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Environmental fate & pathways

Phototransformation in water

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Description of key information

HHCB is photodegraded in water with a half-life time of less than one week

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The photodegradation of HHCB in water was studied by Buerge et al. (2003). HHCB was incubated in lake water from the Zürichsee (CH) or in distilled water at 20 ± 1 ºC and illuminated with actinic lamps (mercury-vapor fluorescent lamps, between 300 and 460 nm with a maximum at 365 nm, comparable to that of 24h-averaged sunlight at 50 ºN in July under clear sky conditions).The rates of photodegradation were 0.15 and 0.12 day-1in lake water and distilled water, respectively (half-lives of 109 and 135 h).The minimal differences between the photolysis rate constants determined in lake water and distilled water indicate that HHCB is degraded primarily via direct photolysis and that indirect photochemical degradation by reactive oxygen species is of minor importance. The photodegradation may explain the decreased concentrations in the epilimnion of the lake in summer.

Sanchez-Prado et al. (2004) also studied the photo-induced degradation of HHCB, using a solid-phase micro-extraction fibre. For the UV radiation low-pressure mercury lamps (8-10 W, 245 nm) were used. The irradiation was conducted with HHCB adsorbed on the fibre, as well as solved in water. 100 µm fibres coated with polydimethylsiloxane (PDMS) were used. Photodegradation of the parent HHCB showed a half life of about 40 minutes. After 120 minutes 90% was degraded. The tentatively identified degradation products show that HHCB is not attacked on the hexamethylcyclopenta-benzene side but at the pyran side of the molecule, either by formation of a five-ring with aldehyde group or by removal of the oxygen moiety.