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Petroleum hydrocarbons in Brazilian Northeast continental shelf waters: baseline values

ABSTRACT

Water quality on the continental shelf off the eastern Brazilian Northeast region was investigated in two oceanographic campaigns during winter and summer, when vertical profiles of salinity, temperature, turbidity, chlorophyll and dissolved oxygen were recorded. Dissolved / dispersed petroleum hydrocarbons (DDPH) were also analyzed in sub-superficial water samples using fixed wavelength fluorescence spectroscopy methods. Shelf waters are dominated by Tropical Waters, with high salinity (> 36.5 g kg-1) and temperature (> 26 °C) and little continental influence. Turbidity was higher during winter, which may be due to the higher continental contribution and/or higher wave action. Chlorophyll was mostly < 1 µg L-1 and dissolved oxygen saturation was predominantly high (> 90%), but innermost costal stations were influenced by the Capibaribe estuary. Median DDPH concentrations were as low as 0.07 and 0.04 µg L-1 Carmópolis oil equivalents during winter and summer respectively, and 0.02 µg L-1 chrysene equivalent for both periods. An exception was observed off Suape Harbor (0.35 µg L-1 Carmópolis oil equiv. and 0.13 µg L-1 chysene equiv.), suggesting navigation activities as the main local source. The overall DDPH median of 0.06 μg L-1 Carmópolis oil equivalents and 0.02 μg L-1 chrysene equivalents are proposed as the baseline concentration for non-polluted coastal water for the tropical western Atlantic Ocean margin.

Descriptors:
Chrysene; Carmópolis oil; Chlorophyll; Dissolved oxygen; Turbidity

Petroleum is the main known energetic source and its exploitation and production is greater than ever to supply the increasing worldwide demand. Polycyclic aromatic hydrocarbons (PAH) are a key group of compounds (~8 to 15%) of oil composition and have become a major environmental concern because they are ubiquitous. PAH in environments can be harmful due to their potential biochemical and behavior alterations (Mrdakovic et al, 2016Mrdakovic, M; Ilijin, L; Vlahovic, M; Matic, D; Gavrilovic, A; Mrkonja; A, Peric-Mataruga, V. 2016. Acetylcholinesterase (AChE) and heat shock proteins (Hsp70) of gypsy moth (Lymantria dispar L.) larvae in response to long-term fluoranthene exposure. Chemosphere. 159: 565-569., Dissanayake et al., 2010Dissanayake, A; Piggott, C; Baldwin, C; Sloman, KA. 2010. Elucidating cellular and behavioural effects of contaminant impact (polycyclic aromatic hydrocarbons, PAHs) in both laboratory exposed and field-collected shore crabs, Carcinusmaenas (Crustacea: Decapoda). Mar Environ Res. 70: 368-373., Torreiro-Melo et al., 2015Torreiro-Melo, AGAG; Silva, JS; Bianchini, A; Zanardi-Lamardo, E; Carvalho, PSM. 2015. Bioconcentration of phenanthrene and metabolites in bile and behavioral alterations in the tropical estuarine guppy Poecilia vivipara. Chemosphere. 132: 17-23.) beside carcinogenic and teratogenic effects (Magi et al., 2002Magi, E; Bianco, R; Ianni, C; Di Carro, M. 2002. Distribution of polycyclic aromatic hydrocarbons in the sediments of the Adriatic Sea. Environ Pollut. 119: 91-98.; Boonyatumanond et al., 2006Boonyatumanond, R; Wattayakorn, G; Togo, A; Takada, H. 2006. Distribution and origins of polycyclic aromatic hydrocarbons (PAHs) in riverine, estuarine, and marine sediments in Thailand. Mar Pollut Bull. 52: 942-956.; Chen et al., 2013Chen, CF; Chen, CW; Dong, CD; Kao, CM. 2013. Assessment of toxicity of polycyclic aromatic hydrocarbons in sediments of Kaohsiung Harbor, Taiwan. Sci Total Environ. 463-464: 1174-1181.; Rahmanpoor et al., 2014Rahmanpoor, S; Ghafourian, H; Hashtroudi, SM; Bastami, KD. 2014. Distribution and sources of polycyclic aromatic hydrocarbons in surface sediments of the Hormuz strait, Persian Gulf. Mar Pollut Bull. 78: 224-229.). PAH can be introduced in coastal waters directly by oil spill accidents, shipping activity, industrial and domestic effluents, fluvial runoff (Zaghden et al., 2007Zaghden, H; Kallel, M; Elleuch, B; Oudot, J; Saliot, A. 2007. Sources and distribution of aliphatic and polyaromatic hydrocarbons in sediments of Sfax, Tunisia, Mediterranean Sea. Mar Chem. 105: 70-89; Lemos et al., 2014Lemos, RTO; Carvalho, PSM; Zanardi-Lamardo, E. 2014. Petroleum hydrocarbons in water from a Brazilian tropical estuary facing industrial and port development. Mar Pollut Bull. 82: 183-188.), or indirectly by atmospheric deposition of products of oil or organic matter combustion (Boehm, 2005Boehm, P.D. 2005. Polycyclic Aromatic Hydrocarbons (PAHs). In: Morrison, R.D., Murphy, B.L. (Eds.), Environmental Forensics. Burlington, Academic Press, p. 313-337.; Meire et al., 2007Meire, RO; Azeredo, A; Torres, JPM. 2007. Aspectos ecotoxicológicos de hidrocarbonetos policíclicos aromáticos. Oecologia brasiliensis. 11: 188-201.; Lemos et al., 2014Lemos, RTO; Carvalho, PSM; Zanardi-Lamardo, E. 2014. Petroleum hydrocarbons in water from a Brazilian tropical estuary facing industrial and port development. Mar Pollut Bull. 82: 183-188.; Maciel et al., 2015aMaciel, DC; Souza JRB; Taniguchi, S; Bícego, MC; Zanardi-Lamardo, E. 2015a. Sources and distribution of polycyclic aromatic hydrocarbons in an urbanized tropical estuary and adjacent shelf, Northeast of Brazil. Mar Pollut Bull. 101: 429-433.; Arruda-Santos et al., 2018Arruda-Santos, RH; Schettini, CAF; Yogui, GT; Maciel, DC; Zanardi-Lamardo, E. 2018. Sources and distribution or aromatic hydrocarbons in a tropical marine protected area estuary under influence of sugarcane cultivation. Sci Total Environ. 624: 935-944.).

