Aquatic Pollution and Coastal Management

6.4.Toxicity of Petroleum Hydrocarbon

Unit 6 : Oil pollution

6.4.Toxicity of Petroleum Hydrocarbons
Oil affects the organisms in a number of ways depending upon the characteristics of the oil fractions and their concentration in water. Aromatic compounds are more toxic than aliphatics and middle molecular weight constituents are more toxic than high molecular weight tars.

Some important effects of oil on organisms are given below

• Oils have smothering effects (suffocation) on most of the aquatic animals.
• In sea birds, the microstructure and waxy nature of feathers attract oil. Buoyancy and thermal insulation of birds are affected. Oils penetrate the plumage, which facilitates the entry of water in it. Heavy oils stick to the feathers, and increase its weight to make the bird drown.
• The body temperature of the birds is kept higher by burning of stored food in the form of muscles. The oiled birds lose their capacity to catch the food efficiently, and can die because of low temperature.
• Several fur-bearing animals in sea, like seals, sea lions, sea otters and musk-rats may be affected by oil like birds, when oil penetrates the fur.
• Small animals can be caught in oil envelops and die.
• Sedimentary animals near the shore also die due to oil, as they are unable to move to safe distances away from oil.
• Oil layers increase the temperature, which may be critical for several organisms, particularly in the tropics. Tropical coral are greatly affected as the prevailing temperature is already very near to their tolerance limits.
• The poisonous effects of oil may be of much greater severity than the mechanical effects. A few aromatics like benzene and its derivatives have a very high penetration power into the body of organisms. They can penetrate the lipid layers of all membrane, thus, affecting the permeability by modifying the spacing of protein molecules on each side of the lipid layer. Brain and nerve cells of animals which depend upon fatty substances are also affected in this manner. A few straight chain and cycloparaffins also cause damage to the nervous system.
• The effects of the oil on lipids are also manifested in the maldevelopment of eggs and larvae following oil spills.
• A few toxic constituents of oils like non-hydrocarbons such as naphthanic acids and those containing nitrogen, sulphur and oxygen together with carbon and hydrogen are more soluble and can affect the enzymatic system and other vital biomolecules in the body.
• Transiting in fish, crustacean, molluscs and others.
• Effect on feeding and mating behaviour in several species. At 10 ppm reduces it the food finding capacity in lobster. 1% of oil stops feeding in mussels. Sexual behaviour of crabs is also modified at 0.0001 ppm.
• It decreases the filter feeding capacity, survival and fecundity in animals.
• It also leads to embryo toxicity and disruption of ionic regulation in sea birds.
• Some polyaromatic hydrocarbons (PAHs) like benzo (a) pyrene, dibenzo (a) pyrene and benzo(a) anthracene are potential carcinogens to a number of animals.
• Several PAHs are mutagenic and teratogenic. Abnormal offsprings have been reported in several aquatic organisms.
• At 0.01 ppm of oil, eggs hatch late and irregularly. Larvae are deformed. Young stages of lobsters are greatly affected at 1 ppm.
• Oils affect the migration behavior in salmon.