Oiling of the continental shelf and coastal marshes over eight years after the 2010 Deepwater Horizon oil spill

Mercury concentrations in Seaside Sparrows and Marsh Rice Rats differ across the Mississippi River Estuary

Mercury (Hg) concentrations and their associated toxicological effects in terrestrial ecosystems of the Gulf of Mexico are largely unknown. Compounding this uncertainty, a large input of organic matter from the 2010 Deepwater Horizon oil spill may have altered Hg cycling and bioaccumulation dynamics. To test this idea, we quantified blood concentrations of total mercury (THg) in Seaside Sparrows (Ammospiza maritima) and Marsh Rice Rats (Oryzomys palustris) in marshes west and east of the Mississippi River in 2015 and 2016. We also tested for a difference in THg concentrations between oiled and non-oiled sites. To address the potential confounding effect of diet variation on Hg transfer, we used stable nitrogen (δ15N) and carbon (δ13C) isotope values as proxies of trophic position and the source of primary production, respectively. Our results revealed that five to six years after the spill, THg concentrations were not higher in sites oiled by the spill compared to non-oiled sites. In both species, THg was higher at sites east of the Mississippi River compared to control and oiled sites, located west. In Seaside Sparrows but not in Marsh Rice Rats, THg increased with δ15N values, suggesting Hg trophic biomagnification. Overall, even in sites with the most elevated THg, concentrations were generally low. In Seaside Sparrows, THg concentrations were also lower than previously reported in this and other closely related passerines, with only 7% of tested birds exceeding the lowest observed effect concentration associated with toxic effects across bird species (0.2 µg/g ww). The factors associated with geographic heterogeneity in Hg exposure remain uncertain. Clarification could inform risk assessment and future restoration and management actions in a region facing vast anthropogenic changes.

Ecological risk assessment of oil & grease (OG) and heavy metals in the surface water of Naf River, Bangladesh

This study aims to fill the gap in our understanding of the distribution and ecological risk of oil and grease (OG) and toxic heavy metals in the surface water of the Naf River, a major transportation route connecting Teknaf to Saint Martin's Island in Bangladesh. Altogether, 6 sampling stations in this river were assessed for OG and heavy metal pollution, revealing the presence of both at each station. The OG concentration is found ranging from 3.6 to 23.6 mg/L and the average concentration is 8.13 mg/L. On the other hand, the contamination factor (Cf) of the toxic heavy metals follows the descending order of Pb (63.97) > Cd (23.94) > Mn (0.94) > Ni (0.64) > Zn (0.22) > Cr (0.09) > Cu (0.04) > As (0.04) in the water samples. Heavy metal pollution index (HPI), Heavy metal evaluation index (HEI), and Nemerow pollution index (PN) indicate that the surface water of the study area includes high levels of pollution category due to the elevated levels of Pb, Cd, and Ni concentrations. The mean values of the single factor pollution index (Pi) for Pi(Pb), Pi(Cd) and Pi(Ni) are found 45.69, 39.41, and 6.43, which exceed the threshold limit. The ecological risk index indicates that around 25 % of the total heavy metals show a very high ecological risk and 75 % exhibit a lower ecological risk. Notably, within the very high ecological risk, Cd is responsible for 53 % of this risk, while Pb contributes the remaining 47 %. Increased OG and heavy metal concentrations in the Naf River are likely due to human activities like waste discharge from municipalities, solar power plants, pesticide use, and fishing trawlers. This research offers insights into the current state of the Naf River and guides policymakers toward more effective initiatives.

Mechanism of nearshore sediment-facilitated oil transport: New insights from causal inference analysis

A quantitative understanding of spilled oil transport in a nearshore environment is challenging due to the complex physicochemical processes in aqueous conditions. The physicochemical processes involved in oil sinking mainly include oil dispersion, sediment settling, and oil-sediment interaction. For the first time, this work attempts to address the sinking mechanism in petroleum contaminant transport using structural causal models based on observed data. The effects of nearshore salinity distribution from the estuary to the ocean on those three processes are examined. The causal inference reveals sediment settling is the crucial process for oil sinking. Salinity indirectly affects oil sinking by promoting sediment settling rather than directly affecting oil-sediment interaction. The increase of salinity from 0‰ to 35‰ provides a natural enhancement for sediment settling. Notably, unbiased causal effect estimates demonstrate the strongest positive causal effect on the settling efficiency of sediments is posed by increasing oil dispersion effectiveness, with a normalized value of 1.023. The highest strength of the causal relationship between oil dispersion and sediment settling highlights the importance of the dispersing characteristics of spilled oil to sediment-facilitated oil transport. The employed logic, a data-driven method, will shed light on adopting advanced causal inference tools to unravel the complicated contaminants' transport.

