Fisheries :: Fish Management

Aquatic Pollution

Degradable wastes are organic materials that can undergo decomposition through bacterial attack. The inputs that can be included under this category are urban sewage, agricultural waste, food-processing waste, distillery waste, paper-pulp mill waste, organic discharges from chemical industry and oil spillages. In addition, inputs like leaves and grass clippings, and run-off from livestock feedlots and pastures also contribute to this. When natural bacteria and other microorganisms in the water break down to organic materials, they use up the oxygen dissolved in water. Most of the fishes and bottom-dwelling animals cannot survive when level of dissolved oxygen drops too low. When this occurs, it kills aquatic organisms in large numbers, which leads to disruptions in food chain.

Fertilizers containing nutrients such as nitrates and phosphates could have effects similar to those of organic wastes. In excess levels, nutrients over-stimulate the growth of aquatic plants and algae. Excessive growth of these clogs waterways, uses up dissolved oxygen as organisms decompose besides blocking light to deeper waters. The depletion of oxygen, in turn, proves very harmful to aquatic organisms as it affects respiration of fish and other organisms that derive oxygen from water.

Heat, acids and alkalies and some chemicals such as cyanides can be considered as dissipating wastes as they lose damaging effects soon after they enter water-body. Particulates like dredging spoil, fly-ash, China clay-waste, colliery waste and a variety of man-made materials like plastics are inert, but they may clog feeding and respiratory structures of animals, may also reduce photosynthesis by reducing light penetration or may smother benthos. Conservative wastes like heavy metals, halogenated hydrocarbons and radioactive materials are not subject to microbial attack, and therefore, exist over a long duration, and cause harm to plants and animals.

Pathogens such as bacteria, viruses and protozoans, are another type of pollution. They can cause many illnesses ranging from typhoid and dysentery to minor respiratory and skin diseases. These organisms enter waterways through untreated sewage, storm drains, septic tanks, run-off from farms, etc. There is also threat from carcasses and other animal materials infecting water supplies following inadequate disposal. Though microscopic, these pollutants have tremendous effect, evidenced by their ability to cause diseases.

Source of Pollution

The sources of water pollution are categorized as point and non-point. Point sources of pollution occur when polluting substance is emitted directly into waterway. A pipe spewing toxic chemicals directly into a river is an example. A non-point source occurs when there is run-off of pollutants into a waterway, for instance, when fertilizers from agricultural fields are carried into a stream by surface run-off. The common point sources of pollution are municipal and industrial waste water effluents; run-off and leachate from solid waste disposal sites; run-off from industrial sites; storm sewer outfalls from urban centres; run-off and drainage from industrial sites, mines and oil fields; discharge from vessels, storage tanks and piles of chemicals; run-off from construction sites; and bypasses from sewers and sanitary pipes.

The non-point sources include flow from agricultural fields and orchards, run-off from logging operations, urban run-off from unsewered areas and septic tank leachates, atmospheric deposition and run-off from roads. When toxic substances enter lakes, streams, rivers, oceans and other water-bodies, these get dissolved, lie suspended in water or get deposited on bed. This results in water pollution, whereby quality of water deteriorates, affecting aquatic ecosystems. Pollutants can also seep down and affect groundwater deposits. The most important sources of pollution are city sewage and industrial waste discharged into rivers by virtue of the quantities in which these are discharged. Presently, only about 10% of the wastewater generated is treated allowing about 90% of it to directly enter receiving water. Due to this, pollutants enter groundwater, rivers and other water-bodies, and may even harbour pathogens. Agricultural run-off or the water from fields that drains into rivers is another major source of water pollution as it could be rich in the major nutrients, viz. nitrogen, phosphorus and also pesticides.

Control and abatement

The high cost of treatment has been the major concern for wastewater management. There is considerable agreement on the need for revised technology to diminish industrial and automotive emissions, to produce degradable wastes and to dispose of all wastes in ways less damaging to environment. For example, by channeling sewage to farms as fertilizer, and by recycling glass and metal materials. Finally, improvement is required in techniques for preventing pollution by especially hazardous wastes.

Remedial actions

Enough resources have already been spent documenting ills caused by municipal wastewater pollution. Although each city, town or community has its own specific environmental and socio-economic conditions, the available research points to a following common conclusion: Sewage pollution is harming environment, and it is affecting ourhealth and economy.Technologicalinnovation would springup, education campaigns would become good investments, financial incentives not to discard harmful substances into sewers would become common, and comprehensive commercial and industrial sources control and monitoring programmes would be set up to exercise tight control over substances discharged into sewerage system.


