(Mine tailings 1)ABSTRACTSoil plays an importantpart 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 becomescontaminated since it is an important factor most of the things suffer becauseof this, it includes things like soil texture, pH and EC, the purpose of thislab experiment was to determine the different parameters for mines, farms,petrol and oil contaminated soils.
The analysis for this parameters helps incharacterization of contaminated soils. In conclusion, for all the soil sampleswere contaminated but the parameters indicated that the results that wereobtained were within the allowable limits. OBJECTIVES· To determine the different parametersand indicators in assessing contaminated soils· To assess the influence of contaminantson the chemical and microbiological properties of soil.INTRODUCTION Soil contamination is caused by the presenceof human made chemicals or any other alteration in the natural soilenvironment. In most cases it is caused by industrial activities, agricultureactivities and waste disposal. The most common involved chemicals includepetroleum hydrocarbons and other heavy metals. Health risks usually comes fromdirect contact with contaminated soil, vapors from the contaminants. Soilquality indicators are used to evaluate how well soil functions, it cannot bemeasured 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 tochanges in soil management and tillage.( Doran 1996)Organic matter, morespecifically soil carbon goes beyond all three indicator categories and I isthe most widely recognized influence on soil quality. Organic matter is mostlytied to all soil functions. Chemical indicators give the information about theequilibrium between soil solution (soil water and nutrients) and exchange sites(clay particles and organic matter), soil reaction (pH) and electricalconductivity are examples of levels of soil contamination indicators. Heavy metals occurnaturally in the soil environment from pedogenic processes of weathering ofparent materials at levels that are either regarded a trace or rarely toxic.Contamination of soils by heavy metals is a very significant problem, whichleads to negative influence on soil characteristics and limitation of productiveand environmental functions.
A number of diversity, microbial activity of soilmicroorganisms are affected by heavy metals. Usually they cause slow downgrowth and reproduction of microorganisms in the soil then prevail slowergrowing microorganisms with lower diversity and higher resistance to heavymetals. Heavy metals have high concerns not only for their toxicity to livingorganisms inhabiting in the soil, but also for their immobilization withindifferent organic and inorganic colloids as suggested by (Nanniaperi 1997).Soil organic matterplays a critical role in the conservation of fertility especially in theextremely coarse textured soils like those in Palapye. In these soils soilorganic matter is both the source of nutrients and mechanism for nutrientretention, it provides favorable conditions for soil biota. Loss on ignition isone of the most used methods for measuring organic matter content in soils butdoes not have a universal standard protocol. Its accuracy can be influenced bya number of factors for example the sample mass, temperature of ignition andduration and clay content of samples. Soil electricalconductivity is a major factor for the determination of the health status ofthe soil.
EC measurements correlate with soil properties that affect cropproductivity such properties are; soil texture, organic matter level, drainageconditions, salinity, cation exchange capacity. Characteristic such as loss oforganic matter, compaction, high salinity and the soil degraded to a point thereis low cat ion exchange in the soil these characteristics shows a degree ofcontamination in the soil. Soil pH is the indication of the acidity andalkalinity in the soils, and is measured in pH units.
The negative logarithm ofthe hydrogen ion concentration defines soil pH. It ranges from 0 to 14. It isan important measurement because the soil acidity and alkalinity determines howeasily the plants can absorb nutrients from it.
MATERIALSAND METHODSMATERIALSUSEDChemical characterization of contaminated soilØ 6soil samplesØ ECmeterØ pHmeterØ DistilledwaterØ BeakersØ Stirringglass rodsOrganic carbon through loss of ignitionØ Porcelaincrucibles Ø 6soil samplesØ AnalyticalbalanceØ MufflefurnaceØ DesiccatorHeavy metal contents and availabilityDigestion of soil samples and heavy metaldeterminationØ 6soil samplesØ CrucibleØ OvenØ AquaregiaØ Deionizeddistilled waterØ FilterpaperØ Milliporefilter paper Microbial populationØ 6soil samples Ø DistilledwaterØ 150ml EflaskØ 10ml ttube Ø Petriplates with potatodextrose agar to which 0.05% (w/v) chloramphenicol Ø 1mlpipette man Ø 1mlpipette tips Ø Petriplates with nutrient agar with nystatin (0.015%)METHODOLOGYA. SOIL SAMPLE PREPARATION500g of soil samples were prepared, and then air-dried a sieve with amesh size of 2x2mm2 was used to remove large particles and rootfragments.
Each sample was then homogenized and divided into sub-samples, thenstored in polyethylene bags at 4?C prior to biological and physicochemicalanalyses. CHEMICAL CHARACTERIZATION OF CONTAMINATED SOILS SOIL pH AND ECFirstly the pH and the EC meter were calibrated using appropriatebuffer solution based on the manufacturer’s instruction. For pH, the readingswere 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 40mldistilled water on a 100ml beaker. The mixture was then mixed well using astirring glass rod for 30minutes. The pH and the EC of the soil watersuspension were then determined.
The results after the determination were thenanalyzed in duplicates. ORGANIC CARBON THROUGH LOSS OF IGNITIONAnalytical 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 tocool for 30 minutes and the weight was measured. The crucibles were then takenout 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 thenprepared in advance. Samples were placed in trays so that they can be ovendried at 105?C for 24 hours.
The trays were labeled with sample ID forrecognition. A blue/green oven located at the back room RCB6301 was used. Theoven 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 theunit). 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 eachcrucible, this was the pre-ignition weight. The crucibles were placed back intothe desiccator after being weighed. The samples were then transported to themuffle 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 sampleswere then allowed to cool off to approximately 150?C.
