Prospects of emerging PAH sources and remediation technologies: insights from Africa.

Remediation of polluted environmental media is critical to realization of the goals of the United Nations Decade on Ecosystem Restoration (UNDER) project. Many natural-resource dependent economies in Africa are characterized by numerous contaminated sites resulting from conventional and artisanal natural-resource mining. Alongside these extractive activities, there are refining, processing, and power plant operations, agriculture, urban, and infrastructure developments that contribute to increased discharges of toxins into the environment, particularly polycyclic aromatic hydrocarbons (PAHs), which are carcinogenic in nature. As a result, human and environmental receptors (i.e., air, water, soil, and biota) face increasing risk of exposure to higher concentrations of PAH. Evidence exists of widespread PAH contamination and in some instances where corrective action has been taken, residual contaminant levels exceeding regulatory thresholds remain in the environment due to the use of inappropriate and unsustainable remedial methods. Considering the long-term harmful effects of PAH on human and ecosystem health, land use, and the complexity of Africa's environmental deterioration, it is essential to explore remediation strategies that benefit both the environment and the economy. This review examined the status, opportunities, and challenges related to the application of emerging green technologies to remediate PAH-contaminated sites in five African countries (South Africa, Nigeria, Angola, Egypt, and Kenya). This paper concludes that bioremediation presents a sustainable option, considering its low net emissions and environmental footprints, and its low economic cost to Africa's poor communities and overburdened economy. However, an integration of biological and physico-chemical approaches could address various compounds and concentrations of PAH contamination.

Assessment of heavy metal pollution in soils and health risk consequences of human exposure within the vicinity of hot mix asphalt plants in Rivers State, Nigeria.

This study evaluated the level of heavy metal pollution in soils within the vicinity of hot mix asphalt (HMA) plants and the health risk consequences of human exposure to the heavy metals. Soil samples collected from two asphalt plants during dry and rainy seasons were analyzed for Cr, Co, Cu, Ni, Mn, Cd, Pb, and Zn with atomic absorption spectrophotometer (AAS). Health risk indices were assessed as chronic daily intake (CDI), hazard quotient (HQ), hazard index (HI), and carcinogenic risk (CR) while the degree of pollution was assessed with geo-accumulation index (Igeo) and contamination factor (CF). The pollution assessment revealed that the soil samples were moderately to highly polluted with Cd. In both seasons, Zn and Mn, respectively, had the highest CDI values for ingestion, inhalation, and dermal route for both asphalt plants while Cd has the least CDI values for all the routes in both plants. The HQ and HI values for all the metals were less than 1.00E + 00 indicating no non-carcinogenic risk from exposure to any of the metals. Furthermore, the dermal route was found to be the least likely model for health risks associated with human exposure to soil heavy metals within the vicinity of the plants. The CR values for the metals were also within threshold value indicating non-significant cancer risk from exposure to the metals. Though no significant health risks were observed in the study, clean and efficient production of hot mix asphalt should be encouraged to minimize health risks and environmental pollution during production and usage.

Evaluation and decontamination of crude oil-polluted soils using Centrosema pubescen Benth and amendment-support options.

Growth performance and phytoremediation of soil of the Niger Delta Region of Nigeria artificially-contaminated with crude oil (up to 100 mL/2 kg soil) using centrosema pubescen Benth was investigated for 12 weeks. The soil samples in which the plants were established were either un-amended, or amended with NPK, or UREA or chicken manure. The extents of removal of PAHs and BTEX were measured as well as the rates of growth of the plants. Gas Chromatographic analysis confirmed the degradation of carcinogenic hydrocarbons like BTEXs and PAHs with this technique. At the highest dose of crude, the contaminant concentrations were 43 mg/kg PAHs, 10 mg/kg BTEX, and 5,613 mg/kg O&G. The greatest percent removal of BTEX was observed at the highest contaminant dose, and with the manure amendment. Similar trends were observed with PAHs and although they were less marked, the trends with PAHs may have been more highly statistically significant. There was no measurable plant uptake of contaminants. Inhibition of plant growth (measured as leaf area, shoot length and production of dry weight) was proportional to the dose of crude oil, but the manure amendment was very effective at reducing the growth inhibition. Interestingly, manure amendment reduced the phytotoxicity significantly in this study.

