SR XRF element analysis of sea plankton

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Nuclear Instruments and Methods in Physics Research A 543 (2005) 259–265 www.elsevier.com/locate/nima

SR XRF element analysis of sea plankton V.A. Bobrov, M.A. Phedorin, G.A. Leonova, Yu.P. Kolmogorov Trofimuk United Institute of Geology, Geophysics and Mineralogy (UIGGM) of SB RAS, Koptyuga av.3, Novosibirsk 630090, Russian Federation Available online 4 March 2005

Abstract Seven samples of plankton from the Beloe Sea sampled at the //Ecolog-2002SS research ship trip were analyzed by the SR XRF method. Measured XRF spectra were processed with the help of an algorithm accounting matrix effects of element interaction. SR XRF results together with high-resolution atomic-absorption and neutron-activation data allowed to determine concentrations of 43 chemical elements in plankton. Comparison with bottom sediments allowed us to calculate enrichment coefficients EF; plankton from the open ocean margin (Beloe Sea) concentrates Br, I, Cd, Zn, Cu, Cr, As, Pb, Se, Sn, Hg, Sb in different degrees (EF from 1000 to 10). r 2005 Elsevier B.V. All rights reserved. PACS: 07.85.Qe; 92.70.Gt; 92.40.Fb; 91.65.Dt Keywords: X-ray fluorescence; Plankton; Biophile; Rare elements; Enrichment factors (EF)

1. Introduction A unique feature of plankton to extract microelements from water has been well known to oceanologists and reported by many investigators [1,2]. Such feature of plankton has been used as an indicator of heavy metal pollution of Siberian water ecosystems [3]. Sea water is characterized by much higher concentrations of mobile/soluble elements compared to fresh water. The usual background concentration for the sea water may Corresponding author. Tel.: +7 3832 332307;

fax: +7 3832 332792. E-mail address: [email protected] (V.A. Bobrov).

appear abnormal for fresh water basins and, in respect to iron group elements, even for some salt lakes. According to recent ecological studies the major area of Beloe Sea is natural background water with a geochemistry typical for marginal seas of an open ocean. The authors performed analysis of trace elements in plankton from Beloe Sea sampled in the Onega, the Dvina and the Kandalaksha gulfs during the ship expedition in September 2002 (Fig. 1). Analytical data characterize two types of sea plankton, surface and abyssal. The surface plankton of the Onega gulf (st. 1a, 64, 66) consists of phytoplankton and detritus with relatively large part of mineral (terrigenous) suspension. The

0168-9002/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2005.01.218

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36°

32°

40°

68°

44°

N

Kandalaksha Gulf ★58 ★3a 66° Beloe Sea 76 ★ 1a ★ ★ 66

★ 78

Dvina Gulf

★ 64

64°

Onega Gulf

Fig. 1. Station location of plankton sampling.

abyssal plankton of the Dvina (st. 76, 78) and the Kandalaksha (st.3a, 58) gulfs are presented by very pure (without suspension) phytoplankton. Traditionally, the element composition of plankton has been studied by the atomic absorption (AA) method, although for a restricted number of elements (about 10). The authors used three analytical techniques: AA together with SR XRF (X-ray fluorescence with the synchrotron radiation) and instrumental neutron activation (INAA), which allowed determination of 43 in few milligrams of natural matter. Of special importance are SR XRF data. The available sensitivity of the method allows qualitative determination of many elements from Cl to Ba, also light lanthanides and Pb, Th in initial plankton substance (phytoplankton). It is important that SR XRF technique does not require incineration of carbon-bearing samples, which is a necessary procedure for AA and INAA. Some methodical difficulties are related to high concentrations of Br and I, because of their essential ability to absorb fluorescence of definable element

group. The absence of attested reference samples to compare with the composition of sea plankton made us to use the below described algorithm for prediction of concentrations based on measured fluorescence fluxes.

