Anthropogenic contamination of an estuarine system evaluated by PIXE

Nuclear Instruments and Methods in Physics Research B 109/1 ! 0 (1996) 506-510

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Anthropogenic contamination of an estuarine system evaluated by PIXE * a

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J.E. M a r t i n , M . A . R e s p a l d i z a b'*, R. G a r c l a - T e n o r l o , J.R B o l i v a r , J. G o m e z - C a m a c h o M.F. d a S i l v a d

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aDpto, de Ffsica Aplicada, ETS Arquitectura, Universidad de Sevilla, Sevilla, Spain bFacultad de F{sica, Aptdo. 1065. 41080 Sevilla, Spain CDpto. de Ffsica Aplicada. EPS La Rdbida, Universidad de Huelva, Huelva, Spain aDpto, de F{sica, ITN, E.N. 10, 2685 Sacavdm, Portugal

Abstract A study of the elemental concentrations of sediments, collected in the estuary formed by the confluence of the rivers Tinto and Odiel in Huelva, Spain, has been performed by PIXE. 2.5 MeV protons from the 3 MV Van de Graaff accelerator of the ITN, Sacavfm (Portugal), were used and two runs for each sample were done with and without a composed Cr + mylar filter. Our main aim has been the evaluation of the environmental impact generated by an industrial complex sited in the surroundings and formed by fertilizer, metal and paint factories that discharge their waste in this area. The results confirm the previously determined anthropogenic impact and give additionally information about the contribution of each factory to the total contamination.

1. Introduction Near the town of Huelva (SW of Spain), along the estuary formed by the confluence of the Tinto and Odiel rivers, there has been for 30-40 years, a large industrial complex. Some of the factories there discharge directly or indirectly their waste to those rivers, producing a clear anthropogenic contamination, as it was confirmed in a previous work [1]. However, that study was only based on a reduced number of sediment samples from the river basins. A more detailed study has been done in this work increasing the number of sediment samples analyzed, and trying to obtain information about the contribution of each factory to the general contamination. The environmental impact of the industrial complex in the sediments of the river basins can be inferred from the determination of their elemental concentrations. In this sense, it is well known that an appropriate technique to determine elemental concentrations is TTPIXE, due to its high sensitivity (ppm), its multi-elemental character and the short collection time [2]. The TTPIXE technique has been applied to a total of 11 sediment samples collected, as it can be seen in Fig.

* Corresponding author.

1, in a small rivulet (Estero Domingo Rubio) that flows into the Tinto river (D samples), and in the estuary (H samples). The samples from Tinto (T samples) and Odiel (O samples) rivers belong to a previous work [1]. Some of the samples were collected in front of a fertilizer factory (FORET S.A.), a metal factory (RTM S.A. formerly UERT), and a paint factory (TIOXIDE), because these factories are releasing a fraction of their waste to the estuary. In this sense, FORET S.A. releases in dissolution a by-product called phosphogypsum (mostly calcium sulphate) that contains traces of phosphorus and heavy metals, RTM S.A. discharges solid waste enriched in iron and other heavy metals while TIOXIDE releases liquid effluents that may contain traces of titanium. Most of the samples from the Tinto river were collected in front of piles constructed artificially to store a fraction of the by-products formed in the fertilizer (FORET) and metal (RTM) factories. Four samples were collected in a rivulet, that is free of industries in their margins, to study the influence of the tides in the extension and distribution of the contamination produced by the industrial complex. Both sample collections were done from a boat using the same dredge. Samples correspond to the first 12 cm of sediment. The O and T samples were taken during the autumn of 1989 and the H and D samples during the autumn of 1992. As the industrial

0168-583X/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved S S D I 0168-583X(95)00960-4

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Table 1 Mass concentrafon (in %) of Si, A1, K and Ti in D and H samples. Numbers within parentheses refer to the error of the last figure(s)

D1 D2 D3 D4 HI H2 H3 H4 H5 H6 H7

SI [%1

A1 [%]

K [%1

Ti [%1)

19.66(10) 24.82(11) 21.03(8) 24.01(8) 19.18(8) 19.11(8) 20.54(8) 21.60(9) 22.67(8) 19.07(8) 28.62(9)

