Water lily (<Emphasis Type="Italic">Nymphaea</Emphasis> sp.): an alternative organic amendment for treatment of hydrocarbon-contaminated soil by chemical–biological stabilization

The chemical–biological stabilization technology has been employed in several successful studies using sugarcane cachasse as the organic amendment. However, in some petroleum-producing areas, there are no sugar mills nearby (which is the source of this material), and the cost of transport to the contaminated site is prohibitive. Therefore, water lily, which is considered a weedy plant in many tropical and subtropical areas, was evaluated as an alternative. In 3-month experiment, water lily was compared (with and without addition of molasses) with cachasse for the treatment of clayey sediment contaminated with > 6% extra-heavy crude oil. All treatments resulted in a reduction in the hydrocarbon concentration of 15–23%, without significant differences (P > 0.05). During this process, the pH was reduced to the 7–7.5 range and water repellency (molarity ethanol drop) to 3.5–3.6 M. Also, field capacity increased to 36.3–38.5% humidity, establishing adequate conditions for the development of vegetation at this site. Likewise, toxicity was reduced to practically null (Vibrio fischeri bioassay), and hydrocarbons in leachates were reduced to 3.4–4.3 mg/l, conditions adequate for the protection of groundwater and human health in rural areas. This study confirms that water lily is an adequate substitute for the application of this treatment method for hydrocarbon-contaminated sites that are far from sugar production areas.     

太仓郊区河流沉积物重金属污染现状及评价

选择太仓市郊区河流沉积物为研究对象,开展了重金属污染现状及评价研究。研究表明,相对于地壳或页岩平均值,沉积物中大部分重金属呈现不同程度的富集;地质累积指数和富集因子分析表明,位于城镇附近的采样点受到污染,且主要污染因子为Cr、Cu、Cd、Pb、Zn等。结果显示,沉积物Zn含量高达1770mg／kg,是农用污泥Zn使用容许最高值500mg／kg的3倍多,沉积物由于Zn、Cr、Cu等的严重污染不能用作施用污泥;利用重金属与Fe之间的相关特征结果显示,城镇工业、生活污水的排放是沉积物重金属污染的主要因素。     

Comparison of the effectiveness of different binders in solidification/stabilization of a contaminated soil

In the current research, solidification/stabilization (S/S) treatment of the contaminated soil using hydraulic binders and additives was used to (1) reduce the mobility of organic and inorganic contaminants and (2) compare the ability of various binders in fixing contaminants. The samples were collected from Franco-Tunisian Petroleum Company, located in Sidi Litayem, Sfax (Southern Tunisia). Leaching tests were performed on contaminated soil, containing metallic elements, and hydrocarbons. Calcium aluminate cement (CAC), ordinary Portland cement (OPC), and ground-granulated blast-furnace slag (GGBFS), additives especially the bentonite and water, were used for S/S treatment. The obtained standard specimens were subjected for treating after treatment the leachability of pollutants, compressive strength (CS), and XRD analysis. The results of analysis conducted on contaminated soils showed that concentrations of metallic elements were in the range of 9.08–427 mg/kg and 15,520 mg/kg of organic compound. Next, 10% of the used binder improved the immobilization of pollutants and gave a satisfactory CS exceeding 1 MPa. Thus, the CAC is more effective in reducing the leachability of metal contaminants than OPC + GGBFS and produces much higher strength, which was of the order of 2.41 MPa. The mechanical characterization was confirmed by XRD analysis. The lowest values of organic compounds are presented in mixtures treated by 10% of used binder, indicating the effectiveness of those with the presence of 10% of bentonite. This work shows that 10% (OPC + GGBFS) +?10% bentonite improved the immobilization of metallic elements and hydrocarbons, thus proving its efficiency due to its low cost.     

