Soil contamination happen
due to many things such as oil spillage, application of fertilizers to soil,
mining activities, proximity to industries and use of pesticide are the some of
the sources of soil contamination. This experiment was performed to
determine the different parameters and indicators in assessing contaminated
soils. The parameters used were the soils pH, EC, Loss of Ignition and metal
contents. The equipment used were the EC and pH meter and the muffle furnace
for loss of ignition. The other reason
for performing this experiment was to assess the
influence of contaminants on the chemical and microbiological properties of
soil. The pH was checked and samples 1, 2, 3 (garden soil,
oil soil, farm soil) had a pH above 7 which indicate alkalinity while samples
4, 5, 6 (petrol soil and two mine soils) had a pH below 7 which means they were
acid. Sample 5 and 6 which were both mine soils had the smallest and largest EC
of 12.64 and 747 respectively. This great difference indicate that even though
they are both mine soils they were picked at different locations so the
properties of soil vary in each location as some heavy metals may be in some
location and not in others hence a difference in EC number.
contamination come from many different sources. Soil properties vary from place
to place and are influenced by many factors. Past land use such as farming were fertilizers
were added to the soil may have contaminated the soil, the accumulation of
heavy metals and metalloids through emissions from mine tailings may also cause
soil contamination. Heavy metals occur naturally in the soil environment from
processes of weathering of rocks that have trace elements or metals such as lead.
Oil spillage occurs due to many things such as accidents, drilling,
transportation of product, and natural disasters. When oil is released, it
resides in the soil system, in the pore space of the soil, modifying the
behaviour of the soil. Soil contamination have some risks on living things. Plants
may absorb contaminants through the soil with their roots or green leafy plants
with their leaves, groundwater may be contaminated as it interacts with contaminated
soil as it follows through it and bioaccumulation may occur when livestock or
people eat food that was grown on contaminated soils. Contaminated soil can be
characterised using pH, loss of ignition, electrical conductivity and metal
determine the different parameters and indicators in assessing contaminated soils.
assess the influence of contaminants on the chemical and microbiological
properties of soil.
METHODS AND MATERIALS
Soil samples – garden soil, contaminated
soil with petroleum, contaminated with heavy metals.
Apparatus to determine pH, EC, loss of
ignition and metal contents
500 g samples were prepared,
air-dried and sieved (mesh size 2 × 2 mm2) to remove large particles and root fragments.
Each sample was homogenized and divided into sub-samples and then they were stored
in polyethylene bags at 4 °C prior to biological and physicochemical analyses.
Chemical characterization of contaminated
Soil pH and EC
The pH and EC meter were calibrated
using appropriate buffer solution based on manufacturer’s instruction. For pH,
the readings were adjusted and stabilized using a known pH of buffer solutions
4.0 and 9.2. Water slurry soil was prepared by mixing 20 g of soil and 40 ml
distilled water on 100 mL beaker. The mixture was well mixed using a stirring
glass rod for 30 minutes. The pH and EC of the soil water suspension were
determined and analyzed in duplicates.
carbon through Loss of Ignition
Material used were: Porcelain
crucibles, Soil samples, Analytical balance, Muffle furnace, desiccator and tongs.
The porcelain crucibles were heated
for 1 hour at 375°C in a muffle furnace and were cooled in the open at about
150°C. They were then placed in a desiccator cooled for 30 minutes and weighed.
The crucibles were then taken out of a desiccator and placed on the scale and
that was the crucible weight. Samples were 2mm size or finer. Mineral soils
were sieved with a 2mm sieve. Forest floor sample with large particulate
material were ground to a 2mm size. Samples were then placed in trays to be oven
dried at 105°C for 24 hours and trays were labelled with sample ID.
5.000g ±0.001g of each oven-dried
sample were weighed and placed each into a crucible and it was the pre-ignition
weight. The number of each crucible corresponding to each sample were recorded.
The crucibles were placed back in the desiccator after being weighed. The samples
were transported to the muffle furnace in the desiccator and the crucibles were
placed in the furnace. The furnace was turned on and set to temperature. The
LOI process required a slow temperature increase of 5°C/min. The furnace was
set to 5 degrees higher every 5 minutes until it reached 375°C.
