Multi-element analysis of sea water from Sepetiba Bay

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Multi-element analysis of sea water from Sepetiba Bay, Brazil, by total reflection X-ray fluorescence spectrometry using synchrotron radiation Article in X-Ray Spectrometry · May 2005 Impact Factor: 1.35 · DOI: 10.1002/xrs.779

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X-RAY SPECTROMETRY X-Ray Spectrom. 2005; 34: 183–188 Published online 21 February 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/xrs.779

Multi-element analysis of sea water from Sepetiba Bay, Brazil, by total reflection x-ray fluorescence spectrometry using synchrotron radiation 3 and C. R. F. Castro1 ´ A. C. M. Costa,1 M. J. Anjos,1,2∗ R. T. Lopes,1 C. A. Perez 1 2 3

Federal University of Rio de Janeiro/COPPE, Nuclear Instrumentation Laboratory, P.O. Box 68509, 21945-970 Rio de Janeiro, Brazil University of Rio de Janeiro State, Physics Institute, Rio de Janeiro, Brazil Brazilian National Synchrotron Light Laboratory, Campinas, SP, Brazil

Received 16 December 2002; Accepted 15 March 2004

Trace elements in the surface waters of Sepetiba Bay were studied by total reflection x-ray fluorescence spectrometry using synchrotron radiation (SRTXRF). The bay is located in the south of Rio de Janeiro State, Brazil. The water samples were collected at 21 sampling stations, prepared in order to preconcentrate the metallic elements with ammonium pyrrolidinedithiocarbamate and to remove the salt matrix. Samples were spiked with an internal standard (Se) and the precipitated dithiocarbamates of trace elements were separated by filtration through a Millipore filter, then transferred to a Perspex reflector and digested with HNO3 for SRTXRF measurement. Elemental concentrations of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo and Pb were determined and a comparison was made between the results obtained and the values given in the literature for sea water. Copyright  2005 John Wiley & Sons, Ltd.

INTRODUCTION One of the most dangerous kinds of pollution in aquatic systems is due to the dumping of heavy metals. Their increasing use in industries and other activities considered to be essential to modern human life has resulted in modifications of the natural geochemical cycle of these elements. In general, the concentrations of trace metals in sea water are extremely low, but often reflect some changes in the aquatic environment due to biological activities or environmental pollution from artificial sources. Hence the monitoring of trace metals in coastal and open sea waters is very important for environmental conservation.

Sepetiba Bay is a semi-enclosed water body with an area of 305 km2 , located in the south of Rio de Janeiro State, Brazil. Since the 1970s, the Sepetiba region has undergone rapid industrial development and mainly metallurgical and chemical facilities have been established in the Sepetiba Bay Basin, releasing their industrial waste either straight into the bay or through local rivers. This rapid and unplanned development has resulted in high contamination of the bay with the consequent need for environmental conservation and sustainable utilization of the bay’s natural resources.1 Total reflection x-ray fluorescence (TXRF) spectrometry is a multielemental technique applied in several areas and in recent years it has been applied in environmental analysis (air, sediments, water, soil, plants, etc.), mainly in the analysis of water.2,3 Although TXRF is a powerful technique for the analysis of trace elements, the limited beam intensity of Ł Correspondence

to: M. J. Anjos, Federal University of Rio de Janeiro/COPPE, Nuclear Instrumentation Laboratory, P.O. Box 68509, 21945-970, Rio de Janeiro, Brazil. E-mail: marcelin@lin.ufrj.br Contract/grant sponsor: CNPq.

conventional tube- or rotating anode-based x-ray sources restricts the sensitivity of the measurements. By coupling the TXRF technique with a high-brightness synchrotron x-ray source, the increased beam flux and reduced background allow a 2–3 orders of magnitude improvement in the attainable detection limits. Total reflection x-ray fluorescence spectrometry with synchrotron radiation (SRTXRF) has become a competitive technique for the determination of trace elements in sea water samples. Since the concentrations of most of the important trace elements (Ti, V, Cr, Fe, Ni, Cu, Zn, Cd and Pb) in sea water are lower than 100 ng l 1 , the direct determination of these elements is very difficult, especially when a simple system is applied.

