The fate of chlorine in sea-water

The consumption of hypohalite (or chlorine demand) in sea-water seems to occur in two phases. Residual chlorine concentration decreased rapidly within the first hour and noticeably slower afterwards. Total consumption of up to 3.3 ppm chlorine was observed within 30 h. The chlorine demand increased with increasing initial hypohalite concentrations and increasing time of contact. No limit of chlorine demand was observed. Data from ultra-violet spectroscopy suggest that the hypochlorite reacts with bromide ion to form hypobromite. The reaction is fast and seems to reach completion within 2.5 min. Hypobromite is thus the major species measured as residual chlorine which is consumed in sea-water. One of the products can liberate iodine from iodide at low pH (pH 1.4). This species, however, is not bromate and it decomposes with time. Further studies on the chemistry and toxicity of bromine containing species in chlorinated sea-water will be necessary in order to realize fully the environmental impact of the chlorination of sea-water.