Environ. Scl. Technol. 1992, 26, 1433-1444
in natural gas combustion because the moisture level is lower. Anything that reduces the moisture level, such as lowering the stoichiometric ratio or predrying the coal, will help to increase fuel rich sulfur capture, especially at lower sulfur levels. Increasing temperature will increase fuel rich sulfur capture only if the sulfur level is significantly above the thermodynamic limit (which increases with temperature). These results suggest that the rate-limiting step under fuel rich conditions is distinctly different than under fuel lean conditions. Theoretical calculations using a distributed pore model (19) have suggested that the relative insensitivity of calcium utilization to SOz concentration under fuel lean conditions is a result of pore closure effeds, as the SOz concentration is increased, the kinetic and diffusion rates increase but this further aggravates the problem of pore closure and results in essentially no overall increase in sulfur capture. The increased calcium utilization measured with increasing sulfur species concentrations under fuel rich conditions may be the direct result of enhanced product layer diffusion; pore closure would not be expected to limit calcium utilization under fuel rich conditions because the molar volume of calcium sulfide is less than either parent sorbent.
Literature Cited (1) Borgwardt, R.H.; Roache, N. F.; Bruce, K. R.Environ. Prog. 1984,3(2), 129. (2) Borgwardt, R. H. AZChE J . 1985,31,103. (3) Silcox, G. D.; Slaughter,D. M.; Pershing, D. W. Symp. (Znt.) Combust., [Proc.] 1985,No. 20. (4) Borgwardt, R. H. AZChE J. 1986,32,239. (5) Milne, C. Ph.D. Dissertation, University of Utah, 1988. (6) Pell, M.; Graff,R. A.; Squires, A. M. Sulfur and SOzDevelopments; Chemical Engineering Progress Technical Manual; AIChE: New York, 1971;pp 151-157. (7) Weatmoreland, P. R.;Gibson, J. B.; Harrison, D. P. Environ. Sei. Technol. 1977,11, 488. (8) Yang, R.T.;Chen, J. M. Environ. Sei. Technol. 1979,13, 549. (9) Kamath, V. S.; Petrie, T. W. Environ. Sci. Technol. 1981, 15,966. (10) Attar, A.; Dupuis, F. Znd. Eng. Chem. Process Des. Dev. 1979,18,607. (11) Zallen, D. M.; Gershman, R.; Heap, M. P.; Nurick, W. H. Proceedings of the Third Stationary Source Combustion U.S. EPA, U.S.GovSymposium; EPA-600/7-79-050b; ernment Printing Office: Washington, DC, 1979;Vol. 11. (12) Freund, H.; Lyon, R. K. Combust. Flame 1982,45, 191. (13) Freund, H. Combust. Sci. Technol. 1981,26,83. (14) Whitney, G. M.; Yunming, Z.; Denn, M. M.; Petersen, E. E. Chem. Eng. Commun. 1987,55,83. (15) Gordon, B.;McBride, B. NASA [Spec. Publ.] SP 1976, SP-273. (16) Smoot, L. D.; Smith, P. J. Coal Combustion and Gasification; Plenum: New York, 1985;p 23. (17) Lindgren, E. R.; Pershing, D. W.; Kirchgessner, D. A,; Drehmel, D. C. J. Chromatogr. 1991,585,353. (18) Lindgren, E. R. Ph.D. Dissertation, University of Utah, 1990. (19) Newton, G. H. Ph.D. Dissertation, University of Utah, 1986.
Acknowledgments
The furnace and analytical systems described in this paper are located at the EPA's research center in Research Triangle Park, NC. We at the University of Utah sincerely thank James Abbott, Blair Martin, and Dennis Drehmel for making it possible to use this equipment. We also gratefully acknowledge the support and assistance of David Kirchgessner, Robert Borgwardt, and Brian Gullett and thank them for the use of their support personnel and analytical equipment. Registry NO.S,7704-34-9;SOz, 7446-09-5; COS, 463-58-1; Ha, 7783-06-4.
Received for review August 22,1991. Accepted March 9,1992. The research summarized in this paper was supported by the US.EPA under Cooperative Agreement CR-811011.
