. [11] Mysovskaya et al. [12]

Estimates from these authors’ data

Trace elements, mg/LF 0.20–0.22 0.18–0.21*

Na 3.56 ± 0.09 3.29–3.45 Mg 3.06 ± 0.02 3.0–3.2 Si 0.75–2.01 0.54–0.84 K 0.94 ± 0.04 0.89–0.95 Ca 16.1 ± 0.3 15.5–16.1

Trace elements, μg/LLi 2.0 1.7–2.2 2.15 ± 0.16 2.0–2.1Be 0.0004–0.0006 0.0070 ± 0.0004 0.0008 ± 0.0004 < 0.0014B 2.9–19.5 5.9 ± 0.9 4.4–5.6Al 68 0.04–1.0 0.28–0.76 1.02 ± 0.5 0.38(< 0.15–0.92)P 11.2–23.5Sc 0.0039 0.0020 ± 0.0017 0.0011–0.0025Ti 0.044 ± 0.029 0.03–0.05V 0.32 0.32–0.48 0.32–0.58 0.33 ± 0.013 0.42 ± 0.04 0.35–0.38Cr 0.53 0.06–0.10 0.034–0.062 0.34 ± 0.045 0.65 ± 0.06 0.06–0.08Mn 1.5 0.06–0.22 0.080 ± 0.007 0.13(0.01–0.53)Fe 30 1.3 ± 0.3 0.38(0.09–1.64)Co 0.047 0.016–0.052 0.038 ± 0.003 0.13 ± 0.02 0.0023–0.0045Ni 0.51 0.08–0.23 0.24–0.90 0.31 ± 0.03 0.13–0.16Cu 1.1 0.14–0.28 1.46 ± 0.12 0.18–0.25 Zn 4.3 0.45–1.3 1.7–4.3 3.55 ± 0.72 3.2(< 0.25–14.0)Ga 0.0018 ± 0.0006 < 0.0008–0.0013Ge 0.0015–0.0029 0.0073 ± 0.0004 0.0027 ± 0.0010 < 0.0015–0.0028As 0.3 0.3–0.5 0.35 ± 0.007 0.31 ± 0.12 0.34–0.47Se 0.06 0.03–0.06Br 20 7.2–8.8Rb 0.34 0.61 ± 0.03 0.41–0.53 0.37 ± 0.02 0.52 ± 0.04 0.53–0.57Sr 53 118 ± 33 101–107 99.5 ± 3.5 96–106Y 0.0039 ± 0.00006 0.005 ± 0.001 0.003–0.004Zr 0.017 ± 0.006 < 0.001–0.003Mo 0.78 1.1–1.5 1.42 ± 0.11 1.3–1.4Ag 0.001 0.0026 ± 0.0011 < 0.002Cd 0.03 0.0002–0.002 0.002–0.010 0.0063 ± 0.0002 0.0086 ± 0.0050 0.008(< 0.005–0.017)Sn 0.04 0.015 ± 0.006 < 0.01Sb 0.17 0.11–0.25 0.37 ± 0.07 0.028–0.034Cs 0.014 0.0027 ± 0.0003 0.0039 ± 0.0002 0.0063 ± 0.0012 < 0.0010–0.0016Ba 5.8 9.13–10.52 9.5–11.1 10.0 ± 0.4 9.5–10.4La 0.07 0.0020 ± 0.0001 0.0018–0.0030 Ce 0.19 0.0012 ± 0.0001 0.0027–0.0041


234 VETROV et al.

concentration levels for elements in Baikal’s water mass recommended in a monograph [7] as “baseline” levels. [7]. Column 3 gives estimates of element contents in the lake’s water made from results reported in [8, 9] in the form of means ± standard (root-mean-square) deviation for data from [8], and confidence (0.1–0.9) intervals of element concentrations for data from [9].

The next two columns, 4 and 5, contain data on concentrations of trace elements in a “standard sample” of water from Baikal [10, 11]. Column 4 presents data from [10] in the form of confidence intervals (0.05–0.95); column 5 provides data from [11] in the form of mean concentrations with standard deviations.

