Dispersed Oil Concentrations Research Articles

Combined effects of chemical dispersant and suspended minerals on the dispersion process of spilled oil

The dispersion process of spilled oil is an important concern for the effective disposal of oil spills. The dispersed oil concentration and oil droplets size distribution were studied through a wave tank test under the application of chemical dispersant and suspended minerals. The results indicated that dispersant and minerals increased the dispersed oil concentration and the effect of dispersant was more significant, and they had a synergistic effect on oil dispersion. When dispersant and minerals were applied together, the volume mean diameter of oil droplets decreased in the first 30 min, then increased and reached a maximum value at 90–120 min, and decreased again. Moreover, suspended minerals could inhibit the coalescence of oil droplets. This study can afford data support for oil spill emergency response that occurs in inshore or estuaries.

Fabrication and characterization of nanoemulsions for encapsulation and delivery of vitexin: antioxidant activity, storage stability and in vitro digestibility.

Nanoemulsions were prepared as an encapsulation and delivery system for vitexin, a poorly water-soluble antioxidant. This study evaluated how the type and concentration of the dispersed oil phase and vitexin loading impacted droplet characteristics and nanoemulsion stability. The influences of storage temperature on antioxidant activity and in vitro gastrointestinal digestion on nanoemulsion stability were also investigated. Nanoemulsions prepared at different dispersed oil concentrations showed diverse characteristics and stability. Highest stability against droplet aggregation and phase separation with small oil droplets (< 150 nm) was observed for nanoemulsions prepared using 300 g kg-1 medium-chain triglyceride oil. These nanoemulsions are able to entrap and deliver vitexin with high encapsulation efficiency (88-90%) with no significant effect on emulsion stability. Vitexin-loaded nanoemulsions were stable during storage when refrigerated (4 °C) and at room temperature (25 °C) for up to 45 days with no effect on their antioxidant activity. Significantly delayed lipolysis rate and decreased extent of lipid digestion were observed in vitexin-loaded nanoemulsions. Stable vitexin-loaded nanoemulsions were successfully produced by high-pressure homogenization using a mixture of Tween 80 and lecithin as emulsifiers. Vitexin-loaded nanoemulsions stabilized with a mixture of these two emulsifiers were effective in retaining antioxidant activity during storage and protecting vitexin from changes during gastrointestinal digestion. Our results suggested that nanoemulsions were effective vitexin delivery systems for food applications. © 2022 Society of Chemical Industry.

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.

Mesopelagic microbial community dynamics in response to increasing oil and Corexit 9500 concentrations.

Marine microbial communities play an important role in biodegradation of subsurface plumes of oil that form after oil is accidentally released from a seafloor wellhead. The response of these mesopelagic microbial communities to the application of chemical dispersants following oil spills remains a debated topic. While there is evidence that contrasting results in some previous work may be due to differences in dosage between studies, the impacts of these differences on mesopelagic microbial community composition remains unconstrained. To answer this open question, we exposed a mesopelagic microbial community from the Gulf of Mexico to oil alone, three concentrations of oil dispersed with Corexit 9500, and three concentrations of Corexit 9500 alone over long periods of time. We analyzed changes in hydrocarbon chemistry, cell abundance, and microbial community composition at zero, three and six weeks. The lowest concentration of dispersed oil yielded hydrocarbon concentrations lower than oil alone and microbial community composition more similar to control seawater than any other treatments with oil or dispersant. Higher concentrations of dispersed oil resulted in higher concentrations of microbe-oil microaggregates and similar microbial composition to the oil alone treatment. The genus Colwellia was more abundant when exposed to multiple concentrations of dispersed oil, but not when exposed to dispersant alone. Conversely, the most abundant Marinobacter amplicon sequence variant (ASV) was not influenced by dispersant when oil was present and showed an inverse relationship to the summed abundance of Alcanivorax ASVs. As a whole, the data presented here show that the concentration of oil strongly impacts microbial community response, more so than the presence of dispersant, confirming the importance of the concentrations of both oil and dispersant in considering the design and interpretation of results for oil spill simulation experiments.

