Recurrent arrival of oil to Galician coast: the final step of the Prestige deep oil spill

Sunken oil mats: A biomarker-based investigation

Sunken oil mats (SOMs) pose a significant threat to marine ecosystems, yet their long-term fate and weathering processes remain poorly understood. This study investigates the degradation of biomarkers in a SOM sample collected from the Brazilian coast following the long-lasting 2019 oil spill. The SOM clearly distinguished from spilt oil and were attributed to tanker-washing residues. Analysis of its sections revealed a consistent depletion pattern, associated with losses of volatile and photooxidation-sensitive compounds, even in the most preserved inner fractions, this suggests weathering of the oil prior SOM formation. While biodegradation was minor, photooxidation revealed a significant weathering factor, especially for aromatic compounds as indicated by preferential degradation of highly-alkylated tricyclic aromatic sulfur heterocycles, and specific methylpyrenes and benzofluorenes. This study underscore the complex interplay of weathering processes shaping the fate of SOMs and the importance of biomarker-based diagnosis in assessing the origin and ecological impacts of long-lasting oil spills.

Tar ball pollution under the influence of ocean circulation in the Bohai Sea, China

The deposition of tar balls of unknown sources on the coast poses a great threat to the fishery, tourism and coastal biodiversity in the Bohai Sea. This work aimed to identify the sources of tar balls by using oil fingerprint technique. Tar ball samples were collected from the seashore of two islands of the western Bohai Sea and divided into two groups (Group I and Group II). Principal component analysis showed that although Caofeidian oilfield was one of the closest oilfields to the sampling area it was not a source. Fingerprints of characteristic hopanes and steranes showed that samples of Group I were similar to the crude oils from the nearby Jidong oilfield, and samples of Group II were similar to the Penglai-19-3 crude oils. Combined with cross-plots of the samples and the reference oils, it indicated that Group I may come from Jidong and Group II may come from Penglai-19-3. The weathering characteristics of alkanes and polycyclic aromatic hydrocarbons showed that the samples were affected by natural weathering processes (e.g., evaporation, photooxidation and biodegradation). It revealed that oil pollution from the nearby oilfields can also affect other areas under the influence of ocean circulation. It is the first study on source identification of tar balls from the Bohai Sea and the effects of ocean circulation on the tar ball transport. This study can considerably help to further understand the evolution of tar balls and consequently determine their sources.

Chemical signatures of polycyclic aromatic hydrocarbons in the emissions from in situ oil burns

This study characterized the parent and alkylated polycyclic aromatic hydrocarbons (PAHs) in gaseous and particulate emissions from the in situ burning (ISB) of oils. The experimental results indicate that the burning of the heavy oil produced the most PAH emissions because of its longest burning time. In addition, the parent PAHs mainly exist in the particulate phase, while alkylated PAHs mostly accumulate in the gaseous phase. In particular, the diagnostic-ratios of PAHs with great stability in both gaseous and particulate emissions from ISB are identified by comparing the laboratory and field data. The presences of bell-, slope- and V-shaped distribution patterns of alkylated PAHs in the emissions precisely indicate their sources to be petrogenic and pyrogenic processes occurring during ISB. The formation of 2-methylanthracene during ISB is confirmed. The overall findings are expected to provide a prospective protocol to characterize PAH pollution from ISB emissions in case of oil spills.

Source identification and weathering processes of tar ball deposited Qinhuangdao coast along the Bohai Sea, China

Deposition of tar balls on the Qinhuangdao beaches along the coasts of the Bohai Sea (China) could affect people's leisure activities and tourism, and even affect the marine ecosystem. In 2020, representative tar balls collected from Qinhuangdao beaches, fingerprint analysis based on diagnostic ratios suggested that these tar balls were all very similar and may belong to the same source. Source identification by cross plot and principal component analysis (PCA), showed that the tar balls were likely from Penglai 19-3 crude oil. The weathering characterizations based on polycyclic aromatic hydrocarbons (PAHs), alkanes parameters and unresolved complex mixture (UCM), indicated that the tar balls had been significantly influenced by natural weathering processes such as evaporation, biodegradation and photooxidation. The study of this leakage provides a powerful support for determining the leakage source, evaluating the potential weathering mechanism and determining the accident liability. This is the first time to use fingerprint technology to identify the source of tar balls in Qinhuangdao coastal zone in the Bohai Sea.

