A component of anti-fouling paints used on ships‘ hulls — an organotin compound that can be released into water and accumulate as a contaminant in seafoods. Tributyltin (TBT) leached from hull coatings into harbours and coastal waters, concentrating in filter-feeding shellfish and sediments; it is an endocrine disruptor notorious for causing imposex in marine snails. International bans on TBT antifouling paints have reduced inputs, but legacy sediment contamination persists. Seafood monitoring programmes test for organotin residues, and maximum limits protect consumers — a case study in how a useful industrial chemical became a marine food-chain contaminant.