Petrogenic Hydrocarbons Research Articles

Petroleum contamination in groundwater/air and its effects on farmland soil in the outskirt of an industrial city in China

To evaluate petroleum contamination of groundwater and air and identify its sources in the Hunpu, a wastewater-irrigated area located in the southwest of Shenyang, concentrations of aliphatic hydrocarbon components were analyzed by gas chromatography. The analysis revealed the presence of biogenic and degraded petrogenic hydrocarbons. For water, petroleum pollution and degradation levels were significantly higher in October 2009 [total aliphatic hydrocarbons (TAH): 909.3–10343.1μgL−1] than those in May of the same year (TAH: 357.0 to 6802.1μgL−1). For air, the concentrations of ∑n-alkanes, unresolved complex mixture (UCM), and TAH were lowest in winter (∑n-alkanes: 76.6μgm−2 d−1, UCM: 147.9μgm−2 d−1, and TAH: 224.5μgm−2 d−1); the n-alkanes were more abundant in spring (841.2μgm−2 d−1); and UCM and TAH were more abundant in summer and autumn (UCM: 13173.7μgm−2 d−1 and TAH: 13859.9μgm−2 d−1). Through principal component analysis, the water and air sampled in different seasons and sites were differentiated based on their degree of petroleum pollution and various aliphatic hydrocarbon compositions. Through redundancy analysis, we found the effect of irrigation water on the surface soil was much higher than that of atmospheric deposition. The variance of hydrocarbon composition in soil, explained by the hydrocarbon composition in water collected in the main irrigation period, May 2009, was 70.5%, whereas the value for atmospheric deposition was only 12.2%.

A Preliminary Study of Total Petrogenic Hydrocarbon Distribution in Setiu Wetland, Southern South China Sea (Malaysia)

The distribution of total petrogenic hydrocarbon was investigated in the subsurface water of Setiu Wetland from July to October 2008. The concentration was quantified by UV-fluorescence spectroscopy and ranged from 4 to 121 μg/L (mean 60 ± 41 μg/L). Higher total petrogenic hydrocarbon concentrations were found in area with high boating activities suggesting that the contribution is likely related to fossil fuel combustion. The present study also revealed that the total petrogenic hydrocarbon values are still lower that those reported in Malaysian coastal waters.

One Step Ultrasound Extraction and Purification Method for the Gas Chromatographic Analysis of Hydrocarbons from Marine Sediments: Application to the Monitoring of Italian Coasts

In this study, we describe the development of an ultrasound-assisted method for the simultaneous extraction and purification of hydrocarbons from marine sediments and then its application to the gas chromatographic analysis for the estimation of the biogenic anthropogenic and petrogenic sources of hydrocarbons present in marine sediments. The extraction of hydrocarbons and their simultaneous purification from other organic compounds present in sediments was performed by sonication of a three phase system consisting of sediment, hexane and a HCl medium at pH 2. This method allowed accurate recoveries of the hydrocarbon content in samples. In the following GC-FID analysis, we examined the hydrocarbon distribution in four different areas of the Italian seas determining the pristane to phytane ratio, the total odd n-alkanes to even n-alkanes ratio (carbon preference index), the low molecular weight to high molecular weight ratio, perylene content and the presence of the so called unresolved complex mixture; according to recent studies, these parameters support the identification of the biogenic, anthropogenic and petrogenic hydrocarbon sources present in environmental samples. GC chromatograms were then re-examined by means of two different statistical multivariate methods: two-dimensional mapping (2DMAP) and independent component analysis (ICA). 2DMAP showed the presence of a significant heterogeneity in the hydrocarbon composition of different areas and within samples of a same area. ICA confirmed the general heterogeneity evidenced by 2DMAP allowing in addition to characterise the hydrocarbon composition of one of the investigated areas.