Field-scale evaluation of the chemical–biological stabilization process for the remediation of hydrocarbon-contaminated soil

Developing countries face the challenge of growing their economy while reducing the negative environmental impacts of industry, thus requiring treatment technologies that are economical and effective. One recent technology developed in the tropical part of Mexico for the remediation of petroleum-contaminated soil was tested in this scale-up project at an industrial level, whereas previously it had only been tested at laboratory scale; 150 m³ of bentonitic mud, contaminated with weathered hydrocarbons (3.4°API) at ~50,000 ppm, was treated with 4 % Ca(OH)₂, 4 % organic amendment, and a fine-root tropical grass. Hydrocarbons in soil and in leachates, as well as pH, and acute toxicity (Microtox) were monitored for 28.8 months. At the end of the study, basal respiration, root density, and earthworm toxicity were also measured. The hydrocarbon concentration in soil was reduced to 45 %, and toxicity was eliminated. Hydrocarbons in leachates were reduced to ~1 mg/l, safe for human consumption. The pH adjustment depended on low soil moisture and was stabilized at 7.1. Intense revegetation resulted in good root density, within 90 % of nearby uncontaminated soil under pasture. Basal respiration was increased to levels comparable to uncontaminated tropical soils with agricultural use, pasture and gallery forest. At an industrial scale, strict moisture control was necessary for good pH stabilization. By controlling these conditions and applying this novel treatment process, it was possible to transform a heavily contaminated geological material into a non-toxic, fertile, soil-like substrate capable of maintaining a complete vegetative cover and microbial activity comparable to similar soils in a tropical environment.     

Hydrocarbons in western North Atlantic surface sediments

High concentrations of hydrocarbons (500–3000 μg/g dry weight) together with a complex and wide molecular weight range of composition, and low ¹⁴C activity of δ¹⁴C = ?833 ± 50%. strongly indicate that fossil fuel hydrocarbons make up the bulk of hydrocarbons in and near the New York Bight dump site areas. The composition and concentrations of hydrocarbons in Hudson Channel sediments suggest some transport of dump site hydrocarbons to areas in the channel midway to the edge of the continental shelf. Sediments at 16 stations in other areas of the continental shelf, continental slope and abyssal plain have hydrocarbon concentrations and compositions indicating that no more than 1 μg/g dry weight of fossil fuel hydrocarbons are present.N-alkanes from land sources were among the most predominant hydrocarbons in all samples except those in the New York Bight region. Their presence in abyssal plain surface sediments documents transport of some land derived organic matter to these deep ocean areas. Two 25-carbon cycloalkenes are among the more predominant hydrocarbons in continental shelf surface sediments except for the dump site areas. These two compounds are present in lower concentrations in slope sediments and are not detected in abyssal plain sediments.     

Treatment of water-repellent petroleum-contaminated soil from Bemidji,Minnesota, by alkaline desorption

A pipeline right-of-way contaminated with light crude in 1979 and subsequently burned shows severe hydrophobicity, poor infiltration rates, and loss of vegetative cover. To evaluate alkaline desorption as a treatment method, surface soil samples were collected and analyzed pre- and post-treatment. Samples had total petroleum hydrocarbon concentrations of 2800–63,100 mg/kg, severe water repellency, critical moisture 2–5 times above the in situ moisture content, but no acute toxicity. Thus, water repellency, rather than toxicity, is causing the loss of vegetation. Samples were treated with 0.1 N NaOH in two doses (1:3; soil/solution), with complete drainage between doses. Finally, each soil sample was washed with an equal volume or water and allowed to drain completely. For more hydrophobic samples, repeated treatments, without rinsing between each treatment, were made. Post-treatment, the samples were re-analyzed for water repellency and critical moisture content. In samples with initial water repellency values in the range of 5.0–6.7 M, the repellency was reduced 94–100 % and below critical levels to avoid soil hydrophobicity in field conditions. The other samples with initial water repellency values in the range of 10–13 M could not be recovered with single treatment, but sequential treatments reduced the hydrocarbon content up to 87 % and reduced the hydrophobicity to levels low enough or nearly low enough to avoid severe water repellency in the field. Currently, field studies are being carried out to evaluate this treatment method at the site, as a stand-alone method and in combination with organic amendment.     

