Quantitative in situ monitoring of organohalogen compounds in domestic sewage resulting from the use of hypochlorite bleach

A field monitoring program was carried out on the sewage of five large apartment blocks in the city of Parma, Italy, to verify under realistic conditions existing laboratory data and model calculations on organohalogen formation by domestic hypochlorite (NaOCl) bleach usage. The average adsorbable organic halogens (AOX) level was determined for three distinct experimental phases: an 'undisturbed period', a 'no bleach period', and a 'controlled bleach usage period'. The study involved participation of the site inhabitants in the second and third phases. In line with what could be predicted from the hypochlorite chemistry, an effect of the use of hypochlorite bleach on the AOX concentration in domestic sewage was detected. In a laboratory simulation conducted in parallel with the field study, the degree of NaOCl-to-AOX conversion ranged from 0.75 to 2.25% (w/w). The degree of conversion in the field study itself was of the order of 1.5% (or 0.075% when expressed for a typical bleach product containing 5% NaOCl). Under the specific conditions of the site, the difference in average AOX concentration in sewage between the 'no bleach' and the 'undisturbed' bleach use period was of the order of 37 μg.l-1 (P < 0.05). The average bleach-related AOX emission at the study site was around 7 mg.(inhabitant.day)-1. Overall, these figures correspond well with existing literature data. Linking the measured amounts of AOX with available ecotoxicity data for treated domestic effluents and their organohalogen constituents, it can be considered unlikely that the organohalogens formed by domestic bleaching will exert or trigger any adverse environmental effect.