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Coupled anthropogenic anomalies of radionuclides and major elements in estuarine sediments
Journal of Environmental Radioactivity 99 (2008) 1329–1334
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Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Coupled anthropogenic anomalies of radionuclides and major elements in estuarine sediments W. Machado a, *, W. Luiz-Silva b, C.J. Sanders a, S.R. Patchineelam a a b
´i, RJ 24020-150, Brazil Departamento de Geoquı´mica, Universidade Federal Fluminense, Nitero Instituto de Geocieˆncias, Universidade Estadual de Campinas, Campinas, SP 13083-970, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 June 2007 Received in revised form 8 December 2007 Accepted 9 April 2008 Available online 19 May 2008
Concentrations of fertilizer industry-derived P (up to 3.4%), Ca (up to 6.1%), 226Ra (up to 744 Bq kg1) and 210 Pb (up to 1317 Bq kg1) at least one order of magnitude above natural levels were recorded in a sediment core from Morra˜o River estuary (SE Brazil). Unsupported 210Pb (¼total 210Pb 226Ra) activities unexplained by atmospheric fallout and deviations from the radionuclides secular equilibrium also indicated strong anomalies. Anomalous constituents were positively correlated with each other and negatively correlated with clay mineral-bearing elements. These negative correlations were explained by a depletion of natural sediment constituents due to a dilution caused by elevated inputs of steel industryderived elements (mainly by Fe levels up to 24%). Absolute data and normalizations by a proxy for clays (Al) and anthropogenic Fe evidenced variabilities in the quality of coastal and land-derived sediment inputs, mainly due to changes in the relative contributions from industrial sources. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Radiochemical contamination Radionuclides disequilibrium Major elements contamination Estuarine sediments
1. Introduction Many efforts to elucidate the contamination record in coastal sediment profiles have been conduced worldwide, because vertical variabilities in anomalous chemical markers in sediments may reflect the temporal evolution of anthropogenic inputs (e.g., Carvalho, 1995; San Miguel et al., 2004; Sanders et al., 2006). Since the spatial and temporal anthropogenic input variability may be coupled with dilution and concentration effects caused by different sediment phases (mainly due to grain size and mineralogical heterogeneities), geochemical normalization methods may be used to improve data interpretation. For example, grain size-related geochemical changes within a sediment column may difficult the evaluation of downcore distributions of stable elements and radionuclides, which may be resolved normalizing it by a clay-bearing conservative element (generally Al), considered as a grain size proxy (e.g., Cundy and Croudace, 1995, 1996; Santschi et al., 2001). Unusual situations may occur when the geochemical record is heavily affected by multiple anthropogenic impacts, as observed in the sediment core investigated in this work, as part of a project intended to elucidate the geochemistry of chemical contaminants within the Santos-Cubata˜o estuarine system, Sa˜o Paulo State, SE Brazil (Fig. 1). This system is located in a region historically affected by anthropogenic activities (e.g., Medeiros and Bı´cego, 2004;
Abessa et al., 2005), receiving the drainage from urban areas and one of the most important industrial areas in Brazil. Braga et al. (2000) demonstrated that the water quality from this system is affected by sewage release and industrial activities, with maximum values of dissolved nitrite, phosphate and silicate concentrations in the same site in the inner, northern part of the system, near steel and fertilizer industries. The Santos-Cubata˜o estuarine system and part of its drainage basin have been also investigated for radionuclides contamination of sediments, since waste generation and storage by fertilizer industries may cause anomalous radionuclide levels, as observed in sites affected by phosphogypsum deposits (Silva et al., 2006a,b). Elevated levels of major and trace elements were recently recorded near these sites, in surface sediments from the Morra˜o River estuary (Fig. 1), in comparison with background levels found in a sediment core from another estuary within the same system (Luiz-Silva et al., 2006). Since the activities of fertilizer manufactures have raised the concentrations of naturally occurring radioactive materials (NORM) in aquatic environments (e.g., Pujol and Sanchez-Cabeza, 2000; Aguado et al., 2004), the present study investigates the distribution of major elements and typical fertilizer industry-derived radionuclides, such as 226Ra and 210Pb (e.g., Bolı´var et al., 2002; El Mamoney and Khater, 2004), in a sediment core from Morra˜o River estuary. 2. Materials and methods
* Corresponding author. Tel.: þ55 21 26292218; fax: þ55 21 26292234. E-mail address: [email protected] (W. Machado). 0265-931X/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2008.04.006
In the study site (23 520 3600 S, 46 210 2700 W), an intertidal sediment core (30 cm length 10 cm diameter) was collected by using a PVC tube in February 2005, during low tide. The sediment core was sectioned in 2 cm intervals over the first
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Fig. 1. Sampling site location in the Santos-Cubata˜o estuarine system, southeastern Brazil.
10 cm, 3 cm intervals over the next 15 cm and 5 cm for the last interval (n ¼ 11). Sediments were oven dried (50 C), disaggregated and homogenized before analyses and its water content was determined as the weight loss after drying. Sediment subsamples were counted for at least 11 h to determine 226Ra and 210Pb activities by gamma ray spectrometry, using a Camberra HPGe spectrometer with an efficiency of 40%, housed in a lead shield and coupled to a multichannel analyzer. Before analysis, sediment sub-samples were packed and stored for at least 21 days to allow the establishment of secular equilibrium between 226Ra and its granddaughters 214Pb and 214Bi. 226Ra activities were determined by a weighted average of two 214Pb energies (295.2 and 351.9 keV) and a 214Bi gamma peak at 609.3 keV (Moore, 1984), while 210Pb activities were determined by the direct measurement of 46.5 keV gamma peak. Background energies were subtracted from the photo-peak areas and self-absorption corrections were calculated (Cutshall et al., 1982). Energy and efficiency calibrations were done using the CANMET uranium ore reference material BL4a. Counting errors were always within 5%. Total concentrations of major elements were determined by wavelength dispersive X-ray fluorescence spectrometry (XRF) in glass disks, using a Philips PW 2404 spectrometer, according to Vendemiatto and Enzweiler (2001). The glass disks were made with the same sub-samples analyzed by gamma ray spectrometry, after pulverized in a mill with agata balls. Precision of XRF duplicate analysis was within 5% and the accuracy was assessed by analyses of reference materials (GSD-9 and GSD-12 Chinese sediments). Sediment weight losson-ignition (LOI) was measured after ignition of sediments at 550 C for 4 h, according to Heiri et al. (2001).