An OMA-SIM Approach to Study OMA Kinetics for the Cleanup of Marine Oil Spill

Breaking waves can break oil slicks into fine droplets and entrain them in the water column. An interesting hypothesis has emerged in recent years that oil droplets and mineral fines may form Oil-Mineral Aggregates (OMAs) and enhance oil dispersion in aquatic environments. The present research investigated physical processes of marine oil spills, including oil slick breakup, the formation of OMAs, and oil/OMAs vertical mixing. In this study, a modeling approach is developed for simulating the formation and vertical mixing of oil droplets and OMAs, namely Oil Droplet and OMAs Simulation (OMA-SIM). This integrated modeling tool combines the oil vertical mixing model and density-based OMAs formation model to examine the dispersion of oil droplets and OMAs. The OMA-SIM is validated using data obtained from a mesoscale wave tank experimental study. Simulation results show that the energy dissipation rate of breaking waves is the predominant factor affecting the concentration and particle size of formed oil droplets and OMAs. It also confirms that oil viscosity has a significant influence on dispersed oil concentration. High temperature, low oil viscosity, together with more formed OMAs lead to a higher concentration of dissolved oil. Other findings based on the validated OMA-SIM approach include that: the dispersants reduce oil/water interfacial tension and decrease the size of oil droplets and OMAs, and the application of mineral fines facilitates the formation of OMAs. This study indicates that the OMA-SIM is an effective modeling tool for examining the vertical dispersion of spilled oil with or without the use of dispersant and other green particle materials like mineral fines under breaking waves.

The influences of phytoplankton species, mineral particles and concentrations of dispersed oil on the formation and fate of marine oil-related aggregates

The formation and fallout of oil-related marine snow have been associated with interactions between dispersed oil and small marine particles, like phytoplankton and mineral particles. In these studies, the influences of phytoplankton species, mineral particle concentration, and oil concentration on the aggregation of oil in seawater (SW) were investigated. The experiments were performed in a low-turbidity carousel incubation system, using natural SW at 13 °C. Aggregation was measured by silhouette camera analyses, and oil compound group distribution and depletion by gas chromatography (GC-FID or GC–MS). Aggregates with median sizes larger than 500 μm in diameter were measured in the presence of dispersed oil and the phytoplankton species Thalassiosira rotula, Phaeocystis globosa, Skeletonema pseudocostatum, but not with the microalgae Micromonas pusilla. When mineral particles (diatomaceous earth) were incubated at different concentrations (5–30 mg/L) with dispersed oil and S. pseudocostatum, the largest aggregates were measured at the lower mineral particle concentration (5 mg/L). Since dispersed oil rapidly dilutes in the marine water column, experiments were performed with oil concentrations of from 10 mg/L to 0.01 mg/L in the presence of S. pseudocostatum and diatomaceous earth. Aggregates larger than 500 μm was measured only at the highest oil concentrations (10 mg/L). However, oil attachment to the marine particles were also measured at low oil concentrations (≤1 mg/L). Depletion of oil compound groups (n-alkanes, naphthalenes, PAHs, decalins) were measured at all oil concentrations, both in aggregate and water phases, with biodegradation as the expected main depletion process. These results showed that oil concentration may be important for oil-related marine snow formation, but that even oil droplets at low concentrations may attach to the particles and be transported by prevailing currents.

Transport of dispersed oil compounds to the seafloor by sinking phytoplankton aggregates: A modeling study

Up to 20% of the oil spilled as a result of the Deepwater Horizon explosion in the Gulf of Mexico in 2010 was deposited as degraded oil compounds on the seafloor. Much of that deposition was likely due to dispersed oil compounds having been integrated into fast-sinking aggregates, which transported it effectively to depth. Understanding the details of this oil transport mechanism, and predicting its potential magnitude, is important for the management and mitigation of future oil spills.The 1-D model described here simulates a) a diatom bloom and the resulting formation of aggregates via coagulation of cells, b) the scavenging of dispersed oil compounds by these aggregates as they sink through the water column, c) the degradation of diatom carbon and oil carbon during transit, and d) the ultimate deposition of aggregates and oil compounds to the seafloor. The model is parameterized using primarily field- and laboratory-collected data and the model results are compared to sediment trap data. Specifically, one large diatom sedimentation event observed shortly after the Deepwater well was capped was modeled. The comparison of simulation results to field data assesses the model’s ability to explain the observed sedimentation event and tests our understanding of the main mechanisms driving such an event.The model results indicate that diatom carbon and oil compounds captured in the trap were linked to a sedimentation event that reached peak intensity just before the trap was deployed. The model simulations predict the measured sedimentation rates of oil compounds and organic carbon reasonably well, indicating that the key mechanisms driving this process were captured by the model. In the baseline case, which simulates the sedimentation of a large Skeletonema bloom in late August 2010, about 10% of the dispersed oil compounds lingering in the water were deposited to the seafloor. The ability of a sinking diatom bloom to scavenge dispersed oil compounds from the water column and deposit them to depth is a robust result of the model over a range of parameter variations. These results suggest that a model that combines satellite data on phytoplankton blooms with water column dispersed oil concentrations to estimate potential oil compound deposistion rates may be able to provide decision makers with guidance during an oil spill. However, additional, independent validation of the model is necessary before it can be adapted for use in an operational setting.

