Contamination and Pollution Studies of Heavy Metals in Sand Filter Media Waste Dumpsite in Yenagoa, Bayelsa State, Nigeria

The contamination and pollution level of five Heavy Metals in spent Sand Filter Media [SFM] waste dumpsite was investigated to ascertain the contamination, pollution and possible migration in that environment. Samples were collected at the surface, 0.1m depth and 100m away from the dumpsite and analysed using Flame Atomic Absorption Spectrophotometer (FAAS) for concentration of Cr, Fe, Mn. Ni and Pb ions. Geochemical Pollution Indices were used to evaluate the contamination and pollution level of the HMs comparatively using the world shale average values and the experimental control value. Results obtained showed highest concentration of 12.50mg/kg for Fe and lowest detectable concentration of 0.2mg/kg for Ni at the top of the dumpsite. All five heavy metals had low concentrations compared to WHO and national standards for soil quality both at the top and 0.1m depth of the dumpsite. Percentage concentrations of the heavy metals at the top showed 78.81, 12.04, 7.88, 1.26% in the order Fe >>> Cr > Mn > Ni > Pb with the values of Ni and Cr at 0.1m depth slightly higher indicating some level of migration. Contamination Factor Cf, depicts very severe contamination to slight pollution at the top with minimum of 0.714 and maximum of 1.471. Degree of Contamination Cd, of <8 and Modified Degree of Contamination mCd <1.5 showed low contamination. The pollution load index, PLI values of < 50 depicts that no drastic rectification measure was needed which concludes that the SFM dumpsite was contaminated but technically not polluted. DOI: https://dx.doi.org/10.4314/jasem.v24i4.6 Copyright: Copyright © 2020 Ikoko et al. This is an open access article distributed under the Creative Commons Attribution License (CCL), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Dates: Received: 11 February 2020; Revised: 16 March 2020; Accepted: 26 March 2020

The surface mobility, biochemical redox reactions and underground bioaccumulation of heavy metal contaminants and their related impact in the ecosystem is of considerable concern to chemists and other environmentalists around the world (Leizou et al., 2015). Among the underground water contaminants, heavy metals are known to be of most concern to environmentalists because their compounds (ligands) are indeed still in reaction and are capable of many more reactions while the central metals are relatively inert and can accumulate from small quantities to quite larger quantities (Dube, et al. 2001). Further environmental concern of HM contaminants reported by Wu et al (2012), are due to their prolonged persistent stay in the environment unchanged, their ability to be recycled biochemically in the same form that they were, their ability to accumulate and increase their concentration biologically, their biological toxicity to flora and fauna, their capability to undergo reduction & oxidation reactions with or without availability of oxygen, their ability to undergo precipitation, solubilisation, to aggregate or flocculate in solutions, the ability of their ligands to undergo chelation and finally their ability to put all the above together and be toxic in nature (Ademeroti 1996).
Specifically, compounds of Cr in both oxidation states (Cr 3+ , Cr 6+ ) are biologically harmful to living things, carcinogenic and damage digestive systems (Fawell et al., 2003). High concentrations of Mn cause hallucination to even forgetfulness and it affects both flora and fauna and the cause of dark colouration to water and pipings (Du, et al. 2011). Ni is carcinogenic at high concentrations and inhalation is known to cause severe lung cancer or nasal tumours as it can replace Zn and Mg ions in DNA-polymerase (Fawell, et al. 2007). Pb is transported through intake and carried by the haemoglobin in blood and is therefore poisonous to man and can even transfer into foetus through umbilical cord. Pb even at small dosages is known to cause adverse mental situations (Cotruvo, et al. 2011). In addition, water treatment chemicals are also a huge sources of HMs and contributors to reaction byproducts that lead to health risk (Stoddart and Gagnon 2015). The process of water purification using SFM requires aluminium sulphate powder (alum) and chlorine gas or powdered sodium hypoclorite HTH as chemical enhancement (Mustafa and Yusuf 2012)). Depending on pH and temperature, sedimentation/flocculation processes produces Al 3+ , Fe 2+, 3+ by-products of organic and inorganic anions (Sielechi, et al, 2010). Disinfection process effectively produces hypochlorous acid with other significant carcinogenic organic by-products like trihalomethanes [THM], haloacetic acids, etc, while ozone disinfectant produces harmful by-products as well (WHO 2011).
The substance of this study, Sand Filter Media [SFM], is commonest, cheapest means and most widely used in water filtration and it is still the best option in developing countries (Lynn et al., 2013). The SFM accumulate these heavy metal and other contaminants to an extent that the filtration is no longer effective and it is removed from the filter vessels into a dumpsite and the filter vessels are recharged (Cakmakci et al., 2009). Studies on trace metals from different areas including the niger delta area of Nigeria, showed HM contamination (Nariman andMohammed, 2011, Babagana et al., 2014). This paper reveals studies carried out to show the concentration level of selected heavy metals adsorbed in the SFM dumpsite and the environmental concern upon evaluation with standard pollution indices. In this part of the world, more attention is focused on environmental degradation activities and wastes mainly from oil exploration, and manufacturing activities with minimal attention on the waste from essential public facilities (municipal water producing or health facilities), since these are mostly government infrastructures. However, several works on waste dumpsites mostly showed significant enrichment and pollution (Li and Feng 2012). Although, a few have reported minimal contamination as well (Amos-Tantua et al., 2014).