2. Analytical procedure Fluorescence spectra were measured at the XRF station with synchrotron radiation SR (in Institute of Nuclear Physics, Novosibirsk). Energies of monochromatic excitation beam were 14, 24 and 47 keV (Figs. 2a and b). The samples were cylindrical ‘‘tablets’’, 6 mm in diameter, with surface density 0.06 g/cm2. We measured seven samples of plankton and two reference samples: grass-mix CBMT-02 [4] and Baikalian mud BIL-1 [5]. The prediction of element concentrations from initial SR XRF data was performed by the method of fundamental parameters [6]. The mathematical model accounted two acts of photo absorption in

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Fig. 2. SR XRF spectra: (a) plankton sample and BIL-1 reference sample, energy of exciting monochromatic beam E 0 ¼ 47 keV; (b) plankton sample, E 0 ¼ 24 keV: Note logarithmic ordinate scale. X-ray detector is LINK semiconductor with 3 mm Si crystal, 8 mkm Be window and less than 150 eV energy resolution (at Mn–Ka line).

the substance, second is for inter-element fluorescence excitation. For estimation of concentrations Ci (g/g) we solved a system of equations either by the outer standard method C i ¼ C RS i 0

Fi =FInc RS

RS

Fi =FInc

11 1  expfai Dg ð1 þ gi Þ C B ai B C B C , RS @1  expfaRS A RS i D g ð1 þ g Þ i RS ai i ¼ 1; :::; N,

ð1Þ

where as reference samples (RS) we used CBMT02 [4] and BIL-1 [5] or by the internal standard method

C i ¼ C Br 0

Fi FBr

11  expfai Dg ð1 þ gi Þ C B ai C , B @ A 1  expfaBr Dg PS_Kj ð1 þ gBr Þ Br sBr ðE 0 Þ aBr i ¼ 1; :::; N, ð2Þ 1 i sPS_Kj ðE 0 Þ i

where as internal standard we used values of Br concentrations determined previously by (1) or taken from the INAA data. The symbols in (1), (2) are as follows: Fi and RS Fi and FBr are measured values of fluorescence intensities (fluxes) from an element i in the sample and in the reference sample (RS) and from the Br; RS FInc and FInc are the measured values of incoherently scattered intensity from the sample and the RS, which are used as a measure of source quanta and of the irradiated sample mass; D and DRS are sample thickness; sPSKj (Eo) is the ‘‘mass crossj section’’ (sm2/g) of the photoabsorption of the quanta with energy Eo at a pure element i, taking into account all probabilities of the irradiation of a fluorescence quantum of Kj characteristic line with the energy EiKj; ai and aRS are functions of total i macroscopic cross-sections SðE o Þ (is function of monochromatic radiation of the source) and SðE iKj Þ (of the fluorescent radiation), ai ¼ ðSðE o Þ=sin yfall Þ þ ðSðE iKj Þ=sin ydetect Þ; where yfall and ydetect are angles of the falling and detected fluxes, respectively; gi ; gRS i ; gBr are the corrections for second-order excitation of fluorescence of element i and of Br, respectively, by fluorescent fluxes from all other elements (expressions for g are taken from [7]); i and Br are detector’s

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response functions with respect to the radiation of an i element and Br. The systems of equations were solved by iterative methods, because all macroscopic crosssections are determined by all concentrations: S ¼ P r N i¼1 C i si ; where si ðEÞ is ‘‘mass’’ cross-sections of X-ray attenuation at pure i-element (i.e. a sum of the cross-section of photoabsorption, Compton scattering and others). All the values of ‘‘mass cross-sections’’ on pure elements i were taken from [7].

3. Results and discussion Table 1 shows the contents of microelements in the Beloe Sea plankton, compared with oceanic zooplankton and oceanic water. For Cr, Fe, Co, Zn, the data of two independent methods AA and INAA (or AA and SR XFR) are compared; data on other elements from individual methods are also presented. Some published data on element concentrations in Beloe Sea plankton are not complete: in cited report [8] the data about Y, Nb, Hf, Ta, heavy lanthanides are absent; in [9] light lanthanides and Th are also absent. The advantage of our data is that we determine, together with Sc, many of rare and rare earth elements for geochemical characterization of terrigenous suspension. Based on the analysis of bottom sediments, the list of hard-to-dissolve elements and their concentrations in suspension can be established (as a first approximation). The consideration of results for sea bottom sediments is beyond the scope of present paper, but we only note that geochemistry of 21 sediment samples from the seven stations (listed in Table 1) is very similar to the clay shale [8]. This fact supports the correctness of using shale for comparison while determining the plankton biogeochemical activity. According to the technique accepted in biogeochemistry, we calculated the enrichment factors (EF) in the plankton with regard to Clarke concentrations of elements in the continental clay (shale) with the preliminary

normalization to Sc, EF ¼ ðxi =ScÞsample =ðxi =ScÞshale .

