Yaorong Qian

Archaeal lipid biomarkers and isotopic evidence of anaerobic methane oxidation associated with gas hydrates in the Gulf of Mexico

Abstract Anaerobic oxidation of methane (AOM) occurs in the Gulf of Mexico gas hydrate systems. Here we show lipid biomarker and isotopic evidence that archaea are involved in AOM. The estimated abundance of total archaeal lipids ranges from 44.8 to 60.4 μg/g (dry sediment) in hydrate-bearing samples but is below detection limit in the hydrate-free sample. The δ13C values of archaeal lipids range from −69 to −99 ‰ in hydrate-bearing samples. These results suggest that biomass of archaea is significantly enhanced through AOM at the gas hydrate deposits. These data also support a currently acknowledged mechanism of AOM mediated by a consortium of sulfate-reducing bacteria and archaea observed in a variety of methane-rich marine settings. Anaerobic oxidation of oil hydrocarbons also occurs in the Gulf of Mexico gas hydrate systems as shown by degradation of n-alkanes (>C15) in the anoxic sediments. These processes convert hydrocarbons to carbon dioxide and increase pore water alkalinity, which promote the precipitation of enormous volumes of authigenic carbonate rock depleted in 13C. This long-term geologic sequestration of carbon may affect models of global climate change.

Chemical characterization of naturally weathered oil residues in arid terrestrial environment in Al-Alamein, Egypt.

The main objective of this study was to investigate compositional changes in a range of source- and weathering-dependent molecular parameters in oil residues in the arid terrestrial environment of Al-Alamein, Egypt. The results of aromatic hydrocarbon analysis demonstrated the stability of several aromatic hydrocarbon ratios in oil residues over a wide range of weathering and hydrocarbon concentrations. The ratios of C2-dibenzothiophenes/C2-phenanthrenes (C2-DBTs/C2-PHENs), C3-dibenzothiophenes/C3-phenanthrenes (C3-DBTs/C3-PHENs), C2-chrysenes/C1-chrysenes (C2-CHRYs/C1-CHRYs), and C2-dibenzothiophenes/C1-dibenzothiophenes (C2-DBTs/C1-DBTs) were nearly constant in oil residues of varying degrees of weathering. Biomarker ratios of hopanes and steranes were useful for source identification even for severely weathered oil residues. The data confirmed previous observations that C29 20S/(20S + 20R) and C29 betabeta/(betabeta+ alphaalpha) sterane epimer ratios, and C29/C30, C30 alphabeta(alphabeta + 3alpha), C31 22S/(22S + 22R) hopane ratios correlate well even after extensive weathering of spilled oils, although some exceptions were encountered for an extensively weathered surface sample. The data provided clear evidence of correlation between samples of the weathered oil residues and the possible source oil. Moreover, the results of biomarker compositions were in good agreement with weathering classification based on alkanes and aromatic hydrocarbons. In general, samples with lowest pregnane indices (PI) and tricyclic terpane indices (TriTI) showed the lowest concentrations of n-alkanes and alkylated polycyclic aromatic hydrocarbon (PAH) homologues, the highest weathering ratios (WRs), the highest values of unresolved complex mixture (UCM)/total resolved peak (TRP) ratios, and the highest ratios of C2 and C3-alkylated CHRYs to their counterparts in the PHEN and DBT series.

Application of Petroleum Hydrocarbon Chemical Fingerprinting in Oil Spill Investigations––Gulf of Suez, Egypt

Abstract In an attempt to examine the suitability of chemical fingerprinting methods in oil spill investigations, multiple parameters sensitive to both sources and degree of weathering were used to characterize spilled oil samples and to distinguish spilled hydrocarbons from sources unrelated to the spill in shoreline of the Gulf of Suez, Egypt. The characterizations of individual aliphatic and aromatic compounds were based on gas chromatography and gas chromatography/mass spectrometry analyses. The distribution of n-alkanes, polynuclear aromatic hydrocarbons (PAHs) and alkyl PAHs in the source oil and an oil slick collected 72 h after the spill were very similar. Major compositional changes observed in a weathered oiled sediment collected nine months after the spill from the shoreline at the spill location were consistent with previous studies. Molecular parameters of hopane and sterane biomarkers were very similar in the source oil, the spilled oil and the highly weathered oiled sediment. The similarity in biomarker compositions provided a strong evidence for a close genetic association of these samples. Ratios of C2-chrysenes/C2-phenanthrenes and C2-chrysenes/C2-dibenzothiophenes, the pregnane index (sum of the concentrations of C21 and C22 steranes over total concentration of steranes×100), and the tricyclic terpane index (sum of the concentrations of C19 and C30 tricyclic terpanes over total concentration of terpanes×100) clearly differentiated the refined oil products from crude oils. The composition of bilge oil indicated enrichment of late eluting steranes and terpanes and showed biomarker distributions similar to natural petroleum. The results further support that sterane and terpane biomarker analyses could differentiate oil samples of different sources even though they were sometimes indistinguishable in PAH and alkane compositions.

