Fe, Mn, Ni AND Cd GEOCHEMICAL PARTITIONING IN
SEDIMENTS FROM THE NEGRO RIVER, ARGENTINA
M.Abrameto, M.I.Gil (FUNDAPA, Viedma, Río Negro, Argentina), R.H.Freije
(Universidad Nacional del Sur, Av.Alem 1251, 8000 Bahía Blanca, Argentina) &
J.Marcovecchio (Instituto Argentino de Oceanografía, Florida 4000
– C.C. 804, 8000 Bahía Blanca, Argentina)
ABSTRACT
The
Negro River is one of the most important in Argentina not only for its length
and high flow but also because it cross away several provinces (i.e.,
Neuquén, La Pampa, Río Negro, Buenos Aires) with intense anthropic activities
such as agriculture, mining, oil extraction, etc. Many cities are located at
the riverside, and usually it is the drink water source for most of them.
A research programme directed to evaluate the Negro
River water quality was started in 1996, including studies on physico-chemical
parameters, heavy metals, sediments, etc. The present paper includes data on
the geochemical partitioning of several trace metals (iron, manganese, nickel
and cadmium) in the sediments obtained in nine (9) sampling stations at the
considered river.
Heavy
metal concentrations were determined following the method of Marcovecchio et
al.(1988) while geochemical partitioning was quantified according to Jackson
et al. (1996).
Each of the analyzed metals
has shown an own geochemical partitioning behavior, but in all the cases
highest percentage of metal was included in the Fraction 5 (residual
fraction) which reflect metal content in the corresponding crystalline
mineral net. Iron has presented most of its concentration related to Fraction 3
(metals linked to Fe and Mn oxides) and Fraction 4 (metals linked to
organic matter and sulfides). By the way, highest percentages of manganese
have been recorded in Fraction 3, while those of nickel were determined in
Fraction 1 (exchangeable metals). Finally, in the case of cadmium,
highest percentages have been obtained in Fraction 1 and Fraction 2 (metals
linked to carbonates).
Obtained
results are discussed with the framework of environmental quality of the river,
and taking into account potential metal sources as well as related ecological
processes such as bioaccumulation or transfer ones.
INTRODUCTION
Different
antropogenic impacts as well as pollutant input have increased the amount of
substances transported through fluvial systems until a depositional area.
Fluvial sediments and suspended particulate matter have demonstrated to be the
most important heavy metal carriers in hydrological systems, and better pollution
indicators than the corresponding dissolved forms (Gaiero et al., 1997).
These kind of pollutants can be affected by bio-geochemical processes which
could modify not only their physico-chemical or environmental properties but
also their bioavailability, changing consequently the corresponding
environmental risk. So, the study of the geochemical fractions associated to
sediments are extremely important in order to understand metals mobility and
potentiality to be incorporated by biological systems (Marcovecchio et al.,
1998).
The
present paper deals with the geochemical partitioning of several trace metals
(iron, manganese, nickel and cadmium) in the sediments obtained in nine (9)
sampling stations at the Negro River, in Argentina.
MATERIALS AND METHODS
The
Negro River starts in the area of the Andes mountains, and flows with an
west-east direction, crossing close to 720 km in the northern Patagonia up to
the outlet in the Southwestern Atlantic Ocean (Figure 1). This
river has an annual average flow of 866.05 m3.sec-1, and
its corresponding drainage basin is close to 8000 km2. Nine (9)
sampling stations were located in this fluvial system, and sediment samples
were obtained and carefully stored in plastic bags until pre-treatment in the
laboratory. Then, samples of total sediment and <63µ sediment fraction were
freeze-dried, and kept in acid-washed glass bottles until analytical treatment.
Total
metal contents were analyzed following the method described by Marcovecchio et
al. (1988), while a sequential extraction protocol were used to determine
the corresponding geochemical partitioning of metals in the analyzed sediments,
according with Jackson et al. (1996). This last technique allows to get
information on percentage of exchangeable metals (Fraction 1), metals
linked to carbonates (Fraction 2), metals linked to Mn and Fe oxides (Fraction
3), metals strongly linked to organic matter and sulfides (Fraction 4),
and residual metals (Fraction 5).
Figure 1:
Location of sampling stations in the Negro River.