Structural Characteristics of the Andaman Forearc Inferred from Interpretation of Multichannel Seismic Reflection Data

The Andaman Forearc Basin(AFB) is asymmetric in configuration and filled with a ~6 kmthick pile of Neogene to Recent sediments(~4 s in two-way travel time:TWT) with distinct zonation.It shows gradual thinning up to ~3 km(0.8 s in TWT) towards the eastern end with a seabed gradient of 1:30.Thick deformed sediments ~2 s(TWT) of the Outerarc are associated with intense faulting and occasional folding caused by recent tectonics.Development of a series of faults within the upwarped sedimentary column of Oligocene top to Recent is observed with a rotated fault block.These features are manifestations of Recent igneous intrusion,and reveal the presence of a mild N–S compressional regime.Its effect on the AFB resulted in further uplift of sediments,which can now be seen as the Invisible Bank.Forward gravity modelling supporting our seismic interpretation reveals that it is associated with igneous intrusion from the Moho(~9 km depth),and also suggests that continental crust underlies the AFB.Strong Bottom Simulating Reflector(BSR)-like features in the Miocene sediments of Outerarc and Forearc basin at a depth of 0.6 s below the seabed suggest the inferred probable occurrence of gas hydrates in the AFB.     

Anaerobic Carbon Mineralisation Through Sulphate Reduction in the Inner Shelf Sediments of Eastern Arabian Sea

Monsoon-induced coastal upwelling, land run-off, benthic and atmospheric inputs make the western Indian shelf waters biologically productive that is expected to lead to high rates of mineralisation of organic matter (OM) in the sediments. Dissimilatory sulphate reduction (SR) is a major pathway of OM mineralisation in near-shore marine sediments owing to depletion of other energetically more profitable electron acceptors (O₂, NO₃ ^?, Mn and Fe oxides) within few millimetres of the sediment-water interface. We carried out first ever study to quantify SR rates in the inner shelf sediments off Goa (central west coast of India) using the ³⁵S radiotracer technique. The highest rates were recorded in the upper 10 cm of the sediment cores and decreased gradually thereafter below detection. Despite significant SR activity in the upper ～12 to 21 cm at most of the sites, pore water sulphate concentrations generally did not show much variation with depth. The depth integrated SR rate (0.066–0.46 mol m^?2 year^?1) decreased with increasing water depth. Free sulphide was present in low concentrations (0–3 μM) in pore waters at shallow stations (depth <30 m). However, high build-up of sulphide (100–600 μM) in pore waters was observed at two deeper stations (depths 39 and 48 m), 7–11 cm below the sediment-water interface. The total iron content of the sediment decreased from ～7 to 5 % from the shallowest to the deepest station. The high pyrite content indicates that the shelf sediments act as a sink for sulphide accounting for the low free sulphide levels in pore water. In the moderately organic rich (2–3.5 %) sediments off Goa, the measured SR rates are much lower than those reported from other upwelling areas, especially off Namibia and Peru. The amount of organic carbon remineralised via sulphate reduction was ～0.52 mol m^?2 year^?1. With an estimated average organic carbon accumulation rate of ～5.6 (±0.5) mol m^?2 year^?1, it appears that the bulk of organic matter gets preserved in sediments in the study region.     

An integrated approach to environmental quality assessment in a coastal setting in Campania (Southern Italy)