Vertical fluxes of aromatic and aliphatic hydrocarbons in the Northwestern Mediterranean Sea

Aliphatic and aromatic hydrocarbon fluxes were measured in time series sediment trap samples at 200 m and at 1000 m depths in the open Northwestern Mediterranean Sea, from December 2000 to July 2002. Averaged fluxes of n-alkanes, UCM and T-PAH 35 were 2.96 ± 2.60 μg m −2 d −1, 64 ± 60 μg m −2 d −1 and 0.68 ± 0.59 μg m −2 d −1, respectively. Molecular compositions of both hydrocarbon classes showed a contamination in petrogenic hydrocarbons well above the background levels of such an open site, whereas pyrolytic hydrocarbons stand in the range of other open Mediterranean locations. Fluxes displayed ample interannual and seasonal variabilities, mainly related to mass flux variation while concentration evolutions trigger secondary changes in pollutant fluxes. High lithogenic flux events exported particles with a larger pollutant load than biogenic particles formed during the spring bloom and during the summer. Sinking hydrocarbons were efficiently transported from 200 m to 1000 m.

Sources of n-alkanes in an urbanized estuary: Insights from molecular distributions and compound-specific stable and radiocarbon isotopes

Diagnostic molecular ratios and compound-specific 13C and 14C analyses were used to identify n-alkane sources in surface sediments collected along a transect from an urbanized estuary draining a peat-rich catchment (Tyne, UK). The most abundant homologues were generally C 29 or C 31, and the carbon preference index (CPI; 1.8 to 6.4) and average chain length (ACL; 28.5 to 29.5) of C 25–C 33 n-alkanes became progressively lower in samples closer to the mouth of estuary. δ 13C signatures of C 19–C 31 n-alkanes ranged from − 37.1 to − 29.3‰ and in general became more depleted with increasing carbon number. Δ 14C values for C 21 (− 945 to − 738‰) were significantly more depleted compared to C 29 (− 591 to − 65‰) and C 31 (− 382 to − 96‰), pointing to a much higher component of fossil (i.e., 14C-free) carbon in the shorter homologue. The radiocarbon contents for these three n-alkanes decreased toward the North Sea, which in conjunction with an up to 4‰ seaward 13C-enrichment in C 29 and C 31 and seaward decreases in CPI and ACL pointed to petrogenic hydrocarbon contamination in lower estuarine sediments. Independent 13C and 14C mass balances used to calculate the relative proportions of modern (i.e., plant wax) and fossil (i.e., petrogenic) n-alkanes yielded similar results and demonstrated that mixing with marine-derived organic matter (OM) or microbial degradation during estuarine transport led to a seaward decline in modern, longer-chain homologues, resulting in an increasingly larger fossil carbon contribution toward the mouth of estuary. The ability to clearly distinguish anthropogenic from natural inputs suggests that compound-specific radiocarbon analysis can successfully delineate the age of terrigenous OM delivered to the coastal zone even near historically polluted systems such as the Tyne.

Alkane and PAH biomarkers as tracers of terrigenous organic carbon in Arctic Ocean sediments

We present the first sedimentary biomarker study encompassing the entire Arctic Ocean. A large data set of organic markers for terrigenous, petroleum and combustion inputs [alkanes, hopanes and steranes, parent and alkyl polycyclic aromatic hydrocarbons (PAHs)] is examined for patterns in space and time using principal components analysis (PCA) and partial least squares (PLS). Biomarker patterns reveal the central Arctic Ocean basin sediments to be compositionally distinct from those of the Mackenzie River/Beaufort Sea and Barents Sea, but similar to those of the Laptev Sea. PAH distributions reflected in PAH ratios and PCA projections demonstrate that Arctic Ocean sediment is dominated by natural inputs to the extent that anthropogenic combustion PAHs are not significant. We find only modest changes between the glacial and post-glacial sediments for atmospherically transported hydrocarbon biomarkers, while particle associated biomarkers were captured strongly at basin edges during the glacial period, and much more evenly transported across basins during the post-glacial period. The orders of magnitude decreases in particle associated petrogenic alkanes and PAHs in central basins during glacial times, coupled with the uniformity of most petrogenic biomarker parameters for most basin and shelf locations, reflect a massive reduction in ice transport that makes the margins the most likely source of petrogenic material for the Pleistocene/Holocene central Arctic basins. The proximity of large coal deposits of various maturity levels along the Lena River, the overlap in PAH and biomarker composition of the Laptev Sea and surficial sediments from the central Arctic Ocean and the location of the Laptev Sea at the origin of the main Transpolar Drift all point to eroded coals from the Lena River/Laptev Sea as the likely source of petrogenic hydrocarbons to the central Arctic Ocean. The ubiquitous presence of allochthonous coal in Arctic Ocean surface sediments provides a major constraint on the use of petrogenic biomarkers to infer the presence of subsurface petroleum reserves.