3. Results and discussion 3.1. Downcore absolute composition The investigated core was composed of fine-grained, dark gray sediments, showing a relatively low variability in the water content and LOI values (Fig. 2; Table 1), which was also generally observed for clay mineral-bearing elements, e.g., Al, Ti, Mg and K (Fig. 2; Table 1). LOI was uncorrelated with other variables, except by a significant negative correlation with Mn (Table 2). Water content and Al were not significantly correlated due to an extreme Al value in the deeper sediment layer (Fig. 2), but these variables were positively correlated with Ti, K and Si (Table 2). Although total Si concentrations can have contributions from aluminosilicates, quartz and biogenic Si, the positive correlations of Si with water content, Ti, Al and K (Table 2) and the fine-grained nature of sediments indicate that clay-bearing Si is probably predominant. However, composition changes were evidenced by differences between subsurface layers depleted in
water, LOI, Si, Ti, Al and K, but enriched in Fe, Mn, Ca, P, 226Ra and Pb (below 6–13 cm depth depending on the variable), and upper layers (Fig. 2). Some major elements (Fe, Mn, Ca and P) and the radionuclides studied presented anomalously high levels, while the other elements showed levels that do not evidence an anomalous input (Table 1). Background concentrations of Fe (2.88%), Mn (0.02%) and Ca (0.27%) reported for the fine sediment fraction (<63 mm) of a sediment core from another estuary within the Santos-Cubata˜o system (Luiz-Silva et al., 2006) indicate that the observed anomaly of major elements is one order of magnitude above natural levels. Local background levels for P were not found, but previous studies in sediments from contaminated and uncontaminated sites in southeastern Brazil reported that p level ranging between <0.01% and 0.23% (Carreira and Wagener, 1998; Jorcin, 2000; Mater et al., 2004), values at least one order of magnitude below the mean concentration observed in the studied core (Table 1). Anomalous constituents were positively correlated with each other and generally correlated negatively with water content and non-anomalous elements (Table 2). Sodium showed only a significant positive correlation (with Ti), while Mg was uncorrelated with the other variables (Table 2). Although associations with organic matter and fine particles may influence the distribution of natural radionuclides (e.g., Yeager and Santschi, 2003) and major elements (e.g., De Lazzari et al., 2004), this was not evidenced for the anomalous constituents, which showed negative correlations with LOI and clay-bearing elements. Considering that the negative correlations between anomalous and non-anomalous constituents were caused by an anthropogenic enrichment of major elements in one order of magnitude, such negative correlations appear to reflect a dilution of natural elements by anthropogenic elements (mainly Fe). While coastal and marine sediments from southeastern and southern Brazil for which there is no evidence of radiochemical contamination present 226Ra and 210Pb levels ranging between 2– 28 Bq kg1 and 13.5–158 Bq kg1, respectively (Wilken et al., 1986; Saito et al., 2001; Vegueria et al., 2002; Sanders et al., 2006), Silva et al. (2006b) showed 226Ra and 210Pb levels ranging between 8– 60 Bq kg1 and 26–538 Bq kg1, respectively, in surface sediments 210
W. Machado et al. / Journal of Environmental Radioactivity 99 (2008) 1329–1334
Fig. 2. Depth profiles of water content, LOI, major elements and radionuclide levels and
from the Santos-Cubata˜o estuarine system and part of its drainage basin. These authors evidenced a strong anthropogenic influence on 210Pb distribution only in the inner, northern area of the system. In the present study, higher radionuclide levels are recorded, reaching the magnitude found in estuaries strongly affected by fertilizer industries, which have caused, for example, 210Pb levels up to 1580 Bq kg1 in the Tagus River estuarine sediments (Carvalho, 1995) and 226Ra levels up to 961 Bq kg1 in sediments from the Tinto and Odiel Rivers estuary (Absi et al., 2004). The 210Pb levels unsupported by 226Ra decay (hereafter called 210 Pbxs), calculated as the difference between total 210Pb and 226Ra (Fig. 2; Table 1), indicated an anomaly unexplained by atmospheric fallout, since values of fallout 210Pb in coastal sediments from southeastern and southern Brazil typically do not exceed 100– 160 Bq kg1 (Wilken et al., 1986; Smoak and Patchineelam, 1999; Marques et al., 2006; Sanders et al., 2006). Moreover, 210Pb/226Ra
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210
Pb/226Ra ratios.