The coastal region of Southern Italy’s Caserta province, known as the Litorale Domitio (Domitia coast) has been subjected to increasing pressure from unsustainably fast economic and urban growth in the last century, that resulted in a induced serious land degradation. To obtain a comprehensive picture of the ecological status of the Domitia coastal zone (Campania, Southern Italy), a holistic methodology has been applied. Sedimentological, geochemical, and biological analyses of the surface sediments and water samples were performed along the submerged beach. The data were integrated using a geographical information system, together with information on past and present land use and human activities along the coast and in inland regions. Heavy metal concentrations in sediments plus As and Se (Cd, Co, Cr, Cu, Hg, Ni, Pb, V, Zn) and their enrichment factors, which are important for identifying polluted areas in countries like Italy (where environmental legislation has not yet established intervention limits), indicate excesses Cd, Cr, Pb, and V of probable anthropogenic origin. A microbiological contamination of marine waters has been detected by the Regional Environmental Protection Agency of Campania. The Bacteriological Quality Index map shows that bathing areas must be classified as “contaminated” and “highly contaminated”. High levels of chemical and biological contamination are particularly common in both bathing seawater and sediments along the coastal zone south of the Volturno River, where the existing wastewater treatment plant is not properly working, to date. Factory farming, which is widespread in the area, is likely to be an additional important source of contamination. In accordance with these conclusions, analyses of the benthic diatom community revealed dominance of eutrophic species.     

The deep subsurface temperature controlled origin of the gaseous and gasoline-range hydrocarbons of petroleum

In recent surface sediments there is no indication of any of the saturated C₃–C₇ gasolinerange hydrocarbons which are so common in petroleum. Appreciable gasoline-range hydrocarbon generation (85–180°C) of 80 ppm by weight of dry rock, or more, occurs only with increased temperature due to deeper burial, below about 8000 ft in the Los Angeles basin and below 12,500 ft in the Ventura basin. Because of the lower temperature gradient in the Ventura basin, the zone of substantial gasoline generation is considerably deeper there than in the Los Angeles basin. However, the subsurface temperature range over which substantial gasoline generation occurs is practically the same in the two basins. This demonstrates that the subsurface temperature, not depth, is the controlling factor in gasoline generation in source rocks. For appreciable gasoline generation somewhat higher subsurface temperatures are required than for equivalent generation of heavy hydrocarbons boiling above 325°C. Appreciable generation of the C₁–C₄ wet gas components of 75 ppm by weight of dry rock, or more, takes place quite deep also; in the Los Angeles basin it occurs below 10,000 ft.The composition of the gasoline-range hydrocarbons generated changes gradually with increasing depth, temperature and age of the shales. In deep strata the gasolines from shale cannot be distinguished from the gasolines of waxy crude oils in the same basin. The gasoline-range hydrocarbons mature with depth, temperature and age of the sediments, very much like the heavy hydrocarbons investigated earlier.Based on the similarity of analyses of heavy as well as of gasoline-range hydrocarbons from crude oils and from certain deep shales, a secure identification has been made of mature oil source beds in the Los Angeles and San Joaquin Valley oil basins of California. The combined results of these studies provide strong evidence for the origin of petroleum from the organic matter of sediments.     

河道疏浚底泥堆土镉污染修复技术分析

城市生活垃圾中重金属Cd污染修复是我国亟待解决的环境问题之一。为了确定最佳Cd污染修复技术,探究了多种镉修复技术在河道治理中的适用性。以华东地区城市河道疏浚底泥堆土修复工程为例,对重金属镉污染土壤的修复工艺进行了对比和分析。拟选定土壤稳定化修复技术、土壤淋洗技术和植物修复技术三种修复工艺对受污染土壤进行治理。实验结果表明,稳定化修复技术可以使土壤中镉的浸出率从33.3%降低到14.3%,能有效降低其在环境中的生物毒性,但镉的总量并不会降低;采用柠檬酸和草酸的土壤淋洗技术,能够使镉的去除率达到90.1%和92.4%;相比而言,植物修复技术具有更为突出的高效性、易操作和二次污染少的特点,但修复周期较长。从技术、经济、环境安全等多方面出发,分别对三种修复工艺进行了分析讨论,综合考虑了研究场地的现状和未来规划,最终确定土壤淋洗技术为治理河道底泥堆土镉污染的最佳选择。      