Variations and Origins of Aliphatic Hydrocarbons in Sediment Cores from Chini Lake in Peninsular Malaysia

Over the past decade, Chini Lake has experienced tremendous changes due to land conversions from forest to agriculture such as oil palm and rubber plantations and also construction of a small barrage downstream of the Chini River. This land conversion has caused changes to the plant community and increased sedimentation rates in the lake. Consequently, this study was carried out to investigate the distribution patterns and sources of n-alkanes in four sediment core samples from Chini Lake and to evaluate the relative changes in organic matter inputs from land and lake flora. In the long-chain n-alkanes (LHC > C23)region, carbon preference index (CPI) values ranged from 1–1.52 in the sediment cores. Most lake sediments analyzed did not contain an unresolved complex mixture (UCM). The average nC17/pristane ratios (nC17/Pr) were 5.34 ± 1.99 and the average nC18/phytane (nC18/Ph) ratios were 1.27 ± 0.25 for the sediment profiles. The n-alkane average chain length (ACL) was 29.68 ± 0.15in the study area. There was significant positive correlation between ACL and CPI in the sediment cores at station B (r = 0.769, p = 0.003), station C (r = 0.735, p = 0.015), station D (r = 0.737, p = 0.006), and station E (r = 0.741, p = 0.006). Positive correlations between diploptene and long-chain n-alkanes (nC25−nC33) were found for sediment core B (r = 0.976, p<0.001), sediment core C (r = 0.836, p = 0.003), sediment core D (r = 0.824, p = 0.001) and sediment core E (r = 0.865, p < 0.001). Terrigenious to aquatic ratio for hydrocarbons (TARHC) and total n-alkanes (∑HC) concentrations increased with depth a pattern that contrast with short chain n-alkanes/total organic carbon (SHC/TOC) ratios. It can be concluded that the petrogenic hydrocarbon contamination in the sediment cores is minimal and that the n-alkanes preserved in Chini Lake sediments are influenced by higher plant waxes and bacteria.

Anthropogenic hydrocarbons in sediments of the northeastern Havana seaboard

The presence of petrogenic hydrocarbons was evaluated in surface sediments from the northeastern Havana littoral (Cuba). Different geochemical biomarkers were used to differentiate between biogenic and anthropogenic hydrocarbons. Sediment samples were Soxhlet extracted and analyzed by gas chromatography with flame ionization and mass spectrometer detectors. Total concentrations of aliphatic hydrocarbons ranged from 5.5 ± 0.3 to 225.7 ± 12.6 µg g–1. The presence of an unresolved complex mixture, and the detection of hopanes and of the isoprenoid compounds pristane and phytane revealed the occurrence of petroleum-derived hydrocarbons in the sediment samples.

