Review on the Fate of Contaminants in the Niger Delta Environment

Niger Delta environment had suffered from impacts of waste over the years. The significant wastes in the region are crude oil and municipal wastes. Studies have shown the effect and fate of contaminants in the environment and human life. This paper reviews the impact and fate of contaminants in the Niger Delta environment with the focus on crude oil waste and municipal waste. The substantial quantities of waste generated resulted from unreasonable consumption and production, non-compliance to environmental laws and regulations, migration to urban cities, and sporadic expansion of unregulated industrial operations. These contaminants affect various life forms, natural resources, and increase the rate of global warming. It is of urgent importance for concerted efforts from corporate bodies, government, and individuals to ensure proper implementation of effective, safe management of waste. This review used Niger Delta environmental contaminant analysis and remediation case studies to highlight the fate of organic and inorganic contaminants and their associated adverse effects on the environment. This review contains secondary data from online journal articles, radio, symposium, doctoral thesis, organisations, and websites.

of soil penetration by crude will be more (Keller & Simmons 2005;Brost & DeVaull 2000;API 1972). When crude oil penetrates the soil to where the NAPL head cannot overcome pore pressures of entry, migration stops. Cessation of crude oil migration is because of capillary forces in the soil column, which leaves behind immobile NAPL. The saturated zone in the soil undergoes various hydrocarbon attenuation and transport processes (Bear & Cheng 2010;McCarty & Ellis 2002). Researchers revealed that hydrocarbons' migration towards the water table does not occur when they are present in the soil at low concentrations. In 99% of various oil dose at 2% (w/w) mixed into the top 15cm of different soil (silty loam, sandy loam, and black clay loam) stayed within 20cm of the surface after one year (Raymond et al.,1976). Brost & DeVaull, (2000) discovered that a range of heavy petroleum products had different soil residual saturation points of 0.5 -15% (w/w), with lower values observed in coarse soils.
When hydrocarbon exceeds its residual soil saturation point, NAPL goes through the soil to the water column. The hydrocarbons dissolve and generate contaminants that transfer to receptors. Pollard et al. (2008) developed level 1 fugacity models that show the partitioning behaviour in water, NAPL, air, and soil systems. Hydrocarbons show a tendency for partitioning into soil and NAPL than air, and water, which means the limited transfer of heavy hydrocarbon into groundwater. Nham et al. (2015) stated that further transport of dissolved hydrocarbons in groundwater is estimated using retardation factors. McMillen et al. (2001) proposed physical and chemical properties that aided the estimation of hydrocarbon retardation factor. The retardation factor of heavy hydrocarbon is very high, resulting in limited transport in groundwater after dissolution. An exception to this position is karstic geological environments where NAPL is transferred over distance. Schwarz et al. (2011) state that an unacceptable impact of karstic transport of heavy hydrocarbons to groundwater is low, which limits the interest of heavy hydrocarbon in hydrogeological risk assessment. Heavy hydrocarbons consideration is essential in risk management of soils or free-floating NAPLs to control exposure points. Coulon et al. (2010) proposed a level 11 fugacity model, which shows that biodegradation effectiveness determines the ultimate heavy hydrocarbons fate. Photooxidation also aids in the mass removal of heavy hydrocarbons.
