*4.1.3 Halogen compounds*

The volatile halogen compounds are rare in terrestrial plants, but quite habitual in marine algae because of the presence of chlorine and bromine ions at a high concentration in seawater. The red algae possess the highest abundance of halogenated organic compounds, which are found as terpenoid, phenols, carbonyl compounds, and fatty acid-derived metabolites [45]. They were produced in marine algae and emitted into the atmosphere; the highest amounts of brominated compounds released were done by *L. saccharina* [72]. Chemical investigations of marine algae have shown the presence of 2-bromophenol, 2,4-dibromophenol, and 2,4,6 tribromophenol in numerous red, green, and brown algae. It has been reported the biosynthesis of bromophenols in *U. lactuca* via the bromoperoxidases in the presence of precursors such as phenol, 4-hydroxybenzoic acid, and 4-hydroxybenzyl alcohol [73]. The bromoperoxidases are involved in the biosynthesis of brominated alkanes, such as CHBr3, CH2Br2, CHClBr2, and others in several marine organisms, among them, the red alga *Asparagopsis* sp. [74]. The biosynthesis of organohalogens has known enormous interest as reported in several literature review [75–77]. As indicated for bromocompounds, the iodoperoxidases are responsible of the production of iodinated compounds in marine algae [78–80]. The chemical investigation of 29 macroalgae species reveals their release of volatile iodocompounds iodoethane, 1-iodopropane, 2-iodopropane, 1-iodo-2-methylpropane, 1-iodobutane, 2-iodobutane, diiodomethane, and chloroiodomethane [81]; it has reported that diiodomethane was the main iodinated compound released by brown macroalgae [82].
