- Email: [email protected]
Characterizing suspended sediments from the Piracicaba River Basin by means of k0–INAA
Nuclear Instruments and Methods in Physics Research A 622 (2010) 479–483
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Characterizing suspended sediments from the Piracicaba River Basin by means of k0–INAA E.J. Franc- a a,, E.A.N. Fernandes a, I.P.O Cavalca a, F.Y. Fonseca a, L. Camilli a, V.S. Rodrigues a, C. Bardini Junior a, J.R. Ferreira a,b, M.A. Bacchi a a b
CENA/USP, Centro de Energia Nuclear na Agricultura, Universidade of Sa~ o Paulo, PO Box 97, 13400-970, Piracicaba, SP, Brazil ~ Paulo, SP, Brazil Instituto de Pesca, Secretaria de Agricultura e Abastecimento (SAA), Avenida Francisco Matarazzo 455, 05031-900, Sao
a r t i c l e in fo
abstract
Available online 10 February 2010
The inorganic chemical characterization of suspended sediments is of utmost relevance for the knowledge of the dynamics and movement of chemical elements in the aquatic and wet ecosystems. Despite the complexity of the effective design for studying this ecological compartment, this work has tested a procedure for analyzing suspended sediments by instrumental neutron activation analysis, k0 method (k0–INAA). The chemical elements As, Ba, Br, Ca, Ce, Co, Cr, Cs, Eu, Fe, Hf, Hg, K, La, Mo, Na, Ni, Rb, Sb, Sc, Se, Sm, Sr, Ta, Tb, Th, Yb and Zn were quantified in the suspended sediment compartment by means of k0–INAA. When compared with World Average for rivers, high mass fractions of Fe (222,900 mg/kg), Ba (4990 mg/kg), Zn (1350 mg/kg), Cr (646 mg/kg), Co (74.5 mg/kg), Br (113 mg/kg) and Mo (31.9 mg/kg) were quantified in suspended sediments from the Piracicaba River, the Piracicamirim Stream and the Marins Stream. Results of the principal component analysis for standardized chemical element mass fractions indicated an intricate correlation among chemical elements evaluated, as a response of the contribution of natural and anthropogenic sources of chemical elements for ecosystems. & 2010 Elsevier B.V. All rights reserved.
Keywords: Eroded material Suspended matter Trace elements Water quality Method k0
1. Introduction The inorganic chemical characterization of suspended sediments is of utmost relevance for the knowledge of the dynamics and movement of chemical elements in the ecosystems. Studies involving the collection, processing and subsequent chemical analysis of suspended sediments are considered complicated because of the characteristics of this kind of matrix [1]. The main issues are the horizontal and vertical cross sectional variations, the variation of silt/ clay (o63 mm) fractions and its relation to the chemical transport, the temporal variation and the correlation of sediment flux with a constant/variable discharge. Divergences could also be expected depending on the type of sampler and sampling design used, as well as the sample mass collected in the field. Moreover, heterogeneity and errors because of the analytical techniques employed for chemical determination should be taken into account for environmental geochemists and researchers in general [1]. Despite the inherent complexity for sampling and analyzing suspended sediments, the compilation of the chemical composition of suspended matter in World Rivers [2] is clearly desirable. Likewise, the more intricate the environmental issues related to agricultural and industrial pollution, the higher is the importance
Corresponding author. Tel.: + 55 19 34294829; fax: + 55 19 34294654.
E-mail address: [email protected] (E.J. Franc-a). 0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.02.055
of punctual assessment of chemical element pathways. For that reason, generation of knowledge by applying analytical techniques to study suspended matter in small rivers and streams is pretty appropriate for geochemical community, as well as for other environmental associated researchers. Recently comparability of results is acclaimed for all environmental studies. The use of adequate technique could minimize analytical uncertainties [1,3]. In the case of analysis of sediments in suspension by spectrometric techniques, dissolution of solids is dependent on the sample matrix. For instance, carbonates are easily soluble than igneous and metamorphic matrices. Chemical comparisons based on these results become complicated across geological gradients/boundaries [1]. Neutron activation analysis (NAA) is a nuclear multi-elemental technique, which is well suited for determining chemical composition of suspended sediments, especially when its instrumental mode and the k0 standardization [4] are used. The main advantages of k0–NAA, as applied at Centro de Energia Nuclear na Agricultura (CENA), have already been described [5]. Therefore, this work has tested a procedure for analyzing suspended sediments by k0–INAA within the context of Project Interface SSV ‘‘Innovation in the biomonitoring of wet ecosystems from the Piracicaba River Basin: Interface Sediment/Soil–Vegetation–Fauna (SSVF)’’. The project aims at the assessment of environmental quality of ecological compartments of riparian areas from the Piracicaba region, Sa~ o Paulo State, Brazil, in which
480
E.J. Franc- a et al. / Nuclear Instruments and Methods in Physics Research A 622 (2010) 479–483
suspended sediment could be a very helpful ecological compartment to understand chemical element pathway.
