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The Niger Delta Basin is one of the most prolific hydrocarbon provinces in the world, yet the origin of the vast amounts of oil and gas found in the numerous sub-basins across the delta remains contested. A total of 180 oil samples from more than 40 oil fields in the Niger Delta were analyzed by gas chromatography (GC), GC-mass spectrometry (GC-MS) and selected samples by GC-tandem mass spectrometry (GC-MSMS). The interpreted thermal maturity and source depositional environments of these hydrocarbons show significant variation depending on the components analyzed, and allow no clear correlation to a single source rock but rather imply extensive mixed contributions. Diamondoid hydrocarbon parameters were used for the first time on these Paleogene–Neogene reservoired oils to investigate source, thermal maturity and mixing effects and to perform cross-correlations of these oils. The diamondoid abundances and distributions support the hypothesis of co-sourcing of oil from a thermally cracked, sub-delta, Type II marine source, which was then mixed with oils of relatively lower maturities in the Paleogene–Neogene reservoirs. Future geochemical interpretations should treat the Niger Delta oils as potential mixtures of oils of variable maturities from different sources, often with the most important source biomarkers depleted because of the extent of thermal cracking.

Bacteria play key roles in the carbon cycle. In many sediments and peatlands, methanotrophic bacteria consume a portion of released methane, reducing the emissions of this potent greenhouse gas. In marine oxygen minimum zones (OMZ) and other anoxic settings, anaerobic ammonium oxidizing (anammox) bacteria remove bioavailable nitrogen while performing chemoautotrophic carbon fixation. Methanotrophic and anammox bacteria synthesize a wide number of complex bacteriohopanepolyols (BHPs), comprising notably several stereoisomers of bacteriohopanetetrols (BHT), which are used as biomarker lipids. While BHT-17β(H), 21β(H), 22R, 32R, 33R, 34S (BHT-34S) is ubiquitous in the environment, its 34R stereoisomer (BHT-17β(H), 21β(H), 22R, 32R, 33R, 34R; BHT-34R) has only five known producers: the freshwater anammox genera ‘Candidatus Brocadia’, the aerobic acidic peatland methanotroph Methylocella palustris, the nitrogen-fixing aerobic bacteria Frankia spp., and the aerobic acetic acid-producing bacteria Acetobacter pasteurianus and Komagataeibacter xylinus. BHT-x—another BHT isomer of unknown stereochemistry—has only one known producer, the marine anammox bacteria ‘Candidatus Scalindua’ (Schwartz-Narbonne et al., 2020). The occurrence and extent of these different carbon cycle processes can be assessed by measuring the concentrations of these BHT stereoisomers and changes in their δ13C values (Hemingway et al., 2018; Lengger et al., 2019).However, the 13C fractionation associated with the different carbon assimilation pathways of these bacteria has been minimally assessed, resulting in poorly constrained ranges in δ13C values and difficulty in interpreting isotope results.We used a gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) method to measure the δ13C of BHT-34S, BHT34R, and BHT-x of cultured bacteria (‘Ca. Scalindua’, ‘Ca. Brocadia’, Methylocella tundrae, Frankia spp., and Komagataeibacter xylinus). These δ13C values were combined with bulk isotopic measurements of the bacterial biomass and δ13C analyses of the bacterial growth substrates to establish carbon isotopic fractionation from substrate to biomass to BHT lipid. We demonstrated that bacteria using different metabolic pathways produced distinct fractionation factors between substrate and BHTs, which potentially allows for distinguishing BHT-34R produced by ‘Ca. Brocadia’ and methanotrophs from other freshwater producers (e.g. in peatlands). Measurement of BHT-specific fractionation factors allowed us to better constrain the contribution of anammox bacteria to fixed carbon in OMZ. This work expands the application of BHT isomers to isotopically identify carbon cycle processes. ReferencesHemingway, Jordon D., et al. "A novel method to measure the 13C composition of intact bacteriohopanepolyols." Organic Geochemistry 123 (2018): 144-147.Lengger, Sabine K., et al. "Dark carbon fixation in the Arabian Sea oxygen minimum zone contributes to sedimentary organic carbon (SOM)." Global Biogeochemical Cycles 33.12 (2019): 1715-1732.Schwartz-Narbonne, Rachel, et al. "A unique bacteriohopanetetrol stereoisomer of marine anammox." Organic Geochemistry (2020): 103994.