Application of Structural Properties of Seismic Data to Prediction of Hydrocarbon Distribution

This article describes how under the influence of traps and trap ranges in size, final moisture content in oil production and changes in the reservoir is very large. Due to this, thin and dispersed oil concentration, facies changes and oil complexes, and strong segmentation, results in poor comparability between wells and conventional methods of seismic reservoir prediction has been more difficult to meet the development needs of the block. Therefore, the introduction of methods of seismic data structure characteristics, with a method based on sequence structure of underground rock formations, rock and petroleum allows the prediction for oil and gas purposes. Through the application of seismic structural properties, the result has been verified in practice and achieved a good application effect.

Toxicity of dispersed oil on Gold–saddle rabbitfish Siganus guttatus fry

The acute toxicity of dispersant Mardeus-455 added to water accommodated fractions (WAF) were evaluated in Gold-saddle rabbitfish Siganus guttatus fry after 72 h exposure under laboratory conditions. Mortalities of fry exposed to different concentrations of dispersed oil were recorded every hour for the first 6 h, every 3 h for the next 12 h, and every 6 h thereafter. Results showed that the higher the ratio of dispersant and WAF, the higher the mortality of the rabbitfish fry which may be due to the enhanced availability of polyaromatic hydrocarbons (PAH). The LC50 was computed at 3.692% of the oil volume. The application of dispersant in cleaning oil spills must be limited to reduce its harmful effect in the marine environment. Assessing toxicity of dispersed oil in fish fry may help understand the extent of environmental damage after cleaning oil spill using dispersant.

Joint Industry Sponsored Effort to Evaluate Post-Macondo Dispersant Research

ABSTRACT As an outcome of the creation of the American Petroleum Institute’s (API) Oil Spill Prevention and Response Joint Industry Task Force (OSPR JITF) following the Macondo oil release, and with support from the IPIECA-IOGP Oil Spill Response JIP, a team was formed to evaluate emerging dispersant-related research. It was clear that there was a need to interact with research and development consortia and other oil spill response-related research groups to provide input and potential guidance in order to encourage real world relevance, especially since the Gulf of Mexico Research Initiative (GoMRI) had been created with a funding level of $500 million over a 10 year period. A specific outcome of the effort has been a review of research papers on dispersant fate and effects published post-Macondo. The main objective was to review results of recent dispersant research with a goal of providing a link to existing dispersant knowledge and to spill response management questions facing spill response planners in the post-Macondo environment. This effort was viewed as an opportunity to solidify a working relationship between federal government and industry personnel and academic researchers in an area of oil spill-related research that would be important for the foreseeable future. Dispersants are one of the tools that may be used to respond to oil spills, especially to those that are large and offshore. When used appropriately, dispersants may prevent slicks from reaching shorelines and adversely impacting sensitive coastal ecosystems. The use of dispersants during the Macondo incident resulted in an increased awareness of their use, especially among the academic community and the general public. The review panel had a primary goal to identify recurring misunderstandings and inconsistencies that might arise due to researchers’ inexperience with the real-world aspects of oil spills, spill response, and the way in which dispersants are designed to be used (spraying on slicks, usually in offshore waters) or with applicable oil toxicity research standards (e.g., use of appropriate dispersed oil concentrations during studies). The objectives were to identify:Potential problems for researchers so that they can be avoided in ongoing studiesEvaluate and share potentially misleading results, especially as they might influence global dispersant regulations inappropriately The paper will review results to date and highlight those areas that are viewed to be the most consistent and problematic (e.g., the inappropriate use of nominal versus measured exposure conditions, a focus on dispersant rather than dispersed oil toxicity).

The Rate of Crude Oil Biodegradation in the Sea

Various groups have studied the rate of oil biodegradation in the sea over many years, but with no consensus on results. This can be attributed to many factors, but we show here that the principal confounding influence is the concentration of oil used in different experiments. Because of dilution, measured concentrations of dispersed oil in the sea are sub-parts-per-million within a day of dispersal, and at such concentrations the rate of biodegradation of detectable oil hydrocarbons has an apparent half-life of 7-14 days. This can be contrasted with the rate of degradation at the higher concentrations found in oil slicks or when stranded on a shoreline; there the apparent half-life varies from many months to many years.

