Sepetiba Bay: Contamination or Pollution ?

Campos, A. N.¹ , Moraes, R.B.² , Borges, A.L. N.²

1- Departamento de Geoquímica - e-mail: alexcampos@gbl.com.br, 2- Departamento de Biologia Marinha, Universidade Federal Fluminense, Niterói, Rio de Janeiro, 24020-150, Brazil, Outeiro São João Batista, s/n^o, Centro).

Abstract

The aim of this work was to search for evidences that would verify if the high concentrations of heavy metals in the sediment (contamination) of Sepetiba Bay may result in some biological damage (pollution). The sediment was analysed for heavy metals concentration, toxicity test and benthic community structure, using an approach based on the “Sediment Quality Triad”. The potential biological damage was expressed in ratio-to-reference (RTR) obtained through the difference between the “critical area” of the Sepetiba Bay and the “reference area” (Ilha Grande). The highest concentration obtained for Cd and Zn corresponds to an accumulated RTR of 868 times higher than those measured at the reference area. The survival percentage of Peneaus schimitti exposed for 40 days, resulted in a RTR of 3,4. The differences in the benthic community structure results in a 3,4 RTR value. This result suggests that a high heavy metals concentration in sediments may affect the development of bottom fauna and shrimp fishery, therefore we can state that the Sepetiba Bay is in fact polluted.

Introduction

Very often, the plain verification that there is an elevation on the natural concentration of chemical substances in the ecosystem (contamination) does not seem to be a strong argument for the authorities and the society to decide on investing in environmental control and remediation programs. However, when there are accumulated evidences indicating the existence of biological damage (pollution) (Chapman, 1995), or even economical damage, the arguments become stronger and the chances of those measures being taken increase.

In the Sepetiba Bay case, the elevated levels of heavy metals contamination on the sediment and in the biota have already been known for about 20 years, and are considered to be the main polluters of the bay (Lacerda et. al. 1987, Barcellos and Lacerda, 1994, Carvalho et. al. 1993). Meanwhile, the fishery of the Sepetiba Bay, wich is one of the most important in the state, has been declining in the last years. This decline is communly attributed to the overfishing and the contamination. However no specific studies were carried out to verify if the contamination level implies harm to living resources.

Therefore, this work has as its main purpose to offer the subside to clarify this issue, particularly trying to answer the following question: “does the heavy metals contamination of the Sepetiba Bay sediment induces to any biological damage?”, or merely: “is there contamination or pollution in the Sepetiba Bay”?

The Sepetiba Bay is a semienclosed lagoon, 447 km² in area, located about 60 km West of Rio de Janeiro City (RJ) (figure 1). Its drainage basin (2617 km²) comprises 1,4 million inhabitants and 10 municipalities. Although 20% of the area corresponds to conservation zones and only 9% to urban areas, the industrial activities introduce a major impact. The industrial development, initiated in the 60’s, nowadays concentrates itself in 4 industrial districts with about 400 industries, mainly siderurgical, metallurgical and chemical; considered to be the leading responsibles for the heavy metals emission into the bay (Barcellos and Lacerda, 1994).

Methods

In the search for evidences of biological damage caused by the heavy metals contamination, the sediment toxicity of the most contaminated area, or “critical area” (Saco do Engenho) was estimated on what is refered to the potential of damaging effects on the shrimp, considering that the fishing resource is the main activity in the region . Based on approach to marine pollution assessment refered to as the Sediment Quality Triad (Chapman, 1991), the sediment of the “critical area” was compared to the sediment of the “reference area”, where the contamination is considered to be low (Baía de Ilha Grande - Sítio Forte) (figure 1). Superficial sediment samples were collected (1994-1996) on two stations of the critical area and on one station of the reference area (figure 1). The following components were measured in all of them: 1) Benthic community structure (Shannon-Weiner diversity index, Pielou evenness index, species richness, numerical dominance, total abundance ); 2) Evaluation of the Peneaus schimitti post-larvae survival in 40 days of direct exposure to the sediment (Moraes et.al.,1999); and 3) Concentration analysis of the metals weakly bound to the sediment (HCl 0,1N, 16h – atomic absorption Varian AA1475). The toxic potential of the “critical area” was expressed in ratio-to-reference values, (RTR), estimated to each component, through the division of values obtained in the “critical area” by the values obtained in the reference area.