Geochemical markers as a tool to assess sedimentary organic matter sources of the Laguna Estuarine System, south Brazil: aliphatic and polycyclic aromatic hydrocarbons

Surface sediment samples from the Laguna Estuarine System were analyzed to identify organic matter sources. The ratios between selected n-alkanes, high concentrations of aliphatic hydrocarbons (AH) (average of 9,168 µg g-1 of organic carbon, OC) and polycyclic aromatic hydrocarbons (PAH) (total average of 426,593 ng g-1 OC), and the hopanes distribution with αβ stereochemistry found in the Santo Antônio Lagoon samples were evidence that hydrocarbon inputs from petrogenic sources predominate over natural sources. In the other samples studied, the AH distribution (from 38 to 2,749 µg g-1 OC), and detection of hopenes and hopanes-ββ suggest mixed sources of hydrocarbons. Nevertheless, PAH concentrations in all samples (from 7,731 to 786,469 ng g-1 OC, whereof alkyl naphthalenes accounted for > 92% of the total) indicated critical petrogenic contamination. Fishing and urban activities are potential sources to the petrogenic hydrocarbons detected in these sediment samples.

Validating a multi-biomarker approach with the shanny Lipophrys pholis to monitor oil spills in European marine ecosystems

Oil spills are an importance source of polycyclic aromatic hydrocarbons (PAHs) in the aquatic environment. Intertidal communities are particularly sensitive since most organisms from these ecosystems are sessile or present reduced mobility. Hence, it is important to validate the use of resident species as sentinels to characterize the impact of oil spills on the rocky shores and the improvement during the restoration process. Recently the advantages of using the shanny Lipophrys pholis in pollution monitoring within the northwestern Atlantic coast has been pointed out. Therefore, with the aim of further validating the use of L. pholis in pollution monitoring associated with petrogenic hydrocarbon contamination, a multi-biomarker approach study was carried out 1 week after a moderate oil spill from the waste treatment plant (WTP) of the major Portuguese refinery in the north of Portugal (Petrogal). Fish collected at 2 km from the accident displayed a significant induction of ethoxyresorufin-O-deethylase activity (EROD) and fluorescent aromatic compounds (FACs) in bile (up to a 5-fold induction) in comparison with the pre-spill scenario, and a 15% induction in erythrocytic nuclear abnormalities (ENA), a biomarker of genotoxicity. In contrast, no significant differences were recorded in the reference site. In order to better characterize the time-course accumulation of FACs in bile after a PAH insult, laboratory exposure of L. pholis to benzo[ a]pyrene (B[ a]P) was performed. A clear dose–response accumulation of B[ a]P metabolites was observed that closely reflected nominal exposure concentrations already after 3 d. Overall, the findings of the present study highlight the potential of L. pholis in pollution monitoring dealing not only with chronic contamination, but also with oil spill accidents of a moderate scale. Taking into consideration that EROD and FACs determinations in L. pholis are cost effective, rapid and easy to use, they offer a great potential to be incorporated into risk assessment of PAHs in the scope of national monitoring programs and the European Water Policy legislation.

Just Add Water and Salt: the Optimisation of Petrogenic Hydrocarbon Biodegradation in Soils from Semi-arid Barrow Island, Western Australia

We investigated the potential of soil moisture and nutrient amendments to enhance the biodegradation of oil in the soils from an ecologically unique semi-arid island. This was achieved using a series of controlled laboratory incubations where moisture or nutrient levels were experimentally manipulated. Respired CO2 increased sharply with moisture amendment reflecting the severe moisture limitation of these porous and semi-arid soils. The greatest levels of CO2 respiration were generally obtained with a soil pore water saturation of 50–70%. Biodegradation in these nutrient poor soils was also promoted by the moderate addition of a nitrogen fertiliser. Increased biodegradation was greater at the lowest amendment rate (100 mg N kg−1 soil) than the higher levels (500 or 1,000 mg N kg−1 soil), suggesting the higher application rates may introduce N toxicity. Addition of phosphorous alone had little effect, but a combined 500 mg N and 200 mg P kg−1 soil amendment led to a synergistic increase in CO2 respiration (3.0×), suggesting P can limit the biodegradation of hydrocarbons following exogenous N amendment.

