Sunken wrecks containing fuel oils pose significant environmental and human health threats
Recent research and lines of evidence suggest that oil in submerged wrecks poses a greater toxic threat, once liberated, compared to background pollution in urban waterways like San Francisco Bay. Despite myriad other pollutant inputs in an urban environment like the Bay, liberated oil from makes a difference, locally, to human health and the aquatic environment.
Following the M/V Cosco Busan incident in 2007, acute toxicity of the spilled oil (Bunker C: Intermediate Fuel Oil) was observed based on evidence of sublethal cardiac effects (i.e., arrhythmia, edema) in herring embryos incubated near oiled shorelines. Significant increases in bradycardia and pericardial edema were observed in caged embryos from oiled sites relative to nonoiled locations. Further, natural spawn from oiled intertidal zones demonstrated tissue necrosis and high rates of morphological abnormalities and lethality when exposed to spilled oil in San Francisco Bay compared to non-spill impacted areas. Researchers demonstrated that this toxicity was due to the Poly Aromatic Hydrocarbon (PAH) fraction of the oil and its environmental fate (Incardona et al. 2012 in The Proceedings of the National Academies of Sciences).
Appreciable concentrations of PAHs are present in residual fuels because of the common practice of using both uncracked and cracked residues in their manufacture. The following table lists the concentrations of three- to five-ring aromatics determined in one sample of No. 6 fuel oil:
|Expected Concentration of known PAHs in No. 6 Fuel Oil in ppm (Phototoxicity Class: H,M,L)|
|Phenanthrene – 482 ppm (L)||Chrysene – 196 ppm (M – NOAA SQuiRT 0.3 ppm)|
|2-Methylphenanthrene – 828 ppm||Triphenylene – 31 ppm (L)|
|1-Methylphenanthrene – 43 ppm||Benzo(a)pyrene – 44 ppm (H – SQuiRT 0.3 ppm)|
|Fluoranthene – 240 ppm (H)||Benzo(e)pyrene – 10 ppm (H)|
|Pyrene – 23 ppm (H – NOAA SQuiRT 0.3 ppm)||Perylene – 22 ppm (H)|
|Benz(a)anthracene – 90 ppm (SQuiRT 0.3 ppm) (H)||Octanol/Water Log: 3.3 to 7.06|
(from Irwin et al. 1997)
Significant amounts of fuel oil have been identified in the “Respect” by EPA contract divers including fuel tanks (as much as 500 gallons total storage), oil sheen in the ship compartments, and heavily oiled sediments on board and ultimately in EPA’s land-based sediment settling tank system. Fuel oil in the “Respect” is likely to be similar in original chemical makeup (also in part, Bunker C) to the M/V Cosco Busan’s fuel oil. The Respect sank in the same year as the M/V Cosco Busan spill, also in the San Francisco Bay.
In the hull of a submerged wreck such as the “Respect”, Bunker C fuel oil is likely to be subject to anaerobic, bacterially mitigated, processes. Anaerobic substitution reactions, for example with sulfur compounds could increase concentrations of toxic PAHs in the oil mixture. These reactions within the submerged oil result in a multitude of toxic PAHs in the oil mixture (e.g., dibenzothiophenes which may demonstrate Microtox toxicity). These reactions also change the physical properties of the oil perhaps increasing solubility of oil fractions. Conversely typical “weathering” from solublization, hydrolysis, and evaporation, commonly observed and understood from surface oil spills is likely not to occur.
Many PAHs are phototoxic (or activated in sunlight) and phytotoxic
Many PAHs are known human carcinogens over chronic, long duration exposures. Following a small, or periodic, oil release in Oakland Estuary, a common boating and fishing area, short term exposures could result in dermatitis, erythema and skin burns as well as eye irritation. These are symptoms are exacerbated by sunlight and may be pre-cancerous (ATSDR 2009). Similarly food species may become contaminated locally by the PAH fraction of spilled oil (Klasing 2013).
PAHs are phototoxic and concentrations have been shown in shallow tidal areas of San Francisco Bay, co-located with impacted herring (Incardona et al. 2012). Aquatic toxic effects similar to the herring exposures may be realized by State and Federal Endangered and Threatened fish species such as the Green Sturgeon and Salmon, especially in juveniles as these species are found in the Oakland Estuary and environs.
Almeda et al. also demonstrated that UV radiation plays an important role in the toxicity of crude oil aquatic life. UV radiation may increase the toxicity of spilled oil by 2- to 50,000-fold due to the photosensitization and/or photomodification of the PAH fraction. These processes impose toxic stress to zooplankton in particular due to the fact that these organisms are translucent/transparent and frequently live in the upper water column where elevated UV radiation is present (Almeda et al. 2013). Similarly PAHs threaten the health of Essential Fish Habitat, especially sub-tidal Eel grass beds, within the central San Francisco and San Leandro Bays.
Almeda, Rodrigo et al. 2013. Effects of Crude Oil Exposure on Bioaccumulation of Polycycl
ic Aromatic Hydrocarbons and Survival of Adult and Larval Stages of Gelatinous Zooplankton. PLoS ONE 8(10): e74476. doi:10.1371/journal.pone.0074476.
Incardona, John et al. 2012. Unexpectedly high mortality in Pacific herring embryos exposed to the 2007 Cosco Busan oil spill in San Francisco Bay. Proceedings of the National Academy of Sciences.
Irwin, Roy et al. 1997. Environmental Contaminants Encyclopedia Fuel Oil Number 6Entry. National Park Service.
Klasing, Susan et al. 2013. Protocol for Risk Assessment to Support Fisheries Re-opening Decisions for Marine Oil Spills in California. Office of Environmental Health Hazard Assessment, California Environmental Protection Agency.
Prepared by Harry L. Allen, MS and Harry Allen Ph.D.; Photos by Todd Thalhamer