PAHs, individually or expressed as total concentration (dissolved / dispersed petroleum hydrocarbons - DDPH), have been reported in water and sediments from many Brazilian estuaries and bays (e.g., Todos os Santos Bay by Venturini and Tommasi, 2004Venturini, M; Tommasi, LR. 2004. Polycyclic aromatic hydrocarbons and changes in the trophic structure and polychaete assemblages in sediments of Todos os Santos Bay, Northeastern Brazil. Mar Pollut Bull. 48: 97-107.; Patos Lagoon by Medeiros et al., 2005Medeiros, PM; Bicego, MC; Castelao, RM; Del Rosso, C; Fillmann, G; Zamboni, AJ. 2005. Natural and anthropogenic hydrocarbon inputs to sediments of Patos Lagoon Estuary, Brazil. Environ Int. 31: 77-87.; Guanabara Bay by Silva et al., 2007Silva, TF; Azevedo, DA; Aquino Neto, FR. 2007. Distribution of polycyclic aromatic hydrocarbons in surface sediments and waters from Guanabara Bay, Rio de Janeiro, Brazil. J Braz Chem Soc. 18: 628-637.; Cocó and Ceará estuaries by Cavalcante et al., 2009Cavalcante, RM; Sousa, FW; Nascimento, RF; Silveira, ER; Freire, GSS. 2009. The impact of urbanization on tropical mangroves (Fortaleza, Brazil): evidence from PAH distribution in sediments. J Environ Manage. 91: 328-335.; Santos Estuary by Martins et al., 2011Martins, CC; Bícego, MC; Mahiques, MM; Figueira, RL; Tessler, MG; Montone, RC. 2011. Polycyclic aromatic hydrocarbons (PAHs) in a large South American industrial zone area (Santos Estuary, Southeastern Brazil): sources and depositional history. Mar Pollut Bull. 63: 5-12.; Arruda-Santos et al., 2018Arruda-Santos, RH; Schettini, CAF; Yogui, GT; Maciel, DC; Zanardi-Lamardo, E. 2018. Sources and distribution or aromatic hydrocarbons in a tropical marine protected area estuary under influence of sugarcane cultivation. Sci Total Environ. 624: 935-944.). Assessments were also made near oil industry hotspots as harbors (São Sebastião channel by Zanardi et al., 1999aZanardi, E; Bícego, MC; Weber, RR. 1999a. Dissolved/Dispersed Petroleum Aromatic Hydrocarbons in the São Sebastião Channel, São Paulo, Brazil.Mar Pollut Bull. 38: 410-413.;b; Silva and Bícego, 2010Silva, DAM; Bícego, MC. 2010. Polycyclic aromatic hydrocarbons and petroleum biomarkers in São Sebastião Channel, Brazil: assessment of petroleum contamination. Mar Environ Res. 68(5): 277-286.; Lemos et al., 2014Lemos, RTO; Carvalho, PSM; Zanardi-Lamardo, E. 2014. Petroleum hydrocarbons in water from a Brazilian tropical estuary facing industrial and port development. Mar Pollut Bull. 82: 183-188.; Maciel et al., 2015aMaciel, DC; Souza JRB; Taniguchi, S; Bícego, MC; Zanardi-Lamardo, E. 2015a. Sources and distribution of polycyclic aromatic hydrocarbons in an urbanized tropical estuary and adjacent shelf, Northeast of Brazil. Mar Pollut Bull. 101: 429-433.; 2016; Zanardi-Lamardo et al., 2018Zanardi-Lamardo, E; Schettini, CAF; Vieira-Campos, AA; Cabral, CB; Silva, MS. 2018. Intratidal variability and transpor of petroleum aromatic hydrocarbons in an anthropized tropical estuarine system: the Suape estuary (8.4S 35W). Braz J Oceanogr. 66: 47-57.) and offshore extraction zones (Potiguar basin by Wagener et al., 2011Wagener, ALR; Carreira, RS; Hamacher, C; Scofield, AL; Farias, CO; Cordeiro, LGMS; Luz, LG; Baêta, AP; Kalas, FA. 2011. Hydrocarbon composition and distribution in a coastal region under influence of oil production in northeast Brazil. Mar Pollut Bull. 62: 1877-1882.) or open waters (South West Atlantic waters, Bícego et al., 2002Bícego, MC; Zanardi-Lamardo, E; Taniguchi, S; Weber, RR. 2002. Natural levels of dissolved / dispersed petroleum hydrocarbons in the South West Atlantic. Mar Pollut Bull. 44: 1166-1169.). This study presents the very first assessment on dissolved / dispersed petroleum hydrocarbons (DDPH) on the eastern sector of the Brazilian Northeast region, off Pernambuco State in open waters on the continental shelf. This region is relatively far from offshore active oil extraction zones, ~400 km southward from Potiguar Basin (Rio Grande do Norte State) and ~ 350 km northward from Sergipe Basin (Sergipe State). The nearest potential sources are the continental runoff through the estuaries and the port and navigation activities. However, during August and September 2019, many tons of crude oil washed on northeastern Brazil shores (Lourenço et al., 2020Lourenço, RA; Combi, T; Alexandre, MR; Sasaki, ST; ZanardiLamardo, E; Yogui, GT. 2020. Mysterious oil spill along Brazil’s northeast and southeast seaboard (2019-2020): Trying to find answers and filling data gaps. Mar Pollut Bull. 156: 111219.). The origin of the oil is still unknown, but given its distribution on landing it appears to have originated from a far offshore source, drifting ashore through regional winds and the South-Equatorial Current (Schettini et al., 2017Schettini, CAF; Domingues, EC; Truccolo, EC; Oliveira Filho, JC; Mazzini, PLF. 2017. Seasonal variability of water masses and currents at the eastern Brazilian continental shelf (7.5-9° S). Reg Stud Mar Sci. 16: 131-144.).

