Do distributions of diamondoid hydrocarbons accumulated in oil-contaminated fish tissues help to identify the sources of oil?

Identifying the sources of environmental oil contamination can be challenging, especially for oil in motile organisms such as fish. Lipophilic hydrocarbons from oil can bioaccumulate in fish adipose tissue and potentially provide a forensic "fingerprint" of the original oil. Herein, diamondoid hydrocarbon distributions were employed to provide such fingerprints. Indices produced from diamondoids were used to compare extracts from fish adipose tissues and the crude and fuel oils to which the fish were exposed under laboratory conditions. A suite of 20 diamondoids was found to have bioaccumulated in the dietary-exposed fish. Cross-plots of indices between fish and exposure oils were close to the ideal 1:1 relationship. Comparisons with diamondoid distributions of non-exposure oils produced overall, but not exclusively, weaker correlations. Linear Discriminatory Analysis on a combined set of 15 diamondoid and bicyclane molecular ratios was able to identify the exposure oils, so a use of both compound classes is preferable.

Fish Fingerprinting: Identifying Crude Oil Pollutants using Bicyclic Sesquiterpanes (Bicyclanes) in the Tissues of Exposed Fish.

In the present study, we investigated the possibility of identifying the source oils of exposed fish using ratios of bicyclic sesquiterpane (bicyclane) chemical biomarkers. In the event of an oil spill, identification of source oil(s) for assessment, or for litigation purposes, typically uses diagnostic ratios of chemical biomarkers to produce characteristic oil "fingerprints." Although this has been applied in identifying oil residues in sediments, water, and sessile filtering organisms, so far as we are aware this has never been successfully demonstrated for oil-exposed fish. In a 35-day laboratory trial, juvenile Lates calcarifer (barramundi or Asian seabass) were exposed, via the diet (1% w/w), to either a heavy fuel oil or to Montara, an Australian medium crude oil. Two-dimensional gas chromatography with high-resolution mass spectrometry and gas chromatography-mass spectrometry were then used to measure selected ratios of the bicyclanes to examine whether the ratios were statistically reproducibly conserved in the fish tissues. Six diagnostic bicyclane ratios showed high correlation (r2 > 0.98) with those of each of the two source oils. A linear discriminatory analysis model showed that nine different petroleum products could be reproducibly discriminated using these bicyclane ratios. The model was then used to correctly identify the bicyclane profiles of each of the two exposure oils in the adipose tissue extracts of each of the 18 fish fed oil-enriched diets. From our initial study, bicyclane biomarkers appear to show good potential for providing reliable forensic fingerprints of the sources of oil contamination of exposed fish. Further research is needed to investigate the minimum exposure times required for bicyclane bioaccumulation to achieve detectable concentrations in fish adipose tissues and to determine bicyclane depuration rates once exposure to oil has ceased. Environ Toxicol Chem 2023;42:7-18. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Multivariate analysis of otolith microchemistry can discriminate the source of oil contamination in exposed fish.

The uptake of metals into the aragonite lattice of the fish otolith (ear-bone) has been used for decades as a historical record of exposure to metals in polluted environments. The relative abundance of two metals in particular, Ni and V, are used in forensic chemical analysis of crude oils to assist in confirming its origin. In this study we investigate the potential for metal accumulation in otoliths to act as a biomarker of exposure to crude oil. Using a 33-day static-renewal laboratory trial design, 56 juvenile Lates calcarifer (commonly known as Asian seabass or barramundi) were fed diets enriched with V (20 mg/kg), Ni (500 mg/kg), Fe (500 mg/kg), and two crude oils with distinctly different metals profiles: a heavy fuel oil (1% w/w) and a typical Australian medium crude (1% w/w). Fish exposed to crude oils showed Ba and Al retained in otoliths in a dose-dependent manner, but fish fed V-, Ni- and Fe-enriched diets showed no metal increase in otoliths, indicating that V, Ni and Fe are not incorporated into the otolith of L. calcarifer via dietary exposure. For crude oils, incorporation into otolith for many metals is likely limited due to porphyrin casing reducing their bioavailability. Principal components analysis (PCA) and subsequent linear discriminatory analysis (LDA) of selected otolith metals demonstrated that, even despite large variability in the metal abundances detected in otolith between individuals within the test groups (cv = 1.00), it is possible to discriminate between fish exposed to different crude oils using multivariate analysis of their otolith microchemistry.

MV Wakashio grounding incident in Mauritius 2020: The world's first major spillage of Very Low Sulfur Fuel Oil.

Very Low Sulfur Fuel Oils (VSLFO, <0.5% S) are a new class of marine fuel oils, introduced to meet recent International Maritime Organization regulations. The MV Wakashio was reported to have released 1000 t of VLSFO when it grounded on a reef in Mauritius on 25th July 2020. A field sample of oily residue contaminating the Mauritian coast was collected on 16th August 2020 and compared with the Wakashio fuel oil. Both oils were analyzed for organic and elemental content, and stable isotope ratios δ13C and δ2H measured. Comprehensive two-dimensional gas chromatography with high-resolution mass spectrometry was used to identify and compare biomarkers resistant to weathering. The aromatic content in the VLSFO was relatively low suggesting that the potential for ecosystem harm arising from exposure to toxic components may be less than with traditional fuel oil spills. The Wakashio oil spill is, to our knowledge, the first documented spill involving VLSFO.

Discriminating source of oil contamination in teleost fish, Lates calcarifer, using multivariate analysis of a suite of physiological and behavioral biomarkers.

The release of petroleum hydrocarbons into the environment from natural seeps, well blowouts, pipeline leaks, shipping accidents and deliberate tank washing poses an ongoing threat to marine ecosystems. Distinguishing the source of oil contamination in exposed biota can be relatively straightforward if samples of the oil are available but, in their absence, such discrimination in fish poses a major challenge. The use of physiological and behavioral biomarker analysis provides a useful tool to describe sub-lethal effects of toxicant exposure. In this study we describe the responses of 12 biomarkers in Lates calcarifer (Asian seabass) following a 33-day dietary exposure (1%w/w) to heavy fuel oil (HFO) and to Montara, a typical Australian medium crude oil (MCO). Principal components analysis was used to differentiate between fish exposed to HFO from those exposed to MCO. Inferences can be made about the composition of an oil from the biomarker profiles produced in exposed fish.

Accumulation of cadmium in the otoliths and tissues of juvenile pink snapper (Pagrus auratus Forster) following dietary and waterborne exposure.

Laboratory experiments were conducted to examine if incorporation of Cd into the otoliths of juvenile pink snapper (Pagrus auratus Forster) was related to levels in the food or water. In the first experiment, fish were fed a regular diet (control group) or a Cd-contaminated diet (500mgCdkg(-1) or 1500mgCdkg(-1)) for 35days. In the second experiment, fish were exposed to waterborne Cd concentrations of <0.002microgL(-1) (control), 50microgL(-1), 100microgL(-1) and 150microgL(-1) for 35days. The sagittal otoliths were analysed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Juvenile fish exposed to higher concentrations of waterborne or dietary Cd showed increased Cd levels in their otoliths. This study clearly demonstrated that both aqueous and dietary Cd exposures can result in Cd incorporation into the otoliths of pink snapper.