HEAVY METAL CONCENTRATIONS IN FISH FROM THE LOWER PORTION OF PARAIBA DO SUL RIVER, RJ, BRAZIL.

Maria E. F. Totti (Laboratório de Estudo do Espaço Antrópico, Universidade Esetadual do Norte Fluminense); Cristina M^a M. Souza & Paulo Pedrosa (Laboratório de Ciências Ambientais, Universidade Estadual do Norte Fluminense, CEP: 28015-620, RJ, Brazil, cristal@cbb.uenf.br).

Abstract

Fe, Mn, Cu, Cr, Zn, Cd and Hg were measured in edible parts of 4 non carnivorous fish species (Prochilodus scrofa, Mugil platanus, Tilapia rendalli, Geophagus brasiliensis) and 1 carnivorous specie (Hoplias malabaricus), in lower portion of Paraiba do Sul river, RJ, Brazil. The samples were obtained from local markets and or directly from local fishermen. In general all metals showed lower concentrations values than that permissible in Brazilian legislation. The exception were Cr for all samples (until 30 times above) and Hg in Hoplias mallabaricus (1.1 times above). Cr values found in this study suggest a point source contamination in the area, probably a tanning, situated in neighborhood. Mercury values found probably can be related with non point sources occurred in the past such as the utilization of organomercurial fungicides and gold mining activities.

Introduction

The role of heavy metals in aquatic organisms has been drawn attention, since the events of mercury and cadmium poisoning through seafood and fish in Japan. Only after this, has the accent been shifted towards investigations dealing with the influences of heavy metals on the metabolism of aquatic organisms and the ability of the latter to accumulate both essential and non-essential metals (Förstner & Wittmann, 1984).

Elements like copper, zinc, iron and cobalt have important biochemical functions in the organism, participating as ligands in complex enzymatic compounds. Therefore, their enrichment does not exceed the level which allows the enzyme system to function without interference (Lowman et al., 1971). This means that the concentrations of essential trace elements are generally higher in the organism than in water. On the other side, if the heavy metal concentration at the source of supply is too high, the homeostatic mechanisms cease to function and the essential heavy metals act in either acutely or chronically toxic manner (Phillips et al., 1982). Thus in the event of a resulting extended bioaccumulation of heavy metals the organism may be damaged (Balkas et al., 1982; Young et al., 1981).

This work investigate the heavy metal concentrations (Fe, Mn, Cr, Cd, Zn and Hg) in edible parts of fish to evaluate the quality of this important protein source to local population.

Methodology

The Paraiba do Sul river is the major freshwater supply to the south-eastern Brazilian coast. It is a medium sized river 1145 km long and also drains (55400 km²) an important industrial park and the second largest sugar cane production area of the country (Carvalho et al, 1999). Some works have been related heavy metals contamination degrees in the area (Torres, 1992; Malm, 1986). Six surveys were carried out in lower portion of the river, Campos dos Goytacazes city (21⁰ 45’23” S, 41⁰ 19’49” W), from April, 1997 to October, 1997. The 29 samples considered in this study are representatives of the 5 species (table 1) caught and commercialized in the area.

Table 1: Fish species considered in this study.

Fish		Food habits
Scientific name	Common name
Prochilodus scrofa	Xingó	I
Mugil platanus	Tainha	D, H
Tilapia rendalli	Tilapia	O
Geophagus brasiliensis	Acará	O
Hoplias malabaricus	Traíra	C

C= carnivorous ; D= detritivorous ; I= iliofagous ; O= omnivorous

These samples were obtained from local markets and or directly from local fishermen. Each fish was weighted and its length measured at the laboratory. The edible parts were separated and frozen until analysis. After lyophilized, the humidity weight was calculated.

The digestion procedure utilized for total metals determination was performed using 1g ± 0.001g of dried samples. After calcination at 450 ⁰C during 24hours, the samples were placed in teflon bomb with an acid mixture (HNO₃/H₂O₂, 3:1) in a oven (110⁰C) during 12h (Krause et al., 1995). For mercury, the samples were wet digested using a oxidant mixture (H₂SO₄/HNO₃, 1:1) and KMnO₄ 5% (Bastos et al., 1998). To certify the quality control, a reference fish sample was analyzed (Standard reference material DORM 1- NIST), in the same way that a internal fresh fish sample supplied by Biophysics Institute in Rio de Janeiro (Radioisotope Laboratory) was performed. The results showed higher than 80% recovery for all metals with variation coefficients for analytical replicates bellow than 10%. All metal determinations was performed by ICP - AES (Varian Liberty Series II), using a VGA accessory for Hg.

