Combustion of crude oil during in-situ burning can introduce polycyclic aromatic compounds (PACs) into small-scale freshwater systems.

In-situ burning (ISB) is the controlled combustion of an oil slick to remove large quantities of spilled oil from the aquatic environment. Prior to employing ISB as a remediation technique, an oil slick must often be corralled by physical or chemical means to achieve a sufficient thickness (typically >1 mm) for ignition. While ISB is an effective means to remove oil mass, less is known about the potential for ISB to mobilize polycyclic aromatic compounds (PACs) into the aquatic environment. The PACs are primary contaminants of concern in crude oil due to their environmental persistence and toxicity. We examined the potential for ISB to mobilize PACs into underlying waters in a series of small-scale burns conducted across a gradient of oil slick thicknesses (0-7 mm). Concentrations of PACs in underlying waters were evaluated and compared to reference conditions using an equivalent gradient of oil slick thicknesses that were not ignited. At thinner slick thicknesses (i.e. 0 - 4 mm) ISB enhanced the mobilization of total PACs, likely a result of heat transfer to underlying waters; this effect increased as slick thickness increased. Among thicker slicks (i.e. 4 - 7 mm), pyrogenic PACs became more prevalent and greater concentrations of 4-ring PACs were detected in underlying waters. The potential for PAC mobilization needs to be considered in scenarios where ISB may be the only viable oil spill remediation option (e.g. wetlands, marshes, or where oil is entrained) and in shallow systems susceptible to temperature changes.

Simulating diluted bitumen spills in boreal lake limnocorrals - Part 1: Experimental design and responses of hydrocarbons, metals, and water quality parameters.

Large-scale, in-lake enclosures (limnocorrals) were used to simulate spills of diluted bitumen (dilbit) in a boreal lake. In this study we use these simulated spills, which covered a range of sizes (oil:water ratio) representative of the upper 25% of onshore crude oil spills in North America (2008-2019), to assess the fate of dilbit-derived hydrocarbons and metals as well as the impacts of the spills on standard water quality parameters. The systems were monitored over 70 days following the application of dilbit amounts ranging between 1.5 and 179.8 L into 10-m diameter, ~100 m3 limnocorrals. The concentration of total petroleum hydrocarbons (TPH) in the water column increased rapidly over the first two weeks reaching a plateau that ranged between 200 µg/L and 2200 µg/L for the lowest and highest treatment respectively. The concentration of total polycyclic aromatic compounds (PACs) also increased over the first two weeks, prior to a slow decrease until day 70. The maximum measured concentrations in the highest treatment were 2858 ng/L for the sum of all 46 quantified PACs, 2716 ng/L for alkylated PACs and 154 ng/L for the 16 EPA priority PAHs. The concentrations of PACs in the sediment increased continuously over the study in the three highest treatments with maximum observed concentrations of 189 ng/g for ΣPAC46, 169 ng/g for ΣPACalk. No significant treatment-related changes in the 16 EPA priority PAHs were observed in the sediment. Of the 25 metals quantified in the water column, only manganese, molybdenum, and vanadium displayed a significant treatment effect with increases of 280, 76 and 25% respectively in the total fraction. These results can help us understand and predict the fate of oil-derived contaminants following a spill and characterize the exposure of freshwater organisms living within them. These results should help inform the risk assessment of future dilbit transportation projects.

Surface-Dwelling Aquatic Insects in Low-Energy Freshwater Environments Are Highly Impacted by Oil Spills and the Surface Washing Agent Corexit EC9580A Used in Oil Spill Response.

Physical impacts of diluted bitumen (dilbit) and the application of surface washing agents (SWAs) in freshwater have not been characterized for aquatic invertebrates. These compounds are known to reduce surface tension in feather and fur microstructures of birds and mammals, and are thus likely to affect the buoyancy of surface-dwelling aquatic insects. We evaluated impacts of fresh dilbit and a SWA on water striders (Metrobates sp.), which are surface-dwelling organisms that rely on fine-hair microstructures to remain buoyant. We report nominal sheen thickness values that cause 50% immobility in 48 h as determined from exposure studies in outdoor tanks. A comparison of our data with those from historic oil spill volumes in Canada and the United States in the past 12 yr indicates that our reported nominal sheen thicknesses could have been reached or exceeded in 99% of historic spills when scaled to a small reference lake. The addition of Corexit EC9580A, a SWA approved for marine use in Canada, led to 100% immobility in striders within minutes, both in combination with oil and alone. Our study reveals an acute sensitivity to Corexit EC9580A and dilbit by surface-dwelling insects and may be driven by disruption of mechanisms of buoyancy. We highlight a need to evaluate physical impacts, typically excluded from standard toxicity testing, within the context of spill impact mitigation assessments. Environ Toxicol Chem 2021;40:1298-1307. © 2020 SETAC.

Toxicity of Cúspide 480SL® spray mixture formulation of glyphosate to aquatic organisms.

In 2011, an alternative formulation of glyphosate (Cúspide 480SL®) was chosen to replace Roundup-SL®, Fuete-SL®, and Gly-41® for the control of Erythroxylum coca, the source of cocaine, in Colombia. Cúspide 480SL contains the active ingredient glyphosate isopropylamine (IPA) salt, which is the same active ingredient used in previous formulations. However, Cúspide 480SL contains an alkyl polyglycoside surfactant rather than the polyethoxylated tallow amine (POEA) surfactant used in other formulations and known to be more toxic to nonprimary producing aquatic organisms than glyphosate itself. An adjuvant, Cosmo-Flux F411, and water also are added to the spray mixture before application. Aquatic ecosystems adjacent to the target coca fields might be exposed to the spray mix, placing aquatic organisms at risk. Because no toxicity data were available for spray mixture on aquatic organisms, acute toxicity tests were conducted on aquatic plants, invertebrates, and fish, by using the Cúspide 480SL spray mix as described on the label. Based on the median effective concentration (EC50) values for similar organisms, the spray mixture was less toxic to aquatic organisms than formulations previously used for the control of coca (i.e., Roundup-SL, Fuete-SL, and Gly-41). A physical effect induced by Cosmo-Flux F411 was observed in Daphnia magna, Ceriodaphnia dubia, and Hyalella azteca, causing the invertebrates to be trapped in an oily film that was present at the surface of the water. However, a hazard assessment for the Cúspide 480SL spray mix, using estimated worst-case exposure scenario concentrations and EC50 values from the toxicity tests, indicated de minimis hazard for the tested aquatic animals, with hazard quotients all <<1.