Mean concentrations of trace elements in Baikal together with standard deviations taken from [12] are given in column 6. The sampling and analysis conditions for 30–40 samples in the just cited reference are the same as used by the authors of the standard of Baikal’s water [10, 11], which is testified by a good agreement of the results for all elements (except for Cr and Со), common to these papers.

Column 7 provides our estimates in the form of confidence intervals or full ranges of concentration

(min–max), as in Table 1. We included in this same column the data from [14, 16] on fluorine and mercury content levels in Baikal.

Thus we have in Table 2 a summary of our data in comparison with results from available findings published after 1996, on content levels of 58 elements in Lake Baikal’s water.

DISCUSSIONIn Table 2, many of the data are represented as

mean values of concentrations with standard deviations obtained in a statistical processing of homogeneous samples of analysis results (using a single method in a single laboratory). However, not nearly al of the results show a smooth (not to mention a normal) distribution.

It was suggested in [7] that an estimation of the value of mean (“baseline”) concentration of the element determine din the water mass of a huge water body, such as Lake Baikal, must take into account, in the first place, variations in analytic data and, second, differences in data obtained by different methods and/or by different groups of analysis. In the latter case, of critical importance in estimating the degree of reliability

Table 2 (Contd.).

ElementVetrov and Kuznetsova

[7]Falkner et al.

[8, 9]Suturin et al.

[10] Paradina et al. [11] Mysovskaya et al. [12]

Estimates from these authors’ data

Pr 0.00037 ± 0.00003 0.0003–0.0005Nd 0.0021 ± 0.0001 0.0011–0.0023Sm 0.00043 ± 0.00004 0.0003–0.0005Eu 0.0034 0.0044 ± 0.0004 < 0.0007Gd 0.00056 ± 0.00005 0.0004–0.0006Tb 0.00007 ± 0.000007 < 0.0001Dy 0.00045 ± 0.00003 0.0003–0.0005Ho 0.00009 ± 0.000006 < 0.0001Er 0.00027 ± 0.00002 0.0002–0.0004Tm 0.00006 ± 0.000005 < 0.0001Yb 0.00033 ± 0.00002 0.0002–0.0004Lu 0.00006 ± 0.000004 < 0.0001W 0.34–0.48 0.072 ± 0.002 0.064 ± 0.009 0.05–0.06Re 0.00060 ± 0.00003 0.00067 ± 0.00009

< 0.0005–0.0020*Hg 0.005 0.00039–0.0014 0.00014–0.00077**Tl 0.00093 ± 0.00005 ≤ 0.0005Pb 0.45 0.028–0.064 0.047 ± 0.007 0.039 ± 0.014 < 0.02Th 0.022 0.002–0.006U 0.4 0.42 ± 0.028 0.38–0.62 0.57 ± 0.02 0.70 ± 0.03 0.51–0.58

* Acc data in [14]. ** Acc data in [16].

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of results should be metrological characteristics of analysis, namely DL, the number of samples, and correctness.

Analysis of the most reliable data thus far published permitted us to indicate the list of elements for which the estimation of their baseline levels (BL) can be thought of as being reliable provided that the distribution of their content levels in the lake’s water mass (except for Al, Mn, Fe, and Zn) is more or less uniform. In a small number of cases (Li, V, As, Rb, Sr, Ba, and U) results of all determinations show a remarkably good agreement.

Table 3 provides our estimates of the most reliable BL limits for 58 elements in Baikal’s water mass. This technique of BL representation in summarizing results from all the investigations considered here and presented in Table 2 was used from the following considerations.

First, given the wide variety of sufficiently reliable methodologies, on the basis of which the data were obtained (see Table 2), we are unable to suggest any “objective” criteria using which it would be possible to favor results obtained by some or other particular authors.

Second, an attempt to characterize the content level of some element in the lake using a single-valued baseline level is in contradiction with the statistical nature of element concentrations in analyte samples,

and in different volumes of the lake’s water mass. In this case, some confidence interval will more closely correspond to the nature of things, which must include results of analysis in a methodologically correct investigation. Hence, the selection of BL intervals (see Table 3) is based on expert evaluation of the degree of reliability and confidence level of results obtained by different researchers.

