**3. Crude oil and its properties**

Crude oil is a complex mixture of organic compounds. These mainly consist of hydrocarbons, in addition to heterocyclic compounds and some heavy metals. The different hydrocarbons that make up crude oil come in a wide range of molecular weights and structure compounds. These compounds include methane gas, high molecular weight tars, asphaltenes, resins, waxes and bitumens. They also include straight and branched chains, single or condensed rings and aromatic rings such as the monocyclic (benzene, toluene, ethylbenzene and xylene). They additionally include polycyclic aromatic hydrocarbons (PAHs) such as naphthalene, anthra‐ cene and phenanthrene. Examples of the chemical structure of some common components of crude petroleum are shown in Figure 2.

#### **3.1. Toxicity of oil**

During the 1990s, the average number of large spills per year was about a third of the amount that was witnessed during the 1970s. When looking at the quantities of oil spilled, it should be noted that 1, 133, 000, 213, 000 tonnes of oil were lost in the 1990s and 2000s, respectively. In a four-year period, 2010-2013, there were 22,000 tonnes of oil lost. Table 2 shows a brief

**Ship name Year Location Spill (103**

Torrey Canyon 1967 Scilly Isles, UK 119 Sea Star 1972 Gulf of Oman 115 Jakob Maersk 1975 Oporto, Portugal 88 Urquiola 1976 La Coruna, Spain 100 Hawaiian Patriot 1977 300 nautical. miles off Honolulu 95 Amoco Cadiz 1978 Off Brittany, France 223 Atlantic Empress 1979 Off Tobago, West Indies 287 Independenta 1979 Bosphorus, Turkey 94 Irenes Serenade 1980 Navarino Bay, Greece 100 Castillo de Bellver 1983 Off Saldanha Bay, South Africa 252 Novo 1985 Off Kharg Island, Iran 70 Odyssey 1988 700 nautical. miles off Nova Scotia, Canada 132 Khark 5 1989 120 nautical. miles off Atlantic coast of Morocco 70 Exxon Valdez 1989 Prince William Sound, Alaska, USA 37 ABT Summer 1991 700 nautical miles off Angola 260 Haven 1991 Genoa, Italy 144 Aegean Sea 1992 La Coruna, Spain 74 Katina P. 1992 Off Maputo, Mozambique 67 Braer 1993 Shetland Islands, UK 85 Sea Empress 1996 Milford Haven, UK 72 Prestige 2002 Off Galicia, Spain 63 Hebel Spirit 2007 South Korea 11

 **) tonnes**

summary of the top 22 major oil spills since 1967.

80 Emerging Pollutants in the Environment - Current and Further Implications

**Table 2.** Top 22 major oil spills since 1967 (http://www.itopf.com/stats.html).

marine environment was considered as the largest in history.

The BP Deepwater Horizon (DWH) oil spill on 20th April, 2010, initiated the discharge of more than 2.6 million gallons (over 800 million litres) of oil into the Gulf of Mexico (Figure 1) over approximately three months. This oil spill was the second largest in human history [19-21]. During the 1991 Gulf War, the deliberate release of over 6 million barrels of oil [22] into the

The general effects of oil toxicity depend on a multitude of factors. These include the oil composition and characteristics (physical and chemical), condition (i.e., weathered or not), exposure routes and regimen, and the bioavailability of the oil [24]. One major effect of oil is

**Figure 2.** Structure of selected components of petroleum [13].

narcosis, a reversible anaesthetic effect caused by the oil partitioning into the cell membrane and nervous tissue. This causes dysfunctions of the central nervous system [25].

The additive toxic effect of hydrocarbons can lead to mortality, if the levels exceed the threshold concentration [24]. When oil hydrocarbons are ingested by marine animals, they travel to the liver where enzymes activate PAHs to become more toxic and reactive products. The metab‐ olites of polycyclic aromatic hydrocarbons (PAHs) and aliphatic hydrocarbons can be highly toxic and carcinogenic [26]. In particular, PAHs are the major contributors to toxicity, with different metabolic pathways producing metabolites. These have oxidative and carcinogenic properties due to their ability to attack and bind to DNA and proteins [24]. Hydrocarbons have a volatile nature and, therefore, inhalation of them results in respiratory tract irritation and narcosis of mammals and birds.