Samples were analyzed in a Perkin Elmer 2380 Atomic
Absorption Spectrophotometer, with air/acetylene flame and deuterium background
correction (D2BGC). Corresponding AQ were checked against reference
material (“pond sediment sample”) provided the NIES (Tsukuba, Japan).
RESULTS AND DISCUSSION
Concentrations of total cadmium,
nickel, iron and manganese were fully determined in sediments of Negro River as
well as the corresponding organic matter ones (Table 1).
|
SAMPLING SITE |
Cadmium (µg/g) |
Nickel (µg/g) |
Iron (mg/g) |
Manganese (mg/g) |
Organic matter (%) |
|
|
|
|
|
|
|
|
Neuquén river |
0.62 ± 0.01 |
9.43 ± 1.03 |
13.63 ± 0.69 |
0.19 ± 0.01 |
5.34 |
|
Limay river |
0.39 ± 0.10 |
6.76 ± 0.20 |
11.69 ± 0.32 |
0.16 ± 0.02 |
2.50 |
|
Confluence |
0.43 ± 0.01 |
6.01 ± 0.12 |
8.41 ± 0.30 |
0.20 ± 0.03 |
1.62 |
|
P II |
0.97 ± 0.25 |
10.09 ± 0.88 |
16.13 ± 2.67 |
0.30 ± 0.04 |
12.82 |
|
Allen |
0.20 ± 0.02 |
5.06 ± 0.46 |
8.25 ± 0.28 |
0.14 ± 0.01 |
1.47 |
|
V.Regina |
0.37 ± 0.11 |
7.28 ± 0.48 |
7.94 ± 0.32 |
0.16 ± 0.01 |
1.53 |
|
Km 2 |
0.82 ± 0.72 |
9.67 ± 1.88 |
18.99 ± 0.35 |
0.26 ± 0.18 |
4.52 |
|
Km 19 |
0.49 ± 0.11 |
11.80 ± 0.70 |
19.03 ± 1.44 |
0.51 ± 0.19 |
7.16 |
Table 1 : Total metal and organic
matter concentrations in sediments from the Negro River.
The distribution of total
metal concentrations has shown to be homogeneous, and large differences have been
not recorded, even though several of the studied sites have presented -as a common trend- higher metal contents than the other ones (i.e.,
P II or Km 2).
Each of the analyzed metals has shown an own geochemical
partitioning behavior, but in most of the cases highest percentage of metal was
included in the Fraction 5 (residual fraction) which reflect metal
content in the corresponding crystalline mineral net.
In the case of cadmium it
could be remarked that several of the total concentrations as determined have
been slightly higher than the standards internationally suggested (CCME, 1999).
Moreover, its geochemical partitioning has shown that most of this metal is on
bioavailable chemical forms (Table 2) and an homogeneous
distribution in most of the studied sites, behavior which has agreed with
previous reports (i.e., López-Sánchez et al., 1993).
SITE
|
Nickel (µg/g) |
Cadmium (µg/g) |
||||||||
|
|
Fraction 1 |
Fraction 2 |
Fraction 3 |
Fraction 4 |
Fraction 5 |
Fraction 1 |
Fraction 2 |
Fraction 3 |
Fraction 4 |
Fraction 5 |
|
Neuquén |
1.13 |
0.15 |
N.D. |
0.16 |
7.99 |
0.38 |
0.14 |
N.D. |
N.D. |
0.10 |
|
Limay |
0.38 |
N.D. |
N.D. |
0.16 |
6.22 |
0.40 |
0.16 |
N.D. |
N.D. |
0.13 |
|
Confl. |
0.71 |
0.24 |
N.D. |
N.D. |
5.06 |
0.38 |
0.24 |
N.D. |
N.D. |
0.11 |
|
P II |
0.37 |
0.02 |
0.75 |
1.36 |
7.59 |
0.44 |
0.19 |
N.D. |
N.D. |
0.34 |
|
Allen |
N.D. |
N.D. |
N.D. |
0.01 |
5.05 |
0.28 |
0.18 |
N.D. |
N.D. |
0.06 |
|
Regina |
0.37 |
N.D. |
N.D. |
0.10 |
6.81 |
0.35 |
0.21 |
N.D. |
N.D. |
0.01 |
|
Km 2 |
0.36 |
0.14 |
0.11 |
0.31 |
8.75 |
0.30 |
0.17 |
N.D. |
N.D. |
0.35 |
|
Km 19 |
N.D. |
0.06 |
0.06 |
0.42 |
11.26 |
0.31 |
0.41 |
N.D. |
N.D. |
0.07 |
Table
2 : Ni and Cd geochemical partitioning in sediments of Negro River.