(3)

Table 2 shows the EF coefficient values for all the seven stations and for oceanic plankton [8] where Sc content is not more than 0.07 mkg/g (for dry substance). As Savenko comments [9], the determination of mean concentration of chemical elements in marine organisms is of great difficulty, because of seasonal and other variations. That is why our data may be treated as characteristic for White Sea plankton only from particular gulfs in September 2002. Concentrations: The ash content in the Onega gulf plankton gives 30–40% of dry substance; Sc content is about 3.8 mkg/g of dry substance; along with Sc, concentrations of all rare and rare-earth elements, connected with mineral suspension, are about 13 of concentration in clay (shale). The concentration levels of biophile elements, such as, Cd, Zn, Cu, Cr, Pb, Hg, Se, Sb (Table 1) well-soluble in sea water, are relatively similar and differ from sample to sample by the factor of 2–4, reaching 10 for Cr. In comparison with oceanic plankton [8,9], plankton of Beloe Sea is more saturated with Cr, Cu, Zn. This fact indicates the specific geochemical environment, typical for the marginal sea of the open ocean. Enrichment Factors: The EF values (Table 2, Fig. 3) of the abyssal plankton for the group of biophile elements are comparable (except Cr and Sn) with the same for oceanic. The high saturation of oceanic plankton by biophile elements due to soluble forms, is well known and universally recognized. We found the same for abyssal plankton of White Sea investigating four samples that were not enriched by clastic material (which is indicated by low concentrations of Sc, and rare and rare-earth elements).

4. Conclusions 1. Using SR XFR, AA and INAA allowed us to update the list of usually determinable chemical

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Table 1 Microelement content in plankton of the Beloe Sea, oceanic plankton (mkg/g of dry mass) and in oceanic water (CSW) 1012 g/g Station

Ash content, % Na, % ** K, % ** Ca, % ** Ti, % * Mn, % * Fe, % Fe, % Sc ** V * Cr Cr * Co Co * Ni * Cu * Zn ** Zn ** AS ** As Se Br, % Rb Sr * Y ** Zr ** Nb ** Mo * Cd ** Sn Sb ** I Cs Ba La Ce Nd Sm Eu Tb Yb Lu Hf Ta * Hg * Pb Th *

Onega gulf

Kandalaksha gulf

Dvina gulf

1a

64

66

3a

58

76

78

57 8 2.5 1 0.080 0.064 1.16 1.63 3.43 20 93 92 5.1 6.9 10.9 99 284 300 4 14 0.6 0.15 30 172 4.3 35 2.4 0.5 0.9 3.5 2.1 277 1 132 11.4 22 11.4 2.12 0.372 0.24 0.51 0.08 1.1 0.17 0.06 10.3 3.1

48 6.90 1.40 1.90 0.095 0.11 1.27 1.77 3.82 23 364 382 6.30 8.90 13.4 83 433 370 4 16 0.60 0.20 31 215 3.5 31 2.3 0.5 1.8 1.9 3.5 318 1.0 143 12 21 13 1.34 0.36 0.24 0.67 0.09 1.00 0.19 0.05 36.4 3.1

49 8.80 1.18 0.93 0.060 0.13 1.23 1.82 3.93 20 78 74 5.90 7.60 12.6 47 643 600 4 9 0.60 0.37 24 214 3 24 1.8 1.0 0.4 1.2 0.9 722 0.6 103 10 22 9 1.08 0.39 0.30 (2.95) (0.49) 0.80 0.15 0.03 10 2.8

28 6.3 1.3 0.6 0.040 0.008 0.246 0.35 0.45 3 620 532 0.85 1.4 3.5 43 362 355 1 13 0.4 0.2 7 106 0.1 3.6 0.8 0.2 3.2 1.2 1.8 139 0.6 28 1.18 2.6 — 0.11 0.034 0.022 0.13 0.014 0.11 0.06 0.051 28.2 0.28