N and P are the key limiting nutrients considered most important for the stimulation of crude oil degradation but other trace nutrients may also be important. Experimental soil microcosms were setup to investigate crude oil degradation in the context of Ni amendments. Amended Nickel as NiO, NiCl2, or, a porphyrin complex either inhibited, had no effect, or, enhanced aerobic hydrocarbon degradation in an oil-contaminated soil. Biodegradation was significantly (95% confidence) enhanced (70%) with low levels of Ni-Porph (12 mg/kg) relative to an oil-only control; whereas, NiO (200 and 350 mg/kg) significantly inhibited (36 and 87%) biodegradation consistent with oxide particle induced reactive oxygen stress. Microbial community compositions were also significantly affected by Ni. In 16S rRNA sequence libraries, the enriched hydrocarbon degrading genus, Rhodococcus, was partially replaced by a Nocardia sp. in the presence of low levels of NiO (12 and 50 mg/kg). In contrast, the highest relative and absolute Rhodococcus abundances were coincident with the maximal rates of oil degradation observed in the Ni-Porph-amended soils. Growth dependent constitutive requirements for Ni-dependent urease or perhaps Ni-dependent superoxide dismutase enzymes (found in Rhodococcus genomes) provided a mechanistic explanation for stimulation. These results suggest biostimulation technologies, in addition to N and P, should also consider trace nutrients such as Ni tacitly considered adequately supplied and available in a typical soil.

Clay minerals are abundant in soils and sediments and often contain Fe. Some varieties, such as nontronites, contain as much as 40 wt.% Fe2O3 within their molecular structure. Several studies have shown that various Fe-reducing micro-organisms can use ferric iron in Fe-bearing clay minerals as their terminal electron acceptor, thereby reducing it to ferrous iron. Laboratory experiments have also demonstrated that chemically or bacterially reduced clays can promote the reductive degradation of various organics, including chlorinated pesticides and nitroaromatics. Therefore, Fe-bearing clays may play a crucial role in the natural attenuation of various redox-sensitive contaminants in soils and sediments. Although the organochlorinated pesticide p,p−-DDT is one of the most abundant and recalcitrant sources of contamination in many parts of the world, the impact of reduced Fe-bearing clays on its degradation has never been documented. The purpose of the present study was to evaluate the extent of degradation of p,p−-DDT during the bacterial reduction of Fe(III) in an Fe-rich clay. Microcosm experiments were conducted under anaerobic conditions using nontronite (sample NAu-2) spiked withpp−-DDT and the metal-reducing bacteria Shewanella oneidensis MR-1. Similar experiments were conducted using a sand sample to better ascertain the true impact of the clay vs. the bacteria on the degradation of DDT. Samples were analyzed for DDT and degradation products after 0, 3, and 6 weeks of incubation at 30°C. Results revealed a progressive decrease in p,p−-DDT and increase in p,p−-DDD concentrations in the clay experiments compared to sand and abiotic controls, indicating that Fe-bearing clays may substantially contribute toward the reductive degradation of DDT in soils and sediments. These new findings further demonstrate the impact that clay materials can have on the natural attenuation of pollutants in natural and artificial systems and open new avenues for the passive treatment of contaminated land.

In addition to previously reported 25-norhopanoic acids with the 17α(H), 21β(H) and 17β(H), 21α(H) configurations, for the first time we report the identification of 25-norhopanoic acids bearing the 17β(H), 21β(H) configuration in a suite of heavily biodegraded oils from China. The 17β(H), 21β(H) stereochemistry is a thermally unstable biologically-derived structure, suggesting that the 17β(H), 21β(H) 25-norhopanoic acids may derive from petroleum-degrading microbes. Rather than representing a direct input, we propose that demethylation of 17β(H), 21β(H) hopanoic acids derived from bacteria in the reservoir may give rise to 17β(H), 21β(H) 25-norhopanoic acids, implying that microbial reworking of biomass is occurring alongside petroleum degradation.