Effects of oil properties on the formation of oil-particle aggregates at the presence of chemical dispersant in baffled flask tests

The formation of oil-particle aggregates (OPA) is the major sedimental pathway of spilled oil, which can bring great harm to both the benthic communities and marine environment. In this paper, effects of GM-2 chemical dispersant and oil properties on the formation of OPA was investigated by the EPA baffled flask test. The addition of dispersant can promote the formation of OPA from montmorillonite and five test oils obviously. With the increase of the dispersant dosage, the size of trapped oil in OPA increased and the density of OPA decreased. The dispersant can increase the kinematic viscosity of crude oil, and high viscosity of the oil is advantageous for the formation of OPA. The oil-seawater interfacial tension is reduced after the addition of dispersant, which makes oil dispersed into the water column easier. A kinematic equation of dispersed oil concentration attenuation was modified by introducing the oil property coefficient β. The modified empirical equation can calculate the mass of oil in sunken OPA in oil spill accidents.

Improving the preparedness against an oil spill: Evaluation of the influence of environmental parameters on the operability of unmanned vehicles

When an oil spill occurs, a prompt response reduces significantly the impact. The preparedness and contingency plans are essential to identify the most appropriate technologies. Unmanned and autonomous vehicles (UAVs) is emerging as a powerful tool of strategic potential in the observation, oil tracking and damage assessment of an oil spill. The SpilLess project explored the suitability of these devices to be the first-line response to an oil spill. This work analyses the operational requirements related to environmental parameters following a two steps approach: 1) Environmental characterization from long wind and waves time series and modelling; 2) Definition of the optimal periods for operating each UAVs. We have defined the periods in which each of these facilities acts best, confirming that the operational limits of UAVs are not significantly more restrictive than the traditional operations. UAVs should be included in contingency plans as available tools to fight against oil spills.

Imprint and short-term fate of the Agia Zoni II tanker oil spill on the marine ecosystem of Saronikos Gulf

In this study we investigate the spatial and temporal imprint of the September 2017 Agia Zoni II tanker heavy fuel oil spill on the marine ecosystem of Saronikos Gulf (Greece). Based on the chemical fingerprinting approach, by means of gas chromatography - flame ionization detector, gas chromatography-mass spectrometry and the use of various diagnostic ratios, we characterize changes in the composition of the spilled oil at various sampling sites and evaluate major mechanisms affecting its fate i.e. dissolution/dispersion, evaporation, biodegradation, photo-oxidation and sedimentation during the first six months from the spill. Overall, the main effects of the incident were confined to the coastal zone during the first three months after the spill, where an extended petroleum imprint was recorded in many cases, with the determined concentrations of the total petroleum hydrocarbons and polycyclic aromatic hydrocarbons falling within the highest range of concentrations previously reported for similar oil spill incidents worldwide. In the first three months following the spill the oil was affected by a combination of volatilization, rapid biodegradation and photodegradation, the later playing a role in its early days weathering. Concerning sediments, an imprint related to the incident was recorded in a few cases, being, however, mild in respect to the high chronic petroleum-associated anthropogenic background of the impacted area.

Quantitative evaluation of n-alkanes, PAHs, and petroleum biomarker accumulation in beach-stranded tar balls and coastal surface sediments in the Bushehr Province, Persian Gulf (Iran)

Coastal areas within the Bushehr Province (BP), Persian Gulf, Iran, face great challenges due to the heavy organic contamination caused by rapid industrialization, and the presence of numerous oil fields. In addition, in 2014, a significant number of tar balls are found along the coasts of BP. A total of 96 samples (48 coastal sediments and 48 tar balls) were taken from eight sampling points at the BP coast during the summer of 2014. These samples were analyzed to identify the sources and characteristics of their organic matter using diagnostic ratios and fingerprint analysis based on the distribution of the source-specific biomarkers of n-alkanes, PAHs,¹ hopanes and steranes. Mean concentration of n-alkanes (μg g^-1 dw) and PAHs (ng g^-1 dw) varied respectively from 405 to 220,626, and 267 to 23,568 in coastal sediments, while ranged respectively from 664 to 145,285 and 390 to 46,426 in tar balls. In addition, mean concentration of hopanes and steranes (ng g^-1 dw) were between 18.17 and 3349 and 184.66 to 1578 in coastal sediments, whereas in tar balls were 235-1899 and 520-1504, respectively. Pri/Phy² ratio was 0.25 to 1.51 (0.65) and 0.36 to 1 (0.63) in coastal sediment and tar ball samples, respectively, and the occurrence of UCM³ in both matrices, reflecting the petrogenic OM⁴ inputs and chronic oil contamination, respectively. The C₃₀ and C₂₉ homologues followed Gammacerane were detected in both matrices, in particular those collected from intensive industrial activities, suggesting petrogenic sources of OM. The coastal sediment PAHs profiles were significantly dominated by HMW⁵-PAHs in the Bahregan Beach (BAB) (78% of total PAHs), Bandare-Genaveh (GP) (66%), and Bandare-Bushehr (BUB) (61%) stations, while the Bashi Beach (BSB) (40%), Bandare-Kangan (KP) (57%), and Bandare-Asaluyeh (AP) (51%) stations exhibited higher proportion of LMW⁶-PAHs. PCA⁷ indicated that the tar ball and coastal sediment samples deposited along the Southwest of the BP beaches are most likely originated from the Abuzar oil. Based on the intensity of the anthropogenic activities, NPMDS⁸ analysis revealed that the GP, BAB, NNP, AP, and KP sampling sites had a high concentration of detected organic pollutants. To the best of our knowledge, this is the first study that investigates oil pollution in costal sediments and tar balls in the BP, providing insights in to the fate of oil in the coastal areas of the Persian Gulf, Iran.