Upstream petroleum degradation of mangroves and intertidal shores: the Niger Delta experience.

This article was inspired by a field reconnaissance survey of outcrops along the Nembe-Brass axis of the petroliferous Niger Delta. It reviews various tradeoffs of the impact of upstream petroleum (seismic and production) operations on the mangrove ecosystems in that region, the largest in Sub-Saharan Africa. Mangroves and intertidal shores are considered critical to the economic well-being of this region owing to the people's dual occupation in fishing and farming. The mangrove ecosystem provides a nutrient medium, which serves as a nursery and spawning ground for many fish species and other biota. Oil and gas activities might destroy these spawn areas, causing reduction in resource output and community pressure. Devegetation of the mangrove forest as a result of seismic delineation leaves the fragile soil exposed, unprotected, and susceptible to erosion. Again, loss of vegetation might discourage the natural role of plants in air purification (CO(2) utilization and O(2) production). The release of nutrients (organic N(2), NH(3), and NO$\rm{{_{3};{-}}}$) and polyaromatic hydrocarbons (PAHs) to the environment, with the attendant increase in microbial load, increases biochemical O(2) demand (BOD) and depletes dissolved O(2) (DO) in H(2)O to a level that is beyond the tolerance limit of organisms. This anoxic situation leads to asphyxiation and subsequent fish kill in affected areas. In order of increasing vulnerability, the mangroves and intertidal shores of the Niger Delta fall under categories 8 to 10 on the environmental sensitivity index (ESI) scale, which predisposes the areas to serious long-term effects and clean-up complexity. Thus, there is need to monitor mangrove systems and shoreline changes in the areas of considerable seismic and production activities, especially in the coastal Niger Delta, where pipeline corrosion due to salt intrusion into the swampy environment and 'unsighted fingers' of sabotage have increased the prevalence of oil spills.

Gas chromatographic fingerprinting of crude oil from Idu-Ekpeye oil spillage site in Niger-delta, Nigeria.

Samples were collected from an oil polluted site in Niger-delta, Nigeria. Gas chromatographic analyses carried out on the samples revealed an abundance of n-alkanes within the n-C8-n-C23 region. The pristane/phytane ratio of 5.70 obtained for the samples depicted a plant/terrestrial source input and a possible oxic depositional environment. The n-C17/pristane and n-C18/phytane ratios of 2.80 and 2.77, respectively, suggested that the spilled oil was only slightly weathered, as corroborated by the presence of peaks in the aromatic hydrocarbon fingerprints. The polycyclic aromatic hydrocarbon (PAH) fractions showed that the hydrocarbon fractions might have undergone combustion and/or that there was bush burning at the site prior to the oil spill incidence. This is supported by the abundance of high-molecular-weight PAHs which are pyrogenic in nature. High molecular weight PAHs are products of the combustion of petroleum or its products. The phenanthrene/anthracene ratio of 0.95, fluorathene/pyrene ratio of 2.23 and the summation operator (other three to six ringed PAHs)/ summation operator (five alkylated PAHs) ratio far greater than unity (4.10) also affirm this. On the other hand, the benzo (a) anthracene to chrysene ratio of 0.24 confirms the petrogenic origin of the spilled oil because chrysene which is highly abundant is a fossil PAH.

Acute toxicity of the water-soluble fraction of spent lubricating oil on the African catfish Clarias gariepinus.