Photooxidation transforms oil spill components at the soil surface by exposure to sunlight. Molecules within the crude oil mixture absorb photons, which start oxidation reactions by radial chain oxidation and singlet oxygen (Shankar et al., 2015). Lee 2003 andMaki et al. (2001) said this oxidation reaction of crude oil molecules in an increase of oxygenated hydrocarbons more susceptible to biodegradation. Garrett et al. (1998) proposed the transformation of oxygenated high molecular weight aromatic hydrocarbons by photooxidation. , and co-workers showed increasing levels of photooxidation with increasing aromaticity and alkylation of Polycyclic aromatic hydrocarbons (PAHs). Prince et al. (2003) state that asphaltenes or resins are not subject to significant photo-oxidative destruction. Photooxidation will be effective only at the soil surface since it requires direct sunlight. Braddock et al. (2003) revealed that reduced removal rates of crude oil over 25 years in soil horizons (>8 cm from the surface) at an Alaskan test site is because of no photooxidation caused by low sunlight penetration. There should be a future investigation on the outcome of soil turning in photooxidation. There are many published studies on hydrocarbon biodegradation; however, light hydrocarbons had more reviews than heavy hydrocarbon degradation (Abbasian et al., 2015;Seo et al., 2009;Widdel & Rabus, 2001;Boonchan et al., 2000;Cerniglia, 1992;Leahy & Colwell, 1990;Atlas, 1981). Throne-Holst et al. (2007) stated a novel monooxygenase from Acinetobacter in biodegradation of heavy hydrocarbons, while there are multiple known enzymes for light hydrocarbon degradation. In laboratory studies, Sakai et al., (1994) showed biodegradation of heavy hydrocarbon like long-chain n-alkanes under aerobic conditions. Studies showed asphaltenes and resins degradation to varying degrees under aerobic and anaerobic conditions (Meslé et al., 2013;Furmann et al., 2013;Tabatabaee et al., 2012;Singh et al., 2012;Uribe-Alvarez et al., 2011;Strąpoć et al., 2008;Kim et al., 2005). Heavy hydrocarbons are susceptible to biodegradation. Gibb's free energy calculations show that potential energy available through biodegradation is only affected by hydrocarbon size under most redox conditions. Laboratory conditions do not reflect field observations. Field studies showed limited heavy hydrocarbon biodegradation. Complete removal of heavy hydrocarbon is often unachievable (Raymond et al., 1976;Francke & Clark 1974;Kincannon 1972).
In hydrocarbons subjected to aerobic conditions, heavy hydrocarbon residue remains after the removal of light hydrocarbon (Huesemann, 1995), after a year of land farming, detected about at least 75% of heavy aromatics, and about 30% heavy saturates remained from a range of crude oils and petroleum products. Loehr et al. (1992) showed (20 - 24%) of an oily sludge remained after two years of land treatment. Salanitro et al. (1997) tested the extent of hydrocarbon biodegradation in soils containing different American Petroleum Institute (API) gravity (14, 30, and 55) of crude oil and observed a fraction after 11 months of treatment. Biodegradation occurred in only 6 -44% of heavy hydrocarbon during the experiment. Soils with higher organic carbon showed least oil biodegradation. McMillen et al. (2001) showed that heavy hydrocarbon determines the final extent of oil removal from soils. Grishchenkov et al. (2000) showed that heavy hydrocarbon biodegradation in the subsurface anaerobic condition is limited than in surface soil. Reddy et al. (2002) showed evidence of little biodegradation from a No. 2 fuel oil spilt on subsurface soil for 30 years, with a result of the oil remaining in the first 20 cm of the soil surface and only partial degradation of the alkane fraction had occurred. Wang et al., (1998), showed that a 25-year-old Journal of Environment and Earth Science www.iiste.org ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online) Vol.10, No.5, 2020 crude spill found just beneath the soil surface, at 10 - 40 cm, showed little degradation. Lundegard & Johnson (2006) showed that hydrocarbons had a half-life of over 400 years and a zero-order attenuation rate constant of 1.5 × 10 −3 a −1 . McCoy et al. (2015) estimated NAPL biodegradation at a disused refinery using CO2 traps and found average rates of biodegradation to be 6.3 × 10 −3 a −1 and the half-life was 108 years, which highlight oil persistence in the subsurface. As heavy hydrocarbons are refractory to biodegradation, their persistence in the subsurface environment will be higher.

