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(Mine tailings 1)ABSTRACT

Soil plays an important
part on the ecosystem, thus it provides nutrients to the plants and the environment.
But the moment the soil comes into contact with the contaminants it becomes
contaminated since it is an important factor most of the things suffer because
of this, it includes things like soil texture, pH and EC, the purpose of this
lab experiment was to determine the different parameters for mines, farms,
petrol and oil contaminated soils. The analysis for this parameters helps in
characterization of contaminated soils. In conclusion, for all the soil samples
were contaminated but the parameters indicated that the results that were
obtained were within the allowable limits.

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OBJECTIVES

·        
To determine the different parameters
and indicators in assessing contaminated soils

·        
To assess the influence of contaminants
on the chemical and microbiological properties of soil.

INTRODUCTION

 Soil contamination is caused by the presence
of human made chemicals or any other alteration in the natural soil
environment. In most cases it is caused by industrial activities, agriculture
activities and waste disposal. The most common involved chemicals include
petroleum hydrocarbons and other heavy metals. Health risks usually comes from
direct contact with contaminated soil, vapors from the contaminants. Soil
quality indicators are used to evaluate how well soil functions, it cannot be
measured directly. Soil indicators have three indicators namely; chemical,
physical and biological. Typical soil tests only look at chemical indicators.
One basic fundamental foundation of environmental quality is the soil quality,
which is largely governed by organic matter(SOM), which in turn responds to
changes in soil management and tillage.( Doran 1996)

Organic matter, more
specifically soil carbon goes beyond all three indicator categories and I is
the most widely recognized influence on soil quality. Organic matter is mostly
tied to all soil functions. Chemical indicators give the information about the
equilibrium between soil solution (soil water and nutrients) and exchange sites
(clay particles and organic matter), soil reaction (pH) and electrical
conductivity are examples of levels of soil contamination indicators.   

Heavy metals occur
naturally in the soil environment from pedogenic processes of weathering of
parent materials at levels that are either regarded a trace or rarely toxic.
Contamination of soils by heavy metals is a very significant problem, which
leads to negative influence on soil characteristics and limitation of productive
and environmental functions. A number of diversity, microbial activity of soil
microorganisms are affected by heavy metals. Usually they cause slow down
growth and reproduction of microorganisms in the soil then prevail slower
growing microorganisms with lower diversity and higher resistance to heavy
metals. Heavy metals have high concerns not only for their toxicity to living
organisms inhabiting in the soil, but also for their immobilization within
different organic and inorganic colloids as suggested by (Nanniaperi 1997).

Soil organic matter
plays a critical role in the conservation of fertility especially in the
extremely coarse textured soils like those in Palapye. In these soils soil
organic matter is both the source of nutrients and mechanism for nutrient
retention, it provides favorable conditions for soil biota. Loss on ignition is
one of the most used methods for measuring organic matter content in soils but
does not have a universal standard protocol. Its accuracy can be influenced by
a number of factors for example the sample mass, temperature of ignition and
duration and clay content of samples. 

Soil electrical
conductivity is a major factor for the determination of the health status of
the soil. EC measurements correlate with soil properties that affect crop
productivity such properties are; soil texture, organic matter level, drainage
conditions, salinity, cation exchange capacity. Characteristic such as loss of
organic matter, compaction, high salinity and the soil degraded to a point there
is low cat ion exchange in the soil these characteristics shows a degree of
contamination in the soil. Soil pH is the indication of the acidity and
alkalinity in the soils, and is measured in pH units. The negative logarithm of
the hydrogen ion concentration defines soil pH. It ranges from 0 to 14. It is
an important measurement because the soil acidity and alkalinity determines how
easily the plants can absorb nutrients from it.