2. Experimental The municipality of Piracicaba with an area of 1385.38 km2 is mainly characterized by agricultural activities. Among them, sugarcane and pasture together account for about 1000 km2 [6]. Diverse industries are also found here, mostly associated with agricultural activities. However, vegetation, mainly riparian forests, occupies a considerable area of about 116 km2 in spite of this intensive land use. The major rivers are Piracicaba and Tietˆe, the latter being mainly polluted in the City of Sa~ o Paulo. As mentioned before, the Project Interface SSVF aimed at the assessment of environmental quality of ecological compartments of riparian areas from the Piracicaba. Several riverine areas were selected from the Piracicamirim Stream (PM; n= 4), Marins Stream (M; n =3) and Piracicaba River (n = 10), as shown in Fig. 1. ¨ According to Koppen, Piracicaba’s climate is classified as Cwa (mild mid-latitude, humid subtropical, mild with dry winter and hot summer). Fig. 2A shows averaged precipitation and temperature during the period between 1917 and 2009, data collected from the climatic station located at the Escola Superior de Agricultura Luiz de Queiroz, Universidade de Sa~ o Paulo (S22 420 300 ; W47 380 0000 ). Fig. 2B presents mean values of discharge (m3 s 1) for the Station PCB02800 (Artemis) for the Piracicaba River [7,8]. With the mean discharge value of 140 m3 s 1 and the basin area, the Piracicaba River can be considered a river of medium dimension [1]. For suspended sediment sampling, composite water samples of 20 l were collected in rivers from the Piracicaba city and surrounding streams (Fig. 1), stored in plastic gallons and in cold chamber at 8 1C for 6 months until the sediment decantation. After this period, surface water was extracted by suction, leaving the sediments in the bottle bottom. The remaining suspension was transferred to high-density polyethylene bottles for centrifugation and, later, freeze-dried for obtaining the test material. A recent work [2] suggests that even mobile chemical elements, such as Ca and K, are transported in the solid form. Therefore, the procedure used for obtaining the solid material should not yield
significant losses of chemical elements in the solution [2] or because of the adsorption of metals onto the container walls. Analytical portions of approximately 100 mg were directly weighted in polyethylene capsules for neutron irradiation. Compared with other techniques [1], this procedure is quite simple because chemical treatment for dissolution is not involved. Moisture was estimated by oven-drying separate portions (up to 500 mg) at 85 1C until constant mass. Portions of 200 mg of the reference materials International Atomic Energy Agency (IAEA) Soil 7 and National Institute of Standards and Technology Standard Reference Material (NIST SRM) 2710 Trace Elements in Montana Soil were also analyzed for quality control purposes. Together with samples, pieces of Ni–Cr alloy (mass=10 mg) were sandwiched between vials for monitoring thermal neutron flux [9]. The material was irradiated in a thermal neutron flux of approximately 1013 cm 2 s 1 for 4 h in the Research Nuclear Reactor IEA-R1 of the Instituto de Pesquisas Energe´ticas e Nucleares, Comissa~ o Nacional de Energia Nuclear, Sa~ o Paulo, Brazil. After 2 days of decay time, irradiated material was transported to CENA. This step allows the quantification of radionuclides with half-lives higher than 0.5 day. Induced radioactivity was measured at 5, 7, 16 and 60 days after irradiation using two Ortec germanium detectors with 45% and 50% of efficiency at the 1332 keV photopeak from 60Co. Monitors were measured at 10 and 15 days after irradiation, in which the thermal neutron flux during the irradiation was 9.4 1012 75.8 1011 cm 2 s 1. For this particular irradiation position, e and a were 69 and 0.067, respectively. The quantification of chemical elements was done by means of the software Quantu dedicated to k0–INAA, which also permits the estimation of analytical uncertainties and detection limits [10]. For Hg and Se mass fractions, appropriate correction for spectral interferences were applied. Whenever necessary, corrections were also carried out for chemical elements present in the vials (blank). Results of chemical elements were reported on a dry weight basis. For assessing the quality of the analytical results, En number was calculated in a Microsoft Excel worksheet taking into account the difference between obtained and reference values and the respective expanded analytical uncertainties at the 95% confidence level. Multivariate analysis was based on standardized chemical element mass fractions (mean n =0; standard deviation
Fig. 1. Hydrological map of the Piracicaba River Basin in the Piracicaba City, Sa~ o Paulo State, Brazil. Detail of sampling points in the Piracicaba River, Piracicamirim Stream and Marins Stream.
E.J. Franc- a et al. / Nuclear Instruments and Methods in Physics Research A 622 (2010) 479–483
300
34 Max
32
Min
Mean
220
P
Y2005 Y2006
200 250
30
180
200
24 22
150
20 18
100
16
160
Discharge (m3/s)
26
Precipitation (mm)
28
Temperature (°C)
481
140 120 100 80
14
60
50
12
40
10
20
0
8 J
F
M
A
M
J
J
S
A
O
N
D
F
J
M
A
M
J
Month
J
A
O
S
N
D
Month
Fig. 2. Climatic and discharge characterization of the Piracicaba River, Piracicaba City, Sa~ o Paulo State, Brazil. A = Precipitation and temperature between 1917 and 2009, Escola Superior de Agricultura Luiz de Queiroz (S22 420 300 ; W47 380 0000 ). B = monthly mean values of discharge (m3 s 1) for the Station PCB02800 (Artemis) for the Piracicaba River in 2005 and 2006.
Table 1 Chemical element composition (mg/kg) of suspended sediments from the Piracicaba River Basin.