MATERIALS AND METHODS
Study Area: The study city, Yenagoa, is the capital city of Bayelsa State, Nigeria and lies between latitude 4° 50' to 5° 00' North and longitude 6° 11' to 6° 25' East. The city is located in a humid tropical wetland area with mean annual rainfall of about 2539mm and an average mean temperature of 26.2°C (Ayolagha, 2001). The SFM dumpsite that is studied is the Ovom Waterworks located at Geographic Positioning System [GPS] 4.934245,6.266297 interpreted to read 4 o 56'03.3''N 6 o 15'58.7''E.
Sampling: Three distinct soil samples were obtained. Sample ATM was 2kg deposit of Sand-Filter-Media [SFM] collected on the surface of the dumpsite between 0-10cm at five (5) different points in the sample location using a soil auger. Half of these were put separately in a black plastic bag, labelled sample ATM 1, 2-5, stored in a cool place for digestion. The other half of the five portions were mixed together to get a representative sample of the entire top surface of the SFM dumpsite and put into a plastic bag, labelled as Sample ATM and stored in a cool place. Sample B was collected at a depth of 100cm in a 100cm x 100cm x 200cm vertical hole dug with a shovel down the centre of SFM dumpsite. Four separate samples were collected after the 100cm marked depth at the four corners of the 100cm x 100cm x 200cm hand-dug hole. The collected four samples from the four-corners were mixed together to get a representative sample at 100cm depth and 1kg of the representatively mixed sample was put into a plastic bag and stored in a cool place and labelled Sample B. Sample C was collected at surface of the top soil of an unoccupied land space at a distance of about 100m away from the SFM dumpsite, as a control sample. About excess of 1kg of each sample was collected, stored in a cool place. All the samples were analysed within 48 hours of sampling.
Sample Preparations: Sample digestion was done using standard procedure for acid digestion (APHA 1992). Portions of Samples ATM1-5, ATM, B and C were each separately mixed thoroughly in the bag, airdried openly for about 5 hours and then sieved to remove the larger coarse particles. 1g of each of the samples was measured and put into 150ml crucible and a 1:2:2 mixture of 5ml of concentrated nitric acid (HNO3, 70% w/w), with 10ml of hyperchloric acid (HClO4, 60% w/w) and 10ml of Hydrofloric acid (HF, 40% w/w) was added. The mixture was digested in a hot plate in a fume cupboard for 3 hours at about 80 o C (Leizou et al.,201. The mixture was allowed to cool and 10ml of distilled water was added to the digest and filtered into 100ml volumetric flask. The digested mixture was made up to 100ml by adding deionized water. The digested mixture was then transferred to a 15ml sample bottle and labelled ATM1. The same procedure was used for samples ATM2-5, sample B and control sample C and these are now re-labelled as ATM2, ATM3, ATM4, ATM5, A-TM, B-TM and C-TM. Analysis of the heavy metals concentration for lead (Pb), Iron (Fe), Nickel (Ni), Chromium (Cr) and Manganese (Mn) was done using a Buck Scientific 210 VGP Flame Atomic Absorption Spectrophotometer AAS following prescribed procedures by the manufacturers.