Bioremediation of oil contamination has been shown to be effective for cobble and sandy shorelines. To assess the operational limitations of this technology, this project studied its potential to treat buried oil in fine sediments. The effectiveness of bioremediation by nutrient enrichment with water-soluble mineral fertilizers was quantified experimentally with a randomised block design with three replicate blocks. Each block consisted of an untreated control plot, a plot treated with fertilizer alone, an oiled plot, and an oiled plot treated with fertilizer. The sediment in each plot was retained in mesh enclosures and buried at a depth of 0.15 m. Weathered and emulsified Arabian Light crude oil was applied to the appropriate plots at 3.7 kg.m−−2. Bioremediation success was monitored by examining in situ CO2 production rates; changes in residual hydrocarbons normalized to 17?(H), 21?H)-hopane; and response of hydrocarbon-degrading microorganisms. Fertilizer treatments significantly increased the biodegradation of petroleum hydrocarbons (p = 0.0001) in the buried sediments. These conclusions were supported by in situ CO2 production data. Microbiological analyses showed that nutrient addition increased the numbers of hydrocarbon-degraders on the oiled plots tenfold. The results clearly showed that bioremediation can treat oil buried in fine sediment following a spill incident.

Availability of inorganic nutrients, particularly nitrogen and phosphorous, is often a primary control on crude oil hydrocarbon degradation in marine systems. Many studies have empirically determined optimum levels of inorganic N and P for stimulation of hydrocarbon degradation. Nevertheless, there is a paucity of information on fundamental kinetic parameters for nutrient enhanced crude oil biodegradation that can be used to model the fate of crude oil in bioremediation programmes that use inorganic nutrient addition to stimulate oil biodegradation. Here we report fundamental kinetic parameters (Ks and qmax) for nitrate- and phosphate-stimulated crude oil biodegradation under nutrient limited conditions and with respect to crude oil, under conditions where N and P are not limiting. In the marine sediments studied, crude oil degradation was limited by both N and P availability. In sediments treated with 12.5 mg/g of oil but with no addition of N and P, hydrocarbon degradation rates, assessed on the basis of CO2 production, were 1.10 ± 0.03 μmol CO2/g wet sediment/day which were comparable to rates of CO2 production in sediments to which no oil was added (1.05 ± 0.27 μmol CO2/g wet sediment/day). When inorganic nitrogen was added alone maximum rates of CO2 production measured were 4.25 ± 0.91 μmol CO2/g wet sediment/day. However, when the same levels of inorganic nitrogen were added in the presence of 0.5% P w/w of oil (1.6 μmol P/g wet sediment) maximum rates of measured CO2 production increased more than four-fold to 18.40 ± 1.04 μmol CO2/g wet sediment/day. Ks and qmax estimates for inorganic N (in the form of sodium nitrate) when P was not limiting were 1.99 ± 0.86 μmol/g wet sediment and 16.16 ± 1.28 μmol CO2/g wet sediment/day respectively. The corresponding values for P were 63 ± 95 nmol/g wet sediment and 12.05 ± 1.31 μmol CO2/g wet sediment/day. The qmax values with respect to N and P were not significantly different (P < 0.05). When N and P were not limiting Ks and qmax for crude oil were 4.52 ± 1.51 mg oil/g wet sediment and 16.89 ± 1.25 μmol CO2/g wet sediment/day. At concentrations of inorganic N above 45 μmol/g wet sediment inhibition of CO2 production from hydrocarbon degradation was evident. Analysis of bacterial 16S rRNA genes indicated that Alcanivorax spp. were selected in these marine sediments with increasing inorganic nutrient concentration, whereas Cycloclasticus spp. were more prevalent at lower inorganic nutrient concentrations. These data suggest that simple empirical estimates of the proportion of nutrients added relative to crude oil concentrations may not be sufficient to guarantee successful crude oil bioremediation in oxic beach sediments. The data we present also help define the maximum rates and hence timescales required for bioremediation of beach sediments.

