Nuclear Pollution

Here’s how some plants will help in removing soil contamination

In today’s world soil contamination is a huge problem. Soil contamination can lead to pollution of underground water and food crops. With increased population, more factories, construction work and use of dangerous chemicals can lead to soil contamination.

The reasons can vary from manufacturing, mineral extraction, accidental spills, illegal dumping, leaking underground storage tanks, pesticide and fertiliser use among others. When it comes to India the situation is getting grave. Heavy metal pollution of soil is emerging at a speedy rate in India due to industrialisation, says a study published in the JNKVV research journal in 2015.

Some recent studies have demonstrated that some plant species could help to remove toxic heavy metals and metalloids from contaminated soil. This would serve as a more environmentally friendly alternative to existing industrial options to remove the heavy metals from polluted soil.

Read | China battles soil pollution caused by industrial waste; looks for someone to foot 5 billion yuan bill

Methods such as soil washing and acid leaching can be costly and often there is use of harsh chemicals.

How soil contamination occurs?

Soil contamination or soil pollution is a part of land degradation and is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activity, agricultural chemicals or improper disposal of waste.

The toxic pollutants are then absorbed by food crops and other plants before they eventually make their way into our food chain. This directly affects human life along with ecology. Generally, soil contamination is cited as a consequence of non-organic farming practices, industrial activity and improper waste disposal.

Common chemicals involved in soil contamination include petroleum hydrocarbons, lead, solvents, pesticides and polynuclear aromatic hydrocarbons, such as naphthalene. Synthetic pesticides, insecticides and herbicides are created in laboratories using a combination of chemicals which are used by farmers in order to protect their crops.

Adverse effects of soil contamination on health

Contaminated soil has been shown to have a negative impact on human health. Chronic exposure to benzene, for example, has been linked to higher rates of leukaemia. Chronic exposure to chromium and lead is thought to cause congenital disorders and other health conditions.

Soil contaminants also have adverse effects on ecosystems. Typically, contaminants have been shown to alter plant metabolism, causing a drop in crop yields.

How to get rid of soil contamination naturally

To get rid of soil contamination, many technologies have emerged. However, such methods can be costly and often there is use of harsh chemicals involved. According to a paper published in the journal Agriculture, these methods have been lacking in terms of sustainability as they come with a large cost and have adverse effects themselves.

A team of researchers from NTU Singapore and Singapore’s National Parks Board (NParks), led by Professor Lam Yeng Ming, Chair of NTU’s School of Materials Science and Engineering, demonstrated that some plant species could help to remove toxic heavy metals and metalloids from contaminated soil .

The development of this plant-based solution to improve soil quality is part of the University’s efforts to mitigate our impact on the environment, that is aligned with the NTU 2025 strategic plan.

Some scientists have developed methods of phytoremediation to get rid of soil contamination. This remediation method uses living organisms like plants, microalgae, and seaweeds. One particular way to remove toxic heavy metals from the soil includes the use of ‘hyperaccumulator’ plants that absorb these substances from the soil.

A paper published in the MDPI Agriculture journal titled, ‘Utilizing Mediterranean Plants to Remove Contaminants from the Soil Environment: A Short Review’, studies the development of this method of remediation.

What are hyperaccumulator plants?

A hyperaccumulator is a plant capable of growing in soil or water with very high concentrations of metals, absorbing these metals through their roots, and concentrating extremely high levels of metals in their tissues. Hyperaccumulators have the unusual ability to absorb hundreds or thousands of times greater amounts of these substances than is normal for most plants.

Three basic hallmarks of hyperaccumulators include a strongly enhanced rate of heavy metal uptake, a faster root-to-shoot translocation and a greater ability to detoxify and sequester heavy metals in leaves. Heavy metal contaminated soils pose an increasing problem to human and animal health.

Using plants that hyperaccumulate specific metals in cleanup efforts appeared over the last 20 years.

How phytoremediation with hyperaccumulators is done?

Turning toward more sustainable and eco-friendly technologies, phytoremediation requires a large surface area of ​​land for remediation. Phytoremediation is used for the remediation of metals, radionuclides, pesticides, explosives, fuels, volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs).

Suitable plant species can be used to absorb the pollutants from the soil through their roots and transport them to their stem, leaves and other parts. After this, these plants can be harvested and either disposed or even used to extract these toxic metals from the plant.

This process can be used to remove metals like silver, cadmium, cobalt, chromium, copper, mercury, manganese, molybdenum, nickel, lead and zinc; metalloids such as arsenic and selenium; some radionuclides; and non-metallic components such as boron. But it cannot be used to remove organic pollutants from the ground due to metabolic breakdown.

(With Inputs from Science and Agriculture journals)

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