Marins Stream (n= 3) Piracicaba River (n= 10)
Piracicamirim Stream (n= 4)
World (5o n o164)
Marins Stream (n= 3) Piracicaba River (n= 10)
Piracicamirim Stream (n= 4)
World [2] (5 on o 164)
Max Min Median Max Min Median Max Min Average STD
Fe
Ca
K
Na
Ba
Zn
Sr
Cr
Rb
53,300 38,600 63,500 229,000 41,300 94,900 173,000 21,200 58,100 48,100
71,900 19,700 15,000 23,200 10,800 25,100 25,800 9260 25,900 28,000
11,900 5760 4740 6740 2050 3420 6410 2970 16,900 10,400
8570 3060 3790 6660 474 2160 7330 520 7100 9300
4300 1340 1260 2230 579 2590 4990 498 522 472
266 116 380 1350 173 632 993 163 208 237
477 170 196 266 76 351 476 124 187 272
121 35 120 291 18 217 646 36 130 155
111.3 32.9 35.5 69.0 17.5 40.6 74.8 19.7 78.5 53.9
Ce
La
As
Co
Br
Sc
Th
Cs
Sm
Max Min Median Max Min Median Max Min Average STD
70.1 30.3 74.5 91.5 59.3 59.7 95.7 36.0 73.6 38.4 Hf
Marins Stream (n= 3) Piracicaba River (n= 10)
Piracicamirim Stream (n= 4)
World [2] (5 on o 164)
Max Min Median Max Min Median Max Min Average STD
31.0 13.2 31.3 41.8 23.0 24.2 39.1 15.8 37.4 24.1 Mo
5.89 2.17 5.20 11.3 1.91 2.99 7.31 1.58 4.04 1.70
90.7 21.1 8.1 14.6 6.2 9.7 52.0 4.3 36.3 27.0 Sb
11.6 4.94 17.8 22.8 6.19 22.6 31.9 14.7 2.98 4.53
28.5 17.6 20.1 67.2 12.1 30.0 74.6 17.8 22.5 19.6 Yb
1.80 0.83 3.48 22.7 0.47 1.11 2.29 0.92 2.19 2.41
63.5 25.8 62.0 73.4 35.7 51.3 113 33.4 21.5 17.3 Eu
2.56 1.23 2.18 2.97 1.76 1.75 2.94 1.20 2.11 1.28
8.57 3.11 8.38 13.4 7.02 6.75 16.4 2.74 18.2 9.30 Ta
0.99 0.43 1.02 1.20 0.92 0.74 1.03 0.57 1.29 0.58
10.4 3.41 7.82 13.6 3.59 5.57 17.4 2.10 12.1 5.86 Tb
1.13 0.42 0.89 1.26 0.51 0.75 2.28 0.20 1.27 0.51
5.36 1.53 2.28 5.94 1.16 2.77 11.2 0.76 6.25 4.68 Hg
0.54 0.26 0.63 0.72 0.52 0.52 0.74 0.32 0.82 0.41
0.51 0.37 0.66 3.02 0.27 1.55 25.6 0.56 0.04b
Nia 94
223
149 74.5 100
5.21 2.20 5.25 6.77 4.61 4.12 5.24 3.07 6.12 2.76 Se 1.66 0.47 2.19 2.90 1.79 2.10 3.10 1.80 1.0b
a
Only few values were determined by k0–INAA. Maximum values of mass fractions for suspended sediment from the Mississipi River [1]; World= World River suspended sediment average mass fraction of chemical elements [2]; STD = standard deviation. b
n =1), using bivariate scatter plots for assessing normal distribution of data. Log and exponential-related transformations were used to approximate data to a normal distribution. Principal
component analysis (PCA) using Statistica software was thus employed to study the correlation of chemical elements because of the excessive number of variables (28).
482
E.J. Franc- a et al. / Nuclear Instruments and Methods in Physics Research A 622 (2010) 479–483
3. Results and discussion To show the applicability of k0–INAA, results of En numbers for IAEA Soil 7 and SRM 2710 for all chemical elements determined were within the range from 1 to 1, indicating the satisfactory performance at the 95% confidence level. Table 1 shows the results of 28 chemical element mass fractions for 17 suspended sediment samples averaged by river and streams. For comparison, Table 1 also shows the average world mass fraction of chemical elements and their respective standard deviations. Analytical uncertainties were within the expected range for chemical elements determined in soils by means of k0–INAA [5]. Owing to the intrinsic characteristics of k0–INAA, uncertainties are easily estimated and expanded to the 95% confidence level [11]. However problems with heterogeneity are still important for this geological material and should be studied before sampling campaign [12,13]. Despite the simple sampling design (one sampling period; one season; one composite sample), contamination with chemical elements was probably detected in diverse stream and river sampling points. Maximum values of chemical element mass fractions from Table 1 were mostly higher than 95% confidence level of world mean (mean+ 2 STD). It is the case of Fe (222,900 mg/kg), Ba (4990 mg/kg), Zn (1350 mg/kg), Cr (646 mg/ kg), Co (74.5 mg/kg), Br (113 mg/kg) and Mo (31.9 mg/kg). Grain size exercises a disproportionate control on sedimentassociated chemical mass fractions in suspended sediments by increasing mass fraction when grain size decreases [1]. At least for the Piracicaba River, silt/clay content was estimated to be 38% [14]. Considering the association between trace elements and silt/ clay fraction, it would be expected higher mass fractions of Zn, Cr, Co, Br and Mo for the suspended sediment compartment of the Piracicaba River. Nevertheless, by excluding sand-sized suspended sediment, results of some chemical elements like Co, Cr, Fe and Zn might be 60% lower than the total chemical element mass fractions [1]. Although some total Cr values