Fate and Sources of Municipal Solid Wastes
Poor waste management strategies industries, urbanisation, technology, and other human anthropogenic activities result in waste that causes environmental pollution (Rajaganapathyet al., 2011). Some contamination sources include uncontrolled in situ burning, lack of waste segregation, inadequate waste containment, surface runoff, dumpsites close to residential area and waterway, lack of knowledge on waste disposal, spills during transport (Shayley et al., 2009;Stavrianou, 2007;Worksafe, 2005). Shayley et al. (2009) showed that the fate and toxicity of pollutants depend on its source, target, and leachability to the environment. Contaminants affect humans through inhalation, ingestion, dermal, or inhalation. Stavrianou (2007) showed that contaminant toxic properties, concentration, and rate of exposure determine its adverse effect. Contaminants in runoffs pose a danger to species that depend on soil or water contaminated by this runoff. Shayley et al. (2009) showed that soil permeability, mineralogy, the potential of hydrogen (PH), moisture, temperature, porosity, and organic matter could intensify the fate of contaminants. Certain elements that biodegrade might mitigate the toxicity of waste or cause a synergistic effect with toxic waste. Obodai et al., (2011), Aderinola et al.,(2009) and Ene et al., (2009 revealed that toxic heavy metal, which is soluble or suspended in water, could settle to the basal zone to bond with sediment or other biotas.

The fate of Heavy Metals in the Environment
Over the years, the fate of heavy metals in the environment discussed the cycle they undergo, which Brady et al. (1994) gave a conceptual cycle of metals in the report as shown in Figure 2. Natural sources of heavy metals include volcanic eruptions, sea-salt sprays, forest fires, rock weathering, biogenic sources, and wind-borne soil particles. In Herawatiet al. (2000), these heavy metals cause serious health problems to people and other mammals. Similarly, He et al. (2005) stated that anthropogenic sources of heavy metals add more to environmental pollution, like lead from car exhaust, arsenic, copper and zinc from smelting, arsenic from insecticides, and burning of fossil fuels which release vanadium, mercury, selenium, nickel, and tin.
Soils are the highest sinks for heavy metals released into the environment by earlier stated anthropogenic activities. Most heavy metals concentration last long after release to the environment as they are not degradable and do not undergo chemical or microbial degradation (Athar and Vohora, 2001;Lepp, 2012). Heavy metals transported by runoff from industries, municipalities, and urban areas accumulate in the soil and sediments of water bodies (Musilovaet al., 2016). Humans suffer health problems as the concentrations of heavy metals increase in the food chain, and some of the health implications are highlighted in Table 1. (Lee et al., 2002;García-Niño and Pedraza-Chaverrí, 2014). Particulate matters are released into the air through natural processes like volcanic eruptions, dust storms, soil erosion, and rock weathering, while anthropogenic activities are more transport and industrial and related (Soleimani et al., 2018). Particulate matters can lead to skin and eye irritation, respiratory infections, premature mortality, and cardiovascular diseases, the formation of acid rain, deterioration of infrastructure, corrosion, eutrophication, and haze (Herawatiet al., 2000).
Journal of Environment and Earth Science www.iiste.org ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online) Vol.10, No.5, 2020 Figure 2: Heavy Metal Sources and their cycle in the Environment (Brady et al., 1994) Heavy metals like Cu, Cd, Pb, Cr, Mn, Ni, V, Zn, Na, K, Ca, Ti, Al, Mg, Feoriginate from traffic, industrial areas, and natural sources, (Ventura et al., 2017;Soleimani et al., 2018). Table1: Heavy metals and their health impacts (García-Niño and Pedraza-Chaverrí, 2014) Health Impact As Cd Cr Pb Hg Cu Skin for removal and attenuation of metals from wastewater (Simate and Ndlovu, 2014;Nleya et al., 2016). Biosorption uses biological materials to remove pollutants from water systems, and it entails the absorption, adsorption, ion exchange, surface complexation, and precipitation. However, further pollutant removal is limited when the concentration of the feed solution is very high as the process reaches a breakthrough (Silvas et al., 2011). Membrane Technologies uses the concentration gradients phenomenon or reverse osmosis and is useful for water that has a high concentration of pollutants. Ultrafiltration, reverse osmosis, microfiltration, nano-filtration, and particle filtration are some membranes that used for mine water treatment (Buzzi et al., 2013;Park et al., 2015;Nleya et al., 2016).

