From Salt Deposits to the Dinner Table: A Systematic Review of Heavy Metal Contamination in Edible Salt; Sources, Limitations of Conventional Purification, Human Exposure, and Regulatory Gaps.

Edible salt is an essential component of the human diet and a critical vehicle for iodine fortification, yet it can also serve as a pathway for chronic dietary exposure to toxic heavy metals. Despite decades of research documenting metal contamination in salt, the sources of contamination, particularly the potential role of mine blasting, remain inadequately characterized, and the efficacy of conventional purification methods has been overestimated. This systematic review aimed to synthesize available evidence on heavy metal contamination in edible salt across four interconnected dimensions: (1) documented sources of contamination, while also highlighting empirically untested hypotheses regarding potential extraction‑related contamination pathways (e.g., mining operations) as priorities for future investigation; (2) limitations of conventional purification methods in achieving complete metal removal; (3) human exposure levels and associated health risks; and (4) existing regulatory frameworks and their shortcomings. A systematic search of PubMed, Scopus, and Web of Science was conducted for original research articles published between January 2016 and June 2026 reporting quantitative measurements of heavy metals in edible salt. Of the 16 studies initially meeting the broad eligibility criteria, 12 provided robust quantitative data on heavy metal concentrations with associated health risk or purification assessments and formed the core evidence base (Table 1). The remaining 4 studies were predominantly method‑development or qualitative classification papers and are summarized separately in Supplementary Table S2. Lead (Pb) was the most frequently reported toxic metal, with concentrations ranging from 0.001 mg/kg in Lake Urmia salt to 18.43 mg/kg in contaminated Pakistani sea salt. Cadmium (Cd) reached 6.08 mg/kg in Ghanaian market salts, and mercury (Hg) reached 15.3 mg/kg in Pakistani sea salt, 153 times the Codex limit. Conventional purification methods substantially reduced heavy metal concentrations, but did not completely eliminate them. Health risk assessments diverged sharply: salts from clean environments posed negligible risks, while contaminated salts exhibited hazard indices exceeding 20 and carcinogenic risks above the USEPA threshold. Importantly, no study investigated the contribution of mine blasting with explosives to salt contamination, a significant research gap. Regulatory standards were inconsistent across jurisdictions, with no limits specified for chromium, nickel, cobalt, aluminum, or antimony. Heavy metal contamination of edible salt is a global phenomenon, with the highest levels found in salts from polluted harvesting sites. Conventional purification methods can substantially reduce heavy metal contamination, often by over 90%, but they do not necessarily eliminate it entirely. Current regulatory frameworks exhibit important inconsistencies and coverage gaps, particularly for several trace metals that are not specifically addressed in existing standards. The absence of direct evidence regarding contamination pathways associated with mining operations highlights an important knowledge gap that warrants future investigation. Strengthened regulatory standards, may help improve food safety oversight and reduce consumer exposure.