Plants can be used to remove toxic contaminants from soil and water in Nepal.

That is the conclusion of researchers at Tribhuvan University in Kathmandu, who say phytoremediation - the use of plants and soil microbes to remove toxic contaminants in the environment - may offer the country an affordable way to deal with contaminants like lead, mercury and arsenic.

The researchers say the global economic impact of heavy metal pollution is estimated at more than US$10 billion per year, with the risks and effects magnified in developing countries because of limited resources and treatment technologies.

“Industrialization, rapid global population growth, and increase in agriculture have all hastened heavy metal poisoning of soil and water environment in the modern society,” says the study, which is published in the journal Chemosphere.

Heavy metal contamination affects infants and children worst. Exposure to lead is associated with poor development, nerve disorders and behaviour-related issues in children, while it causes increased blood pressure in adults.

Mercury affects the nervous system, eyes, skin, kidneys, lungs, and the digestive and immune systems. Long-term arsenic exposure is linked to cancers of the skin, lungs and bladder.

The plants cited in the study include Indian mustard and alfalfa to combat lead, morning glory against copper, ladder brake and needle spikerush for arsenic, and common yarrow for mercury.

“Phytoremediation uses plants for extracting, immobilising, containing, and degrading contaminants in soil, water, and air while preserving their biological and physical state,” explains Shukra Raj Paudel, author of the study and associate professor at Tribhuvan University.

Paudel says that traditional phytoremediation methods are limited by factors such as the biological cycle of plants and heavy metal concentrations: “Some enhancement, either in the plant species or in the surrounding environment is required to improve the phytoremediation process.”

Plant-based remedial measures have been successfully used to remove heavy metals in the US, Canada, Russia and many European countries. However, in developing countries like Nepal, the cost, technical requirements and issues around social acceptance, are all barriers to using plants to decontaminate sites.

However, Nepal could fall back on its botanical riches to develop low cost methods of remediation and maintenance of contaminated sites, the study says. This would involve selecting commercially-viable ‘hyperaccumulator’ species that could absorb large amounts of heavy metal compounds; and introducing them to areas that need decontamination.

The researchers reviewed the status of heavy metals in various polluted sites in Nepal, analysed the mechanisms by which plants absorb heavy metals, and evaluated prospects for plant-based remediation measures. While methods applied in the past have failed to address heavy metal contamination in many places in the Himalayan country, say the researchrs, they continue to be attempted for lack of information on recent advances in enhanced phytoremediation.