Hydrocarbon composition and distribution in a coastal region under influence of oil production in northeast Brazil

Marine Pollution Bulletin 62 (2011) 1877–1882

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Edited by Bruce J. Richardson The objective of BASELINE is to publish short communications on different aspects of pollution of the marine environment. Only those papers which clearly identify the quality of the data will be considered for publication. Contributors to Baseline should refer to ‘Baseline—The New Format and Content’ (Mar. Pollut. Bull. 60, 1–2).

Hydrocarbon composition and distribution in a coastal region under influence of oil production in northeast Brazil Angela de L.R. Wagener a, Renato S. Carreira a,b,⇑, Claudia Hamacher b, Arthur de L. Scofield a, Cassia O. Farias b, Lívia G.M.S. Cordeiro b, Letícia G. Luz a, Aída P. Baêta a, Francine A. Kalas a a b

LABMAM/Departamento de Química, Pontifícia Universidade Católica do Rio de Janeiro, 22453-900 Rio de Janeiro, Brazil LAGOM/Faculdade de Oceanografia, Universidade do Estado do Rio de Janeiro, 20550-013 Rio de Janeiro, Brazil

a r t i c l e Keywords: Hydrocarbons Water Sediment Coastal region Petroleum industry

i n f o

a b s t r a c t Waters and sediments from the Potiguar Basin (NE Brazilian coast) were investigated for the presence and nature of polycyclic aromatic hydrocarbons (PAH) and aliphatic hydrocarbons. The region receives treated produced waters through a submarine outfall system serving the industrial district. The total disP 16PAH and 5– persed/dissolved concentrations in the water column ranged from 10–50 ng L 1 for 1 for total aliphatic hydrocarbons. In the sediments, hydrocarbon concentrations were low 10 lg L P 16PAH and 0.01–5.0 lg g 1 for total aliphatic hydrocarbons) and were consistent (0.5–10 ng g 1for with the low organic carbon content of the local sandy sediments. These data indicate little and/or absence of anthropogenic influence on hydrocarbon distribution in water and sediment. Therefore, the measured values may be taken as background values for the region and can be used as future reference following new developments of the petroleum industry in the Potiguar Basin. Ó 2011 Elsevier Ltd. All rights reserved.

Hydrocarbons are usually found in the marine environment as complex mixtures of substances derived from multiple processes, as for instance, biosynthesis, biomass burning, early diagenesis of biogenic precursors, erosion of terrestrial sediments, exudation from ocean floor and anthropogenic activities (NRC, 2003). The most common anthropogenic sources of hydrocarbon are urban runoff, industrial and domestic effluents, ship activities, oil spills, oil production and transport in offshore areas (NRC, 2003). A significant portion of the aromatic hydrocarbons found in the marine environment derive from the incomplete combustion of recent

⇑ Corresponding author at: LABMAM/Departamento de Química, Pontifícia Universidade Católica do Rio de Janeiro, 22453-900 Rio de Janeiro, Brazil. Tel.: +55 21 3527 1809. E-mail address: [email protected] (R.S. Carreira). 0025-326X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2011.06.006

and fossil organic matter (Bouloubassi et al., 2006; Dachs et al., 1999; Jiang et al., 2009; Kuo et al., 2011; Saha et al., 2009). Reports on the presence of hydrocarbons in marine areas around the globe are frequently found. However, even though most petroleum produced in Brazil is from offshore reservoirs, there are still few data available on these substances in marine waters and sediments under the influence of such activities in the Brazilian continental margin. The present work reports results of the Potiguar Basin Environmental Assessment Project, conducted by CENPES/PETROBRAS during 2002–2004 in the NE coast of Brazil where produced waters from the local basin are discharged via submarine outfalls. The Potiguar Basin, in the northeastern Brazilian region, extends from the outcrops of Rio Grande do Norte and Ceará states to water depths greater than 2000 m (Penteado et al., 2007 and references therein). The activities of oil exploration in the marine portion of

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Fig. 1. Sampling stations of water and superficial sediments in Guamaré coastal region. Group 1 = stations outside outfalls influence; Group 2 = stations around outfall #1; Group 3 = stations around outfall #2.