ratios up to 3.18 (Fig. 2; Table 1) indicate a pronounced disequilibrium between 226Ra and its decay product 210Pb, as have been observed in sediments affected by phosphogypsum input (San Miguel et al., 2004). Downcore variability in such ratios showed a minimum value in the uppermost layer and maximum values at 6–8 cm and 10–13 cm depth intervals (Fig. 2). The 226Ra and 210Pb levels in Brazilian phosphogypsum range between 22–1251 Bq kg1 and 47–1234 Bq kg1, respectively (Mazzilli et al., 2000; Santos et al., 2006; Saueia and Mazzilli, 2006), and it is well recognized that the secular equilibrium between natural radionuclides existing in the phosphate rocks is disturbed during the industrial production of phophoric acid, for which phosphogypsum is the waste product (e.g., Righi et al., 2005). Therefore, the phosphogypsum release into the estuary is the most probable explanation for the anomalous radiochemical data. 226Ra remobilization from anaerobic coastal sediments (e.g., Pardue and
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Table 1 Descriptive statistics for water content, LOI, major elements, radionuclides and 210 Pb/226Ra ratios
Water (%) LOI (%) Al (%) Ca (%) Fe (%) K (%) Mg (%) Mn (%) Na (%) P (%) Si (%) Ti (%) 226 Ra (Bq kg1) 210 Pb (Bq kg1) 210 Pbxs (Bq kg1) 210 Pb/226Ra
Minimum
Maximum
Mean
SD
59 9.2 4.8 2.4 13.1 0.83 1.09 0.16 1.26 0.96 9.6 0.34 178 358 94 1.36
68 13.1 8.5 6.1 24.3 1.49 1.27 0.42 1.63 3.40 18.3 0.41 744 1317 679 3.18
63 11.4 6.0 4.0 17.6 1.13 1.16 0.27 1.43 2.15 13.6 0.38 417 809 392 2.01
3 1.4 1.0 1.3 4.4 0.24 0.06 0.10 0.12 0.80 3.3 0.02 182 322 199 0.56
Guo, 1998) may also contribute to elevate 210Pb/226Ra ratios, while the contrasting half-lives of 210Pb (22.3 yr) and 226Ra (1602 yr) imply in a decrease in such ratios with the increase in sediment age, which possibly also contributed to determine the results found with the increase in sediment depth. Despite the possibility of physical and biological sediment reworking, the vertical distribution of anomalous constituents does not reach natural levels with increasing depth. However, a depletion in all contaminant levels within the upper layers (Fig. 2) suggests a substantial decrease in the anthropogenic input, as observed in sites where industrial inputs were attenuated or avoided (e.g., Absi et al., 2004). 3.2. Geochemical normalizations Normalization approaches were carried out to compensate dilution effects of grain size and anthropogenic elements input. Considering Al as a conservative, major constituent of clay minerals, this metal was chosen as a grain size-related normalizer (e.g., Santschi et al., 2001). Since Fe concentrations were at least one order of magnitude greater than those of any other anomalous constituent (Table 1), the normalization by Fe was considered as a correction for the main dilution effect caused by industrial contamination. 3.2.1. Anomalous constituents Depth profiles of anomalous elements maintained the general shapes of absolute data distributions after Al normalization, evidencing the stronger distribution similarities of Fe with Mn, P with Ca, and 226Ra with 210Pb (Figs. 2 and 3). The later four constituents
presented virtually the same Al-normalized variability below 13 cm depth and maximum values at 13–16 cm depth interval, above the depth of maximum values of Fe/Al and Mn/Al ratios. It was confirmed that the depths for which recent input attenuations are recorded varied between the constituents, suggesting that temporal changes in the proportion between contaminants’ inputs occurred. This possibility may be better evaluated by using Fenormalized data. The Mn/Fe ratios presented a low variability (Fig. 3), showing a tendency of greater values in subsurface layers, possibly reflecting minor variabilities in sediment mineralogy and/or low post-depositional mobilization of Mn due to changes in redox conditions (an element more susceptible than Fe to remobilization in anaerobic conditions; e.g., Laima et al., 1998). Any mobilization of the less mobile Fe would not be expected to substantially reduce the elevated Fe levels found in the sediments. Stronger variabilities were recorded for the other anomalous constituents (Fig. 3). Although P/ Fe and Ca/Fe ratios showed the same generally low variability, a concomitant pronounced increase occurred within the 8–16 cm depth interval, in contrast with absolute and Al-normalized data (Figs. 2 and 3), reflecting changes in the proportion between steel industry and fertilizer industry inputs. The same explanation may be valid for 226Ra/Fe and 210Pb/Fe ratios. Below 13 cm depth, these ratios presented the same distribution of P/Fe and Ca/Fe ratios, though a clear subsurface increase in 226Ra/Fe ratios was not found and the depth interval of the subsurface increase in 210Pb/Fe ratios occurred at the 6–8 cm depth interval, without any pronounced peak (Fig. 3). These results suggest that factors other than temporal contrasts between inputs from different sources contributed to determine the observed profiles, possibly due to compositional changes of wastes from the same industrial source (e.g., due to differences in phosphate rocks used for fertilizer production). 3.2.2. Non-anomalous constituents After Al normalization (Fig. 4), two distinct distribution trends were observed for non-anomalous elements (Si, K, Na, Mg and Ti), confirming that compositional changes between deeper and upper sediment layers occurred. Within the upper 13 cm, K/Al and Si/Al ratios showed a decreasing trend, while Mg/Al, Na/Al and Ti/Al ratios showed an increasing trend downward. Below these layers, low-variable Si/Al and K/Al values are recorded, whereas Mg/Al, Na/ Al and Ti/Al ratios presented stronger oscillations and an abrupt minimum value at the deeper layer. Two distinct tendencies were also evidenced within the upper 13 cm after Fe normalization (Fig. 4), since K/Fe and Si/Fe ratios showed a decreasing trend downward, in contrast with Mg/Fe, Na/Fe and Ti/Fe oscillations without general trends. Between 13 and 25 cm depth, all Fenormalized values showed a pronounced decrease, followed by an elevation in the deeper layer.
