HEAVY METALS DISTRIBUTION IN THE ESTUARINE ECOSYSTEM OF BAHIA BLANCA, ARGENTINA.

 

L.Ferrer, S.Andrade, R.Asteasuain, J.Marcovecchio (Instituto Argentino de Oceanografía, Florida 4000, C.C. 804, 8000 Bahía Blanca, Argentina) & A.Pucci  (Centro Nacional Patagónico, Bv. Brown s/n, 9120 Puerto Madryn, Argentina)

 

 

INTRODUCTION

 

The Bahía Blanca estuary is located between 38°45’ - 39°40’ S, and 61°45’ -  62°30’ W, at the southeast coast of Buenos Aires province, in Argentina. It has elongated shape with a lenght of 80 Km, and is characterized by the presencie of various channels, fine sand and silt-clay sediments. Tidal oscillations of 4m and predominant northwestern wnds create strong tidal currents which facilitate water mixture, leading to a uniform vertical distribution of the main oceanographic parameters. At low tide this estuary encompasses an area of 400 Km2, and at high tide the total area is nearly 1300 Km2. Bahía Blanca is an estuarine environment with a very particular behavior, which includes a relatively small input of inland water, and with several marginal areas which seasonally function as hypersaline ones (Freije et al., 1981).

At the northern boundaries of the estuary various ports, towns (with a population exceeding 350.000 inhabitants) and industries are located, and several streams and channels discharge into the area. Oil refineries and terminals, petrochemical industries, meat factories, leather plants, fish factories, textile plants, wool washing plants, silos and cereal mills discharge their processing residues into the streams or directly into the estuary.  This area is extensively used by fishing boats, oil tankers and cargo vessels and therefore requires regular dredging.

The present study includes information on the occurrence and distribution of cadmium, lead and chromium in surface sediments, finest grain size fraction of sediments (<63µm), dissolved and suspended particulate matter, as well as in several estuarine organisms.

 

MATERIALS AND METHODS

 

The area under study and location of sampling stations are shown in Figure 1. The samples were taken from six sampling stations, monthly frequency, during 1998.

Surface water samples (0,5-1 m) were collected with a Van Dorn oceanografic bottle on deck from a position in the prow which minimized contamination from the ship. Samples of  water were filtered through Millipore HA filters (0,45 µm pore size) for the determination of suspended and dissolved metals. Before use, the filters were soaked overnight in dilute HCL and stored in redestilled water. The filtered samples were acidifed using 3 ml of HNO3. All fractions were frozen until analysis.

Surface sediments were obtained with a sledge and were stored in a freezer at -20°C until their analytical treatment in the laboratory. These samples were oven at 45±5°C up to constant weight, and then subsamples were sifted, and the fraction lower than 63 µm was  removed.

Organisms samples were taken at station 6 (internal station). Phytoplankton samples were collected using a net of 50µm size mesh. Samples were filtered through Millipore HA filters (0,45 µm pore size) for the determination of heavy metals. Samples of estuarine crab Chasmagnathus granulata were collected in the intertidal zone. Organisms were disected and soft tissues and carapace were removed. These samples were oven at 45±5°C up to constant weight and subsequently homogenized.

The disolved metals were simultaneously extracted from water samples by chelation with ammonium pyrrolidine-dithiocarbamato (APDC) followed by extraction into methil iso-butil ketone (MIBK) according to the modification of the method described by Koirtyohann & Wen (1973).

Samples of sediments, finest grain size fraction of sediments, suspended particulate matter and organisms were digested in a mixture of concentrated nitric and perchloric acids (3:1), according to the method descrbed by Dalziel & Baker (1983) modified by Marcovecchio et al. (1988).

A Perkin-Elmer Model 2380 atomic absorption spectrophotometer with air/acetylene flame was utilized to determine heavy metal concentrations (Cd, Pb and Cr). Analitical grade reagents were used to built up the corresponding blanks and calibration curves, and the analytical quality (AQ) was tested against reference materials, provided by The National Institute for Environmental Studies (NIES) from Tsukuba (Japan).

  


Figure 1. Location of sampling stations in the southern area of Bahía Blanca estuary.

 


RESULTS AND DISCUSSION

The distribution of cadmium, lead and chromium in surface sediments, finest grain size fraction of sediments (<63µm), dissolved and suspended particulate matter, are showed in the Figures 2, 3 and 4, respectively. The heavy metal concentrations in phytoplancton and estuarine crab are showed in Table 1.