Fate of Plastics
Littered over the landscape or escaping from landfills, plastic trash makes its way to the sea (Geyer et al., 2017). Different size classes of plastics examined showed less microplastic at the sea surface than expected, given how much plastic litter is estimated to reach the ocean (Eriksen et al., 2014). China, Indonesia, the Philippines, Sri Lanka, and Vietnam-contribute more than half of ocean plastics (Tullo, 2018). The Great Pacific Garbage patch comprising polypropylene and polyethylene is now 1 6 million km², about three times the size of France. Fishing nets make up over 46% of the plastic load, yet microplastics still seem to be missing from the area. An Oceanographer, Laurent Lebreton, and his colleagues predicted that there should be 100 times as much microplastic as they found (Lebreton et al., 2018). Christian Schmidt at the Helmholtz-Centre for Environmental Research and his team combined plastic trash data from 1350 rivers and their watersheds to construct a model of plastic discharges. The researchers estimate that rivers carry as much as 4 million tons of plastic debris to the sea each year. The ten top-ranked rivers transport up to 95% of the global load into the sea (Schmidt et al., 2017). In a separate study, Lebreton found that two-thirds of the plastic pollution comes from the top 20 rivers, led by China's Yangtze River, India's Ganges River, and a suite of other rivers in Asia (Lebreton et al., 2017). Researchers found multiple contamination hotspots, with one location boasting about 517,000 microplastic particles per square meter-the highest concentration ever measured in freshwater. After winter-time record-breaking floods, the team sampled their sites again, finding a vast reduction in microplastic levels (Hurley et al., 2018). The microplastic pieces size is less than 300 µm wide and would pass through the nets used for marine microplastic counting studies; hence, current models may underestimate the concentration of microplastics in the world's oceans. Scientists suspect that wastewater treatment plants could be a significant point source of microplastics in rivers and oceans. The plants are direct recipients of microbeads used in facial scrubs and toothpaste; microfibers washed off of synthetic clothing such as fleece jackets, and tire debris and fragmented plastics from urban runoff. Fionn Murphy of the University of the West of Scotland sampled microplastics at a secondary treatment plant serving a city of 650,000 people. Murphy says the plant releases 65 million microplastics into the River Clyde in Glasgow every day (Murphy et al., 2016).
Chelsea Rochman at the University of Toronto calculates that 8 trillion microbeads per day flow from wastewater treatment plants into aquatic habitats in the United States (Rochmanet al., 2015). Nico Hartline Journal of Environment and Earth Science www.iiste.org ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online) Vol.10, No.5, 2020 estimated that a population of 100,000 people would send 1 kg of fibres each day to a sewage treatment plant and that synthetic jackets could account for a substantial portion of the fibres observed in sewage influents (Hartline et al., 2016). Farm soils, which are not well studied, could be the most significant environmental reservoir of microplastics, according to Luca Nizzetto (Nizettoet al., 2016). Potential sources of microplastics to soil include inputs from plastic mulch on farm fields, application of sewage sludge, litter, and deposition of air-born particles (Rillig, 2012). Plastic debris soaks up Polychlorinated Biphenyls (PCBs) about 100 times better than naturally occurring materials such as sediment and algae (Engler, 2012). Rochman and her team released virgin polystyrene (PS) pellets into San Diego Bay, once in the water PS absorbed up to 200 times more polycyclic aromatic hydrocarbons (PAHs) than other kinds of plastics. The findings suggest that PS, used in disposable drinking cups, may pose a risk of exposure to PAHs than other plastics do when eaten by wildlife (Rochmanet al., 2013). BBC reported, 'the plastic balls on their own are not toxic, but can absorb toxins lethal to any species that might eat them' (Rochman, 2013).

