Iron and water: reaction mechanisms, environmental impact and health effects

Seawater contains approximately 1-3 ppb of iron. The amount varies strongly, and is different in the Atlantic and the Pacific Ocean. Rivers contain approximately 0.5-1 ppm of iron, and groundwater contains 100 ppm. Drinking water may not contain more than 200 ppb of iron.
Most algae contain between 20 and 200 ppm of iron, and some brown algae may accumulate up to 4000 ppm. The bio concentration factor of algae in seawater is approximately 10⁴ - 10⁵. Sea fish contain approximately 10-90 ppm and oyster tissue contains approximately 195 ppm of iron (all are dry mass).
Dissolved iron is mainly present as Fe(OH)₂⁺ (aq) under acidic and neutral, oxygen-rich conditions. Under oxygen-poor conditions it mainly occurs as binary iron. Iron is part of many organic and inorganic chelation complexes that are generally water soluble.