Toxicity and risk management of oil-spiked sediments by diluted bitumen for two freshwater benthic invertebrates

Diluted bitumen (dilbit) is an unconventional oil produced by the oil sands industry in Canada. Despite the knowledge available on hydrocarbon toxicity, the effects of diluted bitumen on benthic organisms are still largely unknown. Moreover, in Quebec there are only provisional threshold values of 164 mg/kg C₁₀-C₅₀ for chronic effects and 832 mg/kg for acute effects. The protectiveness of these values for benthic invertebrates has not been tested for heavy unconventional oils such as dilbit. Two benthic organisms, the larvae of Chironomus riparius and Hyalella azteca, were exposed to these two concentrations and to an intermediate concentration (416 mg/kg) of two dilbits (DB1 and DB2) and a heavy conventional oil (CO). The aim of the study was to assess the sublethal and lethal effects of spiked sediment by dilbit. The oil was rapidly degraded in the sediment, especially in the presence of C. riparius. Amphipods were much more sensitive to oil than chironomids. LC_50-14d values for H. azteca were 199 mg/kg C₁₀-C₅₀ for DB1, 299 mg/kg for DB2 and 8.42 mg/kg for CO compared to LC_50-7d values for C. riparius of 492 mg/kg for DB1, 563 mg/kg for DB2 and 514 mg/kg for CO. The size of the organisms was reduced compared to controls for both species. The defense enzymes (GST, GPx, SOD and CAT) were not good biomarkers in these two organisms for this type of contamination. The current provisional sediment quality criteria seem too permissive for heavy oils and should be lowered.

Disturbance legacies and shifting trajectories: Marsh soil strength and shoreline erosion a decade after the Deepwater Horizon oil spill

Marsh resilience post disturbance is strongly dependent on the belowground dynamics affecting the emergent plants aboveground. We investigated the long-term impacts at the marsh-water interface in coastal wetlands of south Louisiana after the 2010 Deepwater Horizon oil spill with a combination of fieldwork (2010-2018) and spatial analysis (1998-2021). Data were collected on shoreline erosion rates, marsh platform elevation heights and cantilever overhang widths, and soil strength up to 1 m depth. Oil concentration in the top 5 cm of the marsh soil were determined using gas chromatography/mass spectrometry and were 1000 times higher than before the spill and remained 10 times higher eight years post-oiling. The oiling initially caused the marsh edge to subside, and chronic effects lowered soil strength, creating a faster erosion rate and deeper water within 150 cm of the shoreline. Soil strength declined by 50% throughout the 1 m soil profile after oiling and has not recovered. The mean erosion rate for 11 years post-spill was double that before oiling and there was an additive impact on erosion rates after Hurricane Isaac. Erosion appeared to have recovered to pre-spill rates by 2019, however from 2019 to 2021, the rate increased by 118% above the pre-spill rate. The continuing loss of soil strength indicates that the belowground biomass was seriously compromised by oiling. The perpetuation of oil in the remaining marsh may have set a new baseline for soil strength and subsequent storm induced erosional events. The remaining marsh soils retain chronic physical and biological legacies compromising recovery for more than a decade that may be evident in other marsh habitats subject to oiling and other stressors.

Growth responses of Avicennia germinans and Batis maritima seedlings to weathered light sweet crude oil applied to soil and aboveground tissues

Oil spills are a significant stressor to coastal and maritime environments worldwide. The growth responses of Batis maritima and Avicennia germinans seedlings to weathered Deepwater Horizon oiling were assessed through a mesocosm study using a factorial arrangement of 4 soil oiling levels (0 L m^-2, 1 L m^-2, 2 L m^-2, 4 L ^-m^-2) × 3 tissue oiling levels (0% of stem height, 50% of stem height, 100% of stem height). Overall, growth metrics of B. maritima displayed much greater sensitivity to both tissue and soil oiling than A. germinans, which exhibited a relatively high tolerance to both routes of oiling exposure. Batis maritima in the 4 L m^-2 soil oiling treatment demonstrated significant reductions in cumulative stem height and leaf number, whereas no significant effects of soil oiling on A. germinans were detected. This was reflected in the end of the study biomass partitioning, where total aboveground and live aboveground biomass were significantly reduced for B. maritima with 4 L m^-2 soil oiling, but no impacts to A. germinans were found. Tissue oiling of 100% did appear to reduce B. maritima stem diameter, but no effect of tissue oiling was discerned on biomass partitioning, suggesting that there were no impacts to integrated growth. These findings suggest that B. maritima would be more severely affected by moderate soil oiling than A. germinans.