MATERIALS
AND METHODS

MATERIALS
USED

Chemical characterization of contaminated soil

Ø  6
soil samples

Ø  EC
meter

Ø  pH
meter

Ø  Distilled
water

Ø  Beakers

Ø  Stirring
glass rods

Organic carbon through loss of ignition

Ø  Porcelain
crucibles

Ø  6
soil samples

Ø  Analytical
balance

Ø  Muffle
furnace

Ø  Desiccator

Heavy metal contents and availability

Digestion of soil samples and heavy metal
determination

Ø  6
soil samples

Ø  Crucible

Ø  Oven

Ø  Aqua
regia

Ø  Deionized
distilled water

Ø  Filter
paper

Ø  Millipore
filter paper

Microbial population

Ø  6
soil samples

Ø  Distilled
water

Ø  150
ml Eflask

Ø  10
ml ttube

Ø  Petri
plates with potato
dextrose agar to which 0.05% (w/v) chloramphenicol

Ø  1ml
pipette man

Ø  1ml
pipette tips

Ø  Petri
plates with nutrient agar with nystatin (0.015%)

METHODOLOGY

A.     SOIL SAMPLE PREPARATION

500g of soil samples were prepared, and then air-dried a sieve with a
mesh size of 2x2mm2 was used to remove large particles and root
fragments. Each sample was then homogenized and divided into sub-samples, then
stored in polyethylene bags at 4?C prior to biological and physicochemical
analyses.

CHEMICAL CHARACTERIZATION OF CONTAMINATED
SOILS

SOIL pH 
AND EC

Firstly the pH and the EC meter were calibrated using appropriate
buffer solution based on the manufacturer’s instruction. For pH, the readings
were adjusted and stabilized using a known pH of buffer solutions 4.0 and 9.2.
Soil was then prepared using water slurry by mixing 20g of soil and 40ml
distilled water on a 100ml beaker. The mixture was then mixed well using a
stirring glass rod for 30minutes. The pH and the EC of the soil water
suspension were then determined. The results after the determination were then
analyzed in duplicates.

ORGANIC CARBON THROUGH LOSS OF IGNITION

Analytical balance was calibrated to a reading precisely to 0.001g.
The porcelain crucibles were heated for 1 hour at 375?C in a muffle furnace.
They were then cooled in the open to about 150?C and placed in a desiccator to
cool for 30 minutes and the weight was measured. The crucibles were then taken
out of the desiccator and placed near scale. This was then the crucible weight.   

Soil samples that are sieved to a size of 2mm or finer were then
prepared in advance. Samples were placed in trays so that they can be oven
dried at 105?C for 24 hours. The trays were labeled with sample ID for
recognition. A blue/green oven located at the back room RCB6301 was used. The
oven was then turned on; the temperature dial was adjusted to correct position
(indicated by the temperature label on the top right corner of the face of the
unit). After oven-drying the samples were taken out and placed in a desiccator,
and then the oven was switched off.

The desiccator was brought to scale capable of precision to 0.001g.
5.000g±0.001g of each oven-dried samples were weighed and then placed into each
crucible, this was the pre-ignition weight. The crucibles were placed back into
the desiccator after being weighed. The samples were then transported to the
muffle furnace in the desiccator and placed inside the furnace.  The furnace was allowed to heat to 375?C,
heating was indicated by the heating light being on overnight.

After sufficient time elapsed the furnace was turned off, the samples
were then allowed to cool off to approximately 150?C. The temperature of the
furnace was checked by turning it back on and reading  the display and switched off after getting
the readings. After being cooled to approximately 150?C samples were removed
from the oven and placed into desiccators using tongs. After 30 minute elapsed
the samples were then removed from the desiccators and weighed for
post-ignition weight. The crucible weight was subtracted from the post-ignition
weight and the results were tabulated. The %OM was then calculated using the
following equation:

%OM= pre-ignition work (g) –post-ignition weight (g)/pre-ignition
weight (g)*100

HEAVY METAL CONTENTS AND AVAILABILITY

3.1  DIGESTION OF SOIL SAMPLES AND HEAVY METALS
DETERMINATION

Soil samples were oven-dried at 60?C for 24 hours before they were
grinded into a fine powder using a sterile mortar and pestle. The samples of
weight 2.5g were then transferred into a crucible before being mixed with 10ml
of aqua regia, which consisted of HCL:HNO3 (3:1). The mixture was digested on a
hot plate at 95?C for 1hour and allowed to cool to room temperature. The sample
was the diluted to 50ml using deionized distilled water and left to settle
overnight. The supernatant was then filtered through Whatman No.42 filter paper
and (‹0.45?m) Millipore filter paper prior analysis by graphite furnace atomic
absorption spectrometry. (GF-AAS)

