In the microscopic battlefield of plant-microbe interactions, plants are constantly fighting off invading bacteria. New research reveals just how clever these bacterial invaders can be.

Based on data from over 1000 regional studies combined with machine learning, researchers estimate that as many as 1.4 billion people live in areas with soil dangerously polluted by heavy metals like arsenic, cadmium, cobalt, chromium, copper, nickel, and lead. The study reveals a global risk, but also a previously unrecognized high-risk, metal-enriched zone in low-latitude Eurasia, in particular. The growth in demand for critical metals means toxic heavy metal pollution in soils is only likely to worsen. “We hope that the global soil pollution data presented in this report will serve as a scientific alert for policymakers and farmers to take immediate and necessary measures to better protect the world’s precious soil resources,” say the authors. Toxic heavy metal pollution in soil, originating from both natural sources and human activities, poses significant risks to ecosystems and human health. Once introduced into soils, such metals can persist over decades. These pollutants reduce crop yields, affect biodiversity, and jeopardize water quality as well as food safety through bioaccumulation in farm animals. However, while previous studies have shown that toxic metal pollution is ubiquitous in soils, its worldwide distribution remains poorly understood. To address this knowledge gap, Deyi Hou compiled data from 1,493 regional studies encompassing 796,084 soil samples to assess the global distribution of toxic metals in agricultural soils and to identify where concentrations exceed safety thresholds. Using machine learning and modeling approaches, Hou et al. estimate that 14–17% of cropland globally – roughly 242 million hectares – is contaminated by at least one toxic metal, with cadmium being the most widespread, especially in South and East Asia, parts of the Middle East, and Africa. Nickel, chromium, arsenic, and cobalt also exceeded thresholds in various regions, largely due to a mix of natural geological sources and human activities such as mining and industrialization. Moreover, findings revealed a transcontinental “metal-enriched corridor” stretching across low-latitude Eurasia, which likely reflects the cumulative effects of ancient mining, weathering of metal-rich bedrock, and limited leaching over time. By superimposing these data with global population distribution, Hou et al. estimate that 0.9 to 1.4 billion people live in high-risk areas.