Factors affecting pore water hydrocarbon concentrations in Puget Sound sediments

Polycyclic aromatic hydrocarbon (PAH) and aliphatic hydrocarbon concentrations have been determined for sediments and associated pore waters collected at 2 sites (11 stations) in Puget Sound, Washington (northwest U.S.A.). These sediments have been contaminated to varying degrees by hydrocarbons from a creosote plant and from various combustion sources. PAH were not detected in pore waters of sediments whose PAH were primarily derived from combustion and natural sources, even though pore water concentrations predicted from sediment concentrations and two-phase equilibrium partitioning models were above detection limits from most PAH. Equilibrium partition coefficients calculated from field aqueous and solid phase data from an area contaminated with creosote agreed with laboratory-derived coefficients to within a factor of ± 4. Pore water concentrations of creosote-derived aliphatic hydrocarbons increase with increasing concentration in bulk sediments. However, pore water concentrations of natural and contaminant aliphatic hydrocarbons are much higher than predicted by solubility data, possibly due to association with nonfilterable dissolved organic matter and colloids. Other major factors controlling hydrocarbon pore water concentrations include differential hydrocarbon sources, specific particle associations and solubility.     

Reducing leachable petroleum hydrocarbon concentration in weathered fuel oil contaminated soil by chemical oxidation with hydrogen peroxide

Number 6 fuel oil is one of the most used energy sources for electricity generation. However, leaks can contaminate soil and also groundwater due to leaching. At old sites, the oil may have low toxicity but still contaminate groundwater with foul-tasting compounds even at low concentrations. The purpose of this study was to evaluate the feasibility of applying H₂O₂ to reduce the leaching potential of a fuel oil contaminated soil. A silt-loam soil was collected from a contaminated thermal-electric plant with a hydrocarbon concentration of 3.2% in soil producing 4.3 mg/l in leachate. Hydrogen peroxide was applied (0.1, 0.2, 0.3, 0.6, 1.2% dry weight basis), and petroleum hydrocarbons were measured in soil and leachate pre- and post-treatment (72 h). At first, the soil and leachate concentrations diminished linearly (24.4 and 27.3% in soil and leachate, respectively). This was followed by a phase in which the concentration in leachate diminished greatly (75.8%) although the concentration in soil was reduced only moderately (15.1%). Overall, hydrocarbons in leachates were reduced 82.4% even though concentrations in soil were only reduced 35.8%. Correlation analysis showed that at only 1.0% w/w H₂O₂ a concentration of petroleum hydrocarbons in leachate safe for human consumption (≤ 1 mg/l) could be obtained even with a final hydrocarbon concentration in soil > 2%. Thus, this study presents an alternative strategy for remediation of fuel oil contaminated soils in urban environments that protects water sources by focusing on contamination in leachates, without spending extra financial resources to reduce the hydrocarbon concentration in low-toxicity soil.     

Relationship between geomorphology and contamination with weathered hydrocarbons in an old river levee/marsh association

A site evaluation was made for a low-lying property in an old river levee/marsh association, used marginally for cattle raising, which was contaminated due to historical practices. Contamination was related to geomorphology: the lowest areas contained 79 % of the contaminated samples. Other contaminated samples were all rear access roads (probable intentional dumping). There were no samples in the higher, levee areas away from roads with hydrocarbon concentrations above 3,000 mg/kg. Medium and high impact levels, corresponding to average hydrocarbon concentrations of 13,400 mg/kg and 109,700 mg/kg, respectively, were found in 28 % and 27 % of the property area. The medium impact level was predicted to have a reduced pasture production potential of ～ 50 % while at the high impact level practically no pasture production was predicted. Toxicological risk to cattle is present in only 12 % of the sample points although almost all of these are in very marshy areas not apt for cattle raising. Because the hydrocarbons at this tropical site are very weathered, acute toxicity was not related to hydrocarbon concentration. Although slightly more than half of the property has hydrocarbon concentrations above the permissible limit, only about one-third of the contaminated area is apt for cattle raising. This study, based on hydrocarbon distribution related to site geomorphology, soil toxicity bioassay, risk assessment to cattle and evaluation of pasture production allowed to made a more accurate assessment and definition of future use of the site. These criteria could be used for diagnostic studies of sites with similar tropical conditions.     

