The environmental quality of the Jacuípe River's estuary (very important in
northeastern Brazil) was assessed during 2007 and 2008. In water, concentrations (mg L−1) of
Almost 12% of the total fresh water of the planet is in Brazil, and preservation of this huge hydric variety is one of the greatest environmental challenges for this country. In Brazil, Bahia State stands out not only due to its size (564.692.67 km2), but also because of the presence of important and numerous rivers, besides being the state that has the largest seashore in Brazil, with 1,183 kilometres in total.
In the aquatic ecosystem ensemble present in Bahia, the estuaries deserve special attention because of their importance for the procreation of several marine organisms and their natural susceptibility to environmental disequilibrium [
In this sense, Bahia’s north coast needs constant monitoring for hydric quality, with especial attention for the Jacuípe River’s estuary. This river has an extension of 141 km and its mouth is located in Camaçari, near an industrial area where there are several industries, from car manufacture to pharmaceutical factories. Prior to its mouth, the Jacuípe River runs across agricultural areas. In spite of the ecological importance of the Jacuípe River’s estuary and its intense use, the last large-scale investigation regarding environmental conditions in this area was carried out in 1989 [
Thus, this manuscript aims to fill the lack of information about the preservation of an area of huge importance for Bahia, ecologically, economically, and socioenvironmentally. In this sense, analyses of water and sediments were carried out, in that the water analysis referred to the total amounts of Cd, Cu, Pb, Zn (in some samples), as well as levels of
Figure
Description of the investigated area with sampling points.
The researched estuary area has a humid tropical weather with average annual temperatures near 25°C and rainfall levels of up to 1500 mm. In hydrological terms, the Jacuípe River average flux is of 21.8 m3 s−1 at its mouth, controlled by the Santa Maria dam 40 km away, and influenced by the Capivara Pequeno and Capivara Grande affluents, downstream of the dam [
The most common soils found at the Jacuípe River’s mouth are characterised by the translocation of sesquioxides of aluminum and iron, phyllosilicate clays, besides organic matter. The profusion of this kind of soil in Camaçari agrees with the existence of large quantities of sandstones, a type of sedimentary rock [
All the reactants used in the experiments were of analytical degree, Merck brand (Germany), or Vetec (Brazil). The preparation of solutions was carried out with ultrapure water (0.05
Temperature, pH, electrical conductivity, and dissolved oxygen measurements were conducted with portable probes from the following manufacturers and models, respectively: Phtek (Brazil) pH-100, Phtek (Brazil) CD-203, and Lutron (USA) DO-5510. A table of horizontal agitation Nova Ética (Brazil), model 109, was used to extract the exchangeable levels of Cd, Cu, Pb, and Zn from the sediments. Pseudototal extractions of sediments and total decompositions of water samples were carried out with a digestion block Marconi (Brazil), model MA-4025.
Determination of total amounts of the metallic species in water and exchangeable amounts in sediments were completed by inductively coupled plasma optical emission spectrometry (ICP OES), with Varian brand (Australia) equipment, model Vista-RL. The wavelengths employed for the Cd, Cu, Pb, and Zn were 214.439, 327.395, 220.353, and 213.857 nm, respectively. The optical emission spectrometer was operated with measurement power of 1300 W and 40 MHz of radiofrequency. Calibrations were carried out on a daily basis, from successive dilutions of a standard mixed solution at 1.000 mg L−1.
The flame atomic absorption spectrometry (FAAS) was employed for quantifying the pseudototal amounts of Cd, Cu, Pb, and Zn in the sediments, using a Varian (Australia) spectrometer, model SpectrAA 220. In all the analyses, an air-acetylene flame was used; wavelengths for Cd, Cu, Pb, and Zn were 214.438, 324.754, 220.353, and 213.856 nm, respectively. Standard solutions at 1.000 mg L−1 were used for the daily preparation of calibration curves.
X-ray analysis of sediment samples were performed by means of a Rigaku (Japan) diffractometer, model X’Pert Pro PW 3040/60, while a Jeol electron microscope (Japan), model JSM-6610LV, was employed for obtaining micrographs of the sediment particles. The thermogravimetric profile of the sediment was obtained with a TA Instruments Universal V2.3C thermogravimetric analyzer (USA), while a Perkin-Elmer Spectrum 100 infrared spectrometer (USA) was used for identifying functional groups in the sediment.