found in suspended sediments of the Piracicaba River were in the range of 15.5–48.3 mg/kg [14], a mean value of 120 mg/kg obtained by this work could indicate pollution sources of this chemical element in the Piracicaba City area. Similarly results for Zn quantified in 2002 revealed mass fractions varying from 15 to 308 mg/kg, whereas the median value of 380 mg/kg and maximum of 1350 mg/kg were found in this work. As expected for tropical rivers, K and Na mass fractions were quite lower than the world average [2]. Calcium was at maximum mass fraction in Marins Stream of 71,900 mg/kg, about three times over the world average (Table 1). For Hg, maximum values of the Mississipi River were used for comparison [1]. An extremely high mass fraction of Hg (22.6 mg/kg) was found in the Piracicamirim River. The mass fraction of this chemical element of 3476 mg/kg determined in the SRM 2710 compared well with the certified value of 32.671.8 mg/kg, thus proving accuracy of the value found in the suspended sediments of the Piracicamirim Stream. Determination of Hg in other points in the Piracicaba River had detected mass fractions of about 0.10 mg/kg in rural areas [14]. Horowitz et al. [15] have found mass fractions up to 16 mg/kg through the monitoring of urban impacts on suspended sediments within the City of Atlanta, Georgia, USA. Problems with sampling and sample preparation could also be responsible for such variation in Hg mass fractions in water resources. On the other hand, the hypothesis of anthropogenic contribution becomes quite plausible. For that reason, multivariate techniques applied to several variables could solve problems related to the identification of potential sources of chemical elements. It is obvious from Fig. 3
Fig. 3. Scatter plot of principal components 1 (PC1) and 2 (PC2).
that four groups of correlated variables were identified, mainly associated with anthropogenic impacts like Se, Sb, Cr, Mo, Zn and Hg, terrigenous group formed by lanthanoids (Ce, Eu, La, Sm, Tb and Yb), Hf, Sc, Ta and Th, and alkaline group of Cs, K and Rb. A distinct formation was observed for As, Ba, Br, Ca, Co, Fe, Na and Sr (Fig. 3). PC1 and PC2 take into account about 65.6% of total variance, indicating the necessity of using three or more PCs in this analysis. A test realized with three PCs has changed completely the clustering, indicating the complexity of source apportionment of chemical elements for urban and rural suspended sediments. Further studies will be necessary to evaluate all sources of pollution for the Piracicaba River Basin in terms of suspended matter.
4. Conclusions The ecological compartment of suspended sediments of rivers from the Piracicaba River Basin was analyzed by k0–INAA, allowing the determination of about 30 chemical elements, including some of great environmental importance such as Se, Sb, Cr, Mo, Zn and Hg. Despite the time consuming procedure, sampling and sample preparation of suspended sediment’s samples was considered adequate. However, further studies are necessary to study the chemical changes on chemical element distribution in the water–solid interface. Chemical element mass fractions of Fe, Ba, Zn, Cr, Co, Br, Mo and Hg determined in rivers from the Piracicaba River Basin were higher than world river values of suspended sediments, probably associated with a high level of pollution with chemical elements. Results from the first statistical analysis have shown the complexity of source apportionment of chemical elements in suspended sediments.
Acknowledgments The authors are thankful to the staff and operators of the nuclear research reactor IEA-R1, of Instituto de Pesquisas
E.J. Franc- a et al. / Nuclear Instruments and Methods in Physics Research A 622 (2010) 479–483
Energe´ticas e Nucleares, Comissa~ o Nacional de Energia Nuclear (IPEN/CNEN) for carrying out the sample irradiations. The authors are also thankful to Conselho Nacional de Desenvolvimento Cientı´fico e Tecnolo´gico (CNPq) for the financial support (Process no. 555588/06-8). References [1] [2] [3] [4] [5]
A.J. Horowitz, Sci. Total Environ. 400 (2008) 315. J. Viers, B. Dupre´, J. Gaillardet, Sci. Total Environ. 407 (2009) 853. B. Markert, Sci. Total Environ. 176 (1995) 45. A. Simonits, F. De Corte, L. Moens, J. Hoste, J. Radioanal. Nucl. Chem. 72 (1982) 209. M.A. Bacchi, E.A.N. Fernandes, H. de Oliveira, J. Radioanal. Nucl. Chem. 245 (2000) 217. [6] A.G.O. Pereira Barretto, G. Sparovek, M. Giannotti, Atlas Rural de Piracicaba, IPEF, Piracicaba, 2006, in Portuguese. [7] Companhia de Tecnologia de Saneamento Ambiental – CETESB, Relato´rio de Qualidade de A´guas Interiores no Estado de Sa~ o Paulo, CETESB, Sa~ o Paulo,