the basin sea are restricted to the area between the isobaths of 5 and 50 m. Oil and gas produced from both offshore and onshore fields are transported to an effluent treatment plant (oil/water separation) in the industrial district located at the coast of Guamaré municipality. The final effluent (80,000 m3 of produced water) has been discharged to the sea via two submarine outfalls. Human settlements in the region are scarce and subsidence fishery, shrimp cultivation and tourism are the economy basic activities. Climate features are typical of tropical semi-arid region with no marked season unless for a rain period from June to August. The region is subjected to strong persistent winds, principally during the months of September to November. The environmental investigation in the Guamaré coastal region targeted hydrocarbon compounds and comprised water and sediment samples collected in a sampling array of 26 stations. The stations were positioned taking in consideration the two submarine outfalls (Fig. 1), as follows: (i) group 1 stations, formed by stations E01-E16 located in an area credited as unaffected by the outfalls due to the prevailing currents and distance from the points of outflow; (ii) group 2 stations, formed by station E17 (diffusers zone of outfall 1) and stations E18–E21 (500 m from E17); (iii) group 3 stations, formed by station E22 (diffusers zone of outfall 2) and stations E23–E26 (500 m from E22). Water samples, collected with a 2.5 L all-Teflon Go-FloÒ bottle at 0.5 m depth, were immediately transferred to amber glass bottles and extracted onboard. Sediments were collected with a grab sampler and the top 0–2 cm layer was stored in clean aluminum container and stored at 20 °C. Four sampling trips were performed in July/2002 (S1), May/2003 (S2), November/2003 (S3) and May/2004 (S4). Extraction of water and sediments followed methods EPA3510Cand EPA-3540C, respectively. Dissolved and dispersed hydrocarbons in water samples (2 L) were liquid–liquid extracted on board using 3  30 mL aliquots of methylene chloride (pesticide grade). Oven-dried sediment samples (10–15 g) were extracted on the laboratory during 24 h in a Soxhlet apparatus using 200 mL of a 1:1 (v/v) mixture of methylene chloride:acetone (pesticide grade). Before extraction, p-terphenyl-d14 and deuterated n-C16 and n-C30 were added as surrogates for both water and sediment samples. The aliphatic and aromatic fractions of hydrocarbon were isolated by adsorption chromatography using silica-gel and alumina and the following internal standards were added in the final extract for quantitation: deuterated n-C24 (2500 ng mL 1) for the aliphatic

and a mixture of naphthalene-d8, acenaphthene-d10, phenanthrene-d10, chrysene-d12 e perylene-d12 (100 ng mL 1) for the aromatic fractions. The aliphatic hydrocarbons in water and sediment extracts were analyzed using an HP 6890 gas chromatograph equipped with an HP-5 fused silica capillary column (30 m, 0.32 mm i.d., 0.25 lm film thickness) and flame ionization detection. Helium was used as the carrier gas. The GC oven temperature was programmed from an initial 0.5 min hold at 60 °C, followed by 6 °C min 1 up to 300 °C and a final hold of 10 min. The injector and detector temperatures were set at 280 °C and 300 °C, respectively. Identification of n-alkanes (n-C14 to n-C34) was based on retention times obtained from injection of a standard solution. The same solution was used to construct a six-point external calibration curve and to calculate response factors relative to deuterated n-C24, used for quantitation. UCM was measured as the total area below the resolved compounds and quantified using mean response factors of n-alkanes over the elution range. Gas chromatography/mass spectrometry (GC/MS) analysis for polycyclic aromatic hydrocarbons followed the EPA method 8270-C, with modifications. It was carried out in a Finnigan Trace GC interfaced with a Polaris Q mass spectrometry and fitted to a J&W XLB-ITD (30 m, 0.25 mmi.d. and 0.25 lm film thickness) fused silica capillary column. The GC oven temperature was set to 50 °C for 5 min, then at 50 °C min 1 to 80 °C and then at 6 °C min 1 to 280 °C (25 min. final hold). Helium was used as the carrier gas. The mass spectrometer operated in the electron impact (EI) mode (70 eV) and the data acquired in full scan mode (55–450 amu). Instrument was calibrated using a standard mixture containing all the 16 targeted PAH (USEPA priority PAH): naphthalene (N), acenaphthene (Ace), acenaphthylene (Acen), fluorine (Fl), phenanthrene (Ph), anthracene (A), pyrene (Py), fluoranthene (Ft), benz(a)anthracene (BaA), chrysene (Cry), benzo(b)fluoranthene (BbFt), benzo(k)fluoranthene (BkFt), benzo(a)pyrene (BaPy), indeno(1,2,3-cd)pyrene (I-Py), dibenz(a,h)anthracene(DBahA)and benzo(ghi)pyrene (BghiPe). Quality assurance procedures included successful analysis of a reference material (IAEA 417), analytical blank control, recovery control and daily check of calibration curves. The highest detection limit (0.33 lg kg 1) was found for dibenz(a,h)anthracene. Total organic carbon (TOC) and total nitrogen (TN) were determined in a Carlo Erba EA 1110 elemental analyzer. Initially, the sediment samples were treated with hydrochloric acid to remove

