This part of ISO 15587 specifies a method for extracting trace elements from a water sample using aqua regia as a digestion agent. The method is applicable to all types of waters with a suspended solids concentration of less than 20 g/l and a mass concentration of total organic carbon (TOC) expressed as carbon of less than 5 g/l. The aqua regia digestion method is empirical and it will not release elements completely. However, for the most environmental applications the result is fit for the purpose. Aqua regia is suitable for the release of: Ag, Al, As, B, Ba, Be, Ca, Cd, Cr, Co, Cu, Fe, Hg, Mg, Mn, Mo, Na, Ni, K, P, Pb, Sb, Se, Sn, Sr, Tl, V, Zn.