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Chemical herding agents are surfactant mixtures used to coalesce spilled oil and increase slick thickness to facilitate mechanical recovery or in situ burning. Only two herders are currently listed on the United States' National Oil and Hazardous Substances Pollution Contingency Plan or National Contingency Plan product schedule for potential use in spill response: the surface collecting agents Siltech OP-40™ and ThickSlick 6535™. Toxicity data for spill response agents are frequently available only for two estuarine species, mysid shrimp (Americamysis bahia) and inland silversides (Menidia beryllina), and are particularly limited for herding agents. Toxicity can vary over several orders of magnitude across product type and species, even within specific categories of spill response agents. Seven aquatic species were tested with both Siltech OP-40™ and ThickSlick 6535™ to evaluate acute herder toxicity and relative species sensitivity. The toxicity assessment included: acute tests with A. bahia and M. beryllina, the freshwater crustacean Ceriodaphina dubia, and the freshwater fish Pimephales promelas; development of the echinoderm Arbacia unctulate; and growth of a freshwater alga Raphidocelis subcapitata and marine alga Dunaliella tertiolecta. Siltech acute toxicity values ranged from 1.1 to 32.8 ppm. ThickSlick acute toxicity values ranged from 2.2 to 126.4 ppm. The results of present study show greater toxicity of Siltech compared to ThickSlick with estimated acute hazard concentrations intended to provide 95% species protection of 1.1 and 3.6 ppm, respectively, on empirical data and 0.64 and 3.3 ppm, respectively, with the addition of interspecies correlation data. The present study provides a greater understanding of species sensitivity of these two oil spill response agents. Environ Toxicol Chem 2022;41:1311-1318. © 2022 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

The combustion efficiency of simulated at-sea surface oil burns (in situ burns) was determined in a 63 m3 tank while testing varied boom configurations and air-assist nozzles in the presence and absence of waves. Combustion efficiencies of Alaska North Slope oil based on unburned carbon in the plume emissions ranged from 85% to 93% while values based on oil mass loss ranged from 89% to 99%. A four-fold variation in PM2.5 emission factors was observed from the test conditions. The most effective burns in terms of reduced emissions and post-burn residue concentration of total petroleum hydrocarbons were those that had high length to width boom ratios resulting in higher flame front surface area exposure to ambient air. The amount of oil mass lost was not related to any combustion efficiency parameters measured in the plume, representing a potential tradeoff between unburnt oil and air pollution.

Surface washing agents (SWAs) can be used to enhance removal of spilled oil from shoreline surfaces and structures. There are two classes of SWA products, “lift and float” products which remove the oil from the surfaces to create an oil slick which can be recovered mechanically and “lift and disperse” products which emulsify and disperse the oil into the water column, which are more difficult to remove mechanically. Therefore, information regarding the ability of a product to lift oil from a surface and its mechanism of action once the oil has been removed is important for oil spill responders. The SWA effectiveness (SWAE) of 15 products (conducted and reported blind) listed on the NCP Product Schedule was evaluated by applying oil to a sand substrate, allowing time for the oil to adhere to the substrate, treating with SWA, and washing with artificial seawater to release any oil that has been lifted from the substrate surface. The efficiency of SWAs is calculated based on the mass of oil remaining on the substrate relative to the total mass of oil applied. The Dispersant Effectiveness (DE) of SWA products was determined using the Baffled Flask Test and was used to sort products based on their mechanism of action (“lift and disperse” rather than “lift and float”). Using a sand basket approach, the amount of oil remaining in sand varied from 10 to 95% for the various products tested, where a lower percent signifies a better SWA. The DE varied between 8 and 81%. Though previous studies have concluded that good SWAs are poor dispersants and vice versa, the results from this study demonstrate that this is not a general rule. A stoplight decision framework was developed that considers the relationship between DE and SWAE, and serves to identify products whose primary mechanism is “lift and disperse” rather than “lift and float.” Results suggest that regardless of which test is used to evaluate SWAs, coupling findings with DE can provide useful information for decisions during response operations.