20 4.4 0.8 0.4 0.008 0.005 0.145 0.2 0.33 4 106 152 0.49 1.1 6 142 366 335 1 12 0.5 0.09 6 108 0.1 4.9 0.5 0.3 1.7 1.7 3.2 — 0.2 47 0.8 1.9 — 0.16 (0.193) 0.022 0.09 0.012 0.08 0.03 0.029 18.7 0.2

29 6.4 1.7 1.5 — 0.007 0.16 0.16 0.26 4 59 88 0.6 1 3.6 33 386 390 1 17 0.6 0.17 7 129 1 4 1 0.1 2.4 3.5 0.8 70 0.1 7 1.2 1.9 1 0.15 0.029 0.016 0.06 0.005 0.07 0.01 0.028 9.1 0.29

20 4.4 0.9 1.9 0.006 0.005 0.083 0.08 0.09 4 88 53 1.5 0.4 3.2 83 325 333 1 7 0.3 0.14 3 95 0.1 1.7 0.2 0.1 2.4 2.9 0.3 70 0.1 6 0.2 0.6 0.25 0.03 0.012 0.006 0.02 0.002 0.05 0.01 0.026 10.5 0.06

From [9]

From [8]

CSW, from [8]

4.0 1.0 2.0 0.001 0.001 0.060 — 0.2 4 10 — 1.5 — 7 20 200 — 0.1 7 4 0.050 3 120 — 4 — 1.2 1 4 0.07 20 0.04 100 — — — — — — — —

3.3 5.2 1.4 0.001 0.002 0.016 — 0.07 3.5 1.8 — 0.43 — 1.4 12 39 — 0.5 15 0.063 0.044 1.8 1100 — 0.7 — 0.39 0.72 0.29 0.16 1020 0.072 19 0.14 0.23 — — — — — —

— 0.1 13 —

— 0.03 8.7 0.1

10.8  109 390  106 448  106 10 72 250 — 0.86 2150 250 (VI) — 1.2 — 530 210 320 — 1.7 1700(V) 100 (VI) 67  106 0.12  106 7.8  106 — 17 10 10000 79 0.6 150 58000(V) 306 15000 5.6 1.7 4.2 0.84 0.21 0.21 1.5 0.32 3.4 p2.5 0.42 2.7 0.05

Mn, Ni, Cu, Cd, Hg, Pb, Fe, Co, Cr, Zn are determined by atomic absorption (AA) methods (analysts—Iluina V.N., Androsova N.V. Zn, K, Ca, Ti, V, Ga, As, Y, Zr, Nb, Mo, Sn, I—X-ray fluorescence (analysts—Bobrov V.A., Kolmogorov J.P., Phedorin M.A. S); Na, Fe, Sc, Cr, Co, Se, Br, Rb, Sr, Sb, Cs, Ba, La, Ce, Nd, Sm, Eu, Tb, Yb, Lu, Hf, Ta, Th—instrumental neutron activation methods (analysts—Bobrov V.A., Melgunov M. S.); blank—missing data. **

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Table 2 Enrichment factors (EF) of chemical element accumulating by Beloe Sea plankton Station Ash content, %

1a 57

64 48

66 49

3a 28

58 20

76 29

78 20

Oceanic from [8]

Br Na I Ca Sr K Cd Zn Cu Cr As Pb Se Sn Hg Sb Mn Ni Mo V Rb Co Cs Ba Ti Fe Sc Y Zr La Ce Nd Sm Eu Tb Yb Lu Hf Ta Th

246 32 55 1.7 2.2 2.3 11 12 8.3 3.9 4.1 2.0 3.8 2.2 2.3 5.3 2.9 0.6 0.7 0.6 0.8 1.4 0.8 0.9 0.7 1.3 1.0 0.6 0.8 1.4 1.2 1.4 1.4 1.2 1.1 0.6 0.6 0.9 0.8 1.0

344 24 57 3.2 2.4 1.2 20 13 6.3 13.8 4.2 6.2 3.4 1.1 1.7 7.9 4.4 0.7 0.7 0.6 0.8 1.6 0.7 0.8 0.7 1.3 1.0 0.5 0.7 1.3 1.0 1.5 0.8 1.0 1.0 0.7 0.6 0.7 0.8 0,9