Water and sediment samples were collected at the five points shown in Figure
Dates (month/year) of the water and sediment sampling campaigns.
Sampling number | Water | Sediment |
---|---|---|
1 | 03/2007 | 03/2007 |
2 | 05/2007 | 07/2007 |
3 | 06/2007 | 08/2007 |
4 | 07/2007 | 09/2007 |
5 | 08/2007 | 10/2007 |
6 | 09/2007 | 03/2008 |
7 | 10/2007 | 06/2008 |
8 | 11/2007 | 07/2008 |
9 | 03/2008 | — |
10 | 04/2008 | — |
11 | 06/2008 | — |
12 | 08/2008 | — |
13 | 09/2008 | — |
Water samples were collected from the surface, and at a depth of 4 m by immersing polyethylene bottles. A Bailer type collector was used specifically for the deep samples. All the collectors were previously decontaminated using a solution of HCl 10% (v/v) and washed in ultrapure water.
After sampling of almost 1 L of water from the surface and from depth, the volume was divided into two polyethylene bottles, which are stored in foam boxes with ice. In the laboratory, one of the bottles was refrigerated up to 4°C, until determination of the soluble phosphate, within a time limit of 72 h. The second bottle was immediately used for determining nitrite and then refrigerated at 4°C for quantifying nitrate within a time limit of up to 48 h [
All procedures described below were rigorously performed according to standard protocols, which are applicable to environmental analyses related to this work. Furthermore, the determination of metals in all matrices (sediments—pseudototal and exchangeable fractions and water), as well as the quantification of anions in water samples, was carried out in routine/research analytical laboratories subject to constant verification of the quality of results, including the use of certified materials.
During the thirteen sampling campaigns, 65 surface and 65 deep water samples were analysed. Spectrophotometric analyses of the 130 samples were carried out in triplicates, with analytical blanks. Measurements of pH, electrical conductivity, dissolved oxygen, and temperature were done once only, and the two latter quantifications were only performed on surface water samples.
Nitrite determination was carried out in accordance with the Griess method, by means of the reaction of this anion with sulphanilamide and chlorhydrate of N-(1-naphthyl)-ethylenediamine (NED), with a further quantification at a maximum wavelength of 543 nm and in a buffered media at pH 8.5. For nitrate quantification, a procedure of nitrite reduction was firstly adopted; by percolating the samples and standards through a 25.00 mL burette containing copperized Cd [
The pH, temperature, electrical conductivity, and dissolved oxygen determinations were made by direct immersion of portable probes after the required calibration procedures.
Total amounts of Cd, Cu, Pb, and Zn were quantified in surface water samples collected during July, August, September, and October of 2007 and March of 2008. For this purpose, the samples (in triplicate and with analytical blanks) were submitted to a previous preconcentration of 5X by means of an evaporation step at 60°C. After that, the samples were digested with HNO3, according to a standard procedure [
The sample residual acidity was determined and used for normalising the metal standard solutions acidity in order to avoid differences in viscosity. The standards were prepared from individual stock solutions (at 1000 mg L−1) in the following concentration ranges (in mg L−1): 0.1 to 1.0 (Cd), 0.5 to 10.0 (Pb), and 0.5 to 5.0 (Cu and Zn). The acidity correction and concentration ranges of the standards were also maintained for quantifying Cd, Cu, Pb, and Zn in the sediments as described below.
Sediments were sampled at the riverside, in each one of the five sampling sites specified in Figure
Extractions of the exchangeable amounts of Cd, Cu, Pb, and Zn in the sediments collected during the eight sampling campaigns were completed in 5 replicates, also with analytical blanks. For this, almost 1 g of previously dried sediment (0.053 mm) was agitated with 20.00 mL of HCl solution at 0.1 mol L−1 (200 rpm), for 2 hours [
Sediments collected during the sampling campaigns of 09/2007, 03/2008, 06/2008, and 07/2008 were also submitted to quantification of the pseudototal amounts of Cd, Cu, Pb, and Zn, also in 5 replicates and with analytical blanks. The method described by the Environmental Protection Agency and previously cited [
Sediments sampled in 03/2007 were heated (triplicates) in a furnace at 550°C for 4 h, and the mass difference was used to calculate the total concentration of organic matter [
For X-ray diffraction, the sediment sample collected in 03/2007 (point 3) was used. This sample was firstly submitted to granulometric fractioning [
For electron microscopy, sediment collected at point 5 (03/2007) was covered with a thin layer of gold and an electron acceleration voltage of 20 kV was applied. Thermogravimetry of this same sample was performed by heating sediment particles from 25°C to 1,000°C at 10°C min−1, in an oxidant atmosphere.
