Heavy Metal Concentrations in Stream Sediments of the
South Dry Sac River
By
Gwenda J. Schlomer
May
6, 2001
Geochemical
Techniques (GLG 581)
Dr.
Erwin Mantei
Introduction
Numerous studies have documented heavy metal concentrations
in stream sediments caused by contamination sources. Mantei and Sappington (1994), Mantei and Coonrod (1989), and
Mantei and Foster (1991) studied the enrichment of heavy metals in river
sediments influenced by adjacent landfills.
Mantei and Gutierrez (1996) also reported the presence of heavy metals
in sediments influenced by landfill emission plumes. The metal concentrations determined in this study include that
for Zn, Cu, Cd, Pb. Some authors have
documented studies on Cu, Pb, Zn, Cd, Sn, As, Cr, Fe, and Mn concentrations in
sediments of rivers affected by mining activities (Reece and others, 1978;
Wolfenden and Lewin, 1978; Yim, 1981; Chapman and others, 1983; Mann and
Lintern, 1983; Moore, 1985; Leenaers and others, 1988; Axtmann and Luoma, 1991).
This study deals with concentrations of Cu, Pb, Zn, and
Cd that were extracted from the stream sediments located along a stream system
in a populated region of southwest Missouri, USA. Stream sediments were used because heavy metal concentrations selectively
integrate in geochemical phases in sediments.
The potential source of heavy metal concentrations in the vicinity is an
inactive landfill that is located adjacent to the study stream. Even though the landfill has been out of
operation for over 30 years, runoff from the area still has the potential to
carry heavy metals into the study stream.
Location and Geology
The location of the study area is on the Springfield
Plateau in southwest Missouri and lies just north of Springfield,
Missouri. The stream studied was the
South Dry Sac River. The map shown as
Figure 1, page 6 illustrates the location of the sampling sites and the
potential source of heavy metals, which is Fullbright Landfill.
The Fullbright Landfill was active for 6 to 7 years until
operations were closed in 1968. It has
been reported that photographic, battery, electronic, and medical wastes were
added to the landfill sometime throughout its active life (Mantei and Foster,
1991). A small stream was observed
draining directly form the landfill into the study stream that probably
contains leachates form the landfill.
The Mississippian age Burlington-Keokuk Limestone
formation underlies the entire area under study. This limestone is a coarsely crystalline, fossiliferous, crinoidal
formation that dips slightly to the west.
Method or Procedure
Choice of Sediment Size and Sample Collection
Higher heavy metal concentrations are generally found on
smaller grains of sediment because of the higher surface area to grain-size
ratio. Therefore, the smaller the grain
size, the higher the metal concentration accumulation. The project used sediment samples sieved
between 80 and 360 mesh to restrict the grain size for more accurate results.
Nineteen stream sediment samples were collected on the
South Dry Sac River. Nine of these
samples were taken downstream from the landfill and ten samples were taken
upstream. The downstream samples represent the test group and those upstream,
the control group. At each sample site,
the samples were wet sieved and the sediments between the mesh sizes of 80 and
360 were saved for chemical analysis.
At each sample site, a GPS instrument was used to save
the location of the sample site as a waypoint in the instrument. The waypoints were then imported into Arcview
using GPS Trackmaker software (Fig.1, page 6).
Chemical Extraction Methods
The same chemical extraction procedure was used on all 19
sediment samples. The sediments were
placed into separate labeled beakers and then into an oven to dry. We then disaggregated the sediment and
weighed out 2.0 grams for each sample.
The weighed samples were then placed into labeled centrifuge tubes. The 2.0 gram portions were then washed with
20 ml of 3 Normal HNO3 and placed in a shaker/hot water bath set at
85°C
for 24 hours to yield total heavy metal content. Next the samples were centrifuged for five minutes each and then
the decantate was poured into sample tubes to use for the ICP analysis.
Standard of 2 ppm and 10ppm of Cu, Pb, Zn, and Cd were prepared. The ICP was used to determine the
concentrations of Cu, Pb, Zn, and Cd in the 19 sediment samples. Bar graphs were then prepared for Cu, Pb,
Zn, and Cd concentrations in the sediments using Microsoft Excel.