Chemical dispersant formulations typically provide maximum oil dispersion in waters between 30–40 ppt (parts per thousand) salt content, which encompasses typical ocean salinity (~34 ppt). As a result, most laboratory studies of oil dispersion effectiveness (DE) are conducted at low to average ocean salinity. Ocean salinity can vary locally from below 20 ppt during ice and snow melt, to extremely high (over 100 ppt) during freeze up periods or within natural brine pools in deeper waters. In this study, the influence of salinity on DE was evaluated using the baffled flask test (BFT) at a dispersant-to-oil ratio (DOR) of 1:25. Benchtop experiments were conducted with Alaskan North Slope (ANS) crude oil in the presence or absence of chemical dispersant at 5 and 25°C and varying salinities (0.2 to 125 ppt). In addition to DE as determined by BFT, oil droplet size distribution (DSD) and fluorescence intensity was measured via a LISST-100X particle size analyzer (Sequoia Scientific, Inc., Bellevue, WA) and ECO fluorometer (Sea Bird - WET Labs, Inc.; Philomath, OR), respectively. Results indicate that in the presence of dispersant, maximum DE occurred at 25ppt, and decreases above and below this salinity. Concentration of small droplets (

Historically, visual observation is an emergency responder's first ‘tool’ in identifying spilled oil. Optical detection has since expanded to include a myriad of signals from space, aircraft, drone, vessel and submersible platforms that can provide critical information for decision-making during spill response efforts. Spill monitoring efforts below the air-water interface have been vastly improved by advances with in situ optical sensors and vehicle platform technology. Optical techniques using fluorescence, scattering, and holography offer a means to determine dissolved versus droplet fractions, provide oil concentration estimates and serve as proxies for dispersion efficiency. For subsurface spills over large space and time scales, Autonomous Underwater Vehicles (AUVs) can be used to provide subsurface plume footprints and estimate oil concentrations. For smaller, more frequent spills, tethered compact Remotely Operated Vehicles (ROVs) may be more appropriate as they are easy to deploy for rapid detection. Two underwater oil detection technologies have been developed: (1) A Remote Environmental Monitoring UnitS (REMUS-600) AUV equipped with fluorescence and backscatter SeaOWL UV-A (Oil-in-Water Locator; Sea-Bird Scientific WET Labs Inc.), holographic imager (HoloCam; SeaScan, Inc), hydrographic information, video camera, CTD and a water/oil sampler. (2) A tethered ROV system (DTG2, Deep Trekker Inc.) equipped with video camera, UviLux (Chelsea Technologies Group, Inc) fluorometer, a CTD and water/oil sampler. Calibration and validation tests of the sensor suite were conducted at the Coastal Response Research Center flume tank (NH, USA). Oil concentration estimates were verified by chemical analysis of hydrocarbons and particle size analysis (LISST 200X, Sequoia, Inc). Operational performance of the ROV platform and sensors was evaluated at the Ohmsett wave tank (NJ, USA). Field performance of the REMUS and sensor suite was evaluated at natural seeps near Santa Barbara, CA. This research demonstrates the forensic value of in situ optical data for improved understanding of the behavior and transport of spilled oil below the air-sea interface.

NUMBER: 1141223 Simulated in situ oil burning tests were conducted in a 14 m × 2.4 m × 2.4 m tank to characterize variations in boom length/width aspect ratios, the use of injection air, nozzle angle, and presence or absence of waves on combustion efficiency. Tests were done with approximately 35 L of unweathered Alaska North Slope oil within an outdoor, fresh water, 63 m3 tank. The combustion plume was sampled with a crane-suspended instrument system. Emission measurements quantified carbon monoxide, carbon dioxide, particulate matter less than 2.5 μm (PM2.5), and total carbon. Post-burn residue samples were collected with pre-weight oil absorbent to determining oil mass loss and total petroleum hydrocarbons (TPH) in the residue. Plume measurements of modified combustion efficiencies (MCET) ranged from 85% to 93%. Measurement of residual, unburnt oil showed that the oil mass loss ranged from 89% to 99%. A three-fold variation in PM2.5 emission factors was observed from the test conditions where the emission factors decreased with increased MCE. The TPH in the residue were found to decrease with increased oil mass loss percentage. In terms of combustion efficiency and oil consumption, results suggest that the most effective burns were those that have high length to width boom aspect ratios and added injection air.

Levels of total mercury were measured in tissue of six species of migratory fish (alewife, American shad, blueback herring, rainbow smelt, striped bass, and sea lamprey), and in roe of American shad for two consecutive years collected from the Penobscot River or its estuary. The resultant mercury levels were compared to reference doses as established in the U.S. Environmental Protection Agency (EPA) Integrated Risk Information System and wildlife values. Mercury concentrations ranged from 4 μg/kg ww in roe to 1040 μg/kg ww in sea lamprey. Sea lamprey contained the highest amounts of mercury for both seasons of sampling. Current health advisories are set at sufficient levels to protect fishers from harmful consumption of the fish for mercury alone, except for sea lamprey. Based upon published wildlife values for mink, otter, and eagle, consumption of rainbow smelt, striped bass, or sea lamprey poses a risk to mink; striped bass and sea lamprey to otter; and sea lamprey to eagle. For future consideration, the resultant data may serve as a reference point for both human health and wildlife risk assessments for the consumption of anadromous fish. U.S. EPA works with federally recognized Tribes across the nation greatly impacted by restrictions on sustenance fishing, to develop culturally sensitive risk assessments.