The aim of this work was to determine the concentrations of trace elements in the surface water of Sepetiba Bay by using SRTXRF.

EXPERIMENTS Instrumentation SRTXRF analyses were performed at the X-Ray Fluorescence Beamline at the Brazilian National Synchrotron Light Laboratory (LNLS), in Campinas, S˜ao Paulo, using a polychromatic beam with a maximum energy of 20 keV for excitation.4 The detector was Si(Li) with resolution of 165 eV at 5.9 keV. All samples were excited for 200 s and the x-ray spectra obtained were evaluated using the software QXAS in order to obtain the x-ray intensities.

Sampling procedures The samples were collected in two different periods of the year (March and May 2002). The samples were collected in 21 station sites. The study area is shown in Fig. 1. The sea water

Copyright  2005 John Wiley & Sons, Ltd.

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A. C. M. Costa et al.

Figure 1. Map of Sepetiba Bay, with sampling stations.

samples were stored in precleaned polyethylene bottles (500 ml) and kept in a refrigerator at 5 ° C until analysis.

From each sample five replicates were analyzed.

where Ii,BG is the background intensity for element i, ISe the internal standard (Se) intensity, CSe the internal standard concentration, Si the relative sensitivity for element i and t the measuring time.

Sample preparation Direct application of SRTXRF to the determination of trace elements in marine waters is usually impeded by the high salt matrix. Therefore, in order to use the high detection power of the method, it is necessary to separate trace elements from the alkaline and alkaline earth matrix prior to the measurement.5 The preconcentration technique not only improves the analytical detection limit but also reduces matrix effects, and so enhances the accuracy of the results and facilitates calibration. Further, preconcentration allows the sample volume taken to be increased and so improves the representative nature of the results.6 The samples were prepared with ammonium pyrrolidinedithiocarbamate (APDC) to preconcentrate the metallic elements and to remove the salt matrix. Aliquots of 100 ml of each sample were mixed with 100 µl of Se, as internal standard, at pH 3. The metals were precipitated as dithiocarbamates by adding 4 ml of (1%) APDC solution. The carbamates were collected by filtration through a Millipore filter (0.45 µm pore size). Each filter was dried (infrared) and cut in five small disks with a diameter of 3 mm. They were transferred to a Perspex reflector and digested with HNO3 (Suprapur, Merck) for SRTXRF measurement.

Artificial sea water7 was prepared containing 500 µg l 1 of Fe, 400 µg l 1 of Co, 500 µg l 1 of Ni and 500 µg l 1 of Cu to determine the reproducibility of the method. These samples were prepared and measured under the same conditions as the sea water samples. The relative sensitivity was determined by the measurement of standards containing the elements Al, Si, K, Ca, Ti, Cr, Fe, Ni, Zn, Se, Sr and Mo for the K lines and Sr, Mo, Cd, Ba, Sb, Pt, Hg, Tl and Pb for the L lines. The detection limit of an element i DLi was determined using the equation8 CSe DLi D 3 Si ISe Copyright  2005 John Wiley & Sons, Ltd.

Ii,BG t

1

RESULTS AND DISCUSSION In order to check the reproducibility of the method, artificial sea water was analyzed. The results from five replicates are given in Table 1. The values of the concentrations agree with the reference values (artificial sea water) with an accuracy of ¾10%.

In order to determine the overall blank values of the analytical method, five samples were prepared with pure water (Milli-Q). These samples were prepared and measured under the same conditions as the sea water samples. The blank values measured were 0.12 ng l 1 for Cr, 2.44 ng l 1 for Fe, 0.04 µg l 1 for Co, 0.14 µg l 1 for Ni, 0.13 µg l 1 for Cu, 1.40 µg l 1 for Zn and 0.14 µg l 1 for Pb. The blank values for Mn and Mo were below the detection limit. The blank values probably originate from the reagents (APDC, HNO3 and Millipore filter) used in the procedure for sample preparation.