Laboratory Determination of Molybdenum Accumulation Rates as a Measure of Hypoxic Conditions

Enrichment of molybdenum (Mo) in reducing sediments due to authigenic fixation in anoxic interstitial waters could provide an indicator of hypoxic conditions that integrates over substantial temporal extents. Sediments maintained under controlled dissolved oxygen (DO) conditions showed elevated concentrations of Mo when exposed to low DO concentrations. Mo accumulation was linearly related to time of exposure in treatments below 2.8 mg O₂/L, with less or no accumulation at higher concentrations. Rates of accumulation were independent of DO concentration below 2.8 mg/L. Accumulation occurred at DO concentrations higher than those limiting accumulation in field settings, with rates in the lowest treatments similar to those in sediments of deep basins with restricted circulation and low DO concentrations.     

MICP技术联合多孔硅吸附材料对锌铅复合污染土固化/稳定化修复的试验研究

近年来,工业和科技的快速发展使得重金属污染土固化/稳定化的修复研究成为热点。运用微生物诱导碳酸钙沉淀(MICP)技术联合吸附材料对锌铅复合重金属污染土进行固化/稳定化的修复,通过无侧限抗压强度试验、毒性浸出试验,评价处理前后污染土的固化效果与重金属的稳定化效果,结合扫描电镜(SEM)和X射线衍射(XRD)等检测手段,揭示MICP技术处理锌铅重金属污染土的修复机制。研究结果表明,采用MICP技术对锌铅重金属污染土进行固化/稳定化之后,可以有效降低污染土中有害重金属的浸出性。当矿化时间为10d时,试样无侧限抗压强度为942.5k Pa;铅的浸出浓度为4.20mg/L,比未处理时降低了44.81%;锌的浸出浓度为4.31mg/L,比未处理时降低了46.19%,效果显著。在此基础上,添加10%的多孔硅吸附材料后,试样无侧限抗压强度可达到1 021 kPa,强度提高了8.3%;铅的浸出浓度为2.45mg/L,与未经处理时相比,降幅达到了67.81%,与单纯MICP方法处理时相比,铅浸出浓度被二次降低了41.67%;锌的浸出浓度仅为2.93 mg/L,与未经处理时相比,降幅达到了63.4%,与单纯...     

Dissociation of gas hydrates by hydrocarbon migration and accumulation-derived slope failures: An example from the South China Sea

The mechanism of slope failure associated with overpressure that is caused by hydrocarbon migration and accumulation remains unclear. High-resolution seismic data and gas hydrate drilling data collected from the Shenhu gas hydrate field (site SH5) offer a valuable opportunity to study the relations between submarine slope failure and hydrocarbon accumulation and flow that is associated with a ～2 km-diameter gas chimney developed beneath site SH5 where none gas hydrates had been recovered by drilling and sampling despite the presence of distinct bottom simulating reflectors (BSRs) and favorable gas hydrate indication. The mechanism of submarine slope failure resulted from buoyancy extrusion and seepage-derived deformation which were caused by overpressure from a ～1100 m-high gas column in a gas chimney was studied via numerical simulation. The ～9.55 MPa overpressure caused by hydrocarbons that migrated through the gas chimney and then accumulated beneath subsurface gas hydrate-bearing impermeable sediments. This may have resulted in a submarine slope failure, which disequilibrated the gas hydrate-bearing zone and completely decomposed the gas hydrate once precipitated at site SH5. Before the gas hydrate decomposition, the largely impermeable sediments overlying the gas chimney may have undergone a major upward deformation due to the buoyancy extrusion of the overpressure in the gas chimney, and slope failure was initiated from plastic strain of the sediments and reduced internal strength. Slope failure subsequently resulted in partial gas hydrate decomposition and sediment permeability increase. The pressurized gas in the gas chimney may have diffused into the overlying sediments controlled by seepage-derived deformation, causing an effective stress reduction at the base of the sediments and significant plastic deformation. This may have formed a new cycle of submarine slope failure and finally the total gas hydrate dissociation. The modeling results of buoyancy extrusion and seepage-derived deformation of the overpressure in the gas chimney would provide new understanding in the development of submarine slope failure and the link between slope failure and gas hydrate accumulation and dissociation.     