Spatial distribution of heavy hydrocarbons, PAHs and metals in polluted areas. The case of "Galicia", Spain

The aim of this work is to verify the impact of anthropogenic activities and the effects of accidental events, e.g. oil spills, on the marine environment. For this reason, marine sediments and soil samples were collected in the inner part of Vigo and Pontevedra bays, in the Galicia region, northwest Spain, an area interested by many events of oil spills and also characterized by coastal areas with intense anthropic activities; also Cíes Islands, a natural protected area facing the Vigo bay, was investigated, as background site. PAHs, heavy hydrocarbons and metals were analyzed according to standard methods, in order to satisfy quality assurance and quality check constraints. Total PAHs concentration (Σ₁₆ compounds) were in the range of 25-4000ng/g, and 30-800ng/g for marine sediments and soil samples, respectively. Even some samples from the Cíes Islands, show a contamination with values achieving >200ng/g of PAHs. Although contamination levels have been shown to be strong at several locations in the study area, their ranges are those typical of other estuarine sites, with PAHs and hydrocarbons primarily of pyrolytic origin. This observation was further confirmed by enrichment factors of some metals (Cd, Cu, Pb and Zn) that match to those of harbor and shipyard zones of the main industrial and commercial maritime areas.

Oil spills and their impacts on sand beach invertebrate communities: A literature review

Sand beaches are highly dynamic habitats that can experience considerable impacts from oil spills. This review provides a synthesis of the scientific literature on major oil spills and their impacts on sand beaches, with emphasis on studies documenting effects and recoveries of intertidal invertebrate communities. One of the key observations arising from this review is that more attention has generally been given to studying the impacts of oil spills on invertebrates (mostly macrobenthos), and not to documenting their biological recovery. Biological recovery of sand beach invertebrates is highly dynamic, depending on several factors including site-specific physical properties and processes (e.g., sand grain size, beach exposure), the degree of oiling, depth of oil burial, and biological factors (e.g., species-specific life-history traits). Recovery of affected communities ranges from several weeks to several years, with longer recoveries generally associated with physical factors that facilitate oil persistence, or when cleanup activities are absent on heavily oiled beaches. There are considerable challenges in quantifying impacts from spills on sand beach invertebrates because of insufficient baseline information (e.g., distribution, abundance and composition), knowledge gaps in their natural variability (spatial and temporal), and inadequate sampling and replication during and after oil spills. Thus, environment assessments of impacts and recovery require a rigorous experimental design that controls for confounding sources of variability. General recommendations on sampling strategies and toxicity testing, and a preliminary framework for incorporating species-specific life history traits into future assessments are also provided.

Backtrack modeling to locate the origin of tar balls depositing along the west coast of India

Tar ball (TB) deposition along the West Coast of India (WCI) is a common phenomenon during the southwest monsoon season, particularly along the coast of Goa and Gujarat, and it is a major concern to the stake holders. Our earlier studies showed that the source oil for the TBs deposited on the Goa coast in August 2010 is the tanker wash, and the source for subsequent TBs deposited on the Gujarat coast during July 2012 and June 2013 and Goa coast in May 2013 is from Bombay High (BH) oil fields. In the present study, the TBs that were deposited during May 2013 and May 2014 on the Goa coast were backtracked through a trajectory model, primarily to simulate their pathways and identify the reason for the occurrence of TBs only in May, and eventually to identify the origin and the source. The backtracking results re-confirmed that the TBs deposited in 2010 were originated from the tanker routes and that of both 2013 and 2014 TBs from the BH oil fields. The climatology of wind and surface circulation showed that the TBs deposited on the Goa coast during May/June only are from the oil fields and those during August from the tanker route. The results of backtracking simulations showed that the residence time of the oil residues/TBs is approximately 22days for August 2010 TBs, ≈30days for May 2013 TBs and 65days for May 2014 TBs. The residence time (in water) of TBs that deposit (on the coast) in the month of May could be as much as 7months, and could be around one month if deposit in August, primarily because of winds and hydrodynamic conditions of the Arabian Sea.

