select search filters
briefings
roundups & rapid reactions
Fiona fox's blog
A study published in Science looks at global soil contamination by toxic metals.
Dr Lucie Buchi, Senior Lecturer in Crop Ecology at the NRI, University of Greenwich, said:
“While the results of the study seem alarming, the 10×10 scale of the grid cells that the study was based on does not allow any practical application at a local scale. The authors make note of this in the paper: ‘The present study is based on average metal concentrations on a 10-km grid, which is more reflective of diffusive and regional pollution rather than site-specific conditions. The data may be sufficient for risk screening purposes but are inadequate to support risk mitigation. Soil remediation needs to rely upon site-specific delineation of lateral and vertical extent of soil pollution, as well as a better understanding of metal sources, fate and transport dynamics, and bioavailability’.
“Their map also seems to show low risks in the UK, except for a hotspot in the south and Ireland, but the scale of the figure doesn’t allow to understand where it is actually. And again, with a resolution of 10 x 10 km, nothing can be concluded for any particular fields. But farmland in the hotspot would probably need to be careful, but these regions are probably already known for heavy metal presence.
“The authors conclude ‘We hope that the global soil pollution data presented in this report will serve as a scientific alert for policy-makers and farmers to take immediate and necessary measures to better protect the world’s precious soil resources.’, and I think this is what it is, more of an alert about a global problem, but which requires further investigation at smaller spatial scales.”
Prof Oliver Jones, Professor of Chemistry, RMIT University, said:
“I am in two minds about this paper. On the one hand, it takes a clever scholarly approach, and soil pollution is a serious issue in many parts of the world; on the other hand, I feel some of the conclusions are perhaps a little preliminary.
“The authors have not generated new data but combined data from existing studies together and then used some very complex data processing methods to predict concentrations of selected metals across a wider area. This method has generated some interesting insights – such as the potential “metal-enriched corridor” across low-latitude Eurasia (although I think blaming this corridor on multiple ancient cultures might be overspeculative). However, there are also issues here. For example, the authors refer to “toxic metals” throughout the paper, even in the title. This is a little misleading because detection is not the same as relevance. Everything is toxic at the right dose, even water. It would be better to just say ‘metals’ and then discuss concentrations if/where appropriate rather than suggesting everything is toxic right from the title.
“The authors also refer to metal concentrations in soil. The fact that some places on Earth have high levels of metal contamination in their soils and that this could have effects on humans is not new. However, the amount of a compound in the soil does not automatically correlate with the amount that ends up in plants grown in the soil or the amount that people or animals that might eat those plants might eventually be exposed to. According to the supplementary data of the paper, the probability of many of the metals exceeding human health thresholds is low in most cases (including the UK). Context and nuance are important in toxicology and environmental health, as are local conditions. Thus, while certainly worth discussion, the question of whether metal pollution actually threatens agriculture and human health at a global scale is, I think, far from proven”.
Dr Wakene Negassa, Soil Chemist, The James Hutton Institute, said:
Does the press release accurately reflect the science?
“The press release accurately captured the important ideas presented in the published paper.
Is this good quality research? Are the conclusions backed up by solid data?
“The authors did not present original research but reviewed previously published studies. Nevertheless, reviewing existing literature is a conventional and valuable approach for identifying research and technology gaps. What sets this review apart is the authors’ use of artificial intelligence to identify global hotspots of soil pollution, distinguishing it from traditional mapping and review papers. Such global analyses are essential for technological and policy interventions of addressing global soil pollution by heavy metals. Although soil pollution from anthropogenic activities has not been widely addressed, databases like Web of Science (WOS) and the National Library of Medicine (PubMed) have indexed over 2,000 related publications since 1960. As the authors conclude, “We hope that the global soil pollution data presented in this report will serve as a scientific alert for policy-makers and farmers to take immediate and necessary measures to better protect the world’s precious soil resources.”
How does this work fit with the existing evidence?
“This work aligns with existing evidence, as soil pollution has become a global concern. Although the authors did not include a detailed account of polluted areas, a recent review by Khan et al. (2021) reported over five million soil pollution sites worldwide (Khan et al., 2021; DOI: 10.1016/j.jhazmat.2021.126039)
Have the authors accounted for confounders? Are there important limitations to be aware of?
“One major limitation of this review is that the authors did not present the chemical forms (speciation) of heavy metals. It is not the total concentration of heavy metals that determines their potential as pollutants, but rather their bioavailable forms—those that can be taken up by plants and transferred through the food chain to animals and humans. Additionally, the magnitude of global soil pollution may be greater than what is reported in the review, as the authors themselves acknowledge, due to a lack of comprehensive data from many countries.