The isotopic compositions of selected crude oil PAHs during biodegradation

Abstract Compound specific isotope analysis (CSIA) has been used to measure the δ13C of selected individual polycyclic aromatic hydrocarbons (PAHs) from a crude oil that was exposed to enhanced microbial biodegradation. Twenty-one liters of a crude oil were introduced to series of separate 5 m×5 m wetland plots along the San Jacinto River, Texas. Smaller grids were established within each area to serve as control plots, plots for addition with nitrogen fertilizer, or as plots for addition with petroleum degrading microbes. Samples of randomly selected, oil impacted soils were collected at 4, 28, and 56 days after oil inoculation. These samples initially were analyzed using GC/MS for identification of PAH compounds. The initial results on the soils indicated a tendency for samples to shift from low and high molecular weight PAH compounds to eventually predominantly high molecular weight compounds. Fifteen specific PAH compounds, including two containing sulfur, were selected for compound specific isotope analysis based on chromatography and expected abundance in the soils. Five alkylated components, a dimethylnaphthalene, two trimethylnaphthalenes, a methyldibenzothiophene, and a dimethylphenanthrene, were seen to be best resolved and are suggested to be the most reliable for observations of isotopic changes during biodegradation. Isotopic variability during the treatment period follows patterns with an overall trend toward enrichment in the residual PAH pool of 2–8‰. All treatment grids, including the control, underwent isotopic alteration throughout the duration of the experiments. ANOVA testing of the isotopic results indicated that the control grids showed the smallest amount of changes over time, whereas the nutrient and microbe amended grids were not significantly different from each other. Although the trends on isotopic enrichments were predictable, the magnitude of changes was not. One additional finding indicated that time trials beyond 2-month periods were needed to determine if nutrient or microbial additions are advantageous for PAH biodegradation in wetland soils. The results of these tests highlight the importance of understanding the magnitude and direction of isotopic variations in PAH compounds as part of investigations aimed at tracing these compounds from potential sources.

Suspended particulate organic matter (SPOM) in Gulf of Mexico estuaries : compound-specific isotope analysis and plant pigment compositions

Abstract Pigment and stable isotopic compositions of suspended particulate organic matter (SPOM) were determined in several estuaries along the Texas coast of the Gulf of Mexico. Analysis of the composition of accessory pigments suggested that the phytoplankton taxa varied among these bays. The δ 13 C values of SPOM, lipids, and chlorophylls in these bays varied from − 18 to − 27, − 20 to − 31, and − 18 to − 31‰, respectively. The δ 13 C values of SPOM, lipids, and chlorophylls, and the pigment composition together suggest that the 13 C-depleted organic matter in Corpus Christi Bay in June 1992 resulted from the fixation of 13 C-depleted CO 2 derived from riverine water or in situ remineralization of organic matter. The lipids and chlorophyll a isolated from the nearly freshwater system of Aransas Bay in 1992 were 13 C-enriched and most likely derived from local phytoplankton production. The δ 13 C values of SPOM, lipids and chlorophylls in the bays where salinities were closest to that of seawater were in the range expected for marine phytoplankton, i.e., − 18 to − 24‰. The δ 15 N values for SPOM, lipids, and chlorophyll a ranged from + 4 to + 14‰ with most between + 6 to + 10‰. These values are similar to the SPOM of marine systems and indicate a common source of nitrogen throughout the estuaries.

Source apportionment of polychlorinated biphenyls using compound specific isotope analysis

Abstract Reported here are results of the compound specific carbon isotopic analysis (CSIA) of individual PCB congeners. This investigation was designed to determine the suitability of CSIA on this class of compounds in natural materials. Samples of duck tissue, duck liver, duck egg and grass carp were collected from the Housatonic River, Massachusetts, and compared with samples of fresh Aroclor® 1242, 1254,1260, and 1262. Twenty congeners were selected for isotopic analysis based on their ability to be separated chromatographically and their expected abundance in tissue samples. Animal tissue samples showed variable PCB patterns and abundances although all animals were expected to have been exposed to Aroclor® 1260. These characteristics are thought to be related to the structure of the food web or metabolic and physiological features of the individual animals. Grass carp samples had excellent correlation in the isotopic compositions of the congeners. Although the correspondence of δ 13 C in congeners from fresh Aroclor 1260 to congeners from tissue samples may not be expected to be identical, the patterns of similarity were very supportive of the maintenance of the isotopic signal into the food chain. The patterns observed in these and other samples suggest a fractionation process where residual congener pools can become progressively enriched while the congeners produced from degradation are more depleted. The isotopic patterns provide insight to degradation processes and into relative metabolic stability of the various congeners in different animals. The results of this study suggest that CSIA analysis of PCBs at natural abundance can provide significant insight into tracing these compounds through the natural environment. The data also suggest that tracking PCB mixtures may be possible using CSIA techniques after standard chromatographic matching or other fingerprinting techniques become blurred.