Static tests were employed to assess the acute toxicity of the water-soluble fraction (WSF) of spent automotive lubricating oil (of mixed SAE grades) on Clarias gariepinus, a freshwater fish commonly cultured in Nigeria. Median lethal concentrations (LC50) of the WSF were found to decrease as a function of exposure time from 690+/-21 (after 24 h) to 513+/-58 mg/l (after 96 h). The characteristics of the WSF such as mean acidity (pH 6.6), turbidity (40 NTU), total dissolved solids (TDS; 40 mg/l) and significantly reduced (P<0.05) dissolved-oxygen (DO) values (1.44 mg/l) were not compliant with existing standards set for discharged effluents. The solubility of the detected straight-chain aliphatics ranked as C14>C16>C32>C18>C28; that of the simple aromatics was ortho-xylene>para-xylene; and that of the polyaromatic hydrocarbons (PAHs) was acenaphthylene>9H-fluorene>naphthalene>anthracene>phenanthrene>chrysene>benzo[k]fluoranthene>benzo[a]pyrene>benzo[b]fluoranthene, most of which being serious carcinogens. These oil constituents and the overall physico-chemical properties of the WSF are expected to act synergistically on the test organism (C. gariepinus), eliciting the quantal responses observed. The toxicity of the WSF points to the base constituent, oxidative degradation, and mechano-chemical reactions associated with aged crankcase oils. These oils, therefore, should definitely no longer be disposed into water streams or landscape, not even at sub-lethal concentrations, because of the inherent toxicity of their soluble fractions and the associated danger of bioaccumulation.

Chemical and biogeophysical impact of four-dimensional (4D) seismic exploration in sub-Saharan Africa, and restoration of dysfunctionalized mangrove forests in the prospect areas.

Four-dimensional (4D) seismic exploration, an improved geophysical technique for hydrocarbon-data acquisition, was applied for the first time in the Nembe Creek prospect area of Nigeria. The affected soils were slightly alkaline in situ when wet (pH 7.2), but extremely acidic when dry (pH 3.0). The organic carbon content (4.6-26.8%) and other physicochemical properties of soils and water (N, P, and heavy-metal contents, etc.) were higher than the baseline values obtained in 2001 before seismic profiling. Most values also exceeded the baseline compliance standards of the Department of Petroleum Resources (DPR), the World Health Organization (WHO), and the Federal Environmental Protection Agency (FEPA). Rehabilitation of the affected areas was achieved by stabilizing the mangrove floor by liming and appropriate application of nutrients, followed by replanting the cut seismic lines over a distance of 1,372 km with different mangrove species, including juvenile Rhizophora racemosa, R. mangle, and Avicennia species, which were transferred from nursery points. Quicker post-operational intervention is recommended for future 4D surveys, because the time lag between the end of seismic activity and post-impact investigation is critical in determining the relationship between activity and impact: the longer the intervening period, the more mooted the interaction.

Environmental degradation of polluting aromatic and aliphatic hydrocarbons: a case study.

Oil extracts of Ukpeliede spill samples from Niger Delta (Nigeria) were analyzed by gas chromatography. The amount of polycyclic aromatic hydrocarbons (PAHs), especially the lower-molecular-weight naphthene, fluorine, phenathrene, pyrene, and benzo[a]anthracene, decreased within the sampling intervals of 2 months and 5 months. There was a predominance of three-to-six-ring PAHs over the two-ring PAHs. There was marked disappearance of n-C8 to n-C11 hydrocarbon fractions and the acyclic isoprenoids (pristane and phytane). The depletion of these molecules within the two sampling intervals suggests the possible attenuation of hydrocarbons as a result of the environmental modification within the set interval.

Attenuation of petroleum hydrocarbons by weathering: a case study.

Possible alterations in the distribution and composition of total petroleum hydrocarbon (TPH), polycyclic aromatic hydrocarbons (PAHs), and benzene, toluene, ethyl benzene, and xylene isomers (BTEX) in the released oil at Idu-Ekpeye in Niger Delta (Nigeria) were studied within two seasonal variations of two months and six months, with a view to assessing the level of attenuation of these hydrocarbons in impacted soils. Although there were significant contaminations in the kerosene range (n-C10-n-C14) two months after, especially of the n-C12 and n-C13 fractions, the complete disappearance of the n-C8 to n-C23 hydrocarbons, including the acyclic isoprenoids (pristane and phytane), and the reduced amounts of PAHs, and BTEX, six months after, provided substantial evidence of attenuation as indicated in the reduction in total hydrocarbon content (THC) from 61.17 to 42.86%. Soil physicochemical properties such as pH, moisture content, heavy metal, TOC, and TOM, all provided corroborative evidence of hydrocarbon attenuation. The pristane/phytane ratio of the spill samples suggests that the spilled oil was genetically oxic.