The temperature of thefurnace was checked by turning it back on and reading the display and switched off after gettingthe readings. After being cooled to approximately 150?C samples were removedfrom the oven and placed into desiccators using tongs. After 30 minute elapsedthe samples were then removed from the desiccators and weighed forpost-ignition weight. The crucible weight was subtracted from the post-ignitionweight and the results were tabulated. The %OM was then calculated using thefollowing equation:%OM= pre-ignition work (g) –post-ignition weight (g)/pre-ignitionweight (g)*100 HEAVY METAL CONTENTS AND AVAILABILITY 3.1 DIGESTION OF SOIL SAMPLES AND HEAVY METALSDETERMINATIONSoil samples were oven-dried at 60?C for 24 hours before they weregrinded into a fine powder using a sterile mortar and pestle. The samples ofweight 2.5g were then transferred into a crucible before being mixed with 10mlof aqua regia, which consisted of HCL:HNO3 (3:1).
The mixture was digested on ahot plate at 95?C for 1hour and allowed to cool to room temperature. The samplewas the diluted to 50ml using deionized distilled water and left to settleovernight. The supernatant was then filtered through Whatman No.42 filter paperand (‹0.45?m) Millipore filter paper prior analysis by graphite furnace atomicabsorption spectrometry. (GF-AAS) RESULTSTABLE 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 = 14.360Sample 2%OM= (5.00000-5.
17803)/5.00000 * 100 = -3.561Sample 3%OM= (5.00030-4.14135)/5.
00030 * 100 = 17.178 Sample 4%OM= (5.00085-4.8526)/5.
00085 * 100 = 2.964Sample 5%OM= (5.00024- 4.03951)/5.00024* 100 = 19.214Sample 6%OM= (4.
83415-4.00911)/ 4.83415 * 100 = 17.
067 Table 2. Sequentialextraction of Ni Cu and Pb in two mine tailing soils collected from abandonedmine 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. Microbialcount of soil with different form of contamination based on nutrient agarculture. 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 onheavy metals in different soil samples DISCUSSIONFor the resultsobtained, the soil samples for the petrol contaminated and mine tailings have acidic pH, with one for themine tailings 2 having the highest pH.
The soil sample for garden, farm, oilcontaminated soils have basic pH conditions, with the oil contaminated one withthe highest pH. For garden and farm soils their pH is affected by the nutrientsthat are used when the plant use themfor plant growth. The alkalinity for soil samples can be caused by naturalcauses for example there can be a presence of soil minerals that produce sodiumbicarbonate that can happen through weathering. For petrol and mine tailingssamples they appear acidic due to the environment, so they contaminate thesoil.
Some heavy metals are contained in the waste, they affect soil pH.Electrical conductivityis dependent on the dissolved material is high on the soil sample, the EC willalso be high in the sample. Mine tailings 2 was found to have the highestelectrical conductivity; this is so because of more accumulation of metals suchas lead from the waste. For the loss of ignition method, when determining theorganic matter, the results were influenced by the pH, so the more the acidicthe soil sample is the higher the organic matter present in that sample but thisis not so for all the soil samples. The loss of ignition is designated tomeasure the amount of soil moisture also the impurities that are lost when thesoil sample is being ignited. The analysis of LOI calculates %OM by comparingthe weight of a soil sample before and after it has been ignited. From theresults tabulated sample five for mine tailings 1 had the highest %OM . Beforeignition the samples contained organic matter, but after they were ignited allthat remained was the mineral portion of the soil.
The difference that wasnoticed in the weight before and after the ignition represented the amount ofthe organic matter that was present in the sample. When determining theheavy metals availability, metals were expressed in percentages, this showedthose metals are high in pollutants while other metals showed theircontamination to be less significant. LOD showed that metals were not detectedin the soil sample. For the sequential extraction, for the nickelcontamination, mine tailings 2 it had high intensity factor because it has ahigher total concentration while the mine tailings 1 had high intensity factorthis is due to high exchangeability, therefore sample 5 with mine tailings 1casuse more toxicity as compared to mine tailings 2 of sample 6.
For themicrobial population, the counts for the soil samples that appeared to bealkaline, 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 itrender their growth.CONCLUSIONFor the objective ofcontaminants has the influence on the microbial and microbial properties ofsoil, this was proved to be so by the electrical conductivity of the soilsample.
This is so because dissolvedmaterials affect the EC since they contaminate the soil, it shows that the soilcontaining more dissolved materials will have high EC. Furthermore themicrobial population is in agreement with the objective of acidity of soildecreasing with the growth of microbes.STUDY QUESTIONS· What is the effect of contamination ondifferent soil parameters( pH,EC, organic matter and microbial population)tested.
Forph most of the heavy metals contaminants will decrease the pH of the soilmaking it become acidic, as for the EC the contaminants will increase theelectrical conductivity of the soil samples. The organic matter present in thesoil samples will be determined by pH. For the microbial population thecontaminants affect it negatively because some of the contaminants change thesoil property which is not suitable for their growth.· Differentiate the practical implicationbetween the determination of the total heavy metals contents and availableform(bioavailable form)Theimplication of the heavy metals indicates that the quantity factor of the soiland it includes both the bioavailable form and some are bound to other phasesin the soil which is not available for use by the plants.
The determination ofthe heavy metals does not tell one about the amount of pollution in the area· How do contaminants affect the capacityof soil microbial populationTheyaffect the soil capacity of soil microbial population and hence modifying theirdiversity, the contaminants also inhibit the enzyme activities in the soil.Biological processes for example nitrification and decomposition of humus areusually reduced in the soil hence the soil fertility and soil structure.REFERENCESDoran, J.W. and T.B.Parkin.
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