Chemical dispersant agents reduce the interfacial tension between oil and water, and increase the surface area to volume ratio of oil droplets thus facilitating the biodegradation of spilled oil. Dispersants are composed of surface active molecules known as surfactants and various commercial products contain Dioctyl Sulfosuccinate (DOSS) as the active surfactant ingredient. Since previous laboratory studies were conducted at oil and dispersant concentrations significantly higher (~0.7 g/L oil with Dispersant to Oil Ratio (DOR) of 1:25) than those typically found in field conditions, experiments were conducted at low levels of oil and dispersant (28 μg/L oil with DOR of 1:25) in order to determine the degradation trends at environmentally relevant concentrations. Experiments were conducted using two crude oils (Alaskan North Slope (ANS) and Endicott) and two dispersant products (Corexit 9500 and Finasol OSR 52) to study the biodegradation of dispersants and dispersed oil and oil alone samples were used as controls. Two oil degrading cultures, isolated from the surface (meso) and deep sea (cryo) of the Gulf of Mexico, were enriched on crude oil at 25 and 5 °C and were used as the inocula. The biodegradation experiments were performed at 5 °C for 56 days and at 25 °C for 48 days using sterile GP2 artificial seawater as the media. The time series concentration of DOSS, the primary surfactant in the dispersants was monitored using LC-MS/MS in addition to the oil concentration which was measured using GC-MS/MS. Although the initial concentration of DOSS in Finasol OSR 52 was 20% higher than in Corexit 9500, over 95% of the anionic surfactant fraction was metabolized for both types of dispersant products by the end of the experiment at 25 °C while it persisted at 5 °C. The effect of dispersant and oil type on microbial community structure was also analyzed using PCR analysis. Results indicated that the abundance of Thalassospira correlated well with hydrocarbon degradation trends. The results from this study significantly expands on our understanding of biodegradation of DOSS, dispersed, and non-dispersed oil and also provides information regarding bacterial community composition.

2017-271 In recent years, diluted bitumen (or dilbit) has become an important source of hydrocarbon-based fuel. While information on the degradation of crude oils has been well researched, dilbit degradation has been studied at a much lesser extent. The objective of this study was to compare biodegradation of dilbit with a conventional crude oil (CCO) under various conditions. Two different microcosm experiments were set up, one containing a mixed culture acclimated to dilbit (Kalamazoo River Enrichment, KRC) and the other having a mixed culture enriched on soil contaminated with hydrocarbons (Anderson Ferry Enrichment, AFC). The microcosms were run for 60 d at 25 °C and for 72 days at 5 °C in flasks containing sterile Bushnell Hass broth and naturally dispersed oil. Each flask was inoculated with the KRC and AFC mixed cultures, and rotated on an orbital shaker (200 rpm) at the above stated temperatures. On each sampling day, triplicates were sacrificed to determine the residual hydrocarbon concentration. Additionally, some samples were used to determine the bacterial composition using 16S rRNA gene sequencing analysis. Hydrocarbon analysis (alkanes and PAHs) was performed by gas chromatography/mass spectrometry (GC/MS/MS). Higher degradation rates were achieved at 25 °C as compared to 5 °C. All the enrichments metabolized CCO as well dilbit, but the nature and extent of the degradation was distinct. KRC meso culture was the most effective among all, as it completely removed alkanes and most of the PAHs. AFC enrichment performed differently at the two temperatures; an acclimation period (8 d) was observed at 5 °C while there was no lag at 25 °C. KRC cryo culture as well as AFC culture at both temperatures degraded alkanes completely while they were not able to metabolize heavier fractions of the oil (C2–4 homologues of 3- and 4-ring compounds). All cultures showed the presence of diverse oil degrading bacteria and the differences in their compositions affected the biodegradation. Although dilbit was biodegraded, for all the treatments except AFC at 5 °C, the rate of degradation and the extent of degradation was greater for CCO owing to the higher concentrations of lighter hydrocarbons.

