Nature’s way to fight pollution

 By TOSHIRO SHIGAKI

HEAVY metal and other pollutants from mining operations are contaminating soils and water in many parts of the world.

It is particularly problematic in a country such as Papua New Guinea where mining is an important industry.  

The pollution typically includes toxic heavy metals such as cadmium, mercury, copper, and lead.  

Land bordering the contaminated rivers and mine sites are rendered unsuitable for cultivation.  

Decontamination of affected land has been slow at best, and in many sites, no attempts have been made to remove the pollutants.

There are a number of options to clean up pollution caused by mining activities. But they often require prohibitively expensive procedures such as physical removal of contaminated soil and replacing it with clean soil from elsewhere.  

An emerging technology termed phytoremediation (remediation using plants) offers an inexpensive and environmentally friendly alternative to conventional cleanup measures.

Phytoremediation takes advantage of the property of certain plant species that can absorb and tolerate very high concentrations of heavy metals and other toxic materials in their biomass. 

These plants, called hyperaccumulators, are often seen growing at mines and on tailings.  

With many active abandoned mines in the country, PNG is thought to have many useful hyperaccumulators waiting to be discovered.

Phytoremediation is increasingly gaining popularity for the past two decades as an eco-friendly technology.  

For example, in Florida, United States, a fern species that can accumulate arsenic at a very high level was discovered in an abandoned mine.  

The fern is now being used to clean up arsenic-contaminated lands by a commercial company that patented this fern.  

Arsenic soil pollution is a worldwide problem. This  technology should be a cost-effective way to restore productivity to polluted soils.

A few things must be considered when phytoaccumulators are selected for phytoremediation.  

First, the plant must not be edible, either by wildlife or hum-ans because it will poison them.  

Second, the plant should accumulate metals in the shoot system rather than roots because, in practice, only the shoot system is removed for disposal.

Third, a large root system is required when the contamination reaches deep into the soil.

Lastly, a large shoot system will provide more efficient removal of the pollutants.  

In this sense, trees would be ideal.  However, they may not be an option in many situations.

If hyperaccumulators cannot be identified to take up certain metals efficiently, such a plant can be developed using genetic engineering.  

For example, a transporter protein in the plant cell can be designed so that it can absorb any metal of interest, and expressed in any desired plant species.  

This, however, requires extensive biochemical studies followed by field trials for practicality and safety.

A concept closely related to phytoremediation may interest some of the readers.  

When a plant accumulates precious metals rather than toxins, the plant can be used to “mine” the metals from the soil.  

This process is called phytomining.  

A recent discovery of a moss species that accumulates gold can be used for small-scale gold mining from river beds.  

This technology, however, is still in the developmental stage.

Recently, a team of NARI scientists visited a river bed downstream of the defunct Panguna mine in Bougainville.  

In this location, the river appears blue from the copper deposits.  

The soils are likely to be contaminated with copper and other heavy metals.  

Locals told us that when the mine ceased operation in the 1990’s, the location did not have any vegetation. 

Twenty years later, the land is covered mostly with several types of ferns.  

These ferns may be potential hyperaccumulators but lab testing is required to confirm this.

If hyperaccumulators are identified in PNG, these plants are naturally adapted to the local climate and can be directly used for phytoremediation. 

Some hyperaccumulators may find utility in other locations in the world.  

Surveys to find novel hyperaccumulators and the ensuing laboratory tests are relatively inexpensive considering the potential gain of agricultural productivity for the benefit of smallholder farmers who abandoned their gardens because of pollution.

Phytoremediation is an inexpensive, yet highly effective way to clean up polluted soils that is affordable for any typical smallholder farmer in PNG.

However, it still requires processing of the shoots that contain toxic metals.  

When such shoots are handled improperly, it can contaminate soils at the disposal site. 

This will require industry and government intervention for facility and technology development.  

However, phytoremediation is currently one of the most cost-effective ways to remove toxic materials from soils, and should be considered a viable and feasible option for decontaminating PNG farmlands. – NARI.