ABTRACT

The objective of the lab was to analyze the effect of
contaminants on the chemical and microbiological properties of soil .The
methods used included determining pH using Ph meter, temperature, EC using EC
meter and organic carbon through loss of ignition). Different soil samples with
different contaminants showed different results as displayed from table 1-5.

INTRODUCTION

Soil is a dynamic natural body composed of mineral and
organic solids, gases, liquids and living organism which can serve as a medium
for plant growth (Kononova,
2013). Soil exists in different shapes, colors and sizes thus have different
chemical composition and properties. As such Soil has many different functions
to people and the environment. Soil quality refers to the soil’s ability to
perform its functions (Merrington
and Schoeters, 2011). Soil quality is affected by Soil contamination as soil
contamination changes the soil’s properties .It is important establish
parameters that can help detect or act as an indicator to soil contamination,
these include Soil Ph ,Soil electrical Conductivity ,microbial activity and Organic
matter content. These parameters alert one of soil contamination by having
readings/measurements that can be considered to be anomalies too high or far
below the known Background or threshold.

Soil Ph is the degree of soil acidity or alkalinity as
such is a variable that affects a wide range of chemical and biological
properties. It relates to Soil contamination in a sense that soil Ph affects
the mobility of many pollutants in soil by influencing the rate of their
biochemical breakdown, solubility and the absorption of colloids (Whiting, Wilson and Card, 2004). Soil electrical
Conductivity (EC) is the ability of the soil to transmit /conduct an electrical
current. It gives an indirect measurement of the salt content as more salt
means more conductivity of electrical current.

Organic matter is a component of the soil consisting
of dead plants and animal remains at various stages of decomposition. Organic
matter has numerous benefits such as providing 90% of nitrogen in unfertilized
soil, improving soil structure (Kononova,
2013) e.t.c thus it is important to access the organic matter content in the
soil as such the loss of ignition method does just that.

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.

 

METHOD

Soil pH and
Soil EC

Apparatus

·        
Breaker 100 ml

·        
Stirring rod

·        
EC meter

·        
pH meter

·        
analytical balance

20g of each sample were taken and put into separate
100ml beakers along with 40 ml of distilled water and the mixture was stirred
for 30 minutes. Before readings were taken from the pH meter and EC meter,
calibrations were made using the appropriate buffer solutions. For pH the
buffer solutions were 4.0 and the 9.2.After calibrations readings were captured
into table 1.

2. Organic
carbon through loss of ignition

Apparatus

·        
Muffle furnace

·        
 porcelain
crucible

·        
analytical balance

·        
tongs

·        
oven

·        
desiccator

Soil samples
were prepared by grinding and by being passed through 2mm sieve, it is
important to note that samples containing oil and petrol could not pass through
the sieve as such proceeded after grinding. The porcelain crucible were heated
for an hour at 375 degrees in the muffle furnace and later cooled in the open at
150 degrees. They all underwent additional cooling in the desiccator for 30
minutes before being weighed, this in turn was the crucible weight. The samples
were placed in a tray died at 105 degrees for 24 hours in an oven and as such
were labeled beforehand to avoid mixing. After drying the samples were placed
into the desiccator.

Pre-ignition Work

The desiccator
was brought to scale with precision 0.001g and 5.000g +_0.001g of each oven dried
sample was weighed and each placed into a crucible, thus this was recorded as
the pre-ignition weight. The Samples were placed back into the desiccator
before being transported to the muffle furnace which was heated to 375 degrees
overnight.

Post-ignition work

After ~2 ½
hours the furnace was turned off to allow samples to cool off to 150 degrees.
Samples were removed from the furnace after cooling and placed back into the
desiccator using tongs. After 30 minutes the samples were removed from the
desiccator and weighed as the post-ignition weight. The crucible weight was the
subtracted from the post ignition weight and %OM was calculated by

%OM=Pre-ignition
weight –post-ignition weight/pre-ignition weight*100

 

Heavy Metal
Analysis

 Soil samples
were grind to a fine powder through sieving (2mm). The samples were then
compounded within using a spatula plastic container, which was sealed and
labelled with the corresponding sample name. The sealed plastic container was
then placed into the XRF machine. The XRF was calibrated before use using known
standards and a blank.

NB-lack of equipment resulted in sequential extraction
and microbial data being acquired from a different study, results were not
obtained in the lab.

RESULTS

 

Table 1-Measurement
of soil Ph and soil EC

Soil Sample

pH

EC

1.Garden
Soil

7.78

164.9

2.Soil-Oil

7.86

253.0

3.Soil-Petrol

7.33

343.0

4.Soil-Farm

5.82

126.1

5.Soil-Mine
(s)

2.01

12.9

6.Soil-Mine
(black)

3.50

549.0

Table 2-measurement
of organic matter content

Soil Sample

Crucible
weight (g)

Pre-ignition
Weight (g)

Post-ignition
Weight
+crucible (g)

Post
ignition
Weight (g)

%OM

1.Garden
Soil

27.70886

4.92433

31.91303

4.20417

14.62453

2.Soil-Oil

25.60992

5.000

30.86761

5.25769

-5.1538

3.Soil-Petrol

25.88992

5.00030

30.59071

4.70079

5.989841

4.Soil-Farm

27.73606

5.00085

31.75635

4.02029

19.60787

5.Soil-Mine
(s)

23.52656

5.00024

27.56172

4.03516

19.30067

6.Soil-Mine
(black)

28.34111

5.00039

29.16244

0.82133

83.57468

 

 

Table3-Microbial
count of soil with different form of contamination based on nutrient agar
culture.

Soil sample

Bacteria
(cfu)

Fungi (cfu)

Actinomycetes
(cfu)

1.Garden
Soil

3.9 x10
6

2.82 x 10 3

2.29 x10 6

2.Soil-Oil

1.1 x10 6

2.52 x 10 4

1.92 x10 6

3.Soil-Petrol

2.2 x10 6

3.21 x 10 4

3.19 x10 6

4.Soil-Farm

1.9 x10 6

3.72 x 10 3

1.11 x10 6

5.Soil-mine

3.1 x10 4

2.72 x 10 2

2.119 x10
4

6.Soil-Mine
(black)

4.8 x10 3

6.72 x 10 2

3.119 x10 4

 

Table 4.
Sequential extraction of Ni Cu and Pb in two mine tailing soils collected from
abandoned mine site in Selebe-Phekwi, Botswana

Sample

 

Ni

Cu

Pb

S5(Soil-Mine)

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(Soil-Mine
(Black))

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

Table5-XRF
results from heavy metal analysis of contaminated soils in ppm.

Field Label 1

Field 1

Mn

Fe

Ni

Cu

Zn

As

Mo

Cd

Pb

Sample ID

nist 2710a

1476.98

40382.1

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