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Table 1 P P Water total (dissolved and dispersed) concentrations of 16-EPA PAH ( 16PAH), total aliphatic hydrocarbon (TAH), unresolved complex mixture (UCM) and sum of P C14–C34 n-alkanes ( alk) in Guamaré coastal region. Mean ± SD and range for 96 samples collected in four samplings (n = number of samples in each sampling). Sampling

*

S1 (n = 28)

S2 (n = 26)

S3 (n = 20)

S4 (n = 22)

P 16PAH (ngL 1) TAH*(lg L 1)

235.7 ± 452.8 (1.0–1828) –

n-alkane (lg L 1) UCM (lg L 1)

2.6 ± 8.2 (0.01–44.3) n.d.

50.5 ± 116.2 (1.0–563.0) 11.0 ± 13.3 (0.01–22.1) 3.6 ± 3.2 (0.80–12.9) 1.8 ± 8.2 (0.01–37.7)

16.0 ± 24.5 (1.0–100.5) 2.0 ± 5.0 (0.01–22.1) 0.6 ± 1.7 (0.01–9.2) 1.0 ± 2.8 (0.01–12.8)

28.4 ± 46.2 (2.3–206.9) 13.5 ± 29.9 (0.01–114.6) 0.5 ± 0.8 (0.01–16.1) 11.5 ± 26.0 (0.01–98.6)

TAH was not calculated for the first sampling (S1).

inorganic carbon, and the dried sediment (at 60 °C to constant weight) were weighed (2–5 mg; ±0.01 mg) in duplicate tin capsules (Hedges and Stern, 1984). Results were corrected for carbonate content. quantitation was performed by calibration curves and using cystine as standard. Reference material MESS-2 (National Research Council of Canada) was used to verify accuracy. Analytical precision was ±1.7% for TOC and ±2.8% for TN. Detection limits were 0.30 mg g 1 for TOC and 0.10 mg g 1 for TN. Results for aromatic and aliphatic hydrocarbons in the water column are presented in Table 1as the sum of dispersed and dissolved fractions. The mean R16PAHin S1 was 235.6 ± 452.8 ng L 1. The extremely asymmetricspace distribution of PAH concentrations in S1 resulted from values at stations E01 (1828 ng L 1) and E03 (1,158 ng L 1) in group 1 (outside the outfall´s influence region), as well as stations E17, E18, E20, E21 (group 2, outfall #1) and E22 (group 3, outfall #2), with values in the range of 108–1120 ng L 1. P In S2, 16PAH were lower in comparison to S1 although showing also a large range of values (50.5 ± 116.2 ng L 1; Table 1) with maxima in stations of group 2 (210 ng L 1 in E17 and 563 ng L 1 in E19). In the last two samplings (S3 and S4), the concentrations of P the 16PAH were low (respectively, 16.0 ± 24.5 ng L 1 and 28.4 ± 46.2 ng L 1; Table 1)and only stations in the outfall’s diffusers zone exhibited relatively higher concentrations: station E17 (49 ng L 1 in S3 and 207 ng L 1 in S4) and station E22 (100 ng L 1 in S3). P Only 15% of the whole data set (n = 96) showed 16PAH con1 centration higher than 100 ng L . Except for the first sampling (S1), almost all these concentrations were found in the outfalls zone (group 2 and group 3). However, statistical data evaluation (Kruskal–Wallis, at p < 0.05) showed no significant difference between those stations nearer the outfalls (groups 2 and 3) and stations outside the outfall zone of influence (group 1). This statistical result is heavily influenced by the large fraction of samples (80%) with concentrations below 50 ng L 1. The low concentrations constrained the calculation of diagnostic ratios used to assess petrogenic and/or pyrolitic origins for PAH (Wang et al., 1999; Yunker et al., 2002). Only for some samples with higher concentrations (E1, E3, E12, E17, E20, E21, E22, first sampling; E17 and E19, second sampling) the ratios Fl/(Fl + Py) and A/(A + Ph) were calculated since the compounds were present well above the quantitation limit. The cross plot of these ratios (not shown) indicate samples E17 and E19 (second sampling) as contaminated by oil derived PAH while the others contained PAH from combustion as well as from oil. On the other hand, it is evident that naphthalene, followed by phenanthrene, pyrene and fluoranthene (see Fig. 2 for some examples), were the most abundant individual PAH in samples collected in the diffuser zones (groups 2 and 3). The analysis of the effluent produced by the