Coconut oil and fermented palm wine biodiesel production for oil spill cleanup: experimental, numerical, and hybrid metaheuristic modeling approaches

This paper for the first time synthesizes novel biodiesel experimentally using low-cost feedstocks of coconut oil, caustic soda, and fermented palm wine contaminated by microorganisms. The alkaline catalyzed transesterification method was used for biodiesel production with minimal glycerol. The produced biodiesel was biodegradable and effective in cleaning a shoreline oil spill experiment verified by our developed oil spill radial numerical simulator. For the first time, an adaptive neuro-fuzzy inference system (ANFIS) was hybridized with invasive weed optimization (IWO), imperialist competitive algorithm (ICA), and shuffled complex evolution (SCE-UA) to predict biodiesel yield (BY) using obtained Monte Carlo simulation datasets from the biodiesel experimental seed data. The test results indicated ANFIS-IWO (MSE = 0.0628) as the best model and also when compared to the benchmarked ANFIS genetic algorithm (MSE = 0.0639). Additionally, ANFIS-IWO (RMSE = 0.54705) was tested on another coconut biodiesel data in the literature and it outperformed both response surface methodology (RMSE = 0.72739) and artificial neural network (RMSE = 0.68615) models used. The hybridized models proved to be robust for biodiesel yield modeling in addition to the produced biodiesel serving as an environmentally acceptable and cost-effective alternative for shoreline bioremediation.

Machine learning-aided causal inference for unraveling chemical dispersant and salinity effects on crude oil biodegradation

Chemical dispersants have been widely applied to tackle oil spills, but their effects on oil biodegradation in global aquatic systems with different salinities are not well understood. Here, both experiments and advanced machine learning-aided causal inference analysis were applied to evaluate related processes. A halotolerant oil-degrading and biosurfactant-producing species was selected and characterized within the salinity of 0-70 g/L NaCl. Notably, dispersant addition can relieve the biodegradation barriers caused by high salinities. To navigate the causal relationships behind the experimental data, a structural causal model to quantitatively estimate the strength of causal links among salinity, dispersant addition, cell abundance, biosurfactant productivity and oil biodegradation was built. The estimated causal effects were integrated into a weighted directed acyclic graph, which showed that overall positive effects of dispersant addition on oil biodegradation was mainly through the enrichment of cell abundance. These findings can benefit decision-making prior dispersant application under different saline environments.

Prior exposure to weathered oil influences foraging of an ecologically important saltmarsh resident fish

Estuarine ecosystem balance typically relies on strong food web interconnectedness dependent on a relatively low number of resident taxa, presenting a potential ecological vulnerability to extreme ecosystem disturbances. Following the Deepwater Horizon (DwH) oil spill disaster of the northern Gulf of Mexico (USA), numerous ecotoxicological studies showed severe species-level impacts of oil exposure on estuarine fish and invertebrates, yet post-spill surveys found little evidence for severe impacts to coastal populations, communities, or food webs. The acknowledgement that several confounding factors may have limited researchers’ abilities to detect negative ecosystem-level impacts following the DwH spill drives the need for direct testing of weathered oil exposure effects on estuarine residents with high trophic connectivity. Here, we describe an experiment that examined the influence of previous exposure to four weathered oil concentrations (control: 0.0 L oil m⁻²; low: 0.1 L oil m⁻²; moderate: 0.5–1 L oil m⁻²; high: 3.0 L oil m⁻²) on foraging rates of the ecologically important Gulf killifish (Fundulus grandis). Following exposure in oiled saltmarsh mesocosms, killifish were allowed to forage on grass shrimp (Palaeomonetes pugio) for up to 21 h. We found that previous exposure to the high oil treatment reduced killifish foraging rate by ~37% on average, compared with no oil control treatment. Previous exposure to the moderate oil treatment showed highly variable foraging rate responses, while low exposure treatment was similar to unexposed responses. Declining foraging rate responses to previous high weathered oil exposure suggests potential oil spill influence on energy transfer between saltmarsh and off-marsh systems. Additionally, foraging rate variability at the moderate level highlights the large degree of intraspecific variability for this sublethal response and indicates this concentration represents a potential threshold of oil exposure influence on killifish foraging. We also found that consumption of gravid vs non-gravid shrimp was not independent of prior oil exposure concentration, as high oil exposure treatment killifish consumed ~3× more gravid shrimp than expected. Our study findings highlight the sublethal effects of prior oil exposure on foraging abilities of ecologically valuable Gulf killifish at realistic oil exposure levels, suggesting that important trophic transfers of energy to off-marsh systems may have been impacted, at least in the short-term, by shoreline oiling at highly localized scales. This study provides support for further experimental testing of oil exposure effects on sublethal behavioral impacts of ecologically important estuarine species, due to the likelihood that some ecological ramifications of DwH on saltmarshes likely went undetected.