No dissolved chromium levels were detected in the study area. Moreover, dissolved Cd and Pb, have presented distributions with different range of concentration values but with similar trends. Thus cadmium contents have varied between 0.29 and 0.69 µg/L; those of lead did between 1.96 and 3.51 µg/L; highest values for these metals are found in the station #4 (“oil terminal”). Cadmium and lead levels of the present study are in the same order of magnitude than those found previously in the same area, ten years ago (Pucci, 1988).

The concentrations of particulate trace metals (Cd, Cr and Pb) were measured. Cadmium contents have varied between 3.32 and 5.88 µg/g, dry wt.; those of chromium ranged between 5.47 and 8.91 µg/g, dry wt.; while those of lead did between 30.29 and 55.0 µg/g, dry wt. The values of all trace metals as reported in the present paper have clearly agreed with those presented as natural background ones for different regions all over the world by several authors (i.e., Harper, 1991; Lewis et al.,1992).

The studied metals in surface sediments have presented distribution with diferent range of concentrations but with similar trends; highest values for these metals are found in the station #3 (“White harbour”) and the minimum at station 1 (external). Thus, cadmium concentrations have varied between 0.60 and 1.64 µg/g, dry wt.; those of chromium ranged between 4.14 and 8.93 µg/g, dry wt.; while those of lead did between 8.67 and 18.33 µg/g, dry wt.

Trace metals distribution in finest grain size fraction of sediments not present great variations, especially cadmium and chromium levels. Cadmium contents ranged between 2.01 and 2.34 µg/g, dry wt.; those of chromium have varied between 10.87 and 11.69 µg/g, dry wt.; while those of lead did between 24.35 and 36.08 µg/g, dry wt. Chromium values reported in the present study agree with those reported from non industrial areas, while Cd and Pb content agree with those reported from industrial areas (Lacerda et al., 1988).

 


 

 


Figure 2. Cadmium distribution in differents fractions: dissolved (µg/L); SPM, surface sediments and fine grain size fraction (µg/g, dry wt.).

 

 


 


Figure 3. Chromium distribution in differents fractions: SPM, surface sediments and fine grain size fraction (µg/g, dry wt.).

 


 


Figure 4. Lead distribution in differents fractions: dissolved (µg/L); SPM, surface sediments and fine grain size fraction (µg/g, dry wt.).

 

Table 1. Heavy metal concentrations in phytoplancton samples and tissues of estuarine crab (wide carapace: 25-30 mm), expressed in µg/g, dry wt. N.d.=non detectable.

 

 

Cd

Cr

Pb

Phytoplancton

n=12

0.81

8.22

11.14

Estuarine crabs

 

n=23

Soft tissue

 

0.96

0.95

n.d.

Carapace

 

5.15

0.78

3.06

 

 

The process of transference of both essential and non-essential metals to estuarine organisms has been observed in Bahía Blanca. Metal contents in phytoplankton samples were close to 1000 times higher than those recorded for the neighbouring estuarine water, which has indicated the occurrence of an accumulation process. This fact is extremely important, keeping in mind phytoplankton is the basis of the corresponding trophic web.

Table 1 shows Cd and Pb concentrations in crab carapaces, possible detoxification way during the moult time. The occurrence of both cadmium and lead in samples of phytoplankton and crabs (Chasmagnathus granulata) was significant, considering they are non essential metals.

 

 

Acknowledgements: This paper have information belongs to Doctoral Thesis of Lic.S.Andrade and Lic.L.Ferrer, to be presented at Universidad Nacional del Sur (Bahía Blanca, Argentina).

 

 

REFERENCES

 

DALZIEL, J. & C. BAKER (1983). FAO, Doc. Tecn. Pesca, 212: 15-22.

FREIJE H., R. ASTEASUAIN, A.SCHMIDT & J.ZAVATTI (1981). Contr. Cient. IADO n°57, 20pp.

HARPER, D.J. (1991). Marine Chemistry, 33:131-143.

KOIRTYOHANN, S.R. & J. N. WEN, (1973). Analytical Chemistry, 45 (12): 1986-1989.

LACERDA, L.D., C.M.M.SOUZA  &  M.H.D.PESTANA,   (1988). In : “Metals in coastal environments of Latin America”, U.Seeliger, L.D.Lacerda & S.R.Patchineelam (eds), Springer-Verlag, Heidelberg, pp.86-99.

LEWIS B.L.& W.M.LANDING (1992). Marine Chemistry, 40:105-141.

MARCOVECCHIO, J. E., V.J.MORENO & A.PEREZ (1988). Sci.Tot.Environ., 75:181-190.

PUCCI, A.E., (1988). In: Metals in coastal environments of Latin America. U.Seeliger, L.D. de Lacerda & S.R. Patchineelam (Eds.); pp 9-15.