ABSTRACT
Heavy metal concentrations and degradation efficiency of total petroleum hydrocarbons (TPHs) on environment in Ibeno Local Government Area, Akwa Ibom State, Nigeria was investigated. Experimental design method was adopted for this study. Fifteen composite samples each of soil, leaves of Telfairia occidentalis, sediment and water were collected in December 2012 and June 2013. The sediment and water samples were collected using corer and clean plastic bottles respectively. Soil and sediment samples were air dried, mechanically ground using mortar and pestle, and 2 mm mesh size obtained for further analysis. The soil
and sediment samples (1.0 g) each were weighed into Kjeldahl flasks. Aqua regia (15 cm3)
was added, swirled to mix and kept overnight. The flasks were heated on a hot plate to 50 oC for 30 min; temperature was later adjusted to 120 oC and heated continuously for 2 h. The mixture was cooled, and 0.2 M HNO3 (10 cm3) added. The resulting mixture was filtered with a Whatman no. 541 filter paper. The filtrate was transferred into a 50 cm3 standard flask and made up to the mark with 0.2 M HNO3. The leaves samples were washed with de-ionized
water, dried to constant weight in an oven at 105 oC, pulverized and 2 mm mesh size obtained
for further analysis. The ground leaves were digested with 1.0 cm3 concentrated HClO4, 5 cm3 concentrated HNO3 and 0.5 cm3 concentrated H2SO4 in 50 cm3 Kjeldahl flask. Each water sample (10 cm3) was digested with 2 cm3 concentrated HNO3. Concentrations of the heavy metals were determined using AAS Unicam 939 model. The soil samples (150 g) each
were transferred into four (4) plastic buckets labeled A, B, C and D. Varying concentrations palm bunch ash (PBA) (0.0 g, 50.0 g), Tween 80 (50.0 g) and PBA + Tween 80 (25.0 g) each were added to A, B, C, and D, where A served as control. Portions (5 g each) of A, B, C and
D were weighed into standard flasks, 25 cm3 of xylene added and shaken, NaCl (5 g) was
added and left for 72 h. The liquid portion was decanted into a separatory funnel, corked and shaken. The xylene layer was transferred into 100 cm3 centrifuge tube containing 5 g of Na2SO4 and agitated for 15 min, the absorbance of the solution was measured at 425 nm and used for calculating concentrations of TPHs. Concentrations of TPHs were determined at 20
days intervals for 60 days. The data were analyzed on the basis of first order kinetic model
InC = InCo- kt. Heavy metal concentrations (mg kg-1) during dry season were, soil: Fe (15.15
± 5.91), Mn (10.36 ±3.18), Cd (0.23±0.31 ), V (0.17 ± 0.29), Ni (0.19 ± 0.05), leaves of Telfairia occidentalis: Mn (7.73 ± 3.06), Fe (5.93±1.28), V (0.16±0.26), Cd (0.21 ± 0.16), Ni (0.02 ± 0.01), sediment: Fe (22.18 ± 14.82), Mn (9.67±2.75), V (3.39±3.30), Ni (2.18±0.78), Cd (0.48 ± 0.75), and water: Mn (2.80±0.93), V (1.53±1.42), Ni (1.50 ± 1.53), Fe (0.86 ±
0.25), Cd (0.27±0.21), During wet season, soil: Fe (12.09±4.98), Mn (9.66 ± 2.18), Ni (0.05±0.03), V (0.04±0.01), Cd (0.04±0.02); leaves of Telfairia occidentalis: Mn (7.75±3.76), Fe (5.96±4.07), V (0.21±0.09), Cd (0.19±0.06), Ni (0.03±0.06), sediment: Fe (23.28±0.24), Mn (9.45±2.63), V (3.31±3.34), Ni (1.94±1.48), Cd (0.48±0.74), and water: Mn (3.13 ±
0.79),V (1.88 ±1.45), Ni (1.45 ±1.04), Fe(1.05 ± 0.25), Cd (0.10 ± 0.13), were obtained. The correlation coefficients were: V (0.556), Ni (0.376), Cd (-0.043), Pb (0.856), Mn (0.813), Co
(0.255), Zn (- 0.193), Fe (- 0.383), and V (-0.419), Ni (- 0.355), Cd (0.248), Pb (0.745), Mn (0.974), Co (- 0.022), Zn (0.886) and Fe (-0.384) for dry and wet seasons respectively. The mean concentration of TPHs in the soil was 14.55±0.01 mg kg1. Degradation efficiencies
obtained were PBA (86.69 %), PBA + Tween 80 (85.63 %), Tween 80 (76.70 %), and control
(5.40 %). The rates of degradation (mg kg-1 day-1) ranged from 2.70×10-2 to 1.30×10-2;
5.00×10-1 to 2.18×101; 2.49×10-1 to 1.84×10-1 and 4.67×10-1 to 2.09×10-1 for A, B, C and D
respectively. k ranged from 2.09 × 10-2 to 2.78 × 10-2, 3.79×10-2 to 5.81×10-2, 2.78×10-2 to