Physicochemical Speciation of Trace Elements in River Waters by Size Fractionation Yoshlyukl Tanlzakl, Toshlnarl Shimokawa, and Masaru Nakamura Tokyo Metropolltan Isotope Research Center, 2-1 1-1 Fukazawa, Setagaya-ku Tokyo, Japan 158
Size fractionation method has been used for the speciation of trace elements in river waters. Both filtration and ultrafiltration techniques were applied to fractionate the trace elements into various sizes and/or molecular weight ranges. The size distribution was determined for 39 elements by means of neutron activation analysis to estimate their physicochemical forms. Alkali and alkaline earth elements, heavy rare earth elements (REEs), As, Co, Mn, Ni, Sb, Se, V, W, and Zn were mainly present in the dissolved phase, while Ag, Al, Fe, Sc, and light REEs were predominantly associated with the suspended particles. The dominant dissolved species for alkali and alkaline earth elements, Al, V, Mn, Sb, and Au were regarded as simple ions, while heavy REEs, Sc, Co, Ni, and Zn were apt to form soluble complexes with organic ligands. Light REEs, Fe, and Ag were mainly associated with colloidal materials. Introduction
It is well-known that trace elements in natural water systems are present in various physical or chemical forms 0013-936X/92/0926-1433$03.00/0
such as ions, ion pairs, organic or inorganic complexes, colloids, and suspended particles. The interactions between trace elements and the components in the aquatic system, including the biota, sediments, and colloids, are largely influenced by the forms of these trace elements. The determination of the chemical or physical forms for trace elements, therefore, is of great importance not only to substantiate the geochemical behavior of the trace elements in natural waters but also to estimate the availability and toxicity toward organisma and to choose the optimal conditions to be used in chemical water treatments. However, it is very difficult to directly determine the chemical species of ultratrace amounts of these elements and actually impossible to simultaneously determine a great number of trace elements. A model calculation method based on thermodynamic data is not easily applicable to real natural water systems because of the scarcity of experimental data available for calculation. In recent years, physicochemical speciation techniques utilizing centrifugation, gel filtration, dialysis, filtration, and ultrafiltration have been developed to differentiate
0 1992 American Chemical Society
Envlron. Sci. Technol., Vol. 26, No. 7, 1992
1433
~~
~
Table I. Water Qualities of River Waters at the Time of Sampling date
pH
water temp, "C
EC," pS/cm
S-6
Nov 18, 85 Jun 4,90 Dec 1,86 Oct 31, 83 Sep 4, 89 Dec 12,83
7.5 7.7 7.3 7.0 7.1 6.9
12.5 22.1 12.9 13.9 23.7 9.3
97 210 260 246 140 275
0.82 3.22 4.68 1.54 2.57 3.67
s-7 5-8
Jun 18,85 Dec 13,88
6.8 7.2
17.2 9.0
120 142
0.89 1.15
sampling locality Tamagawa River Hamura Sekidobashi Noborito Kinuta FutagotamagawaC Denenchofu Sagamigawa River Sagamiko Atsugi a
s-1 5-2 5-3 5-4
s-5
mg/L
EC, electric conductivity. bTOC,total organic carbon. Futagotamagawa at flooding by heavy rainfall.
the forms of trace elements in natural waters (1-3). These speciation techniques have been proven to be simple and convenient methods, and normally free from contamination by the elements of interest because they do not involve any chemical procedures. Among them, the filtration and ultrafiltration techniques are especially suited for the analysis of multitrace elements because both techniques make possible the treatment of a large volume of water sample within a relatively short period of time. Stumm and Bilinski (4) first proposed that trace metal species in natural waters could be usefully classified according to their size distribution. Laxen and Harrison (5-7) applied the filtration technique to separate some trace elements between dissolved and suspended species using Nuclepore membrane filters with different pore sizes. The ultrafiltration technique was effectively utilized by Smith (8), Hoffmann et al. (9), and Tanizaki et al. (10, 11) to classify the dissolved species of trace elements into various molecular weight ranges, so that makes it possible to estimate the chemical species of trace elements in freshwater. In this paper, we tried to speciate 39 elements and six major components in several river waters using both the filtration and ultrafiltration techniques combined with neutron activation analysis in order to clarify the physicochemical forms of trace elements.