Distribution and sources of hydrocarbons in lagoon sediments of Setiu Wetland, Terengganu, Malaysia

Hydrocarbon compounds viz. aliphatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), sterols, long chain fatty acids, alkanones and alkanals in surface sediment of Setiu Wetland were analysed and characterized using GCMS. The concentration of total identified resolved n-alkanes (TIRNA) in sediment ranged from 2.99–11.6 μ g g− 1 dry weight. The distribution of the aliphatic fraction showed the presence of n-alkanes ranging from C12 to C36 with high predominance for long chain homologues (C25-C31) and a carbon maximum at C29 and C31 with CPI &amp;gt; 3; these observations provide evidence for the presence of biogenic terrigenous input corresponding to epicuticular plant waxes into the lagoon sediments. Positive and strong correlation between n-alkanes associated with terrigenous input (ALK TER) and TIRNA suggest terrestrial input is the main sources of TIRNA in this study area. The absence of unresolved complex mixture (UCM) in the chromatogram and the absence of hopanes, steranes and PAHs compounds are indicative of uncontaminated sediment by petrogenic and pyrogenic hydrocarbons. The concentration of total identified sterols (TIS) ranged from 1.41 μ g g− 1 dry weight to 3.11 μ g g− 1 dry weight with cholesterol, β -Sitosterol and stigmasterol were generally the most dominant and abundant components detected at almost all stations. A positive and strong correlation was observed between B-Sitosterol and TIS and the distribution of long chain n-alkan-2-ones in the range of C21 to C27 with odd to even predominance and n-alkanals (C20 to C28), n-alkanols (C22–C30) and n-alkanoic acids (C22–C30) with even to odd predominance provide further evidence for biogenic sources of hydrocarbons with terrestrial plant input as the predominant source. It was noted that a minor contribution associated with marine phytoplankton (algae) as well as bacteria were also observed in some of the sediment samples superimposing with the terrigenous plant wax input. In general results from this study clearly showed the lagoon sediment of Setiu Wetland is still in uncontaminated condition where terrestrial plants input are the dominant contributor of organic compounds in the sediments with a minor input from marine organisms.

Hydrocarbons characterization in coastal sediments of the Argentine Patagonia using the nuclear magnetic resonance (NMR) spectroscopy

Hydrocarbons in Patagonian sediments were analyzed to evaluate their biogenic or petrogenic origins. Structural determination by 1H-NMR spectrometry and principal component analysis (PCA) show that the first two principal components accounted for more than 75.7% of the variance. The results indicate that biogenic hydrocarbons have mainly linear hydrocarbon chains and polar groups (high H2, H4, H5, and HCOOH), while petrogenic hydrocarbons show more branched chains and mainly mono-aromatic components, e.g., crude oil (high H1, H1A, and H3) or mainly poly-aromatic components (high H4, and H2A) in weathering oil.

Temporal trends of hydrocarbons in sediment cores from the Pearl River Estuary and the northern South China Sea

Concentrations and fluxes of unresolved complex mixture of hydrocarbons (UCM) and polycyclic aromatic hydrocarbons (PAHs) were analyzed for two (210)Pb dated sediment cores from the Pearl River Estuary (PRE) and the adjacent northern South China Sea (NSCS). Compound-specific stable carbon isotopic compositions of individual n-alkanes were also measured for identification of the hydrocarbon sources. The historical records of PAHs in the NSCS reflected the economic development in the Pearl River Delta during the 20th century. PAHs in the NSCS predominantly derive from combustion of coal and biomass, whereas PAHs in the PRE are a mixture of petrogenic and pyrogenic in origins. The isotopic profiles reveal that the petrogenic hydrocarbons in the PRE originate predominantly from local spillage/leakage of lube oil and crude oils. The accumulation rates of pyrogenic PAHs have significantly increased, whereas UCM accumulation has slightly declined in the NSCS in the recent three decades.