Pernambuco State coast has several estuaries that could act as potential PAH sources from the continental drainage. Instead, a combination of geomorphology, tidal regime and fluvial discharge act as a filter, trapping most of the continental load of pollutants (Maciel et al., 2015aMaciel, DC; Souza JRB; Taniguchi, S; Bícego, MC; Zanardi-Lamardo, E. 2015a. Sources and distribution of polycyclic aromatic hydrocarbons in an urbanized tropical estuary and adjacent shelf, Northeast of Brazil. Mar Pollut Bull. 101: 429-433.; 2016; Arruda-Santos et al., 2018Arruda-Santos, RH; Schettini, CAF; Yogui, GT; Maciel, DC; Zanardi-Lamardo, E. 2018. Sources and distribution or aromatic hydrocarbons in a tropical marine protected area estuary under influence of sugarcane cultivation. Sci Total Environ. 624: 935-944.). The Capibaribe estuary is the main coastal system in terms of social and economic importance because it crosses the densely populated Recife Metropolitan Area. This system has also high trapping capacity (Schettini et al., 2016aSchettini, CAF; Paiva, BP; Batista, RAL; Oliveira Filho, JC; Truccolo, EC. 2016a. Observation of na estuarine turbidity maximum in the highly impacted Capibaribe Estuary, Brazil. Braz J Oceanogr. 64:185-190.), but the higher loads of pollutants discharged in its lower stretch can effectively export material to the adjacent shelf (Maciel et al., 2016Maciel, DC; Souza, JRB; Taniguchi, S; Bicego, MC; Schettini, CAF; Zanardi-Lamardo, E. 2016. Hydrocarbons in sediments along a tropical estuary-shelf transition area: sources and spatial distribution. Mar Pollut Bull. 113: 566-571.; Schettini et al., 2016bSchettini, CAF; Miranda, JB; Valle-Levinson, A; Truccolo, EC. 2016b. The circulation of the lower Capibaribe estuary (Brazil) and its implications for the transport of scalars. Braz J Oceanogr. 64: 263-276.). Another potential coastal source is the Suape Estuary, located ~50 km south of Recife, where a major industrial and harbor development started in the mid- 1980s (Lemos et al., 2014Lemos, RTO; Carvalho, PSM; Zanardi-Lamardo, E. 2014. Petroleum hydrocarbons in water from a Brazilian tropical estuary facing industrial and port development. Mar Pollut Bull. 82: 183-188.; Zanardi-Lamardo et al., 2018Zanardi-Lamardo, E; Schettini, CAF; Vieira-Campos, AA; Cabral, CB; Silva, MS. 2018. Intratidal variability and transpor of petroleum aromatic hydrocarbons in an anthropized tropical estuarine system: the Suape estuary (8.4S 35W). Braz J Oceanogr. 66: 47-57.).