The early diagenesis of aliphatic hydrocarbons and organic matter in sedimentary particulates from Dabob Bay,Washington

Aliphatic hydrocarbon compositions were quantitatively characterized in plankton, sediment trap-collected particulate materials and sediments from Dabob Bay using high resolution glass capillary gas chromatography. The average net accumulation of individual hydrocarbons measured in a 1-yr series of sediment traps was compared with the net accumulation of corresponding compounds measured in three depth intervals of ²¹⁰Pb-dated bottom sediments. Systematic and rapid decreases in the net accumulation of individual hydrocarbons were observed from the sediment traps to the sediments. Most pronounced decreases were measured for planktonically derived hydrocarbon constituents (e.g. pristane and two unsaturated compounds) which are rapidly remineralized at or near the sediment-water interface. Consequently, the amount of each compound measured in deposited sediments is not necessarily a quantitative indication of its initial flux to the sediments. The n-alkanes (C_25,27,29,31). characteristic of terrestrial plant waxes, are the predominant hydrocarbons measured by 4–6 cm depth in these sediments and show reasonably constant net accumulation below this interval.Significant diagenetic alteration of the bulk organic matter contained in the average sediment trap particulate material is also noted through comparison with bottom sediments on the basis of organic C/N and δ¹³C measurements. Organic matter elementally similar to marine plankton is preferentially remineralized upon deposition of the sedimentary particulates. The residual organic matter remaining and buried in the bottom sediments closely resembles terrestrial organic matter.     

Hydrocarbon contamination of a typical mangrove floor in Niger Delta, Nigeria

The impact of petroleum hydrocarbons on the floor of a mangrove system located on one of the intertidal lands behind the barrier islands of Niger Delta basin of southern Nigeria was evaluated following the Obiafu-14 oil spillage. The area covered by the oil spill was delimited by reconnaissance and soils were sampled by grid method from the bottom and middle slopes of oil-affected and unaffected (control) sites. Soil samples were later brought to the laboratory where total hydrocarbon content was determined by extraction and spectrophotometric techniques. A lower pH range of 4.28–4.36 in the oil impacted soils meant that the site was more acidic; a higher moisture content of 33.34% and lower electrical conductivity (EC) of 31.75μS/cm in the affected area presupposed oxygen deprivation and lower salt content respectively. On the strength of the baseline data on the study area and evidence from the uncontaminated, geographically similar control site, it can be said that the Obiafu-14 oil spillage had severely contaminated the affected mangrove floor. This is corroborated by a total extractable hydrocarbon content of 6.32×10³ ± 344 mg/kg (no overlap in Standard Error at 95% Confidence Limit), and the abysmal degradation of the mangrove system at the site. Although soils of the mangrove floor under consideration may well be of limited cultivation value on account of the people’s dual occupation in fishing and farming, the presence of such levels of petroleum hydrocarbons at the study site might hamper agricultural productivity.     

Laboratory methods for evaluating migrated high molecular weight hydrocarbons in marine sediments at naturally occurring oil seeps

A laboratory study has been conducted to determine the best methods for the detection of C₁₀–C₄₀ hydrocarbons at naturally occurring oil seeps in marine sediments. The results indicate that a commercially available method using n-C₆ to extract sediments and gas chromatography–flame ionization detection (GC–FID) to screen the resulting extract is effective at recognizing the presence of migrated hydrocarbons at concentrations from 50 to 5000 ppm. When non-biodegraded, the amount of oil charge is effectively tracked by the sum of n-alkanes in the gas chromatogram. However, once the charge oil becomes biodegraded, with the loss of n-alkanes and isoprenoids, the amount of oil is tracked by the quantification of the unresolved complex mixture (UCM). Gas chromatography–mass spectrometry (GC–MS) was also found to be very effective for the recognition of petroleum related hydrocarbons and results indicate that GC–MS would be a very effective tool for screening samples at concentrations below 50 ppm oil charge.