Table 2 Correlation matrix for water content, LOI, major elements and radionuclides
LOI Si Ti Al Fe Mn Mg Ca Na K P 226 Ra 210 Pb
Water %
LOI
Si
Ti
Al
Fe
Mn
Mg
Ca
Na
K
P
0.55 0.69 0.66 0.47 0.80 0.79 0.28 0.49 0.59 0.67 0.39 0.67 0.65
0.36 0.33 0.05 0.57 0.63 0.42 0.27 0.25 0.52 0.05 0.43 0.19
0.64 0.80 0.91 0.91 0.25 0.92 0.31 0.96 0.88 0.85 0.89
0.79 0.82 0.78 0.37 0.42 0.73 0.55 0.38 0.63 0.51
0.77 0.71 0.24 0.75 0.51 0.67 0.78 0.81 0.76
0.99 0.09 0.73 0.55 0.88 0.63 0.85 0.76
0.09 0.74 0.49 0.90 0.62 0.82 0.74
0.45 0.52 0.20 0.56 0.15 0.26
0.10 0.92 0.97 0.83 0.88
0.18 0.08 0.46 0.39
0.83 0.82 0.82
0.77 0.87
Significant correlation coefficients (p < 0.05) are in bold.
226
Ra
0.83
W. Machado et al. / Journal of Environmental Radioactivity 99 (2008) 1329–1334
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Fig. 3. Depth profiles of anomalous major elements and radionuclides, normalized by Al and Fe concentrations.
These results evidenced that, besides the dilution by anomalous elements suggested by absolute data, the distribution of nonanomalous elements may be affected by changes in the input of detrital minerals. The concurrent increase in K/Al and Si/Al ratios and depletion in Mg/Al, Na/Al and Ti/Al ratios in the upper layers in contrast with the deeper, older layers may be explained by a recent
greater input of K- and Si-bearing minerals that do not have Mg, Na and Ti as major constituents (e.g., muscovite, illite and K-feldspars). Considering that the drainage basin of the system is influenced by human occupation (implying in deforestation and urbanization processes), sediment dredging has been made in the inner, northern part of the system to allow the harboring activities (Fig. 1) and
Fig. 4. Depth profiles of non-anomalous major elements normalized by Al concentrations.
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variabilities in the sediment delivery from land and sediment dredging may affect coastal sediment mineralogy (e.g., Friend et al., 2006), the observed compositional variability may be affected by these processes. 4. Conclusions A coupled contamination from steel and fertilizer industries, reaching levels an order of magnitude above background levels, was evidenced by geochemical records in sediments from Morra˜o River estuary. The concomitant release of wastes from steel industry (for Fe and Mn) and fertilizer industry (for P, Ca and radionuclides) appears to be the most reliable explanation for the elevated anomalies observed, and for the correlations between anomalies from different sources. This peculiar geochemical record was affected by a strong dilution effect caused by inputs of major anthropogenic elements (mainly Fe). Distribution variabilities of absolute and normalized data (e.g., depths in which surface attenuations of anomalous concentrations occurred and in which maximum levels were recorded) indicated contrasts in the quality of coastal and land-derived sediment input, mainly due to inputs of contaminants from different industrial sources. Acknowledgements We thank the financial support from FAPESP (project no. 04/ 00059-6) and the analytical support from the Institute of Geosciences of the State University of Campinas. We also thank the comments from an anonymous referee. References Abessa, D.M.S., Carr, R.S., Rachid, B.R.F., Sousa, E.C.P.M., Hortelani, M.A., Sarkis, J.E., 2005. Influence of a Brazilian sewage outfall on the toxicity and contamination of adjacent sediments. Mar. Pollut. Bull. 50, 875–885. ˜ ez, R., 2004. Self-cleaning in an Absi, A., Villa, M., Moreno, H.P., Manjo´n, G., Peria´n estuarine area formerly affected by 226Ra anthropogenic enhancements. Sci. Total Environ. 329, 183–195. Aguado, J.L., Bolı´var, J.P., Garcı´a-Tenorio, R., 2004. Sequential extraction of 226Ra in sediments from an estuary affected historically by anthropogenic inputs of natural radionuclides. J. Environ. Radioact. 74, 117–126. Bolı´var, J.P., Garcı´a-Tenoriob, R., Masa, J.L., Vaca, F., 2002. Radioactive impact in sediments from an estuarine system affected by industrial wastes releases. Environ. Int. 27, 639–645. Braga, E.S., Bonetti, C.V.D.H., Burone, L., Bonetti, J., 2000. Eutrophication and bacterial pollution caused by industrial and domestic wastes at the Baixada Santista estuarine system – Brazil. Mar. Pollut. Bull. 40, 165–173. Carreira, R.S., Wagener, A.L.R., 1998. Speciation of sewage derived phosphorus in coastal sediments from Rio de Janeiro, Brazil. Mar. Pollut. Bull. 36, 818–827. Carvalho, F.P., 1995. 210Pb and 210Po in sediments and suspended matter in the Tagus estuary, Portugal. Local enhancement of natural levels by wastes from phosphate ore processing-industry. Sci. Total Environ. 159, 201–214. Cundy, A.B., Croudace, I.W., 1995. Sedimentary and geochemical evaluations in a salt marsh/mud flat environment from the mesotidal Humble estuary, southern England. Mar. Chem. 51, 115–132. Cundy, A.B., Croudace, I.W., 1996. Sediment accretion and recent sea-level rise in the Solent, southern England: inferences from radiometric and geochemical studies. Est. Coastal Shelf Sci. 43, 449–467. Cutshall, N.H., Larsen, I.L., Olsen, C.R., 1982. Direct analysis of 210Pb in sediment samples: self-absorption corrections. Nucl. Instrum. Methods 206, 309–312. De Lazzari, A., Rampazzo, G., Pavoni, B., 2004. Geochemistry of sediments in the Northern and Central Adriatic Sea. Est. Coastal Shelf Sci. 59, 429–440. El Mamoney, M.H., Khater, A.E.M., 2004. Environmental characterization and radioecological impacts of non-nuclear industries on the Red Sea coast. J. Environ. Radioact. 73, 151–168.