 

RESULTS

TABLE 1. SOIL pH 
AND EC

  SOIL SAMPLE                    

Ph

TEMP
pH (?C)

EC  (µm/cm)

TEMP
(EC) (?C)

TIME
(sec)

1

7.78

28.5

164.9

28.3

53

2

7.86

29.0

253

28.3

24

3

7.33

29.7

343

28

31

4

5.84

28.8

126.1

29.1

1.28

5

1.95

28.0

12.64

29.9

51

6

3.26

29.7

747

29.1

1.37

 

TABLE 2. ORGANIC CARBON THROUGH LOSS OF IGNITION

 

SAMPLE

PRE
IGNITION WEIGHT

CRUCIBLE
WEIGHT

POST
IGNITION  + CRUCIBLE WEIGHT

POST
IGNITION WEIGHT

1.
garden soil

4.92433

27.70884

31.92602

4.21718

2.
oil contaminated

5.00000

25.690

30.86803

5.17803

3.
farm soil

5.00030

25.88992

30.03127

4.14135

4
.petrol contaminated

5.00085

27.73606

32.58866

4.8526

5
(Mine tailings 1)

5.00024

23.52632

27.56583

4.03951

6(Mine
tailings 2)

4.83415

25.16388

29.17299

4.00911

 

 

Sample 1

%OM= (4.92433-
4.21718)/4.92433 * 100

          = 14.360

Sample 2

%OM= (5.00000-
5.17803)/5.00000 * 100

          = -3.561

Sample 3

%OM= (5.00030-
4.14135)/5.00030 * 100

          = 17.178

 

 

 

Sample 4

%OM= (5.00085-
4.8526)/5.00085 * 100

          = 2.964

Sample 5

%OM= (5.00024- 4.03951)/5.00024
* 100

          = 19.214

Sample 6

%OM= (4.83415-
4.00911)/ 4.83415 * 100

          = 17.067

 

Table 2. Sequential
extraction of Ni Cu and Pb in two mine tailing soils collected from abandoned
mine site in Selebi-Phikwe, Botswana

Sample

 

Ni

Cu

Pb

S5

Mine tailings 1

125.81

3390.55

26.13

1

Exchangeable

15.10

262.24

1.57

2

Organic matter

4.78

128.84

1.20

3

Mn oxides

21.65

402.87

3.66

4

Amorphous Fe oxides

27.68

610.30

3.81

5

Crystalline Fe oxides

47.81

712.02

7.16

6

Residual fraction

7.70

1251.28

8.05

 

Total

124.71

3367.55

25.45

 

% recovery

99.13

99.32

97.39

 

 

 

 

 

s6

Mine tailings 2

392.81

3908.44

106.69

1

Exchangeable

5.50

54.72

1.49

2

Organic matter

16.89

168.06

2.13

3

Mn oxides

42.14

312.67

11.74

4

Amorphous Fe oxides

70.71

615.35

13.87

5

Crystalline Fe oxides

102.13

703.52

22.41

6

Residual fraction

148.45

2004.11

54.05

Total

385.81

3858.44

105.69

% recovery

98.22

98.72

99.06

 

Table 3. Microbial
count of soil with different form of contamination based on nutrient agar
culture.

Sample

Bacteria (cfu)

Fungi (Cfu)

Actinomycetes (cfu)

S1

garden soil

3.9 x10 6

2.82 x 10 3

2.29 x10 6

S4

Farm Soil

1.9 x10 6

3.72 x 10 3

1.11 x10 6

S2

Oil contaminated

1.1 x10 6

2.52 x 10 4

1.92 x10 6

S3

Petrol Contaminated

2.2 x10 6

3.21 x 10 4

3.19 x10 6

S5

Mine tailings 1

3.1 x10 4

2.72 x 10 2

2.119 x10 4

s6

Mine tailings 2

4.8 x10 3

6.72 x 10 2

3.119 x10 4

 

Table 3.1: Analysis on
heavy metals in different soil samples

 

 

 

DISCUSSION

For the results
obtained, the soil samples for the 
petrol contaminated and mine tailings have acidic pH, with one for the
mine tailings 2 having the highest pH. The soil sample for garden, farm, oil
contaminated soils have basic pH conditions, with the oil contaminated one with
the highest pH. For garden and farm soils their pH is affected by the nutrients
that are used when  the plant use them
for plant growth. The alkalinity for soil samples can be caused by natural
causes for example there can be a presence of soil minerals that produce sodium
bicarbonate that can happen through weathering. For petrol and mine tailings
samples they appear acidic due to the environment, so they contaminate the
soil. Some heavy metals are contained in the waste, they affect soil pH.