First and foremost it is necessary to highlight the group of elements for which similar (consistent, at least) results were obtained in all investigations: Li, B, Sc, V, Со, Ni, Cu, As, Se, Br, Rb, Sr, Y, Mo, Ag, Sn, Sb, Ba, Eu, and U (see Table 2). Based on analyzing relevant publications, most (17 elements among 29) of the first estimates of BL made in [7] were found to be sufficiently reliable in spite of the large differences in the methodology with subsequent investigations. A significant excess of the indicators from the first BL estimations [7], when compared with the more reliable results from later investigations, occurs for Al, Cr, Mn, Fe, Cd, Cs, La, Ce, Hg, Pb, and Th. The reason has to do with the differences in the methodology of determining trace element concentrations at all the stages: from sampling and sample preparation (filtering, preservation, concentration, etc.) to analytical completion (using the more sensitive ICP-AE) techniques.

As might be expected, the narrowest BL intervals with the max/min ratio as small as 1.7 for the following

Table 3. Baseline level intervals for elements in Lake Baikal

Element Baseline level interval Data sourceBackground content in surface freshwaters

Yaroshevskii [17], Korzh [18] Markert [20], Gaillardet [21]Trace elements, mg/L

F 0.18–0.22 [10, 14] 0.1 0.1Na 3.3–3.6 [8, 10] 5–5.3 5Mg 3.0–3.2 [8, 10] 2.9–3.4 4Si 0.5–2.0 [10] 6–7.6K 0.9–1.0 [8, 10] 1.5–2 2Ca 15.5–16.4 [8, 10] 12–14 2

Trace elements, μg/LLi 1.7–2.2 [8-10, 12, o.d.] 2.5 2–3Be 0.0004–0.0012 [8, 12] 0.002 0.01–0.1В 4.4–6.8 [12, o.d.] 17–20 10Al 0.1–1 [8-10, 12, o.d.] 50–160 30–200P 11–24 [o.d.] 40 20Sc 0.001–0.004 [7, 12, o.d.] 0.004 0.002–1.2Ti 0.03–0.05 [o.d.] 3 0.5–3V 0.3–0.6 [7-13, o.d.] 1 0.7–1Cr 0.03–0.09 [9, 10, o.d.] 1 0.7–1Mn 0.01–0.53 [o.d.] 8–10 5–34Fe 0.1–1.6 [o.d.] 40 66–500


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Table 3 (Contd.).

Element Baseline level interval Data sourceBackground content in surface freshwaters

Yaroshevskii [17], Korzh [18] Markert [20], Gaillardet [21]Co 0.02–0.05 [7, 10, 11] 0.2–0.3 0.15–0.5Ni 0.1–0.5 [7-10, 12, o.d.] 0.5 0.3–0.8Cu 0.2–1 [7-10, o.d.] 1.5–7 1.5–3Zn 0.4–4.3 [7-10, 12, o.d.] 0.15–20 0.6–5Ga 0.001–0.002 [11, o.d.] 0.1 0.03–0.1Ge 0.002–0.007 [9, 11, 12, o.d.] 0.014–0.07 0.007As 0.3–0.5 [7, 10-12, o.d.] 1.7–2 0.5–0.6Se 0.03–0.06 [7, o.d.] 0.2–20 0.07–0.2Br 7–9 [o.d.] 20–200 15Rb 0.3–0.6 [7-12, o.d.] 1.5–2 1–1.6Sr 96–107 [10, 12, o.d.] 50–60 50–60Y 0.003–0.006 [11, 12, o.d.] 0.7 0.04–0.4Zr 0.001–0.003 [12, o.d.] 2.6–2.7 3Mo 0.8–1.5 [7, 10, 11, o.d.] 0.5–1 0.4–1Ag 0.001–0.004 [7, 9, 12] 0.2 0.3Cd 0.001–0.010 [10, 12, o.d.] 0.01–0.2 0.08–0.2Sn 0.01–0.04 [7, 12] 0.04 0.01Sb 0.03–0.2 [7, 10, o.d.] 0.04–1 0.07–0.2Cs 0.002–0.008 [8, 11, 12, o.d.] 0.02–0.03 0.01–0.05Ba 9–11 [7-10, 12, o.d.] 30–60 10–23La 0.001–0.003 [11, o.d.] 0.05 0.1–0.3Ce 0.001–0.004 [11, o.d.] 0.007–0.08 0.3–0.4Pr 0.0003–0.0005 [11, o.d.] 0.007 0.04–0.06Nd 0.001–0.002 [11, o.d.] 0.04 0.15–0.2Sm 0.0003–0.0005 [11, o.d.] 0.008 0.03–0.04Eu 0.003–0.005 [7, 11] 0.001–0.004 0.01Gd 0.0004–0.0006 [11, o.d.] 0.008 0.004–0.1Tb 0.00006–0.00008 [11] 0.001 0.0055–0.008Dy 0.00004–0.0005 [11, o.d.] 0.005 0.03–0.04Ho 0.00008–0.00010 [11] 0.001 0.007–0.01Er 0.0002–0.0004 [11, o.d.] 0.004 0.02–0.03 Tm 0.00005–0.00007 [11] 0.001 0.003–0.008Yb 0.0002–0.0004 [11, o.d.] 0.001–0.004 0.002–0.03Lu 0.00006 [11] 0.001 0.002W 0.05–0.07 [11, 12, o.d.] 0.03 0.03–0.1Re 0.0006–0.0008 [11, 12] – 0.0004Hg 0.0001–0.0014 [9, 16] 0.07 0.1Tl 0.0005–0.0010 [11, o.d.] 0.007–1 0.04Pb 0.03–0.06 [10-12] 0.1–1 0.08–3Th 0.002–0.02 [7, o.d.] 0.1 0.04–0.1U 0.4–0.7 [7- 12, o.d.] 0.24–0.4 0.1–0.4