Meta-analysis of salt marsh vegetation impacts and recovery: a synthesis following the Deepwater Horizon oil spill

Marine oil spills continue to be a global issue, heightened by spill events such as the 2010 Deepwater Horizon spill in the Gulf of Mexico, the largest marine oil spill in US waters and among the largest worldwide, affecting over 1,000 km of sensitive wetland shorelines, primarily salt marshes supporting numerous ecosystem functions. To synthesize the effects of the oil spill on foundational vegetation species in the salt marsh ecosystem, Spartina alterniflora and Juncus roemerianus, we performed a meta-analysis using data from 10 studies and 255 sampling sites over seven years post-spill. We examined the hypotheses that the oil spill reduced plant cover, stem density, vegetation height, aboveground biomass, and belowground biomass, and tracked the degree of effects temporally to estimate recovery time frames. All plant metrics indicated impacts from oiling, with 20-100% maximum reductions depending on oiling level and marsh zone. Peak reductions of ~70-90% in total plant cover, total aboveground biomass, and belowground biomass were observed for heavily oiled sites at the marsh edge. Both Spartina and Juncus were impacted, with Juncus affected to a greater degree. Most plant metrics had recovery time frames of three years or longer, including multiple metrics with incomplete recovery over the duration of our data, at least seven years post-spill. Belowground biomass was particularly concerning, because it declined over time in contrast with recovery trends in most aboveground metrics, serving as a strong indicator of ongoing impact, limited recovery, and impaired resilience. We conclude that the Deepwater Horizon spill had multiyear impacts on salt marsh vegetation, with full recovery likely to exceed 10 years, particularly in heavily oiled marshes, where erosion may preclude full recovery. Vegetation impacts and delayed recovery is likely to have exerted substantial influences on ecosystem processes and associated species, especially along heavily oiled shorelines. Our synthesis affords a greater understanding of ecosystem impacts and recovery following the Deepwater Horizon oil spill, and informs environmental impact analysis, contingency planning, emergency response, damage assessment, and restoration efforts related to oil spills.

Cardiac assessments of bottlenose dolphins (Tursiops truncatus) in the Northern Gulf of Mexico following exposure to Deepwater Horizon oil

The Deepwater Horizon (DWH) oil spill profoundly impacted the health of bottlenose dolphins (Tursiops truncatus) in Barataria Bay, LA (BB). To comprehensively assess the cardiac health of dolphins living within the DWH oil spill footprint, techniques for in-water cardiac evaluation were refined with dolphins cared for by the U.S. Navy Marine Mammal Program in 2018 and applied to free-ranging bottlenose dolphins in BB (n = 34) and Sarasota Bay, Florida (SB) (n = 19), a non-oiled reference population. Cardiac auscultation detected systolic murmurs in the majority of dolphins from both sites (88% BB, 89% SB) and echocardiography showed most of the murmurs were innocent flow murmurs attributed to elevated blood flow velocity [1]. Telemetric six-lead electrocardiography detected arrhythmias in BB dolphins (43%) and SB dolphins (31%), all of which were considered low to moderate risk for adverse cardiac events. Echocardiography showed BB dolphins had thinner left ventricular walls, with significant differences in intraventricular septum thickness at the end of diastole (p = 0.002), and left ventricular posterior wall thickness at the end of diastole (p = 0.033). BB dolphins also had smaller left atrial size (p = 0.004), higher prevalence of tricuspid valve prolapse (p = 0.003), higher prevalence of tricuspid valve thickening (p = 0.033), and higher prevalence of aortic valve thickening (p = 0.008). Two dolphins in BB were diagnosed with pulmonary arterial hypertension based on Doppler echocardiography-derived estimates and supporting echocardiographic findings. Histopathology of dolphins who stranded within the DWH oil spill footprint showed a significantly higher prevalence of myocardial fibrosis (p = 0.003), regardless of age, compared to dolphins outside the oil spill footprint. In conclusion, there were substantial cardiac abnormalities identified in BB dolphins which may be related to DWH oil exposure, however, future work is needed to rule out other hypotheses and further elucidate the connection between oil exposure, pulmonary disease, and the observed cardiac abnormalities.