I: Biomarker quantification in fish exposed to crude oil as input to species sensitivity distributions and threshold values for environmental monitoring

The aim of this study was to determine a suitable set of biomarker based methods for environmental monitoring in sub-arctic and temperate offshore areas using scientific knowledge on the sensitivity of fish species to dispersed crude oil. Threshold values for environmental monitoring and risk assessment were obtained based on a quantitative comparison of biomarker responses. Turbot, halibut, salmon and sprat were exposed for up to 8 weeks to five different sub-lethal concentrations of dispersed crude oil. Biomarkers assessing PAH metabolites, oxidative stress, detoxification system I activity, genotoxicity, immunotoxicity, endocrine disruption, general cellular stress and histological changes were measured. Results showed that PAH metabolites, CYP1A/EROD, DNA adducts and histopathology rendered the most robust results across the different fish species, both in terms of sensitivity and dose-responsiveness. The reported results contributed to forming links between biomonitoring and risk assessment procedures by using biomarker species sensitivity distributions.

Crude oil exposures reveal roles for intracellular calcium cycling in haddock craniofacial and cardiac development.

Recent studies have shown that crude oil exposure affects cardiac development in fish by disrupting excitation-contraction (EC) coupling. We previously found that eggs of Atlantic haddock (Melanogrammus aeglefinus) bind dispersed oil droplets, potentially leading to more profound toxic effects from uptake of polycyclic aromatic hydrocarbons (PAHs). Using lower concentrations of dispersed crude oil (0.7–7 μg/L ∑PAH), here we exposed a broader range of developmental stages over both short and prolonged durations. We quantified effects on cardiac function and morphogenesis, characterized novel craniofacial defects, and examined the expression of genes encoding potential targets underlying cardiac and craniofacial defects. Because of oil droplet binding, a 24-hr exposure was sufficient to create severe cardiac and craniofacial abnormalities. The specific nature of the craniofacial abnormalities suggests that crude oil may target common craniofacial and cardiac precursor cells either directly or indirectly by affecting ion channels and intracellular calcium in particular. Furthermore, down-regulation of genes encoding specific components of the EC coupling machinery suggests that crude oil disrupts excitation-transcription coupling or normal feedback regulation of ion channels blocked by PAHs. These data support a unifying hypothesis whereby depletion of intracellular calcium pools by crude oil-derived PAHs disrupts several pathways critical for organogenesis in fish.

Influence of UVB radiation on the lethal and sublethal toxicity of dispersed crude oil to planktonic copepod nauplii

Toxic effects of petroleum to marine zooplankton have been generally investigated using dissolved petroleum hydrocarbons and in the absence of sunlight. In this study, we determined the influence of natural ultraviolet B (UVB) radiation on the lethal and sublethal toxicity of dispersed crude oil to naupliar stages of the planktonic copepods Acartia tonsa, Temora turbinata and Pseudodiaptomus pelagicus. Low concentrations of dispersed crude oil (1 μL L−1) caused a significant reduction in survival, growth and swimming activity of copepod nauplii after 48 h of exposure. UVB radiation increased toxicity of dispersed crude oil by 1.3–3.8 times, depending on the experiment and measured variables. Ingestion of crude oil droplets may increase photoenhanced toxicity of crude oil to copepod nauplii by enhancing photosensitization. Photoenhanced sublethal toxicity was significantly higher when T. turbinata nauplii were exposed to dispersant-treated oil than crude oil alone, suggesting that chemical dispersion of crude oil may promote photoenhanced toxicity to marine zooplankton. Our results demonstrate that acute exposure to concentrations of dispersed crude oil and dispersant (Corexit 9500) commonly found in the sea after oil spills are highly toxic to copepod nauplii and that natural levels of UVB radiation substantially increase the toxicity of crude oil to these planktonic organisms. Overall, this study emphasizes the importance of considering sunlight in petroleum toxicological studies and models to better estimate the impact of crude oil spills on marine zooplankton.