Identification of sources of tar balls deposited along the Southwest Caspian Coast, Iran using fingerprinting techniques

In 2012, a significant number of tar balls occurred along the Southwest coasts of the Caspian Sea (Iran). Several oil fields of Turkmenistan, Azerbaijan and Iran might be sources of oil spills and lead to the formation of these tar balls. For source identification, 6 tar ball samples were collected from the Southwest beaches of the Caspian Sea and subjected to fingerprint analysis based on the distribution of the source-specific biomarkers of pentacyclic tri-terpanes and steranes. Comparing the diagenic ratios revealed that the tar balls were chemically similar and originated from the same source. Results of double ratio plots (e.g., C29/C30 versus ∑C31-C35/C30 and C28 αββ/(C27 αββ+C29 αββ) versus C29 αββ/(C27 αββ+C28 αββ)) in the tar balls and oils from Iran, Turkmenistan and Azerbaijan indicated that the tar balls might be the result of spills from Turkmenistan oil. Moreover, principle component analysis (PCA) using biomarker ratios on the tar balls and 20 crude oil samples from different wells of Azerbaijan, Iran and Turkmenistan oils showed that the tar balls collected at the Southwest beaches are highly similar to the Turkmenistan oil but one of the Azerbaijan oils (from Bahar field oils) was found to be also slightly close to the tar balls. The weathering characterizations based on the presence of UCM (unresolved complex mixture) and low/high molecular weight ratios (L/H) of alkanes and PAHs indicated the tar ball samples have been significantly influenced by natural weathering processes such as evaporation, photo-degradation and biodegradation. This is the first study of its kind in Iran to use fingerprinting for source identification of tar balls.

A theoretical model to estimate the oil burial depth on sandy beaches: A new oil spill management tool

In oiled sandy beaches, unrecovered fuel can be buried up to several metres. This study proposes a theoretical approach to oil burial estimation along the intertidal area. First, our results revealed the existence of two main patterns in seasonal beach profile behaviour. Type A is characterized by intertidal slopes of time-constant steepness which advance/recede parallel to themselves in response to changing wave conditions. Type B is characterized by slopes of time-varying steepness which intersect at a given point in the intertidal area. This finding has a direct influence on the definition of oil depth. Type A pattern exhibits oil burial along the entire intertidal area following decreasing wave energy, while the type B pattern combines burial in high intertidal and exhumation in mid and/or low intertidal zones, depending on the position of the intersection point. These outcomes should be incorporated as key tools in future oil spill management programs.

The effect of oil spills on the bacterial diversity and catabolic function in coastal sediments: a case study on the Prestige oil spill

The accident of the Prestige oil tanker in 2002 contaminated approximately 900 km of the coastline along the northern Spanish shore, as well as parts of Portugal and France coast, with a mixture of heavy crude oil consisting of polycyclic aromatic hydrocarbons, alkanes, asphaltenes and resins. The capacity of the autochthonous bacterial communities to respond to the oil spill was assessed indirectly by determining the hydrocarbon profiles of weathered oil samples collected along the shore, as well as through isotope ratios of seawater-dissolved CO2, and directly by analyses of denaturing gradient gel electrophoresis fingerprints and 16S rRNA gene libraries. Overall, the results evidenced biodegradation of crude oil components mediated by natural bacterial communities, with a bias towards lighter and less substituted compounds. The changes observed in the Proteobacteria, the most abundant phylum in marine sediments, were related to the metabolic profiles of the sediment. The presence of crude oil in the supratidal and intertidal zones increased the abundance of Alpha- and Gammaproteobacteria, dominated by the groups Sphingomonadaceae, Rhodobacteraceae and Chromatiales, whilst Gamma- and Deltaproteobacteria were more relevant in subtidal zones. The phylum Actinobacteria, and particularly the genus Rhodococcus, was a key player in the microbial response to the spill, especially in the degradation of the alkane fraction. The addition of inorganic fertilizers enhanced total biodegradation rates, suggesting that, in these environments, nutrients were insufficient to support significant growth after the huge increase in carbon sources, as evidenced in other spills. The presence of bacterial communities able to respond to a massive oil input in this area was consistent with the important history of pollution of the region by crude oil.

