SOURCES OF OIL POLLUTION ALONG THE INDIAN COASTS OF ARABIAN SEA, BAY OF BENGAL INDIAN OCEAN, AND ITS IMPACT ON COMMERCIAL FISHERIES

Trabajo recibido el 19 de noviembre de 1982 y aceptado para su publicación el 24 de enero de 1983.

RESUMEN

INTRODUCCIÓN

India as a maritime state occupies a pivotal position flanked by the Arabian Sea, Indian Ocean and the Bay of Bengal. It has a coastline of 6000 Km. In particular the west coast of Arabian Sea is exposed to the risks oil pollution on account of the heavy transportation of crude oil by Tankers from the middle east oil fields to the south east Asia and far east. Added to this, is the movement of country's own imports to the refineries and the movements on the coasts. Hence oil pollution is currently a problem along the Indian coasts. Besides affecting human health through contaminated Sea Foods the pollution also reduces the recreational utility of coastal waters especially the beaches and thus lowers the revenue from tourism.

Studies on the Petroleum hydrocarbons along the coasts of Arabian Sea, Bay of Bengal & Indian Ocean are very scanty. Some of the important studies in the recent years pertaining to the distribution of tarball and petroleum hydrocarbons are mentioned below:

Ayyappan Nair et al. (1972) studied the tarball distribution in some of the sandy beaches along the central west coast of India. Qasim (1975) made a general review of tarball deposition along the beaches of west and cast coast of India. Sen Gupta et al. (1980) studied dissolved petroleum hydrocarbons in some regions of Northern Indian Ocean. Ramamurthy (1982) reported the oil pollution in the west coast of India off Arabian Sea from 1971 to 1980.

The present paper gives on account of the sources of oil pollution in certain strategic points along the Indian coasts of Arabian sea, Bay of Bengal and Indian Ocean and its impact on short term and long term changes on commercial fisheries.

Oil pollution in the Indian Ocean in general originates from

1) Oil tanker disasters

2) Offshore oil wells

3) Harbours and marine terminals

4) Land sources

Oil tanker disasters: On 4th August 1970 in North west coast of India, the greek oil tanker 'Ampuria' went aground off Kutch with a full load (15,622 tonnes) of furnace oil (Fig. 1). There was a positive danger to fishing grounds if the oil had spilled out. However, the Indian Navy mounted an emergency operation and saved about 12,000 tonnes of oil. Only 3,500 tonnes of oil leaked out. Again on 18th june 1973 another oil tanker 'M T. Cosmos Pioneer" went aground in the same north west coast of India of Arabian Sea and broke into two releasing 18,000 tonnes of LDO (Fig. 1). This resulted in mortality of marine life around North West coast of India. On 26th September 1974 an American Oil Tanker 'Transhuron' carrying 18,500 tonnes furnace oil ran aground at Kiltan in the Lakshadweep area of south west coast of India of Arabian Sea spilling 3,325 tonnes of furnace oil and adversely affecting the marine life in the vicinity of Kiltan and south west coast of Arabian Sea (Fig. 1).

Offshore oil wells: The source of oil pollution from the offshore oil wells in the west and east coast of India in the coming decade will pose a serious threat to the Sea Food Processing Industry in general and to the Shrimp Processing industry in particular. With the extensive reach for oil in the continental shelf and offshore regions, the chances of spills from the oil wells during the drilling operations or subsequently from permanent structures are going to be greater. An instance of blow out of the recent mishap of the offshore drilling ship 'Sagar Vikas' in the Bombay high which was operating from platform of the SJ the fifth offshore well that caught fire after a blow out on july '82 (Fig. 1). The well has a capacity o produce around 5,000 barrels per day corresponding to an around production of 1/4 million tonnes which at current international price is worth about US S 53 million (Rs. 50 crores). Considerable amount of spill has taken place when extinguishing the fire of the well. However, the actual amount of spill and the fall out of 'he natural gas are still under estimation.

Fig. 1. Shows the location of oil tanker disasters and off shore oilwell blow out along the west coast of India of Arabian Sea. A. "Ampuria" oil tanker disaster, C. "Cosmos pioner" disaster, T. "Trans-huron" disaster, Sj. Offshore oil well blow out.