Preliminary investigation on Mgbede-20 oil-polluted site in Niger Delta, Nigeria.

Soil physicochemical properties (pH, electrical conductivity (EC), % moisture, total organic carbon (TOC), total organic matter (TOM)), total extractable hydrocarbon content (THC), and micronutrient (Mn, Fe, Cu, Zn) levels of the Mgbede-20 oil-impacted site in Niger Delta, Nigeria, were investigated. Both oil-impacted and their background control soils were found to be acidic especially at surface depth. A slightly higher EC value of 107.4+/-15.0 microS cm(-1) was obtained for the subsurface-polluted soils. Of the micronutrients investigated, only Fe exceeded its acceptable limit (>100 mg/kg). The observed increase in moisture content resulting from the oil's aggregation of soil particles may lower soil porosity, and increase resistance to penetration and hydrophobicity. Soil pH can be adjusted by aeration to complete the microbially mediated oxidation of the organic acids, followed by the addition of agricultural lime to provide some buffering capacity to the soil.

Petroleum industry effluents and other oxygen-demanding wastes in Niger Delta, Nigeria.

In this article, we review the fundamental phenomenon of oxygenation within the overriding context of petroleum-industry effluents and the other oxygen demanding wastes in Niger Delta, Nigeria. Drill cuttings, drilling mud (fluids used to stimulate the production processes), and accidental discharges of crude petroleum constitute serious land and water pollution in the oil-bearing province. Effluents from other industrial establishments such as distilleries, pulp and paper mills, fertilizer plants, and breweries, as well as thermal effluents, plant nutrients (such as nitrates and phosphates), and eroded sediments have also contributed to the pollution of their surrounding environment. Since these wastes are oxygen-demanding in nature, their impact on the recipient environment can be reversed by the direct application of simple chemistry. The wastes can be reduced, particularly in natural bodies of water, by direct oxidation-reduction processes or simple chemical combinations, acid-base reactions, and solubility equilibria; these are pH- and temperature-dependent. A shift in pH and alkalinity affects the solubility equilibria of Na+, Cl-, SO(2-), NO3(-), HCO3(-), and PO4(3-), and other ions and compounds.

Assessment and treatment of hydrocarbon inundated soils using inorganic nutrient (N-P-K) supplements: II. A case study of eneka oil spillage in Niger Delta, Nigeria.

Polluted soils from Eneka oil field in the Niger delta region of Nigeria were collected two months after recorded incidence of oil spillage as part of a two-site reclamation programme. The soils were taken on the second day of reconnaissance from three replicate quadrats, at surface (0-15 cm) and subsurface (15-30 cm) depths, using the grid sampling technique. Total extractable hydrocarbon content (THC) of the polluted soils ranged from 1.006 x 10(3)-5.540 x 10(4) mg/kg at surface and subsurface depths (no overlap in Standard Errors at 95% Confidence Level). Greenhouse trials for possible reclamation were later carried out using (NH(4))(2)SO(4), KH(2)PO(4) and KCl (N-P-K) fertilizer as nutrient supplements. Nitrogen as NO(3)-N and potassium were optimally enhanced at 2% (w/w) and 3% (w/w) of the N-P-K supplementation respectively. Phosphorus, which was inherently more enhanced in the soils than the other nutrients, maintained same level impact after 20 g treatment with the N-P-K fertilizer. Total organic carbon (%TOC), total organic matter (%TOM), pH and % moisture content all provided evidence of enhanced mineralization in the fertilizer treated soils. If reclamation of the crude oil inundated soils is construed as the return to normal levels of metabolic activities of the soils, then the application of the inorganic fertilizers at such prescribed levels would duly accelerate the remediation process. This would be, however, limited to levels of pollution empirically defined by such THC values obtained in this study. The data on the molecular compositional changes of the total petroleum hydrocarbon content (TPH) of the spilled-oil showed the depletion of the fingerprints of the n-paraffins, nC(8)-nC(10), and complete disappearance of C(12)-C(17) as well as the acyclic isoprenoid, pristane, all of which provided substantial evidence of degradation.