Results and Discussion

The elevated values of RTR to Cd (633) and Zn (4573) were already expected due to the proximity of the rejects from a metal factory that produces Cd and Zn (Barcellos and Lacerda, 1994). The total sum of the RTR value of all metal normalized by the values of the reference area, denominated aggregated ratio-to-reference (ART) indicated that the sediment of the critical area showed a degree of contamination around 868 times bigger then the observed in the reference area (table 1). The P. schimitti survival of the critical area was significantly smaller than in the reference area (p< 0,05), dimensioned in 3,4 RTR (table 1). In what refers to the structure of the benthic community, the ART obtained for the critical area (3,4) suggests that this is more degraded than the reference area (table 1). The main responsibles for the difference were: i) the lack of species richness (TR=3,3), ii) the low total abundance (TR = 7,0), and iii) the high percentage of polychaetes (TR = 7,4), in wich the dominance of Capitela capitata is also a strong indicator of the elevated contamination (Chapman, 1996; Weisberg et. al., 1997).

The use of a critical area was important to identify the existence of a biological damage. Although the dimension of this damage as well as the responsible contaminants, can only be better identified through more specific studies, they can even be smaller than imagined. In fact, the values of RTR in the nearer region to the critical area (Ilha da Madeira), could be considerably lower for metal concentration (ATR = 262) and for the structure of the benthic fauna (ATR = 1,1).

The employment of the triad in more detailed studies is not yet possible in Brazil, because the sediment toxicity tests, with native organisms, are not yet standardized. So this kind of preliminary approach, although being far from showing a cause-and-effect relationship, allows, based on the precautionary principle (Sindermann, 1997), the fit justification of the remediation actions

Conclusions

Although those results do not confirm the existence of cause-and-effect relation, they strongly indicate that the elevated contamination of the sediment of the Sepetiba Bay may induce to a biological damage, which means it is in fact polluted.

This simple scientific indicator justifies the implementation of a more detailed study program, which would to measure the extension of the impact, as well as its remediation strategies.

References

Barcellos C,. Lacerda L. D.(1994) Environmental Monitoring and Assessment. 29:183-199.

Carvalho CEV, Lacerda LD, Gomes MP. (1993).. Acta Limnologica. Brasiliense 6: 222-229.

Chapman PM. (1991). Environ. Toxicol. Chem. 10: 407-424.

Chapman PM. (1995).. Mar. Pollut. Bull. 31 (4-14): 167-177.

Chapman, PM, Paine MD, Arthur AD, Taylor LA. (1996). Mar. Pollut. Bull. 32 (1): 47-64.

Lacerda LD, Pfeiffer WC, Fiszman M. (1987). The Sci. of Total Environ. 65:163-173.

Moraes RBC, Pfeiffer, WC, Guimarães JRD, Borges ALN, Campos, AN (2000) Environ. Toxicol. Chem. (In press).

Sindermann CJ (1997) Marine Pollution Bulletin, v.34, n.4 218-221p. 1997.

Weisberg, S. B., Dauer, D. M., Schaffner, L. C., Diaz, R. J. & Frithsen, L. B. (1997). Estuaries 20(1):149-158.

Figure 1 – Map of Sepetiba Bay and Ilha Grande Bay showing sampling stations in critical area (Saco do Engenho) and reference area (Síto Forte).

Table 1 – Ratio-to-reference (RTR) of Triad components for

critical area (Saco do Engenho – Baía de Sepetiba) and

reference area (Sítio Forte – Baía de Ilha Grande).

Heavy Metals Concentration ^a
	Reference area		Critical area
	Value	RTR	Value	RTR
Cd	0,003	1	1,90	633
Cr	0,26	1	0,25	1,0
Cu	0,12	1	0,14	1,2
Ni	0,85	1	1,57	1,9
Zn	1,1	1	5030	4573
Pb	0,25	1	0,40	1,6
	ART	1	ART	868
Benthic Community Structure
1/Richness	0,26	1	0,86	3,31
1/Diversity	0,57	1	1,12	1,96
1/Abundance	0,01	1	0,07	7
Dominance	0,4	1	0,35	0,88
% molluscs	0,57	1	0,04	0,07
% polychaetes	0,13	1	0,96	7,38
	ART	1	ART	3,43
Toxicity Test ^b
Survival	85%(1)	1	25%(3)	3,4

Note: ^a – ppm dry weight; ^b – percentage of survival shrimps after 40 days with a water feedback system and a sediment layer of 2 cm (n=60).