Integrative description of changes occurring on zebrafish embryos exposed to water-soluble crude oil components and its mixture with a chemical surfactant.

The effects of crude oil spills are an ongoing problem for wildlife and human health in both marine and freshwater aquatic environments. Bioassays of model organisms are a convenient way to assess the potential risks of the substances involved in oil spills. Zebrafish embryos (ZFE) are a useful to reach a fast and detailed description of the toxicity of the pollutants, including both the components of the crude oil itself and substances that are commonly used for crude oil spill mitigation (e.g. surfactants). Here, we evaluated the survival rate, as well as histological, morphological, and proteomic changes in ZFE exposed to Water Accumulated Fraction (WAF) of light crude oil and in mixture with Dioctyl Sulfosuccinate Sodium (DOSS, e.g. CEWAF: Chemically Enhanced WAF), a surfactant that is frequently used in chemical dispersant formulations. Furthermore, we compared the hydrocarbon concentration of WAF and CEWAF of the sublethal dilution. In histological, morphological, and gene expression variables, the ZFE exposed to WAF showed less changes than those exposed to CEWAF. Proteomic changes were more dramatic in ZFE exposed to WAF, with important alterations in spliceosomal and ribosomal proteins, as well as proteins related to eye and retinal photoreceptor development and heart function. We also found that the concentration of high molecular weight hydrocarbons in water was slighly higher in presence of DOSS, but the low molecular weight hydrocarbons concentration was higher in WAF. These results provide an important starting point for identifying useful crude-oil exposure biomarkers in fish species.

Histological Effects of Light Crude Oil on Sciaenops ocellatus Under Experimental Conditions.

The health status of Sciaenops ocellatus was studied by qualitative and quantitative histopathological analysis through histological damage prevalence and degree of tissue change (DTC) in response to 96 h and 9 days of exposure to 0.1, 0.8, and 8 g/L of light crude oil in seawater. The histology of the liver, spleen, kidney, and gills of the fish were analyzed and compared between treatments. Our results showed that the exposed fish developed lesions associated with degenerative and necrotic changes. The highest frequency of damage and DTC scores were observed in the liver and kidney from 96 h to 9-days post-exposure. Generalized additive models of location, scale, and shape, showed that the DTC was strongly associated with crude oil compounds such as napthalene, Cd, Ni, Pb, and bile polycyclic aromatic hydrocarbon metabolites. Our findings suggest that exposure to crude oil affects fish health, producing irreversible histological damage.

Effects of a Light Crude Oil Spill on a Tropical Coastal Phytoplankton Community.

Oiling scenarios following spills vary in concentration and usually can affect large coastal areas. Consequently, this research evaluated different crude oil concentrations (10, 40, and 80 mg L-1) on the nearshore phytoplanktonic community in the southern Gulf of Mexico. This experiment was carried out for ten days using eight units of 2500 L each; factors monitored included shifts in phytoplankton composition, physicochemical parameters and the culturable bacterial abundance of heterotrophic and hydrocarbonoclastic groups. The temperature, salinity, and nutrient concentrations measured were within the ranges previously reported for Yucatan Peninsula waters. The total hydrocarbon concentration (TPH) in the control at T0 indicated the presence of hydrocarbons (PAHs 0.80 µg L-1, aliphatics 7.83 µg L-1 and UCM 184.09 µg L-1). At T0, the phytoplankton community showed a similar assemblage structure and composition in all treatments. At T10, the community composition remained heterogeneous in the control, in agreement with previous reports for the area. However, for oiled treatments, Bacillariophyceae dominated at T10. Hydrocarbonoclastic bacteria were associated with oiled treatments throughout the experiment, while heterotrophic bacteria were associated with control conditions. Our results agreed with previous works at the taxonomic level showing the presence of Bacillariophyceae and Dinophyceae in oil-related treatments, where these groups showed the major interactions in co-occurrence networks. In contrast, Chlorophyceae showed the key node in the co-occurrence network for the control. This study aims to contribute to knowledge on phytoplankton community shifts during a crude oil spill in subtropical oligotrophic regions.

