Evidence for the Zircon Origin of Cadmium Anomalies in Bottom Sediments from the Littoral Zone of the Northern Part of Lake Ladoga Corresponding Member of the RAS E
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ISSN 1028334X, Doklady Earth Sciences, 2016, Vol. 468, Part 2, pp. 607–610. © Pleiades Publishing, Ltd., 2016. Original Russian Text © E.V. Ivanter, Z.I. Slukovskii, D.S. Dudakova, A.S. Medvedev, S.A. Svetov, 2016, published in Doklady Akademii Nauk, 2016, Vol. 468, No. 5, pp. 562–565. GEOCHEMISTRY Evidence for the Zircon Origin of Cadmium Anomalies in Bottom Sediments from the Littoral Zone of the Northern Part of Lake Ladoga Corresponding Member of the RAS E. V. Ivantera, Z. I. Slukovskiib, D. S. Dudakovac, A. S. Medvedevb, and S. A. Svetovb Received July 20, 2015 Abstract—The minorelement composition of bottom sediments from the littoral zone of the northern part of Lake Ladoga was studied. Close relationships between the anomalous Cd concentrations in lake sediments and Quaternary glacial formations on the territory of Karelia were shown. A negative correlation of Cd with other heavy metals and a positive correlation with Zr were observed. Most likely, Cd is an impurity in zircons from sandy and sandy loam sedimentary formations on the northern coastal area of Lake Ladoga. DOI: 10.1134/S1028334X16060118 Cadmium (Cd) is a minor scattered element. The Ladoga may be a peculiar depot on the path of migra anomalously high concentrations of Cd in atmo tion of various chemical elements including heavy sphere, soil, water, and bottom sediments (BSs) are metals to the major part of the lake. often related to the anthropogenic influence on the Our study is aimed at understanding the genesis of studied natural objects. The highly toxic properties of anomalously high concentrations of Cd in BSs from Cd for living beings are well known, and, therefore, the littoral zone of the northern part of Lake Ladoga this heavy metal is among the most dangerous pollut on the basis of ICPMS analysis. ants of the environment. Nonferrous metallurgy, paint The field investigations in the North Ladoga area and plastic production, the electronic industry, and were performed in 2013 and 2014. We studied the sur agriculture provide the basic contribution to environ face layer of BSs from the littoral zone (depths of 1– mental contamination with Cd. More than 90% of Cd 1.5, 3, and 8 m) of Lake Ladoga (Fig. 1). and its compounds from the total budget of this metal in the natural cycle of matter come to the biosphere The samples of sediments were collected using an from anthropogenic sources [1, 2]. Ekman bottom grab; the laboratory studies included drying of collected bottom sediments, sieving with a Lake Ladoga, the largest freshwater reservoir in cell size of 2 mm and grinding to a powdered state. The Europe (17 700 km2), has a high economic and recre minorelement composition of sediments studied was ational importance for the northwestern part and the analyzed on an XSeries2 ICPMS mass spectrometer entire Russia [3]. In light of changes in the ecosystem [5, 6]. Computer processing of the data was performed of the lake and the related high anthropogenic influ using the Microsoft Excel 2007 and Inkscape 0.48.4 ence, ecological and chemical studies of Lake Ladoga software. are of paramount importance [4]. Interest in the study of Cd in BSs from the littoral Study of BSs is an important component of com zone of the northern part of Lake Ladoga was stimu plex limnological investigations. The chemical com lated by the anomalous concentrations of this element position of BSs is an indicator of numerous complex (0.66–2.77 ppm) in sediments collected in the area of processes of natural and anthropogenic character, Lekhmalakhti Bay, Lunkulansaari Island, and Khu which proceed in the catchment area of the lake, as nuka Peninsula. These concentrations are 2–7 times well as in the hydroecological system. Sediments in the higher than the regional geochemical background of coastal zone of large water reservoirs such as Lake this heavy metal (0.39 ppm) for BSs of freshwater res ervoirs. There is no significant correlation of Cd with Li, which is an indicator of fine granulometric frac a Petrozavodsk State University, Petrozavodsk, Russia tions in BSs [7], and basic minor elements and pollut b Institute of Geology, Karelian Research Centre, ants (Fig. 2), high contents of which are usually typical Russian Academy of Sciences, Petrozavodsk, Russia of shale, aleuritic, and finesandy sediments (Kirjava c Institute of Limnology, Russian Academy of Sciences, lakhti and Impilakhti bays). ul. Sevastiyanova 9, St. Petersburg, 196105 Russia To the contrary, the concentrations of Cd from 0.19 email: [email protected]; [email protected] to 0.46 ppm in BSs