Nest survival of Seaside Sparrows (Ammospiza maritima) in the wake of the Deepwater Horizon oil spill

In 2010, the Deepwater Horizon oil spill released an estimated 4.9 million barrels of oil into the Gulf of Mexico, damaging coastal ecosystems. Seaside Sparrows (Ammospiza maritima)-a year-round resident of Gulf Coast salt marshes-were exposed to oil, as shown by published isotopic and molecular analyses, but fitness consequences have not been clarified. We monitored nests around two bays in Plaquemines Parish, Louisiana, USA from 2012-2017 to assess possible impacts on the nesting biology of Seaside Sparrows. A majority of nests failed (76% of known-fate nests, N = 252 nests, 3521 exposure-days) during our study, and predation was the main cause of nest failure (~91% of failed nests). Logistic exposure analysis revealed that daily nest survival rate: (1) was greater at nests with denser vegetation at nest height, (2) was higher in the more sheltered bay we studied, (3) decreased over the course of the breeding season in each year, and (4) was not correlated with either sediment polycyclic aromatic hydrocarbon concentrations or estimated predator abundance during the years for which we had those data. Although the Deepwater Horizon spill impacted other aspects of Seaside Sparrow ecology, we found no definitive effect of initial oiling or oiled sediment on nest survival during 2012-2017. Because predation was the overwhelming cause of nest failure in our study, additional work on these communities is needed to fully understand demographic and ecological impacts of storms, oil spills, other pollutants, and sea-level rise on Seaside Sparrows and their predators.

Spatial and temporal distribution of surface water contaminants in the Houston Ship Channel after the Intercontinental Terminal Company Fire

BACKGROUND

The fire at the Intercontinental Terminals Company (ITC, Deer Park, La Porte, TX, USA) from March 17 to 20, 2019 resulted in substantial releases of chemical contaminants to the environment, including the surface waters of the Houston Ship Channel.

OBJECTIVE

To characterize spatial and temporal trends, as well as potential human health risks, from these releases.

METHODS

Out of 433 substances with available data, seven were selected for analysis: benzene, toluene, ethylbenzene, xylenes, oil and grease, suspended solids, and total petroleum hydrocarbons. Spatial and temporal concentration trends were characterized, and hazard quotients and cancer risks were calculated to estimate the potential for human health impacts from these contaminants.

RESULTS

Temporal analysis showed presence of these chemical contaminants in water immediately after the event; their concentrations dissipated substantially within 4 weeks. The spatial distribution of contaminants indicated the highest concentrations in the waterways within about 1 km of the ITC. The greatest potential human health risks stemmed from presence of benzene.

SIGNIFICANCE

A short-term but substantial spike in the concentrations of a number of hazardous contaminants occurred near the incident, with concentrations returning to apparent baseline levels within 1 month likely due to a combination of volatization, dilution and degradation.

Estuarine oiling increases a long-term decline in mussel growth

The ribbed mussel, Geukensia granosissima, cycles nutrients, contributes to soil stability, and can be a major component of predator-prey communities in salt marshes. Mussels were exposed to the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, and salt marshes remain contaminated eight years later. We hypothesized that the oiled mussels had reduced annual growth, altered population size frequency, and perhaps changed valve morphometrics. We sampled 10 marshes near Port Sulphur, LA, to measure the morphometrics of 133 mussels and their age-specific growth rate, and also the marsh oil content and percent vegetative cover. The relationships between valve weight, length and biomass weight were stable as mussels aged. A Year 1 growth decline from 1994 to 2018 is not easily explained by estuarine acidification, flooding, and temperature rise; freshening of estuarine waters is suggested to be a probable causal factor in the declining growth rate. The average valve length and dry biomass per valve declined with oiling in 2010. A multiple regression equation using the percent cover and oil concentration in 2018 described 70% of the variation in valve length. Sites with the highest oiling had few mussels with 14 annual growth bands and more of the younger mussels compared to sites with the lowest oiling. Valve growth in Year 1 declined for four years after the oil spill and was not compensated by higher growth rates in older mussels. Annual growth was below the amount predicted in a regression equation for the five years after the oil spill. Mussel populations may also have been structured by predators that were also responsive to oiling in subtle ways.

