The Basics of Oil Spill Cleanup - Chapter 13

CHAPTER 13 Effects of Oil Spills on the Environment Oil spills have many adverse effects on the environment. Oiled birds are one frequent and highly publicized outcome of oil spills, but there are many other less obvious effects such as the loss of phytoplankton and other microscopic forms of life. These effects are varied and influenced by a number of factors. This chapter reviews the effects of oil on the environment and touches on how damage from oil spills is assessed. Before discussing the actual effects of an oil spill on various elements of the environment such as birds and fish, the types of effects will be discussed. Toxic effects are classified as chronic or acute, which refers to the rate of effect of toxin on an organism. Acute means toxic effects occur within a short period of exposure in relation to the life span of the organism. For example, acute toxicity to fish could be an effect observed within 4 days of a test. The toxic effect is induced and observable within a short time compared to the life span of the fish. Chronic means occurring during a relatively long period, usually 10% or more of the life span of the organism. It might take a significant portion of the life span for a chronic toxic effect to be observable, although it could have been induced by exposure to a substance that was normally acutely toxic. Chronic toxicity refers to long-term effects that are usually related to changes in such things as metabolism, growth, reproduction, or ability to survive. The effects of exposure to a toxic substance can be lethal or sublethal. Lethal exposure is often described in terms of the concentration of the toxicant that causes death to 50% of a test population of the species within a specified period of exposure time. This is referred to as the LC50. For example, tests of the effects of various crude oils on Daphnia magna, the water flea, show that 5 to 40 mg/L of the oil for a period of 24 hours is lethally toxic. The units of milligrams/litre (mg/L) are approximately equivalent to parts-per-million (ppm). Sublethal means detrimental to the test organism, but below the level that directly causes death within the test period. For example, it has been found that a concentration of 2 ppm of crude oil ©2000 by CRC Press LLC Photo 137 Heavily oiled birds, such as this one, have little chance of survival. (Environment Canada) in water causes disorientation in Daphnia magna when the organism is exposed for 48 hours. Oil can affect animals in many ways, including changing their reproductive and feeding behaviour and causing tainting and loss of habitat. Oiling of more highly developed animals such as birds may result in behavioral changes, such as failure to take care of their nests, resulting in the loss of eggs. Even a light oiling can cause some species of birds to stop laying eggs altogether. Feeding behaviour might also change. Seals sometimes react to oiling by not eating, which compounds the negative effects of the oil. The loss of an organism’s habitat due to oiling can be as harmful as direct oiling because alternative habitats may not be available and the animal can perish from exposure or starvation. ©2000 by CRC Press LLC Finally, tainting becomes an issue with fish and shell fish after an oil spill. Tainting occurs when the organism takes in enough hydrocarbons to cause an unpleasant, oily taste in the flesh. These organisms are unsuitable for human con-sumption until this taste disappears, which could take up to a year after the spill. After an oil spill, food species in the area are often tested using both chemical methods and a taste panel and the area is sometimes closed to commercial fishing as a precaution. Oil can enter organisms by several exposure routes: physical exposure, ingestion, absorption, and through the food chain. Animals or birds can come into direct contact with oil on the surface of water, on shorelines, or on land. The effects from this form of exposure are usually quite different than the effects of direct ingestion. Ingestion occurs when an organism directly consumes oil, usually by accident as in the case of birds when oil is ingested as they preen or groom their feathers. Absorption of volatile components of oil is a common method of exposure, especially for plants and sessile (immobile) organisms, although it also occurs in birds and mammals. Fresh crude oil has a relative abundance of volatile compounds such as benzene and toluene that are readily absorbed through the skin or plant membrane and are toxic to the organism. After a spill, organisms can also be exposed to oil that passes through several organisms via the food chain. Bioaccumulation, the accumulation of toxins in the flesh, rarely occurs since the components of oil are generally metabolized by the receiving organism. The effects of oil on the flora and fauna of a region are influenced by many factors, including the sensitivity of an organism, its recovery potential, its tendency to avoid an oil spill, its potential for rehabilitation, and the particular life stage of the organism. Sensitivity describes how prone an organism is to the oil and any effects. It varies with such factors as species, season, and weather conditions. Often sensitivity maps used by spill cleanup crews include information on the vulnerability of local species to oil spills. Recovery potential refers to the ability of organisms or ecosystems to return to their original state, or the state they were in before the spill event. Recovery time varies from days to years. For example, the ecosystem of a rocky shoreline can recover from an oil spill within months as organisms from unoiled areas can move in and restore the population. Avoidance is another response to oil spills. Some species of fish, seals, and dolphins will avoid surface slicks and move to unoiled areas. Some birds, however, are attracted to oil slicks, mistaking them for calm water. Further research is being done in this area. Another factor that influences the effects of oiling is the potential for rehabili-tation of oiled animals. Birds, otters, and seals are often cleaned, treated, and returned to the environment. Many species cannot be rehabilitated, however, as they are difficult to catch and the stress of being caught and kept in captivity may be worse than the effects of oiling. And finally, the effects of oil on any species often depend on the age or life stage of the organism. For example, juveniles of a species are often much more ©2000 by CRC Press LLC Photo 138 Oiling can affect a large variety of organisms, including this periwinkle. (Environ-ment Canada) sensitive to oiling than the adults and seals are much more sensitive to oiling when they are molting. Aquatic Environments The sea includes a wide variety of ecosystems, species, and habitats. When looking at the effects of oil spills, it is convenient to divide these into fish, plankton, benthic invertebrates, epontic organisms, marine mammals, intertidal and shoreline organisms, marine plants, and special ecosystems. Many freshwater biota respond to oil in a manner similar to their salt water counterparts. Although freshwater studies have not been as extensive as those for marine situations, few differences were noted. While oil is less soluble in freshwater, this is largely offset by the fact that many freshwater bodies are much shallower than oceans. A spill in a slough or pond can easily result in toxic concentrations throughout the entire water column. The high water circulation in most rivers, however, means that hydrocarbon concentrations in the water are diluted quickly. Fish There is often concern about the effect of oil on fish, from both an environmental and a commercial viewpoint, as fish are an important food source. Both pelagic (mid-water) and demersal (bottom-dwelling) fish are exposed to toxicity primarily through aromatic hydrocarbons in the water column. The concentration of aromatic ©2000 by CRC Press LLC Photos 139 (above) and 140 (below) Wildlife are sometimes attracted to oil spill operations. This beluga whale is playing with the boom during an oil spill exercise. (Environment Canada) hydrocarbons in oils varies, as does the toxicity of the different aromatic compounds. Although lethal concentrations are rarely found in open seas, such concentrations can occur in confined waters, such as bays and estuaries, directly under or near spills. Whereas high concentrations of oil have caused massive fish mortality in ©2000 by CRC Press LLC ... - tailieumienphi.vn