The local continental shelf is ~40 km wide with the shelf break at ~60 m deep (Brazilian Navy Nautical Chart N.o 22.200). A better geomorphological description of the shelf is provided by Barcellos et al. (2020)Barcellos, RL; Melo, MCSS; Sial, AN; Manso, VAV. 2020. Sedimentary organic matter characterization on a tropical continental shelf in Northeastern Brazi. Int J Geosci. 11(6):101166. It is dominated by the presence of oligotrophic Tropical Water with salinity > 36.5 g kg-1 and temperature > 26 °C. The continental inflow of fresh water is very limited by the regional semi-arid climate countryside and small river drainage basins. The regional tides are semi-diurnal, ranging between 1.5 and 3 m. The wind regime is dominated by the South Atlantic High and blows steadily westwards. Wintertime currents are stronger and northwards and summertime currents are sluggish and southwards (Schettini et al., 2017Schettini, CAF; Domingues, EC; Truccolo, EC; Oliveira Filho, JC; Mazzini, PLF. 2017. Seasonal variability of water masses and currents at the eastern Brazilian continental shelf (7.5-9° S). Reg Stud Mar Sci. 16: 131-144.; Domingues et al., 2017).

Two oceanographic campaigns were carried out during austral winter (18-22 August 2013) and summer (10-14 January 2014), when water properties (salinity, temperature, turbidity, chlorophyll and dissolved oxygen) were recorded and water samples collected to analyze dissolved and/or dispersed petroleum hydrocarbons (DDPH). A total of 36 sampling stations were distributed across the shelf, from as near as possible from the shore until the shelf break between 7.5° to 9° south, comprising mostly the continental shelf off Pernambuco State (Figure 1). During the campaigns, currents were monitored at a central point study area with a moored acoustic Doppler current profiler (Schettini et al., 2017Schettini, CAF; Domingues, EC; Truccolo, EC; Oliveira Filho, JC; Mazzini, PLF. 2017. Seasonal variability of water masses and currents at the eastern Brazilian continental shelf (7.5-9° S). Reg Stud Mar Sci. 16: 131-144.).

The water properties were recorded with a CTD probe, JFE Advantech, Rynko Profiler, with sensors resolutions of: (a) depth: 0.01 m ± 0.3 % FS; (b) temperature: 0.001 ± 0.01 °C; (c) conductivity: 0.001 ± 0.01 mS m-1; (d) turbidity by optical backscattering: 0.03 ± 0.3 FTU; (e) chlorophyll by fluorimeter: 0.01 ppb ± 0.1 % FS; and (f) dissolved oxygen by phosphorescence: 0.004 mg L-1 ± 2% FS. Salinity was calculated using temperature and conductivity by PSS-78 (UNESCO, 1981UNESCO 1981. Background papers and supporting data on the Pratical Salinity Scale 1978. UNESCO Techn. Papers Mar. Sci. 37, UNESCO, Paris, p. 144.). Surface water samples (1 m depth) were taken with 4 L pre-cleaned amber glass bottles attached to a stainless steel device. Water samples were collected at the bow just prior to stopping the boat to avoid potential contamination from the boat engine oil.