Succession pattern and phylotype analysis of microphytobenthic communities in a simulated oil spill seagrass mesocosm experiment

Microphytobenthic communities play a significant role in nutrient modulation, sediment stabilization, and primary production in seagrass beds, which provide various ecosystem services. We hypothesized that microphytobenthic communities in sediments of chronically oil-exposed seagrass beds will exhibit increased resiliency to stressors associated with oil exposure as opposed to seagrass beds never exposed to oil spills. We prepared 14-liter seawater mesocosms, each containing a submersed macrophyte Ruppia maritima collected from the Chandeleur Islands, Louisiana, and Estero Bay, Florida. Mesocosms were initially exposed to 50% water-accommodated oil fractions (WAF) and subsequently diluted by 50% with daily artificial seawater exchanges over 8 days to simulate tidal dilution. High-throughput amplicon sequencing based on 23S rRNA gene targeting cyanobacteria and chloroplasts of eukaryotic microphytobenthos was conducted to assess the impact of oiling on microphytobenthic communities with additional assessment via microscopy. High-throughput sequencing in combination with traditional microscopic analysis provided a robust examination in which both methods roughly complemented each other. Distinct succession patterns were detected in benthic algal communities of chronically oil-exposed (Louisiana) versus unexposed (Florida) seagrass bed sediments. The impact of oiling in microphytobenthos across all samples showed that benthic diatoms dominated all algal communities with sample percentages ranging from 42 to 97%, followed by cyanobacteria (2 to 50%). It is noteworthy that drastic changes in microphytobenthic community structure in terms of the larger taxonomic level were not observed, rather change occurred at the phylotype level. These results were also confirmed by microscopy. Similarity percentages (SIMPER) analysis identified seven phylotypes (Cyanobacteria, Bacillariophyceae, and Mediophyceae) in the Louisiana samples and one phylotype (Bacillariophyceae) in the Florida samples that increased in relative sequence abundance after oil exposure. The detailed phylotype analysis identifying sentinel microphytobenthic indicators provides a base for future research on benthic microalgae response to ecosystem disturbance.

Stable isotope analyses identify trophic niche partitioning between sympatric terrestrial vertebrates in coastal saltmarshes with differing oiling histories

Bioindicator species are commonly used as proxies to help identify the ecological effects of oil spills and other stressors. However, the utility of taxa as bioindicators is dependent on understanding their trophic niche and life history characteristics, as these factors mediate their ecological responses. Seaside sparrows (Ammospiza maritima) and marsh rice rats (Oryzomys palustris) are two ubiquitous terrestrial vertebrates that are thought to be bioindicators of oil spills in saltmarsh ecosystems. To improve the utility of these omnivorous taxa as bioindicators, we used carbon and nitrogen stable isotope analysis to quantify their trophic niches at saltmarshes in coastal Louisiana with differing oiling histories. We found that rats generally had lower trophic positions and incorporated more aquatic prey relative to seaside sparrows. The range of resources used (i.e.,trophic niche width) varied based on oiling history. Seaside sparrows had wider trophic niches than marsh rice rats at unoiled sites, but not at oiled sites. Trophic niche widths of conspecifics were less consistent at oiled sites, although marsh rice rats at oiled sites had wider trophic niches than rats at unoiled sites. These results suggest that past oiling histories may have imparted subtle, yet differing effects on the foraging ecology of these two co-occurring species. However, the temporal lag between initial oiling and our study makes identifying the ultimate drivers of differences between oiled and unoiled sites challenging. Even so, our findings provide a baseline quantification of the trophic niches of sympatric seaside sparrows and marsh rice rats that will aid in the use of these species as indicators of oiling and other environmental stressors in saltmarsh ecosystems.

Long-Term Immunological Alterations in Bottlenose Dolphin a Decade after the Deepwater Horizon Oil Spill in the Northern Gulf of Mexico: Potential for Multigenerational Effects

Health assessments were conducted on bottlenose dolphins in Barataria Bay, Louisiana, USA, during 2011 to 2018, to assess potential health effects following the Deepwater Horizon oil spill, compared to the unoiled Sarasota Bay, Florida, USA, reference dolphin population. We previously reported significant increases in T-lymphocyte proliferation, as well as lower T helper 1 (Th1) cytokines, higher Th2 cytokine IL-4, and lower T regulatory (Treg) cytokine IL-10 in Barataria Bay in 2011 compared to Sarasota Bay, consistent with Deepwater Horizon oil exposure. Although values between 2013 and 2016 were more similar to those observed in Sarasota Bay, T-cell proliferation was again elevated and cytokine balance tilted toward Th2 in Barataria Bay during 2017-2018. In 2018, Barataria Bay dolphins had significantly more circulating Treg cells than Sarasota Bay dolphins. Mice experimentally exposed to oil also had significantly increased T-lymphocyte proliferation and circulating Treg cell number, including effects in their unexposed progeny. In vitro stimulation resulted in greater Th2 responsiveness in Barataria Bay compared to Sarasota Bay dolphins, and in vitro oil exposure of Sarasota Bay dolphin cells also resulted in enhanced Th2 responsiveness. Evidence points to Treg cells as a potential target for the immunomodulatory effects of oil exposure. The immunological trends observed in Barataria Bay appeared exaggerated in dolphins born after the spill, suggesting the possibility of continued oil exposure or multigenerational health consequences of exposure to oil, as observed in mice. Environ Toxicol Chem 2021;40:1308-1321. © 2021 SETAC.