Dual effects of a dispersant and nutrient supplementation on weathered Endicott oil biodegradation in seawater

Laboratory-scale experiments were conducted to evaluate the biodegradation of physically (WAF) and chemically dispersed (CEWAF) Endicott oil in seawater (salinity: 29.1‰) from Prince William Sound, Alaska, under low nutrient (LN) (background seawater) and high nutrient (HN) (addition of 100 mg NO3-N/L and 10 mg PO4-P/L to background seawater) at 15 ± 0.5 °C for 42 days. The dispersant was Corexit 9500. The dispersed oil concentration of the WAF (0.019 g/L ± 0.002) was an order of magnitude lower than that in the CEWAF (0.363 g/L ± 0.038). While remaining negligible in the WAF, the total oil removal in the CEWAF was 26% and 44% in LN and HN treatments, respectively. Nutrient supplementation significantly accelerated the rate of oil biodegradation as confirmed by ANOVA coupled with Tukey’s test at 95% confidence intervals (α = 0.05). GC/MS analyses revealed that biodegradation affected mainly alkane compounds. In the CEWAF, O2 consumption, CO2 production and biomass were much larger in HN than in LN treatments, which suggests that chemical dispersion of oil coupled with high nutrient concentration could be very useful in terms of remediation strategies and effective responses to oil spill at sea.

How much crude oil can zooplankton ingest? Estimating the quantity of dispersed crude oil defecated by planktonic copepods

We investigated and quantified defecation rates of crude oil by 3 species of marine planktonic copepods (Temora turbinata, Acartia tonsa, and Parvocalanus crassirostris) and a natural copepod assemblage after exposure to mechanically or chemically dispersed crude oil. Between 88 and 100% of the analyzed fecal pellets from three species of copepods and a natural copepod assemblage exposed for 48 h to physically or chemically dispersed light crude oil contained crude oil droplets. Crude oil droplets inside fecal pellets were smaller (median diameter: 2.4–3.5 μm) than droplets in the physically and chemically dispersed oil emulsions (median diameter: 6.6 and 8.0 μm, respectively). This suggests that copepods can reject large crude oil droplets or that crude oil droplets are broken into smaller oil droplets before or during ingestion. Depending on the species and experimental treatments, crude oil defecation rates ranged from 5.3 to 245 ng-oil copepod−1 d−1, which represent a mean weight-specific defecation rate of 0.026 μg-oil μg-Ccopepod1 d−1. Considering a dispersed crude oil concentration commonly found in the water column after oil spills (1 μl L−1) and copepod abundances in high productive coastal areas, copepods may defecate ∼1.3–2.6 mg-oil m−3 d−1, which would represent ∼0.15%–0.30% of the total dispersed oil per day. Our results indicate that ingestion and subsequent defecation of crude oil by planktonic copepods has a small influence on the overall mass of oil spills in the short term, but may be quantitatively important in the flux of oil from surface water to sediments and in the transfer of low-solubility, toxic petroleum hydrocarbons into food webs after crude oil spills in the sea.

Impact of salinity and dispersed oil on adsorption of dissolved aromatic hydrocarbons by activated carbon and organoclay

Adsorption capacity of phenol and naphthalene by powdered activated carbon (PAC), a commercial organoclay (OC) and a lab synthesized organoclay (BTMA) was studied using batch adsorption experiments under variable feed water quality conditions including single- and multi- solute conditions, fresh water, saline water and oily-and-saline water. Increasing salinity levels was found to reduce adsorption capacity of OC, likely due to destabilization, aggregation and subsequent removal of organoclay from the water column, but did not negatively impact adsorption capacity of PAC or BTMA. Increased dispersed oil concentrations were found to reduce the surface area of all adsorbents. This decreased the adsorption capacity of PAC for both phenol and naphthalene, and reduced BTMA adsorption of phenol, but did not negatively affect naphthalene removals by either organoclay. The presence of naphthalene as a co-solute significantly reduced phenol adsorption by PAC, but had no impact on organoclay adsorption. These results indicated that adsorption by PAC occurred via a surface adsorption mechanism, while organoclay adsorption occurred by hydrophobic or pi electron interactions. In general, PAC was more sensitive to changes in water quality than either of the organoclays evaluated in this study. However, PAC exhibited a higher adsorption capacity for phenol and naphthalene compared to both organoclays even in adverse water quality conditions.

Unexpected interaction with dispersed crude oil droplets drives severe toxicity in Atlantic haddock embryos.