Table
Physical-chemical parameters of water collected in the Jacuípe River’s estuary.
Date (sampling) | Point | Temperature (°C) | pH | Conductivity (mS cm−1) | DO (mg L−1) | ||
S | S | D | S | D | S | ||
03/2007 (1) | 1 | 29.3 | 7.79 | 7.89 | 40.60 | 40.00 | 5.5 |
2 | 27.2 | 7.12 | 7.88 | 10.20 | 39.90 | 7.8 | |
3 | 28.6 | 6.73 | 6.82 | 1.46 | 1.57 | 8.6 | |
4 | 28.4 | 6.77 | 6.88 | 0.20 | 0.21 | 8.8 | |
5 | 28.1 | 6.79 | 6.94 | 0.12 | 0.12 | 9.6 | |
05/2007 (2) | 1 | 28.5 | 7.45 | 7.24 | 7.45 | 2.52 | 6.3 |
2 | 27.0 | 7.32 | 7.20 | 3.24 | 1.90 | 7.5 | |
3 | 27.6 | 7.22 | 7.24 | 1.22 | 0.62 | 8.4 | |
4 | 26.8 | 7.14 | 7.20 | 0.21 | 0.21 | 8.6 | |
5 | 27.2 | 7.19 | 7.25 | 0.22 | 0.18 | 8.6 | |
06/2007 (3) | 1 | 27.2 | 7.30 | 7.10 | 1.33 | 0.74 | 3.9 |
2 | 26.6 | 6.80 | 7.00 | 0.93 | 0.43 | 7.6 | |
3 | 30.1 | 6.80 | 7.00 | 0.36 | 0.28 | 4.9 | |
4 | 27.5 | 7.20 | 7.20 | 0.16 | 0.17 | 5.1 | |
5 | 28.4 | 7.00 | 7.00 | 0.16 | 0.16 | 8.0 | |
07/2007 (4) | 1 | 28.2 | 6.00 | 6.20 | 6.92 | 7.64 | 8.3 |
2 | 26.7 | 6.30 | 6.40 | 4.43 | 5.21 | 8.8 | |
3 | 26.5 | 7.00 | 7.10 | 0.97 | 1.21 | 7.6 | |
4 | 26.6 | 7.80 | 7.70 | 0.17 | 0.14 | 6.0 | |
5 | 27.5 | 8.00 | 7.80 | 0.13 | 0.18 | 9.1 | |
08/2007 (5) | 1 | 27.5 | 5.60 | 6.20 | 43.00 | 43.00 | 8.9 |
2 | 26.8 | 7.30 | 6.70 | 1.20 | 39.40 | 9.4 | |
3 | 26.4 | 7.00 | 6.70 | 19.56 | 19.74 | 8.5 | |
4 | 27.3 | 7.10 | 7.20 | 6.93 | 9.85 | 8.2 | |
5 | 27.0 | 7.10 | 6.90 | 7.95 | 15.49 | 6.9 | |
09/2007 (6) | 1 | 26.0 | 7.43 | 7.35 | 22.20 | 22.10 | 8.8 |
2 | 25.6 | 7.19 | 7.20 | 17.11 | 17.21 | 7.5 | |
3 | 26.5 | 6.87 | 6.79 | 5.68 | 6.14 | 9.3 | |
4 | 27.8 | 6.60 | 6.56 | 0.45 | 0.47 | 9.6 | |
5 | 26.8 | 6.50 | 6.60 | 0.38 | 0.40 | 8.7 | |
10/2007 (7) | 1 | 28.2 | 6.00 | 6.70 | 29.00 | 30.90 | 7.2 |
2 | 27.3 | 7.30 | 7.00 | 17.19 | 29.50 | 7.9 | |
3 | 28.2 | 6.90 | 6.90 | 16.79 | 23.50 | 7.4 | |
4 | 28.0 | 7.10 | 6.80 | 4.28 | 6.83 | 7.7 | |
5 | 27.5 | 7.10 | 6.90 | 3.64 | 4.97 | 8.1 | |
11/2007 (8) | 1 | 27.7 | 7.90 | 7.90 | 48.60 | 48.50 | 7.9 |
2 | 28.1 | 8.00 | 8.10 | 46.80 | 47.40 | 6.5 | |
3 | 28.4 | 8.00 | 8.10 | 41.30 | 42.80 | 7.1 | |
4 | 27.9 | 8.00 | 8.00 | 0.20 | 0.21 | 7.0 | |
5 | 27.9 | 7.90 | 7.90 | 0.12 | 0.12 | 6.8 | |
03/2008 (9) | 1 | 28.4 | 7.37 | 7.36 | 48.60 | 48.50 | 7.9 |
2 | 29.4 | 7.39 | 7.28 | 46.80 | 47.40 | 6.5 | |