Identification, Abundance and Origin of Aliphatic Hydrocarbons in the Fine Atmospheric Particulate Matter of Athens, Greece

The organic chemical composition of the fine fraction of atmospheric particulate matter in Athens has been studied, in order to establish emission sources. The results of the analyses of the aliphatic fraction indicate that all samples contain n-alkanes ranging from C14 to C32, with C25, C26, C27 and C29 being the more abundant congeners. Fossil fuels biomarkers such as extended tricyclic terpanes (hopanes, steranes) and isoprenoid hydrocarbons (pristane, phytane) were observed in our samples on a daily basis. Source reconciliation was conducted using molecular diagnostic ratios (such as the carbon preference index – CPI). The mean CPI value (1.84) indicates the mixed origin of the Athenian fine particles. The notable presence of an unresolved complex mixture or “hump” of hydrocarbons in our gas chromatograms is indicative of petrogenic hydrocarbon inputs. An approximate measure of this kind of contamination is the ratio of the concentrations of unresolved components to the resolved n-alkanes and other major compounds (U:R). The high U:R value of 25.25 further confirmed the major contribution of fossil fuels. Yet, the percent contribution of leaf wax n-alkanes (25.15%) indicated the parallel contribution of biogenic sources. This work supports the conclusion that vehicular emissions were the major source of aliphatic organic compounds with a smaller contribution of biogenic n-alkanes during the study period in Athens.

Vertical fluxes and organic composition of settling material from the sewage impacted Buenos Aires coastal area, Argentina

Settling particulates collected upstream and downstream of Buenos Aires main sewer in the Río de la Plata were analyzed for total organic carbon (TOC), nitrogen (TN), resolved aliphatic hydrocarbons (ALI), unresolved complex mixture (UCM), terpane biomarkers, linear alkylbenzenes (LABs) and PCBs to evaluate the composition, sources and variability of anthropogenic fluxes. Sediment traps collected a substantial amount of material (19.9 ± 13.5 g cm −2 yr −1) with relatively high organic contents (TOC: 7.7 ± 5.5%; TN: 0.65 ± 0.34%; C/N: 13 ± 3.2) and contaminant loads (UCM: 949 ± 737, ALI: 115 ± 111, LABs: 18 ± 12; PCBs: 0.07 ± 0.04 μg g −1). The resulting vertical fluxes are very large (TOC: 1.9 ± 2.5 g cm −2 yr −1; total hydrocarbons: 21 ± 23 mg cm −2 yr −1; LABs: 0.42 ± 0.62 mg cm −2 yr −1; PCBs: 1.6 ± 1.8 μg cm −2 yr −1). The settling material showed a clear organic enrichment downstream the sewer and during rainy, warm months. A variance component analysis revealed that spatial differences were less significant (13–27%) than the seasonal trend (30–63% total variability) which is inversely related to compound stabilities. The organic composition indicated slightly altered inputs of petrogenic hydrocarbons, detergents and Aroclor 1242:1254:1260 residues, with limited contribution of terrestrial plant waxes and negligible from plankton. The seasonal variation of individual compounds revealed a summer enrichment of labile components inversely correlated to molecular weight, with terpane biomarkers showing an opposite pattern. Rainy, warm months showed higher total mass fluxes and C/N ratios with signatures enriched in < n-C 22 alkanes, external LABs, less chlorinated PCBs and >C 30 hopanes suggesting a more efficient washout of fresher organic residues. Conversely, cold months showed more degraded signatures depleted of low molecular weight components and enriched in UCM, internal LABs and tricyclic terpanes.