Water samples were liquid-liquid extracted according to previous studies (Lemos et al., 2014Lemos, RTO; Carvalho, PSM; Zanardi-Lamardo, E. 2014. Petroleum hydrocarbons in water from a Brazilian tropical estuary facing industrial and port development. Mar Pollut Bull. 82: 183-188.; Zanardi-Lamardo et al., 2018Zanardi-Lamardo, E; Schettini, CAF; Vieira-Campos, AA; Cabral, CB; Silva, MS. 2018. Intratidal variability and transpor of petroleum aromatic hydrocarbons in an anthropized tropical estuarine system: the Suape estuary (8.4S 35W). Braz J Oceanogr. 66: 47-57.). In brief, 20 mL of n-hexane (pesticide grade) was added to the 4 L amber glass bottle immediately after water sampling. An aliquot of 100 µL of a deuterated PAH solution (1,000 ng mL-1of AccuStandard, Internal Standard Mix containing naphthalene-d8, acenaphthene-d10, phenanthrene-d10 and chrysened12) was added as recovery surrogate to all samples, including the field blank. The bottle was vigorously agitated for 2 minutes to extract hexane-soluble organic matter. In the laboratory, the organic extract was separated from water using a separating funnel. Anhydrous Na2SO4 (previously combusted at 450 °C) was added to the extract for binding traces of water. Subsequently, the extract was concentrated down to 10 mL on a rotary evaporator. DDPH were analyzed by fluorescence spectroscopy (SpectraMax M3 Molecular Devices), using UV-Vis fixed wavelength methodology. The organic extract was excited at 310 nm and fluorescence emission was recorded at 360 nm (Ehrhardt (1983)Ehrhardt, M. 1983. Determination of dissolved/dispersed hydrocarbons, in: Grasshoff, K., Ehrhardt, M., Kremling, K. (Eds.), Methods of seawater analysis, 2 ed. Verlag Chemie Weinheim, New York, pp. 190-281.; Knap et al., 1986Knap, AH; Burns, KA; Dawson, R; Ehrhardt, M; Palmork, KH. 1986. Dissolved/dispersed hydrocarbons, tarballs and the surface microlayer: Experiences from an IOC/UNEP Workshop in Bermuda, December, 1984. Mar Pollut Bull. 17: 313-319.; Zanardi et al., 1999aZanardi, E; Bícego, MC; Weber, RR. 1999a. Dissolved/Dispersed Petroleum Aromatic Hydrocarbons in the São Sebastião Channel, São Paulo, Brazil.Mar Pollut Bull. 38: 410-413., 1999bZanardi, E; Bícego, MC; Miranda, LB; Weber, RR. 1999b. Distribution and origin of hydrocarbons in water and sediment in São Sebastião, SP, Brazil. Mar Pollut Bull. 38: 261-267.; Lemos et al., 2014Lemos, RTO; Carvalho, PSM; Zanardi-Lamardo, E. 2014. Petroleum hydrocarbons in water from a Brazilian tropical estuary facing industrial and port development. Mar Pollut Bull. 82: 183-188.). Spectroscopy is a sensitive, fast and cheap technique for measuring petroleum (aromatic) hydrocarbons in water (Law et al., 1987Law, RJ; Marchand, M; Dahlmann, G; Fileman, TW. 1987. Results of two bilateral comparisons of the determination of hydrocarbon concentrations in coastal seawater by fluorescence spectroscopy. Mar Pollut Bull. 18: 486-489.; Ehrhardt and Petrick, 1989Ehrhardt, M; Petrick, G. 1989. Relative concentrations of dissolved/dispersed fossil fuel residues in Mediterranean surface waters as measured by UV fluorescence. Mar Pollut Bull. 20: 560-565.; Bícego et al., 2002Bícego, MC; Zanardi-Lamardo, E; Taniguchi, S; Weber, RR. 2002. Natural levels of dissolved / dispersed petroleum hydrocarbons in the South West Atlantic. Mar Pollut Bull. 44: 1166-1169.; Li et al., 2010Li, Y; Zhao, Y; Peng, S; Zhou, Q; Ma, LQ. 2010. Temporal and spatial trends of total petroleum hydrocarbons in the seawater of Bohai Bay, China from 1996 to 2005. Mar Pollut Bull. 60: 238-243). This methodology was originally developed for monitoring petroleum hydrocarbons in marine waters and expressed as dissolved/dispersed petroleum hydrocarbons. It does not discriminate sources of hydrocarbons, though. In fact, results may include products of oil degradation, combustion products and other natural materials that absorb/emit light at the 310/360 nm wavelength pair. This excitation/emission pair is typical of benzene-containing hydrocarbons, therefore results were expressed as dissolved/dispersed petroleum hydrocarbons (DDPH) in bulk water. Despite limitations, ultraviolet fluorescence is a good tool for understanding the fate of aromatic hydrocarbons after release in the water and has been proposed for investigation of petroleum hydrocarbon accumulation (hot spot) (Knap et al., 1986Knap, AH; Burns, KA; Dawson, R; Ehrhardt, M; Palmork, KH. 1986. Dissolved/dispersed hydrocarbons, tarballs and the surface microlayer: Experiences from an IOC/UNEP Workshop in Bermuda, December, 1984. Mar Pollut Bull. 17: 313-319., Zanardi et al., 1999aZanardi, E; Bícego, MC; Weber, RR. 1999a. Dissolved/Dispersed Petroleum Aromatic Hydrocarbons in the São Sebastião Channel, São Paulo, Brazil.Mar Pollut Bull. 38: 410-413.;b; Lemos et al., 2014Lemos, RTO; Carvalho, PSM; Zanardi-Lamardo, E. 2014. Petroleum hydrocarbons in water from a Brazilian tropical estuary facing industrial and port development. Mar Pollut Bull. 82: 183-188.; Zanardi-Lamardo et al., 2018Zanardi-Lamardo, E; Schettini, CAF; Vieira-Campos, AA; Cabral, CB; Silva, MS. 2018. Intratidal variability and transpor of petroleum aromatic hydrocarbons in an anthropized tropical estuarine system: the Suape estuary (8.4S 35W). Braz J Oceanogr. 66: 47-57.; Arruda-Santos et al., 2018Arruda-Santos, RH; Schettini, CAF; Yogui, GT; Maciel, DC; Zanardi-Lamardo, E. 2018. Sources and distribution or aromatic hydrocarbons in a tropical marine protected area estuary under influence of sugarcane cultivation. Sci Total Environ. 624: 935-944.).