The results obtained in the analysis of sea water samples are displayed in Figs 2–10. The elemental concentrations of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo and Pb were calculated according to the sampling stations in two different periods of the Table 1. Comparison of elemental concentrations in artificial sea water and the measured values using TXRF Concentration µg l 1 n D 5

Element Fe Co Ni Cu

SRTXRF

Artificial sea water reference values

Range

Mean

500 400 500 500

580–479 458–372 566–471 625–516

557 š 51 412 š 43 531 š 48 546 š 58

X-Ray Spectrom. 2005; 34: 183–188

Multi-element analysis of sea water by SRTXRF

5.0E-03

May March

4.0E-03 3.0E-03 2.0E-03 1.0E-03

1.0E-02 5.0E-03 SP102 SP105 SP106 SP108 SP109 SP111 SP112 SP115 SP116 SP117 SP118 SP119 SP120 SP121 SP122 SP125 SP126 SP130 SP131 SP134 SP142 Sampling station

Figure 5. Cobalt distribution in Sepetiba Bay.

2.5E-02

2.5E-03 2.0E-03 1.5E-03 1.0E-03 5.0E-04

2.0E-02

1.0E-02 5.0E-03 0.0E+00

Sampling station

Figure 3. Manganese distribution in Sepetiba Bay.

Figure 6. Nickel distribution in Sepetiba Bay.

May March

1.0E-02

5.0E-03 Concentration (mg/L)

1.0E-01

SP102 SP105 SP106 SP108 SP109 SP111 SP112 SP115 SP116 SP117 SP118 SP119 SP120 SP121 SP122 SP125 SP126 SP130 SP131 SP134 SP142

Concentration (mg/L)

Iron

May March

1.5E-02

Sampling station

1.0E+00

Nickel

SP102 SP105 SP106 SP108 SP109 SP111 SP112 SP115 SP116 SP117 SP118 SP119 SP120 SP121 SP122 SP125 SP126 SP130 SP131 SP134 SP142

May March Concentration (mg/L)

Manganese

3.0E-03

0.0E+00

1.5E-02

Sampling station

SP102 SP105 SP106 SP108 SP109 SP111 SP112 SP115 SP116 SP117 SP118 SP119 SP120 SP121 SP122 SP125 SP126 SP130 SP131 SP134 SP142

Concentration (mg/L)

3.5E-03

May March

2.0E-02

0.0E+00

Figure 2. Chromium distribution in Sepetiba Bay. 4.0E-03

Cobalt

2.5E-02

Sampling station

Copper

4.0E-03

May March

3.0E-03 2.0E-03 1.0E-03 0.0E+00

SP102 SP105 SP106 SP108 SP109 SP111 SP112 SP115 SP116 SP117 SP118 SP119 SP120 SP121 SP122 SP125 SP126 SP130 SP131 SP134 SP142

0.0E+00

3.0E-02 Concentration (mg/L)

Chromium

SP102 SP105 SP106 SP108 SP109 SP111 SP112 SP115 SP116 SP117 SP118 SP119 SP120 SP121 SP122 SP125 SP126 SP130 SP131 SP134 SP142

Concentration (mg/L)

6.0E-03

Sampling station

Figure 4. Iron distribution in Sepetiba Bay. Figure 7. Cooper distribution in Sepetiba Bay.

year. In March, the sea water samples were collected in a tide with a larger amplitude than in May. The influence of local rivers releasing their industrial waste straight into the bay can be noted in May mainly for Cr, Mn and Zn. On the other hand, in March the influence of ocean waters was more evident.

Figure 2 shows that chromium in May (tide with small amplitude) showed the highest concentrations at sites SP 105, SP 109, SP 111, SP 115 and SP 120. This can be explained because these sites are near to the coastal area suffering the greatest influence of the local rivers and mainly the sites SP 111, SP 115 and SP 120 are near to Sepetiba’s port. On the other hand, the chromium distribution in March (tide with large amplitude) showed the highest concentrations in the central part of the bay.

Copyright  2005 John Wiley & Sons, Ltd.