Field reconnaissance and estimation of petroleum hydrocarbon and heavy metal contents of soils affected by the Ebocha-8 oil spillage in Niger Delta, Nigeria.

Field reconnaissance of the Ebocha-8 oil spill-affected site at Obiobi/Obrikom in the Niger Delta region of Nigeria was carried out to assess the extent of damage to the terrestrial ecosystem and delimit the epicenter of oil spillage. Following three successive reconnaissance surveys, the area to be sampled was delimited (200 x 200 m2), and soil samples were collected using the grid method from three replicate quadrats at two depths, surface (0-15 cm) and subsurface (15-30 cm). A geographically similar area located 50 m adjacent to the oil-polluted area was used as a reference (control) site. Total hydrocarbon content (THC) and heavy metal concentrations were later determined in the laboratory by extraction and spetrophotemetric techniques. Generally, the THC of soils at surface and subsurface depths of the oil-polluted plots was 2.06 x 10(4) +/- 4.97 x 10(3) mg/kg and 1.67 x 10(3) +/- 3.61 x 10(2) mg/kg soil, respectively, (no overlap in standard errors at 95% confidence limit) while concentrations of heavy metals(Pb, Cd, V, Cu and Ni) were enhanced, especially at the surface. The high levels of THC and heavy metals may predispose the site, which hitherto served as arable agricultural land, to impaired fertility and possible conflagration. When concentrations of heavy metals reach the levels obtained in this study, they may become toxic to plants or possibly bio-accumulate, thus leading to toxic reactions along the food chain. While the spilled-oil may have contributed to the enhanced levels of the metals in the affected soils, physico-chemical properties of the soils, mobility of metals, and the intense rainfall and flooding that preceded the period of study may have also contributed in part to their enhanced concentrations. The presence of high hydrocarbon content may cause oxygen deprivation, which may result in the death of soil fauna by asphyxiation. There is, therefore, an urgent need to clear the affected site of these excess hydrocarbon deposits so as to enhance the rehabilitation process of the affected mat layer of soils. Other appropriate mitigating measures, such as subsequent monitoring of hydrocarbon levels at suitable intervals after the clean up activities, are also recommended, with reference to the findings of this study, for effective management of the affected area.

Extractable hydrocarbons, nickel and vanadium contents of Ogbodo-Isiokpo oil spill polluted soils in Niger Delta, Nigeria.

An oil spill polluted site at Ogbodo-Isiokpo in Ikwere Local Government Area of Rivers State in southern Nigeria, was identified for study following three successive reconnaissance surveys of oil fields in the Agbada west plain of Eastern Niger Delta. A sampling area of 200 m x 200 m was delimited at the oil spill impacted site using the grid technique and soils were collected at surface (0-15 cm) and subsurface (15-30 cm) depths from three replicate quadrats. A geographically similar, unaffected area, located 50 m adjacent to the polluted site, was chosen as a control (reference) site. Total extractable hydrocarbon contents of the polluted soils ranged from 3.02-4.54 and 1.60-4.20 mg/kg (no overlap in standard errors) at surface and subsurface depths respectively. The concentrations of two "diagnostic" trace heavy metals, nickel (Ni) and vanadium (V), which are normal constituents of crude oil, were also determined in the soils by atomic absorption spectrophotometric method after pre-extraction of cations with dithionite-citrate carbonate. Ni varied from 0.15 to 1.65 mg/kg in the polluted plots and from 0.18 to 0.82 mg/kg in the unpolluted plots; vanadium varied from 0.19 to 0.70 mg/kg in the polluted plots and from 0.14 to 0.38 mg/kg in the unpolluted plots. Ni and V were more enhanced (p < 0.05) in the oil-polluted soils, especially at subsurface depth. Whilst the oil spillage could be said to be indirectly responsible for the enhanced concentrations of nickel and vanadium via the injection and availability of the petroleum hydrocarbons that might have increased the activities of biodegradation on site, the physico-chemical properties of the soils and inherent mobility of metals, as well as the intense rainfall and flooding that characterized the period of study, may have also contributed, at least in part, to these enhanced concentrations. Such levels of Ni and V may result to enhanced absorption by plants, which may bring about possible bioaccumulation in such plants and the animals that depend on them for survival and all of these may lead to toxic reactions along the food chain.