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Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Coupled anthropogenic anomalies of radionuclides and major elements in estuarine sediments W. Machado a, *, W. Luiz-Silva b, C.J. Sanders a, S.R. Patchineelam a a b
´i, RJ 24020-150, Brazil Departamento de Geoquı´mica, Universidade Federal Fluminense, Nitero Instituto de Geocieˆncias, Universidade Estadual de Campinas, Campinas, SP 13083-970, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 June 2007 Received in revised form 8 December 2007 Accepted 9 April 2008 Available online 19 May 2008
Concentrations of fertilizer industry-derived P (up to 3.4%), Ca (up to 6.1%), 226Ra (up to 744 Bq kg1) and 210 Pb (up to 1317 Bq kg1) at least one order of magnitude above natural levels were recorded in a sediment core from Morra˜o River estuary (SE Brazil). Unsupported 210Pb (¼total 210Pb 226Ra) activities unexplained by atmospheric fallout and deviations from the radionuclides secular equilibrium also indicated strong anomalies. Anomalous constituents were positively correlated with each other and negatively correlated with clay mineral-bearing elements. These negative correlations were explained by a depletion of natural sediment constituents due to a dilution caused by elevated inputs of steel industryderived elements (mainly by Fe levels up to 24%). Absolute data and normalizations by a proxy for clays (Al) and anthropogenic Fe evidenced variabilities in the quality of coastal and land-derived sediment inputs, mainly due to changes in the relative contributions from industrial sources. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Radiochemical contamination Radionuclides disequilibrium Major elements contamination Estuarine sediments
1. Introduction Many efforts to elucidate the contamination record in coastal sediment profiles have been conduced worldwide, because vertical variabilities in anomalous chemical markers in sediments may reflect the temporal evolution of anthropogenic inputs (e.g., Carvalho, 1995; San Miguel et al., 2004; Sanders et al., 2006). Since the spatial and temporal anthropogenic input variability may be coupled with dilution and concentration effects caused by different sediment phases (mainly due to grain size and mineralogical heterogeneities), geochemical normalization methods may be used to improve data interpretation. For example, grain size-related geochemical changes within a sediment column may difficult the evaluation of downcore distributions of stable elements and radionuclides, which may be resolved normalizing it by a clay-bearing conservative element (generally Al), considered as a grain size proxy (e.g., Cundy and Croudace, 1995, 1996; Santschi et al., 2001). Unusual situations may occur when the geochemical record is heavily affected by multiple anthropogenic impacts, as observed in the sediment core investigated in this work, as part of a project intended to elucidate the geochemistry of chemical contaminants within the Santos-Cubata˜o estuarine system, Sa˜o Paulo State, SE Brazil (Fig. 1). This system is located in a region historically affected by anthropogenic activities (e.g., Medeiros and Bı´cego, 2004;
Abessa et al., 2005), receiving the drainage from urban areas and one of the most important industrial areas in Brazil. Braga et al. (2000) demonstrated that the water quality from this system is affected by sewage release and industrial activities, with maximum values of dissolved nitrite, phosphate and silicate concentrations in the same site in the inner, northern part of the system, near steel and fertilizer industries. The Santos-Cubata˜o estuarine system and part of its drainage basin have been also investigated for radionuclides contamination of sediments, since waste generation and storage by fertilizer industries may cause anomalous radionuclide levels, as observed in sites affected by phosphogypsum deposits (Silva et al., 2006a,b). Elevated levels of major and trace elements were recently recorded near these sites, in surface sediments from the Morra˜o River estuary (Fig. 1), in comparison with background levels found in a sediment core from another estuary within the same system (Luiz-Silva et al., 2006). Since the activities of fertilizer manufactures have raised the concentrations of naturally occurring radioactive materials (NORM) in aquatic environments (e.g., Pujol and Sanchez-Cabeza, 2000; Aguado et al., 2004), the present study investigates the distribution of major elements and typical fertilizer industry-derived radionuclides, such as 226Ra and 210Pb (e.g., Bolı´var et al., 2002; El Mamoney and Khater, 2004), in a sediment core from Morra˜o River estuary. 2. Materials and methods
* Corresponding author. Tel.: þ55 21 26292218; fax: þ55 21 26292234. E-mail address: [email protected] (W. Machado). 0265-931X/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2008.04.006
In the study site (23 520 3600 S, 46 210 2700 W), an intertidal sediment core (30 cm length 10 cm diameter) was collected by using a PVC tube in February 2005, during low tide. The sediment core was sectioned in 2 cm intervals over the first
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Fig. 1. Sampling site location in the Santos-Cubata˜o estuarine system, southeastern Brazil.
10 cm, 3 cm intervals over the next 15 cm and 5 cm for the last interval (n ¼ 11). Sediments were oven dried (50 C), disaggregated and homogenized before analyses and its water content was determined as the weight loss after drying. Sediment subsamples were counted for at least 11 h to determine 226Ra and 210Pb activities by gamma ray spectrometry, using a Camberra HPGe spectrometer with an efficiency of 40%, housed in a lead shield and coupled to a multichannel analyzer. Before analysis, sediment sub-samples were packed and stored for at least 21 days to allow the establishment of secular equilibrium between 226Ra and its granddaughters 214Pb and 214Bi. 226Ra activities were determined by a weighted average of two 214Pb energies (295.2 and 351.9 keV) and a 214Bi gamma peak at 609.3 keV (Moore, 1984), while 210Pb activities were determined by the direct measurement of 46.5 keV gamma peak. Background energies were subtracted from the photo-peak areas and self-absorption corrections were calculated (Cutshall et al., 1982). Energy and efficiency calibrations were done using the CANMET uranium ore reference material BL4a. Counting errors were always within 5%. Total concentrations of major elements were determined by wavelength dispersive X-ray fluorescence spectrometry (XRF) in glass disks, using a Philips PW 2404 spectrometer, according to Vendemiatto and Enzweiler (2001). The glass disks were made with the same sub-samples analyzed by gamma ray spectrometry, after pulverized in a mill with agata balls. Precision of XRF duplicate analysis was within 5% and the accuracy was assessed by analyses of reference materials (GSD-9 and GSD-12 Chinese sediments). Sediment weight losson-ignition (LOI) was measured after ignition of sediments at 550 C for 4 h, according to Heiri et al. (2001).
