April 23, 2007	Monday	Rabi-us-Sani 05, 1428

ALMOST 97 per cent of water on earth is salt water of oceans and seas. The remaining three per cent is in the form of polar ice caps, glaciers, in the atmosphere or underground. Only a small fraction, 0.4 per cent of it is available for use.

In a world faced with population explosion and rapid industrialisation, the demand for clean water is becoming urgent. In our country hardly 10 per cent of the population has access to pure drinking water. Similar is the situation in many countries of the world. We are moving into water-starved age, and only in intelligent use of water is our salvation.

In our country water pollution has greatly damaged the aquatic ecosystem and the agriculture sector. The streams, rivers, ponds, lakes and sea are polluted with various kinds of solid and liquid wastes. Like air pollution, water pollution is also caused due to population explosion, industrial expansion, energy consumption and rapid rate of urbanisation.

Industrial wastes are the largest contributor to water pollution. These wastes are produced from textile, chemical, petrol, paper and pulp industry as well as from tanneries etc. About 9,000 million gallons of wastewater is daily discharged into our water bodies from the industrial sector. Automobile service stations are other major contributors to surface water pollution. Untreated oil, grease and dirt find its way into nearby canals and rivers. Tannery effluents are great threat to people of the areas and its constant flow into rivers and sea is a threat to marine life in particular and to agriculture sector in general.

Industrial wastewater contains toxic chemicals. It is alarming that most industries have been working without proper planning and waste treatment plants. They just dispose of untreated toxic waste into nearby drains, canals or rivers. Industries in Lahore, Faisalabad, Karachi, and Sialkot heavily pollute the water bodies.

Agro-remediation (Phytoremediation) is the use of living green plants for risk reduction and/or removal of contaminants from soil, water and air. Specially selected or engineered plants are used in the process. Risk reduction can be through a process of removal, degradation of a contaminant or a combination of any of these factors. Agro-remediation is energy efficient, aesthetically pleasing method of remedying sites and water bodies with low to moderate levels of contamination and it can be used in conjunction with other more traditional remedial methods as a finishing step to the remedial process.

The cost of agro-remediation has been estimated at $25 - $100 per ton of soil and $0.6 - $6 per 1000 gallons of polluted water with remediation of organics being cheaper than remediation of metals. In many cases agro-remediation has been found to be less than half the price of alternative methods. It also offers a permanent remediation rather than simply translocation of the problem. However agro-remediation is not without its faults, it is a process which is dependent on the depth of roots and tolerance of the plant to the contaminant. Exposure of animals to plants which are hyper-accumulators concern environmentalists as herbivorous animals may accumulate contaminate particles in their tissues which could in turn affect a whole food web.

As various plants have different abilities to uptake and withstand high levels of pollutants, they are used according to the requirements. This is of particular importance on sites that have been polluted with more than one type of metal contaminant. Hyper accumulator plant species (species which absorb higher amounts of pollutants than most other species) are used on many sites due to their tolerance of relatively extreme levels of pollution.

Once the plants have grown and absorbed the metal pollutants they are harvested and disposed of safely. This process is repeated several times to reduce contamination to acceptable levels. In some cases it is possible to recycle the metals through a process known as phytomining, though this is usually reserved for use with precious metals. Metal compounds that have been successfully phytoextracted include zinc, copper, and nickel, but there is promising research being completed on lead and chromium absorbing plants.

Advantages: It is economically viable using the same tools and supplies as agriculture.

It is less disruptive to environment and does not involve waiting for new plant communities to re-colonise the site.

Disposal sites are not needed. It is more likely to be accepted by public as it is aesthetically pleasing than traditional methods. It avoids excavation and transport of polluted media thus reducing the risk of spreading the contamination. It has the potential to treat sites polluted with more than one type of pollutant.

The first goal in agro-remediation is to find a plant species which is resistant to or tolerate a particular contaminant with a view to maximising its potential for agro-remediation. Resistant plants are usually located growing on soils with underlying metal ores or on the boundary of polluted sites. Once a tolerant plant species has been selected traditional breeding methods are used to optimise the tolerance of a species to a particular contaminant. Genetic modification offers a new hope for agro-remediation.

Despite significant success, complete potential of agro-remediation technique has not been fully exploited. Agro-remediation is essentially an agronomic approach and its success depends ultimately on agronomic practices applied at the site. At present, the effects of different agronomic practices (plant selection, sowing, soil manuring and conditioning, pest control, irrigation, crop rotation) on metal removal by plants are largely unknown. So there is dire need to investigate the agronomic practices to maximise the clean-up potential of remedial plants. The application of various agronomic practices will make this technique easy, interesting, feasible and economical in all agricultural production areas returning high quality products to the growers.