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 1.006×10³–5.540× 10⁴ 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 (NH₄)₂SO₄, KH₂PO₄ and KCl (N-P-K) fertilizer as nutrient supplements. Nitrogen as NO₃-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, nC₈–nC₁₀, and complete disappearance of C₁₂–C₁₇ as well as the acyclic isoprenoid, pristane, all of which provided substantial evidence of degradation.     

Effects of an Oil Spill on Soil Physico-Chemical Properties of a Spill Site in a Typic Udipsamment of the Niger Delta Basin of Nigeria

Physico-chemical analysis of soil samples at an oil spill site in a Typic Udipsamment of the Niger Delta Basin of Nigeria showed that the total hydrocarbon content of top soil layers ranged from 18.6 to 23.6 ppm in the heavy impact zone and the oil had penetrated to a depth op 8.4 m. The concentration of hydrocarbons in the medium impact zone ranged from 10.04 to 10.38 ppm while hydrocarbons were not detected in 85% of samples from the unimpacted reference zone. Heavy metal concentration measurements in the soil revealed a significant build-up (P < 0.05) of lead, copper and zinc in the heavy impact zone. Other quality parameters including electrical conductity, exchangeable cations, total nitrogen and available phosphorus in impacted soils were relatively low, while the total organic carbon was high compared with the reference site. Textural class of soil from the different depths showed a predominantly brown sand at the topsoil, loamy sand and grey coarse sand at medium depths, and grey coarse sand and greyish sandy clay at greater depths.     

Inorganic Ion Levels of Soils and Streams in some Areas of Ogoniland, Nigeria as Affected by Crude Oil Spillage

The inorganic ion concentrations of soils and streams in the three locations (Yorla, Zaakpon and Goi) in Ogoniland,Nigeria affected by crude oil spillage were investigated. In general, inorganic ion concentrations of polluted soilsand streams varied significantly (p = 0.05) from those of unpolluted soils and streams. Anions such as nitrate (NO ₃ ^- ), sulphate (SO ₄ ^2- ) and chloride(Cl^-) showed significantly (p = 0.05) higher values inthe polluted soils and steams than in the unpolluted controls. The phosphate (PO ₄ ^3- ) values were lowerin the polluted soils and streams than in the unpolluted controls.PO ₄ ^3- , NO ₃ ^- , SO ₄ ^2- and Cl^- concentrations were generally significantly (p = 0.05) higher in soils and streams from Yorla, Zaakpon and their control than in Goi North, Goi South and Goi control.Exchangeable cations and trace metal concentrations weresignificantly (p = 0.05) higher in the polluted soils andstreams than in the unpolluted controls. Yorla and Zaakponpolluted soils and streams had higher concentrations of theexchangeable cations and trace metals compared to valuesfrom Goi, except for Na. Results also showed significantlyhigher values of heavy metals (Pb, Cd, Cr and Ni) in the polluted soils compared to their controls, and values werealso significantly (p = 0.05) higher in Yorla, Zaakpon andtheir control compared to Goi North, Goi South and Goicontrol. Values obtained in polluted streams were higherthan in the unpolluted though not significant at the 5%level (p = 0.05). The anionic and cationic concentrationsof Yorla and Zaakpon soils and streams were generally higherthan those of Goi, indicating that Yorla and Zaakpon areaswere more polluted than Goi.Although the concentrations of most of the anions andcations analysed in the polluted soils and streams werewithin the World Health Organisation's permissible valuesfor the protection of humans and environment, the streams ofYorla, Zaakpon and Goi are in general being polluted withinorganic ions. This may make these soils and streamsunacceptable for domestic and industrial uses if not treated,and soils (farmlands) may also become unsuitable for agricultural purposes.     