3. Results and discussion 3.1. Downcore absolute composition The investigated core was composed of fine-grained, dark gray sediments, showing a relatively low variability in the water content and LOI values (Fig. 2; Table 1), which was also generally observed for clay mineral-bearing elements, e.g., Al, Ti, Mg and K (Fig. 2; Table 1). LOI was uncorrelated with other variables, except by a significant negative correlation with Mn (Table 2). Water content and Al were not significantly correlated due to an extreme Al value in the deeper sediment layer (Fig. 2), but these variables were positively correlated with Ti, K and Si (Table 2). Although total Si concentrations can have contributions from aluminosilicates, quartz and biogenic Si, the positive correlations of Si with water content, Ti, Al and K (Table 2) and the fine-grained nature of sediments indicate that clay-bearing Si is probably predominant. However, composition changes were evidenced by differences between subsurface layers depleted in
water, LOI, Si, Ti, Al and K, but enriched in Fe, Mn, Ca, P, 226Ra and Pb (below 6–13 cm depth depending on the variable), and upper layers (Fig. 2). Some major elements (Fe, Mn, Ca and P) and the radionuclides studied presented anomalously high levels, while the other elements showed levels that do not evidence an anomalous input (Table 1). Background concentrations of Fe (2.88%), Mn (0.02%) and Ca (0.27%) reported for the fine sediment fraction (<63 mm) of a sediment core from another estuary within the Santos-Cubata˜o system (Luiz-Silva et al., 2006) indicate that the observed anomaly of major elements is one order of magnitude above natural levels. Local background levels for P were not found, but previous studies in sediments from contaminated and uncontaminated sites in southeastern Brazil reported that p level ranging between <0.01% and 0.23% (Carreira and Wagener, 1998; Jorcin, 2000; Mater et al., 2004), values at least one order of magnitude below the mean concentration observed in the studied core (Table 1). Anomalous constituents were positively correlated with each other and generally correlated negatively with water content and non-anomalous elements (Table 2). Sodium showed only a significant positive correlation (with Ti), while Mg was uncorrelated with the other variables (Table 2). Although associations with organic matter and fine particles may influence the distribution of natural radionuclides (e.g., Yeager and Santschi, 2003) and major elements (e.g., De Lazzari et al., 2004), this was not evidenced for the anomalous constituents, which showed negative correlations with LOI and clay-bearing elements. Considering that the negative correlations between anomalous and non-anomalous constituents were caused by an anthropogenic enrichment of major elements in one order of magnitude, such negative correlations appear to reflect a dilution of natural elements by anthropogenic elements (mainly Fe). While coastal and marine sediments from southeastern and southern Brazil for which there is no evidence of radiochemical contamination present 226Ra and 210Pb levels ranging between 2– 28 Bq kg1 and 13.5–158 Bq kg1, respectively (Wilken et al., 1986; Saito et al., 2001; Vegueria et al., 2002; Sanders et al., 2006), Silva et al. (2006b) showed 226Ra and 210Pb levels ranging between 8– 60 Bq kg1 and 26–538 Bq kg1, respectively, in surface sediments 210
W. Machado et al. / Journal of Environmental Radioactivity 99 (2008) 1329–1334
Fig. 2. Depth profiles of water content, LOI, major elements and radionuclide levels and
from the Santos-Cubata˜o estuarine system and part of its drainage basin. These authors evidenced a strong anthropogenic influence on 210Pb distribution only in the inner, northern area of the system. In the present study, higher radionuclide levels are recorded, reaching the magnitude found in estuaries strongly affected by fertilizer industries, which have caused, for example, 210Pb levels up to 1580 Bq kg1 in the Tagus River estuarine sediments (Carvalho, 1995) and 226Ra levels up to 961 Bq kg1 in sediments from the Tinto and Odiel Rivers estuary (Absi et al., 2004). The 210Pb levels unsupported by 226Ra decay (hereafter called 210 Pbxs), calculated as the difference between total 210Pb and 226Ra (Fig. 2; Table 1), indicated an anomaly unexplained by atmospheric fallout, since values of fallout 210Pb in coastal sediments from southeastern and southern Brazil typically do not exceed 100– 160 Bq kg1 (Wilken et al., 1986; Smoak and Patchineelam, 1999; Marques et al., 2006; Sanders et al., 2006). Moreover, 210Pb/226Ra
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210
Pb/226Ra ratios.