above the mentioned areas are 607 608 IVANTER et al. Kirjavalakhti1 Kirjavalakhti2 N Sortavala Impilakhti Pitkyaranta Lakhdenpokhya Khunuka1, 2, 3 Lunkulansaari Valaam Island Lake Ladoga Lekhmalakhti 30 km Fig. 1. Schematic map of the studied area. The stations of bottom sampling are indicated by asterisks. Correlation coefficients 1.0 0.862 0.861 0.843 0.840 0.8 rcrit = 0.497 at р < 0.01 0.666 0.657 0.589 0.6 0.558 0.544 0.4 0.2 Cd 0 Сr Ni Сo Zn Сu Pb Mo Mn W Heavy metals –0.2 –0.244 –0.4 Fig. 2. Correlations between the concentrations of Li and heavy metals in bottom sediments from the littoral zone of Lake Ladoga. close to the background level, with a median of the samples of BSs ranges from 135 to 1998 ppm, with 0.32 ppm. The high level of accumulation of other a median of 1116 ppm (Fig. 3). heavy metals (Pb, Zn, Cu, and W) in the samples pro The behavior of Cd similar to that described above vides clear evidence for the technogenic influence on was previously observed during study of BSs from the hydroecosystem of the North Ladoga area. There water reservoirs of Petrozavodsk located on the shore is a significant correlation of Cd with Zr in all samples of Lake Onega, another large water reservoir in studied (rCd–Zr = 0.99, p < 0.01), especially for BSs of Europe [5, 6]. The studies showed that the high con Lekhmalakhti Bay, Lunkulansaari Island, and centrations of Cd had a poor influence on the ecology Khunuka Peninsula, where the concentration of Zr in of the regulated city watercourse, in particular, on the DOKLADY EARTH SCIENCES Vol. 468 Part 2 2016 EVIDENCE FOR THE ZIRCON ORIGIN OF CADMIUM ANOMALIES 609 Areas of the study Impilakhti Kirjavalakhti1 Kirjavalakhti2 Lekhmalakhti Lunkulansaari Khunuka1 Khunuka2 Khunuka3 180 2500 1 150 2000 120 1500 90 2 1000 60 500 Concentration of Cd, ppm 30 ppm Concentration of Zr, 0 00.51.0 1.5 2.0 2.5 3.0 Concentration of Cd, ppm Fig. 3. Cd–Zr binary diagram illustrating the differences in chemistry of two groups of bottom sediments from the littoral zone of Lake Ladoga. The left scale of Zr concentrations is given for points in area (1); the right scale, for points in area (2). species diversity of diatomic flora of the Lososinka As is evident from [11], the concentration of Cd in River [8]. The Cd anomaly (4.0 ppm) was registered in hydrothermal zircons from orebearing amphibolite BSs from the southern part of Lake Onega. This from the Belomorian mobile belt (North Karelia) anomaly is not verified by numerous finds of sphalerite ranges from 73.7 to 777.6 ppm of mineral grain weight. (or other sulfides) in heavy fractions, which does not Such high concentrations of Cd have never been regis agree with the classic ideas on the natural isomor tered in zircons (personal communication of the phism between Cd and Zn. Note that this sample is author of [11]). In this case, Cd is an impurity in Kare represented by sand of lake–glacial origin with a high lian zircons formed during the longterm hydrother concentration of zircon ZrSiO4 from the heavy frac mal process, which accompanied intense magmatic and tion of sediments. metamorphic activity on the territory 1–3 b. y. ago. The A glacial and most likely zircon “sign” was also reg unique finds of native Cd in the North Tirvas deposit istered for Cd anomalies (up to 3.55 ppm) in the hori in Karelia are also the product of hydrothermal activ zon of surface–podzolic soils of Karelia abundant on ity in the area of the Koikar structure composed of fluvioglacial deposits [9]. Extremely high concentra magmatic rocks [12]. It is mentioned that BSs of the tions of Cd in BSs of the littoral zone of Lake Ladoga, Pacific Ocean enriched in Cd are localized in zones in Lekhmalakhti Bay, Lunkulansaari Island, and with significant volcanic and hydrothermal activity Khunuka Peninsula are associated with surface out [13]. More than 60% of natural Cd annually entering crops of sandy and sandy loam (with pebbles and boul the Earth’s atmosphere from various sources is con ders) fluvioglacial Pleistocene formations of the Valdai trolled by modern volcanism of the planet [1]. The superhorizon [10]. The shore line in the Kirjavalakhti1, concentration of Cd in magmatic and volcanogenic– Kirjavalakhti2, and Impilakhti areas is composed of sedimentary rocks of the shore line in the studied Archean and Proterozoic rocks, which stimulates pre regions of Lake Ladoga is low, ranging within 0.03– dominant deposition of aleurite and shale in the lit 0.51 ppm; however, Fig. 4 shows the correlation toral area of the lake. between Cd and Zr in the rocks studied. The behavior of Cd in BSs from the western part of Because of the high resistence of zircon to weather Lake Ladoga is an insoluble problem in the study of ing, the mentioned correlation is clearer in modern E.A.