Also
nickel has presented an homogeneous distribution in the studied sediments, not
only in its total concentration (Table 1) but also in the
corresponding geochemical fractions (Table 2), even in this case
the levels as found are in the order of the background ones (López-Sánchez et
al., 1993).
|
SITE |
Iron (µg/g) |
Manganese (µg/g) |
||||||||
|
|
Fraction 1 |
Fraction 2 |
Fraction 3 |
Fraction 4 |
Fraction 5 |
Fraction 1 |
Fraction 2 |
Fraction 3 |
Fraction 4 |
Fraction 5 |
|
Neuquén |
21.52 |
N.D. |
1422.9 |
711.6 |
11473.9 |
11.87 |
1.42 |
11.19 |
6.51 |
159.01 |
|
Limay |
0.52 |
N.D. |
1248.6 |
258.01 |
10182.9 |
2.54 |
1.60 |
31.08 |
6.16 |
118.62 |
|
Confl. |
0.46 |
N.D. |
679.3 |
283.7 |
7446.5 |
6.31 |
2.86 |
38.05 |
5.75 |
147.03 |
|
P II |
0.61 |
0.41 |
1314.4 |
3033.7 |
11781.3 |
4.49 |
10.58 |
114.58 |
39.88 |
130.47 |
|
Allen |
5.42 |
N.D. |
628.1 |
133.5 |
7482.9 |
5.83 |
0.96 |
9.72 |
3.57 |
119.92 |
|
Regina |
1.20 |
N.D. |
1141 |
184.8 |
6613 |
4.60 |
2.23 |
29.11 |
4.21 |
119.85 |
|
Km 2 |
1.44 |
N.D. |
1817.8 |
575.1 |
16595.7 |
8.16 |
4.03 |
36.08 |
13.6 |
198.13 |
|
Km 19 |
0.67 |
N.D. |
2584.1 |
1293.5 |
15151.7 |
13.31 |
9.64 |
89.88 |
35.38 |
361.79 |
Table 3
: Fe and Mn geochemical partitioning in sediments of Negro River.
Most
of the recorded iron was obtained in non-bioavailable chemical forms, mainly
linked with the mineral crystalline net (Fraction 5). Its distribution
has seemed to be homogeneous along the studied area (Table 3), an
the obtained values were similar to those reported for other rivers (i.e.,
Gibbs, 1973 ; Gaiero et al., 1997).
Finally,
manganese was the metal with most heterogeneous distribution, not only in its
total concentration (Table 1) but also in those of the
corresponding geochemical fractions (Table 3).
As
a second phase of this study, research directed to identify the possible
sources of heavy metal to the assessed areas of Negro River are being carried
out, and corresponding results would
allow to have an integral evaluation of the environmental status of this large
system.
Acknowledgements: this study is a part of the
Doctoral Thesis of Lic. Mariza Abrameto (FUNDAPA) at the Universidad Nacional
del Sur (Bahía Blanca, Argentina).
REFERENCES
1.
CCME
(1999) Canadian Environmental Quality Guidelines, Environment Canada.
2.
Gaiero,D., R.Ross, P.Depetris & M.Kempe (1997) Water,Air & Soil.Pollut., 93:
303-319.
3.
Gibbs,R.J. (1973) Science, 180: 71-73.
4.
Jackson,T. & N.Guyen (1996) Natl.Wat.Res.Inst.Contrib. (Canada),
98-230: 41-68.
5.
López-Sánchez,J., R.Rubio & G.Rauret (1993) Internatl.J.Environ.Anal.Chem., 51:
113-121
6.
Marcovecchio,J.,
V.Moreno & A.Pérez (1988) Sci.Tot.Environ., 75: 181-190.
7.
Marcovecchio,J., L.Ferrer, A.Barral, M.Scagliola & A.Pucci (1998) In: Environmental
Geochemistry in the Tropics, Wasserman,J., E.Silva Filho &
R.Villas-Boas (eds), Springer-Verlag: 139-148.