Figure 1
Localization of the study area in South America (a) and in northeastern Brazil (b). The pink rectangle is the assessed area, and the red squares indicate the areas of active oil rigs of Sergipe Basin (in the south) and Potiguar Basin (in the north). The sampling stations (red circles) are presented in (c); ports of Recife and Suape are indicated.

DDPH concentrations were calculated based on two analytical curves: one prepared with chrysene (99% purity, Sigma-Aldrich) and the other prepared with Carmópolis weathered crude oil. Concentration in the analytical standards ranged between 0 and 2.5 μg L-1. Results were expressed as chrysene and Carmópolis oil equivalents, respectively. Considering that oil is a complex mixture, the use of chrysene as a standard (IOC, 1984IOC, 1984. Manual for Monitoring Oil and Dissolved/dispersed Petroleum Hydrocarbons in Marine Waters and on Beaches. Intergovernmental Oceanographic Commission, Manual and Guides 13. 35 pp.) has raised some disagreement among researchers although it has been accepted because it provides a worldwide basis for comparison of results. On the other hand, Carmópolis oil comes from one of the oldest active oil fields along the northeastern coast of Brazil, and it has been widely used as a standard oil for the Brazilian coast, southwestern Atlantic and western Antarctic Peninsula (Zanardi et al., 1999aZanardi, E; Bícego, MC; Weber, RR. 1999a. Dissolved/Dispersed Petroleum Aromatic Hydrocarbons in the São Sebastião Channel, São Paulo, Brazil.Mar Pollut Bull. 38: 410-413.; b; Bícego et al., 2002Bícego, MC; Zanardi-Lamardo, E; Taniguchi, S; Weber, RR. 2002. Natural levels of dissolved / dispersed petroleum hydrocarbons in the South West Atlantic. Mar Pollut Bull. 44: 1166-1169.; 2009; Lemos et al., 2014Lemos, RTO; Carvalho, PSM; Zanardi-Lamardo, E. 2014. Petroleum hydrocarbons in water from a Brazilian tropical estuary facing industrial and port development. Mar Pollut Bull. 82: 183-188.; Maciel et al., 2015bMaciel, DC; Costa, BVM; Santos, LPS; Souza, JRB; Zanardi-Lamardo, E. 2015b. Avaliação da toxicidade dos sedimentos do Sistema Estuarino do Capibaribe (Pernambuco, Brasil) utilizando o copépodo bentônico Tisbe biminiensis Volkmann Rocco (1973).Tropic Oceanogr. (Online) 43: 26-37.; Arruda-Santos et al., 2018Arruda-Santos, RH; Schettini, CAF; Yogui, GT; Maciel, DC; Zanardi-Lamardo, E. 2018. Sources and distribution or aromatic hydrocarbons in a tropical marine protected area estuary under influence of sugarcane cultivation. Sci Total Environ. 624: 935-944.; Zanardi-Lamardo et al., 2018Zanardi-Lamardo, E; Schettini, CAF; Vieira-Campos, AA; Cabral, CB; Silva, MS. 2018. Intratidal variability and transpor of petroleum aromatic hydrocarbons in an anthropized tropical estuarine system: the Suape estuary (8.4S 35W). Braz J Oceanogr. 66: 47-57.). Field blank samples and internal standard recovery (surrogate) were used for quality control purposes. The field blank fluorescence was subtracted from sample readings. The method detection limit (DL) was calculated as three times the standard deviation of blank concentrations (Quevauviller et al., 1992Quevauviller, PH; Cofino, W; Vijverberg, A; Wells, DE; Griepink, B. 1992. Quality assurance in marine monitoring. EUR Report, 14297 EN, European Commission, Brussels. Proceedings of the workshop held in Noordwijkerhout. 21-23, p 43.). DLs expressed in chrysene and Carmópolis oil equivalents were 0.01 and 0.03 μg L-1, respectively. Mean recovery of the surrogate was 70.7 ± 8.4% (95% level of confidence).