Gill and liver transcriptomic responses of Achirus lineatus (Neopterygii: Achiridae) exposed to water-accommodated fraction (WAF) of light crude oil reveal an onset of hypoxia-like condition.

Crude oil is one of the most widespread pollutants released into the marine environment, and native species have provided useful information about the effect of crude oil pollution in marine ecosystems. We consider that the lined sole Achirus lineatus can be a useful monitor of the effect of crude oil in the Gulf of Mexico (GoM) because this flounder species has a wide distribution along the GoM, and its response to oil components is relevant. The objective of this study was to compare the transcriptomic changes in liver and gill of adults lined sole fish (Achirus lineatus) exposed to a sublethal acute concentration of water-accommodated fraction (WAF) of light crude oil for 48 h. RNA-Seq was performed to assess the transcriptional changes in both organs. A total of 1073 differentially expressed genes (DEGs) were detected in gills; 662 (61.69%) were upregulated, and 411 (38.30%) were downregulated whereas in liver, 515 DEGs; 306 (59.42%) were upregulated, and 209 (40.58%) were downregulated. Xenobiotic metabolism and redox metabolism, along with DNA repair mechanisms, were activated. The induction of hypoxia-regulated genes and the generalized regulation of multiple signaling pathways support the hypothesis that WAF exposition causes a hypoxia-like condition.

Effects of chronic exposure to water accommodated fraction (WAF) of light crude oil on gut microbiota composition of the lined sole (Achirus lineatus).

Exposure of marine fish to hydrocarbon compounds from crude oil can cause physiological and ecological alterations that can result in several cytotoxic, genotoxic, and teratogenic damages. One consequence of this exposure is the dysbiosis of the gut microbiota, where the normal bacterial composition is modified. Herein, we assessed the effect of the exposure to water accommodated fraction (WAF) of a light crude oil into the gut microbiota of a native species, the lined sole Achirus lineatus, a benthonic fish widely distributed in the Gulf of Mexico (GoM). We performed a chronic bioassay using two WAF concentrations (5 and 10% v/v), collecting lined sole entire gastrointestinal tracts for microbiota analyses at two timepoints, 14 and 28 days. Changes in the gut microbiota composition were determined by high throughput amplicon sequencing of the gene 16S rRNA. Diversity analyses showed that WAF exposure produced similar changes in the microbiota composition at both concentrations. Metagenomic functional prediction showed that these alterations could result in a shift in the gut redox status, towards a more anoxygenic environment. Enrichment of bacteria capable of use hydrocarbon as carbon source seems to be fast regardless time of exposure or WAF concentrations. Our results suggest that chronic WAF exposure can cause a dysbiosis in this benthic native species from the GoM.

Toxicity evaluation and microbiota response of the lined sole Achirus lineatus (Chordata: Achiridae) exposed to the light petroleum water-accommodated fraction (WAF).

Exposure to contaminants might directly affect organisms and alter their associated microbiota. The objective of the present study was to determine the impact of the petroleum-water-accommodated fraction (WAF) from a light crude oil (API gravity 35) on a benthic fish species native from the Gulf of Mexico (GoM). Ten adults of Achirus lineatus (Linnaeus, 1758) were exposed to a sublethal WAF/water solution of 50% v/v for 48 hr. Multiple endpoints were measured including tissue damage, presence of polycyclic aromatic hydrocarbons (PAHs) metabolites in bile and gut microbiota analyses. Atrophy and fatty degeneration were observed in livers. Nodules and inflammation were detected in spleen, and structural disintegration and atrophy in the kidney. In gills hyperplasia, aneurysm, and gills lamellar fusion were observed. PAHs metabolites concentrations in bile were significantly higher in exposed organisms. Gut microbiome taxonomic analysis showed significant shifts in bacterial structure and composition following WAF exposure. Data indicate that exposure to WAF produced toxic effects in adults of A. lineatus, as evidenced by histological alterations and dysbiosis, which might represent an impairment to long-term subsistence of exposed aquatic organisms.