Iodine and water: reaction mechanisms, environmental impact and health effects Iodine
is naturally present in water. The average concentration in seawater is about 60 ppb, but varies from place to place. Rivers usually contain about 5 ppb of iodine, and in mineral sources some ppm can even be found. Brown algae accumulate up to 0.45% (dry mass) of iodine. Corals, sea sponges, shells and fishes accumulate high iodine concentrations, usually in the shape of thyroxin or tri-iodine thyroxin.