Flared gases and other pollutants associated with air quality in industrial areas of Nigeria: an overview.

Nigeria, like any other developing nation, is faced with the twin problem of development without destruction. Industrialization, though an important component of development, has had a large share in the despoilation of air quality in the country by the release of high amounts of pollutants into the atmosphere. Petroleum hydrocarbons from refineries, flared gases, dusts, and fumes of metal-smelting and cement works, odorous gases of chemical and allied industries, carbon monoxide and oxides of sulfur and nitrogen of internal combustion engines, the charred particulates and sulfur dioxide emissions of the steel industries etc., all constitute pollutants or co-pollutants of the Nigerian atmosphere. This review article gives an insight into the phenomenal concentrations of some of these pollutants in the Nigerian atmosphere, which point to their unsafe levels and concomitant health risks. It is against this background that there should be continuous but sound monitoring exercise of the Nigerian environment, devoid of the peculiar mix of politics and science, in order to properly audit the quality of air, especially in areas of heavy industrial pollution. Such checks and balances would provide empirical data to assess the various trade-offs of atmospheric pollution in industrial areas of the country such as the Niger Delta region where oil and gas are produced. There should also be enforcement, thereof, of all existing and/or revised standards or regulations such as the compliance limits of the Department of Petroleum Resources (DPR) or the erstwhile Federal Environmental Protection Agency (FEPA).

Post-oil-spill fires at Ugbomro (Niger Delta): a new vista in soil-pollution studies.

Reconnaissance of the post-oil-spill, fire-scourged site at Ugbomro, in the Niger Delta, was contingent upon the loud public outcry and galvanizing hue that ensued the widespread conflagration. Sampling was carried out by the grid technique, and fire-scourged soils and their unaffected controls were analyzed. Contrary to the 'celebrated' opinion of some that the fires improvised bush fallowing for cropping, the site had witnessed severe impoverishment as evidenced by the hitherto neglected insidious impact of such infernos on soil macronutrients. Alterations in physico-chemical properties (pH, conductivity, etc.) provided adequate bases for this conclusion, and offered broad explanations for the paucity of macronutrients in affected soils. For instance, a pH range of 3.1-3.8 hindered N2 fixation and other metabolic activities that enhance mineralization. Elaeis guineensis in a density of 3 stands/m2 at the control site was the only tree-form not charred beyond recognition.Against future fires, it is important to strengthen contingencies for more-expedient clean-up responses to oil spills to severe possibilities of in situ conflagrations. Nutrient supplementations, revegetation, and site surveillance should disengage the 'unsighted fingers' of sabotage. A careful husbandry of these measures might re-establish nutrient stability, and forestall future re-occurrence of such effacing incidents.

The Isiokpo oil-pipeline leakage: total organic carbon/organic matter contents of affected soils.

The environmental impact of the 1997 leakage of the high-pressure crude-oil pipeline at Isiokpo in the Niger Delta in the southeast of Nigeria was evaluated, with particular reference to total-organic-carbon (TOC) and total-organic-matter (TOM) contents of soils within the vicinity of the oil spillage. The soils, taken from depths of 0-15 cm (surface) and 15-30 cm (subsurface), were found to be more acidic (pH 4.2-5.6) than the unpolluted soils, with a high average moisture content of 6.8%. The extractable hydrocarbon content ranged from 2.71-3.48 mg/kg, indicating hydrocarbon contamination. However, contrary to expectation, the TOC and TOM contents of the polluted soils did not show any significant increase in concentration, supposedly due to natural rehabilitation of the affected mat layer of soils. Thus, notwithstanding the possible proliferation of heterotrophic organisms by the presence of the added petroleum hydrocarbons, environmental conditions such as weathering and climatic predispositions, as well as physico-chemical parameters such as pH, moisture content, and temperature must have encumbered the carbon-mineralizing capacity of the heterotrophs, thereby reducing the turnover of carbon and the decomposition of organic matter. The restrictions by high moisture content might not come directly from H(2)O itself, but are probably a consequence of hindered soil ventilation, which reduces O(2) supply and gaseous diffusion, conditions that might have been substantially aggravated by the added petroleum hydrocarbons.