Experimental Methods Sample Collection. Eight water samples were collected from six sites in the Tamagawa River, Hamura (S-1), Sekidobashi (S-2), Noborito (S-3),Kinuta (S-4), Futagotamagawa (S-5), and Denenchoufu (S-6), and from two sites in the Sagamigawa River, Sagamiko (S-7)and Atsugi (S-8). The sampling sites are shown in Figure 1. The Hamura, Sagamiko, and Atsugi sites lie near prime agricultural land, while the other five sites lie near industrial/urban stretches. Twenty-five liter samples were collected in a Pyrex-glass bottle precleaned with 10% nitric acid. The water qualities at the time of sampling are listed in Table I. The samples were immediately prefiltered through a Millipore membrane with a 8-pm pore size to separate larger suspended particles so that it would facilitate the later filtration procedures. Filtration Procedures (Size Fractionation). The prefiltered water sample was divided into four 5-L portions. One of the 5-L portions was filtered once again through a 142-mm-diametertype HA Millipore membrane with a 0.45-pm pore size (12). The filtrate was transferred into a clean 5-L polyethylene bottle and then acidified immediately with 30 mL of Spec-pure nitric acid to avoid any adsorption of trace elements on the wall of the bottle. A model UHP-150 ultrafiltration apparatus (Toyo Roshi Corp.) and three types of ultrafilters, UK-10 (molecular weight cutoff lo4;corresponded to about 10-nm pore size), 1434
Environ. Sci. Technoi., Voi. 26,
No. 7, 1992
Flgure 1. Map of the Tamagawa River and the Sagamigawa River showing the sampling locality.
UH-1 (MW lo3),and UH-05 (MW 500; about 1-nm pore size) with a 150-mm diameter, were utilized for the ultrafiltration experiment. Three 5-L portions of the prefiltered water samples were filtered through the three types of ultrafilters one by one. Details of the procedure for ultrafiltration experiment have been described in our previous papers (10, 11). Neutron Activation Analysis (NAA). Four kinds of filtrates and two residues on the filters resulting from the filtration and ultrafiltration experiment were analyzed for 39 elements using a NAA method. Three kinds of the residual waters in the cell were also analyzed in order to estimate the material balance during the ultrafiltration experiment. The procedures for the NAA experiment, the preparation of the neutron irradiation samples, the neutron irradiation, and the y-ray measurement were reported in detail in our previous papers (13, 14). Analysis of Major Components. The concentration of silica (SOz) in the water samples was determined by colorimetry using ammonium molybdate, while the pH 4.3 alkalinity (4.3Bx) was titrated with 0.01 mol/L sulfuric acid in the presence of a Bromocresol Green (BCG) indicator. The determination of total organic carbon (TOC) concentration was performed by utilizing a TOC analyzer (Shimazu Model-1OA). The concentrations of chloride (Cl-), sulfate (SO:'), and phosphate (PO:-) ions, on the other hand, were determined by a type QIC ion analyzer (Dionex Corp.). Classification Method. The size distributions in diameter (in micrometers) and in molecular weight (MW) ranges were calculated for six major components and 39 elements according to the scheme shown in Figure 2 (10). Each element (or component) was first separated by size between two fractions, the suspended size fraction (SS fraction; >0.45 pm) and the dissolved size fraction (DS
Table 11. Classification of Various Components in Natural Waters with Particle Size or Molecular Weight Ranging (Modified from Ref 3) category suspended particulates dissolved species colloids larger soluble species smaller soluble species
example of component3 organic cell, detritus, soils, clays, minerals, precipitates clay minerals, metal hydroxides, organic colloids (humic acid, proteins) organic complexes (fulvic acid, fatty acids), inorganic complexes (polyhydroxo complexes, polysilicate) small organic molecules, hydroxo complexes, ions, ion pairs
