Cl naturally exists as both inorganic chloride (Cl?) and organic chlorine (Clorg) in soil, vegetation, water as well as in the atmosphere (Öberg, 2002). Primarily Cl occurs in nature with two stable isotopes, 35Cl (ca 76%) and 37Cl (ca 24%). Along with stable isotopes, seven radioactive isotopes of Cl do exist of which 36Cl has a very long half-life, 300,000 years. For a longer time, it was widely believed that all chlorinated organic compounds (Clorg) are anthropogenic, were considered not to participate in biological processes and that chlorine is mainly present in the environment as chloride ions (Cl?) or inorganic chlorine (Clinorg) (Schlesinger, 1997). However, today many studies are documented that chloride participates in a complex biogeochemical cycle (Asplund and Grimvall, 1991; Van Peè, 2001; Winterton, 2000; Öberg, 1998). These studies reported that large amounts of naturally produced Clorg are present in all environmental compartments. For example, in boreal and temperate soils, 48% to almost 100% of the total Cl has been found as Clorg in the upper soil layers (Johansson et al., 2003a; Johansson et al., 2003b; Redon et al., 2011). Clorg  has also been found in streams, ground water, sea water and surface waters (Grimvall et al., 1991; Manninen and Lauren, 1995; Öberg, 2002). Until recently, more than 5000 natural halogenated compounds have been identified so far (Gribble, 2012; Gribble, 2015), of which 2300 are Clorg. Thisindicates the widespread distribution of Clorg in the environment and natural chlorination (transformation of Cl? to Clorg) is considered the main source of Clorg in the environment (Johansson et al., 2001; Öberg, 2002). Chlorination and de-chlorination processes occur simultaneously in the soils and considered the important processes controlling the Cl cycling in the environment (Montelius, 2015). The proposed summary of the natural Cl cycling in the terrestrial ecosystem is presented in Figure 1. Briefly, from the atmosphere, Cl is deposited on land, taken up by the plants and is returned to the soil via through-fall, stemflow and litter fall.