Results And Discussion

Table 2 presents the average total concentration of heavy metals and its respective concentration ranges in all samples analyzed in this study. The ranges for all elements are: Fe= 0.2 – 18 mg.g ^-1 wet wt; Mn= 0.24 – 0.80mg.g ^-1 wet wt; Cd= <DL – 0.23mg.g ^-1 wet wt; Zn= 2.4 – 5.8mg.g ^-1 wet wt; Cr= 0.2 – 2.8mg.g ^-1 wet wt.

In general all metals showed lower concentrations values than that permissible in Brazilian legislation. The exception were Cr for all samples (until 30 times above) and Hg in Hoplias mallabaricus (1.1 times above).

Table 2: Heavy metals in muscle tissues of fresh fish (mg.g ^-1 wet wt). Average, and concentration ranges.

Fish species	Metals (mg.g ^-1 w wt)
	Fe	Mn	Cr	Cd	Zn	Hg
	----	----	0.1*	1.0*	50*	0.5*
Prochilodus scrofa n = 6	8.1 5.1-10.5	0.53 0.30-0.70	0.31 0.15-0.52	<DL	3.5 3.2-4.1	0.09 0.05-0.14
Mugil platanus n = 5	18.4 8.9-38.3	0.80 0.27-1.6	0.23 0.17-0.30	<DL	4.1 3.8-4.8	0.11 0.05-0.16
Tilapia rendalli n = 6	15.2 1.5-48.5	0.34 0.08-0.62	2.8 0.23-10.4	<DL	3.7 3.2-3.9	0.09 0.06-0.15
Geophagus brasiliensis n = 6	0.2 0.12-0.25	0.39 0.11-0.78	0.20 0.12-0.25	<DL-0.01	2.4 4.1-5.2	0.27 0.25-0.29
Hoplias malabaricus n = 6	0.27 0.25-0.29	0.24 0.16-0.34	0.27 0.25-0.29	<DL-0.23	5.8 4.2-6.7	0.53 0.49-0.57

w wt = wet weight <DL= lower than detection limit *safety limit for human consumption in Brazilian legislation (Ministério da Saúde, 1975).

Chromium concentrations (0.12 - 10.4 mg.g ^-1 wet wt) in all analyzed samples were higher than that established for the Brazilian legislation. In comparison with other works these results are upper than that found by Fernandes et al. (1994) (0.08 mg.g ^-1 wet wt) realized in a tropical lake without contamination, considering similar species like Geophagus sp and Tilapia sp. On the other hand, study realized in an area with a knowledge chromium contamination, Jordão et al. (1997) found high concentrations (0.2 - 1.6 mg.g ^-1 wet wt) in different fish species and sediments (about 80mg.g ^-1 ). Similar results in suspended particulate matter (81± 42 mg.g ^-1 ) were found by Carvalho et al. (1999) in lower portion of Paraiba do Sul river, suggesting chromium remobilization processes from sediment to water. The probably source in the area is a tanning, situated in neighborhood.

Mercury concentration ranges showed higher values for carnivorous (0.49 - 0.57 mg.g ^-1 wet wt) than the other fish species (0.05 - 0.29 mg.g ^-1 wet wt). This behavior is commonly described in the literature, since this heavy metal typically undergoes biomagnification through food chains, presenting the highest concentrations in high trophic level fish (Huckabee et al., 1979, Lacerda & Salomons, 1998). Besides, non point sources occurred in the past such as utilization of organomercurial fungicides (Câmara, 1986) and gold mining activities (Souza, 1994), probably were responsible to metal cycling inside the system.

The concentrations of Fe, Mn, Cd, Zn, and Cr compared with Azcue (1987) in a work developed in medium portion of Paraiba do Sul River (Fe= 8 – 77mg.g ^-1 ; Mn= 1.6 – 5.4mg.g ^-1 ; Cd= <DL – 0.11mg.g ^-1 ; Zn= 11 – 21mg.g ^-1; Cr= <DL – 0.84 mg.g ^-1) showed values lower than that, exceptions for Cd (almost 10 times above) and Cr (5 times above).

In conclusion, the Cr values found in this study suggest a point source contamination in the area, since another research in medium portion described by Azcue did not show that. Since these species are considered largely caught and consumed by the local population, it should be take with care, since the hexavalent chromium may induce carcinogenic effects. The high mercury value is restricted to carnivorous specie (Hoplias malabaricus) suggesting organification processes occurring in the area.

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