Problems Associated with Crude Petroleum Pollution

The problems associated with pollution caused by petroleum crude and their distillates can be grouped into the following categories:

(1) Light and Medium Fraction of Crude Oil :

Light and medium fraction of crude petroleum are mixtures of various hydrocarbons containing one to sixteen carbon atoms joined together in straight chains or are simple compounds containing an aromatic ring. Lighter of these are gases and volatile substances vapours of which are poisonous. When refined and processed some are good solvents while most of this fraction is used as air-craft or automobile fuels or as kerosene and diesel to provide energy. Combustion of these fuels results in pollution of atmosphere.

The toxicity of hydrocarbons is usually indirectly proportional to their boiling point and viscosity. As the viscosity and boiling point rise the toxicity decreases. Satruated hydrocarbons or paraffin like methane and ethane are asphyxants, gases which cause suffocation. Some of these hydrocarbons are depressant of central nervous system. Liquid paraffins can remove oil and coating of wax from exposed skin and caused dermatitis and pnumonitis.

Inhalation of vapours can cause acute intoxication and anaesthesia. Benzene is particularly toxic and long term exposures even at low concentrations can cause anaemia and leukopenia. Oral ingestion of these chemicals cause symptoms of mucous membrane irritation, vomitting and central nervous system depression. In acute cases albuminurea, haematuria and derangement of hepatic enzyme system may occur.

Due to low boiling point and highly volatile nature, light and medium fraction of petroleum crude evoporate quickly and as such poses no long term problems. Depending upon the quality this fraction may represent as much as 35-65% or more of the crude oil and is lost to the atmosphere as vapours within a week’s time after the oil silk or spill.

The hydrocarbons which are thus released into the atmosphere are either photooxidized and end up as carbon dioxide and water or are reacted upon by different atmospheric constituents to the cause various problems like photo-chemical or oxidizing type of pollution. Heavier fraction of light and medium oils persists for a longer duration in the environment.

(2) Heavier Fraction, Greases, Wax and Tar Etc :

Heavy oils, greases, waxes and solid fraction consists of 16-40 carbon joined together in various ways forming complicated chains, rings, polycyclic and heterocyclic structures and fused ring systems. It is this structural complexity which makes these compounds remarkably resistant to natural decay and degradation. Though these compounds have a considerably low toxicity but their recalcitrant and refractory nature makes them important environmental pollutants.

It is not unusual to find near places where automobilies are repaired and serviced, that the soil is blackened and unfit for growing plants. Heavy oils and lubricants spilled or discarded on the soil take months to oxidize and be decomposed.

Aromatic, heterocyclic and polycyclic hydrocarbons which form an important constituent of heavy oils, greases, wax asphaltic bitumen etc. and the smoke derived from their combustion have been implicated in many instances of carcinogenesis. Most of these chemicals are strongly lipophilic in nature and these results in their unrestricted entry into a biological system.

Teratogenic and mutagenic properties have also been attributed to these complex organic molecules. They have been suspected to be involved in affecting adversely the reproductive processes and immune system of living beings. On contact, skin irritation, eczema, cancer of skin etc. are caused by many of these chemicals. Nitro- , chloro-, and sulphur derivatives of these compounds are even more dangerous.

(3) Ecological Problems Caused by Crude Petroleum:

The problems caused by crude petroleum and its associated chemicals in marine ecosystems such as land locked bays, main oil tanker routes, ports and harbour areas etc. have been causing us much concern. Important aspects of crude petroleum pollution can be summarized as follows:

(1) Crude oil floats over the water surface and forms an insulating layer between the water and the atmospheric air above. This stops exchange of gases which regularly occurs at the air-water interface. This layer also restricts light penetration which retards photosynthesis. Thus oxygen generation by green plants is drastically reduced and as little oxygen is able to dissolve into the water from air above oxygen deficient conditions rapidly develops. Oxygen deficit causes large scale death of aquatic organisms. Rapid bio-degradation of crude oil also consumes plenty of oxygen and adds to the oxygen deficient conditions.

(2) Oils form a layer around eggs, larvae, smaller plants and animals thus encapsulating them from the surrounding environment which prevents exchange of gases and other materials. This kills most of the smaller organisms. Even fishes are affected as oil sticking on the gills interferes with their normal respiratory process.

(3) Sea birds exposed to petroleum crude are unable to fly when their feathers get soaked in oil. Oil dissolves away the protective oil or wax-like coating as consequence of which feathery coat loses its insulating capacity and thereby ability to withstand low temperatures.

(4) A large proportion of compounds present in petroleum crude are lipophilic. They can cross the lipo-protein membranes by the process of simple diffusion and accumulate in lipid and fats present in the body of the organisms exposed. Thus fishes and other sea-produce may be tainted with oil which imparts an unpleasant flavour and render them unpalatable to consumers.

(5) Water soluble fraction of petroleum crude contains a number of toxic substances which exert their toxic effects. Sulphur compounds, such as carbonyl sulphide present in the crude can he highly poisonous and so are a number of other compounds containing nigtrogen, phosphorus and heavy metal ions which are almost invariably present in small amounts in the crude oil.

(6) Crude oil almost invariably contains a small amount of a number of carcinogenic, teratogenic and mutagenic substances which pose a grave threat to those exposed to it. Though definite evidence of these dreaded properties is available in case of only few of these chemicals but the evidence so far available should be enough to caution us to avoid such exposures.

(7) When the magnitude of pollution diminishes only those forms, which are able to survive in waters contaminated with crude petroleum and its decomposition products come up and multiply. The resultant biota which thus emerges has an altogether different characteristic and it takes a fairly long time for the old constituents to re-establish in the locality.