Fig. 2. 16 PAH composition in effluent, samples E01, E03, E17, and E22 from the first sampling (S1). See text for abbreviations.

Guamaré treatment plant showed a median concentration of P 15.53 ng L 1 for 16PAH and a PAH composition that includes 44.6% of naphthalene and 26.9% of phenanthrene; Table 2. The similarity in the composition of PAH in the water samples and in the effluent is a strong indication of the outfall’s influence on the hydrocarbon typology in the coastal zone of Guamaré. However,

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Table 2 PAH composition of effluent from Guamaré treatment plant, obtained in the period 2002–2004. Compound Naphthalene Acenaphtene Acenaphthylene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo(a)anthracene Crysene Benzo(b)fluoranthene Benzo(k)fluoranthene Benzo(a)pyrene Indeno(1,2,3cd)pyrene Dibenz(a,h)anthracene Benzo(ghi)perylene P 16PAH

Median (ng L 1)

Min. (ng L

6924 143 293 2128 4170 93 67 402 132 826 122 42 59 18

14 69 38 782 1200 23 19 80 25 75 10 3 9 10

20,615 290 779 5376 12,744 705 798 8066 702 2029 468 150 717 538

44.6 0.9 1.9 13.7 26.9 0.6 0.4 2.6 0.9 5.3 0.8 0.3 0.4 0.1

57 51 15,527

14 14 –

393 992 –

0.4 0.3 –

1

)

Max. (ng L

1

)

Normalized median*(%)

*

Normalized median: median value for individual PAH divided by the sum of 16 PAH, in percentage.

it is also evident from the concentration data that the effluent is effectively dispersed upon discharge (10–1000 folds) resulting in low PAH levels or concentrations below detection limits at distances more than 500 m from the diffuser zone. The comparison of PAH levels obtained for different regions is limited in value due to the use of distinct methodologies and determination of different number of individual compounds in each study. Having this limitation in mind, the range of PAH concentrations found in the present study (0.10–20 ng L 1; Table 1) have been considered by several authors as background values for coastal and marine waters (Boehm et al., 2007; Guitart et al., 2008; Neff, 2002). Stations in the outfalls zone showed PAH concentrations comparable to contaminated areas, like Guanabara Bay in southP east Brazil (mean 16PAH concentration around 600 ng L 1and a range of 79–1592 ng L 1) (Silva et al., 2007), as well as in other contaminated rivers and estuaries around the world (e.g. Wang et al., 2008). It is noteworthy, however, that in only 5 samples (mainly in S1) concentrations of heavy PAH (5–6 rings) were above the Brazilian legal threshold of 18 ng L 1for marine waters of Class 1 (waters used for primary contact and preservation of natural conditions). Amongst these samples are waters collected outside the outfall´s influence zone and, therefore, the contamination is not likely related to effluent discharge but to combustion products. In Table 1 the results for total aliphatic hydrocarbons (TAH), n-alkanes and UCMin water are presented. Mean concentrations of TAH in each sampling (no data for S1) were relatively similar, Table 3 P Sediment concentrations of total organic carbon (TOC), sum of 16 PAH ( 16PAH), total aliphatic hydrocarbon (TAH), unresolved complex mixture (UCM) and sum of P C14–C34 n-alkanes ( alk) in Guamaré coastal region. Mean ± SD and range for all individual samples, including replicates (n = number of samples in each sampling).