What are the implications in the real world? Is there any overspeculation?
“As mentioned in previous responses, the actual extent of global soil pollution may far exceed what is presented by the authors, due to limited data availability and likely underestimation.
What is the significance of heavy metal contamination in croplands – how does it affect food and/or biodiversity?
“Soil pollution by heavy metals disrupts plant cellular functions and enzyme activities, resulting in reduced growth and yield, as well as shifts in soil microbial populations. Consuming food or feed grown on contaminated soils, or direct exposure to such soils, poses significant health risks, including kidney damage, neurotoxic effects, and increased carcinogenic potential.
What is the relevance of this study for UK agriculture and/or public health?
“It is also worthwhile to investigate UK agricultural soils, as over half a century of intensive farming practices, including continuous use of agrochemicals and the application of various agricultural and urban waste materials, may have led to the accumulation of heavy metals. This could pose potential risks to plant, animal, and human health and ecosystem services.”
Prof Mark Tibbett, Chair of Soil Ecology, University of Reading, said:
“After many years working post-mining landscapes and in industries that supply metals to soil in organic wastes, it has been intuitively obvious to me that our food production and natural ecosystems are commonly replete with toxic metal, often of human origin. This comprehensive analysis, which seems long overdue, provides clear and worrying empirical evidence of the extent and expanse of this global issue. It is clear that anthropogenic toxic metals are a global and growing pollution issue in our soils, with human activities at the core of the patterns seen.”
Prof Chris Collins, Professor of Environmental Chemistry, University of Reading
“This is a very useful study and highlights the issue of global soil pollution. Congratulations to the authors for compiling such a large data set. Although as the authors state the real issues only potentially exist in Eurasia rather than worldwide. It should be noted that presence in soil does not mean the crop grown in that soil will absorb and be contaminated by an element as this depends on the chemical form. The authors do acknowledge this along with other exposure factors e.g. if crops are for human consumption. The study will be of use in identifying those areas where edible crops should be avoided and alternatives, e.g. biomass crops, should be grown. The UK is relatively unaffected (Fig 2B). There are some areas e.g. the SW but this is known and is probably arsenic which is in a form not freely transferred into crops.”
Dr Liz Rylott, Senior Lecturer, Department of Biology, University of York, said:
“Deyi Hou and colleagues used cutting edge technologies to globally map the distribution of toxic metals. Their findings reveal the deeply worrying extent these natural poisons are polluting our soils, entering our food and water, and affecting our health and our environment.
“Of concern are cadmium, copper, nickel and lead, and the metalloid arsenic. Often collectively called heavy metals, these elements cause a range of devastating health problems, including skin lesions, reduced nerve and organ functions, and cancers. While some of the contamination is due to naturally occurring geological outcrops of these metals, much of the pollution is from mining and associated industrial activities. As our drive for technology-critical metals to build the green infrastructure required to tackle climate change (wind turbines, electric vehicle batteries and photovoltaic panels) will exacerbate this pollution.
“Other scientists (Fuller et al The Lancet 2022) calculated that 16% (9 million) of all deaths globally each year are caused by environmental pollution, of which, heavy metals comprise a significant proportion. This new research links the presence of these heavy metals in the agricultural soils and water, with the food that we eat.
“To track these elements, extensive regional studies and AI technology were used to build a map detailing soil metal concentrations at a 10 km grid resolution across the world. The analysis reveals previously unrecognised hotspots of metal-enriched areas, including a zone across southern Europe.
Much of the pollution is in low- and middle-income countries, where communities are directly affected, exacerbating poverty. The effect of these contaminated crops entering global food networks is not as clear. The authors call for soil pollution surveys in data-sparse areas such as sub-Saharan Africa to understand more about its effects on local, and global, human and environmental health.
“There are ongoing global initiatives (the United Nations Environment Programme (UNEP) and FAO) to remediate contaminated soils. This map will be a powerful tool to help us to identify high-risk areas, understand how natural and human activities have contributed to the pollution, and design mitigation and remediation strategies.
“This map also illustrates how metal pollution is independent of human borders; to tackle this problem, countries will have to work together.”
‘Global soil pollution by toxic metals threatens agriculture and human health’ by Hou et al. was published in Science at 19:00 UK time on Thursday 17th April.
DOI: 10.1126/science.adq6807
Declared interests
Dr Lucie Buchi “I don’t have any conflict of interests to declare”
Prof Oliver Jones “I have no conflicts of interest to declare in this case.”
Dr Wakene Negassa “None”
Prof Chris Collins “None”
Dr Liz Rylott “no conflict of interest”
For all other experts, no reply to our request for DOIs was received.