3 | 29.6 | 7.21 | 7.36 | 41.30 | 42.80 | 7.1 | |
4 | 28.7 | 6.73 | 6.87 | 0.20 | 0.21 | 7.0 | |
5 | 29.3 | 6.67 | 6.89 | 0.12 | 0.12 | 6.8 | |
04/2008 (10) | 1 | 28.5 | 7.48 | 7.62 | 41.60 | 42.80 | 6.4 |
2 | 29.0 | 7.66 | 7.69 | 16.10 | 38.90 | 8.8 | |
3 | 29.1 | 7.59 | 7.46 | 1.53 | 1.83 | 8.1 | |
4 | 29.0 | 7.80 | 7.57 | 0.28 | 0.32 | 6.1 | |
5 | 29.3 | 7.50 | 7.31 | 0.14 | 0.15 | 6.1 | |
06/2008 (11) | 1 | 27.8 | 7.87 | 7.68 | 35.20 | 35.00 | 8.4 |
2 | 28.1 | 7.45 | 7.70 | 5.87 | 32.70 | 7.2 | |
3 | 28.7 | 7.30 | 7.60 | 21,70 | 32.20 | 6.9 | |
4 | 28.2 | 7.21 | 7.03 | 8.47 | 9.51 | 8.0 | |
5 | 28.5 | 6.90 | 6.98 | 6.63 | 8.87 | 7.0 | |
08/2008 (12) | 1 | 25.1 | 7.54 | 7.64 | 3.80 | 36.80 | 8.4 |
2 | 24.6 | 7.51 | 7.47 | 9.16 | 35.40 | 8.2 | |
3 | 23.7 | 7.15 | 7.28 | 31.00 | 33,90 | 8.5 | |
4 | 22.7 | 6.76 | 7.42 | 25.00 | 37.30 | 8.7 | |
5 | 22.7 | 6.76 | 7.15 | 24.50 | 30.20 | 8.7 | |
09/2008 (13) | 1 | 26.4 | 7.90 | 7.97 | 27.40 | 27.40 | 8.0 |
2 | 26.6 | 7.74 | 7.81 | 22.00 | 22.10 | 8.5 | |
3 | 26.7 | 7.40 | 7.40 | 9.85 | 9.95 | 8.5 | |
4 | 26.4 | 7.14 | 7.05 | 0.49 | 0.55 | 8.0 | |
5 | 26.3 | 7.06 | 7.03 | 0.38 | 0.41 | 7.9 |
S: surface and D: deep.
The average temperature distribution during the 13 sampling campaigns (Figure
Average water temperature for all of the sampling points.
(a) Average pH (surface water) for all of the sampling points. (b) Average pH (deep water) for all of the sampling points.
As shown in Table
Electrical conductivity levels found in different river mouths can only be compared if these areas belong to regions with similar climatic and geographical characteristics. In this context, the conductivities reported in this study were compared with those of the Formoso River mouth [
At the mouth of the Jacuípe River, a tendency towards a decrease in electrical conductivity after the first sampling site was observed in most cases. Moreover, significant differences between the conductivity of surface and deep samples were not identified and, when present, such differences occurred at points 1 and/or 2, as can be exemplified by the samples collected in 08/2008. This behaviour is explained by the higher density of seawater and its incomplete mixture with freshwater. Figure
Electrical conductivity in water samples collected in July of 2007.