2.09×10-2, 5.13×10-2 to 3.23×10-2 for A, B, C and D respectively. Concentrations of heavy metals in wet and dry seasons were variables. The concentrations of all the investigated heavy metals in soil were within permissible range as recommended by DPR, but higher than the reference soil samples. Mean concentrations of some of the investigated heavy metals (Ni, V, Pb, Zn and Co) in leaves of Telfairia occedentalis were within the normal range of WHO and FME standards for vegetables and food stuff except Cd, Fe and Mn. The concentrations of Ni, V, Cd, Pb, and Mn in water were higher than WHO and DPR standards. Also, the concentrations of Mn, Ni, Pb, and Zn in sediment were higher in dry season compared to wet season except Fe, V and Co. Concentrations of Fe were the highest in all the seasons; sediment retained the highest concentrations of heavy metals. Telfairia occidentalis can be used as a resident indigenous plant bio indicator for monitoring anthropogenic influenced V, Pb, Mn and Zn in the soil of the study area. Degradation efficiency of TPHs were as follows: PBA (86.69 %) > PBA + tween 80 (85.63 %) > tween 80 (76.70 %) > control (5.40 %). The rate of degradation of TPHs decreased as the concentrations of the surfactants decreased with time.
INTRODUCTION
CHAPTER ONE
Metal pollutants have been a part of human history since the dawn of civilization. However, toxic metals pollution of the biosphere has intensified rapidly since the onset of the industrial revolution, posing major environmental and health problems1. Recently, environmental scientists have raised concern on the increasing ecological and toxicological problems arising
from pollution of the environment. Heavy metals represent an important source of the pollution 2. Heavy metals like As, Pb, Hg, Cd, Co, Cu, Ni, Zn, and Cr are phyto-toxic at all concentrations or above certain threshold levels3. Toxic metals are biologically magnified through the food chain. They infect the environment by affecting soil properties, its fertility, biomass, crops yield and human health3.
Heavy metals occur naturally in small quantities in soil though rarely at toxic level, but human activities have raised these to exceptionally high levels at many polluted land and water sites. Soil is a crucial component of rural and urban environments, and in both places,
land management is the key to soil quality4. Human endeavours such as technology,
industrialization, agriculture, transportation, education, construction, trade, commerce, as well as nutrition have rendered the whole environmental system a “throwing society”. This is true because indiscriminate disposal of wastewater coupled with increasing world population and urbanization have combined to worsen the situation. The use of synthetic products e.g. (pesticides, paints, batteries, industrial waste, and land application of industrial and domestic
sludge) can result in heavy metal contamination of urban and agricultural soils.4
The extent of soil pollution by heavy metals and metal base ions, some of which are soil micronutrients is very alarming. Ademoroti 5, reported positive linear correlation between cadmium, lead, and nickel contents in the soil and vegetable.
Essein et al. 4, observed the trend of mean heavy metals concentrations in Mkpanak a
community in the study area as Fe > Zn > Pb > Ni > V > Cd. The mean concentration of iron in the soil was quite high and exceeded the critical toxicity level. The result obtained also showed that the mean concentration of Cd was high and exceeded the lower limit of 0.01 mg kg-1. Also, Osuji et al.6, had earlier reported possible bio-magnification of Ni, V, Pb, Cu and Cd in the area. Industrial wastes are the major sources of soil pollution and originate from mining industries, chemical industries, metal processing and petroleum industries; the wastes include a variety of chemicals like heavy metals.6
While many heavy metals are essential elements at low levels, they can exert toxic effects at concentration higher. Soil receives heavy metals coming from different sources and at the same time acts as a buffer, which controls the movement of these heavy metals to other
natural components2.
