By Ghazala Mustafa and Faizan Wazir
MANKIND HAS been blessed with the natural resources like soil, water and air. These natural resources serve as a backbone in the sustainable development of a countrys agriculture. Nature has created a unique balance in these resources. Man has been using these resources from thousands of years for its survival. With the current advancements in technology this natural balance is disrupted which has caused pollution and other environmental problems. Therefore, at present the main concern of the environmentalist is to lessen the threat of pollution and second is to restore the polluted sites.
Phytoremediation is a technique in which plants are used to remove, detoxify or immobilize environmental contaminants from soil, water or sediments, through natural, biological, chemical and physical activities. This method is based on the fact that green plants can absorb/extract certain elements from their ecosystem and accumulate those substances either as a part of their body or convert them to a non-hazardous form.
In the current situation we are more concerned with heavy metals because these are harmful to humans, animals and they have ability to accumulate in the food chain. Once they are accumulated in the food chain these can cause serious health problems. Heavy metal contamination of soils resulting from agricultural (e.g., chemical fertilizers and sewage sludge) or industrial activities (e.g., metal mining and smelting) is one of the major environmental issues in many parts of the world. Plant roots uptake these metal contaminants from the soil and translocate them to their above soil tissues. For example some plants have natural ability to grow in the saline or metal contaminated soil; they extract the subsequent metal with the help of their extensive root system and then accumulate that metal within their tissues. So in this way they help to remove toxic metals from soil without being damaged. For this purpose different plant species are used depending upon the type of contaminant and area to be reclaimed.
Approximately 400 plant species from at least 45 plant families have been reported to hyper-accumulate heavy metals and could be good sources for the removal of toxic metals from contaminated sites. The Indian mustard is a common plant which has the capacity to accumulate large quantities (1000 ppm) of lead. Sunflower has proven effective in the remediation of radionuclides and certain other heavy metals. Mulberry has been found to be effective in the reclamation of pesticide contaminated soils.
A species of ferns commonly known as Brake fern has been identified as arsenic hyper-accumulator. It can accumulate up to 7500 mg as/kg on a contaminated site. Some plants like Alfalfa, Sunflower and Millet can take up lead, copper, cadmium, iron and mercury from the soil. Research shows that Corn plant is ideal to extract very high concentration of lead from the contaminated soil. Many other plants like Eucalyptus, Mustard, Tobacco and Mangroves are known for their ability to reclaim soil from metals like chromium, lead, copper and nickel. In Pakistan mangroves forests are present at the costal line where they are playing important role in protecting the soil from contamination and degradation.
Phytoremediation is an economical, sustainable and can be helpful in protecting and cleaning soils contaminated with heavy metals. However, it requires technical strategy, expert project designers with field experience that can choose regions throughout the country with heavy metals contamination. The government support to private companies and other bodies dealing with phytoremidiation will boost the public interest in remediation of contaminated land. Moreover, these contaminated sites can also be used as demonstration and research areas for higher education and other research institutes. Collaboration with universities, research institutes and government bodies could create the multidisciplinary teams necessary to address questions related with phytoremidiation.