Oil ports and terminals: In India shipping activities have increased immensely in recent years. The Indian Merchant fleet in 1947 had in operation of 59 ships with gross tonnage of 1.92 lakhs. This increased o 304 ships with a gross tonnage of 38.71 lakhs in 1974 and in 1980 the gross tonnage was nearly 50.00 lakhs. Handling losses at oil terminals in the east and west coast of India in the recent years also shown there have been a phenominal increase in the oil traffic. There are nine major ports having oil terminal facilities to haundle average of 9,500 tankers per year (Fig. 2).

Through some tankers followed 'LOT' System but majority of the tankers do not observe the internationally prescribed conventions. The oil carrying vessels, after unloading the oil cargo, seldom get completely empty. There is always some oil left in the tanks. In order to clear up their storage tanks, these tankers pump in sea water and then pump out the residual oil with sea water. Such cleansing of the s'orage tanks are unlawfully done especially in the west coast of India Off Arabian Sea. Though the oil tankers are instructed to discharge their residual oil in large storage tanks provided in ports, but the recent trend in building super tankers largely dictated by economic considerations pose several serious problems.

Similar problems, of although smaller in magnitude develop in fishing harbours which provide berthing facilities to fishing trawlers and landing jetties for small mechanised fishing boats and coastal barges (Fig. 3). There are about 16,000 mechanised fishing trawlers are playing in and around the coastal belt. In addition to this equal number of ferries, cargo ships, barges and out board motors are playing all along the coast. In these harbours a thick film of oil is always present as a discharge from bilge over the water and very often it covers several kilometers around the harbour.

Fig. 2. Major oil terminals and coastal oil refineries in the west and cast coast of India (Refineries in land locked states are not shown).

Fig. 3. Fishing ports and major fish landing centres in the cast and west coast of India.

Land sources: The land source of oil and petroleum by-product enter the Indian coastal water as a waste material from land sources through drain pipes, open channels tributaries, rivers etc. India is importing an average of 14.0 million tons of crude to her coastal & inland refineries to close the gap between the domestic output and an average estimate demand of 35.00 million tonnes. In certain northern part of the west and cast coast of India, the quantity of the waste material entering through land sources is quite substantial. In conjunction the shore based refineries also contributed ot oil pollution as a coolant and as a process water mixed with oil.

To study large oil spills for a preliminary visual assessment mechanised boats and fishing trawlers were used. The mortality of fish was estimated on the basis of visual observation and only representative samples were collected on board the vessels. Tar was sampled using standard methods specified by UNESCO (1976) in which all tar lumps on 1 m wide transacts between high tide mark and water edge were collected by hand and weighed. For long term monitoring fishes were caught by trawl & purse seine nets and immediately dissected into liver and muscle samples. Tissues for organic analysis were packed in solvent washed aluminium foil. All sampling gear and dissection instruments were precleaned and procedures were designated to minimize contamination from boats, gear or handling. Frozen samples were defrosted and analysed. Analytical methods used for hydrocarbons are detailed in Burns & Smith (1981) was followed. Other precautionary methodological details given in UNEP (1981) were also followed.

Crude oil or oil is a mixture of many different organic compounds. Crude oils from various sources differ markedly in composition and physical properties as well as in the relative concentrations of their individual components. Hydrocarbons are the most important constituents of petroleum and form upto 98% of certain crude oil. Some oil components such as lower aromatics, paraffins and nonhydrocarbon constituents are soluble in water and while oil spreads over the surface of the sea, these get dissolved into the water rapidly, other oils like fuel oil, motor oil are very thick and heavy. All crude oils contain compounds toxic to marine organisms. Some are soluble in the water, some evaporate on the surface, some form extensive and widespread slicks, and others settle on the bottom and incorporate large amounts of sand in globules. The residues which remains after the evaporation of volatile substances are generally much denser than this oil originally spilled and in deeper areas those readily sink to the bottom and never reappeared but in shallow areas the slicks deposited at the bottom are stirred up by the wave action particularly during monsoon season and these are washed ashore frequently. Thus, depending upon which of these processes is predominant, different types of oil spills can be expected to have somewhat different effects. Complete understanding of the toxicity and ecological effects of oil spills will probably require extensive studies of the effects of individual components, or at least of the classes of components which make up the original oil. The divergent scientific views found in the literature today probably stem from the lack of comprehensive data. Only a few oil spills have had adequate scientific investigation, and our understanding of the ecological effect has changed and developed greatly over the last few years. Most of this influx of hydrocarbons takes place in the coastal regions.