ratios up to 3.18 (Fig. 2; Table 1) indicate a pronounced disequilibrium between 226Ra and its decay product 210Pb, as have been observed in sediments affected by phosphogypsum input (San Miguel et al., 2004). Downcore variability in such ratios showed a minimum value in the uppermost layer and maximum values at 6–8 cm and 10–13 cm depth intervals (Fig. 2). The 226Ra and 210Pb levels in Brazilian phosphogypsum range between 22–1251 Bq kg1 and 47–1234 Bq kg1, respectively (Mazzilli et al., 2000; Santos et al., 2006; Saueia and Mazzilli, 2006), and it is well recognized that the secular equilibrium between natural radionuclides existing in the phosphate rocks is disturbed during the industrial production of phophoric acid, for which phosphogypsum is the waste product (e.g., Righi et al., 2005). Therefore, the phosphogypsum release into the estuary is the most probable explanation for the anomalous radiochemical data. 226Ra remobilization from anaerobic coastal sediments (e.g., Pardue and
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Table 1 Descriptive statistics for water content, LOI, major elements, radionuclides and 210 Pb/226Ra ratios
Water (%) LOI (%) Al (%) Ca (%) Fe (%) K (%) Mg (%) Mn (%) Na (%) P (%) Si (%) Ti (%) 226 Ra (Bq kg1) 210 Pb (Bq kg1) 210 Pbxs (Bq kg1) 210 Pb/226Ra
Minimum
Maximum
Mean
SD
59 9.2 4.8 2.4 13.1 0.83 1.09 0.16 1.26 0.96 9.6 0.34 178 358 94 1.36
68 13.1 8.5 6.1 24.3 1.49 1.27 0.42 1.63 3.40 18.3 0.41 744 1317 679 3.18
63 11.4 6.0 4.0 17.6 1.13 1.16 0.27 1.43 2.15 13.6 0.38 417 809 392 2.01
3 1.4 1.0 1.3 4.4 0.24 0.06 0.10 0.12 0.80 3.3 0.02 182 322 199 0.56
Guo, 1998) may also contribute to elevate 210Pb/226Ra ratios, while the contrasting half-lives of 210Pb (22.3 yr) and 226Ra (1602 yr) imply in a decrease in such ratios with the increase in sediment age, which possibly also contributed to determine the results found with the increase in sediment depth. Despite the possibility of physical and biological sediment reworking, the vertical distribution of anomalous constituents does not reach natural levels with increasing depth. However, a depletion in all contaminant levels within the upper layers (Fig. 2) suggests a substantial decrease in the anthropogenic input, as observed in sites where industrial inputs were attenuated or avoided (e.g., Absi et al., 2004). 3.2. Geochemical normalizations Normalization approaches were carried out to compensate dilution effects of grain size and anthropogenic elements input. Considering Al as a conservative, major constituent of clay minerals, this metal was chosen as a grain size-related normalizer (e.g., Santschi et al., 2001). Since Fe concentrations were at least one order of magnitude greater than those of any other anomalous constituent (Table 1), the normalization by Fe was considered as a correction for the main dilution effect caused by industrial contamination. 3.2.1. Anomalous constituents Depth profiles of anomalous elements maintained the general shapes of absolute data distributions after Al normalization, evidencing the stronger distribution similarities of Fe with Mn, P with Ca, and 226Ra with 210Pb (Figs. 2 and 3). The later four constituents
presented virtually the same Al-normalized variability below 13 cm depth and maximum values at 13–16 cm depth interval, above the depth of maximum values of Fe/Al and Mn/Al ratios. It was confirmed that the depths for which recent input attenuations are recorded varied between the constituents, suggesting that temporal changes in the proportion between contaminants’ inputs occurred. This possibility may be better evaluated by using Fenormalized data. The Mn/Fe ratios presented a low variability (Fig. 3), showing a tendency of greater values in subsurface layers, possibly reflecting minor variabilities in sediment mineralogy and/or low post-depositional mobilization of Mn due to changes in redox conditions (an element more susceptible than Fe to remobilization in anaerobic conditions; e.g., Laima et al., 1998). Any mobilization of the less mobile Fe would not be expected to substantially reduce the elevated Fe levels found in the sediments. Stronger variabilities were recorded for the other anomalous constituents (Fig. 3). Although P/ Fe and Ca/Fe ratios showed the same generally low variability, a concomitant pronounced increase occurred within the 8–16 cm depth interval, in contrast with absolute and Al-normalized data (Figs. 2 and 3), reflecting changes in the proportion between steel industry and fertilizer industry inputs. The same explanation may be valid for 226Ra/Fe and 210Pb/Fe ratios. Below 13 cm depth, these ratios presented the same distribution of P/Fe and Ca/Fe ratios, though a clear subsurface increase in 226Ra/Fe ratios was not found and the depth interval of the subsurface increase in 210Pb/Fe ratios occurred at the 6–8 cm depth interval, without any pronounced peak (Fig. 3). These results suggest that factors other than temporal contrasts between inputs from different sources contributed to determine the observed profiles, possibly due to compositional changes of wastes from the same industrial source (e.g., due to differences in phosphate rocks used for fertilizer production). 3.2.2. Non-anomalous constituents After Al normalization (Fig. 4), two distinct distribution trends were observed for non-anomalous elements (Si, K, Na, Mg and Ti), confirming that compositional changes between deeper and upper sediment layers occurred. Within the upper 13 cm, K/Al and Si/Al ratios showed a decreasing trend, while Mg/Al, Na/Al and Ti/Al ratios showed an increasing trend downward. Below these layers, low-variable Si/Al and K/Al values are recorded, whereas Mg/Al, Na/ Al and Ti/Al ratios presented stronger oscillations and an abrupt minimum value at the deeper layer. Two distinct tendencies were also evidenced within the upper 13 cm after Fe normalization (Fig. 4), since K/Fe and Si/Fe ratios showed a decreasing trend downward, in contrast with Mg/Fe, Na/Fe and Ti/Fe oscillations without general trends. Between 13 and 25 cm depth, all Fenormalized values showed a pronounced decrease, followed by an elevation in the deeper layer.
