DISTRIBUTION OF TRACE, MINOR AND MAJOR ELEMENTS IN SEDIMENTS AROUND THE PETROLEUM PRODUCTION PLATFORMS,

CAMPOS BASIN – RIO DE JANEIRO, BRAZIL.

Alvaro Ramon Coelho Ovalle⁽¹⁾, Carlos Eduardo Veiga de Carvalho⁽¹⁾,

Maria Eulália Carneiro⁽²⁾, Luiz Drude de Lacerda⁽³⁾ & Carlos Eduardo Rezende⁽¹⁾

⁽¹⁾Universidade Estadual do Norte Fluminense, LCA–CBB, Av. Alberto Lamego, 2000, Campos dos Goytacazes, 28.015–620, RJ; ⁽²⁾Centro de Pesquisas Leopoldo A. Migues de Mello – PETROBRAS/CENPES, RJ; ⁽³⁾Universidade Federal Fluminense – IQ, DG, Niterói, RJ. (Email:ramon@cbb.uenf.br).

ABSTRACT

The Brazilian Petroleum Company (PETROBRAS) have been developing a monitoring program using the bottom sediments. Sediment samples (0–2 cm) were collected during winter and summer in two Production Platforms (Pampo and Pargo) with a radiate transect (250, 500, 1,000 and 3,000 m). Total element concentrations intervals were: 1) Pampo: Al=5.29-18,4mg/g; Fe=4.39-8.97mg/g; Ba=76.2-402µg/g; Cu=3.92-9.48µg/g; Cr=9.85-20.6µg/g; Zn=11.6-84.6µg/g; Ni=5.11-14.2µg/g; V=13.3-22.5µg/g; Pb=1.57-10.9µg/g; and Cd<0,10-0.27µg/g; 2) Pargo: Al=4.32-11.1mg/g; Fe=4.43-9.18mg/g; Ba=70.4-269µg/g; Cu=1.86-7.06µg/g; Cr=9.36-20.4µg/g; Zn=9.56-50.1µg/g; Ni=2.27-9.51µg/g; V=10.6-23.6µg/g; Pb=3.50-11.9µg/g; and Cd<0,10-0.21µg/g. There is no difference between sampling periods, excepted for Al and Ni in Pargo. PCA identified different control factors (percentage of variance) controlling heavy metals distribution nearby the two platforms: 1) Pampo: Spatial distribution was influenced by the distance from the effluent discharge (38%); depositional direction (16%) and carbonate influence (12%); 2) Pargo: Spatial distribution was influenced by continental source to Cr, Fe, Ni and Al (36%); the distance from the effluent discharge (19%); silt and clay sediment content (13%).

INTRODUCTION

During last decades oil production in continental shelves have received increasing attention concerning potential impacts in the marine environment. As a result of this activity hydrocarbon, heavy metals and nutrients can be liberated in coastal waters, affecting mainly sediment compartment and associated benthic community due to its low mobility. Several studies have considered that contaminant distribution, bottom sediments texture and benthic community structure are important aspects in environmental impact assessment of this activity (Kennicutt II, 1995; Chapman et al, 1991). The Rio de Janeiro State contributes with 96% of the actual Brazilian oil reserves and Campos Basin is the major production marine area, corresponding at 60% of the total national production. The Brazilian Petroleum Company have conducted an Environmental Monitoring Program during the last 3 years, and the objective of this work is to evaluate the heavy metals distribution in bottom sediments nearby two production platform in Campos Basin, RJ, Brazil.

IA 1B

Figure 1: Pargo and Pampo Production Platfoms (1A) and their Location in Brazil and Rio de Janeiro State (1B).

MATERIAL & METHODS

Pargo and Pampo production platforms are localized at 22^o15’26”S, 40^o19’51” W and 22^o48’32” S, 40^o 46’ 41” W, respectively (Fig.1). Two stations 3,000m distant from production area were used as reference values. Surface sediment samples (0–2 cm) were collected using a box grab during winter and summer in both platforms with a radiate transect (250, 500, 1,000 and 3,000 m). At the laboratory, samples were sieved (<2.0 mm) and dried (40^oC, ~72h) and stored in polyethylene vials. Total element concentrations of Al, Fe, Mn, Cu, Cr, Ba, Zn, Ni, V, Pb and Cd were determined by ICP–AES (Varian Liberty Series II Model), after acidic digestion of samples (1.0g of dried sediment; HF+NHO₃ conc; 10mL+ 5mL) in teflon bombs at 110^oC for 18h, followed by dissolution of the digested sediment with 20 mL of HNO₃ 0.5N. All samples were analyzed in duplicate (CV<10%), and simultaneously 10 sub-sample of a reference standard (NIST, 1646a) were analyzed with a good confidence limits (>95%).

RESULTS & DISCUSSION

No parametric statistic test (Kruskal-Wallis) showed no difference between distances and, winter and summer sampling results, then they were treated as a single data set. Mean value and range of variation of heavy metals analyzed for each platform are presented in Table 1. Aluminum and Cu were significantly higher in Pampo platform (P<0,05), together with organic carbon, carbonates and silt + clay fraction (not shown). Comparing with other areas of Rio de Janeiro State coastal sediments (Tab.1), only Ba showed values up to 400 µg.g^-1 in Pampo, probably associated with a preferential sediment deposition area originated from drilling activities in the oil platforms. Barite is a high density, low solubility sulfate, that tends to present high residence time platform sediments (Hartley, 1996). However those values are still incipient

compared with data from Gulf of Mexico (Kennicutt II, 1995).