Figure 2
Distribution of (a) salinity (g kg-1), (b) temperature (°C), (c) chlorophyll (µg L-1), (d) turbidity (NTU), (e) oxygen saturation (%), and (f) DDPH expressed as chrysene equivalents (µg L-1) on surface (top 1.5 m) waters from Pernambuco continental shelf during (W) winter (Aug 2013) and (S) summer (Jan 2014). Dots indicate sampling stations and dashed line represents isobaths.

Table 1 presents the summary of basic statistics of the near surface waters. A detailed analysis of the salinity and temperature distributions and currents regime are presented in Schettini et al. (2017)Schettini, CAF; Domingues, EC; Truccolo, EC; Oliveira Filho, JC; Mazzini, PLF. 2017. Seasonal variability of water masses and currents at the eastern Brazilian continental shelf (7.5-9° S). Reg Stud Mar Sci. 16: 131-144. and Dominguez et al. (2017)Dominguez, EC; Schettini, CAF; Truccolo, EC; Oliveria Filho, JC. 2017. Hydrography and currents on the Pernambuco Continental Shelf. Brazilian Journal of Water Resources. 22, e43.. The main aspects are: (1) the shelf is dominated by high salinity (s > 36.5 g kg-1) and high temperature (t > 26 °C) Tropical Water originated by the southern branch of the Atlantic South Equatorial Current, which bifurcates south of the study area; (2) even during the winter, when the local river contribution is maximum, fresh water influence is very low and limited to the inner shelf (Figure 2a); (3) The horizontal temperature distribution relatively monotonous with warmer waters at the inner shelf. The winter water temperature was ~ 2 °C cooler than in summer (26 °C and 28 °C, respectively) (Figure 2b).

Chlorophyll, turbidity, oxygen saturation and DDPH have not been described for the region yet. Chlorophyll mean values were 0.6 and 0.7 µg L-1 during winter and summer, respectively (Table 1). The chlorophyll spatial distributions (Figure 2c) present a mild gradient towards the shore, and some patches of higher chlorophyll especially during summer. One patch is adjacent to the Capibaribe estuary mouth and another is located to the north. Both presented values of ~ 5 µg L-1. Turbidity was higher during winter than summer, which can be attributed to the increased continental runoff during the rainy season (winter), potentially delivering more fine sediment to the shelf, and also due to the higher wind action expected during the winter (Figure 2d). The winter time distribution does not show any particular pattern, though the higher values were recorded in the north. During summer there is a mild gradient towards the shore. Oxygen saturation was high (> 95%) in both seasons. However, the oxygen saturation (Figure 2e) was lower near the Capibaribe estuary mouth. During winter, there is a tongue of lower oxygen saturation from the Capibaribe mouth influence extending northwards along the inner shelf. During summer, the patch of lower oxygen saturation advances to the middle shelf, but it is shorter northwards. These distributions are likely related with the current regime (Schettini et al., 2017Schettini, CAF; Domingues, EC; Truccolo, EC; Oliveira Filho, JC; Mazzini, PLF. 2017. Seasonal variability of water masses and currents at the eastern Brazilian continental shelf (7.5-9° S). Reg Stud Mar Sci. 16: 131-144.; Domingues et al., 2017). Currents are stronger and predominantly northwards during the winter. During the summer the currents are sluggish, with major importance to the tides that allow the cross-shelf transport.

Table 1
Summary of basic statistics (mean, median, standard deviation and 10% and 90% percentiles, n=36) for salinity (g kg-1), temperature (°C), chlorophyll (µg L-1), turbidity (NTU), oxygen saturation (%), DDPH expressed as Carmópolis (µg L-1) and chrysene (µg L-1) equivalents, for near surface water on the Pernambuco continental shelf waters during winter 2013 and summer 2014 (winter/summer).