Increase in anthropogenic activities, heavy metals pollution of soil, water and atmosphere represent a growing environmental problem affecting food quality and human health 7 in the Niger Delta region of Nigeria. Nigeria as a major producer and exporter of crude petroleum oil continue to experience oil spill and this exposes the environment to hazards and its effects on agricultural lands as well as on plant growth8. Oil pollution of soil leads to the buildup of essential (Organic carbon, P, Ca, Cu) and non-essential (Mn, Pb, Zn, Fe, Co, Cu) elements in soil and the eventual translocation in plant tissues9. Industrialization coupled with an ever-increasing demand for petrochemicals have resulted in prospecting for more oil wells with consequent pollution of the environment. Causes of oil pollution in Nigeria include discharge from sludge, production test, drilling mud, and spills from pipelines, well blowouts, gas flaring and sabotage10. Oil spills have long effects on soil; an immediate effect of petroleum products in the soil is a depression in population of soil microorganisms. Besides the economic and aesthetic damages caused by oil spills, plants and
animals life in both aquatic and terrestrial environment are affected as most life form die rapidly following spillage. Many unique plants and animals’ species have gone into extinction in the Niger Delta regions11.
Pollution of the ecosystem by toxic metals during man’s activities poses serious concerns because heavy metals are not biodegradable and are persistent in the ecosystem. Once metals are introduced and contaminate the environment, they will remain for a very long time.11
The presence of heavy metals in toxic concentrations can result in the formation of
super oxide radicals, hydrogen peroxide (H2O2), hydroxide radicals (OH-), bio-molecules like lipids, protein and nucleic acid. Chromium, Copper and Zinc can induce the activity of various antioxidant enzymes and non-enzymes like ascorbate and glutathione3. Petroleum renders the soil infertile, burns vegetation and kills useful soil organism12.
In Nigeria, a study of heavy metals concentration near Warri refinery found three to seven times elevated levels of various heavy metals in the soil13. Although the petroleum industry is by far the largest industrial sub-sector in the Niger Delta, at least eight of the most polluting sub-sectors in Nigeria (steel work, metal fabrication, food processing, textile,
refineries and paints manufacturing) operate in the Niger Delta13, 14.
Oil exploration and exploitation have uplifted Nigerian economy leading to rapid development but the impact on the environment is receiving less attention15. One of the major anthropogenic sources of heavy metals enrichment in terrestrial habitats of oil producing area of Nigeria is the frequent spills of crude oil on land and gas flaring 12. Nigerian crude oil is known to contain heavy metals such as Zn, As, Ba, Fe, Pb, Co, Cu, Cr, Ga, Mn, Ni and V.
Toxicity of ingested heavy metals has been an important health issue for decades 16.
Some species of Brassica (cabbage) are high accumulators of heavy metals in the edible parts of the plants 17 and this can be an important exposure pathway for people who consume vegetable grown in heavy metal contaminated soil 15. The level of heavy metals for examples lead, cadmium and copper where determined in cassava from different location of oil
exploration areas of Delta State, Nigeria. The results of different heavy metals have higher values when compared with WHO standard. These metals have damaging effects on the plants themselves and may become hazardous to man and animals. Above certain concentrations and over a narrow range, the heavy metals turn toxic. Moreover, these metals adversely affect natural microbial population leading to disruption of vital ecological processes. Plants can accumulate heavy metals in their tissues and uptake increases generally in plants that are grown in areas with increased soil contamination with heavy metals and therefore, many people could be at risk of adverse health effects from consuming common
garden vegetables cultivated in contaminated soil 12.
Streit and Strum, and Ruszewski et al 18, 19, classified the exchange of chemicals between soil and plants; they divided the most common method of assessing metal toxicity to plants from soil into three categories:
i. monitoring of the presence or absence of specific plant ecotypes and or plant species (indicator plant).
ii. measurements of metal concentration in tissues of selected species
(accumulative bio-indicators).
iii. recording of physiological and biochemical responses (bio-makers) in sensitive bio-indicators.
The pollution of rivers, lakes, underground water, bays of oceans, and streams with
chemical contaminants (heavy metals, organic and inorganic compounds) has become one of the most critical environmental problems of the century.4 Non-degradable, bio-persistent stock pollutant such as heavy metals and mineral hydrocarbons could get into aquatic environment from a wide range of natural and anthropogenic point sources. In aquatic
ecosystems, heavy metals are contained in four reservoirs, namely; the suspended sediment,
the bottom sediment, the surface water and the pore water. Studies have revealed that contaminants in aquatic system are usually in pore water-surface water-sediment dynamic with bottom sediment acting as the major depository of heavy metals5. The questions of heavy metals in water first became an issue only in Sweden and later in Canada.
Writing on the impact of economic activities on the environment of the Niger Delta, Agbozu 13, stated that water bodies have been heavily polluted due to the recurring incident of oil spillage. Most micro-populations and invertebrates are eliminated following large-scale spillage, while sub lethal levels of oil following several scale spillages have generally
affected aquatic resources.
