Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Abiotic degradation:

Hydrolysis: A review of structure of styrene shows that it contains no potentially hydrolysable functional groups. Therefore, based on the structure of styrene (i. e. lack of hydrolysable functional groups), it is not expected to hydrolyze significantly in the environment.

Photolysis (air): Half life of 0.38 days is estimated for reaction of styrene with hydroxyl radicals in the atmosphere at 25oC [AOPWIN Program, v.1.92] and a half-life of 0.55 days is calculated for reaction of styrene with ozone [AOPWIN Program, v.1.91]. Overall QSARs estimated half-life for degradation of styrene in air based upon AOPWIN Model is 3.28 hours.Based on the data on photochemical degradation of styrene in the air, it is considered to rapidly degrade in the atmosphere via photooxidation process.

Biodegradation:

Biodegradation in water, sediments and soil:

The QSAR models predicts timeframe within days-weeks for primary biodegradation of styrene and weeks for its ultimate degradation. The hydrocarbons QSAR model estimated half-life for styrene is 3.943 days.

The environmental fate of styrene in water and sediment will be determined by biotic and abiotic degradation.

The QSARs estimated half-lives for biodegradation of styrene in water and sediment based upon BIOWIN Ultimate Biodegradation are 360 hours (15 days) and 3240 hours (135 days), respectively. Whereas the half-lives of styrene for volatilization from water are estimated as 1.259 hours (for a river) to 4.138 days (for a lake) using EPI Suite software.

QSAR models developed and used by the US EPA (i.e. BIOWIN (v.4.10) software) predict that styrene is biodegradable in the environment. QSARs estimated half-life for biodegradation of styrene in soil based upon BIOWIN Ultimate Biodegradation Model is 720 hours (30 days) .

Environmental distribution:

QSAR modeling predicts that styrene will volatize rapidly from surface water with TD50 = 0.05 days (river) and 4.12 days (lake).

 

The low value for soil organic carbon-water partition coefficient (logKoc = 2.56 -2.65) suggests that styrene will not adsorb onto soil and sediment and, therefore, together with its volatility, will not persist in these environmental media.

 

The data on environmental distribution of styrene obtained from the level III fugacity model confirms that styrene degrades fast and depending on various emission scenarios, most of styrene will be removed from the environment by means of abiotic and biotic degradation.

Bioaccumulation:

Aquatic bioaccumulation:

It is generally assumed that non-ionised organic substances with a log Kow below 3 are not significantly bioaccumulative (refer Section R7c of the ECHA Guidance on information requirements). Styrene has an estimated log Kow of 2.89 (a very close default value used in EPI Suite (v.4.00) software for styrene is log Kow=2.95).

The Bioconcentration Factor (BCF), Bioaccumulation factor (BAF) as well as Biotransformation Rate in fish were estimated by the BCFBAF software using the Arnot-Gobas method. This method model estimates steady-state BCF (L/kg) and BAF (L/kg) values for non-ionic organic chemicals in three general trophic levels of fish (i. e. lower, middle and upper) in temperate environments (default temperature is 10oC).

The estimated log Kow for styrene is 2.89 which is below the cut-off value of 3 for bioaccumulation. Moreover, in the GHS classification system the cut-off value of log Kow for bioaccumulation is 4.

Biotransformation Half-Life (normalized to 10 g fish at 15oC) of 0.501 days was estimated for styrene in fish.

In addition, estimated BCF/BAF values of styrene in fish (about 41 L/ kg wet-wt) are well below the cut-off value of 500 for bioconcentration potential in aquatic organisms.

Generally, a BCF in fish of ≥ 500 is indicative of the potential to bioconcentrate for classification purposes in accordance with CLP/GHS criteria. The BCF/BAF values estimated for styrene are well below the cut-off values for bioaccumulation. Therefore, styrene is not likely to bioaccumulate in aquatic organisms.

Terrestrial bioaccumulation:

Tests on terrestrial bioaccumulation are not required to be performed under Annexes VII to X of REACH.

No experimental data on terrestrial bioaccumulation of styrene were located or performed by the registrant. In addition, no QSAR model estimation was performed for terrestrial bioaccumulation.

By applying the Tier 1 assessment and, in particular, taken into account the structure of styrene (i. e. a non-ionised organic substance), its physico-chemical properties (i. e. log Kow <3) and environmental fate data suggesting that this chemical will not adsorb to soil particles (logKoc = 2.56 -2.65) and will likely to volatize from soil, it is considered that the substance is unlikely to be significantly bioaccumulative.