Chlorine [Cl, 17]
73
11.3 WATERS
The median Cl concentration in seawater is estimated at 19,400 mg/L, and its mean
contents in stream water vary within the range of 1.4–5.3 mg/L (Reimann and de
Caritat 1998). Chlorine contents in precipitation are much lower, and do not exceed
2.1 mg/kg (Table 11.1). Rainwater over Kola Peninsula contain Cl between <0.1 and
2.1 mg/L, whereas rainwater over the United Kingdom has, on an average, 3 mg Cl/L
(Fuge 1988).
Chlorine is easily transported along with stream and river water to all water
basins. Chlorine concentration in water is usually measured as salinity (NaCl) content. Throughout the world, rivers carry about four billion tons of dissolved salts
to the oceans and seas annually. Similar amounts of salt are deposited in bottom
sediments. Thus, there is a balanced salt input and outgo. Salinity of the total ocean
water is 3.5%, and of some salty lakes may be up to 27%. The highest salt content,
about 34%, is in water of the Dead Sea (Salt Sea).
Chlorine is produced in large amounts and widely used, both industrially and
domestically, as an important disinfectant and bleach. In particular, it is widely used
as a disinfectant in swimming pools and is the most commonly used disinfectant
and oxidant in drinking water treatment. In water, Cl reacts to form hypochlorous
acid and hypochlorites. Concentrations of chlorate and some perchlorates increase
in hypochlorite solutions, upon storage at high ambient temperatures or when new
hypochlorite is added to old hypochlorite.
No health-based guideline value is proposed for Cl in drinking water. However,
its concentrations in excess of about 250 mg/L can give rise to detectable taste in
water. Presence of Cl in the most disinfected drinking water is within the concentrations of 0.2–1 mg/L (WHO 2011a).
11.4 AIR
World median Cl concentrations vary from about 0.023 μg/m 3 in air of remote world
sites to 0.24 μg/m 3 in polluted areas (Reimann and de Caritat 1998). Its concentration in the atmospheric air is (in μg/m 3 ) in Antarctica 0.003, and up to around 10 in
some urban areas (Table 11.1). Chlorine easily evaporates from the surface of seas
and oceans, and therefore its Cl content increases in air. Additional sources of Cl are
volcanic exhalations, most often in the form of hydrochloric acid (HCl).
Chlorine in air is of important health risk to human. Acute exposure to Cl is when
its concentration is about 200  μg/m 3 (OEHHA 2000). Air in enclosed swimming
pools may contain highly elevated Cl amounts, up to about 4000 μg/m 3 . Children
exposed to Cl gas have acute respiratory distress and eye irritation.
11.5 PLANTS
Soluble Cl species in soils are passively taken up by roots and easily transported in
plants. Plant leaves are capable of absorbing Cl directly from air. Chlorine as a compound of monovalent cations (e.g., NaCl) is more readily absorbed than from other
compounds. Some plants may accumulate relatively high amounts of Cl, especially