CURRENT RESEARCH AND REVIEW ON THE FATE OF ORGANIC AND INORGANIC CONTAMINANTS
Below are some highlighted researches and reviews on the fate of organic and inorganic contaminants in the Niger Delta. 3.1 Case 1: Source Identification of Chemical Contaminants in Environmental Media of a Rural Settlement. Etchie et al., (2011) used Principal Component Analysis (PCA) to identify the source of contaminants such as oil, grease, total petroleum hydrocarbon, chromium (Cr), copper (Cu), cadmium (Cd), nickel (Ni), lead (Pb), and zinc (Zn)) in Ubeji, Niger Delta area. Gravimetry synthetic washing to measure grease, oil, and total petroleum hydrocarbon (TPH), while atomic absorption spectrophotometry detected heavy metals. Significant contamination was detected from a nearby refinery and petrochemical company by grease, oil, TPH, Cd, Cr, and Pb. 3.2 Case 2: Environmental Impacts of Oil Exploration and Exploitation in the Niger Delta of Nigeria. Kadafa, Adati Ayuba, (2012) used secondary data to show that although oil is of great benefit to Nigeria, its spillage in the Niger Delta environment has destroyed sources of drinking water, fishing, farmlands, relocation of communities, and the decline of various life forms. dichlorodiphenyltrichloroethane (DDT), endrin, endrin aldehyde, endrin ketone, dieldrin, endosulfan I, endosulfan II, -chlordane, heptachlor, endosulfan sulfate, methoxychlor, -chlordane, heptachlor epoxide, and aldrin from fish samples analysed. The concentration of total OCP compounds amongst the different fish species varied above the World health organisation (WHO) guideline value of 2000 g/kg fresh weight, and therefore implied potential harmful effects on humans. The contaminated fish makes the river unsuitable for drinking. 3.7 Case 7: Bioremediation of Crude Oil Contaminated Soil using inorganic and organic fertilisers. Ofoegbuet al.
(2014) used first-order kinetics model in the remediation of contaminated arable soil at 2, 4, and 6% crude oil spill, and stimulated with cow dung (CD), palm kernel husk ash (PKHA), nitrogen, phosphorus, potassium (NPK)) applied alone and in combinations (cow dung and inorganic fertiliser); (cow dung and palm kernel husk ash) in a 50:50 ratio in the laboratory for forty days. The results show that amendments with (cow dung & inorganic fertiliser) have a low half lifetime (∕) and a higher biodegradation rate constant (k) and gradually varies with other biostimulants. Ugoadi (2014) determined that Ogoni indigenes economic and social were affected, and the land may lose its regenerative capacity. The study alerts policymakers to test sustainable development practices from the perspectives of voiceless and powerless indigenous communities that host strategic resource wealth. 3.9 Case 9: Elevated Indoor Volatile Organic Compound Exposure in the Niger Delta Region of Nigeria. Kaléet al. (2018) monitoring volatile organic compounds (VOCs) across different media (water, soil, and air) in Ogoniland at the Niger Delta region, which showed the concentration of benzene and naphthalene that exceed risk benchmark, creating a need for further studies to characterise VOC sources, exposures, and associated health risks in the Niger Delta. 3.10 Case 10: Petroleum Hydrocarbons Contamination of Surface Water and Groundwater in the Niger Delta Region of Nigeria. Aniefioket al. (2018) stated that findings from several studies revealed variable negative impacts of petroleum hydrocarbons toxicity in Nigeria's Niger Delta region, which include environmental pollution, degradation, human health risks, deterioration of cultural heritage items, and socioeconomic problems. This review examines the problems of petroleum hydrocarbons contamination of marine environments associated with unsustainable practices of the petroleum industry in the region. They investigated some of the water quality issues and human health implications of petroleum hydrocarbons contamination of surface-water and groundwater in the oil-producing host communities in Nigeria's Niger Delta region. 3.11 Case 11: Effects of oil spills on fish production in the Niger Delta. Osuagwu and Olaifa (2018) used the Cobb Douglas production function to examine the impact of oil spills into the water body on fish production in the Niger Delta of Nigeria from 1981-2015. The findings were negative and suggested a sustainable approach to oil exploration activities. 3.12 Case 12: Geoenvironmental assessment of hydrocarbon contaminated sites in parts of central swamp depobelt, Eastern Niger delta. Nwankwoala and Mzaga (2017) showed that the effective mitigation of health and socioeconomic impacts of hydrocarbon is a site-specific science and depends on the determination of the extent of spread and prediction of contaminant behaviour. Soil and water samples analysed gave some negative results. They suggested sustainable pollution management strategies by all stakeholders.