A new laboratory testing protocol for evaluating effectiveness of solidifiers in removing crude oil slicks on the water surface has been developed by the U.S. Environmental Protection Agency (EPA). Since an assessment of a testing protocol requires validation through an inter laboratory study with several independent research partners, a round-robin test was performed by five operators across two laboratories. The protocol was qualitatively and quantitatively evaluated to determine if it can satisfactorily differentiate product effectiveness, while still accounting for experimental and operational errors. Each operator evaluated the efficiency of six solidifier products with Arabian Light, Endicott and IFO 120 crude oils. All the experiments were carried out in triplicates and, additionally, an oil alone control sample was run for quality control purposes. The five operators were provided with all the supplies required to conduct the experiment and a detailed standard operating procedure. The results were collected and analyzed statistically to quantify repeatability and reproducibility. The average repeatability and reproducibility standard deviations were 5.1, 2.7, and 3.3% and 11.2, 10.1, and 13.1% for Arabian Light, Endicott and IFO, respectively. The within-operator error was ≤ 5% regardless of operator and oil type. Due to the difficulty and uncertainty associated with the separation of the solidified and un-solidified mass, the between-operator error was around 10%. The oil alone control had an average repeatability and reproducibility standard deviation of 4.8 and 6.1%, respectively. The variability among operators was also examined with h-statistics and the differences in operator means were found to be statistically insignificant. The variability is deemed acceptable for purposes of differentiating effective from ineffective solidifier products in the laboratory. The results from this round robin experiment will serve as an initial screening tool for the solidifier products in the market and will also help response teams determine the desirability and appropriateness of using a specific solidifier for oil spill remediation.

To address knowledge gaps and the lack of benchmarks on the toxicity of dilbit oiled sediments, weathered Cold Lake Blend (CLB) and Western Canadian Select (WCS) were assessed in 10-day sediment tests with the amphipods Hyalella azteca and Leptocheirus plumulosus. Lowest observed effect concentrations (LOECs) and 20% effect levels (EC20s) were determined for wet weight sediment concentrations of TPH and total PAHs normalized to 1% organic carbon. LOECs and EC20s for TPH ranged from 216 to 1165 mg/kg sediment in H. azteca, and from 64 to 75 mg/kg sediment in L. plumulosus. Dilbit LOECs and EC20s for total PAHs ranged from 2.9 to 11.8 mg/kg sediment in H. azteca, and from 0.75 to 0.87 mg/kg in L. plumulosus. Comparison of toxicity-based benchmarks derived from the current study to sediment concentrations from past spills indicate that dilbit spills in aquatic habitats may pose substantial risks to freshwater and estuarine benthic organisms.

Chemical countermeasures for oil spill remediation have to be evaluated and approved by the U.S. Environmental Protection Agency before they may be used to remove or control oil discharges. Solidifiers are chemical agents that change oil from a liquid to a solid by immobilizing the oil and bonding the liquid into a solid carpet-like mass with minimal volume increase. Currently, they are listed as Miscellaneous Oil Spill Control Agent in the National Contingency Plan and there is no protocol for evaluating their effectiveness. An investigation was conducted to test the oil removal efficiency of solidifiers using three newly developed testing protocols. The protocols were qualitatively and quantitatively evaluated to determine if they can satisfactorily differentiate effective and mediocre products while still accounting for experimental error. The repeatability of the three protocols was 15.9, 5.1, and 2.7 %. The protocol with the best performance involved measuring the amount of free oil remaining in the water after the solidified product was removed using an ultraviolet–visible spectrophotometer and it was adopted to study the effect of solidifier-to-oil mass ratio, mixing energy, salinity, and beaker size (i.e., area affected by the spill) on solidifier efficiency. Analysis of Variances were performed on the data collected and results indicated that the beaker size increased spreading, which reduced removal efficiency. Mixing speed appears to impart a ceiling effect with no additional benefit provided by the highest level over the middle level. Salinity was found to be mostly an insignificant factor on performance.

The majority of aquatic toxicity data for petroleum products has been limited to a few intensively studied crude oils and Corexit chemical dispersants, and acute toxicity testing in two standard estuarine test species: mysids (Americamysis bahia) and inland silversides (Menidia beryllina). This study compared the toxicity of two chemical dispersants commonly stock piled for spill response (Corexit EC9500A®, Finasol®OSR 52), three less studied agents (Accell Clean®DWD dispersant; CytoSol® surface washing agent; Gelco200® solidifier), and three crude oils differing in hydrocarbon composition (Dorado, Endicott, Alaska North Slope). Consistent with listings on the U.S. National Contingency Plan Product Schedule, general rank order toxicity was greatest for dispersants and lowest for the solidifier. The results indicate that freshwater species can have similar sensitivity as the conventionally tested mysids and silversides, and that the sea urchin (Arbacia punctulata) appears to be a reasonable addition to increase taxa diversity in standardized oil agent testing.