The emergence of biotechnology as the tool has over-ruled chemical technologies used for pollution abatement, which are costly, non-ecofriendly and generate more secondary wastes, which impair ecosystem functioning. Most of these engineering technologies have failed in effluent clean-up process. As alternatives, though slowly, biological tools are being substituted in pollution abatement programmes. Bioremediation has been recognized as an inexpensive, effective and environment-friendly safe technology that offers new and innovative ways to clean up hazardous wastes. However, the use of the technology is limited by poor understanding of biodegradation process.

This is a tool that can be used for abatement of pollution resulting from a variety of compounds, biodegradable as well as recalcitrant. There is evidence that microbes in anaerobic sediments can dechlorinate even polychlorinated biphenyls, which are otherwise resistant. Genetic engineering holds a great potential in this area. Though bacteria and other microbes are natural sources of bioremediation tools, the most applicable one could be phytoremediation, especially with reference to aquatic pollution abatement. The use of specially selected and (or engineered) pollutant-accumulating plants for environmental clean-up is an emerging area in pollution abatement. Phytoremediation works best at sites with low to medium amount of pollution, and at sites contaminated with metals and nutrients. Plants are used either to stabilize or to remove metals from soil and contaminated water through five mechanisms: Phytoextraction (plants to remove toxic or heavy metals from soil), Rhizofiltration (use of plant roots to remove toxic or heavy metals from polluted water), Phytostabilization (elimination of bioavailability of toxic or heavy metals from soils using plants), Phytotransformation (degradation of contaminants through plant metabolism, which is applicable to both soil and water) and Phytostimulation (plant­assisted biodegradation, used for both soil and water, involving stimulation of microbial biodegradation through activities in plant rhizosphere). Once absorbed by the plants, toxic or heavy metals can be stored in the roots, stems or leaves; converted into less harmful substances within the plant; or changed into gaseous forms and released into the atmosphere through transpiration.


Waste management is simply minimization, destruction, treatment and disposal. In the simplest way, pollution prevention has two components: prevention of pollutants being generated and preventing pollutants from being introduced into environment. In pollution prevention, the Government machinery and regulatory agencies have to playa major role, though many prevention initiatives need voluntary efforts rather than ref!uirements imposed by a regulatory agency.

Pollution is a global problem and does not respect national boundaries. The first major International Conference on Environmental Issues was held in Stockholm (Sweden) in 1972 which was sponsored by the United Nations. This meeting, at which of aquatic pollution prevention. The Water (Prevention and Control of Pollution) Act, 1974 and Rules, 1975, were enacted to provide for prevention and control of water pollution, the maintenance or restoration of wholesomeness of water, and for establishment of boards for prevention and control of water pollution. The Water (Prevention and Control of Pollution) Cess Act, 1977 and Rules, 1978, have been enacted for levy and collection of a cess on water consumed by persons carrying on certain industries and by local authorities, with a view to augment resources of the central and state boards for prevention and control of water pollution. The Environment (Protection) Act, 1986 and Rules, 1986, are meant to provide for protection and improvement of environment and for matters connected there with, and the Environmental Impact Assessment Notification, 1994,is a imedatimposing restrictions and prohibitions on expansion and modernization of any activity or new projects being undertaken in any part of India unless environmental clearance has been accorded by the Central Government or the State Government concerned.

A comprehensive pollution prevention programme should include redesigning or reformulation of products, substitution of raw materials or alternative chemicals that introduce smaller quantities of hazardous substances into agricultural and industrial production processes, improved process technology and equipment to alter primary source of waste generation, improved plant operations (housekeeping), and recycling of polluted substances at the site of their generation (closed loop recycling). Pollution prevention programmes should include a comprehensive toxin reduction programme with defined goals for reducing the loading of toxic pollutants over time, identification of areas where pollution prevention techniques should be implemented, and for monitoring and reporting of success in meeting these goals.

Creation of awareness among users of water and environmental education are two most important ways to curb water pollution. It has been said that a successful corporate pollution prevention programme can improve global competitiveness, enhance consumer acceptance of products, reduce environmental impacts, improve working conditions and enhance community relations. It is generally agreed that the key to the resolution of water problems is controlled by water quality management planning, by enforcement of standards, by licensing and policing of discharges, by following approved procedures in agriculture, and by good environmental awareness on the part of the public. It is unrealistic to prohibit all discharges to our water-bodies. Instead, the careful, diligent control of discharges to rivers and lakes will go a long way towards restoring and preserving good quality of water.


Hand book of Fisheries and Aquaculture. 2006. Indian Council of Agricultural Research. New Delhi.


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