[8]
[9] [10] [11] [12] [13]
[14]
[15]
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2005, in Portuguese. Available on /htpp:\\http://www.cetesb.sp.gov.br/ Agua/rios/publicacoes.aspS. Companhia de Tecnologia de Saneamento Ambiental – CETESB, Relato´rio de Qualidade de A´guas Interiores no Estado de Sa~ o Paulo, CETESB, Sa~ o Paulo, 2006, in Portuguese. Available on /htpp:\\http://www.cetesb.sp.gov.br/ Agua/rios/publicacoes.aspS. E.J. Franc- a, E.A.N. Fernandes, M.A. Bacchi, J. Radioanal. Nucl. Chem. 257 (2003) 113. M.A. Bacchi, E.A.N. Fernandes, J. Radioanal. Nucl. Chem. 257 (2003) 577. P. Bode, E.A.N. Fernandes, R.R. Greenberg, J. Radioanal. Nucl. Chem 245 (2000) 109. E.J. Franc- a, E.A.N. Fernandes, M.A. Bacchi, P. Bode, R.T.M. van Soldt, J. Radioanal. Nucl. Chem. , doi:10.1007/s10967-009-0326-x. F.Y. Fonseca, E.A.N. Fernandes, V.S. Rodrigues, I.P.O. Cavalca, L. Camilli, C. Bardini Jr., E.J. Franc-a, J. Radioanal.Nucl. Chem. , doi:10.1007/s10967-0090336-8. Companhia de Tecnologia de Saneamento Ambiental – CETESB, Relato´rio de Qualidade de A´guas Interiores no Estado de Sa~ o Paulo, CETESB, Sa~ o Paulo, 2002. In Portuguese. Available on: /htpp:\\http://www.cetesb.sp.gov.br/ Agua/rios/publicacoes.aspS. A.J. Horowitz, K.A. Elrick, J.J. Smith, Hydrol. Process 22 (2008) 1473.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Characterizing suspended sediments from the Piracicaba River Basin by means of k0–INAA E.J. Franc- a a,, E.A.N. Fernandes a, I.P.O Cavalca a, F.Y. Fonseca a, L. Camilli a, V.S. Rodrigues a, C. Bardini Junior a, J.R. Ferreira a,b, M.A. Bacchi a a b
CENA/USP, Centro de Energia Nuclear na Agricultura, Universidade of Sa~ o Paulo, PO Box 97, 13400-970, Piracicaba, SP, Brazil ~ Paulo, SP, Brazil Instituto de Pesca, Secretaria de Agricultura e Abastecimento (SAA), Avenida Francisco Matarazzo 455, 05031-900, Sao
a r t i c l e in fo
abstract
Available online 10 February 2010
The inorganic chemical characterization of suspended sediments is of utmost relevance for the knowledge of the dynamics and movement of chemical elements in the aquatic and wet ecosystems. Despite the complexity of the effective design for studying this ecological compartment, this work has tested a procedure for analyzing suspended sediments by instrumental neutron activation analysis, k0 method (k0–INAA). The chemical elements As, Ba, Br, Ca, Ce, Co, Cr, Cs, Eu, Fe, Hf, Hg, K, La, Mo, Na, Ni, Rb, Sb, Sc, Se, Sm, Sr, Ta, Tb, Th, Yb and Zn were quantified in the suspended sediment compartment by means of k0–INAA. When compared with World Average for rivers, high mass fractions of Fe (222,900 mg/kg), Ba (4990 mg/kg), Zn (1350 mg/kg), Cr (646 mg/kg), Co (74.5 mg/kg), Br (113 mg/kg) and Mo (31.9 mg/kg) were quantified in suspended sediments from the Piracicaba River, the Piracicamirim Stream and the Marins Stream. Results of the principal component analysis for standardized chemical element mass fractions indicated an intricate correlation among chemical elements evaluated, as a response of the contribution of natural and anthropogenic sources of chemical elements for ecosystems. & 2010 Elsevier B.V. All rights reserved.
Keywords: Eroded material Suspended matter Trace elements Water quality Method k0
1. Introduction The inorganic chemical characterization of suspended sediments is of utmost relevance for the knowledge of the dynamics and movement of chemical elements in the ecosystems. Studies involving the collection, processing and subsequent chemical analysis of suspended sediments are considered complicated because of the characteristics of this kind of matrix [1]. The main issues are the horizontal and vertical cross sectional variations, the variation of silt/ clay (o63 mm) fractions and its relation to the chemical transport, the temporal variation and the correlation of sediment flux with a constant/variable discharge. Divergences could also be expected depending on the type of sampler and sampling design used, as well as the sample mass collected in the field. Moreover, heterogeneity and errors because of the analytical techniques employed for chemical determination should be taken into account for environmental geochemists and researchers in general [1]. Despite the inherent complexity for sampling and analyzing suspended sediments, the compilation of the chemical composition of suspended matter in World Rivers [2] is clearly desirable. Likewise, the more intricate the environmental issues related to agricultural and industrial pollution, the higher is the importance
Corresponding author. Tel.: + 55 19 34294829; fax: + 55 19 34294654.
