Human Toxicity and Marine Ecotoxicological Risk of Methanol as a Ship Fuel: A Critical Narrative Review of Exposure, Fate and Aquatic Effects

Methanol is being adopted as a marine fuel on a safety profile that is quoted more often than it is checked. This review audits the provenance of that profile. Four load-bearing claims—rapid dilution, a one-to-seven-day aqueous half-life, negligible bioaccumulation and manageable human toxicity—were traced backward from the maritime literature to the document generating each, every transfer was examined for whether the measurement conditions stated at origin were carried forward, and every record was verified against the issuing body’s own version. Of nine quantitative claims traced, two reached the sector with their conditions intact, five lost them, and two rest on primary records that could not be retrieved, with one being the only marine acute determination located. Three mechanisms recur: one term, half-life, carrying both a clinical elimination window and an environmental turnover figure; values transmitted without the method that produced them; and one property cited for opposite conclusions by bodies that do not cite each other. Methanol remains milder than heavy fuel oil and ammonia, but conditionally so. The first gas alarm, at twenty percent of the lower explosion limit, falls near 11,000 to 12,000 ppm, whereas 6000 ppm is immediately dangerous to life.