Case 13: Influence of Organic Amendment on Microbial Activities and Growth of Pepper Cultured on Crude
Oil Contaminated Niger Delta Soil. Raimi and Sabinus, (2017) showed the effect of Brewers Spent Grains (BSG) on microbial activities and growth of Capsicum annum L cultured in crude oil-contaminated soil. Crude oil increased the acidity and the total organic carbon content while there was a decrease in total nitrogen and available phosphorus levels. BSG promoted the growth of plant height, leaves, flowers, number of branches, fruits, and the leaf area, which shows that plants grow in crude oil contaminated soil if there is an alternative source of nutrients. BSG also enhances the activities of microorganisms and subsequent degradation of hydrocarbons in contaminated soil; hence, it should be a conditioner in contaminated soils to expose nutrients. 3.14 Case 14: Remediation of contaminated lands in the Niger Delta, Nigeria: Prospects and challenges. Zabbeyet al. (2017), stated that remediation attempts in Ogoni land failed because of wrong operational conclusions (oil industry operators concluded that the Niger Delta soil has a layer of clay which makes remediation by enhanced natural attenuation (RENA) suitable for the region as oil percolates on the topsoil) and the use of ineffective remediation techniques. Other challenges include poor regulatory oversight and prolonged conflicts. Case studies showed the effectiveness of bioremediation combined with other technologies for the cleanup of the Niger Delta.

Case 15: Evaluation of the Effects of Fertilizers and Activated Carbon on Bioremediation of Soil
Contaminated with Weathered Crude Oil. Agarry (2018) showed the amount of inorganic NPK fertiliser, organic fertiliser, and activated carbon determines the removal rate of weathered crude oil as they microbial density and activity of the soil, which enhances biodegradation of hydrocarbon and reduces time and cost of bioremediation. 3.16 Case 16: Oil Spillage and Heavy Metals Toxicity Risk in the Niger Delta, Nigeria. Chinedu and Chukwuemeka (2018) used secondary data from governmental and non-governmental organisations to determine that 3.1 million barrels of crude oil containing lead (Pb), nickel (Ni), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), cobalt (Co), cadmium (Cd) and chromium (Cr) were spilt from 1976 to 2014 in the Niger Delta. Therefore, the inhabitants of this region may be at risk of heavy metals toxicity.  Ogwugwa et al. (2018) collected samples from five communities in Ogoniland and found heavy metal concentration in these sampled sites exceeded the maximum limit set by the Standard Organization of Nigeria. From the results, Barium had the highest concentration of heavy metal, which is because of the use of barium sulfate to increase the density oil during drilling operations. Barium present in the environment is of public health concern, and uptake of water-soluble Journal of Environment and Earth Science www.iiste.org ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online) Vol.10, No.5, 2020 Barium may cause a person to experience abdominal cramps, diarrhoea, difficulties in breathing, vomiting, increased or decreased blood pressure, and numbness around the face and muscle weakness. 3.19 Case 19: Biodeterioration of plastics by weevils from an environmental and stored food product perspective. Elijah et al. (2015) tested a comparative biodeterioration of nylon by three species of weevils (Tribolium, Sitophilus, and Oryzaephilus) using three types of plastic types and two substrates (plantain flour and rice) for six weeks. The number of borings or holes was considered as an index of biodeterioration. The number of borings increased from the first week to week 6 (P<0.05); the substrate and types of plastic bags used affected plastic degradation (P<0.05). The order of preference for biodeterioration is thin black > thick transparent> thin transparent plastics, plantain being the preferred substrate. 3.20 Case 20: Evaluation of Solid Waste Generation, Categories, and Disposal Options in Developing Countries: A Case Study of Nigeria. Babeyemi and Dauda (2009) investigated the quantity and rate of solid waste generation in several cities in Nigeria, factors influencing the generation, solid waste types and categories, collection, disposal, reuse and recycling, and environmental problems. The results showed a large generation at a high rate without a corresponding efficient technology to manage the wastes. 3.21 Case 21: An Assessment of the Socioeconomic Impact of Crude Oil Pollution on Aquaculture in Gokana Local Government Area Rivers State, Nigeria (Akankali and Nwafili, 2017). It was established that crude oil pollution has adverse and severe socioeconomic impacts on fish farming and led to increased fish mortality rates, reduced yield, and poor quality of cultured fishes.