The effect of pressure variation on droplet size distribution of dispersed oil under simulated deep-water conditions

Droplet size distribution of dispersed oil in deep-water is critical to the transport and biodegradation of spilled oil in deep-sea. Few studies have focused on the effects of pressure on chemically dispersed oil through experiments. This study thus simulated how the crude oil homogenously pre-dispersed by Corexit 9500A using baffled flasks would behave after being exposed to deep-water conditions. Key factors included dispersant-to-oil ratio (DOR), mixing energy (energy dissipation rate and Kolmogorov microscale), and pressure (up to 150 bar). The variations of pressure were demonstrated to have insignificant effects on the size distribution of pre-dispersed oil. Both the average and medium droplet sizes were correlated negatively with DOR and mixing energy in an established model with a p-value ≤ 0.0011. The log-normal and log-logistic distributions provided a reasonable fit to simulate the droplet size distribution. The two parameters of log-logistic distribution were dependent on DOR and mixing energy with a p-value < 0.005. The results would be valuable to advance the understanding of the behaviours and trajectories of chemically dispersed oil under deep-water conditions. The research helped provide more scientific evidence to improve the understanding of dispersed oil behaviours under high pressure and support deep-sea oil spill research and potential extension of the existing results from shallow water to deep water conditions.

A novel method to evaluate chemical concentrations in muddy and sandy coastal regions before and after oil exposures

Oil spills can result in changes in chemical concentrations along coastlines. In prior work, these concentration changes were used to evaluate the date sediment was impacted by oil (i.e., oil exposure date). The objective of the current study was to build upon prior work by using the oil exposure date to compute oil spill chemical (OSC) concentrations in shoreline sediments before and after exposure. The new method was applied to OSC concentration measures collected during the Deepwater Horizon oil spill with an emphasis on evaluating before and after concentrations in muddy versus sandy regions. The procedure defined a grid that overlaid coastal areas with chemical concentration measurement locations. These grids were then aggregated into clusters to allow the assignment of chemical concentration measurements to a uniform coastal type. Performance of the method was illustrated for ten chemicals individually by cluster, and collectively for all chemicals and all clusters. Results show statistically significant differences between chemical concentrations before and after the calculated oil exposure dates (p < 0.04 for each of the 10 chemicals within the identified clusters). When aggregating all chemical measures collectively across all clusters, chemical concentrations were lower before oil exposure in comparison to after (p < 0.0001). Sandy coastlines exhibited lower chemical concentrations relative to muddy coastlines (p < 0.0001). Overall, the method developed is a useful first step for establishing baseline chemical concentrations and for assessing the impacts of disasters on sediment quality within different coastline types. Results may be also useful for assessing added ecological and human health risks associated with oil spills.

Oil spill trajectory modelling and environmental vulnerability mapping using GNOME model and GIS

This study develops an oil spill environmental vulnerability model for predicting and mapping the oil slick trajectory pattern in Kota Tinggi, Malaysia. The impact of seasonal variations on the vulnerability of the coastal resources to oil spill was modelled by estimating the quantity of coastal resources affected across three climatic seasons (northeast monsoon, southwest monsoon and pre-monsoon). Twelve 100 m³ (10,000 splots) medium oil spill scenarios were simulated using General National Oceanic and Atmospheric Administration Operational Oil Modeling Environment (GNOME) model. The output was integrated with coastal resources, comprising biological, socio-economic and physical shoreline features. Results revealed that the speed of an oil slick (40.8 m per minute) is higher during the pre-monsoon period in a southwestern direction and lower during the northeast monsoon (36.9 m per minute). Evaporation, floating and spreading are the major weathering processes identified in this study, with approximately 70% of the slick reaching the shoreline or remaining in the water column during the first 24 h (h) of the spill. Oil spill impacts were most severe during the southwest monsoon, and physical shoreline resources are the most vulnerable to oil spill in the study area. The study concluded that variation in climatic seasons significantly influence the vulnerability of coastal resources to marine oil spill.