The summer chlorophyll levels and oxygen saturation in both seasons indicate the influence of the Capibaribe estuary waters on the adjacent shelf, mainly in terms of inorganic nutrients and organic matter contribution. This influence was not observed in the DDPH distribution. Figure 2f presents the spatial distribution of DDPH expressed in chrysene equivalents, nearly identical to the Carmópolis distribution. What catches the eye at first glance are the highest values off Suape in both periods, suggesting that large ship navigation activity in the vicinity of Suape Port is likely the main source of petroleum hydrocarbons. In fact, such contribution has already been reported elsewhere (Lemos et al., 2014Lemos, RTO; Carvalho, PSM; Zanardi-Lamardo, E. 2014. Petroleum hydrocarbons in water from a Brazilian tropical estuary facing industrial and port development. Mar Pollut Bull. 82: 183-188.; Zanardi-Lamardo et al., 2018Zanardi-Lamardo, E; Schettini, CAF; Vieira-Campos, AA; Cabral, CB; Silva, MS. 2018. Intratidal variability and transpor of petroleum aromatic hydrocarbons in an anthropized tropical estuarine system: the Suape estuary (8.4S 35W). Braz J Oceanogr. 66: 47-57.). Interestingly, higher concentrations also occurred at outer shelf stations during winter. A second important pattern, in the summer, is the occurrence of a patch of higher concentrations on the outer shelf in the north. During the summer, the prevalent current is southwards; probably these compounds came from some source other than Suape that was located north of the studied area. Although small differences could be observed among stations, the DDPH concentrations represent a well mixed aquatic system. Concentrations were low when compared to other studies (Bícego et al., 2009Bícego, MC; Zanardi-Lamardo, E; Taniguchi, S; Martins, CC; Silva, DAM; Sasaki, ST; Albergaria-Barbosa, ACR; Paolo, FS; Weber, RR; Montone, RC. 2009. Results from a 15-year study on hydrocarbon concentrations in water and sediment from Admiralty Bay, King George Island, Antarctica. Antarct Sci. 21: 209-220.; Li et al., 2010Li, Y; Zhao, Y; Peng, S; Zhou, Q; Ma, LQ. 2010. Temporal and spatial trends of total petroleum hydrocarbons in the seawater of Bohai Bay, China from 1996 to 2005. Mar Pollut Bull. 60: 238-243; Maciel et al., 2015; Arruda-Santos et al., 2018Arruda-Santos, RH; Schettini, CAF; Yogui, GT; Maciel, DC; Zanardi-Lamardo, E. 2018. Sources and distribution or aromatic hydrocarbons in a tropical marine protected area estuary under influence of sugarcane cultivation. Sci Total Environ. 624: 935-944.) and even compared to the proposed baseline for open water of the Southwest Atlantic (0.31 µg L-1 oil Carmópolis equivalents at Bícego et al., 2002Bícego, MC; Zanardi-Lamardo, E; Taniguchi, S; Weber, RR. 2002. Natural levels of dissolved / dispersed petroleum hydrocarbons in the South West Atlantic. Mar Pollut Bull. 44: 1166-1169.). Based on that, the authors suggest that the median concentration (including both winter and summer) of 0.02 µg L-1 chrysene equivalents or 0.06 Carmópolis oil equivalents be considered as the baseline concentration for non-polluted coastal water for the tropical western Atlantic Ocean margin. A set of data reported prior to possible accidents is rarely available for comparison and / or recovery assessment. Therefore, this information will be very important for upcoming PAH in water studies, mainly those related to the mysterious oil spill that reached the Brazilian coast, primarily along the coast of the Northeast Region.

ACKNOWLEDGMENTS

The authors thank Ernesto C. Domingues and José C. Oliveira Filho for the execution of the oceanographic campaigns; Daniele C. Maciel, Roxanny H.Arruda-Santos, and undergraduate students at OrganoMAR for helping laboratorial analysis. National Council funds EZL for Scientific and Technological Development (CNPq grants nº. 311771/2019-0). The work presented here was funded by the Brazilian Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Project #485964/2011-2, CNPq/ INCT-AmbTropic (#565054/2010-4), and FACEPE/ FAPESP (#APQ79-1.08/11).

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Edited by

Editor: Rubens M. Lopes

Publication Dates

  • Publication in this collection
    11 Mar 2022
  • Date of issue
    2022

History

  • Received
    27 Aug 2021
  • Accepted
    18 Nov 2021
Instituto Oceanográfico da Universidade de São Paulo Praça do Oceanográfico 191, CEP: 05508-120, São Paulo, SP - Brasil, Tel.: (11) 3091-6501 - São Paulo - SP - Brazil
E-mail: diretoria.io@usp.br