Sea weeds are the chief source of:

Marine algae (seaweeds) are highly efficient at absorbing and concentrating dissolved minerals from seawater. Among these minerals, iodine is absorbed and stored by brown algae and kelp at concentrations many thousand times higher than in the surrounding seawater — a property that is especially strong in these marine plants.

Because kelp and other seaweeds concentrate iodine so effectively, seaweed ash (kelp ash) was historically the world's first large-scale commercial source of iodine — iodine itself was discovered in 1811 by Bernard Courtois while processing seaweed ash for saltpetre production. Even today, seaweed and marine algae remain one of the richest dietary sources of iodine, an element essential for the synthesis of the thyroid hormone thyroxine.

The other elements offered have different principal natural sources, unrelated to this seaweed-concentration property:

• Chlorine is obtained chiefly from rock-salt (halite) deposits and by the electrolysis of brine/seawater chloride.

• Bromine is recovered industrially from natural brine deposits and salt lakes such as the Dead Sea, which are rich in bromide salts.

• Iron is sourced chiefly from ores such as hematite and magnetite, and from iron-rich foods like leafy greens and legumes.