Note. o.d. – our data (see Tables 1 and 2).

237



trace elements: F, Na, Mg, K, and Ca; this group of the most “stable” elements also includes Li, B, Ti, As, Br, Sr, Ba, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Tm, W, and Re. The group of the most “problematic” eight trace elements with the max/min ratio equal to 10 or more, now includes the familiar “unstable” Al, Mn, Fe, Zn, and Cd (see Table 3) as well as Zr, Hg, and Th. For most of the other elements (see Table 3), relatively narrow BL intervals with the max/min ratio in the range from 1.8 to 6 are suggested.

We availed ourselves of our technique to obtain reliable results in determining the BL intervals for 41 out of the 50 elements which we analyzed. Table 3 provides data on background contents of chemical elements in unpolluted surface freshwaters of the world as reported in overviews of national and foreign authors [17–20]. Comparison of the BL intervals for the elements in Baikal which we adopted, with data published worldwide intimates that according to the levels of the 58 elements considered in this study, Lake Baikal belongs to the cleanest water bodies of biosphere.

Rejection of single-valued estimates of element BL in the lake’s water, and also the forecasted low rates of their growth under the effect of anthropogenic sources make any attempts at direct analytical detection of BL growth unpromising for the observing period shorter than 20–30 years [7].

CONCLUSIONS

A necessary condition for the methodology of determining trace elements in unpolluted freshwater bodies involves making use of a set of analytical (mostly instrumental) methods. This furnishes a means of copying with a very important issue of monitoring the validity of results with due regard for statistical characteristics of data, and for the differences between data obtained by different methods and/or by different groups of analysts.

We made up a summary of the most representative data thus far published, concerning contents of 58 elements in Baikal’s water as obtained since 1997 till the present (2012) by six teams of authors, including the authors of this paper. These data were used to make estimates of the most reliable intervals (limits) of baseline levels for 58 elements in the lake’s water mass, based on expert evaluation of the reliability and certainty of results obtained by different research teams. This BL representation procedure most closely corresponds to the statistical nature of element concentration variations in analytical samples, and in different volumes of the lake’s water mass. Comparison of the BL intervals for the elements in Baikal which we adopted, with data published worldwide intimates that according to the levels of the 58 elements considered in this study, Lake Baikal belongs to the cleanest water bodies of biosphere.

ACKNOWLEDGMENTSThis work was done with financial support from

the Russian Foundation for Basic Research (09–05–00884) and under SB RAS investment projects (Nos. 110 and 5).

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Baseline levels of chemical elements in the water of Lake Baikal