Enhanced marine monitoring and toxicity study of oil spill dispersants including Corexit EC9500A in the presence of diluted bitumen.

Observations made for the analysis of the oil spill dispersant tracer dioctyl sulfosuccinate (DOSS) during LC50 toxicity testing, highlighted a stability issue for this tracer compound in seawater. A liquid chromatography high-resolution quadrupole time-of-flight mass spectrometry (LC/QToF) was used to confirm monooctyl sulfosuccinate (MOSS) as the only significant DOSS breakdown product, and not the related isomer, 4-(2-ethylhexyl) 2-sulfobutanedioate. Combined analysis of DOSS and MOSS was shown to be applicable to monitoring of spill dispersants Corexit® EC9500A, Finasol OSR52, Slickgone NS, and Slickgone EW. The unassisted conversion of DOSS to MOSS occurred in all four oil spill dispersants solubilized in seawater, although differences were noted in the rate of MOSS formation. A marine microcosm study of Corexit EC9500A, the formulation most rapid to form MOSS, provided further evidence of the stoichiometric conversion of DOSS to MOSS under conditions relevant to real world dilbit spill. Results supported combined DOSS and MOSS analysis for the monitoring of spill dispersant in a marine environment, with a significant extension of sample collection time by 10 days or longer in cooler conditions. Implications of the unassisted formation of MOSS and combined DOSS:MOSS analysis are discussed in relation to improving dispersant LC50 toxicity studies.

Improved oil spill dispersant monitoring in seawater using dual tracers: Dioctyl and monoctyl sulfosuccinates sourced from corexit EC9500A.

A high resolution mass spectrometry method was developed for the environmental impact monitoring of oil spill dispersants. Previously reported instability of dioctyl sulfosuccinate (DOSS) dispersant tracer was addressed by the new procedure. The method monitors both DOSS and its degradation product, monooctyl sulfosuccinate (MOSS), by liquid chromatography time-of-flight mass spectrometry. The related isomer, 4-(2-ethylhexyl) 2-sulfobutanedioate, was chromatographically resolved from MOSS but was not a product of DOSS degradation. Using this direct injection method (10 µL), the practical lower limit of quantitation was 0.5 nM for each analyte, a concentration equivalent to 0.22 ng mL-1, or 0.30 ng mL-1 including initial dilution factor with acetonitrile. The method was shown applicable to analysis of the dispersants Corexit® EC9500 A, Finasol OSR 52, Slickgone NS, and Slickgone EW for which DOSS is an active ingredient. A marine microcosm study of Corexit EC9500A, together with diluted bitumen (dilbit), at 15 ± 1 °C, provided evidence of the stoichiometric conversion of DOSS to MOSS under conditions reflecting a western Canadian marine environment. The advantage of the developed method is in its ability to extend environmental seawater sample collection time from 4 days for DOSS alone, to 14 days when both DOSS and MOSS are simultaneously analysed and results combined. The collection time is likely extended beyond the 14 day period with cooler temperatures. Preservation of collected seawater samples using sodium hydroxide, converting DOSS into MOSS in situ, was rejected due to stability issues. Addition of disodium ethylenediaminetetraacetic acid did not improve hold times, thus eliminating the theory of cation induced micelle effects causing DOSS loss.

Acute toxicity of Corexit EC9500A and assessment of dioctyl sulfosuccinate as an indicator for monitoring four oil dispersants applied to diluted bitumen.

The present study investigated oil dispersant toxicity to fish species typical of the cooler regions of Canada, together with less well-documented issues pertaining to oil dispersant monitoring. The oil dispersant toxicity of Corexit EC9500A was assessed for the freshwater fish species rainbow trout and the seawater species coho, chinook, and chum, with a final median lethal concentration (LC50) acute lethality range between 35.3 and 59.8 mg/L. The LC50 range was calculated using confirmed 0-h dispersant concentrations that were justified by fish mortality within the first 24 h of exposure and by variability of the dispersant indicator dioctyl sulfosuccinate (DOSS) used to monitor concentrations at later time points. To investigate DOSS as an oil dispersant indicator in the environment, microcosm systems were prepared containing Corexit EC9500A, Finasol OSR52, Slickgone NS, and Slickgone EW dispersants together with diluted bitumen. The DOSS indicator recovery was found to be stable for up to 13 d at 5 °C, 8 d at 10 °C, but significantly less than 8 d at ≥15 °C. After 3 d at temperatures ≥15 °C, the DOSS indicator recovery became less accurate and was dependent on multiple environmental factors including temperature, microbial activity, and aeration, with potential for loss of solvents and stabilizers. A final assessment determined DOSS to be a discrepant indicator for long-term monitoring of oil dispersant in seawater. Environ Toxicol Chem 2018;37:1309-1319. © 2018 SETAC.