A new study published in the journal Science shows that pollution from elevated levels of heavy metals and metalloids is leading to lower crop yields and food supply contamination. An interesting revelation from the study is that there is an east-west corridor of elevated heavy metals concentration that spans across low-latitude Eurasia, including southern Europe, India, the Middle East, South Asia, and southern China. Susan Chacko, for Down to Earth, writes:
“This zone coincides with regions that were home to ancient civilisations such as the Greeks, Romans, Persians, and early Chinese dynasties. The study suggests that centuries of human activity — including mining, smelting, and agriculture — combined with natural factors like metal-rich bedrock and low rainfall have contributed to the accumulation of these pollutants.”
In the editor’s summary of
the paper, Bianca Lopez notes that the researchers:
“…analyzed data from more than 1000 regional studies to
identify areas of metal toxicity and explore drivers of these trends. They
estimate that 14 to 17% of cropland exceeds agricultural thresholds for at
least one toxic metal. Climate and topography, along with mining activity and
irrigation, predicted which soils would exceed metal thresholds. Soil metal
pollution is a global issue that will likely increase with the growing demand
for toxic metals in new technologies.”
Heavy metal pollution in soils does not degrade over time
and is thus persistent. They also accumulate in the human body. Cadmium was
found to be the most widespread heavy metal, exceeding safe level thresholds in
9% of global cropland soils. India, Pakistan, Bangladesh, southern China, and
parts of Africa and Latin America are the hotspots for cadmium pollution.
Nickel and chromium are most prevalent in the Middle East, subarctic Russia,
and eastern Africa. Arsenic is most prevalent in southern China, Southeast
Asia, and West Africa. Cobalt pollution, largely linked to mining, is
particularly severe in Zambia, the Democratic Republic of the Congo, and
Ethiopia.
The researchers note that the
problem is likely underestimated due to lapses in data for several regions.
They recommend international efforts to expand soil monitoring in many areas.
They also note that global food trade is likely to spread heavy metal pollution
to our food supply. I believe we have already seen this with some spices
showing unsafe levels of heavy metals. Chacko writes that a 2014 study in China
showed 16% of soils were contaminated with heavy metals, and a 2016 EU study
showed that 28% of soils were contaminated.
Rice has been shown to draw
up arsenic from the soil, and unsafe levels of arsenic have long been a concern
with rice. Leafy greens can accumulate cadmium. Heavy metals are linked to many
serious health issues. Dr. Jagannath Biswakarma writes for The Conversation:
“Heavy metal contamination in cropland varies by region,
often shaped by geology, land use history, and water management. Across central
and south-east Asia, rice fields are irrigated with groundwater that naturally
contains arsenic. That water deposits arsenic into the soil, where it is taken
up by the rice.”
Biswakarma also notes that in places where a single staple
crop is a major part of the diet, the concentrations of heavy metals and the
corresponding health effects can be increased.
Possible Solutions and Remediation Methods
Dr.
Biswakarma has been involved with the remediation of arsenic and other heavy
metals in soil, surface water, and groundwater.
“There is no single fix. We’ll need reliable assessment
of contaminated soils and groundwater, especially in vulnerable and smallholder
farming systems. Reducing exposure requires cleaner agricultural inputs,
improved irrigation, and better regulation of legacy industrial sites. Equally
critical is empowering communities with access to information and tools that
enable them to farm safely.”
Biswakarma was involved with a team that developed a low-cost filtration system to remove up to 95% of geogenic (natural geological) arsenic from groundwater used for drinking in Burkina Faso. Their work was published in 2020 in the Science of the Total Environment. The team used zero-valent iron (ZVI) in the form of iron nails sandwiched between sand and gravel layers for the filtration. Highlights from the paper and a model of the filtration system are shown below. Laboratory column filters work better than household filters but both work well.
Biswakarma is also the lead
author of a groundbreaking study published in Environmental Letters in October
2024 which found that a dangerous arsenic compound, arsenite can be converted
chemically through a redox reaction to a benign form, arsenate, which offers a
great opportunity to reduce arsenic pollution in drinking water, which is a big
problem in parts of the world. He described the discovery in a University of
Bristol science news story.
“Dr Biswakarma said: “I’ve seen the daily battle for
safe drinking water in my hometown Assam. It’s very hard to find groundwater
sources that aren’t contaminated with arsenic, so for me this research hits
close to home. It’s an opportunity to not only advance science, but also better
understand the extent of a problem which has affected so many people in my own
community and across the world for many decades.”
“Scientists previously believed arsenite could only be
turned into the less harmful form, called arsenate, with oxygen. But this new
study has shown it can still be oxidised, even in the absence of oxygen, with
small amounts of iron which act as a catalyst for oxidation.”
