Assessment of Some Heavy Metals in Soil Samples Along Gutters in Nkpor, Anambra State
CHAPTER ONE
OBJECTIVES OF THIS STUDY
The objectives of this study are:
- To determine the total concentration of some selected heavy metals in
- To use sequential extraction technique to fractionate metals in soil
CHAPTER TWO
MATERIALS AND METHODS
REAGENTS
Hydrochloric acid, nitric acid, hydrofluoric acid, boric acid, aqua regia (HCl + HNO3 , 3:1), sodium acetate, ammonium acetate, hydroxylaminehydrochloric acid, hydrogen peroxide, deionized water.
MATERIALS
50ml burettes, glass funnels, sample containers. 250ml conical flask, platinum dishes, 150ml beaker, pulverizer, what man No.1 filter paper. Soil samples, centrifuge 1000 Retort.
INSTRUMENT
Atomic Absorption Spectrophotometer (varian 220fs), electronic weighing balance (Ohans adventurer), pH meter.
SAMPLE COLLECTION AND PREPARATION
The samples were collected at five selected drainage systems and prepared following the steps outlined.
The soils were dried at ambient temperature (28-310C), pulverized with the pulverizer (ball grinder) and sieved thoroughly using a sieve of 100-µm mesh size and stored in a polyethere bag.
Soil sample (lg) each was digested to obtain the soil solutions by adding 5mls of aqua Regina followed by 5ml of HF and heated for 1hr 30 mins. The process was repeated to ensure complete digestion. On cooling, 20 ml of boric acid (H3BO3) was added to complex with residual hydrofluoric acid (Hf), which would otherwise attack glass wares. The digests were filtered into 50ml volumetric flasks using What man No.1 filter paper and were made up to the mark after quantitatively transferring rinsates and deionised water. The filtrates were transferred into a clean dry plastic container for storage.
Blank digest was carried out i.e. a total mixture of 10ml HF and 10ml aqua regia were transferred into Teflon beaker without the sample and heated in water both at 100oC for 3 hours. 20mls of boric acid was added and the mixture filtered into 50ml volumetric flask and made up to mark with deionized water. The blank solution and the digest were analyzed using chemtech Analytical Alpha Star Model Atomic Absorption Spectrophotometer machine (AAS).
SEQUENTIAL EXTRACTION
This involves the treatment of the samples with a series of reagents in order to partition the trace element contents. The reagents used are generally similar to those employed as single extractant to liberate metals bound to particular compound of the sample matrix. The principal advantage of sequential extraction over the use of single extractants is that phase specificity is removed. The method employed for the sequential extraction (speciation) was the method of Tessier, et al [4]. 1.0g of the sieved soil sediment samples were used for the sequential extraction processes.
PREPARATION OF REAGENTS
- 1M Sodium Acetate (NaOAc) 35g of NaOAc powder was weighed into 500ml volumetric flask, dissolved with deionised water and made up to the mark. The mixture was thoroughly shaken to effect
- 0.02M HNO3.1.3cm3 of concentrated HNO3 was measured and transferred into a 100ml volumetric flask and made up to mark with deionized water
- 04M hydroxylamine hydrochloric acid (NH2OH.HCl) in 25% (v/v) HOAc. 1.39g of NH2OH.HCl was weighed into a 500ml volumetric flask, dissolved with 25% (v/v) HOAc and made up to mark with deionised water. This was thoroughly shaken to achieve homogeneity.
CHAPTER THREE
RESULTS AND DISCUSSIONS
Table 1 : MOISTURE CONTENT OF THE SOIL SAMPLES
Table 2 showed the digestion of the soil samples with HF, aqua Regia and boric acid, and the total concentration of all the metals analyzed in each soil sample. It was observed that sample A had the highest concentration of heavy metal and the trend is Ni> Cr> Hg> Zn> As = Cd (0.0000), it was followed by sample B with Ni> Cr> Zn> cd> Hg> = arsenic (0.0000). Sample C had a total of 0.3132 with Ni> cr Zn> Cd> hg> As (0.0000). Sample D had the concentration of Cr> Ni> Zn> Cd> Hg> As (0.0000) whereas in sample E , Ni> Zn> Cd> Hg> As.
Further Table 2 also indicated the total concentration of each metal in all soil samples with Ni appearing in all soil samples with the highest value of 0.2118mg followed by Cr with a value of 0.0806 and Hg Cd have 0.0035 and 0.0031 respectively, Again there was no trace of As.
FIG 2: MEAN CONCENTRATION OF CrIN mg/mg
In Table 3, the varying concentration of Cr is seen to be highest in sample C (a drainage system along Limca Road Nkpor). This could be attributed to the numerous paint and cement stores along this road, as Cr is used in metal alloys and pigment for paints, cement, paper and rubber. Cr is an essential nutrient and it is non-toxic when its level is low but long-term exposure can cause kidney and liver damage. The EPA recommended limited for concentration of Cr is 0.15mg / kg so the concentration of it found along this road does not pose damage to human beings.
CHAPTER FOUR
CONCLUSION AND RECOMMENDATIONS
CONCLUSION
The results of this analysis indicate that these soil samples contain reasonable proportions of the heavy metals analyzed which include Cr, Ni, Zn, Cd, Hg and As, in tolerable concentrations. Therefore the lives of people residing in these areas are not under threat.
However, caution should be taken in order not to increase the concentrations of these toxic heavy metals through Urbanization and industrialization as this will be disastrous to both human and plant lives
RECOMMENDATIONS
There should be a legislation to stop the indiscriminate dumping of waste in the gutters in Nkpor metropolis, appropriate sites should also be chosen for dumping of waste.
Again, I recommend the use of continuous flow sequential extraction method for heavy metals fractionation in soils since it has the benefit of exposing the sources and toxicity levels of the metals in the soil samples.
Further work should be done on the analysis of heavy metal concentration using more sensitive instruments such as GT.AAS.
REFERENCES
- C Adriano, (2001) trace elements in terrestrial environment; Biogeochemistry, Bioavailability and Risks of metal, 2nd ED. Springer, new York , pp 105—108
- Springer, A dictionary of chemistry (2000) Oxford University press; Oxford reference on line. Oxford University press pp57—80
- P Tessier, G. C. Campbell, and M. Bisson (1999) .sequential extraction procedure for the speciation of particulate trace metals chem… pp. 51;844- 95.
- B.C John, H. Dufius (2002) “Heavy metals” a meaningless term? (IUPAC technical report) pure and applied chemistry, Vol.74pp793-807.
- M Okonkwo and A.N Eboatu, (1999). Environment pollution and degradation book 2 Onins excel company publishers Zaria Nig. p2
- Pilgrim W and Schroeder W (1999); Multi-media. Concentration of heavy metals and major ions from urban and rural sites in new Brunswick, Canada environment monitoring and assessment, Vol.47 pp.89-108 B1fep org/ heavy metals htm.