from 2.0 ± 5.0 lg L 1 to 13.5 ± 29.9 lg L 1. For n-alkanes, S1 and S2 showed higher concentrations (2.6 ± 8.2 lg L 1 and 3.6 ± 3.2 lg L 1, respectively) in comparison to S3 and S4 (0.6 ± 0.7 lg L 1 and 0.5 ± 0.8 lg L 1), while UCM was significant only in S4 (11.5 ± 26.0 lg L 1; Table 1). In more than 80% of the 68 examined water samples (no data for S1), THA was below 10 lg L 1,which is usually considered as the baseline concentration for contaminated coastal and marine waters (Burns and Codi, 1999; Cincinelli et al., 2001; Reddy and Quinn, 2001). Few exceptions occurred in the outfall´s diffuser zone, like stations E17, E23, and E24 in S2, E24 in S3 and E20 and E25 in S4, and in 3 samples outside diffuser zones in S4 (E05, E06 and E07), where TAH concentration ranged from 10 to 250 lg L 1. There was a weak but significant correlation (r = 0.28, p < 0.05) between total aliphatics and PAH, indicating the two hydrocarbon fractions have distinct transport patterns in the coastal zone, as already observed for other regions (Readman et al., 2002). The data for organic carbon and hydrocarbon in the sediments are shown in Table 3. The mean, standard deviation and range were calculated considering the three replicates collected in each station and analyzed as individual samples, totalizing 295 samples analyzed (17 collected samples were lost during processing). The mean concentrations of total organic carbon (TOC) in sediments were similar and varied over a relatively narrow range in the four samplings, from 0.59 ± 0.29 mg g 1 to 0.85 ± 0.91 mg g 1 (Table 3). In 40% of the samples TOC was not detected (<0.30 mg g 1). Total nitrogen detected in less than 10 % of the samples is not reported here. The sediments are composed predominantly by siliciclastic sands, but the presence of submarine sand dunes result in a complex mosaic of sedimentary facies (Vital et al., 2005). These sediment characteristics concur with the low TOC contents and the data scattering (Table 3). In fact, the investigated sediments have the lowest TOC content in the Brazilian continental margin (Table 4), which, in turn, results from the general oligotrophic conditions (Manuel Montes et al., unpublished results) and small river inputs observed in the area. The data for PAH in sediments are shown in Table 3. The mean ± SD concentrations of PAH in all samplings are between 0.88 ± 1.56 ng g 1 and 18.9 ± 98.3 ng g 1. In more than 95% of the P 295 samples the 16PAH was below 10 ng g 1 whereas for 50% of them PAH were not detected. These values are comparable to those found in sediments from pristine areas (Curtosi et al., 2007 and references therein). The relatively large range of PAH concentrations in S1 and S4 (Table 3) derives from values between 25 and 798 lg kg 1 obtained in only eight replicates randomly distributed in several stations. These samples are outliers while median values for each station indicate no significant influence of the outfalls on the spatial distribution of sedimentary PAH, as can be seen in Fig. 3a. Only at station E22, in the diffuser zone of outfall 2, the 3 P replicates collected in S4 showed similar 16PAH concentration 1 (26.3–43.0 ng g ), however these values are at least 1–2 order of magnitude lower than those reported for contaminated sediments in the Brazilian coastal zone (Da Silva et al., 2007; Medeiros et al.,

Sampling

TOC (mg g

1

)

P 16PAH (ng g TAH (lg g

1

)

)

n-alkane (lg g UCM (lg g

1

1

)

1

)

S1 (n = 63)

S2 (n = 77)