“Dr Biswakarma said: “This study presents a new approach
to addressing one of the world's most persistent environmental health crises by
showing that naturally occurring iron minerals can help oxidise, lowering the
mobility of arsenic, even in low-oxygen conditions.”
A January 2024 paper in the
journal Toxics explored the sources, influencing factors, and remediation
strategies of heavy metal contamination in agricultural soils. Anthropogenic
sources of heavy metals in agricultural soils include atmospheric deposition,
animal manure, mineral fertilizers, and pesticides.
Plant characteristics and soil factors influence the accumulation of heavy metals in soils. Remediation strategies include low-metal cultivar selection/breeding, physiological blocking, water management, and soil amendment.
Phytoremediation is considered
in terms of remediation efficiency and applicability.
“Soil phytoremediation refers to the utilization of
certain heavy metal accumulating plants to reduce the metal content or
alleviate the toxic effects in the soils, which is an eco-friendly and
sustainable approach to restoring contaminated land.”
The paper’s conclusion notes
the suitability of different remediation methods in terms of soil chemistry and
reducing food plant uptake.
“The application of these technologies is relatively
mature, but there are some limitations. For example, water management is a
practical and inexpensive strategy to lower Cd accumulation in rice, but it is
not suitable for upland crops. Soil amendments such as lime are effective in
immobilizing Cd in acidic soil but have limited effects in alkaline and neutral
soil. Phytoremediation is time-consuming, and the addition of leaching agents
can cause secondary pollution. Low-metal cultivar planting is proposed as a
practical method to address the low-to-medium heavy metal-contaminated
farmland. Due to the diversity of soil types and pollution sources, and the
heterogeneity of spatial change of heavy metals in soils, it is difficult to
promote a universal and cost-effective method; therefore, it is necessary to
develop appropriate measures suitable for the local areas and make the
management more precise and effective.”
The tables below show different heavy metal limits by country and limits of heavy metals in organic fertilizers by country respectively.
References:
Heavy
metals taint nearly 1 in 6 croplands worldwide, say scientists. Jagannath
Biswakarma; Phys.org. April 18. 2025. Heavy
metals taint nearly 1 in 6 croplands worldwide, say scientists
‘Heavy
metals’ contaminate 17% of the world’s croplands, say scientists. Jagannath
Biswakarma. The Conversation. April 17, 2025. ‘Heavy
metals’ contaminate 17% of the world’s croplands, say scientists
About
242 million hectares of world's agricultural land contaminated by toxic heavy
metal pollution: Study. Susan Chacko. April 17, 2025. Down to Earth. Global
Agricultural Land Crisis: 242 Million Hectares Polluted by Toxic Heavy Metals
Global
soil pollution by toxic metals threatens agriculture and human health. Deyi Hou,
Xiyue Jia, Liuwei Wang, Steve P. McGrath, Yong-Guan Zhu, Qing Hu, Fang-Jie Zhao,
Michael S. Bank, David O’Connor, and Jerome Nriagu. Science. 17 Apr 2025. Vol
388, Issue 6744. pp. 316-321. Global soil
pollution by toxic metals threatens agriculture and human health | Science
Heavy
Metals in Agricultural Soils: Sources, Influencing Factors, and Remediation
Strategies. Yanan Wan, Jiang Liu, Zhong Zhuang, Qi Wang, and Huafen. Editor:
Luis Alberto Henríquez-Hernández. Toxics. 2024 Jan 12;12(1):63. Heavy Metals in
Agricultural Soils: Sources, Influencing Factors, and Remediation Strategies -
PMC
Scientist
on personal mission to improve global water safety makes groundbreaking
discovery. University of Bristol. Press release issued: 29 October 2024. October:
Global water safety | News and features | University of Bristol
Arsenic
removal with zero-valent iron filters in Burkina Faso: Field and laboratory
insights. Anja Bretzler, Julien Nikiema, Franck Lalanne, Lisa Hoffmann, Jagannath
Biswakarma, Luc Siebenaller, David Demange, Mario Schirmer, and Stephan J. Hug.
Science of The Total Environment. Volume 737, 1 October 2020, 139466. Arsenic
removal with zero-valent iron filters in Burkina Faso: Field and laboratory
insights - ScienceDirect
Redox
Dynamic Interactions of Arsenic(III) with Green Rust Sulfate in the Presence of
Citrate. Jagannath Biswakarma, Molly Matthews, and James M. Byrne. Environmental
Science & Technology Letters. Vol 11/Issue 11. October 15, 2024. Redox Dynamic
Interactions of Arsenic(III) with Green Rust Sulfate in the Presence of Citrate
| Environmental Science & Technology Letters
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