ABSTRACTSoil contamination happendue to many things such as oil spillage, application of fertilizers to soil,mining activities, proximity to industries and use of pesticide are the some ofthe sources of soil contamination. This experiment was performed todetermine the different parameters and indicators in assessing contaminatedsoils.
The parameters used were the soils pH, EC, Loss of Ignition and metalcontents. The equipment used were the EC and pH meter and the muffle furnacefor loss of ignition. The other reasonfor performing this experiment was to assess theinfluence of contaminants on the chemical and microbiological properties ofsoil.
The pH was checked and samples 1, 2, 3 (garden soil,oil soil, farm soil) had a pH above 7 which indicate alkalinity while samples4, 5, 6 (petrol soil and two mine soils) had a pH below 7 which means they wereacid. Sample 5 and 6 which were both mine soils had the smallest and largest ECof 12.64 and 747 respectively. This great difference indicate that even thoughthey are both mine soils they were picked at different locations so theproperties of soil vary in each location as some heavy metals may be in somelocation and not in others hence a difference in EC number. INTRODUCTIONSoilcontamination come from many different sources. Soil properties vary from placeto place and are influenced by many factors. Past land use such as farming were fertilizerswere added to the soil may have contaminated the soil, the accumulation ofheavy metals and metalloids through emissions from mine tailings may also causesoil contamination. Heavy metals occur naturally in the soil environment fromprocesses 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, itresides in the soil system, in the pore space of the soil, modifying thebehaviour of the soil. Soil contamination have some risks on living things. Plantsmay absorb contaminants through the soil with their roots or green leafy plantswith their leaves, groundwater may be contaminated as it interacts with contaminatedsoil as it follows through it and bioaccumulation may occur when livestock orpeople eat food that was grown on contaminated soils.
Contaminated soil can becharacterised using pH, loss of ignition, electrical conductivity and metalcontents.Objectives: 1. Todetermine the different parameters and indicators in assessing contaminated soils.2. Toassess the influence of contaminants on the chemical and microbiologicalproperties 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 contentsA. Soilsample preparation 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 storedin polyethylene bags at 4 °C prior to biological and physicochemical analyses.
B. Chemical characterization of contaminatedsoils 1. Soil pH and ECThe pH and EC meter were calibratedusing appropriate buffer solution based on manufacturer’s instruction. For pH,the readings were adjusted and stabilized using a known pH of buffer solutions4.0 and 9.2. Water slurry soil was prepared by mixing 20 g of soil and 40 mldistilled water on 100 mL beaker.
The mixture was well mixed using a stirringglass rod for 30 minutes. The pH and EC of the soil water suspension weredetermined and analyzed in duplicates. 2. Organiccarbon through Loss of Ignition Material used were: Porcelaincrucibles, Soil samples, Analytical balance, Muffle furnace, desiccator and tongs. MethodThe porcelain crucibles were heatedfor 1 hour at 375°C in a muffle furnace and were cooled in the open at about150°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 andthat was the crucible weight. Samples were 2mm size or finer. Mineral soilswere sieved with a 2mm sieve.
Forest floor sample with large particulatematerial were ground to a 2mm size. Samples were then placed in trays to be ovendried at 105°C for 24 hours and trays were labelled with sample ID. Pre-Ignition Work5.
000g ±0.001g of each oven-driedsample were weighed and placed each into a crucible and it was the pre-ignitionweight. The number of each crucible corresponding to each sample were recorded.The crucibles were placed back in the desiccator after being weighed.
The sampleswere transported to the muffle furnace in the desiccator and the crucibles wereplaced in the furnace. The furnace was turned on and set to temperature. TheLOI process required a slow temperature increase of 5°C/min. The furnace wasset to 5 degrees higher every 5 minutes until it reached 375°C.
Post-Ignition WorkWhen sufficient time had passed the furnace was turned off andsamples were allowed to cool to 150°C. When cooled to 150°C the samples wereremoved from the oven and placed in a desiccator using tongs. Wait 30min thenthe samples were removed from the desiccators and weighed for theirpost-ignition weight.
Finally %OM was calculated using the followingequation: %OM= Pre-ignition – Post-ignition *100Pre-ignition C. 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 andpestle. The samples (2.5 g) were transferred into a crucible before being mixedwith 10 mL of aqua regia, which consisted of HCl:HNO3 (3:1). The mixture wasthen 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 leftto settle overnight. The supernatant was filtered through Whatman No. 42 filterpaper 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 DISCUSSIONWhenmeasuring pH values greater than 7 are alkaline while values less than 7 areacidic 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 isfarm soil has a pH of 7.
33 that means all the three soils samples are alkalinesoil. Sample 4 soil which is petrol soil has a pH of 5.84, sample 5 and 6 whichare both mine soil has a pH of 1.95 and 3.26 respectively which indicate thatthis three soil samples are acidic soils. In the electric conductivity resultssoil sample 6 which is mine soil has the highest EC while soil sample 5 whichis also a mine soil has the lowest EC of 12.64, this means that the two soilswere picked at different spots on the mine and so they were not contaminated bythe same contaminants.
Inthe loss if ignition results, sample 2 which is oil soil has the lowest %OMwhich is negative of -3.6 because its pre-ignition weight is lower than itspost-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 apositive %OM of 14.6, 17.1, 2.96, 19.
2 and 17.1 respectively because its pre-ignitionis higher than the post-ignition. The errors that could have been encounteredare parallex error when one was using the measuring cylinder by not taking thereading below the meniscus, the human reaction time error where one may take along time to take readings form the pH meter and lastly the calibration errorwhere the reading is taken before the equipment read zero.CONCLUSION AND IMPLICATIONSContaminatedsoils from the garden, oil and farm are alkaline soil samples and contaminatedsoils from the petrol and mine are acidic as a result of high concentration ofheavy metals. Contaminated soils from mines have a big difference in EC due tothe fact that soil samples were taken from two different locations in the mineso heavy metals may be highly concentrated on one part of the mine and on theother may have low concentration of heavy metals.
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