E-mail address: [email protected] (E.J. Franc-a). 0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.02.055
of punctual assessment of chemical element pathways. For that reason, generation of knowledge by applying analytical techniques to study suspended matter in small rivers and streams is pretty appropriate for geochemical community, as well as for other environmental associated researchers. Recently comparability of results is acclaimed for all environmental studies. The use of adequate technique could minimize analytical uncertainties [1,3]. In the case of analysis of sediments in suspension by spectrometric techniques, dissolution of solids is dependent on the sample matrix. For instance, carbonates are easily soluble than igneous and metamorphic matrices. Chemical comparisons based on these results become complicated across geological gradients/boundaries [1]. Neutron activation analysis (NAA) is a nuclear multi-elemental technique, which is well suited for determining chemical composition of suspended sediments, especially when its instrumental mode and the k0 standardization [4] are used. The main advantages of k0–NAA, as applied at Centro de Energia Nuclear na Agricultura (CENA), have already been described [5]. Therefore, this work has tested a procedure for analyzing suspended sediments by k0–INAA within the context of Project Interface SSV ‘‘Innovation in the biomonitoring of wet ecosystems from the Piracicaba River Basin: Interface Sediment/Soil–Vegetation–Fauna (SSVF)’’. The project aims at the assessment of environmental quality of ecological compartments of riparian areas from the Piracicaba region, Sa~ o Paulo State, Brazil, in which
480
E.J. Franc- a et al. / Nuclear Instruments and Methods in Physics Research A 622 (2010) 479–483
suspended sediment could be a very helpful ecological compartment to understand chemical element pathway.
2. Experimental The municipality of Piracicaba with an area of 1385.38 km2 is mainly characterized by agricultural activities. Among them, sugarcane and pasture together account for about 1000 km2 [6]. Diverse industries are also found here, mostly associated with agricultural activities. However, vegetation, mainly riparian forests, occupies a considerable area of about 116 km2 in spite of this intensive land use. The major rivers are Piracicaba and Tietˆe, the latter being mainly polluted in the City of Sa~ o Paulo. As mentioned before, the Project Interface SSVF aimed at the assessment of environmental quality of ecological compartments of riparian areas from the Piracicaba. Several riverine areas were selected from the Piracicamirim Stream (PM; n= 4), Marins Stream (M; n =3) and Piracicaba River (n = 10), as shown in Fig. 1. ¨ According to Koppen, Piracicaba’s climate is classified as Cwa (mild mid-latitude, humid subtropical, mild with dry winter and hot summer). Fig. 2A shows averaged precipitation and temperature during the period between 1917 and 2009, data collected from the climatic station located at the Escola Superior de Agricultura Luiz de Queiroz, Universidade de Sa~ o Paulo (S22 420 300 ; W47 380 0000 ). Fig. 2B presents mean values of discharge (m3 s 1) for the Station PCB02800 (Artemis) for the Piracicaba River [7,8]. With the mean discharge value of 140 m3 s 1 and the basin area, the Piracicaba River can be considered a river of medium dimension [1]. For suspended sediment sampling, composite water samples of 20 l were collected in rivers from the Piracicaba city and surrounding streams (Fig. 1), stored in plastic gallons and in cold chamber at 8 1C for 6 months until the sediment decantation. After this period, surface water was extracted by suction, leaving the sediments in the bottle bottom. The remaining suspension was transferred to high-density polyethylene bottles for centrifugation and, later, freeze-dried for obtaining the test material. A recent work [2] suggests that even mobile chemical elements, such as Ca and K, are transported in the solid form. Therefore, the procedure used for obtaining the solid material should not yield
significant losses of chemical elements in the solution [2] or because of the adsorption of metals onto the container walls. Analytical portions of approximately 100 mg were directly weighted in polyethylene capsules for neutron irradiation. Compared with other techniques [1], this procedure is quite simple because chemical treatment for dissolution is not involved. Moisture was estimated by oven-drying separate portions (up to 500 mg) at 85 1C until constant mass. Portions of 200 mg of the reference materials International Atomic Energy Agency (IAEA) Soil 7 and National Institute of Standards and Technology Standard Reference Material (NIST SRM) 2710 Trace Elements in Montana Soil were also analyzed for quality control purposes. Together with samples, pieces of Ni–Cr alloy (mass=10 mg) were sandwiched between vials for monitoring thermal neutron flux [9]. The material was irradiated in a thermal neutron flux of approximately 1013 cm 2 s 1 for 4 h in the Research Nuclear Reactor IEA-R1 of the Instituto de Pesquisas Energe´ticas e Nucleares, Comissa~ o Nacional de Energia Nuclear, Sa~ o Paulo, Brazil. After 2 days of decay time, irradiated material was transported to CENA. This step allows the quantification of radionuclides with half-lives higher than 0.5 day. Induced radioactivity was measured at 5, 7, 16 and 60 days after irradiation using two Ortec germanium detectors with 45% and 50% of efficiency at the 1332 keV photopeak from 60Co. Monitors were measured at 10 and 15 days after irradiation, in which the thermal neutron flux during the irradiation was 9.4 1012 75.8 1011 cm 2 s 1. For this particular irradiation position, e and a were 69 and 0.067, respectively. The quantification of chemical elements was done by means of the software Quantu dedicated to k0–INAA, which also permits the estimation of analytical uncertainties and detection limits [10]. For Hg and Se mass fractions, appropriate correction for spectral interferences were applied. Whenever necessary, corrections were also carried out for chemical elements present in the vials (blank). Results of chemical elements were reported on a dry weight basis. For assessing the quality of the analytical results, En number was calculated in a Microsoft Excel worksheet taking into account the difference between obtained and reference values and the respective expanded analytical uncertainties at the 95% confidence level. Multivariate analysis was based on standardized chemical element mass fractions (mean n =0; standard deviation
Fig. 1. Hydrological map of the Piracicaba River Basin in the Piracicaba City, Sa~ o Paulo State, Brazil. Detail of sampling points in the Piracicaba River, Piracicamirim Stream and Marins Stream.