Evaluation of biogenic and anthropogenic inputs of aliphatic hydrocarbons to Lake Taihu sediments using biomarkers

Surficial sediments from 13 sites throughout Lake Taihu, one of the largest urbanized freshwater lake systems in China, were analyzed for biomarkers (e.g., n-alkanes and hopanes) to track the origin of organic inputs (biogenic or anthropogenic), and, thus, to identify any ‘hot spots’ of hydrocarbon contamination. A distinct spatial distribution of aliphatic hydrocarbons in sediments was observed in Lake Taihu. At the northern tip of the lake (i.e., Meiliang and Wuli Bays), the highest mean aliphatic hydrocarbon concentration, with a significant contribution of an unresolved complex mixture (UCM), was found, indicating possible anthropogenic petroleum contamination (mainly from untreated and partially treated industrial and domestic sewage from Wuxi, Changzhou and other cities). This was supported by the n-alkane indices (e.g., small Carbon Preference Index and odd-to-even values) and a high degree of maturity of the hopane biomarkers. However, hydrocarbons from East Taihu were mainly biogenic, with the lowest mean concentrations, negligible or no contribution of UCM, abundance of vascular plant C23–C33 n-alkanes with a high odd-to-even predominance, and the presence of biogenic hopanes (e.g., 17β(H), 21β(H)-hopanes and hopenes). In the other areas of the lake, however, the predominance of biogenic in combination with petrogenic hydrocarbons was indicated by the biomarkers.

An evaluation of petrogenic hydrocarbons in northern Gulf of Alaska continental shelf sediments – The role of coastal oil seep inputs

We compared hydrocarbons in water, suspended particulate matter (SPM), and riparian sediment collected from coastal watersheds along the Yakataga foreland with corresponding hydrocarbons in Gulf of Alaska benthic sediments. This comparison allows an evaluation of hydrocarbon contributions to marine sediments from natural oil seeps, coal and organic matter (e.g., kerogen) associated with eroding siliciclastic rocks. The samples from oil seeps show extensive loss of low-molecular weight n-alkanes (< n-C 14) and the presence of large, bimodal unresolved complex mixtures (UCMs), in contrast to the hydrocarbon fingerprints on the SPM and riparian sediment samples collected upstream from the oil seeps. After entering the fluvial systems, hydrocarbons from seep oils are rapidly diluted, and associate with the SPM phase as oil-mineral-aggregates (OMA). Johnston Creek, the watershed containing the most prolific seep, conveys detectable seep-derived hydrocarbons to the Gulf of Alaska, but overall seep inputs are largely attenuated by the (non-seep) petrogenic hydrocarbon content of the high SPM loads. In contrast to the geochemical signature of seep oil, Gulf of Alaska benthic sediments are characterized by abundant alkylated naphthalene homologues, relatively smooth n-alkane envelopes ( n-C 9 through n-C 34, but with elevated levels of n-C 27, n-C 29, and n-C 31), and small UCMs. Further, hydrocarbons in benthic sediments are highly intercorrelated. Taken together, these characteristics indicate that seep oil is a negligible petrogenic hydrocarbon source to the Gulf of Alaska continental shelf. Coaly material separated from the benthic sediment samples using a dense liquid (∼2.00 g cm −3) also accounted for a minor portion of the total PAH (1–6%) and total n-alkanes (0.4–2%) in the benthic samples. Most of the hydrocarbon burden in the sediments is found in the denser sediment fraction and likely derives from organic matter contributed by denudation of siliciclastic formations in the Yakutat terrane. We therefore conclude that previous investigations relying on source allocation models have considerably overestimated oil seeps as a hydrocarbon source to the Gulf of Alaska.

Negligible risks to corals from antifouling booster biocides and triazine herbicides in coastal waters of the Chagos Archipelago