Average dissolved oxygen concentrations (surface water) for all of the sampling points.
Still in comparative terms, Silva et al. (2010) [
All the levels of dissolved oxygen throughout the 5 sampling points were above the minimum required by Brazilian environmental legislation, which is 5.0 mg L−1 for Class 2 water [
The N-
Concentrations (mg L−1) of nitrite (N-
Date (sampling) | Point | Nitrite (N- | Nitrate (N- | Phosphate (P- | |||
S | D | S | D | S | D | ||
03/2007 (1) | 1 | <0.004*** | <0.004 | 0.03 | 0.09 | <0.02* | <0.02* |
2 | 0.02 | <0.004 | 0.07 | 0.07 | <0.02 | <0.02 | |
3 | 0.01 | 0.02 | 0.07 | 0.06 | <0.02 | <0.02 | |
4 | 0.02 | 0.03 | 0.07 | 0.04 | <0.02 | <0.02 | |
5 | 0.02 | 0.02 | 0.06 | 0.05 | <0.02 | <0.02 | |
05/2007 (2) | 1 | 0.01 | 0.01 | 0.12 | 0.12 | 0.09 | 0.12 |
2 | 0.01 | 0.01 | 0.05 | 0.12 | 0.08 | 0.11 | |
3 | 0.01 | 0.02 | 0.11 | 0.13 | 0.11 | 0.09 | |
4 | 0.01 | 0.01 | 0.13 | 0.15 | 0.03 | 0.03 | |
5 | 0.02 | 0.01 | 0.10 | 0.14 | 0.08 | 0.03 | |
06/2007 (3) | 1 | 0.01 | 0.02 | 0.11 | 0.09 | 0.11 | 0.14 |
2 | 0.01 | 0.02 | 0.09 | 0.09 | 0.09 | 0.14 | |
3 | 0.03 | 0.02 | 0.09 | 0.10 | 0.16 | 0.16 | |
4 | 0.02 | 0.01 | 0.10 | 0.09 | 0.14 | 0.14 | |
5 | 0.02 | 0.01 | 0.10 | 0.10 | 0.13 | 0.14 | |
07/2007 (4) | 1 | 0.01 | 0.01 | 0.07 | 0.09 | 0.06 | 0.07 |
2 | 0.01 | 0.01 | 0.06 | 0.09 | 0.09 | 0.09 | |
3 | 0.01 | 0.01 | 0.06 | 0.09 | 0.09 | 0.09 | |
4 | 0.01 | 0.01 | 0.15 | 0.12 | 0.05 | 0.05 | |
5 | 0.01 | 0.01 | 0.13 | 0.15 | 0.04 | 0.05 | |
08/2007 (5) | 1 | <0.004 | <0.004 | 0.07 | 0.05 | 0.16 | 0.09 |
2 | <0.004 | <0.004 | 0.06 | 0.05 | 0.06 | 0.08 | |
3 | < 0.004 | <0.004 | 0.06 | 0.05 | 0.10 | 0.12 | |
4 | 0.01 | 0.01 | 0.09 | 0.05 | 0.10 | 0.13 | |
5 | 0.01 | 0.01 | 0.08 | 0.07 | 0.15 | 0.10 | |
09/2007 (6) | 1 | <0.004 | <0.004 | 0.13 | 0.11 | 0.06 | 0.06 |
2 | <0.004 | 0.01 | 0.21 | 0.12 | 0.08 | 0.07 | |
3 | 0.01 | 0.01 | 0.14 | 0.14 | 0.08 | 0.08 | |
4 | 0.01 | 0.01 | 0.11 | 0.10 | 0.05 | 0.21 | |
5 | 0.01 | 0.01 | 0.12 | 0.10 | 0.04 | 0.04 | |
10/2007 (7) | 1 | <0.004 | <0.004 | 0.01 | 0.09 | 0.22 | 0.06 |
2 | <0.004 | <0.004 | 0.06 | 0.09 | 0.04 | 0.08 | |
3 | <0.004 | 0.01 | 0.07 | 0.08 | 0.06 | 0.09 | |
