Global Potential Risk of Thallium in Topsoil: A Cropland-Focused Quantification Framework

Thallium
(Tl) pollution from natural and anthropogenic
sources
is increasingly recognized for its environmental and health risks,
with localized threats in polluted areas despite low global background
levels. Utilizing over 20,000 topsoil Tl measurements with 21 related
environmental variables, a CatBoost classification model (AUC = 0.89,
recall = 0.80, balanced accuracy = 0.84) was applied to predict whether
global topsoil Tl concentrations exceeding 1 mg/kg, identifying both
known and unreported hotspots. A CatBoost regression model (R2 = 0.62) further predicted Tl concentration
distributions, highlighting regional variations. This study reveals
that high-risk areas are highly overlapped with anthropogenic factors
(mining activities and land cover) and geological conditions (mineralized
zones, lithology, and geological structures), collectively influencing
14.81% of the model outputs. By integrating cropland cover maps with
our predictions, we found that approximately 9.9% of the world’s
cropland has a greater than 47% probability of Tl concentrations exceeding
1 mg/kg, particularly in South America (34.7%), Asia (12.3%), and
Africa (10.8%). These findings underscore the need for heightened
attention to soil Tl testing in high-risk croplands to ensure agricultural
safety.