RESULTS AND DISCUSSION
Results obtained from the analysis done for selected five selected HMs is showed in  Geochemical Indices: Geoaccumulation Index, Igeo, is used to determine the level of contamination of heavy metals in soils essentially for recognizing and managing soil pollution. It is expressed as; = 1.5 Where Cn = measured conc. of element in the sediment or soil, Bn = geochemical background value, and 1.5 = constant to analyse fluctuations in the environment.
The result of the Geoaccumulation Index, Igeo, is expressed in USA, Europe and Nigeria as comparative of seven grades as given in table 3. The baseline value, Bn, of each heavy metal is the concentration of that element in average shale either directly measured from relatively presumed uncontaminated soil of the same texture or taken from the literature of a related work in that area. However, getting actual background concentration levels of most soils is questionable because of unquantifiable anthropogenic inputs of heavy metals over time (Hamon et al, 2004). The table 4 shows geochemical index calculated using the Sample C being the experimental control value (EC) taken 100m way from SFM dumpsite (relatively presumed uncontaminated soil of the same texture) and world shale average values (WSA) for the five metal considered in the study (Edori and Kpee 2017). The Geo-accumulation, Igeo, evaluations showed that almost all the results are < 0. The results belong to class I of the Igeo scale as given by Muller et al (1981).
Results showing negative or < 0 implies that there is no significant difference between the baseline concentration values Bn and the accumulated concentration of that contaminant HM. Thus, there is no significant accumulated contamination in the metals considered at both the surface of the SFM and 100m depth below the surface of the SFM (Alfred, et al. 2013). However, the Igeo values calculated using the WSA values as the baseline concentrations, Bn, were lower since they had higher negative values. This is so because the Bn values were higher than those from the EC values gotten from the research area.
Contamination Factor and Degree of contamination Cd:: The contamination Factor is a single element evaluation and thus it is given as; is the mean concentration of metals from least five sampling sites, and is the pre-industrial concentration of the individual element.
The Cf is determined upon comparison with standard table of index established in figure 5. The Contamination Factor Cf, at the top of the SFM and 100cm below the SFM were calculated using both the concentrations of the experimental control, EC, and the world shale average, WSA, concentration established as given in table 6. The Degree of Contamination, is the sum of contamination factors for all five elements examined and is given as;

=
The Contamination factors Cf for the five element studied [Pb, Fe, Ni, Cr & Mn] and the Degree of Contamination Cd classes and terminologies is given in table 7 (Alfred, et al. 2013). The calculated values for the Degree of Contamination, Cd for the five studied metals at the top of the SFM using the EC and WSA respectively is given in table 8a and 8.b. Again the overall sum of the contamination factors ∑Cf of all five elements called the Cd was less than 8 (<8) and is termed low contamination.
Modified Degree of Contamination mCd: This is the modified or generalised form of equation for the calculation of the modified degree of contamination, mCd for a given sampling site. It is given as;

= ∑
Where, n = number of analysed elements; = Contamination Factor Accordingly, the mCd for the five metals using the two scenarios of Cn-ctrl from experimental control and that of Cn-wsa from world shale average is calculated and compared to the standard index table for the mCd and their classes given in table 9. Calculated results of the mCd is given in table 10.0. The results showed that the mCd is lower for the calculated values using the world shale average, Cn-wsa being 0.005179 at the top 0.005726 at 100cm depth as compared to calculated mCd values of 0.8104 at the top and 0.6632 at 100cm depth of SFM from the experimental reference Cn-crl, However, the values of mCd using both reference cases were below the lowest class of contamination in the standard index. Therefore, the modified degree of contamination for the five metals in this study were less than 1.5 and are classified as very low degree of contamination. Pollution Load Index, PLI: The Pollution Load Index, PLI is used for detecting pollution which permits a comparison of pollution levels between sites and at different times. It enables or gives an estimate of the metal contamination status and the necessary action that should be taken. It is given in the equation below (Qingjie, et al. 2008   The PLI at the top of the SFM using the experimental control Cn-ctrl was 0.9802 and that using the world shale average Cn-swa was 0.00754. Both results are less than the minimal pollution index scale of <50. Therefore, the top of the SFM was not polluted with the five metals analysed. Table 11 shows the PLI at 100m in the SFM. The results showed that the PLI at 100m in the SFM using the experimental control Cnctrl was 0.798 and that using the world shale average standard values was 0.00613. These two values were both below the minimal pollution index of <50. This implies at 100m in the SFM, there was no need for drastic remediation measure because there was minimal pollution at this point.

Conclusion:
The investigation of the contamination and pollution level of selected five Heavy Metals [HMs] in spent Sand Filter Media [SFM] waste dumpsite revealed generally low total HMs concentrations with those at 100cm depth, relatively lower, revealing that there was mobility of metal ions possibly due to leaching and chemical reactions. Generally, the concentrations were lower or within the permissible limits given by WHO and national standards with the trend; Fe > > > Cr > Mn Ni > Pb which agrees with high concentration of Fe in the underground water in this region. Geochemical Indices evaluation carried out using the world shale average (WSA) and the experimental control (EC) values revealed that for the Geoaccumulation Index, Igeo, there was no contamination. But the Contamination Factor, Cf, showed that was contamination at the top using EC values with slight pollution by Fe and Mn and at 100cm depth, there was 'moderate contamination' from Mn, while Fe, Cr, Ni were classified 'very severe contamination'. The Degree of contamination, Cd, and Modified Degree of Contamination, mCd, indices revealed 'low contamination'. The Pollution Load Index, PLI, index classified the dumpsite as 'requires no remediation measure' due to non-pollution at the time of this study.