13.5(3) 14.1(4) 10.2(3) 11.6(3) 8.8(3) 8.3(3) 9.6(3) 9.2(4) 5.4(4) 8.3(3) 6.0(4)

1.676(14) 1.603(14) 1.225(10) 1.540(12) 1.490(12) 1.392(12) 1.686(13) 1.639(14) 1.166(11) 1.506(13) 1.165(13)

0.448(8) 0.451(8) 0.345(6) 0.466(7) 0.367(7) 0.398(7) 0.429(7) 0.516(9) 0.235(6) 0.652(9) 0.276(7)

suppress the soft X-rays. The X-ray spectra were fitted and the elemental concentrations obtained using the GUPIX program [3]. The samples from the previous work were analysed following a similar way [1].

3. Results and discussion

Fig. 1. Map showing the estuary formed by the Tinto and Odiel rivers near Huelva (SW of Spain). It shows the fertilizer (FORET), metal (RTM) and paint (TIOXIDE) factories, the phosphogypsum piles, the Estero Domingo Rubio rivulet and the sample names sited in the collection points.

activity has not changed significantly on these years, we consider that both samplings are comparable.

2. Experimental methods Each of the new samples was homogeneized, and the water content and the organic matter were determined by conventional methods [1]. Later, over 0.3 g of each new sediment and 0.1 g of wax Hoescht-C were mixed, homogeneized and pressed into pellets of 11 mm of diameter. The pellets were analyzed by TTPIXE using 2.5 MeV protons from the Van de Graaff accelerator of the ITN. Characteristic X-rays were measured with a Si(Li) detector, with 0.2 keV resolution at 5.9 keV, connected to a multichannel analyzer through a conventional electronic chain. Two runs were made on each pellet; one with 10 nA intensity, to accumulate 1 ixC charge, and the other with 40 nA intensity, to accumulate 20 IxC charge, but putting a C r + mylar composed filter in front of the Si(Li) to

Concentrations of about 20 elements have been obtained for each new sample. Table 1 shows the concentrations of some major elements (in %) in these samples, while Table 2 shows the concentrations of the considered trace elements (in ppm) in these samples. Similar tables can be found for the old samples in the previous work [1]. Due to the high number of results the discussion will be done by elements, in general. The A1 and Si concentrations give a useful information about the composition of the sediments [4]. In the studied samples the A1 and Si concentrations are in general uniform and are in agreement with the ~iverage values expected in sediments [5], except in five cases: the samples 03 and 05 show depletion of the A1 and Si concentrations Table 2 Mass concentrations of Cu, Zn, As and Pb (in ppm) in the D and H samples. Numbers within parentheses refer to the error of the last figure(s). N.D.: not detected

D1 D2 D3 D4 HI H2 H3 H4 H5 H6 H7

Cu

Zn

As

Pb

2146(17) 1384(14) 1347(14) 119(8) 2034(24) 1970(24) 2550(30) 2150(30) 649(16) 1998(24) 855(16)

2385(19) 1422(15) 1489(15) 557(12) 2013(25) 2400(30) 2140(30) 2760(30) 1229(20) 2770(30) 1164(18)

1344(17) 629(12) 1417(20) 90(6) 971(22) 911(22) 881(21) 1206(24) 545(15) 826(20) 487(15)

780(80) 400(50) 1330(90) N.D. 860(90) 900(80) 860(80) 1020(100) 310(60) 700(80) 360(60)