Case 22:
Phthalate Ester Plasticizers in the Orogodo River Delta State and Their Potential Health Effects. (Edjereet al., 2015) analysed different phthalates such as diethyl phthalates (DEP), dibutyl phthalate (DBP), dimethyl phthalate (DMP), butyl benzyl phthalate (BBP), di-n-octyl phthalate (DNOP), di-2-ethyl hexyl phthalate (DEHP) in Orogodo River. The highest concentrations of phthalates were DEHP and DBP, consistent with their use in plastic materials and other industrial chemicals. The high concentrations may result from emissions arising from the burnt refuse containing plastic materials and dumping of untreated effluent/solid waste along the stretch of the river. Phthalates in the water samples give cause for health and environmental concern for people living downstream of the river.

EFFECTS OF CONTAMINATION ON THE BIODIVERSITY AND NIGER DELTA ENVIRONMENT
Crude oil, a mixture of many thousands of organic compounds, can vary in composition from one source to another. Therefore, it suggests that the effects of the crude oil spill will vary from source to source. However, details of the potential biological damage will depend on the ecosystem where the spill occurred.
Niger Delta comprises brackish swamp forests, mangrove forests, and rainforests. According to Ibesemin (2010), the degree of oil impact on plant depends on various factors such as the type and amount of oil, the extent of oil coverage, the plant species, the season of the spill and the habitat composition. These impacts range from reduction in population and growth rate or abnormal growth and regrowth to plant mortality. Nwilo et al. (2007) stated that mangrove forests cover 5,000 to 8,580 km² of land. Janice (2002) mentioned petroleum spills on mangrove halt cellular respiration, starve root of oxygen, and acidify the soils. The increase of toxicity in mangrove soils supporting R. racemose attracts Nypa fruticans, which colonise the area. Nypa fruticans shallow root system affects sediment distribution lower in the delta system by destabilising the bank along the waterway. N. fruticans impedes navigation and decreases biodiversity. Nigerian Conservation Foundation, (1996) stated that in places N. fruticans has invaded, communities are investigating the palm use by the locals. Mangrove forests are a source of wood for local people, and its loss affects not only animals and plants but humans (locals who do not see the economic benefit of petroleum but depend on species vital to subsistence practices).
There are settlements along the banks of the Niger River as it provides water for cleaning, drinking, bathing, and fishing for trading to make a profit and both the dinner table. Settlement of people along the shores of the coasts and rivers, terrestrial and marine habitats are lost, and it changes ecosystems drastically. Molles (2005) stated that shrubs, trees, and the shoreline along the Niger River are vital in maintaining the temperature of the water as temperature change is fatal to some marine species. World Wild Life Fund (2006) stated that the Niger River is home to about 250 fish species, of which 20 are found only in the Niger River. Prevention of temperature rise, oil spills, and pollutions are vital to keeping some of the marine environments. Natural pesticides minimise water contamination from pesticides used in agriculture. The contamination risk can be reduced by enforcing laws and holding oil companies accountable for their actions. Amaize and Emma (2012) stated that biodiversity and productivity of the marine environment could be reduced by holding oil companies accountable, enforcing laws, reducing overfishing, habitat loss, and pollution.
