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Environmental fate & pathways

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HHCB does not mineralise under the conditions in screening tests for readily biodegradation (KEY study Jenkins 1991).

From other biodegradation studies in water and/or sediment it is concluded that primary biodegradation to a series of more polar metabolites takes place, with HHCB-lactone and hydroxycarboxylic acid as likely intermediates. These substances still contain the same amount of organic carbon and only a small fraction of the theoretical oxygen demand has been incorporated. Thus this metabolism is in agreement with the observed low degree of mineralisation.

From the studies with activated sludge spiked with 14C-radio-labelled HHCB in batch experiments (a.o. Schaefer 2005) it is concluded that the parent substance was transformed to a series of polar metabolites. In general the radio-labelled parent HHCB disappeared with half-life values in activated sludge of 10 – 15 hours (Schaefer 2005). In the river die-away test with 5 µg/l the parent HHCB disappeared with a half-life of 100 hours (4 days, KEY study Schaefer 2005).

Field measurements on sludge amended soil indicate that HHCB disappeared almost completely from soil within one year. The residues in soil after one year ranged from below 10% to 14% of the initial concentrations (Envirogen 1998). The half-life of 105 days in the sludge amended soil test is most relevant for the fate of HHCB in soil in the EUSES model, whereas 79 days was noted for the sediment (KEY study Envirogen 1998).

Subsequently, for the environmental risk assessment, HHCB may be considered as 'inherently biodegradable, not fulfilling criteria' (terminology of the EU-TGD, EC 2003). For surface water, sediment and soil, the PECs used on the risk assessment will be calculated using conservative biodegradation rate constants expressed as half-life times: 60 d in surface water (20 ºC) and 150 d in the soil and sediment compartments (12 ºC). For the PBT assessment, the studies of Schaefer (2005) shows that HHCB is 'not P' in water, whereas the studies of Envirogen (1998) show that HHCB is 'not P' in sediment and in soil.