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Chemical Fractionation of Radionuclides and Stable Elements in Aquatic Plants of the Yenisei River Alexander Bolsunovsky* Institute of Biophysics SB, Russian Academy of Sciences, Krasnoyarsk, Russia ABSTRACT: The Yenisei River is contaminated with artificial radionuclides released by one of the Russian nuclear plants. The aquatic plants growing in the radioactively contaminated parts of the river contain artificial radionuclides. The aim of the study was to investigate accumulation of artificial radionuclides and stable elements by submerged plants of the Yenisei River and estimate the strength of their binding to plant biomass by using a new sequential extraction scheme. The aquatic plants sampled were: Potamogeton lucens, Fontinalis antipyretica, and Batrachium kauffmanii. Gamma-spectrometric analysis of the samples of aquatic plants has revealed more than 20 radionuclides. We also investigated the chemical fractionation of radionuclides and stable elements in the biomass and rated radionuclides and stable elements based on their distribution in biomass. The greatest number of radionuclides strongly bound to biomass cell structures was found for Potamogeton lucens and the smallest for Batrachium kauffmanii. For Fontinalis antipyretica, the number of distribution patterns that were similar for both radioactive isotopes and their stable counterparts was greater than for the other studied species. The transuranic elements 239Np and 241Am were found in the intracellular fraction of the biomass, and this suggested their active accumulation by the plants.
’ INTRODUCTION The Yenisei River, one of the largest rivers in the world, is contaminated with radioactivity from the Mining-and-Chemical Combine (MCC) of Rosatom.13 Aquatic plants growing in the radioactively contaminated parts of the river contain artificial radionuclides.2,3 Submerged macrophytes contribute greatly to radionuclide migration in aquatic ecosystems as they are able to accumulate and retain radionuclides. While, however, mechanisms of accumulation and distribution of stable isotopes of heavy metals in aquatic plants have been thoroughly discussed in the literature, there are very few studies addressing the corresponding aspects of behavior of radionuclides. Laboratory experiments showed that artificial radionuclides are not uniformly distributed among different components of plant biomass.49 Localization of radionuclides in the biomass of macrophytes determines further migration of radionuclides in the aquatic ecosystem, doses to specific cellular constituents and the subsequent radiotoxic effect.10 In most previous studies, aquatic plants were subjected to sequential extraction procedures to reveal mechanisms of accumulation of heavy metals.11,12 There is, however, no generally accepted sequential extraction scheme for aquatic plants, similar to the Tessier procedure for soils and sediments.13 Different authors used one or several chemical reagents—NiCl2, EDTA, HCl, HNO3, and other chemicals—to treat plant biomass in order to determine the location of the metals and their binding strength to plant biomass.11,1418 We have developed a scheme of sequential extraction of radionuclides from the biomass of aquatic plants that is based on the modified Tessier procedure and includes the following fractions: I, the exchangeable fraction; r 2011 American Chemical Society
II, the adsorbed fraction; III, the organic fraction; and IV, residual solids.5,7,8 This scheme was used to investigate the strength of actinide binding to the biomass of aquatic plants in laboratory experiments. Results of chemical fractionation of actinides (241Am and 242Pu) proved that actinides are incorporated into Elodea cells and that with time actinides can be redistributed and the fraction of the actinides tightly bound to biomass can increase.5,8 These results, however, were obtained in short-term laboratory experiments, with radionuclides interacting with plant biomass for 714 days. In the aquatic environment contaminated with radionuclides, radionuclides interact with aquatic plants continuously, for extended periods of time, and this can cause a different distribution of radionuclides in the biomass. In our previous studies we estimated the distribution of radionuclides in the biomass of submerged plants of the Yenisei River (in the adsorbed layer or inside the biomass) using a chemical separation technique (with a 0.2 M HCl).19 This method of separation of the adsorbed layer was used by other authors to determine the biosorption of heavy metals by algae and plants.1418 Zotina20 studied the distribution of artificial radionuclides in the biomass of macrophytes of the Yenisei River using chemical fractionation techniques, with such reagents as Na2EDTA and HNO3. Artificial radionuclides were detected in extracellular and intracellular compartments of the macrophytes.20 In these experiments, however, chemical fractionation was performed on Received: March 17, 2011 Accepted: August 4, 2011 Revised: July 6, 2011 Published: August 04, 2011 7143
dx.doi.org/10.1021/es2008853 | Environ. Sci. Technol. 2011, 45, 7143–7150
Environmental Science & Technology both fresh and dry biomass of aquatic plants, and, thus, the results cannot be interpreted unambiguously. Our scheme of chemical fractionation of radionuclides in aquatic plants (four fractions) was only used to perform sequential extraction in the fresh biomass of plants.5,7,8 This scheme, however, was not used for sequential extraction of radionuclides in the aquatic plants that had been exposed to radioactively contaminated water from the MCC for extended periods of time. The purpose of this study was to investigate accumulation of artificial radionuclides and stable elements by submerged plants of the Yenisei River and estimate the strength of their binding to plant biomass by using a new sequential extraction scheme.
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Table 1. Radionuclide Composition of Aquatic Plants Collected from the Yenisei River (2008)a
radionuclide
kauffmanii,
Bq/kg
Bq/kg
Bq/kg
54 ( 4
49 ( 5
368 ( 73
194 ( 40
K
431 ( 35
977 ( 53
453 ( 78
Sc
130 ( 4
24 ( 1
25 ( 1
Cr
353 ( 23
235 ( 10
171 ( 8
Na
40 46 51
46 ( 3
22 ( 1
16 ( 1
109 ( 4
63 ( 2
49 ( 1.5
Fe 60 Co
34 ( 3 523 ( 11
12 ( 1 242 ( 5
15 ( 1 177 ( 4
65
Zn
154 ( 7
123 ( 4
241 ( 6
76
As
330 ( 70
200 ( 20
248 ( 11
95
Nb
20 ( 2
19 ( 1
4.0 ( 0.5
95
Zr
14 ( 3
12.5 ( 0.5
4(2
6(1
4(2
7(3
103
11 ( 2
2.6 ( 0.4
1.4 ( 0.4
106
Ru 131 I
63 ( 15 24 ( 4
33 ( 2 4.8 ( 0.7
14 ( 4 4.6 ( 0.9
134
6.9 ( 1.2
137
56 ( 2
9.9 ( 0.7
33.4 ( 1.3
140
30 ( 3
12 ( 2
17 ( 1
141
28 ( 3
12 ( 1
13 ( 1
144
43 ( 7
13 ( 3
12 ( 2
152
37 ( 2
8.4 ( 0.6
5.8 ( 0.2
239
318 ( 23 5.4 ( 1.9
124 ( 9 2.1 ( 0.9
174 ( 21
