Halogens, Sulfur, Metals, and Metalloids
specific trace elements. A thorough, updated review of the scientific literature is recommended for project design. A number of substances are considered measures of water quality, but are seldom of concern as pollutants to be treated in constructed wetlands. These include common metals (e.g., sodium, potassium, calcium, and magnesium) as well as halogens (e.g., fluorine, chlorine, bromine, and iodine). Together with sulfate, these compounds often dominate the total ion content of natural waters and wastewaters.