Physical contact is the major route of exposure and usually affects birds and furred mammals. These animals rely on their outer coats for buoyancy and warmth. Consequently, they often succumb to hypothermia, drowning and smothering when oil flattens and adheres to the outer layer [24]. A second general exposure route is through the ingestion or inhalation of the hydrocarbon by organisms that reside on the surface [24]. Exposure by these routes leads to absorption into the bloodstream via the gastrointestinal or respiratory tracts.

#### **3.2. Toxicity of oil dispersants**

narcosis, a reversible anaesthetic effect caused by the oil partitioning into the cell membrane

The additive toxic effect of hydrocarbons can lead to mortality, if the levels exceed the threshold concentration [24]. When oil hydrocarbons are ingested by marine animals, they travel to the liver where enzymes activate PAHs to become more toxic and reactive products. The metab‐ olites of polycyclic aromatic hydrocarbons (PAHs) and aliphatic hydrocarbons can be highly toxic and carcinogenic [26]. In particular, PAHs are the major contributors to toxicity, with different metabolic pathways producing metabolites. These have oxidative and carcinogenic properties due to their ability to attack and bind to DNA and proteins [24]. Hydrocarbons have a volatile nature and, therefore, inhalation of them results in respiratory tract irritation and

and nervous tissue. This causes dysfunctions of the central nervous system [25].

narcosis of mammals and birds.

**Figure 2.** Structure of selected components of petroleum [13].

82 Emerging Pollutants in the Environment - Current and Further Implications

Oil dispersants (57 chemical ingredients approved for use by the US EPA) are a common tool used after oil spills in marine environments. They break up oil slicks on the water surface and increase the oil's rate of biodegradation. Oil dispersants are quickly used when other means, such as oil containment and removal, are insufficient. However, consequences of the toxicity of oil spill dispersants alone or in the presence of oil must be evaluated. Generally, undispersed oil poses the greatest threat to shorelines and surface dwelling organisms. However, most dispersed oil remains in the water column where it mainly threatens pelagic and benthic organisms [27]. A complete and updated list of used oil dispersant is available from the US EPA at the website http://www2.epa.gov/emergency-response/alphabetical-list-ncp-productschedule-products-available-use-during-oil-spill.

Several studies have compared the toxicity of oil spill dispersants alone or in the presence of oil. Analyses of tests conducted on a variety of species of aquatic life showed that crustaceans are more sensitive to oil dispersant exposure, compared with fish [28]. A study by [29] indicated that the species with the least amount of protective shell or external tissue is the most sensitive to oil dispersant exposure.

It has been shown that the use of oil dispersants increases the exposure and uptake of PAHs by fish. This is particularly the case with fish that live throughout the water column of coastal areas, the ocean and lakes. Researchers found that 'the risk of PAH toxicity... especially to sensitive life stages, such as eggs and larvae, is enhanced by chemical dispersion' [30]. In addition, 'concentrations of LMWPAHs and HMWPAHs (low and high molecular weight PAHs) were found to be higher in the water column following the application of chemical dispersants to the surface slicks' [31]. 'For example, see [31]'. They reported that chemical dispersants mobilize PAHs to toxic concentrations as the biomarker ethoxyresorufin-Odeethylase (EROD) activity is increased after exposing newly-hatched mummichog (*Fundu‐ lus heteroclitus*) for 96 h to crude oil and chemically dispersed crude oil.

Reference [29] compared the toxicity of a new dispersant, Superdispersant-25 (SD-25), to Corexit 9527 using four species of marine invertebrates at 15 C. The most sensitive species was the snakelocks anemone *Anemonia viridis* with a 48-hour LOEC of 20 ppm (nominal). This was followed by mussel (*Mytilus edulis*) feeding rate (50 ppm), seagrass (*Zostera marina*) photo synthetic index (80 ppm), burrowing amphipod (*Corophium volutator*) (mortality 175 ppm) and mussel lethality (250 ppm).

Moreover, in a study by [32], adults of four species of wild-caught Newfoundland nearshore fishes were exposed for four days in flow-thru conditions to the dispersant Corexit 9527 alone, water accommodated fraction (WAF) of Hibernia light crude oil alone and dispersed Hibernia crude oil. Test toxicants (20 to 50 ml) were added daily to 300 L tanks for four days, followed by up to six weeks in clean water. The investigators did not report exposure temperatures or toxicant concentrations except to note that initial daily concentrations were 50-100 ppb for Hibernia water-accommodated fraction (WAF). On the first day, the caplein responded to the dispersant by swimming erratically. On the second and subsequent days, they responded by death accompanied by hemorrhaging of the gill lamellae.
