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1
Toxic Nature of Crude Oil
1.1 High Risk Areas
In general, spilled oil is most harmful when shallow, productive waters, porous sediments, low-energy aquatic environments, or special-use habitats are impacted. Examples of high-risk locations include wetlands, sheltered tidal flats, shallow bays, coarse sand and gravel beaches, and sites with concentrated reproductive and migratory activities.
1.2 Potential Impacts
The impacts on local shore regions from a crude oil spill can be economically devastating. There are impacts on the fishing and tourism industries, shipping, recreation, and property values, to mention a few. In addition to the economic impacts on the coastal communities, the environmental damages can be devastating to the local ecosystems. The BP Gulf oil spill threatens to destroy an entire ecosystem, a way of life that has existed for generations, and national treasures and can possibly have global implications. Recent computer models suggest that the ongoing spill is likely to contaminate the entire eastern shoreline and move on to the shores of foreign countries.
Crude oil and petroleum products vary in their toxicity, and the sensitivity of fish to petroleum varies according to species. The water-soluble fractions of crude oil can stunt fish growth. Negative impacts on fish are primarily seen in the eggs, larvae, and early juveniles, with varied effects on the adults.
The following are some negative impacts from oil spills:
- Pink salmon fry are affected by exposure to water-soluble fractions of crude oil, while pink salmon eggs are tolerant of benzene and water-soluble petroleum.
- Fish rapidly metabolize aromatic hydrocarbons due to their enzyme system.
- Depressed feeding, decreased swimming activity, and increased mortality occur in fish.
- The mortality of eggs and larvae increases (such as after the Argo Merchant No. 6 fuel oil discharge where 20% of the cod eggs and 46% of the Pollock eggs in the discharge zone were dead). During the Torrey Canyon (Bunker C) discharge, 90% of the pilchard eggs in the discharge area were killed. Following the Amoco Cadiz (crude oil) discharge, a one-year old class of flatfish was thought to have been reduced.
- Exclusion of fishermen from the fishing grounds and other disruptions of fishing can change the population balance to date (e.g., salmon over-escapement in Prince William Sound after the Exxon Valdez (crude oil) spill).
- The fouling of costly fishing gear during the spill can set the fisherman back even after the fishing restrictions are lifted.
- The tainting of fish (such as change in flavor or smell) and the publicās fear of tainting, mortality, or other effects of non-motile inshore species, such as rockfish, occurs.
- Mortality and the tainting of fish maintained in mari-culture enclosures, where the escape of fish is prevented, is common (e.g., the Braer oil discharge off the Shetlands affected salmon in mariculture enclosures).
- Sublethal effects occur, such as fin erosion, ulceration of the integument, liver damage, lesions in the olfactory tissue, reduced hatching success, reduced growth, change in egg buoyancy, malformations that inter-fere with feeding, arrest of cell division, and genetic damage.
- The oiling of feathers is considered to be the primary cause of most bird deaths following oil spills. Oil disrupts and destroys the fine strand structure of the feathers, resulting in the loss of water repellency and body insulation. As the oiled plumage becomes matted, water penetrates the feathers and chills the animalās body. The combined results are a loss of buoyancy and hypothermia. The natural response to oil matted plumage is preening, subsequent to which oiled birds ingest the oil while attempting to remove the petroleum from their feathers. The ingestion of petroleum results in anemia, pneumonia, kidney and liver damage, stunted growth, altered blood chemistry, and decreased egg production.
- Chicks are exposed to petroleum by ingesting food regurgitated by impacted adults, and they may also be poisoned.
- Recovery from the effects of oil spills on local populations of invertebrates can require up to 10 years depending on the type of oil, the circumstances of the spill, and the organisms affected. Invertebrates (zoo- plankton) in the water column of large bodies of water return to pre-spill conditions much faster than invertebrates in small bodies of water (fresh-water lakes, streams); however, this is a broad generalization.
