HEAVY METAL PARTITIONING IN BOTTOM SEDIMENTS OF PARAÍBA DO SUL RIVER, BRAZIL.

Molisani, M.M.*; Salomão, M.S.M.; Ovalle, A.R.C.

* Laboratório de Ciências Ambientais, Centro de Biociências e Biotecnologia, Universidade Estadual do Norte Fluminense. Av. Alberto Lamêgo, 2000, Horto, Campos dos Goytacazes, Rio de Janeiro, Brazil, CEP: 28.015-620 (mussi@geoq.uff.br).

ABSTRACT

Many works deal with the contamination of Paraíba do Sul River (PSR) by heavy metals. The sequential extraction was used to identify the chemical forms of heavy metals accumulation in bottom (fluvial and inner estuary) and floodplain sediments along the lower PSR. All samples were analyzed for total concentration of heavy metal. Representative samples were selected in areas of lower PSR to perform the sequential extraction that determine the exchangeable, oxidable, reducible and residual phases. The sequential extraction showed that Cd, Zn, Pb and Mn were mainly associated with non-residual phases, while Fe, Cu, Cr and Ni were in residual one. The high participation of mobile phases for Cd, Pb and Zn can be associated with pollution sources in middle basin but with a contribution of local sources. The Mn distribution reflects its geochemical mobility. The heavy metal partitioning among the areas in lower PSR showed differences because some physical and chemical process can control this distribution.

INTRODUCTION

The heavy metal partitioning in sediments can be used to determine its mobility and related with possible sources. The Paraíba do Sul River (PSR) received heavy metals both in natural and antropogenic sources and many works showed high levels of heavy metals in the middle basin (Pfeiffer et al, 1986; Malm, 1988; Azcue, 1987). Some works performed in the lower basin showed a decrease in total and 0.5 N HCl extractable heavy metals concentrations in sediments in relation with middle basin (Carvalho et al, 1999; Molisani et al, 1999), but the effective dilution of the the middle basin was not characterize. The distribution of heavy metals in different phases is an approach that have been used to evaluated relative contribution from different sources.

The aim of this work is determine the total heavy metals (Fe, Mn, Zn, Cr, Cu, Ni, Pb and Cd) contents and its geochemical phases in bottom (fluvial and inner estuary) and floodplain sediments along the lower basin of Paraíba do Sul River. From this dates we could identify the main sources of this elements to the study area.

MATERIAL AND METHODS

The superficial sediments samples were collected, in dry season, in 28 stations (14 fluvial, 9 inner estuary and 5 floodplain) along the lower basin of PSR, between the São Fidélis and Atafona cities. All samples were sieved (< 63 µ) and analized for total concentrations of Fe, Mn, Zn, Cr, Cu, Ni, Pb and Cd. Representative stations (n=8) selected by Principal Component Analysis were submitted to sequencial extraction in order to identify the exchangeable, oxidable (organic matter and sulfides), reducible (iron and manganese oxide/hidroxides) and residual phases (Quevauviller et al, 1984). All elements were determined by ICP – AES.

RESULTS AND DISCUSSION

The total heavy metals concentrations in areas of lower PSR were in Table 1. The total heavy metal values were in according with Molisani et al, 1999, exception for Fe, that were 2 times smaller. This annual variations in Fe values can be associated to changes in particles supply with different Fe concentrations caused by an atypical raining with low values .

The areas sampled in lower PSR had the same heavy metals concentrations, exception Mn (Table 1). The decrease of total concentrations toward the sea in inner estuary, exception for Fe, showed a dilution effects caused by marine sediments that have low heavy metals contents comparing with riverine sediments.

When compared with the middle basin results (Malm et al, 1988), the study area had lower concentrations for all elements, except for Cd, that was 3 times higher. This Cd concentrations were similar to Paraibuna River (Torres, 1992), that is a tributary river of PSR, showed that this river can be a source of the Cd-rich particles for the lower PSR.

Table 1: Mean/Standart desviation of total concentration of heavy metals in bottom sediments of PSR and inner estuary (n=28, Fe %; others µg/g)

	Cd	Cr	Cu	Mn	Ni	Pb	Zn	Fe
River	1.0/0.7	101/9	49/3	974/353	44/4	31/11	165/22	4.6/0.8
Floodplain	1.0/0.4	98/8	51/5	640/194	44/4	31/13	158/15	4.3/0.8
Inner Estuary	0.8/0.3	103/9	51/8	576/288	45/6	28/12	155/25	4.0/1.0

The heavy metal partitioning showed that Fe, Cr, Cu and Ni occured mainly in the residual phase, like in the mineralogical structure, indicating that the distribution of this elements is determined by natural sources that is a environmental quality indicative (Fig. 1).

The other group of heavy metals like Cd, Zn, Pb and Mn the non -residual phases (exchangeable, reducible and oxidable) prevailed upon the residual one (Figure 1). For Cd, Zn and Pb those distribution is a indicative of pollution sources in area. The antropogenic sources can be originate from the middle basin (industrial) but associated to a local input (sewage or agriculture). The Cd distribution was a good indicative of polluted sources, with higher concentration in São Fidélis station (2.4 µg/g) that reduce downstream. When observed the exchangeable Cd concentrations in São Fidélis station, it represented 80% of total Cd; downstream this values decrease to 42 % showed with good agreement the reduce of a Cd polluted source. For Mn, the greater participation in exchangeable and reducible reflects its geochemical mobility.

CONCLUSION

Despite of the decrease of total metal concentration in lower PSR compared with middle basin, some metals like Cd, Pb, Zn presented a dominance of non-residual phases in bottom sediments, suggesting a contribution from pollution sources. The sources of those metals could be associated not only with local contribution, but also originated from middle basin. Fe, Cr, Ni and Cu were mostly associated with the residual phase with low geochemical mobility.

Figure 1: Mean heavy metal distribution between geochemical phases in bottom sediments of lower Paraíba do Sul River (n=8).

Financial Support: FAPERJ & FENORTE

REFERENCE

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