Figure 3 shows that manganese in May showed the highest concentration in sites SP 102, SP 105, SP 106, SP 108, SP 109, SP 111 and SP 112. These sites are also located near to the coastal area. This can be explained because in May (tide with small amplitude), these points of sampling suffered a great influence of the geological formation of the region.

Figure 4 indicates that the iron distribution was practically homogeneous at all sites. Iron is present in the oceans at very low concentrations, in spite of its large abundance in the Earth’s crust. However, the concentrations found in Sepetiba Bay were high. This can be explained by the geological formation of the region and because the coastal

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Zinc

May March

1.2E-02 8.0E-03 4.0E-03 0.0E+00

SP102 SP105 SP106 SP108 SP109 SP111 SP112 SP115 SP116 SP117 SP118 SP119 SP120 SP121 SP122 SP125 SP126 SP130 SP131 SP134 SP142

Concentration (mg/L)

1.6E-02

Sampling station

4.5E-02 4.0E-02 3.5E-02 3.0E-02 2.5E-02 2.0E-02 1.5E-02 1.0E-02 5.0E-03 0.0E+00

Molybdenum

May March

SP102 SP105 SP106 SP108 SP109 SP111 SP112 SP115 SP116 SP117 SP118 SP119 SP120 SP121 SP122 SP125 SP126 SP130 SP131 SP134 SP142

Concentration (mg/L)

Figure 8. Zinc distribution in Sepetiba Bay.

Sampling station

Figure 9. Molybdenum distribution in Sepetiba Bay. 6.0E-03

Lead

5.0E-03

May March

4.0E-03 3.0E-03 2.0E-03 1.0E-03 0.0E+00

SP102 SP105 SP106 SP108 SP109 SP111 SP112 SP115 SP116 SP117 SP118 SP119 SP120 SP121 SP122 SP125 SP126 SP130 SP131 SP134 SP142

Concentration (mg/L)

186

Sampling station

Figure 10. Lead distribution in Sepetiba Bay.

regions contain higher dissolved concentrations of iron than the waters of the open ocean owing to the proximity of terrestrial sources.9 Figures 5, 6 and 7 show the concentrations of Co, Ni and Cu, respectively. These elements show a practically homogeneous distribution from sampling point SP 108 to SP 142. However, the concentrations of these elements at points SP 102, SP 105 and SP 106 were much higher than at the other points. These points were investigated and there was no reason for such high concentrations. This may suggest contamination in the process of sample preparation.

Figure 8 shows the concentration of Zn. This element is reported to be largely of anthropogenic origin in this region.10 The highest concentration of this element is observed at site

Copyright  2005 John Wiley & Sons, Ltd.

105 (May). In May, the highest concentrations of Zn occurred at sampling points near to the coastal areas. In March, the largest concentrations were found near to Sepetiba’s port and in the central part.

Figure 9 shows a homogeneous distribution of Mo over all sampling stations. It can reflect the presence of this element is common in ocean waters. Although the Mo concentrations are above the levels reported in the literature, it can be considered that these values are close to the natural levels of the region. Finally, Fig. 10 shows the concentrations of Pb found at the different sampling stations. Lead is commonly present because of anthropogenic pollution activities (urban, industrial). The highest concentrations occurred at site SP 105 (March and May).

Table 2 gives the maximum and minimum values for elemental concentrations at the first and second samplings; the concentrations of Co, Ni and Cu relative to points SP 102, SP 105 and SP 106 were not considered. Table 2 compares the concentration ranges obtained in Sepetiba Bay with those taken from the literature. The concentrations of Cr, Mn (second sampling), Fe, Co, Ni, Zn, Mo and Pb showed higher concentrations than the values found in the literature.3,11,12 This result is indicative that Sepetiba Bay already has some contamination by these metals. All the medium values of elemental concentration were below the limits established

by Brazilian legislation.

