Scientists demonstrate that some tropical plants have potential to
remove toxic heavy metals from the soil
Date:
April 13, 2022
Source:
Nanyang Technological University
Summary:
A team of researchers has demonstrated that some plant species
could help to remove toxic heavy metals and metalloids from
contaminated soil.
FULL STORY ==========================================================================
A team of researchers from Nanyang Technological University, Singapore
(NTU Singapore) and Singapore's National Parks Board (NParks), has
demonstrated that some plant species could help to remove toxic heavy
metals and metalloids from contaminated soil.
========================================================================== Phytoremediation is the use of plants to extract and store contaminants
from soil. As a first step to determine if candidate plants had phytoremediation abilities, the team examined samples of them for levels
of heavy metals and metalloids. A high concentration detected suggested
an ability to absorb the pollutants.
The study by the Singapore research team discovered that there are
existing tropical plants which could potentially play a role in the
remediation of contaminated lands. The plants examined in the study are
widely available and include species that are native or naturalised to Singapore. They could thus, be introduced and removed from plots of land
with minimal impact to ecosystems and could lead to the development of
a sustainable and environmentally friendly way of managing contaminants
in soil.
The findings were published in the scientific peer-reviewed journal Environmental Pollution 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." The team conducted a field survey and collected
soil and plant samples between March 2019 and January 2020. A total of 46
plant species were studied as potential candidates for phytoremediation.
========================================================================== Among them, 12 plant species, which include the commonly seen Cow Grass (Axonopus compressus), hyperaccumulators like the Brake Fern (Pteris
vittata) and the Indian Pennywort (Centella asiatica), were effective
for the accumulation of several types of heavy metals and metalloids.
The elements investigated in the study were heavy metals and metalloids
that are potentially toxic to humans and animals, such as cadmium,
arsenic, lead, and chromium. They occur naturally in soils, but rarely
at toxic levels.
However, they can accumulate and reach higher levels over a long period of time, as heavy metal particles from air pollution (e.g. vehicle emissions, construction activities) tend to accumulate and remain in the top layers
of soil.
Other factors that could result in high levels of heavy metals in soil
include the use of synthetic products such as pesticides, paints,
batteries, industrial waste, and land application of industrial or
domestic sludge.
To assess whether the levels of heavy metal were dangerous, the team used
the Dutch Standard, which provides values for the acceptable threshold
of environmental pollutants in soils. This mode of assessment has also
been adopted by Singapore's government agencies.
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 NParks researchers involved in the
study are from its Centre for Urban Greenery and Ecology. They include
Dr Subhadip Ghosh, Senior Researcher and Mr Mohamed Lokman Mohd Yusof,
Senior Research Executive.
==========================================================================
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, which aims
to develop sustainable solutions to address some of humanity's pressing
grand challenges.
Team's findings expand potential of environmentally friendly methods Phytoremediation could serve as a more environmentally friendly
alternative to existing industrial options to remove the heavy metals
from polluted soil, which include methods such as soil washing and acid leaching. These methods can be costly and may utilise harsh chemicals
to remove pollutants from soil.
Heavy machinery to conduct excavation and transportation of soil is also usually required in such processes and these procedures may negatively
affect the environment by affecting soil health and fertility. These
methods also run a high risk of exposing humans or animals to the
heavy metals.
However, phytoremediation is a slow and long-term commitment and requires prudent management in the removal and disposal of the contaminated
plant samples. Using different types of efficient plants to carry out phytoremediation in polluted soils, and with enough growth cycles through repeated planting, can ultimately lead to reductions in the level of
heavy metals and metalloids in the soil.
The joint research team is currently testing the plants on plots of land
in Singapore that have high concentrations of heavy metals to better
determine the effectiveness of the plants in an urban setting.
They are also testing the usage of other inorganic particles that are incorporated into plants and that can both help in the plant growth and
improve the uptake of these contaminants by the plants. This will reduce
the time taken for the absorption of the heavy metals and hence speed
up the remediation time.
========================================================================== Story Source: Materials provided by
Nanyang_Technological_University. Note: Content may be edited for style
and length.
========================================================================== Journal Reference:
1. Yamin Wang, Swee Ngin Tan, Mohamed Lokman Mohd Yusof, Subhadip
Ghosh,
Yeng Ming Lam. Assessment of heavy metal and metalloid levels and
screening potential of tropical plant species for phytoremediation
in Singapore. Environmental Pollution, 2022; 295: 118681 DOI:
10.1016/ j.envpol.2021.118681 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/04/220413104203.htm
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