Differentiating the roles of photooxidation and biodegradation in the weathering of Light Louisiana Sweet crude oil in surface water from the Deepwater Horizon site

We determined the contributions of photooxidation and biodegradation to the weathering of Light Louisiana Sweet crude oil by incubating surface water from the Deepwater Horizon site under natural sunlight and temperature conditions. N-alkane biodegradation rate constants were ca. ten-fold higher than the photooxidation rate constants. For the 2-3 ring and 4-5 ring polycyclic aromatic hydrocarbons (PAHs), photooxidation rate constants were 0.08-0.98day(-1) and 0.01-0.07day(-1), respectively. The dispersant Corexit enhanced degradation of n-alkanes but not of PAHs. Compared to biodegradation, photooxidation increased transformation of 4-5 ring PAHs by 70% and 3-4 ring alkylated PAHs by 36%. For the first time we observed that sunlight inhibited biodegradation of pristane and phytane, possibly due to inhibition of the bacteria that can degrade branched-alkanes. This study provides quantitative measures of oil degradation under relevant field conditions crucial for understanding and modeling the fate of spilled oil in the northern Gulf of Mexico.

Marine Tar Residues: a Review

Marine tar residues originate from natural and anthropogenic oil releases into the ocean environment and are formed after liquid petroleum is transformed by weathering, sedimentation, and other processes. Tar balls, tar mats, and tar patties are common examples of marine tar residues and can range in size from millimeters in diameter (tar balls) to several meters in length and width (tar mats). These residues can remain in the ocean environment indefinitely, decomposing or becoming buried in the sea floor. However, in many cases, they are transported ashore via currents and waves where they pose a concern to coastal recreation activities, the seafood industry and may have negative effects on wildlife. This review summarizes the current state of knowledge on marine tar residue formation, transport, degradation, and distribution. Methods of detection and removal of marine tar residues and their possible ecological effects are discussed, in addition to topics of marine tar research that warrant further investigation. Emphasis is placed on benthic tar residues, with a focus on the remnants of the Deepwater Horizon oil spill in particular, which are still affecting the northern Gulf of Mexico shores years after the leaking submarine well was capped.

The effect of sand composition on the degradation of buried oil

The potential effects of the mineralogical composition of sediment on the degradation of oil buried on sandy beaches were investigated. Toward that purpose, a laboratory experiment was carried out with sandy sediment collected along NW Iberian Peninsula beaches, tar-balls from the Prestige oil spill (NW Spain) and seawater. The results indicate that the mineralogical composition is important for the physical appearance of the oil (tar-balls or oil coatings). This finding prompted a reassessment of the current sequence of degradation for buried oil based on compositional factors. Moreover, the halo development of the oil coatings might be enhanced by the carbonate concentration of the sand. These findings open new prospects for future monitoring and management programs for oiled sandy beaches.

Long-term reproductive impairment in a seabird after the Prestige oil spill

Large oil spills are dramatic perturbations on marine ecosystems, and seabirds are one of the worst affected organisms in such events. It has been argued that oil spills may have important long-term consequences on marine organisms, but supporting evidence remains scarce. The European shag (Phalacrocorax aristotelis) was strongly impacted at population level by the Prestige oil spill, the biggest spillage in the eastern North Atlantic. In this paper, we report on the long-term consequences on reproduction of this coastal seabird, using temporal and spatial replicated data (before-after-control-impact design). Our study revealed long-term reproductive impairment during at least the first 10 years since the Prestige oil spill. Annual reproductive success did not differ before the impact, but after the impact it was reduced by 45% in oiled colonies compared with unoiled ones. This is a rare documentation of long-term effects after a major oil spill, highlighting the need for long-term monitoring in order to assess the real impact of this type of disturbance on marine organisms.

Assessment of photochemical processes in marine oil spill fingerprinting

Understanding weathering processes plays a critical role in oil spill forensics, which is based on the comparison of the distributions of selected compounds assumed to be recalcitrant and/or have consistent weathering transformations. Yet, these assumptions are based on limited laboratory and oil-spill studies. With access to additional sites that have been oiled by different types of oils and exposures, there is a great opportunity to expand on our knowledge about these transformations. Here, we demonstrate the effects of photooxidation on the overall composition of spilled oils caused by natural and simulated sunlight, and particularly on the often used polycyclic aromatic hydrocarbons (PAHs) and the biomarker triaromatic steranes (TAS). Both laboratory and field data from oil released from the Macondo well oil following the Deepwater Horizon disaster (2010), and heavy fuel-oil from the Prestige tanker spill (2002) have been obtained to improve the data interpretation of the typical fingerprinting methodology.