S3 (n = 77)

S4 (n = 78)

0.85 ± 0.91 (0.35–5.95) 3.50 ± 10.54 (0.10–76.0) 0.61 ± 1.23 (0.01–7.97) 0.56 ± 1.19 (0.01–7.97) 0.06 ± 0.27 (0.01–1.62)

0.59 ± 0.29 (0.16–2.11) 1.09 ± 2.35 (0.10–16.0) 1.62 ± 1.29 (0.34–8.35) 0.39 ± 0.30 (0.02–1.84) 1.14 ± 1.05 (0.13–6.13)

0.83 ± 2.00 (0.17–17.9) 0.88 ± 1.56 (0.10–7.90) 1.60 ± 2.17 (0.01–9.30) 0.38 ± 0.50 (0.01–2.13) 1.07 ± 1.64 (0.01–7.10)

0.64 ± 0.21 (0.47–3.50) 18.9 ± 98.3 (0.10–798) 2.06 ± 5.70 (0.01–33.4) 0.42 ± 0.80 (0.01–5.50) 1.90 ± 4.60 (0.01–28.4)

Table 4 Range of mean total organic carbon (TOC) contents in sediments from different regions in the Brazilian continental margin. Brazilian continental margin

TOC (mg g

South and south-eastern regions Siliciclastic sediments

3.0–12 1.2–7.2

Carbonate-rich sediments

1.4–3.8

Guamaré coastal region/ Potiguar Basin

0.6–0.8

1

)

Reference Mahiques et al. (2004) Jennerjahn and Ittekot (1997) Jennerjahn and Ittekot (1997) Present study

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of organic material and the oligotrophic nature of the coastal waters do not provide sufficient flux of suspended matter capable of binding organic compounds in active surface centers and thereby transfer contaminants to the sediments. Moreover the region is continuously subjected to trade winds that cause strong turbulence and fast dispersion of materials released in the water. Therefore, the investigated region is still pristine in respect to the 16 PAH, however the presence of alkylated PAH homologues must be investigated in future works since these compounds are the predominant hydrocarbons in oils. The results of the present study identify the water column as the most relevant physical compartment to be monitored for possible impacts of the oil industry in the region of Guamaré. Acknowledgements The authors are grateful to PETROBRAS (Brazilian oil company) for funding this research. References

Fig. 3. Median (bar), first and third percentiles (box) and non-outlier range (whisker) values in each station for (a) sum of 16 polycyclic aromatic hydrocarbons (RPAH, ng g 1) and (b) total aliphatic hydrocarbon (TAH, lg g 1) in sediments from Guamaré coastal region considering the four samplings (S1–S4).

2005; Meniconi et al., 2002) as well as for other regions in the world (Liu et al., 2008; Maskaoui and Hu, 2009; Readman et al., 2002; Tolosa et al., 2004; Wang et al., 2006). The mean concentrations of TAH (Table 3) ranged from 0.61 ± 1.23 to 2.06 ± 5.70 lg g 1and in 75% of the samples TAH was below 2.0 lg g 1. These values for TAH are typical of sediments from remote regions free of anthropogenic influence and are consistent, as mentioned for the PAH, with the presence of coarse sediments with low organic matter contents (Bouloubassi and Saliot, 1993 and references therein; Readman et al., 2002). The uniformity of TAH space distribution (Fig. 3b) is an indication that the effluent discharged via the outfall played no role on the hydrocarbon distribution in sediments during the observation period. In all samples with TAH concentrations higher than 7.0 lg g 1 the UCM was the main fraction of the aliphatic fraction, indicating the presence of degraded petroleum compounds in the sediment.

Conclusions The low concentrations of both aromatic and aliphatic compounds in sediment and water samples hindered, in general, the calculation of diagnostic ratios and the inference about the sources of hydrocarbons (petroleum and/or combustion). Sediments very poor in organic carbon are not accumulating PAH. In stations E17 and E22, for instance, where relatively elevated concentrations were found in waters (of the order of 500–1000 ng L 1) levels of individual PAH in sediments were below quantitation limits (between 0.5 and 1.0 ng g 1). The lack of significant land inputs

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