Enrichment Factors were calculated using reference stations (X_s/X_r; X_s is mean value of samples at same distance from the platforms, and X_r mean value of samples from reference stations). For Pargo platform EF revealed an two times increase of Cu and Ni between 250 and 1000m, and three times of Zn in samples 250m distant from platform. Other parameters presented an equivalent values compared with reference stations. For Pampo platform Ba, Zn and Pb presented an two fold enrichment in all distances sampled compared. Those results may be reflecting the high content of silty+clay fraction in the sediments near Pampo platform, more than different deposition rates or intensities of exploration activities between both platforms.

Principal Component Analysis was performed to produce an hierarchic ordination of the main control factors of metal distribution in bottom sediments. In the Pampo platform Factor I (38% of variance explanation) identified the distance from the platform as the most important control factor of metal distribution, with high values of Fe, Al, Cr, Ni, Ba, Cu and Zn nearby the platform. Factor II (16% of variance explanation) was related with preferential SW deposition of Al, Ba, Fe and Cr discharged from the platform. In the Pargo platform Factor I (36% of variance explanation) pointed out an enrichment of Cr, Fe, Mn, Ni and Al in the stations far from the platform. This inverse pattern compared with Pampo platform, suggests an additional source other than discharge from the platform. The localization of Pampo platform, at the northeast portion of Campos Basin (Fig. 1A), indicates the possibility of a coastal transport of continental materials by a inner branch of the Brazil Current . The potencial source of those materials can be the Paraíba do Sul River (Fig.1B), that discharges in the coastal zone 1.6x10⁶ ton MPS/ year, mostly (>80%) in the silt+clay fraction (Figueiredo,1999). The Factor II (19% of variance explanation) related with high values of Cu, Zn and Ba at the stations close to the platform, influenced by its discharges.

CONCLUSIONS

Elements concentrations in bottom sediments influenced by offshore platforms were in the same magnitude of other coastal areas in a regional scale, except for Ba. Fe, Al, Cr, Ni, Ba, Cu and Zn presented higher values nearby Pampo platform, whereas in Pargo area the results suggested that a continental source could be considered other than discharges from platform.

Despite of reduced sampling, the results indicated the necessity of establish the regional background of element concentration in bottom sediments of Campos Basin.

ACKNOWLEDGEMENTS

This work was mainly supported by PETROBRAS (Brazilian Petroleum Company; Contract BioRio 960020). The authors would like to thank the support in the field and laboratory activities to the technician of the Laboratório de Ciências Ambientais Arizolli A. R. Gobo. CER and ARCO received a grant from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and UENF – FENORTE.

Elements	Rio de Janeiro State	Pargo Platform	Pampo Platform
Al (mg.g^-1)	21.1 11.2 – 31.4	6.79 4.32 – 11.1	10.6 5.29 – 18.4
Fe (mg.g^-1)	9.86 6.10 – 16.4	6.92 4.43 – 9.18	5.81 4.39 – 8.97
Mn (µg.g^-1)	168 140 – 217	88.0 47.1 – 104	73.8 50.3 – 132
Ba (µg.g^-1)	193 103 – 242	165 70.4 – 269	188 76.2 – 402
Cr (µg.g^-1)	24.4 5.74 – 47.2	15.0 9.36 – 20.4	14.0 9.85 – 20.6
Cu (µg.g^-1)	7.29 0.30 – 11.2	3.38 1.86 – 7.06	6.30 3.92 – 9.48
Ni (µg.g^-1)	12.2 2.90 – 31.4	6.19 2.27 – 9.51	7.70 5.11 – 14.2
Pb (µg.g^-1)	15.4 0.40 – 34.1	5.54 3.50 – 11.9	6.70 1.57 – 10.9
V (µg.g^-1)	28.4 6.13 – 51.5	15.7 10.6 – 23.6	17.0 13.3 – 22.5
Zn (µg.g^-1)	32.4 22.1 – 50.1	24.5 9.56 – 50.1	28.9 11.6 – 84.6
Cd (µg.g^-1)	0.52 < 0.10 – 2.61	< 0.10 < 0.10 – 0.21	< 0.10 < 0.10 – 0.27

Table 1: Mean and range of variation of elements concentrations in bottom sediments influenced by offshore platforms in Campos Basin (Pampo and Pargo) and others coastal areas of Rio de Janeiro State.

REFERENCES

Chapman PM, Power EA, Dexter RN, Andersen HB (1991), Environmental Toxicology and Chemistry, 10:407-424.

Figueiredo, RO (1999) Transporte de Carbono e Nitrogênio no Baixo Paraíba do Sul: Fluxos e Processos. PhD Thesis, UENF, Brasil, 177p.

Hartley, J.P. (1996), Marine Pollution Bulletin, 32(10): 727 – 733.

Kennicutt II, MG (1995), Gulf of Mexico Offshore Operation Monitoring Experiment, Final Report (Phase 1: Sublethal responses to contaminant exposure).