The Complexity of Spills: The Fate of the Deepwater Horizon Oil

The Deepwater Horizon oil spill was the largest, longest-lasting, and deepest oil accident to date in US waters. As oil and natural gas jetted from release points at 1,500-m depth in the northern Gulf of Mexico, entrainment of the surrounding ocean water into a buoyant plume, rich in soluble hydrocarbons and dispersed microdroplets of oil, created a deep (1,000-m) intrusion layer. Larger droplets of liquid oil rose to the surface, forming a slick of mostly insoluble, hydrocarbon-type compounds. A variety of physical, chemical, and biological mechanisms helped to transform, remove, and redisperse the oil and gas that was released. Biodegradation removed up to 60% of the oil in the intrusion layer but was less efficient in the surface slick, due to nutrient limitation. Photochemical processes altered up to 50% (by mass) of the floating oil. The surface oil expression changed daily due to wind and currents, whereas the intrusion layer flowed southwestward. A portion of the weathered surface oil stranded along shorelines. Oil from both surface and intrusion layers were deposited onto the seafloor via sinking marine oil snow. The biodegradation rates of stranded or sedimented oil were low, with resuspension and redistribution transiently increasing biodegradation. The subsequent research efforts increased our understanding of the fate of spilled oil immensely, with novel insights focusing on the importance of photooxidation, the microbial communities driving biodegradation, and the formation of marine oil snow that transports oil to the seafloor.

Hepatobiliary PAHs and prevalence of pathological changes in Red Snapper

Red Snapper (Lutjanus campechanus) were collected throughout the Gulf of Mexico (GoM) from 2011 to 2017 and analyzed for biliary (n = 496) fluorescent aromatic compounds (FACs), hepatic (n = 297) polycyclic aromatic hydrocarbons (PAHs) and microscopic hepatobiliary changes (MHC, n = 152). Gross and histological evaluations were conducted with liver tissues to identify and characterize pathological changes. This is the first report to interrelate hepatobiliary PAH concentrations and MHCs in Red Snapper. Hepatic PAHs measured in GoM Red Snapper ranged from 192 to 8530 ng g^-1 w.w. and biliary FACs ranged from 480 to 1,100,000 ng FAC g^-1 bile. Biliary FACs in Red Snapper collected along the west Florida Shelf and north central region declined after 2011 and were relatively stable until a sharp increase was noted in 2017. Increases in the PAH exposures are likely due to a number of sources including leaking infrastructure, annual spills, riverine input and the resuspension of contaminated sediments. In contrast, hepatic PAH concentrations were relatively stable indicating Red Snapper are able to maintain metabolic clearance however this energetic cost may be manifesting as microscopic hepatic changes (MHCs). Virtually all (99 %) of the evaluated Red Snapper had one to nine MHCs with an average of five coinciding changes in an individual fish. The observed changes were broadly classified as inflammatory responses, metabolic responses, degenerative lesions, nonneoplastic proliferation and neoplastic lesions. Biliary FACs were associated with parasitic infection and intracellular breakdown product accumulation such as intra-macrophage hemosiderin, lipofuscin and ceroid laden prevalence. Whereas, hepatic PAHs were associated with increased myxozoan plasmodia prevalence. This study evaluates relationships between hepatobiliary PAH concentrations and biometrics, somatic indices, condition factors and microscopic hepatic changes in Red Snapper located in the north central GoM. Together, these results may be signaling increased disease progression in Gulf of Mexico Red Snapper more than likely resulting from chronic environmental stressors including elevated PAH exposures and concentrations.

A First Comprehensive Baseline of Hydrocarbon Pollution in Gulf of Mexico Fishes

Despite over seven decades of production and hundreds of oil spills per year, there were no comprehensive baselines for petroleum contamination in the Gulf of Mexico (GoM) prior to this study. Subsequent to the 2010 Deepwater Horizon (DWH) spill, we implemented Gulf-wide fish surveys extending over seven years (2011–2018). A total of 2,503 fishes, comprised of 91 species, were sampled from 359 locations and evaluated for biliary polycyclic aromatic hydrocarbon (PAH) concentrations. The northern GoM had significantly higher total biliary PAH concentrations than the West Florida Shelf, and coastal regions off Mexico and Cuba. The highest concentrations of biliary PAH metabolites occurred in Yellowfin Tuna (Thunnus albacares), Golden Tilefish (Lopholatilus chamaeleonticeps), and Red Drum (Sciaenops ocellatus). Conversely, biliary PAH concentrations were relatively low for most other species including economically important snappers and groupers. While oil contamination in most demersal species in the north central GoM declined in the first few years following DWH, more recent increases in exposure to PAHs in some species suggest a complex interaction between multiple input sources and possible re-suspension or bioturbation of oil-contaminated sediments. This study provides the most comprehensive baselines of PAH exposure in fishes ever conducted for a large marine ecosystem.