Ibeno Local Government Area is a coastal sub-region characterized by abundant water resources. The absence of potable water supply for domestic use in some parts of Ibeno has compelled the population to rely heavily on natural sources of water supply for domestic uses. The quality of most of these sources of water is doubtful. The study area is one of the coastal area as well as an oil producing area in Akwa Ibom State bordered by the Atlantic ocean and has various environmental problems including pollution of available water resources. There are many types of water sources available for domestic, recreational, fishing and industrial uses. These include ponds, streams, boreholes, lakes, rivers, oceans and rain water, but they are all polluted by human and industrial activities in the area. The anthropogenic and natural phenomena seem to affect water quality in the study area. These include gas flaring, oil spillage, washing wastewater and sludge from industrial processes, poor sanitation, storm surges, salt-water extrusion and intrusion, release of untreated human waste and sewage into waterways.
Water pollution occurs when chemical, physical or biological substances exceed the capacity of water body to assimilate or break down the substance that can cause harm to the aquatic ecosystem. Precipitation that reaches the earth’s surface follows two basic pathways;
it either flows overhead or soaks into the soil20. Water that flows over the ground is often
called run off. The term surface water refers to water flowing in streams and rivers as well as water stored in natural or artificial lakes. Surface water is water that flows or rests on land and is open to atmosphere; lakes, pond, lagoons, rivers, streams, oceans, ditches, man-made impoundments are bodies of surface water 20. Analysis of soil samples from Uyo town by
Akaeze 106 disclosed that heavy metals such as lead, copper and iron are present in the soil,
these may contaminate soil water, which constitutes the major sources of drinking water 21. Oil spillage and dumping of petroleum effluents on land are common phenomena. Gas flaring also contributes to heavy metals contamination of soil15.
The contamination of the environment by heavy metals is viewed as an international problem because of the effects on the ecosystem in most countries. In Nigeria, the situation is no better by the unethical activities of most industries and because of countries inability to manage industrial wastes with the increasing level of pollution of water bodies. Environmental degradation of the oil rich Niger Delta region has caused a wanton destruction and continuous harm to their health, social and economic consequences for its people, for over a decade. Petroleum refineries produce a wide variety of air and water pollutants and the distillation products of refining and industrialization, intensive agriculture and other anthropogenic activities have led to land degradation, environmental pollution and decline in crop productivity and sustainability. These have been of great concern to human and animal health 22, 23. One of the prominent sources contributing to increased load of soil contamination is the disposal of municipal and industrial wastes. The wastes are either dumped on roadsides or used in landfills. These wastes although useful as sources of nutrients are also sources of carcinogens and toxic metals 23. In the study of the socio-economic impact of oil pollution, Worgu 23 stated that crude oil exploration has had adverse environmental effect on soil, forest and water bodies in host communities in the Niger Delta. All stages of oil exploration impacted negatively on the environment and the greatest single intractable environment problem caused by crude oil exploration in the Niger Delta region is oil spillage. According to Annual reports of the Department of Petroleum Resources (DPR) 1997, over 6,000 spills have been recorded in the 40 years of oil exploration in Nigeria with an average of 150 spills per annum. In the period 1976 – 1996, 647 incidents occurred resulting in the spillage of 2,369,407.00 barrels of crude oil with only 549,040.38 barrel recovered, while 1,820,410.50 barrels of oil were lost to the ecosystem23. These chemicals if not properly controlled according to guidelines and standards set by regulating agencies like Department of Petroleum Resources, it can pollute the soil and groundwater system in the area where such operation is carried out. Thousands of spills occur across the fragile Niger Delta and have destroyed livelihoods of fishermen and farmers, fouled water sources and polluted the ground and air. The Nigerian government estimates that there were over 7,000 spills, large and small, between 1970 and 2000. That is approximately 300 spills a year and some spills have been leaking for years. Vast swathes of the Delta are covered with tar and stagnant lakes of crude. By some estimate, over 13 million barrels of oil have spilled into the Delta. An additional 2,405 spills by all major oil companies in the region have occurred since 2006. Corroded pipes caused a spill in 2010 that leaked about 232 barrels of crude oil 23.
This material content is developed to serve as a GUIDE for students to conduct academic research
HEAVY METAL CONCENTRATIONS AND DEGRADATION EFFICIENCY OF TOTAL PETROLEUM HYDROCARBONS ON ENVIRONMENT IN IBENO LOCAL GOVERNMENT AREA AKWA IBOM STATE NIGERIA>
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