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

Seawater contains about 400 ppm potassium. It tends to settle, and consequently ends up in sediment mostly. Rivers generally contains about 2-3 ppm potassium. This difference is mainly caused by a large potassium concentration in oceanic basalts. Calcium rich granite contains up to 2.5% potassium. In water this element is mainly present as K⁺ (aq) ions.
⁴⁰K is a naturally abundant radioactive potassium isotope. Seawater contains a natural concentration of about 4.5 . 10^-5 g/L.