Short-time-scale (year) variations of petroleum fluids from the U.S. Gulf Coast

Abstract Evolving short-term (less than 5 yr) compositional changes in hydrocarbon charge from some Eugene Island Block 330 (EI-330) wells are demonstrated. Storage, analytical, and production artifacts are shown to be minimal. In some wells, compositions remain constant from 1985 to 1993, whereas in others in the same reservoir, significant changes are observed. In some cases, temporal variability is greater than spatial variability. Maximum temporal change is strongest for specific compounds: toluene and C 6 to C 9 normal alkanes, but is also observed to a lesser extent for higher-molecular-weight components (up to n -C 32 ). Principal coordinate analysis shows the highest degree of overall temporal compositional change over an 8-yr period in the shallowest wells where there is also evidence of biodegradation. Small temporal compositional changes are also observed in two deeper wells that are below the thermal window favorable for biodegradation. An exception is an unusual oil, where a very large increase in toluene, as well as smaller changes in a number of n -alkanes, was observed in 1993. The δ 13 C compound-specific isotopic signature of toluene, in addition to several other C 7 -C 8 compounds in this oil, yields convincing evidence that it is related to the same family as other EI-330 oils and unlikely to be due to a drilling or laboratory contaminant. Minor isotopic differences in other C 7 compounds (1.5‰) are consistent with extensive gas washing of this oil. The short-term compositional changes in EI-330 oils are attributed to gas washing, which causes overprinting of biodegraded oils with light n -alkanes in shallower GA and HB reservoirs where oils are currently being biodegraded in situ. Patterns of smaller changes in heavier compounds in both shallower and deeper wells are also consistent with this interpretation.

Sources and Bioavailability of Polynuclear Aromatic Hydrocarbons in Galveston Bay, Texas

Oyster and sediment samples collected from six sites in Galveston Bay from 1986 to 1998 were analyzed for polynuclear aromatic hydrocarbons (PAHs). Total concentrations of parent PAHs in oysters ranged from 20 ng g−1 at one site to 9,242 ng g−1 at another and varied randomly with no clear trend over the 13 year period at any site. Concentrations of alkylated PAHs, which are indications of petroleum contamination, varied from 20 to 80,000 ng g−1 in oysters and were in higher abundance than the parent PAHs, indicating that one source of the PAH contaminants in Galveston Bay was petroleum and petroleum products. Four to six ring parent PAHs, which are indicative of combustion source , were higher than those of 2–3 ring parent PAHs, suggesting incomplete combustion generated PAHs was another source of PAHs into Galveston Bay. Concentrations of parent PAHs in sediments ranged from 57 to 670 ng g−1 and were much lower than those in oysters. Sediments from one site had a high PAH concentration of 5,800 ng g−1. Comparison of the compositions and concentrations of PAHs between sediment and oysters suggests that oysters preferentially bioaccumulate four to six ring PAHs. PAH composition in sediments suggests that the sources of PAH pollution in Galveston Bay were predominantly pyrogenic, while petroleum related PAHs were secondary contributions into the Bay.

An Overview of Metal Pollution in the Western Harbour of Alexandria, Egypt

Limited data are available on the concentration of metals in sediments in the Western Harbour of Alexandria. The most comprehensive record is from a survey conducted more than a decade ago. Industrial and human activities in and around this area have increased dramatically in the last 20 years. The purpose of this study was to determine the concentrations of heavy metals in surfacial bottom sediments of the harbor, to assess their potential biological effects and to identify their possible sources. Sediment samples from 21 stations throughout the harbor were analyzed for grain size, total organic carbon content (TOC), and metals (Al, As, Ba, Be, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Se, Sn, V, and Zn) to assess the extent of contamination in the area. The results indicated that concentrations of metals in the sediments varied widely depending on the location. High levels of metals were observed in the Arsenal Basin and the outfall area of El Mahmoudiya Canal in the inner harbor. The concentrations of metals were found to be higher than those recorded in the previous study. However, with some exceptions, most of the changes in the metal concentrations could be accounted for by the variations in aluminum, which represents the variations in mineralogy and grain size, indicating that the majority of the metals were of “natural” origin. The present data were also compared with results from other areas.