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due to the heavy impact of the fertilizer (FORET) and the metal (RTM) waste respectively, as it will be confirmed later: the sample T1 collected up-stream the Tinto river is affected by the surrounding mining, and the samples H5 and H7 show very low A1/Si ratio and additionally very low organic matter content, indicating as it was checked visually the existence of a high amount of sand in their composition. These facts indicate that contamination does not affect considerably the bulk composition of the sediments, except in places affected heavily by waste. The K and Ti concentrations follow the general pattern of the A1 and Si results. It is interesting to note that the average K concentration over the area is in agreement with the estimated value from the radioactive measurements of 4°K in the sediments [6], and that the slightly higher Ti concentrations in the samples H4 and H6, can be related to the liquid waste discharged by TIOXIDE. This factory processes a mineral, ilmenite, rich in Ti, for the production of paint pigments, and as a consequence, it can be expected that some amounts of this metal are released to the river. Nevertheless, it is clear from the obtained data that this increase is not considerable and that the possible Ti contamination is very local (it is not extended to all the estuary). Concerning the P results, that are shown in Fig. 2, the obtained values show the existence of a clear contamination over all the studied area. In general the concentrations of this element are extremely high over the estuary in comparison with the average values in unperturbed sediments (below 0.1%) [5]. Its origin is the industrial activity in the fertilizer factory [4]. In this factory, phosphoric acid is produced through the drastic chemical treatment of phosphate rocks (rich in P) with sulphuric acid, and additionally a by-product called phosphogypsum (mostly calcium sulphate) is obtained which generally is either stored in the extensive piles (about 1200 ha) placed in the bank of the Tinto river (see Fig. 1) or released directly to the Odiel. Obviously, the chemical treatment for the obtention of phosphoric acid is not effective 100%, and traces of phosphorus can be found in the phosphogypsum

waste. These traces can be dissolved in the waters of the Odiel river and in the waters used to transport the phosphogypsum to the piles that afterwards are discharged in the Tinto, producing the contamination of both fiver basins. The P concentrations in the rivulet Estero Domingo Rubio are also extremely high, decreasing their values in the up-stream direction. This fact indicates that the contamination of the rivulet has its origin in the Tinto River entering the P in the rivulet by the tides. On the other hand, the high and uniform concentrations in the H samples indicate that the P contamination has an unlocalized effect. The slightly lower concentrations in the samples H5 and H7 are related to their special composition (high fraction of sand). Low values of P are only obtained in the samples T1 and D4, that cannot be affected by the effluents of the fertilizer factory and/or the phosphogypsum piles, and in the sample 05 where the expected P contamination has been masked by other elements released by the metal industry. Fig. 3 shows the concentrations of S, Ca as well as the S / C a ratios in all the samples analyzed. From the data it is possible to note the existence of extremely high concentrations of both elements in the samples 03 and T2, indicating that a high proportion of these sediments are formed by calcium sulphate that has its origin in the discharges of the fertilizer factory to the Odiel, in the case of the sample 03, and the uncontrolled deposition of phosphogypsum from the piles in the Tinto, in the case of the sample T2, as it was mentioned in Ref. [1]. It is also interesting to note that the S concentration in the sample T1 is very high, but not the concentration of Ca. This can be explained because this sample was collected in an area with high abundance of pyrite (mineral rich in S), as it was discussed in Ref. [1]. The high S / C a ratio obtained in the sample 05 can be also explained because RTM is treating pyrite mineral and 0 5 is affected heavily by the waste of this factory. On the other hand, the concentrations of S and Ca in the H and D samples are uniform and for S, higher than the average concentrations of this element in unCa(%) F7~,S(%)1-]

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perturbed sediments [5]. This information, together with the fact that the S / C a ratios correspond to calcium sulphate, can indicate the deposition and general contamination of a small fraction of phosphogypsum over all the estuary. This conclusion, on the other hand, is in accordance with a previous study of the radioactive contamination in this zone [6]. Finally, it is interesting to comment that the sample 04, collected quite near the fertilizer factory, contains a considerably amount of calcium, but the S / C a ratio is very low, indicating that the obtained values can not be related to the deposition of phosphogypsum. This sample was collected in the place where the phosphate rock, rich in P and Ca, and coming mostly from Morocco and Senegal, is unloaded to be treated in the factories, and for that reason, the obtained Ca and S concentrations can be related to the uncontroled deposition in the river of some phosphate mineral during the discharge process. A more detailed explanation, in comparison with the results obtained in Ref. [1], need to be done concerning the heavy metal concentrations (Table 2). As a general comment, it is possible to indicate that the values of all the heavy metals analyzed in the estuary are much higher than the obtained ones in sediments collected in undisturbed areas. Looking at their distribution over the estuary the existence of three possible sources of heavy metals that are responsible of these increases can be inferred. The main one is the metal factory RTM, that, as was mentioned in Ref. [1], releases large amounts of heavy metals in the Odiel river. However, we have recently found that some of the waste is deposited in the phosphogypsum piles of the Tinto river, so it may directly affect the pollution in this river, instead of affecting it indirectly through tidal effects, as was suggested in Ref. [1]. The other source is the fertilizer plant FORET, while the third source has its origin in that the waters of both rivers up-stream the estuary have very low pH (2-3) and consequently high concentrations of dissolved heavy metals, due to the mining activity. The pH of the waters changes drastically to more neutral values in the estuary, due to the influence of the sea water, and some precipitation of the previously dissolved heavy metals can be produced. All the possible sources commented in the last paragraph are not contributing to the obtained concentrations for all the metals. In the case of iron (see Fig. 4), it is clear that the waste of the fertilizer factory contains very low proportion of this metal, as41080 it can be deduced from the result obtained in the sample 0 3 (sample mostly formed by phosphogypsum), while extremely high values are obtained in the sample 05 and its surroundings, indicating that the waste released by RTM are extremely enriched in Fe. A very high value is also obtained in the sample up-stream the Tinto river (sample T1) indicating the existence of pyrite in its composition (as it was deduced previously from the S data). The two sources of Fe contamination can explain also the relatively high