Table 2 Correlation matrix for water content, LOI, major elements and radionuclides
LOI Si Ti Al Fe Mn Mg Ca Na K P 226 Ra 210 Pb
Water %
LOI
Si
Ti
Al
Fe
Mn
Mg
Ca
Na
K
P
0.55 0.69 0.66 0.47 0.80 0.79 0.28 0.49 0.59 0.67 0.39 0.67 0.65
0.36 0.33 0.05 0.57 0.63 0.42 0.27 0.25 0.52 0.05 0.43 0.19
0.64 0.80 0.91 0.91 0.25 0.92 0.31 0.96 0.88 0.85 0.89
0.79 0.82 0.78 0.37 0.42 0.73 0.55 0.38 0.63 0.51
0.77 0.71 0.24 0.75 0.51 0.67 0.78 0.81 0.76
0.99 0.09 0.73 0.55 0.88 0.63 0.85 0.76
0.09 0.74 0.49 0.90 0.62 0.82 0.74
0.45 0.52 0.20 0.56 0.15 0.26
0.10 0.92 0.97 0.83 0.88
0.18 0.08 0.46 0.39
0.83 0.82 0.82
0.77 0.87
Significant correlation coefficients (p < 0.05) are in bold.
226
Ra
0.83
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Fig. 3. Depth profiles of anomalous major elements and radionuclides, normalized by Al and Fe concentrations.
These results evidenced that, besides the dilution by anomalous elements suggested by absolute data, the distribution of nonanomalous elements may be affected by changes in the input of detrital minerals. The concurrent increase in K/Al and Si/Al ratios and depletion in Mg/Al, Na/Al and Ti/Al ratios in the upper layers in contrast with the deeper, older layers may be explained by a recent
greater input of K- and Si-bearing minerals that do not have Mg, Na and Ti as major constituents (e.g., muscovite, illite and K-feldspars). Considering that the drainage basin of the system is influenced by human occupation (implying in deforestation and urbanization processes), sediment dredging has been made in the inner, northern part of the system to allow the harboring activities (Fig. 1) and
Fig. 4. Depth profiles of non-anomalous major elements normalized by Al concentrations.
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variabilities in the sediment delivery from land and sediment dredging may affect coastal sediment mineralogy (e.g., Friend et al., 2006), the observed compositional variability may be affected by these processes. 4. Conclusions A coupled contamination from steel and fertilizer industries, reaching levels an order of magnitude above background levels, was evidenced by geochemical records in sediments from Morra˜o River estuary. The concomitant release of wastes from steel industry (for Fe and Mn) and fertilizer industry (for P, Ca and radionuclides) appears to be the most reliable explanation for the elevated anomalies observed, and for the correlations between anomalies from different sources. This peculiar geochemical record was affected by a strong dilution effect caused by inputs of major anthropogenic elements (mainly Fe). Distribution variabilities of absolute and normalized data (e.g., depths in which surface attenuations of anomalous concentrations occurred and in which maximum levels were recorded) indicated contrasts in the quality of coastal and land-derived sediment input, mainly due to inputs of contaminants from different industrial sources. Acknowledgements We thank the financial support from FAPESP (project no. 04/ 00059-6) and the analytical support from the Institute of Geosciences of the State University of Campinas. We also thank the comments from an anonymous referee. References Abessa, D.M.S., Carr, R.S., Rachid, B.R.F., Sousa, E.C.P.M., Hortelani, M.A., Sarkis, J.E., 2005. Influence of a Brazilian sewage outfall on the toxicity and contamination of adjacent sediments. Mar. Pollut. Bull. 50, 875–885. ˜ ez, R., 2004. Self-cleaning in an Absi, A., Villa, M., Moreno, H.P., Manjo´n, G., Peria´n estuarine area formerly affected by 226Ra anthropogenic enhancements. Sci. Total Environ. 329, 183–195. Aguado, J.L., Bolı´var, J.P., Garcı´a-Tenorio, R., 2004. Sequential extraction of 226Ra in sediments from an estuary affected historically by anthropogenic inputs of natural radionuclides. J. Environ. Radioact. 74, 117–126. Bolı´var, J.P., Garcı´a-Tenoriob, R., Masa, J.L., Vaca, F., 2002. Radioactive impact in sediments from an estuarine system affected by industrial wastes releases. Environ. Int. 27, 639–645. Braga, E.S., Bonetti, C.V.D.H., Burone, L., Bonetti, J., 2000. Eutrophication and bacterial pollution caused by industrial and domestic wastes at the Baixada Santista estuarine system – Brazil. Mar. Pollut. Bull. 40, 165–173. Carreira, R.S., Wagener, A.L.R., 1998. Speciation of sewage derived phosphorus in coastal sediments from Rio de Janeiro, Brazil. Mar. Pollut. Bull. 36, 818–827. Carvalho, F.P., 1995. 210Pb and 210Po in sediments and suspended matter in the Tagus estuary, Portugal. Local enhancement of natural levels by wastes from phosphate ore processing-industry. Sci. Total Environ. 159, 201–214. Cundy, A.B., Croudace, I.W., 1995. Sedimentary and geochemical evaluations in a salt marsh/mud flat environment from the mesotidal Humble estuary, southern England. Mar. Chem. 51, 115–132. Cundy, A.B., Croudace, I.W., 1996. Sediment accretion and recent sea-level rise in the Solent, southern England: inferences from radiometric and geochemical studies. Est. Coastal Shelf Sci. 43, 449–467. Cutshall, N.H., Larsen, I.L., Olsen, C.R., 1982. Direct analysis of 210Pb in sediment samples: self-absorption corrections. Nucl. Instrum. Methods 206, 309–312. De Lazzari, A., Rampazzo, G., Pavoni, B., 2004. Geochemistry of sediments in the Northern and Central Adriatic Sea. Est. Coastal Shelf Sci. 59, 429–440. El Mamoney, M.H., Khater, A.E.M., 2004. Environmental characterization and radioecological impacts of non-nuclear industries on the Red Sea coast. J. Environ. Radioact. 73, 151–168.
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