413 30 126 1.4 2.4 1.1 4 21 3.5 2.9 2.3 1.7 3.3 0.7 1.1 2.0 5.0 0.6 1.3 0.5 0.6 1.3 0.4 0.6 0.4 1.3 1.0 0.4 0.5 1.1 1.1 1.0 0.6 1.1 1.1 3.1 3.4 0.6 0.6 0.8

2889 190 211 10.8 10 14 308 108 28 199 29 41 19.3 5.8 14.7 35 2.7 1.5 2.2 0.7 1.4 2.1 1.2 1.4 2.5 2.1 1.0 0.1 0.7 1.1 1.1 — 0.6 0.8 0.7 1.2 0.8 0.7 2.2 0.7

1773 181 — 9.8 14 12 223 139 124 46 36 37 33 11.2 11.4 84 2.3 3.5 4.5 1.2 1.7 2.3 1.6 3.2 0.7 1.7 1.0 0.2 1.2 1.0 1.1 — 1.1 6.3 1.0 1.1 1.0 0.7 1.5 0.7

4750 333 184 47 22 32 400 205 37 33 65 23 50 29 14 27 4.1 2.6 1.9 1.5 2.5 2.6 1.0 0.6 — 1.7 1.0 1.9 1.3 1.9 1.4 1.6 1.3 1.2 0.9 1.0 0.5 0.8 0.6 1.2

10111 662 532 172 46 49 1156 506 266 141 78 76 72 70 38 29 8.5 6.8 5.6 4.4 3.1 3.0 2.9 1.5 1.9 2.4 1.0 0.6 1.5 0.9 1.2 1.2 0.8 1.4 1.0 0.9 0.6 1.6 1.8 0.7

4086 638 9970 162 681 363 446 76 50 3.7 214 81 19.5 9.0 56 20 4.4 3.8 28 5.0 2.4 4.2 2.7 6.1 0.4 0.6 1.0 — 0.8 0.8 0.6 — — — — — — — — 1.5

elements up to 43 when studying the Beloe Sea plankton. 2. SR XFR results based on correct consideration of matrix effects in initial dry plankton allowed to correct AA and INAA measurements.

3. Analytical data justify the opinion about the specific geochemical condition in the Beloe Sea gulfs that is typical for the marginal seas of the open ocean and appears in increased concentrations of biophile elements of Fe group.

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100000.0

10000.0

CT

64

CT

76

CT

78

OKeaH

EF

1000.0

100.0

10.0

1.0

Br Na I Ca Sr K Cd Zn Cu Cr As Pb Se Sn Hg Sb Mn Ni Mo V Rb Co Cs Ba Ti Fe Sc Y Zr La Ce Nd Sm Eu Tb Yb Lu Hf Ta Th

0.1

Fig. 3. Chemical elements ranking according to enrichment factor EF in samples of total (st.64), abyssal (st.76 and 78) of the Beloe Sea and oceanic plankton.

Acknowledgements The work was performed under RFBR support (Grants Nos. 04-05-65168 and 02-05-64638). References [1] A.P. Vinogradov, Chemical elements composition of organisms and periodical system, Trudy Biogeokhemicheskoi Laboratorii AN SSSR, Issue 3, 1935, pp. 3–30 (in Russian). [2] A.P. Lisitzin, Geol. Geophys. 45 (1) (2004) 15–48 (in Russian).

[3] G.A. Leonova, Water Resour. 31 (2) (2004) 195–202 (in Russian). [4] N.V. Arnautov, Standard models of chemical composition of the natural mineral materials, Methodical recommendations, Novosibirsk, release IGG SB AS USSR, 1990, 220p. (in Russian). [5] K. Govindaraju, Geostandards Newslett 18 (1994) 1. [6] A.V. Bakhtiarov, XRF in Geology and Geochemistry, Nedra, Leningrad, 1985, 142p. (in Russian). [7] M.J. Berger, J.H. Hubbell, S.M. Seltzer, J.S. Coursey, D.S. Zucker, XCOM: Photon Cross Sections Database—U.S. Secretary of Commerce, National Institute of Standards and Technology, 1998. [8] Li Yuan-hui, Geochim. Et Cosmochem. Acta. 55 (1991) 3223. [9] V.S. Savenko, Geochemistry 8 (1988) 1084 (in Russian).