The effects of petroleum aromatic hydrocarbons (PAHs) on the embryonic and larval life stages of teleosts have been extensively examined. However, very little work has been conducted on how spilled oil affects fish sperm and there is no related knowledge concerning oil dispersing agents. The objective of our study was to determine sperm performance of a teleost fish under direct exposure to different concentrations of WAF (water accommodated fraction) and CEWAF (chemically enhanced water accommodated fraction). Capelin sperm motility, swimming behaviour, and sperm fertilization ability were evaluated in a scenario of an oil spill untreated (WAF) and treated (CEWAF) with the dispersant Corexit® EC9500A. Sperm fertilizing ability was lower when exposed to CEWAF concentrations of 16.1 × 103 μg/L total petroleum hydrocarbons and 47.9 μg/L PAH, and when exposed to the dispersant alone. The mechanism responsible for this reduced fertilizing ability is not clear. However, it is not related to the percentage of motile sperm or sperm swimming behaviour, as these were unaffected. WAF did not alter sperm swimming characteristics nor the fertilizing ability. We suggest the dispersant rather than the dispersed oil is responsible for the decrease in the sperm fertilizing ability and hypothesize that the surfactants present in the dispersant affect sperm membrane functionality.

During the Deepwater Horizon oil spill rapid natural weathering of Macondo crude oil occurred during the transport of oil to coastal areas. In response to the DWH incident, dispersant was applied to Macondo crude oil to reduce the movement of oil to coastal regions. This study aimed to assess the narcotic and phototoxicity of water-accommodated fractions (WAFs) of weathered Macondo crude oil, and chemically-enhanced WAFs of Corexit 9500 to Pacific (Crassostrea gigas) and eastern (Crassostrea virginica) oyster larvae. Phototoxic effects were observed for larval Pacific oysters exposed to combinations of oil and dispersant, but not for oil alone. Phototoxic effects were observed for larval eastern oysters exposed to oil alone and combinations of oil and dispersant. Corexit 9500 did not exhibit phototoxicity but resulted in significant narcotic toxicity for Pacific oysters. Oyster larvae may have experienced reduced survival and/or abnormal development if reproduction coincided with exposures to oil or dispersant.

The atmospheric concentrations of volatile organic compounds (VOCs) generated by surface slicks during an oil spill have not been extensively studied. We modeled oil transport and fate, air emissions, and atmospheric dispersion of VOCs from a hypothetical deepwater well blowout in De Soto Canyon of the Gulf of Mexico assuming no intervention and use of SubSea Dispersant Injection (SSDI) at the source during three week-long periods representing different atmospheric mixing conditions. Spatially varying time histories of atmospheric VOCs within ~2 km from the release site were estimated. As compared to the no-intervention case, SSDI dispersed the discharged oil over a larger water volume at depth and enhanced VOC dissolution and biodegradation, thereby reducing both the total mass of VOCs released to the atmosphere and the concentration of VOCs within 2 km from the release site. Atmospheric conditions also influenced the VOC concentrations, although to a lesser degree than SSDI.

During the Deepwater Horizon blowout, unprecedented volumes of dispersant were applied both on the surface and at depth. Application at depth was intended to disperse the oil into smaller microdroplets that would increase biodegradation and also reduce the volumes buoyantly rising to the surface, thereby reducing surface exposures, recovery efforts, and potential stranding. In forensically examining 5300 offshore water samples for the Natural Resource Damage Assessment (NRDA) effort, profiles of deep-plume oil droplets (from filtered water samples) were compared with those also containing dispersant indicators to reveal a previously hypothesized but undocumented, accelerated dissolution of the polycyclic aromatic hydrocarbons (PAH) in the plume samples. We interpret these data in a fate-and-transport context and conclude that dispersant applications were functionally effective at depth.