4 | 0.01 | 0.01 | 0.05 | 0.09 | 0.06 | 0.06 | |
5 | 0.01 | 0.01 | 0.07 | 0.10 | 0.06 | 0.06 | |
11/2007 (8) | 1 | 0.011 | 0.015 | 0.11 | 0.10 | 0.12 | 0.12 |
2 | 0.015 | 0.011 | 0.10 | 0.11 | 0.12 | 0.14 | |
3 | 0.012 | 0.013 | 0.11 | 0.12 | 0.13 | 0.13 | |
4 | 0.015 | 0.015 | 0.11 | 0.10 | 0.10 | 0.15 | |
5 | 0.016 | 0.015 | 0.11 | 0.11 | 0.12 | 0.13 | |
03/2008 (9) | 1 | <0.004*** | <0.004 | 0.07 | 0.09 | 0.02 | 0.03 |
2 | 0.005 | 0.01 | 0.08 | 0.09 | 0.03 | 0.03 | |
3 | 0.005 | 0.01 | 0.08 | 0.10 | 0.05 | 0.04 | |
4 | 0.01 | 0.01 | 0.10 | 0.12 | 0.03 | 0.03 | |
5 | 0.01 | 0.01 | 0.09 | 0.08 | 0.03 | 0.03 | |
04/2008 (10) | 1 | <0.004 | <0.004 | 0.07 | 0.08 | 0.03 | 0.02 |
2 | <0.004 | <0.004 | 0.07 | 0.14 | 0.04 | <0.02* | |
3 | 0.01 | 0.01 | 0.30 | 0.32 | 0.09 | 0.05 | |
4 | 0.01 | 0.01 | 0.20 | 0.33 | 0.04 | 0.03 | |
5 | 0.01 | 0.01 | 0.20 | 0.24 | 0.04 | 0.03 | |
06/2008 (11) | 1 | <0.04 | <0.004 | 0.12 | 0.01 | 0.03 | 0.03 |
2 | <0.004 | <0.004 | 0.09 | 0.09 | <0.02 | 0.04 | |
3 | 0.008 | 0.010 | 0.09 | 0.10 | 0.07 | 0.05 | |
4 | 0.005 | 0.01 | 0.01 | 0.09 | 0.03 | 0.03 | |
5 | 0.010 | 0.02 | 0.09 | 0.09 | 0.03 | 0.03 | |
08/2008 (12) | 1 | <0.004 | <0.004 | 0.07 | 0.10 | 0.03 | 0.04 |
2 | <0.004 | <0.004 | 0.09 | 0.14 | <0.02 | 0.05 | |
3 | 0.01 | 0.013 | 0.07 | 0.09 | 0.07 | 0.06 | |
4 | 0.008 | 0.01 | 0.10 | 0.10 | 0.04 | 0.03 | |
5 | 0.010 | 0.01 | 0.08 | 0.08 | 0.02 | 0.08 | |
09/2008 (13) | 1 | <0.004 | <0.004 | 0.08 | 0.09 | 0.03 | 0.03 |
2 | <0.004 | <0.004 | 0.01 | 0.10 | 0.03 | <0.02 | |
3 | 0.01 | 0.01 | 0.13 | 0.10 | 0.03 | <0.02 | |
4 | 0.01 | 0.01 | 0.11 | 0.09 | 0.03 | 0.03 | |
5 | 0.01 | 0.01 | 0.10 | 0.10 | 0.03 | 0.04 |
S: surface and D: deep. *In order to simply the data exposition, the relative standard deviations were omitted, but all of these values were smaller than 10%. **Soluble phosphate. ***Limit of detection as 3
The phosphate comprises another anion of great importance for assessing the quality of an aquatic ecosystem, as it can be responsible for eutrophication, along with nitrate [
For the three quantified anions (
Soluble phosphate concentrations in water samples collected in July of 2007.