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300
34 Max
32
Min
Mean
220
P
Y2005 Y2006
200 250
30
180
200
24 22
150
20 18
100
16
160
Discharge (m3/s)
26
Precipitation (mm)
28
Temperature (°C)
481
140 120 100 80
14
60
50
12
40
10
20
0
8 J
F
M
A
M
J
J
S
A
O
N
D
F
J
M
A
M
J
Month
J
A
O
S
N
D
Month
Fig. 2. Climatic and discharge characterization of the Piracicaba River, Piracicaba City, Sa~ o Paulo State, Brazil. A = Precipitation and temperature between 1917 and 2009, Escola Superior de Agricultura Luiz de Queiroz (S22 420 300 ; W47 380 0000 ). B = monthly mean values of discharge (m3 s 1) for the Station PCB02800 (Artemis) for the Piracicaba River in 2005 and 2006.
Table 1 Chemical element composition (mg/kg) of suspended sediments from the Piracicaba River Basin.
Marins Stream (n= 3) Piracicaba River (n= 10)
Piracicamirim Stream (n= 4)
World (5o n o164)
Marins Stream (n= 3) Piracicaba River (n= 10)
Piracicamirim Stream (n= 4)
World [2] (5 on o 164)
Max Min Median Max Min Median Max Min Average STD
Fe
Ca
K
Na
Ba
Zn
Sr
Cr
Rb
53,300 38,600 63,500 229,000 41,300 94,900 173,000 21,200 58,100 48,100
71,900 19,700 15,000 23,200 10,800 25,100 25,800 9260 25,900 28,000
11,900 5760 4740 6740 2050 3420 6410 2970 16,900 10,400
8570 3060 3790 6660 474 2160 7330 520 7100 9300
4300 1340 1260 2230 579 2590 4990 498 522 472
266 116 380 1350 173 632 993 163 208 237
477 170 196 266 76 351 476 124 187 272
121 35 120 291 18 217 646 36 130 155
111.3 32.9 35.5 69.0 17.5 40.6 74.8 19.7 78.5 53.9
Ce
La
As
Co
Br
Sc
Th
Cs
Sm
Max Min Median Max Min Median Max Min Average STD
70.1 30.3 74.5 91.5 59.3 59.7 95.7 36.0 73.6 38.4 Hf
Marins Stream (n= 3) Piracicaba River (n= 10)
Piracicamirim Stream (n= 4)
World [2] (5 on o 164)
Max Min Median Max Min Median Max Min Average STD
31.0 13.2 31.3 41.8 23.0 24.2 39.1 15.8 37.4 24.1 Mo
5.89 2.17 5.20 11.3 1.91 2.99 7.31 1.58 4.04 1.70
90.7 21.1 8.1 14.6 6.2 9.7 52.0 4.3 36.3 27.0 Sb
11.6 4.94 17.8 22.8 6.19 22.6 31.9 14.7 2.98 4.53
28.5 17.6 20.1 67.2 12.1 30.0 74.6 17.8 22.5 19.6 Yb
1.80 0.83 3.48 22.7 0.47 1.11 2.29 0.92 2.19 2.41
63.5 25.8 62.0 73.4 35.7 51.3 113 33.4 21.5 17.3 Eu
2.56 1.23 2.18 2.97 1.76 1.75 2.94 1.20 2.11 1.28
8.57 3.11 8.38 13.4 7.02 6.75 16.4 2.74 18.2 9.30 Ta
0.99 0.43 1.02 1.20 0.92 0.74 1.03 0.57 1.29 0.58
10.4 3.41 7.82 13.6 3.59 5.57 17.4 2.10 12.1 5.86 Tb
1.13 0.42 0.89 1.26 0.51 0.75 2.28 0.20 1.27 0.51
5.36 1.53 2.28 5.94 1.16 2.77 11.2 0.76 6.25 4.68 Hg
0.54 0.26 0.63 0.72 0.52 0.52 0.74 0.32 0.82 0.41
0.51 0.37 0.66 3.02 0.27 1.55 25.6 0.56 0.04b
Nia 94
223
149 74.5 100
5.21 2.20 5.25 6.77 4.61 4.12 5.24 3.07 6.12 2.76 Se 1.66 0.47 2.19 2.90 1.79 2.10 3.10 1.80 1.0b
a
Only few values were determined by k0–INAA. Maximum values of mass fractions for suspended sediment from the Mississipi River [1]; World= World River suspended sediment average mass fraction of chemical elements [2]; STD = standard deviation. b
n =1), using bivariate scatter plots for assessing normal distribution of data. Log and exponential-related transformations were used to approximate data to a normal distribution. Principal
component analysis (PCA) using Statistica software was thus employed to study the correlation of chemical elements because of the excessive number of variables (28).