Treatability experiments were conducted to determine the biodegradation of diluted bitumen (dilbit) at 5 and 25 °C for 72 and 60 days, respectively. Microbial consortia obtained from the Kalamazoo River Enbridge Energy spill site were enriched on dilbit at both 5 (cryo) and 25 (meso) oC. On every sampling day, triplicates were sacrificed and residual hydrocarbon concentrations (alkanes and polycyclic aromatic hydrocarbons) were determined by GC MS/MS. The composition and relative abundance of different bacterial groups were identified by 16S rRNA gene sequencing analysis. While some physicochemical differences were observed between the two dilbits, their biodegradation profiles were similar. The rates and extent of degradation were greater at 25 °C. Both consortia metabolized 99.9% of alkanes; however, the meso consortium was more effective at removing aromatics than the cryo consortium (97.5 vs 70%). Known hydrocarbon-degrading bacteria were present in both consortia (Pseudomonas, Rhodococcus, Hydrogenophaga, Parvibaculum, Arthrobacter, Acidovorax), although their relative abundances depended on the temperatures at which they were enriched. Regardless of the dilbit type, the microbial community structure significantly changed as a response to the diminishing hydrocarbon load. Our results demonstrate that dilbit can be effectively degraded by autochthonous microbial consortia from sites with recent exposure to dilbit contamination.

Temperature can play a significant role in the efficacy of solidifiers in removing oil slicks on water. We studied and quantified the effect of temperature on the performance of several solidifiers using 5 different types of oils under a newly developed testing protocol by conducting experiments in constant temperature rooms set at 22°C and 5°C. The results indicated that solidifier efficiency decreased substantially at the lower temperature, especially at lower application rates. The removal efficiency of the solidifier was in general directly proportional to temperature, except for the heavier oils, where removal by attachment was observed. Solidifier products with lower powder bulk density exhibited the best removal effectiveness. Analysis of experimental data yielded empirical correlations involving certain operational variables such as application rate, temperature, solidifier property (bulk density), and oil property (viscosity). Regression analysis was used to fit a mathematical model to the experimental solidifier effectiveness data.

A laboratory investigation was conducted to test the effectiveness of solidifiers with fresh water and artificial seawater using Prudhoe Bay Crude oil. Experiments were designed to study the effects of salinity, solidifier type, solidifier-to-oil mass ratio (SOR), mixing energy and beaker size using five solidifiers. The U.S. Environmental Protection Agency is developing a protocol for testing the effectiveness of solidifiers in a laboratory setting. This involves measuring the amount of free oil remaining in the water after the solidified product is removed using an ultraviolet–visible spectrophotometer. For these experiments, 0.25 mL of oil was added to salinized beaker containing 80 mL of water. Milli-Q water and sterile GP2 seawater were used as the exposure media. The mass of the solidifier was changed depending on the SOR. Each of the solidifier was added to a slick of crude oil on water. After stirring the mixture for 30 minutes, the solidifier was removed. The water with the remaining oil was transferred from the beaker to 250 mL separatory funnel. The solution in the funnel was extracted three times with 20 mL of dichloromethane and the final volume adjusted to 60 mL. The extracted samples were analyzed for oil content with an Agilent 8452 ultraviolet–visible spectrophotometer. All experiments were carried out in triplicate. An analysis of variance (ANOVA) was performed on the data collected, which helped quantify the main and interactive effects of the variables. Salinity of the water was mostly found to be an insignificant factor. Results indicated that SOR and solidifier type are the most important variables affecting removal efficiency.

The physical characteristics and chemical composition of oil spill solidifiers were studied, and correlation of these properties with product effectiveness enabled determination of characteristics that are desirable in a good solidifier. The analyses revealed that the commercial products were primarily comprised of organic polymers and a few trace elements. A natural sorbent, which was composed entirely of plant based matter, was also evaluated, and it had the highest oil removal capacity, but it did not produce a solid mat-like final product. Generally, solidifiers with a carbonate group, pore size greater than 5 μm, and bulk densities lower than 0.3 g cm(-3) were found to have better efficiency and produced a cohesive rubbery final product that facilitated removal compared to sorbents. The importance of bulk density and pore size in the performance of the solidifier suggest that the primary mechanism of action was likely physical sorption.