The toxicity resulting from exposure to oil droplets in marine fish embryos and larvae is still subject for debate. The most detailed studies have investigated the effects of water-dissolved components of crude oil in water accommodated fractions (WAFs) that lack bulk oil droplets. Although exposure to dissolved petroleum compounds alone is sufficient to cause the characteristic developmental toxicity of crude oil, few studies have addressed whether physical interaction with oil micro-droplets are a relevant exposure pathway for open water marine speices. Here we used controlled delivery of mechanically dispersed crude oil to expose pelagic embryos and larvae of a marine teleost, the Atlantic haddock (Melanogrammus aeglefinus). Haddock embryos were exposed continuously to two different concentrations of dispersed crude oil, high and low, or in pulses. By 24 hours of exposure, micro-droplets of oil were observed adhering and accumulating on the chorion, accompanied by highly elevated levels of cyp1a, a biomarker for exposure to aromatic hydrocarbons. Embryos from all treatment groups showed abnormalities representative of crude oil cardiotoxicity at hatch (5 days of exposure), such as pericardial and yolk sac edema. Compared to other species, the frequency and severity of toxic effects was higher than expected for the waterborne PAH concentrations (e.g., 100% of larvae had edema at the low treatment). These findings suggest an enhanced tissue uptake of PAHs and/or other petroleum compounds from attached oil droplets. These studies highlight a novel property of haddock embryos that leads to greater than expected impact from dispersed crude oil. Given the very limited number of marine species tested in similar exposures, the likelihood of other species with similar properties could be high. This unanticipated result therefore has implications for assessing the ecological impacts of oil spills and the use of methods for dispersing oil in the open sea.

Reproduction dynamics in copepods following exposure to chemically and mechanically dispersed crude oil.

Conflicting reports on the contribution of chemical dispersants on crude oil dispersion toxicity have been published. This can partly be ascribed to the influence of dispersants on the physical properties of the oil in different experimental conditions. In the present study the potential contribution of dispersants to the reproductive effects of dispersed crude oil in the marine copepod Calanus finmarchicus (Gunnerus) was isolated by keeping the oil concentrations and oil droplet size distributions comparable between parallel chemically dispersed (CD, dispersant:oil ratio 1:25) and mechanically dispersed oil (MD, no dispersant) exposures. Female copepods were exposed for 96 h to CD or MD in oil concentration range of 0.2-5.5 mg·L(-1) (THC, C5-C36) after which they were subjected to a 25-day recovery period where production of eggs and nauplii were compared between treatments. The two highest concentrations, both in the upper range of dispersed oil concentrations reported during spills, caused a lower initial production of eggs/nauplii for both MD and CD exposures. However, copepods exposed to mechanically dispersed oil exhibited compensatory reproduction during the last 10 days of the recovery period, reaching control level of cumulative egg and nauplii production whereas females exposed to a mixture of oil and dispersant did not.

DISCOBIOL: Assessment of the Impact of Dispersant Use for Oil Spill Response in Coastal or Estuarine Areas

ABSTRACT Dispersants are known to be an appropriate solution for offshore spill response when sea conditions provide enough energy to disperse and then dilute oil into surface waters. In shallow coastal areas, the use of dispersant is restricted due to the potential that the dispersed oil might come into contact with sensitive resources before dilution can take place. However, after assessing the advantages and potential risks of dispersing oil in coastal areas, it may emerge after careful consideration that and in some cases the use of dispersants could provide a net environmental benefit. The DISCOBIOL research program aimed to provide practical recommendations on dispersant use in coastal and estuarine areas by acquiring relevant (in terms of likely dispersed oil concentrations) and robust experimental information on the impact of mechanically and chemically dispersed oil on living resources. The main conclusion from these experiments was that there is no significant difference between the impacts from oil with and without dispersant use in terms of acute toxicity. However there are some observable sub-lethal effects from exposure to dispersed oil which do not persist more than a few weeks. In a natural environment, on a medium or long timescale, biota which have been exposed to oil (with and without dispersant) do exhibit some symptoms which could affect their survival rate in the field even though they do not lead to acute toxicity effects. However the DISCOBIOL project demonstrated that effects of dispersed oil were less severe than previously recorded for near shore environments. In terms of applying these results to decision making at an oil spill, it highlights the need in coastal areas prior to the use of dispersant to complete a “Net Environmental Benefit Analysis” (NEBA) to determine whether the use of dispersant is expected to minimize the overall damage resulting from the pollution. As it is difficult to cover the number of possible spill scenarios at the contingency planning stage, instead of completing a NEBA, many countries define geographical limits where dispersion can be undertaken, based on the water depth and the distance to the shore as well as the presence of sensitive resources. The DISCOBIOL study confirmed the appropriateness of these pre-defined limits for France's coastal waters but demonstrated that they could be less restrictive since the exposure to dispersed oil could be at least five times higher than was previously considered the safe limit.