482
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3. Results and discussion To show the applicability of k0–INAA, results of En numbers for IAEA Soil 7 and SRM 2710 for all chemical elements determined were within the range from 1 to 1, indicating the satisfactory performance at the 95% confidence level. Table 1 shows the results of 28 chemical element mass fractions for 17 suspended sediment samples averaged by river and streams. For comparison, Table 1 also shows the average world mass fraction of chemical elements and their respective standard deviations. Analytical uncertainties were within the expected range for chemical elements determined in soils by means of k0–INAA [5]. Owing to the intrinsic characteristics of k0–INAA, uncertainties are easily estimated and expanded to the 95% confidence level [11]. However problems with heterogeneity are still important for this geological material and should be studied before sampling campaign [12,13]. Despite the simple sampling design (one sampling period; one season; one composite sample), contamination with chemical elements was probably detected in diverse stream and river sampling points. Maximum values of chemical element mass fractions from Table 1 were mostly higher than 95% confidence level of world mean (mean+ 2 STD). It is the case of Fe (222,900 mg/kg), Ba (4990 mg/kg), Zn (1350 mg/kg), Cr (646 mg/ kg), Co (74.5 mg/kg), Br (113 mg/kg) and Mo (31.9 mg/kg). Grain size exercises a disproportionate control on sedimentassociated chemical mass fractions in suspended sediments by increasing mass fraction when grain size decreases [1]. At least for the Piracicaba River, silt/clay content was estimated to be 38% [14]. Considering the association between trace elements and silt/ clay fraction, it would be expected higher mass fractions of Zn, Cr, Co, Br and Mo for the suspended sediment compartment of the Piracicaba River. Nevertheless, by excluding sand-sized suspended sediment, results of some chemical elements like Co, Cr, Fe and Zn might be 60% lower than the total chemical element mass fractions [1]. Although some total Cr values found in suspended sediments of the Piracicaba River were in the range of 15.5–48.3 mg/kg [14], a mean value of 120 mg/kg obtained by this work could indicate pollution sources of this chemical element in the Piracicaba City area. Similarly results for Zn quantified in 2002 revealed mass fractions varying from 15 to 308 mg/kg, whereas the median value of 380 mg/kg and maximum of 1350 mg/kg were found in this work. As expected for tropical rivers, K and Na mass fractions were quite lower than the world average [2]. Calcium was at maximum mass fraction in Marins Stream of 71,900 mg/kg, about three times over the world average (Table 1). For Hg, maximum values of the Mississipi River were used for comparison [1]. An extremely high mass fraction of Hg (22.6 mg/kg) was found in the Piracicamirim River. The mass fraction of this chemical element of 3476 mg/kg determined in the SRM 2710 compared well with the certified value of 32.671.8 mg/kg, thus proving accuracy of the value found in the suspended sediments of the Piracicamirim Stream. Determination of Hg in other points in the Piracicaba River had detected mass fractions of about 0.10 mg/kg in rural areas [14]. Horowitz et al. [15] have found mass fractions up to 16 mg/kg through the monitoring of urban impacts on suspended sediments within the City of Atlanta, Georgia, USA. Problems with sampling and sample preparation could also be responsible for such variation in Hg mass fractions in water resources. On the other hand, the hypothesis of anthropogenic contribution becomes quite plausible. For that reason, multivariate techniques applied to several variables could solve problems related to the identification of potential sources of chemical elements. It is obvious from Fig. 3
Fig. 3. Scatter plot of principal components 1 (PC1) and 2 (PC2).
that four groups of correlated variables were identified, mainly associated with anthropogenic impacts like Se, Sb, Cr, Mo, Zn and Hg, terrigenous group formed by lanthanoids (Ce, Eu, La, Sm, Tb and Yb), Hf, Sc, Ta and Th, and alkaline group of Cs, K and Rb. A distinct formation was observed for As, Ba, Br, Ca, Co, Fe, Na and Sr (Fig. 3). PC1 and PC2 take into account about 65.6% of total variance, indicating the necessity of using three or more PCs in this analysis. A test realized with three PCs has changed completely the clustering, indicating the complexity of source apportionment of chemical elements for urban and rural suspended sediments. Further studies will be necessary to evaluate all sources of pollution for the Piracicaba River Basin in terms of suspended matter.
4. Conclusions The ecological compartment of suspended sediments of rivers from the Piracicaba River Basin was analyzed by k0–INAA, allowing the determination of about 30 chemical elements, including some of great environmental importance such as Se, Sb, Cr, Mo, Zn and Hg. Despite the time consuming procedure, sampling and sample preparation of suspended sediment’s samples was considered adequate. However, further studies are necessary to study the chemical changes on chemical element distribution in the water–solid interface. Chemical element mass fractions of Fe, Ba, Zn, Cr, Co, Br, Mo and Hg determined in rivers from the Piracicaba River Basin were higher than world river values of suspended sediments, probably associated with a high level of pollution with chemical elements. Results from the first statistical analysis have shown the complexity of source apportionment of chemical elements in suspended sediments.
Acknowledgments The authors are thankful to the staff and operators of the nuclear research reactor IEA-R1, of Instituto de Pesquisas
E.J. Franc- a et al. / Nuclear Instruments and Methods in Physics Research A 622 (2010) 479–483
Energe´ticas e Nucleares, Comissa~ o Nacional de Energia Nuclear (IPEN/CNEN) for carrying out the sample irradiations. The authors are also thankful to Conselho Nacional de Desenvolvimento Cientı´fico e Tecnolo´gico (CNPq) for the financial support (Process no. 555588/06-8). References [1] [2] [3] [4] [5]
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