Mesocosm Scale Evaluation of Dispersant Effectiveness and Toxicity

1. Mesocosm Scale Evaluation of Dispersant Effectiveness and Toxicity Kenneth Lee, Kats Haya, Les Burridge, Simon Courtenay, Zhengkai Li Fisheries and Oceans Canada Peter Hodson Queens University Michel C. Boufadel Temple University Albert D. Venosa US Environmental Protection Agency

2. Rational • For ecological relevance, the replication of natural sea-state conditions and knowledge of environmental factors is essential for oil dispersant studies. • National Research Council (NRC) Committee on Understanding Oil Spill Dispersants: Efficacy and Effects (2005) identified three factors to be addressed in oil dispersant efficacy studies: • Energy Dissipation Rate • Particle Size Distribution • Toxicity • To address these specific issues, a wave tank facility was constructed at the Bedford Institute of Oceanography, Nova Scotia Canada

3. Wave Conditions (a) (b) • Regular Non-breaking • Spilling Breaking • Plunging Breaking (c)

4. Factorial Experimental Designfor Dispersant Effectiveness Evaluation • Factors: • Dispersants: Water (control), Corexit 9500, SPC 1000 • Waves: regular non-breaking wave, spilling breaker, plunging breaker • Oil types: Mediun South American (MESA), Alaska North Slope (ANS) • Effectiveness indicators: • Oil concentration • Droplet size distribution • Analytical methods • Ultraviolet Spetrophotometry • Ultraviolet Fluorometry • Laser In-Situ Scattering and Transiometry • Epi-fuorescent microscopy

5. Flap-type wave maker Wave absorbers 5 70 200 70 1500 2000 125 4000 8000 200 200 3200 Locations for UVS samplers Locations for laser particle counter Dimension in cm; not to scale Sampling Locations

6. Energy Dissipation Rates

7. Physical Dispersion

8. Chemical Dispersion

9. Droplet Size Distribution

10. Dispersant Effectiveness of ANS • Higher levels of chemical DE was observed for Corexit 9500 at the two high ε • High DE was also achieved for SPC1000 at high ε • Fresh ANS appears to be more readily dispersible than the weathered MESA crude,

11. Dispersant Effectiveness • Chemical dispersion has DE significantly higher than physical dispersion • Spilling and plunging breakers increased dispersant effectiveness • Dispersion kinetics data demonstrate the change of the dispersed oil droplet size distribution as a function of time • Corexit 9500 dispersed MESA and ANS to <70 μm at high ε at t=3min, and to <50 μm at 2 h at all three ε • SPC 1000 needs higher ε to disperse MESA than ANS to smaller droplets • The droplet size distribution of chemically dispersed oil has a larger number of small droplets (less than 10 um) compared to the physically dispersed oil droplets.

12. Toxicity • Despite test results that show effective dispersion at sea, authorization and guidance for the use of these products is suppressed by concerns over biological effects on commercial species of fish from exposure to low concentrations of oil • A key recommendation of National Research Council of the National Academy of Science was “Quantitative assessment of toxicological impacts from dispersed oil in the water column”

13. System Modification for Continuous Flow Studies • A “flow-through” system will allow simulation of natural exposure levels that result from dilution of dispersed oil in an open environment influenced by both tides and currents • Operation in a flow-through mode will provide a controlled environment to study: • Dissolution and uptake kinetics of toxic components as a function of oil type and environmental conditions (including influence of SPM) • The influence of exposure time and wave- and current-driven hydrodynamic regime with mixture and dilution • Environmental persistence (biodegradation of dispersed oil)

14. Flow-through Wave Tank Facilities

15. Mode of Action • Toxicity of oils to fish is correlated to the concentration of alkyl-substituted-polynuclear aromatic hydrocarbons (PAH) in the water accommodated fraction (WAF) of oil • Low molecular weight (LMW) hydrocarbons, such as BTEX, napthalenes, and C1-C12 aliphatics are acutely toxic by narcosis, they do not contribute to chronic toxicity because they are highly volatile and readily diluted in water • High molecular weight (HMW) hydrocarbons such as waxes, resins and asphaltenes, are too large to be accumulated to toxic concentrations • Difference in toxicity between WAF and CEWAF is likely due to the effect of dispersion on the solubilization of oil.

16. 2008 – 2009 Objectives • Compare the biological responses of selective marine organisms to environmentally relevant time of exposure and concentrations of dispersed and non-dispersed oil • The sequence of tasks will be: • lethality tests (acute toxicity tests - LC50) • Sublethal dose response tests • Identification of sensitive endpoints based on relevant exposure times The information generated will improve the capacity of on site spill managers to gauge the risks associated with dispersant applications and contribute to optimal control strategies

17. Test Species • Multi-endpoint toxicity analysis on commercially important marine finfish: • Atlantic salmon smolts (Salmo salar) • Juvenile cod (Gadus morhua) • Evaluate the toxicity of dispersed oil to function of developmental stage, exposure time, and dispersed oil concentration. • Atlantic herring embryos (Clupea harengus) • The results will define the critical exposure windows for the greatest and least toxicity, and provide statistical models describing the relationship between exposure time and concentrations of dispersed oil causing lethal and sublethal effects • Shrimp (Pandalus sp. or Crangon sp.) depending on availability from local live harvesting in winter) will be used as a sensitive indicator of invertebrates in the acute lethality tests

18. Toxicity Endpoints