Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

- Abiotic degradation:

Air: Based on a study conducted by Aschmann et al. (2001), HHCB undergoes in air rapid degradation after reaction with hydroxyl radicals. The atmospheric DT50 value after reaction with hydroxyl radicals is 3.7 hours. The half-life time of the substance is < 2 days. The substance will not reach the stratosphere and is therefore not considered to be a long-range transported chemical in air (http://www.unece.org/fileadmin/DAM/env/documents/2000/ece/eb/ece%20eb%20air.60.e.pdf).

The substance does not have an ozone depletion potential because it does not contain halogens and does not have the potential to reach the stratosphere (CLP, 2008, Part 5).

Water: Published studies show that HHCB is photodegraded in water, with a half-life time of less than one week. The substance is hydrolytically stable, because it does not contain hydrolysable groups in its chemical structure such as esters, carbamates, epoxides, halomethanes, acylhalides (see Hydrowin, EpiSuite for all hydrolysable groups). The half-life at 20°C is therefore expected to be > 1 year.

- Biotic degradation:

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'. 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).

- Bioaccumulation:

Based on review of the EU Risk Assessment Report for HHCB (2008), a key value for the BCF in aquatic organism of 1584 was selected as the key value. It can be concluded that the substance has a moderate bioaccumulation potential.

The BCF in earthworms was estimated to be 2395 l/kg ww with the equation from Jager (1998), indicating that the potential for bioaccumulation in terrestrial organisms will also be moderate.

- Transport and distribution:

The substance is a lipophilic substance with log Kow 5.3. The sorption to organic matter, log Koc, has been determined using log Kow and is 4.39. This indicates that the substance will have a high potential to adsorb to sediment/soil.

To assess the volatilisation potential of the substance a Henry's law constant was determined which showed a value of 36.9 Pa. m3/mol. Distribution modelling showed that volatilisation only plays a minor role in the environmental behaviour of HHCB. 

Based on Level III distribution modelling using EPISUITE (assuming equal and continuous releases to air, water and soil) using the CAS number 1222-05-5 and the determined log Kow, it is estimated that the majority of the substance released to the environment will partition mainly into soil (83%), with smaller amounts to sediment (10%) and water (6.73%) and a negligible amount to air (0.27%).

The SimpleTreat model, which is incorporated in EUSES, simulated the distribution of the substance in a Sewage Treatment Plant based on vapour pressure, water solubility, log Kow and biodegradability. The model predicts that 0% of the substance will biodegrade, 25.4% will partition to water, 69.1% to sewage sludge and 5.5% to air.