Subsea dispersant injection (SSDI) was a new oil spill response (OSR) technology deployed during the Deepwater Horizon accident. To integrate SSDI into future OSR decisions, a hypothetical deepwater oil spill to the Gulf of Mexico was simulated and a comparative risk assessment (CRA) tool applied to contrast three response strategies: (1) no intervention; (2) mechanical recovery, in-situ burning, and surface dispersants; and, (3) SSDI in addition to responses in (2). A comparative ecological risk assessment (CRA) was applied to multiple valued ecosystem components (VECs) inhabiting different environmental compartments (ECs) using EC-specific exposure and relative VEC population density and recovery time indices. Results demonstrated the added benefit of SSDI since relative risks to shoreline, surface wildlife and most aquatic life VECs were reduced. Sensitivity of results to different assumptions was also tested to illustrate flexibility of the CRA tool in addressing different stakeholder priorities for mitigating the impacts of a deepwater blowout.

Subsea blowouts have the potential to spread oil across large geographical areas, and subsea dispersant injection (SSDI) is a response option targeted at reducing the impact of a blowout, especially reducing persistent surface oil slicks. Modified Weber scaling was used to predict oil droplet sizes with the OSCAR oil spill model, and to evaluate the surface oil volume and area when using SSDI under different conditions. Generally, SSDI reduces the amount of oil on the surface, and creates wider and thinner surface oil slicks. It was found that the reduction of surface oil area and volume with SSDI was enhanced for higher wind speeds. Overall, given the effect of SSDI on oil volume and weathering, it may be suggested that tar ball formation, requiring thick and weathered oil, could possibly be reduced when SSDI is used.

The main objective with this study has been to study injection techniques for subsea dispersant injection (SSDI) to recommend techniques relevant for both laboratory studies and operational response equipment.The most significant factor was the injection point of the dispersant in relation to the release of the oil. The dispersant should be injected immediately before or after the oil is released. Then the dispersant will mix into the oil and reduce IFT before the oil enters the turbulent zone where initial droplet formation occurs.All injection techniques tested gave significant reductions in oil droplet sizes. However, due to the rapid oil droplet formation in turbulent jets and possible formation of surfactant aggregates in the oil, premixing of dispersants should not be used for experimental studies of subsea dispersant injection. This could underestimate dispersant effectiveness and produce results that might not be representative for up-scaled field conditions.

Microbial communities are ecologically important in aquatic environments and impacts on microbes have the potential to affect a number of functional processes. We have amended seawater with a crude oil and assessed changes in species composition as well as a measure of functional diversity (the ability of the community to utilise different carbon sources) and the community level metabolic signature. We found that there was a degree of functional redundancy in the community we tested. Oiled assemblages became less diverse and more dominated by specialist hydrocarbon degraders, carbon source utilisation increased initially but there was no change in metabolic signature in this small scale laboratory experiment. This study supports the decision framework around management of oil spills. This package of methods has the potential to be used in the testing and selection of new dispersants for use in oil spill response.

In case of an oil spill, dispersant application represents a response option, which enhances the natural dispersion of oil and thus reduces coating of seabirds and coastal areas. However, as oil is transferred to the water phase, a trade-off of potential harmful effects shifted to other compartments must be performed. This paper summarizes the results of a workshop on the current knowledge on risks and benefits of the use of dispersants with respect to specific conditions encountered at the German sea areas. The German North Sea coast is a sensitive ecosystem characterised by tidal flats, barrier islands and salt marshes. Many prerequisites for a potential integration of dispersants as spill response option are available in Germany, including sensitivity maps and tools for drift modelling of dispersed and undispersed oil. However, open scientific questions remain concerning the persistence of dispersed oil trapped in the sediments and potential health effects.

Biodegradation of chemically dispersed oil at low temperature (0–2 °C) was compared in natural seawater from Arctic (Svalbard) and a temperate (Norway) fjords. The oil was premixed with a dispersant (Corexit 9500) and small-droplet oil dispersions prepared. Faster biotransformation of n-alkanes in the Arctic than in the temperate seawater were associated with the initially higher abundance of the alkane-degrading genus Oleispira in the Arctic than the temperate seawater. Comparable transformation of aromatic hydrocarbons was further associated with the late emergences Cycloclasticus in both seawater sources. The results showed that chemically dispersed oil may be rapidly biodegraded by microbial communities in Arctic seawater. Compared to oil biodegradation studies at higher seawater temperatures, longer lag-periods were experienced here, and may be attributed to both microbial and oil properties at these low seawater temperatures.