Petroleum hydrocarbons released into the environment are affected by processes that alter the chemical composition of the petroleum hydrocarbon which alters the toxicity. Physical weathering may transform the petroleum hydrocarbon to a form partially available to the organism. The chemical and physical properties of the petroleum hydrocarbon components determine the rate it passes into an organism. The bioavailability and persistence of specific hydrocarbons, the ability of an organism to accumulate and metabolise, The fate of the Journal of Environment and Earth Science www.iiste.org ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online) Vol.10, No.5, 2020 metabolised products, metabolites of the hydrocarbon interphase with the normal metabolic process may alter an organism's chances of survival and reproduction in the environment. The narcotic effects of hydrocarbon on nerve transmission are the primary biological factors in determining the environmental impacts of any release; other factors include photo-degradation and photo-activation. Birds and mammals are vulnerable to oil spills when their habitats become contaminated, and this may reduce reproductive rates, survival and physiological impairment (Briggs et al., 1996). In water, oil film floating on the water surface prevents natural aeration and leads to death of freshwater or marine life and on land lead to retardation of vegetation growth, cause the soil infertility for an extended period (Ukoli, 2005). Ukoli, 2005 in his study made a summary of some significant pollutants from the oil industry released into the environment as follows: 1. Exploration and Production activities include Drilling Muds, Cuttings, Oil and Greases, Salinity, Sulphides, Turbidity, Suspended Solids, Temperature, pH, Heavy metals, Biological Oxygen Demand and COD. 2. Petroleum refining activities include; Oil & Greases, BOD, COD, Phenol, Cyanide, Sulphide, Suspended solids, Toxic Additives, Hydrocarbons and Total Suspended Solids.
Effects can be either direct damage of a resource or the ability of the environment to support a resource; an effect is over when complete recovery has taken place. To quantify the effects and recovery is difficult; damage to a small area containing highly valued resources can be of greater significance than damage to a much larger area devoid of valued resources. The US DOE has reported that the Niger Delta area has experienced 4,000 oil spills incidences since 1960. These spills result in the loss of mangrove trees to high toxicity levels of the petrochemicals in the environment. The spills have also had adverse effects on the marine habitat which has become contaminated. These splits pose an enormous human health risk from the consumption of contaminated seafood (Twumasi and Merem 2006). The environmental problems of the Niger Delta resulting in generally land resource degradation, renewable resource degradation and environmental pollution, agricultural land degradation, fisheries depletion, deforestation, biodiversity loss, oil pollution, gas flaring and mangrove degradation.
Friends of the Earth (2004) revealed that gas flares release poisonous chemical including sulfur dioxide, a volatile organic compound like benzene, nitrogen dioxides, toluene, xylene, and hydrogen sulfide, benzopyrene and dioxins which can aggravate asthma, chronic bronchitis, cause breathing difficulties and pain, leukaemia, other blood-related diseases, and cancer. Gas flares lack protection for villagers as it causes acid rain which corrodes their homes and other structures. In 2004, the Agency of toxic substances and disease registry stated that some people use asbestos in construction, which repels acid rain. Bronwen Manby (1999) noted that asbestos causes pleural and peritoneal mesothelioma, and asbestosis, and lung cancer. Bronwen Manby (1999) stated that older flares coat the land and communities with soot and damage adjacent vegetation because of heat. Gas flaring violates the constitutional right to life and dignity, and a Nigerian law court ruled that flaring cannot lawfully continue as it is wasteful and damaging. Radio Netherlands Worldwide (2011) and Bloomberg (2011) stated that Shell had not ceased gas flaring.

CONCLUSIONS AND FUTURE PERSPECTIVES
Research on the fate and transport of heavy hydrocarbons should include understanding heavy hydrocarbon biodegradation, which assists with effective remediation strategies, provide a basis for establishing remediation end-points and help detect whether heavy hydrocarbons are a vital source of metabolic intermediates that become mobile in groundwater or change the risk profile of contaminated soils. Improved analytical capabilities and composition of heavy hydrocarbon will contribute to characterising degradation intermediates and develop realistic physical and chemical properties for this complex fraction. These data can form an overall biodegradation route and bioavailability for heavy hydrocarbons. All stakeholders should be committed to safe waste disposal by providing treatment and recycling facilities, sensitisation of population, and effective legislation. Oil exploration cause harm to the environment. Therefore, oil corporations activities should be monitored. For effective monitoring, funds and qualified human resources must be available. Furthermmore, regulatory bodies should review fines and licenses of oil companies to ensure compliance with legislation.