Electrical conductivity
is dependent on the dissolved material is high on the soil sample, the EC will
also be high in the sample. Mine tailings 2 was found to have the highest
electrical conductivity; this is so because of more accumulation of metals such
as lead from the waste. For the loss of ignition method, when determining the
organic matter, the results were influenced by the pH, so the more the acidic
the soil sample is the higher the organic matter present in that sample but this
is not so for all the soil samples. The loss of ignition is designated to
measure the amount of soil moisture also the impurities that are lost when the
soil sample is being ignited. The analysis of LOI calculates %OM by comparing
the weight of a soil sample before and after it has been ignited. From the
results tabulated sample five for mine tailings 1 had the highest %OM . Before
ignition the samples contained organic matter, but after they were ignited all
that remained was the mineral portion of the soil. The difference that was
noticed in the weight before and after the ignition represented the amount of
the organic matter that was present in the sample.

When determining the
heavy metals availability, metals were expressed in percentages, this showed
those metals are high in pollutants while other metals showed their
contamination to be less significant. LOD showed that metals were not detected
in the soil sample. For the sequential extraction, for the nickel
contamination, mine tailings 2 it had high intensity factor because it has a
higher total concentration while the mine tailings 1 had high intensity factor
this is due to high exchangeability, therefore sample 5 with mine tailings 1
casuse more toxicity as compared to mine tailings 2 of sample 6. For the
microbial population, the counts for the soil samples that appeared to be
alkaline, this may be due to the conditions that are suitable for their growth.
The population of microbes appeared to be low in acidic because the pH for it
render their growth.

CONCLUSION

For the objective of
contaminants has the influence on the microbial and microbial properties of
soil, this was proved to be so by the electrical conductivity of the soil
sample. This is so because  dissolved
materials affect the EC since they contaminate the soil, it shows that the soil
containing more dissolved materials will have high EC. Furthermore the
microbial population is in agreement with the objective of acidity of soil
decreasing with the growth of microbes.

STUDY QUESTIONS

·        
What is the effect of contamination on
different soil parameters( pH,EC, organic matter and microbial population)
tested.

For
ph most of the heavy metals contaminants will decrease the pH of the soil
making it become acidic, as for the EC the contaminants will increase the
electrical conductivity of the soil samples. The organic matter present in the
soil samples will be determined by pH. For the microbial population the
contaminants affect it negatively because some of the contaminants change the
soil property which is not suitable for their growth.

·        
Differentiate the practical implication
between the determination of the total heavy metals contents and available
form(bioavailable form)

The
implication of the heavy metals indicates that the quantity factor of the soil
and it includes both the bioavailable form and some are bound to other phases
in the soil which is not available for use by the plants. The determination of
the heavy metals does not tell one about the amount of pollution in the area

·        
How do contaminants affect the capacity
of soil microbial population

They
affect the soil capacity of soil microbial population and hence modifying their
diversity, the contaminants also inhibit the enzyme activities in the soil.
Biological processes for example nitrification and decomposition of humus are
usually reduced in the soil hence the soil fertility and soil structure.

REFERENCES

Doran, J.W. and T.B.
Parkin. 19996. Quantitative indicators of soil quality: a minimum data set.

In J.W Doran and A.J
Jones, eds. Methods for Assessing soil quality: SSSA, Inc, Madison, Wisconsin

Nannipieri P.,
Badalucco L., Landi L., Pietramel Lava G. 1997: Measurement in assessing the
risk of chemicals to soils ecosystem. OECD workshop. SOS. Publ. Fair Haven, New
york, 507-534

Castaldi S., Rutigliand
F.A, Vizzo de Santo A.:suitability of soil microbial parameters as indicators
of heavy metal pollution. Water, air, and soil pollutio

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