size, nm
MWR“
>450 C450 450-10
>lo6 CyY + CZZ
(3)
loss
CXX
Thus, the experimental error (E)during the ultrafiltration is calculated from E (%) = ((CyY + CzZ) - C x X J X lOO/CxX (4) In eq 4 if the E value is given in plus, it is regarded that the water sample has been contaminated by the elements of interest induced from the apparatus, filters, and experimental environment. On the other hand, when the E value is given in minus, it can be explained that the element was lost by adsorption on the wall of the cell and/or on the filters. The E values were calculated from eq 4 for six major components and 33 elements in 13 river water samples including those already reported (11). The results are given in the average value of three experiments for each sample utilizing three types of the ultrafiiten with different molecular weight cutoffs and shown in Figure 3. The figure shows that the E values for most of the major components and the elements are found to be within the range of f 1 5 % . It can be said that, therefore, there are no insidious contaminations and losses affected to the speciation results during the ultrafiltration procedure. For the elements Fe, Ag, and Eu, however, the E values went up to -30%. This can be explained that the dissolved species Environ. Sci. Technol., Vol. 26, No. 7, 1992
1435
Table 111. Fractionation Results of Major Components (in mg/L)" component ER'
sampling locality
(>0.45 pm)
s-1
s-2 s-3 s-4 s-5 S-6 s-7 S-8
Si02
SS fractionb
1 2 (4.4)
16 (4.6) 0 (0)
s-1 s-2 s-3 s-4 s-5 S-6 s-7 S-8
4.3Bxf
sods-
P042TOO
c1
s-1
s-2 s-3 s-4 s-5 S-6 s-7 S-8
s-1
s-2 s-3 s-4 s-5 S-6 s-7 S-8 s-5 s-1 s-2 s-3 s-4 s-5 S-6 s-7 S-8
s-1 s-2 s-3 s-4 s-5 S-6 s-7 S-8
0.25 (14.0) 0.39 (9.6) 0.60 (40.3) 0 (0) 0 (0) 0 (0) 0 (0) 0.01 (0.1) 0 (0) 0 (0) 0 (0)
DS fractionc (104)
middle MWR (MW 104-500)
111 (-) 298 (-) 341 (-) 261 (95.6) 122 (-) 332 (95.4) 143 (100) 199 (-) 8.5 (-) 22.6 (-) 17.5 (-) 20.6 (-)
0 (0) 6 (2.0) 7 (2.0) 0 (0) 2 (1.6) 4 (1.2) 5 (3.5) 2 (1.0) 0 (0) 0.6 (2.7) 1.1 (6.3) 0 (0)
15 (13.5) 27 (9.1) 48 (14.1) 44 (16.9) 23 (18.9) 60 (18.1) 17 (11.9) 34 (17.1) 0 (0) 3.6 (15.9) 3.0 (17.1) 1.8 (8.7)
96 (86.5) 265 (88.9) 286 (83.9) 217 (83.1) 97 (79.5) 268 (80.7) 121 (84.6) 163 (81.9) 8.5 (100) 18.4 (81.4) 13.4 (76.6) 18.8 (91.3)
20.4 (-) 18.2 (-)
0 (0) 0.5 (2.7)
2.1 (10.3) 0.7 (3.9)
18.3 (89.7) 17.0 (93.4)
20.7 (-) 38.7 (-) 44.7 (-) 34.8 (-) 18.1 (-) 48.3 (-) 22.2 (-) 28.8 (-) 6.2 (-) 10.7 (-) 9.9 (-) 28.3 (-) 13.8 (-) 52.8 (-) 11.9 (-) 19.2 (-) 0.234 (-) 0.82 (-) 5.05 (-) 4.68 (-) 1.54 (86.0) 2.57 (-) 3.67 (90.4) 0.89 (59.7) 1.15 (-) 6.75 (100) 37.2 (100) 44.8 (100) 26.9 (100) 7.93 (99.9) 41.6 (100) 7.96 (100) 11.5 (100)
0 (0) 0.5 (1.3) 2.7 (6.0) 0 (0) 0 (0) 0 (0) 0.6 (2.7) 0.9 (3.1) 0 (0) 0 (0) 0.7 (7.1) 0.9 (3.2) 1.2 (8.7) 0 (0) 0 (0) 0 (0) 0.051 (21.8) 0.07 (8.6) 0.74 (14.6) 1.54 (32.9) 0.35 (22.7) 0.91 (35.4) 1.18 (32.1) 0.19 (21.3) 0.22 (19.2) 0.04 (0.6) 0.3 (0.8) 0.2 (0.4) 0 (0) 0.10 (1.3) 0 (0) 0 (0) 0 (0)
3.3 (15.9) 5.9 (15.2) 1.5 (3.4) 6.3 (18.1) 1.5 (8.3) 7.5 (15.5) 2.1 (9.5) 3.1 (10.8) 4.7 (75.8) 7.5 (60.0) 2.4 (24.2) 16.4 (57.9) 8.0 (58.0) 28.8 (54.5) 8.4 (70.6) 10.8 (56.3) 0.113 (48.3) 0.58 (70.7) 1.60 (31.7) 1.47 (31.4) 1.01 (65.6) 0.64 (24.9) 1.97 (53.7) 0.50 (56.2) 0.58 (50.4) 0.13 (1.9) 0.6 (1.6) 0.4 (0.9) 0.4 (1.5) 0.22 (2.8) 0.6 (1.4) 0.09 (1.1) 0 (0)
17.4 (84.1) 32.3 (83.5) 40.5 (90.6) 28.5 (81.9) 16.6 (91.7) 40.8 (84.5) 19.5 (87.8) 24.8 (86.1) 1.5 (24.2) 5.0 (40.0) 6.8 (68.7) 11.0 (38.9) 4.6 (33.3) 24.0 (45.5) 3.5 (29.4) 8.4 (43.7) 0.070 (29.9) 0.17 (20.7) 2.71 (53.7) 1.67 (35.7) 0.18 (11.7) 1.02 (39.7) 0.52 (14.2) 0.20 (22.5) 0.35 (30.4) 6.58 (97.5) 36.3 (97.6) 44.2 (98.7) 26.5 (98.5) 7.61 (95.9) 41.0 (98.6) 7.87 (98.9) 11.5 (100)
small MWR (MW lo4 and MW 104-500). Therefore, it can be said that the most likely form of the dissolved vanadium in the waters is a simple hydroxo anion, V02(OH),2-, while manganese is dominantly present as a divalent cation, Mn2+(aq). The