Post-impact assessment of oil pollution in Agbada west plain of Niger Delta, Nigeria: field reconnaissance and total extractable hydrocarbon content.

Typical post-impact assessment of an oil-spill-impacted site in Agbada west plain of the Niger Delta basin of Nigeria was carried out 13 months after recorded incidence of spillage, using empirical indices of reconnaissance and extractable hydrocarbon content. Field-reconnaissance surveys revealed lower species' numbers and diversity of surface and subterranean flora and fauna. The presence and absence of such plant species as Elaeis guineensis, Musanga cecropiodes, and Andropogon gayanus, as well as animal species like earthworms and nematodes in sampled plots, corroborated the evidence provided by the total extractable hydrocarbon content (of (2.53+/-0.43)x10(2) mg/kg and (2.00+/-0.76)x10(2) mg/kg at surface and subsurface depths, resp.) on the level of degradation and/or regeneration at the polluted site. The most important evidence that oiling must have been responsible, at least in part, for the reduction in species' number and diversity was provided by the plant cover, Andropogan gayanus, which occurred at a lower density of 0.9 plants/m2 in the oil-impacted plots and 14.00 plants/m2 in the unimpacted reference plots of an adjacent, geographically similar area. The presence of this species on site thus presented a significant difference (P<0.05) of over 85%, and indicated exhaustion or impoverishment of impacted soils. Elaeis guineensis, with a population density of 0.1 stands/m2, provided evidence of past cultivation on site, while species like Musanga cecropioides, with a density of 0.5 stands/m2, at the unimpacted site, confirmed the abandonment of the farmstead over a long period of time. For the fauna, the most sensitive indicator of hydrocarbon toxicity was provided by nematode Xiphinema sp. that were completely absent in the oil-impacted site.

Trace heavy metals associated with crude oil: a case study of Ebocha-8 oil-spill-polluted site in Niger Delta, Nigeria.

The Ebocha-8 oil-spill-polluted site was identified as study site according to field reconnaissance surveys of oil-polluted sites in Obiobi/Obrikom prospect area of Niger Delta. A sampling area was delimited at each of the oil-spill-affected sites by the grid technique, and soils were collected at surface (0-15 cm) and subsurface (15-30 cm) depths from three replicate quadrants. A geographically similar, unaffected area, located in 50-m distance from each contaminated site, was chosen as control site. Trace heavy metals, Ni, V, Cu, Cd, and Pb, which are normal constituents of crude oil, were determined in the soils by atomic-absorption spectrophotometry after pre-extraction of cations with dithionite-citrate carbonate. Ni varied from 0.53 to 18.00 mg/kg, Cu from 0.15 to 0.30 mg/kg, and Pb from 0.32 to 0.80 mg/kg in surface and subsurface soils, respectively; Cd and V were less than 0.20 mg/kg in all sampled plots. Ni, Cu, and Pb were more enhanced (P<0.05) in the oil-spill-polluted soils, especially at surface depth, and this may be attributed to the fact that metal profiles in polluted soils penetrate a little below the 10-cm region, even after many years, thereby making the metal concentration in surface soils usually higher. Whilst the Ebocha-8 oil spillage may be responsible, at least in part, for the enhanced concentrations and paucity of variations in the metal concentrations of sampled plots, other factors such as the physicochemical characteristics of soils (e.g., soil pH and organic-matter content) and relative mobility of these metals, as well as the intense rainfall and flooding that preceded the period of sampling, may also have contributed in part. Enhanced levels of these micronutrients in the soils may result in enhanced absorption by plants, which may bring about possible bioaccumulation by such plants and the animals that depend on them for survival, and all of these may lead to toxic reactions along the food chain.