Fe(%) 60

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concentrations of this metal in the samples collected in the Tinto river, in front of the phosphogypsum piles. The accumulation in these samples of some amounts of Fe can be related to the deposition of a fraction of this metal coming from up-stream the river, as well as its possible leaching from the piles sited in front of the samples. Concerning the Zn results, extremely high concentrations have been obtained over the two river basins, indicating the high degree of contamination in this metal. The existence of this contamination can be also deduced, for example, observing the high gradient of concentrations in the rivulet Estero Domingo Rubio, amounts of Zn are entering in this rivulet from the Tinto river. The three sources described above are contributing to the general Zn contamination: the fertilizer factory (see Zn concentration in O3), the metal factory (see Zn concentration in O5), and the mining developed up-stream the river (see Zn concentration in T1). This contamination is extended to all the estuary, affecting even clearly the H samples, indicating that the contamination is unlocalized. High values have been obtained in the samples collected in the Tinto river in front of the piles. The explanation of this is similar to the comments done for the same samples, when the Fe results were studied. Finally, extremely high concentrations can be also observed for Cu, Pb and As. The contamination of these metals is also extended over the two river basins (see the high gradient of concentrations in the rivulet Estero Domingo Rubio), indicating the unlocalized influence of the contaminant sources. Also, it is possible to deduce that the waste of the fertilizer factory is relatively free of Cu, As and Pb (see results sample 03), in opposition to the waste from RTM (see results sample 05). Nevertheless, the distributions for Cu, Pb and As are similar in general to the commented distribution for Zn. It is clear to deduce from this work, how through the application of the TTPIXE technique to environmental samples, the contamination produced for a big industrial complex can be evaluated, and even how the contribution

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of the different possible sources to the general contamination can be discerned.

Acknowledgments This work has been supported by ENRESA under a I + D contract. The Spanish authors acknowledge deeply the help and kind hospitality given by the Solid State Physics Group from ITN. The PIXE setup calibration and the help given by Mr. Luis Cerqueira is also acknowledged deeply. And finally, the assistance given by the environmental radioactivity group from the University of Seville in the sample collection is also acknowledged.

References [1] M.A. Respaldiza, A.J. L6pez-TArrida and J. G6mez-Camacho, Nucl. Instr. and Meth. B 75 (1993) 334. [2] M.A. Respaldiza, M. Garcla-le6n and G. Madurga, J. Trace Microprobe Techn. 6 (1988) 87. [3] J.A. Maxwell, J.L. Campbell and W.J. Teesdale, Nucl. Instr. and Meth. B 43 (1989) 218. [4] J.E. Martin, J.P. Bolivar, M.A. Respaldiza, R. Garcia-Tenorio and M.F. da Silva, Nucl. Instr. and Meth. B. 103 (1995) 477. [5] R.C. Weast et al. (eds.), Handbook of Chemistry and Physics, 65th Ed. (CRC Press, 1984-1985) p. F-146. [6] J.P. Bolivar, PhD. Thesis, University of Seville, 1995, in Spanish.