The Chagos Archipelago is the most isolated and biologically diverse group of atolls in the central Indian Ocean. It contains 5 islanded atolls, including the world’s largest atoll, the Great Chagos Bank. Following the abandonment of the copra plantations, in 1973, most islands are uninhabited and have rarely been visited. The only exception is Diego Garcia, part of which is a strategic military base with appropriate infrastructure to support long range aircraft and ships which visit and reside for extended periods in the lagoon which provides anchorage. In 1996, a research programme was undertaken in Chagos (Sheppard and Seaward, 1999) to assess the atolls biodiversity, biogeographic role with respect to fisheries, and the degree of their pristine condition. Analyses of sediment samples from throughout the Archipelago revealed that hydrocarbons present were predominantly of biogenic origin (Readman et al., 1999). However, these studies also revealed some petrogenic and pyrogenic polycyclic aromatic hydrocarbons (PAHs) at sub to low ng g 1 dry sediment. Organochlorine analyses revealed that only some polychlorinated biphenyl (PCB) congeners and the pesticide lindane were above limits of detection. It was concluded that atmospheric transport (from industrial parts of the world) was the major route for the introduction of organochlorines to the region. A parallel study (Everaarts et al., 1999), based upon analysis of anthropogenic organic contaminants and toxic metals in sediments and biota, confirmed that, at least in 1996, Chagos belonged to the category of least impacted coastal areas. During recent years, antifouling products used in boat paints have tended to incorporate organic ‘‘booster’’ biocides to enhance performance and to move away from tributyltin compounds (which were restricted in most countries due to their demonstrated toxicity to non-target organisms at very low concentrations). The booster biocide products are primarily herbicidal and contain active ingredients including: Irgarol 1051 (2-methylthio-4-tert-butylamino-6-cyclopropylamino-s-triazine), Sea-Nine 211 /kathon 5287 (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one), chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile), dichlofluanid (1,1-dichloro-N-[(dimethylamino)sulfonyl]-1-fluoro-Nphenylmethanesulfenamide), diuron (DCMU, [3-(3,4-dichlorophenyl)-1,1-dimethylurea]), TCMS pyridine, TCMTB, zinc pyrithione and zineb. Irgarol 1051 has recently been shown to be a potent inhibitor of coral photosynthesis in both isolated endosymbiotic coral zooxanthellae (i.e. isolated algal symbionts in vitro) and in the intact coral symbionts (i.e. in vivo) for a number of Atlantic and Pacific coral species (Owen et al., 2002, 2003; Jones and Kerswell, 2003; reviewed by Jones (2005)). In in vitro experiments, Owen et al. (2002) report no CðHCO 3 Þ incorporation in zooxanthellae isolated from the common branching coral Madracis mirabilis after a 6 h exposure to 63 ng l 1 Irgarol 1051 . In vivo, the The objective of BASELINE is to publish short communications on different aspects of pollution of the marine environment. Only those papers which clearly identify the quality of the data will be considered for publication. Contributors to Baseline should refer to ‘Baseline—The New Format and Content’ (Mar. Pollut. Bull. 42, 703–704).

Higher plant n-alkane average chain length as an indicator of petrogenic hydrocarbon contamination in marine sediments

The n-alkane average chain length (ACL) is the weight-averaged number of carbon atoms of the higher plant C 25–C 33 n-alkanes. The abundance of individual n-alkanes from higher plant sources generally increases with increasing carbon number in coastal marine sediments around Taiwan, but this trend is reversed for petrogenic hydrocarbons. The ACL would potentially be lowered if petrogenic hydrocarbons were added to sediments containing biogenic hydrocarbons alone. To test this idea, a marine environment off southwestern Taiwan known to contain both biogenic and petrogenic hydrocarbons and two nearby rivers were selected for investigating possible difference in ACL values between their sediments. The average CPI of C 25–C 33 n-alkanes was 4.08 ± 2.04 (range 1.90–8.96, n = 15) for the river sediments and 1.70 ± 0.16 (range 1.43–1.97, n = 15) for the marine sediments. The ACL of C 25–C 33 n-alkanes for river sediments ranged from 29.2 to 30.5 (average 29.9 ± 0.4), and for marine sediments from 28.4 to 29.3 (average 28.9 ± 0.3). The ACL difference between marine and river sediments was significant (Student's t test at 99% confidence) although it appeared small. It is suggested that the ACL can be an additional indicator for detection of petrogenic hydrocarbons in coastal marine sediments.