All samples of surface water collected from 5 sampling campaigns (July to October of 2007 and March of 2008) revealed levels of cadmium, copper, lead, and zinc below the method’s detection limit: 0.001 (Cd); 0.01(Cu); 0.01(Pb); 0.1(Zn) mg L−1, which are lower than the maximum allowed by Brazilian environmental legislation [
Table
Exchangeable concentrations of Cd, Cu, Pb, and Zn (mg kg−1) in sediments collected from the Jacuípe River’s estuary,
Date (sampling) | Point | Cd | Cu | Pb | Zn |
03/2007 (1) | 1 | <0.05* | 10, | <5.0* | <1.3* |
2 | <0.05 | <5.0 | |||
3 | <0.05 | <5.0 | |||
4 | <0.05 | <5.0 | |||
5 | <0.05 | <5.0 | |||
07/2007 (2) | 1 | <5.0 | <1.3 | ||
2 | <5.0 | ||||
3 | <5.0 | ||||
4 | <5.0 | ||||
5 | <5.0 | ||||
08/2007 (3) | 1 | <5.0 | |||
2 | <5.0 | ||||
3 | <5.0 | ||||
4 | <5.0 | ||||
5 | <5.0 | <1.3 | |||
09/2007 (4) | 1 | <0.05 | <5.0 | ||
2 | <0.05 | <5.0 | <1.3 | ||
3 | <0.05 | <5.0 | |||
4 | <0.05 | <5.0 | |||
5 | <0.05 | <5.0 | |||
10/2007 (5) | 1 | <0.05 | <1.3* | <5.0 | <1.3 |
2 | <0.05 | <1.3 | <1.3 | ||
3 | <0.05 | <5.0 | |||
4 | <0.05 | ||||
5 | <0.05 | <1.3 |
*Limit of detection as 3
For cadmium, exchangeable levels in some samples were found to be very close to the maximum recommended [
Although the presence of lead is equally troubling, all of the exchangeable concentrations encountered were below the maximum recommended [
Despite the industrial development present in the Jacuípe River’s estuary and widespread use of copper and zinc, the exchangeable concentration of both metals in sediments did not exceed the maximum recommended limits of 73 (Cu) and 145 (Zn) mg kg−1 [
The pseudototal levels of Cd, Cu, Pb, and Zn in some of the estuarine sediments are listed in Table
Pseudototal concentrations of Cd, Cu, Pb, and Zn (mg kg−1) in some sediment samples collected from the Jacuípe River’s estuary,
Date | Point | Cd | Cu | Pb | Zn |
09/2007 | 1 | ||||
2 | 48, | ||||
3 | |||||
4 | |||||
5 | |||||
03/2008 | 1 | ||||
2 | |||||
3 | |||||
4 | |||||
5 | |||||
06/2008 | 1 | ||||
2 | |||||
3 | |||||
4 | |||||
5 | |||||
07/2008 | 1 | ||||
2 | |||||
3 | |||||
4 | |||||
5 |
The differences observed in metal retentions on sediment particles can be partially explained by charge’s density of the analytes. Lead ions have the smallest hydrated radius (or highest charge’s density) among the other metallic ions, thus showing great adsorptive fostering related to electrostatic retentions. Contrarily, zinc ions present the highest hydrated radius and smallest charge’s density, thus justifying its low affinity by the adsorptive sites. For cadmium and copper, intermediate characteristics are observed. Despite considerations about occurrence of electrostatic forces, retentions of the four analytes by specific interactions (e.g., chemical bounds) cannot be disregarded.
From an environmental point of view, a reasonable difference between exchangeable and pseudototal levels is important, because it indicates that an expressive portion of metals will not be assimilate by the local biota, considering only the natural conditions of water bodies. This statement is true, because the metals belonging to the pseudototal fraction are more effectively (or less reversibly) retained since they form, for example, very stable complexes with humified organic matter. Nevertheless, benthic organisms ingest sediment particles and they can be directly contaminated with spillover effects for the entire food chain.
Sarkar et al. (2004) [
With the aim of evaluating the minerals present in estuarine sediments and relating them to the adsorptive capacity, the sediment sample collected at point 3 (Figure
Positions
Mineral (chemical formula) | Positions |
---|---|
Kaolinite (Al2Si2O5(OH)4) | 14.2139 and 28.8365 |
Feldspar (CaAlSi3O8, KAlSi3O8 or NaAlSi3O8,) | 31.93 |
Illite [general formula: Kx(Al2)(Si4-x Alx)O10 (OH)2] | 10.1354 and 20.5040 |
Quartz (SiO2) | 24.1458 and 30.9085 |
X-ray diffractogram of the sediment collected at sampling point 3 (March of 2007).