Pristane (2,6,10,14-tetramethylpentadecane), frequently the most abundant biomarker hydrocarbon in crude oils and rock extracts, was thought originally to be derived directly from phytol or, later, from thermal degradation of tocopherols. We present new evidence supporting the hypothesis that pristane, under certain conditions, may result from the catagenic decomposition of methyltrimethyltridecylchromans (MTTCs) derived during diagenesis from condensation reactions between chlorophyll and alkylphenols. We show that phytol can condense, under mild conditions, with phenolic systems (in free or polymeric form) to produce free or bound structures that generate pristenes on flash pyrolysis. We suggest straightforward tests of this hypothesis.

General procedures are outlined for the asymmetric syntheses of lignans of the dibenzylbutyrolactone, dibenzylbutanediol, aryltetralin and dibenzocyclooctadiene series, from tandem addition products derived from 4-menthyloxybutenolide.

Bioremediation and activated carbon (AC) amendment were compared as remediation strategies for sediment from the River Tyne containing 16.4 +/- 7.3 microg/g polycyclic aromatic hydrocarbons (PAHs) and approximately 5% coal particles by total dry sediment weight. Unamended, nutrient amended (biostimulated) and nutrient and Pseudomonas putida amended (bioaugmented) sediment microcosms failed to show a significant decrease in total sediment PAH concentrations over a one month period. Polyethylene passive (PE) samplers were embedded for 21 days in these sediment microcosms in order to measure the available portion of PAHs and accumulated 4.70 +/- 0.25, 12.43 +/- 1.78, and 23.49 +/- 2.73 microg PAHs/g PE from the unamended, biostimulated, and bioaugmented microcosms, respectively. Higher PAH uptake by PE samplers in biostimulated and bioaugmented microcosms coincided with slower degradation of spiked phenanthrene in sediment-free filtrate from these microcosms compared to filtrate from the unamended microcosms. Microbial community analysis revealed changes in the bacterial community directly following the addition of nutrients, but the added P. putida community failed to establish itself. Addition of 2% by dry sediment weight activated carbon reduced PAH uptake by PE samplers to 0.28 +/- 0.01 microg PAHs/g PE, a greater than 90% reduction compared to the unamended microcosms.

Addition of sulphur stabilised carbanions to a chiral non-racemic butenolide followed by reaction with an aromatic aldehyde affords a short synthesis of homochiral dibenzylbutyrolactone derivatives. Desulphurisation of the first formed adducts proceeds in almost quantitative yield to afford the parent lignan.

Enolate anions obtained by conjugate addition to (–)-5-(1-menthyloxy)furan-2(5H)-one are quenched with benzyl bromides or iodides to yield homochiral dibenzylbutyrolactones. Desulfurisation followed by lithium aluminium hydride reduction affords homochiral 2,3-dibenzylbutane-1,4-diols, including (–)dimethylsecoisolariciresinol and (–)-dihydroclusin. Desulfurisation followed by reduction with NaBH4/KOH gives the homochiral 2,3-dibenzylbutyrolactones (–)-dimethylmatairesinol, (–)kusunokinin and (–)-yatein, which undergo stereoselective oxidative coupling with DDQ in trifluoroacetic acid to give homochiral tetrahydrodibenzocyclooctene lignans belonging to the isostegane series.

Addition of sulfur-stabilised carbanions to (–)-5-(1-menthyloxy)furan-2(5H)-one followed by reaction with an aromatic aldehyde affords a short synthesis of enantiomerically pure dibenzylbutyrolactone derivatives. Desulfurisation with NaBH4/NiCl2 proceeds in almost quantitative yield, and reduction with NaBH4/KOH gives the parent dibenzylbutyroactones including (–)-6-epi-podorhizol. These undergo cyclisation with acid to give homochiral aryltetralins including (–)-deoxyisopodophyllotoxin in high yield.