The detection limits of the elements in Table 2 are in agreement with the values in the literature obtained with SRTXRF.13 The detection limits varied from 45 ng l 1 for Cr, 28 ng l 1 for Zn, 12.5 µg l 1 for Mo to 33 ng l 1 for Pb. Sepetiba Bay is a semi-enclosed water body. Although not very close to the open ocean, it can rapidly reflect the influence of polluted effluents, releasing into the waters residues from chemical and metal industries, domestic activities, etc. Over the last few decades, the study of sediment cores has been shown to be an excellent tool for establishing the effects of anthropogenic and natural processes on depositional environments. On the other hand, the study of metal concentrations in the water column is an important tool when there is a need for a rapid answer such as in the case of an environmental accident. Analysis of water can be considered on-line in comparison with sediment analysis.

The results show that the type of tide has an important influence on metal concentrations. At high tide, the elemental concentrations are influenced by the volume of water that enters into the bay. On the other hand, at low tide, the elemental concentrations are influenced by the hydrographic water basin.

CONCLUSIONS The method for the determination of these elements in sea water, after precipitation with APDC, filtration on a Millipore filter, cutting of the filters into small disks and transfer of carbamates to a Perspex reflector for subsequent SRTXRF measurement, proved to be simple, rapid, reproducible, sensitive and reliable.

The detection limits achieved are at least as good as those reported in the literature, relating to SRTXRF

X-Ray Spectrom. 2005; 34: 183–188

Copyright  2005 John Wiley & Sons, Ltd.

0.05

0.04

100

50

3.5–0.5 [1.0]

2.7–0.4 [0.6]

— 1.30–0.25 1.78–0.64 1.26–0.28 0.28

1.5–0.4 [0.4]

5.2–0.1a [1.0]b

— — — — 0.05

Mn

Cr

b

Fe

0.03

300

12.8 0.86–0.47 3.86–1.46 11.4–1.57 0.49

308.8–30.3 [78.8]

523.2–13.7 [171.0]

Range values.

Standard deviation. c National Environment Council, Resolution 20/86 (class 5). d Detection limit.

a

DL

d

Gerwinski and Schmidt12 Brazilian legislationc

Prange et al.11

Costa et al.3

This work n D 5

Reference

0.02

—

1.1 <0.02 0.05–0.02 0.08–0.01 —

2.1–0.2 [0.6]

4.4–0.04 [1.3]

Co

0.02

100

0.6 0.94–0.72 0.98–0.82 0.90–0.75 0.40

1.7–0.3 [0.3]

2.5–0.2 [0.6]

Ni

Cu

0.02

50

0.5 1.10–0.69 1.15–0.89 0.89–0.80 0.57

1.0–0.2 [0.2]

1.3–0.2 [0.2]

Elemental concentration µg l 1

Table 2. Elemental concentrations obtained in sea water from Sepetiba Bay using SRTXRF

0.03

170

7 2.30–0.75 1.51–0.69 2.41–1.17 1.15

14.8–2.7 [2.9]

11.5–0.5 [2.5]

Zn

12.3

—

— 3.00–1.64 1.68–1.56 1.55–0.85 —

37.0–26.4 [3.0]

39.5–17.5 [5.0]

Mo

0.03

10

0.8 0.13–0.04 0.08–0.07 0.30–0.19 0.11

5.0–0.1 [1.1]

4.2–0.1 [1.1]

Pb

—

—

Sepetiba Bay (March 2002) Sepetiba Bay (May 2002) Atlantic Ocean Central Baltic Gulf of Finland Gulf of Bothnia North Sea

Sampling location

Multi-element analysis of sea water by SRTXRF

X-Ray Spectrom. 2005; 34: 183–188

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measurements of residues of the precipitate dissolved in HNO3 . The elemental concentrations of Cr, Mn, Fe, Co, Ni, Zn, Mo and Pb in the sea water samples from Sepetiba Bay were higher than those found in the literature for sea water. On the other hand, Cr, Mn, Co, Ni, Zn and Pb are typically of anthropogenic origin. This may reflect the influence of polluted effluents releasing into the waters residues from chemical and metallurgical industries. The results are potentially useful as a reference database for metal concentrations under similar conditions to Sepetiba Bay.

Acknowledgements This work was developed partially at the Brazilian National Synchrotron Light Laboratory (LNLS) and received financial support from CNPq.

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