HEAVY METAL CONCENTRATIONS AND DEGRADATION EFFICIENCY OF TOTAL PETROLEUM HYDROCARBONS ON ENVIRONMENT IN IBENO LOCAL GOVERNMENT AREA AKWA IBOM STATE NIGERIA

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.

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