- Gulls, storm petrels, and guillemots experience elevated corticosterone, thyroxin, and increased size of adrenal glands after ingesting a single dose of 0.1% (of diet) crude oil.
- Exposure to oil by birds has been shown to lead to changes in behavior that ultimately cause reduced reproductive success. Effects include cessation or delay of egg laying, increased nesting phenology, nest abandonment, reduced feeding of young, mate switching, interruption of courtship behavior, egg rejection, parental rejection of chicks, impairment of incubation behavior, and reduced nest attentiveness.
- Epifauna, such as mussels and bivalves, generally survive oiling as adults due to their protective shells, but they have no enzymatic system for purging. Therefore, bioaccumulation occurs, resulting in reduced feeding absorption efficiency followed by growth reductions.
- Oiling of chicks by the externally treated adult has been reported to result in the rejection of the chicks.
- Wedge-tailed shearwaters orally exposed to Santa Barbara crude oil had a laying and incubation frequency significantly lower than controls.
- Oil concentrations as low as 1 uL/egg (1.3% of the surface of a mallard egg) are toxic. This is attributed to a function of the aromatic component of crude oil rather than impaired gas exchange.
- Mallards that ingest crude oil experience delayed laying, decreased oviposition, and decreased shell thickness.
- The hatching success of herring and black-backed gull eggs decreased in response to 10 uL of crude or weathered crude oil applied externally to eggshells.
- Heron, tern, and brown pelican eggs experience reduced hatchability when oiled either directly or via the adultās feathers.
- Following the Santa Barbara oil spill, a large number of premature births were observed in sea lions.
Crude oil is toxic to humans. The industry downplays this and argues crude oil is of low toxicity to humans. Table 1.1 tabulates compositions of crude oil as reported on Material Safety Data Sheets from different suppliers. Crude oil contains both chemical toxins and carcinogens. Among the chemicals are benzene, toluene, ethylbenzene, xylene, polyaromatic hydrocarbons (PAHs), and toxic heavy metals not listed on MSDSs. While concentrations are low, when there is a spill of the magnitude of the Deepwater Horizon spill (the BP disaster of the Gulf) covering thousands of square miles of surface area, the volatile organic compounds (VOCs) rapidly evaporate accelerated by constant surface area renewal caused by waves. Personnel working on vessels that skim up the surface oil or combat the spill along shorelines and marshes are being exposed to carcinogens and other toxic chemical ingredients that are known teratogens, or systemic poisons, which are known to impair liver and kidney functions. Crude oils contain similar chemicals to coal tar pitch volatiles, or PAHs, which are a large family of toxic chemicals that are suspected and confirmed human carcinogens. When oil is burned at the surface in order to combat the spill, more carcinogenic PAHs are created as these are products of incomplete combustion.
Table 1.1 Compositions of Crude Oil Reported on various MSDSs
The toxicity of crude oil involves an incredibly complex mixture of inorganic and organic chemicals. There is uncertainty in the application of dose-response relationships based on crude oil as a whole mixture to both humans and aquatic life. A simplified approach to determining toxicity is an āindicator chemical approachā which involves selecting a subset of chemicals from the whole mixture that represents the āworst caseā in terms of mobility and toxicity. This approach has been used with crude oil with the subsets of chemicals being volatile organics such as benzene, toluene, ethyl-benzene, and xylenes (collectively referred to as BTEX) and polycy-clic aromatic hydrocarbons (PAHs).
The BTEX group is of significance because the chemicals in the family are soluble in water, highly mobile in the environment, and represent the more volatile and soluble components of crude oil. In addition, benzene is an EPA defined Class A carcinogen.
In contrast, PAHs are not highly mobile. These chemicals tend to have low solubility and vapor pressures (hence, they are referred to as semi-volatile organic chemicals or SVOCs) but they are of interest because they range from toxic to carcinogenic. These chemicals are prevalent in crude oil, representing the heavier or less volatile crude oil components. PAHs ...