The identification of these four major minerals is consistent with the predominant soil types in the area studied, which are described in Figure
It should be noted that the relation between soil type and the mineral composition of sediments is valid because the erosion of the first is an important source of particles in river beds. Notably, the identification of kaolinite and illite plays an important role in the dynamics of retaining metallic species, due to high surface area and important adsorptive chemical groups, including hydroxyls [
The clay and organic matter levels of the sediments sampled in 03/2007 are shown in Table
Clay and total organic matter levels (%, m/m) of sediments collected in March of 2007.
Sampling point | Clay content | Total organic matter content ( |
---|---|---|
1 | ND* | |
2 | ND | |
3 | 8.8 | |
4 | 10.7 | |
5 | 12.0 |
*Not detected.
Infrared spectrum of the sediment sample collected at point 5 (March of 2007). Black and continous line is related to sediment not impregnated, while gray and continous line is related to sediment with Pb.
Figure
Thermogravimetric analysis showed organic matter volatilisation from 100 to 550°C (Figure
Thermogravimetric profile of the sediment collected at sampling point 5 (March of 2007).
Electron micrograph of the sediment collected at sampling point 5 (March of 2007—Magnification of 1.200×).
Infrared, electron microscopy and thermogravimetric analyses were conducted on the sediment collected at point 5, because of their interesting structural characteristics, including high contents of clay and total organic matter (Table
Despite the desirable structural features of the sediments for metal adsorption, the exchangeable and pseudototal concentrations of Cd, Cu, Pb, and Zn were within the normal limits for most samples. This finding reinforces the absence of significant pollution sources concerned with the evaluated analytes.
The analyses of water and sediment samples from the Jacuípe River’s estuary revealed good environmental conditions in relation to the different physical-chemical parameters, despite the large regional development in terms of population growth and industrial diversification.
Concerning the water compartment, the nitrite and nitrate levels point to an absence of significant quantities of biodegradable organic material, and adequate oxygenation levels also support this conclusion. The normal levels of soluble phosphate indicate that there is no appreciable source of waste containing detergents. This last result, along with normal concentrations of nitrate, shows an aquatic ecosystem preserved from eutrophication. It must be noted that this environmental panorama was observed, despite increasing human pressure promoted by real-estate development and tourism. The pH parameters and electrical conductivity were also classified as normal when checked against Brazilian environmental legislation and other works.
The reduced total concentrations of Cd(II), Cu(II), Pb(II), and Zn(II) in the water point to an absence of continuous sources of discharges, especially of industrial origin, regardless of the proximity to the Camaçari petrochemical complex.
For the sediments, the mineralogical composition, the morphological aspect of particles, the infrared spectrum, as well as the total levels of organic matter helped in elucidating the sediment’s potential adsorptive capacity. The decrease in clay levels after the fifth sampling site is consistent with the geographical characteristics of estuarine areas.
All the samples displayed exchangeable levels of Cd, Cu, Pb, and Zn well below those established in the literature. The exception to this behaviour was found in some few results for cadmium. The presence of higher levels of all four metals in the pseudototal fraction is coherent with the theoretical expectations, although most of the pseudototal results are below the maximum allowable levels.
Finally, this study updated and increased the database on the environmental quality of the Jacuípe River Estuary, an area of great ecological importance to the preservation of tropical ecosystems on the Brazilian northeastern coast, and of pronounced economic importance to the Bahia State.
The authors would like to thank the Camaçari Civil Defense for providing the boats for the collections, and the State University of Bahia Research and Development Center (CEPED, Camaçari, BA) for the use of their laboratories for chemical analysis. They would also like to thank the National Council for Scientific and Technological Development (CNPq, Brasília, DF, Brazil), the Coordination for the Improvement of Higher Education Personnel (CAPES, Brasília, DF, Brazil), the Research Support Foundation of the State of Bahia (FAPESB, Salvador, BA, Brazil), and the Laboratory of Cell Ultrastrucuture Carlos Alberto Redins of the Federal University of Espírito Santo (Vitória, ES, Brazil).