Metal Pollution Assessment of Surface Sediments Along a New Gas Pipeline in the Niger Delta (Nigeria)

Chromium, nickel, copper, zinc and cadmium were determined in sediments of the Niger Delta (Nigeria) in order to discriminate between natural metal sources and anthropogenic ones. Surface sediments were collected at seven sites along a new gas pipeline near Port Harcourt, between the New Calabar River and the Bonny River towards Bonny town. Chemical characterisation is obtained by hydrofluoric–nitric acid digestion procedure, providing the ‘total’ (‘residual’) metal contents. Information about the anthropogenic metal fraction was obtained by cold diluted hydrochloric acid extraction procedure. This ‘labile’ acid soluble fraction of metals, perhaps due to relatively recent inputs in the sediments, constitutes the fraction more likely to be available to marine organisms, and furnishes a first evaluation of the possible toxicity of sediments of this sensitive ecosystem. Zinc appears to be the most available of all the heavy metals: its ‘labile’ fraction attains 40–50% of the ‘total’ zinc in sediment. Sites near Port Harcourt city are the most contaminated. All the examined metals are one order of magnitude below the respective values proposed as a limit for toxicity and are comparable with those observed by other authors in similar Niger Delta areas. Some anomalous data found near Port Harcourt city suggest that zinc and cadmium are the metals that require further monitoring. Their anthropogenic source could be derived from urban and industrial sewage.     

Effect of Common Pesticides Used in the Niger Delta Basin of Southern Nigeria on Soil Microbial Populations

The effects of eleven pesticides on the populations of bacteria, actinomycetes, fungi and protozoa was investigated by treating a garden soil with their recommended rates. The microbial populations were estimated using the standard plate-count technique. Of the ll pesticides investigated, phenylmercuric acetate (agrosan) at 50 g g^-1 inhibited bacterial density the most, i.e. from 4,600,000 to 220 cells g^-1. The pesticides were Pentachloronitrobenzene (PCNB), tetramethylmethylthiuram disulphide (thiram),1- naphthylmethylcarbamate (Vetox 85), 1,2,3,4,5,6-hexachlorocyclohexane (Gammalin 20), phenylmercuric acetate (Agrosan), tetrachloroterephthalic acid (Dacthal), 4-nitrophenyl –2-nitro-4-trifluoromethylphenyl ether (Preforan), 2-ethyl-6-methyl –N-2-methoxy –1-methyl ethyl-chloroacetanide (Dual), Benlate, Brestan and Gramoxone. Pentachloronitrobenzene (PCNB) at 240,000 g g^-1 reduced bacterial population from 4,600,000 to 2,100 cells g^-1, whereas tetramethylthiuram disulphide (thiram) at 100 g g^-1 suppressed it by 2 log orders of magnitude. Soil application of 1-naphthylmethylcarbamate (Vetox 85) at 100 g g^-1 and 1,2,3,4,5,6,-hexachlorocyclohexane (Gamalin 20) at 1,300 g g^-1 repressed the bacterial numbers by 2 log orders of magnitude each. Pentachloronitrobenzene reduced the actinomycetes density from 340,000 to 320 cells g^-1 and completely eliminated all fungal and protozoan propagules from the soil. The Gammalin 20 completely wiped out all the fungi, whereas phenylmercuric acetate totally eliminated all the protozoa and reduced the fungal population from 34,000 to 60 cells g^-1. In general, protozoa and fungi were more susceptible to fungicides than bacteria and actinomycetes. Pentachloronitrobenzene, 1,2,3,4,5,6,-hexachlorocyclohexane and phenylmercuric acetate were toxic particularly to soil microorganisms, whereas the herbicides dacthal, Preforan and Dual were quite harmless in soil at application rates of 0.1, 0.06 and 0.02 g g^-1 respectively.     

Effects of exposure of crocodiles to sublethal concentrations of Petroleum waste drilling fluid in the Niger Delta basin of Midwestern Nigeria

Static bioassay were carried out using two aquatic crocodiles (the short nosed crocodile, Osteolemus tetraspis and the Nile crocodile, Crocodilus niloticus) as test organisms in soft natural dilution water, with Petroleum waste drilling fluid as the test material, at 28 ± 2 °C. Comparison of results for the control and different concentrations of the waste drilling fluid were made by means of the F-statistic method. Both crocodile species exhibited a high insensitivity to the undiluted waste drilling fluid and the different dilutions. Differences in concentration of waste drilling fluid did not influence the response of crocodiles to the potential toxicant. Percentage of deaths which was never greater than 0.2% in control tanks was not significantly different from that in test tanks where mortality values of organisms was typically 1.6% or less in most cases. There was a delay toxicant – induced mortality effect.