presence of Mn2+must be related to reductive conditions in some part of the river systems. Furthermore, the formation of complexes with organic ligands (21) and the adsorption on the small inorganic colloids for both elements cannot be neglected. The dissolved Co, Ni, and Zn, on the other hand, were mainly distributed in the two smaller MWRs (MW 104-500 and MW lo4). It was recognized that there were good correlations between these elements and total organic carbon (TOC) with respect to their concentrations fractionated in the middle MWR. These elements are well-known to form their soluble complexes with naturally occurring organic materials such as fulvic acid in freshwaters (15,17,22). Considerable parts of these elements are also present as simple divalent cations (M2+). The dominant dissolved species of Ni and Zn are simple cations for the Sagamigawa River waters (S-7 and S-8) having a poor TOC concentration. The dissolved species of chromium was roughly divided between the two smaller MWRs, although at S-2 and S-6 it was divided into the three MWRs. In natural environment, the most stable oxidation states of chromium are Cr(II1) and Cr(V1). Major species of the dissolved Cr(II1) are CrOH2+and Cr(OH)3,whereas those of the Cr(V1) are HCr04- and Cr042-(24). Furthermore, some of the Cr(II1) may form soluble complexes with natural organic acids (25). Interactions with solid phase, including colloidal materials, can also greatly regulate the chromium concentration in the river waters. It is predicted that the Cr(II1) and Cr(V1) species exhibit typical cationic and anionic sorption behavior, respectively. Most portions of the dissolved Fe and Ag were observed in the large MWR, although 11-34% of the iron was also found in the middle MWR. Published evidence shows that a large portion of the dissolved iron in freshwater exists as colloidal particles stabilized by organic materials (26, 27). On the other hand, Whitlow and Lice (28) predicted that most of the dissolved silver in natural waters would be complexed by C1- and stabilized by colloidal materials. I t seems that iron forms soluble complexes with natural organic ligands to some extent, even though it is chiefly associated with organic colloids having a size larger than MW lo4. The dissolved scandium was roughly divided between the two larger MWRs, although it was predominantly found in the middle MWR except for the sample from S-8. A good correlation was observed between scandium and TOC with respect to their concentrations fractionated in the two larger MWRs. It can be predicted, therefore, that natural organic acids also greatly contribute to the dissolution of scandium. In general, transition metal cations having between 0 and 10 d electrons are known to have a strong complexing ability for natural organic acids such as humic and fulvic acids. The order of metal complexing ability has been reported to be Mn2+< Fez+< Zn2+ ICo2+< Ni2+ < Cu2+(22, 29). In our experiment, the order given by the proportions fractionated in the middle MWRisfoundto be V IFe < Mn < Cr IZn 5 Ni ICo ISc. It seems reasonable to predict from the results that Sc, Co, Ni, Zn, and Cr tend to form their soluble complexes with fulvic acid with a molecular weight less than lo4,while Fe and Ag dissolved in the waters tend to be associated with colloidal humic acid with a molecular weight greater than lo4. Rare Earth Elements (La, Ce, Sm, Eu, Tb, Ho, Tm, Yb, and Lu). The fractionation results of rare earth elements (REEs) are listed in Table VI. The light REEs (La, Ce, Sm, and Eu) including terbium were mostly (63-99%) Environ. Sci. Technol., Vol. 26, No. 7, 1992
1441
P
W
I
E1
1
x
v . I -
v)
3 L-
v L
L
2 \aJ w
