Global cereal trade drives bidirectional cadmium redistribution across income groups

Cadmium governance assumes that controlling contamination where cereals are grown is sufficient to protect consumers, yet how international trade redistributes this exposure remains unquantified. Here we reconstruct four-decade (1980-2023) national cadmium concentration time series for rice, wheat and corn from 182,873 grain measurements across 55 countries using crop-specific random forest models, and couple them with bilateral trade flows to quantify trade-embedded cadmium-the fraction of dietary exposure originating from imports rather than domestic production. Three transmission pathways operate in opposing directions: wheat exports carry cadmium consistent with long-term phosphate fertilizer accumulation from high-income producers to low-income importers; rice channels cadmium associated with mining-affected production regions from low-income exporters into high-income diets; and corn from major exporters consistently carries lower concentrations than recipients' domestic production, diluting rather than amplifying exposure. By 2023, trade-embedded cadmium accounted for 86% of wheat-related exposure in low-income countries and 62% of rice-related exposure in high-income countries, up from 73% and 11% in 1986. Screening-level assessment under a 60-kg adult reference scenario identifies rice in Bangladesh as exceeding the JECFA health-based guidance value, with additional exceedances under the more conservative EFSA benchmark. These crop-specific flows are not captured by production-focused governance, indicating a need for complementary supply-chain accounting and source-resolved import monitoring.