In case of large spill caused by 'Cosmos pioneer' disaster in North west coast of India and 'Trans huron' disaster in south west coast of India invariably we noticed two distinct series of events within first few hours or days after the accident (Ramamurthy 1974). There was a heavy kill of organisms that come into contact with the oil, the effect extended over all phyla and over benthic, pelagic and intertidal organisms (Nammalvar & Ramamurthy 1976). Next within weeks or month after the spill, the oil spread to areas that had not been affected initiallv, and the kill extended although in some cases more siowly than the spread of the oil. For a considerable time after the spill, the oil prevented resettlement of the sediments by the original fauna. It was also observed the degradation of the oil in and around the locality of the disaster areas. The degradation of oil appears to involve both bacterial utilization and partial dissolution. In the present investigation the bacterial degradation of crude oils were maily done by the following strains of Pseudomonas, Bacillus, and Flavobacterium and the biodegradation was in the following order alkanes > cycloalkanes > aromatics. Concurrently with the chemical changes in the oil the immediate toxicity of the oil in the sediment has been reduced due to evaporation of lighter fractions (Ramamurthy 1976). This reduction in the toxicity has permited resettlement of the polluted region first by most resistant fauna and later by more varied and normal fauna. Apart from the above short term effects the long term effects like the tar ball deposition occurs intensively either just before the monsoon or during the early part of the monsoon (June-July) in west coast of the Arabian Sea but in east cow of Bay of Bengal the tar ball depositions were found with very less intensity and with varying degrees during September & October. The magnitude of deposition varies from coast to coast. Maximum depositions are generally found at the high water marks, where the tar lumps are also larger and heavier. Many marine creatures ranging from fish, crustaceans, echinoderms response to chemical stimuli due to tar ball deposition that trigger numerous kinds of behavioural response including feeding, preening movement display and many others. In presence of added fractions from crude oil, the normal responses are effected in many different ways, suggesting that oil pollution may be ecologically harmful at concentrations far below those proved significant by ordinary toxicity tests based on short term mortality. Blumer and Saas (1972) describe detailed experiments on the sub-lethal effects of crude oil on the lobster (Homorus americanus) in which they noted chances in the sensing movements, feeding behaviour and gill operation in presence of 10 mg dm-3 of insoluble crude oil components. As a result they foresaw more serious effects caused bv chronic low levels of contamination competing with normal "Feeding smells" and other chemical messengers than by direct damage to animals or their receptor organs. In long term experiments (Blackman and Mackie. 1973) to follow the uptake and accumulation or elimination of hydrocarbons supplied as crude oil, Plaice, Pleuronectes, were fed on a diet of brown shrimps Crangon sp. dosed with oil. The levels of normal alkanes were determined in used water, faeces and fish muscle over a period of 10 days on oiled diet followed by 30 days or clean food. It was deserved the n-alkane, distribution pattern was very different in the control plaice not treated with oil. In the control shrimp, faeces and water were compared with those treated for three days which show uptake of unaltered crude oil alkanes (Blackman and Mackie, 1973).

There is considerable petroleum traffic in the west coast of India off Arabian Sea and the hydrocarbon content of this surface microlayer and of the subsurface sea water are considerably higher than the east coast of India off the Bay of Bengal. However it may be noted in general die hydrocarbon content of Arabia Sea, Bay of Bengal, Indian Ocean are far less than North Sea, Firth of Clyde, Western Atlantic and Gulf of Maine. Objectionable taste of oil in Sea food requires 10 to 50 ppm contaminant (ie) 10-50 mg/kg of wet wt. additional to the natural hydrocarbon content to product any detectable effect. The Hydrocarbon content of the Indian sea food in general as per the present investigation ranges from 0.6 to 3.0 mg/kg of wet wt. Further there is a differential variation in concentrations from the fishes caught from the Arabian Sea, Bay of Bengal and Palk Strait of Indian Ocean. It may also be noted within the indicated range the fishes caught from Arabian Sea showed the maximum concentration and the fishes from Bay of Bengal showed the least hydrocarbon content.

The fact that coastal waters are not devoid of marine life even after decades of oil contamination indicates Chat the sea is capable of recovery from this type of pollution. But the fact remains that once the recovery capacity of an environment is exceeded, deterioration can be rapid and catastrophic, and we do not know how much oil pollution the Indian Ocean including Arabian Sea and Bay of Bengal can accept and still recover.

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