general, the correlation was recognized between the light REEs and iron with respect to their concentrations found in the large MWR (colloidal species). The heavy REEs, on the other hand, were highly correlated to both iron and TOC with respect to their concentrations found in the middle MWR (soluble complexed species). It seems that the dissolution of the light REEs are greatly related to the stabilization by the colloidal iron (34),while the heavy REEs are mainly dissolved in the river waters by forming their soluble complexes with natural organic acids such as fulvic acid. Other Elements (AI, As,Br, Se, Mo, Sb,Hf, Ta, W, Ir, Au, Th,and U). The elements As, Br, Se, Mo, Sb, W, Au, and U were mostly fractionated in the DS fraction with the exception for S-5, while the elements Al, Hf, Ta, and Th were mostly classified in the SS fraction, as can be seen in Table VII. The dissolved Al, Sb, and Au were mainly (58-100%) fractionated in the small MWR, although 13-34% of antimony was also found in the middle MWR. It seems that these three elements are present in the waters as simple ions such as Al(OH)4-,Sb(OH)6-,and Au(OH),- (35,36). The Al-organic (37)and Au-organic (38)complexes were not dominant species in our experimental river waters. The elements As, $e, Mo, and W on the other hand were roughly divided between the two smaller MWRS. As, Mo, and W are known to form their oxoanions, HASO:-, Moo4,-, and WOZ- in most natural waters, and only a few percent of them are present as their organic compounds (29,39,40).Our data apparently show that considerable amounts of these oxoanions are associated with inorganic substances having a size smaller than MW lo4 or about 10 nm. The preliminary ultrafiltration experiment previously described for and PO?-indicated that only about one-half of MOO:- and W0:- can pass through the type UH-05 ultrafilter, although HAsOd2-quantitatively passes through the filter. Therefore, it is difficult to estimate exactly the dissolved forms for some oxoanions by the size fractionation method. Although the selenium is present as oxoanions, Se02- and Se04,-, in ordinary natural waters, it also tends to form Se-organic complexes in most natural environments (41,42).It can be predicted, therefore, that the species distributed in the middle MWR can include organically complexed selenium to a substantially extent. The dissolved bromine was chiefly distributed in the small MWR, although it was also observed in the middle MWR to some extent (13-38%). This suggests that bromine is predominantly present as halide ion in the waters, but a part of bromine exists also as soluble organic or inorganic complexed species. The dissolved Ta and Ir were roughly divided between the two smaller MWRs, while hafnium was divided into the three MWRs with the exception for 5-3. The aquatic chemistry of these elements is poorly understood, and because of the lack of analytical data in this work, it is difficult to draw any quantitative conclusions. The T h and U abundances for the dissolved fraction normalized to the earth’s crust, (Th), and (U), values, are 0.045-0.13 x lo4 (average 0.088 X lo4) and 2.3-11.4 X 10-6 (average 5.5 X 10-6),while those for the suspended fraction are 1.2-4.3 x lo4 (average 2.2 X lo4) and 0.86-2.9 X lo4 (average 1.6 X lo4), respectively,with the exception of S-5. The (U),/(Th), ratios for the dissolved and suspended fractions are resulted to be 62 and 0.73, respectively. Thus, the Th and U abundances for the suspended fraction are close to those for the earth’s crust, while the dissolved fraction is more enriched in the uranium concentration.
-v 0
La
Tb
Sm
Ce
Eu
Lu
Tm
Ho
Yb
Figure 4. REE abundance patterns for the DS (0,A)and SS (0,A) fractlons in the river waters normallzed to the earth’s crust. The patterns for the Tamagawa River (TG) and Sagamlgawa River (SG) waters are given in the average for five sampling sites, except for S-5, and two sampling sites, respectively.
found in the SS fraction (>0.45 pm), with the exception of terbium at S-6. On the contrary, the heavy REEs (Ho, Tm, Yb, and Lu) were mainly (59-91%) classified in the DS fraction (
