Some plant species could help remove hazardous heavy metals and metalloids from polluted soil, according to a team of researchers from Nanyang Technological University, Singapore (NTU Singapore) and Singapore’s National Parks Board (NParks).
Plants are used in phytoremediation to remove and store pollutants from soil. The team tested samples of prospective plants for levels of heavy metals and metalloids as a preliminary step in determining if they possessed phytoremediation capability. The presence of a high concentration meant that the contaminants could be absorbed.
According to the findings of the Singapore research team, there are tropical plants that could potentially help with the cleanup of contaminated soils. The plants used in the study are widely available and comprise native and naturalized Singapore species.
They may thus be introduced and removed from plots of land with little influence on ecosystems, paving the door for the creation of a long-term and environmentally beneficial method of managing pollutants in soil. Environmental Pollution, a peer-reviewed scientific magazine, published the findings in February.
Professor Lam Yeng Ming, Chair of NTU’s School of Materials Science and Engineering, who co-led the study, said: “In a small nation like Singapore, land may be repurposed to support new development plans, so it is important that we have a green and sustainable way to remediate land that is contaminated.”
“We set out to uncover how to better make use of tropical plants to do phytoremediation and through advanced characterisation techniques, we showed how some of these tropical plant species can be an environmentally friendly and literally a “green” way to remove contaminants in soil. Phytoremediation also has benefits of cost effectiveness, simplicity of management, aesthetic advantages, and long-term applicability and sustainability. The strategy prevents erosion and metal leaching by stabilising or accumulating heavy metals, so that helps reduce the risk of contaminant spread.”
Between March 2019 and January 2020, the team conducted a field survey and collected soil and plant samples. A total of 46 plant species were investigated as phytoremediation possibilities.
Twelve plant species, including the common Cow Grass (Axonopus compressus), hyperaccumulators such as the Brake Fern (Pteris vittata), and the Indian Pennywort (Centella asiatica), were found to be successful at accumulating various heavy metals and metalloids.
We set out to uncover how to better make use of tropical plants to do phytoremediation and through advanced characterisation techniques, we showed how some of these tropical plant species can be an environmentally friendly and literally a “green” way to remove contaminants in soil. Phytoremediation also has benefits of cost effectiveness, simplicity of management, aesthetic advantages, and long-term applicability and sustainability. The strategy prevents erosion and metal leaching by stabilising or accumulating heavy metals, so that helps reduce the risk of contaminant spread.
Professor Lam Yeng Ming
Heavy metals and metalloids that are potentially hazardous to humans and animals, such as cadmium, arsenic, lead, and chromium, were explored in the study. They are found in soils naturally, but only in trace amounts that are hazardous.
Heavy metal particles from air pollution (e.g., automobile emissions, building activities) tend to concentrate and remain in the top layers of soil, allowing them to accumulate and reach larger levels over time.
Other factors that could lead to excessive amounts of heavy metals in soil include the usage of synthetic items like pesticides, paints, batteries, industrial waste, and the application of industrial or domestic sewage to the ground.
The researchers used the Dutch Standard to determine whether the quantities of heavy metal were harmful. The Dutch Standard establishes values for the allowable threshold of environmental contaminants in soils. Singapore’s government agencies have also adopted this method of evaluation.
Associate Professor Tan Swee Ngin, from the Academic Group of Natural Sciences and Science Education at NTU’s National Institute of Education, who was the study’s co-author, said:
“Our results revealed there were regions where levels of heavy metals and metalloids were relatively high and could affect the environment and the health of flora and fauna in Singapore. This would call for preventive actions, such as our method of using plants to remove these toxic materials, to be employed to minimise heavy metal contamination.”
The study’s researchers are from the National Park Service’s Centre for Urban Greenery and Ecology. Mr. Mohamed Lokman Mohd Yusof, Senior Research Executive, and Dr. Subhadip Ghosh, Senior Researcher, are among them.
The creation of this plant-based solution to improve soil quality is part of the University’s efforts to reduce our environmental impact, which are in line with the NTU 2025 strategic plan, which aspires to create long-term solutions to some of humanity’s most critical major challenges.
Team’s findings expand potential of environmentally friendly methods
Existing commercial methods for removing heavy metals from polluted soil, such as soil washing and acid leaching, could be replaced with phytoremediation as a more environmentally friendly approach. These procedures can be expensive, and they may include the use of harsh chemicals to remove pollutants from the soil.
In such activities, heavy machinery is frequently necessary to undertake excavation and soil transportation, and these procedures may have a severe impact on the environment by compromising soil health and fertility. These approaches also put humans and animals at danger of being exposed to heavy metals.
Phytoremediation, on the other hand, is a sluggish and long-term process that necessitates careful management of the contaminated plant samples’ removal and disposal. Using various types of effective plants to carry out phytoremediation in polluted soils, and allowing for sufficient growth cycles through recurrent planting, can lead to reductions in heavy metal and metalloid levels in the soil.
The plants are currently being tested on parcels of land in Singapore with significant concentrations of heavy metals to better establish their usefulness in an urban setting, according to the collaborative research team.
They’re also experimenting with the use of additional inorganic particles that are integrated into plants and can aid plant growth as well as assist the uptake of pollutants by the plants. This will speed up the cleanup process by reducing the time it takes for heavy metals to be absorbed.
