Mercury in croplands adjacent to artisanal and small-scale gold mining: evidence of cyanide co-contamination, transport pathways and screening dietary risk

Artisanal and small-scale gold mining (ASGM) uses mercury (Hg) for amalgamation and sometimes cyanide (CN) for gold recovery, potentially transferring contaminants from mine wastes to croplands. We systematically reviewed and narratively synthesized evidence on Hg and CN in cropland soils and edible tissues, mine-to-cropland pathways, crop effects, and screening-level dietary risk. Hg was consistently quantified in soils and detected in rice grain, vegetables, and plantain, whereas CN was rarely assessed: only one study reported soil CN, and none quantified CN in edible tissues. Using national food-supply-based ingestion rates and conservative toxicological assumptions, crop Hg concentrations often produced hazard quotients above 1. Plausible pathways included runoff, sediment redistribution, contaminated irrigation water, and atmospheric Hg deposition. Evidence that Hg–CN complexation affects plant-available Hg in agricultural soils remains limited. Future research should prioritize paired soil–plant monitoring of Hg species and CN fractions, local dietary surveys, and mitigation strategies.