Results
The results of the concentrations of the heavy metals in
the geochemical phases of the stream sediment samples are given in Table 1,
page 5.
|
Sample ID |
Zn |
Cu |
Pb |
Cd |
|
|
(ppm) |
(ppm) |
(ppm) |
(ppm) |
|
S9 |
93 |
28 |
37 |
1.1 |
|
S8 |
94 |
26 |
35 |
1.3 |
|
S7 |
91 |
40 |
44 |
1.2 |
|
S6 |
96 |
32 |
36 |
1.2 |
|
S5 |
89 |
44 |
54 |
1.1 |
|
S4 |
89 |
28 |
38 |
1.0 |
|
S3 |
110 |
53 |
41 |
1.3 |
|
S2 |
100 |
35 |
42 |
1.3 |
|
S1 |
123 |
68 |
60 |
1.5 |
|
|
|
|
|
|
|
C10 |
46 |
8 |
26 |
0.5 |
|
C9 |
38 |
10 |
20 |
0.3 |
|
C8 |
35 |
9 |
23 |
0.4 |
|
C7 |
32 |
6 |
17 |
0.2 |
|
C6 |
42 |
16 |
25 |
0.4 |
|
C5 |
44 |
9 |
25 |
0.3 |
|
C4 |
48 |
20 |
27 |
0.5 |
|
C3 |
33 |
7 |
18 |
0.3 |
|
C2 |
43 |
12 |
28 |
0.5 |
|
C1 |
56 |
20 |
30 |
0.6 |
Table 1: The concentration of heavy metals in each
sample.
The heavy metal
concentrations are shown in Table 1.
Samples, C1 through C10 are the control samples. Samples ,S1 through S9 are the test samples,
seemingly affected by the Fullbright Landfill.
Graphs 1 through 4, pages 6-7 inclusive, compare the concentrations
analyzed at the test sites versus the control sites.
Figure
1: Map showing the sample site
locations.
Graph 1:
Concentrations of Zn at each sample site.
Graph
2: Concentrations of Cu at each sample
site.
Graph 3:
Concentrations of Pb at each sample site.
Graph 4: Concentrations of Cd at each sample site.
These charts show higher
concentrations of Zn, Pb, Cu, and Cd in the test samples compared to that in
the control. The space between S1 and
C10 shows the location of the landfill in reference to the sample sites. At sample site S1, which was the first test
sample taken, each metal reached its highest concentration. Zn, Pb, and Cd
seemed to have the most stable values in the control values and the test
values. The concentrations of Cu were
erratic and varied from sample to sample more than the other metals.
Using the control area as a
background, it would appear that the landfill does in fact affect the South Dry
Sac River with heavy metal concentrations.
A t-test was performed on the data
to show the correlation of the hypothesis that the landfill emits heavy metals
into the study area and the actual data that was collected. The results are shown in Table 2,
below.
Table
2:
|
|
Mean Concentration |
|
|
|
|
Element |
of Control |
Test |
T-value |
Critical Value |
|
Zn |
41.65 ppm |
98.26 |
13.16 |
2.11 |
|
Cu |
11.87 ppm |
39.24 |
5.86 |
2.11 |
|
Pb |
0.4 ppm |
1.23 |
12.61 |
2.11 |
|
Cd |
23.93 ppm |
42.96 |
6.1 |
2.11 |
|
|
|
|
|
|
|
|
|
|
|
|
Conclusion
The purpose of this study was to
show the variation in concentrations of Cu, Pb, Zn, and Cd in the sediments of
the South Dry Sac River that is affected by a landfill. The chemical analysis of the data shows that
concentrations of metals are higher downstream from the landfill than in the
control sites upstream from the landfill.
Fullbright Landfill is a possible point-emission source that could be
emitting heavy metals into the stream via runoff. However, further studies should be projected that consider
alternative sources for the high heavy metal content. Other possibilities of the pollution could be found in sediment
sampling of P-Ridge Creek, which flows directly into the South Dry Sac River
directly upstream from the landfill.
Taking into account pH levels at each sample site and also collecting
more samples of the study area could improve this study.