When sufficient time had passed the furnace was turned off and
samples were allowed to cool to 150°C. When cooled to 150°C the samples were
removed from the oven and placed in a desiccator using tongs. Wait 30min then
the samples were removed from the desiccators and weighed for their
post-ignition weight. Finally %OM was calculated using the following
%OM= Pre-ignition – Post-ignition *100
Heavy metal Contents and availability
Digestion of soil samples and heavy metals determination
Soil samples were oven dried at 60
°C for 24 h before being ground into a fine powder using a sterile mortar and
pestle. The samples (2.5 g) were transferred into a crucible before being mixed
with 10 mL of aqua regia, which consisted of HCl:HNO3 (3:1). The mixture was
then digested on a hot plate at 95 °C for 1 h and allowed to cool to room temperature.
The sample was then diluted to 50 mL using deionized distilled water and left
to settle overnight. The supernatant was filtered through Whatman No. 42 filter
paper and (<0.45 ?m) Millipore filter paper, (Merck Millipore, Darmstadt, Germany) prior to analysis by graphite furnace atomic absorption spectrometry (GF-AAS). RESULTS 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 SAMPLE PRE IGNITION WEIGHT CRUCIBLE WEIGHT POST IGNITION + CRUCIBLE WEIGHT POST IGNITION WEIGHT %OM 1 4.92433 27.70884 31.92602 4.21718 14.6 2 5.00000 25.690 30.86803 5.17803 -3.6 3 5.00030 25.88992 30.03127 4.14135 17.1 4 5.00085 27.73606 32.58866 4.8526 2.96 5 5.00024 23.52632 27.56583 4.03951 19.2 6 4.83415 25.16388 29.17299 4.00911 17.1 DISCUSSION When measuring pH values greater than 7 are alkaline while values less than 7 are acidic and 7 is neutral. Soil sample 1 which is garden soil has a pH of 7.78, soil sample 2 which is oil soil has a pH of 7.86 and soil sample 3 which is farm soil has a pH of 7.33 that means all the three soils samples are alkaline soil. Sample 4 soil which is petrol soil has a pH of 5.84, sample 5 and 6 which are both mine soil has a pH of 1.95 and 3.26 respectively which indicate that this three soil samples are acidic soils. In the electric conductivity results soil sample 6 which is mine soil has the highest EC while soil sample 5 which is also a mine soil has the lowest EC of 12.64, this means that the two soils were picked at different spots on the mine and so they were not contaminated by the same contaminants. In the loss if ignition results, sample 2 which is oil soil has the lowest %OM which is negative of -3.6 because its pre-ignition weight is lower than its post-ignition weight. Sample 1 (garden soil), sample 3 (farm soil), sample 4 (petrol soil), sample 5 (mine soil) and sample 6 (mine soil) all have a positive %OM of 14.6, 17.1, 2.96, 19.2 and 17.1 respectively because its pre-ignition is higher than the post-ignition. The errors that could have been encountered are parallex error when one was using the measuring cylinder by not taking the reading below the meniscus, the human reaction time error where one may take a long time to take readings form the pH meter and lastly the calibration error where the reading is taken before the equipment read zero. CONCLUSION AND IMPLICATIONS Contaminated soils from the garden, oil and farm are alkaline soil samples and contaminated soils from the petrol and mine are acidic as a result of high concentration of heavy metals. Contaminated soils from mines have a big difference in EC due to the fact that soil samples were taken from two different locations in the mine so heavy metals may be highly concentrated on one part of the mine and on the other may have low concentration of heavy metals. REFERENCES A. Kabata-Pendias and H. Pendias, (2001). 2nd edition. Trace Metals in Soils and Plants, CRC Press, Boca Raton, Fla, USA. Pierzynski, G.M., Sims, J.T. and Vance, G.F., (2000). 2nd edition. Soils and Environmental Quality, CRC Press, London, UK. Rosen, C.J. (2002). Contaminants in the Home garden and urban soil environment. Extension Guide FO- 02453. Grand Rapids, MN: University of Minnesota Extension Services, Department of Soil, Water and Climate. SINGH, S., SRIVASTAVA, R. & JOHN, S. (2008). Settlement characteristics of clayey soils contaminated with petroleum hydrocarbons. Soil & Sediment Contamination, 17, 290-300.