Gases (petroleum), light steam-cracked, butadiene conc.

Endpoint summary

Description of key information

Constituents of Category D are all gases and as such the evaluation carried out for it is tailored to the physical state of the constituents and the composition. Constituents within the Category D are not classified for the environment or human health with the exception of 1,3-butadiene which has a human health classification. Therefore, it was prioritised for inclusion in the ecotoxicological evaluation.

Environmental exposure was not performed for the Category D as the representative constituents do not have any environmental classifications. For Category D 1,3-butadiene was modelled in the environment but only to assess man via the environment exposure and not for any other environmental endpoint as butadiene does not have an environmental classification. The exposure working group agreed this approach as the most sensible approach to implement for Category D.

As per ECHA UVBC guidance, representative constituents were those with concentration greater or equal to 10% (v/v) and/or are CMRs.

The members of this category are gases at standard temperature and pressure and will predominantly partition to the atmosphere. The use of QSAR to predict the environmental fate properties of representative constituents of these streams is an appropriate technique.

 

The representative constituents of the category studied and used as supporting read-across are But-1-en-3-yne (CAS 689-97-4), But-1-ene (CAS 106-98-9), But-2-ene, cis- (CAS 590-18-1), But-2-ene, trans- (CAS 624-64-6), Buta-1,2-diene (CAS 590-19-2), Buta-1,3-diene (CAS 106-99-0), Butane (CAS 106-97-8), Prop-1-ene, 2-methyl- (CAS 115-11-7), Propane, 2-methyl- (CAS 75-28-5).

 

Members of the category are not expected to hydrolyse based on a lack of hydrolysable functional groups. According to Atkinson (1985), the kinetic rate constant for the reaction of members of the category with OH radicals is therefore considered to be from 2.53E-12 to 6.68E-11 cm3/mol/s, indicating that the atmospheric half-life would be in the range of 0.24 to 6.3 days, signifying that members of this category are expected to be rapidly degraded through photooxidative reaction mechanisms.

 

No reliable measured biodegradation data exists; however model calculations (QSAR) indicate that represantative constituents of this category can be considered to be readily biodegradable. Results from predictions using BIOWIN showed the constituents except But-1-en-3-yne, Buta-1,2-diene and Buta-1,3-diene to be readily biodegradable. But-1-en-3-yne, Buta-1,2-diene and Buta-1,3-diene, although not readily biodegradable, were shown to biodegrade rapidly. Results from predictions using BioHCwin showed the substances to have rapid half-lives in water of between 1.92 and 3.46 days. Based on the available data, it is considered that this Category would be classed as readily biodegradable.

 

The predicted BCF values of representative constituents range from 4 to 37 L/kg ww (regression based estimation) and 1 to 29 L/kg ww (Arno-Gobas method (upper trophic)). The predicted log Koc for representative constituents of this category ranged from 1.21 - 2.51 (Kow method) and 1.5 - 1.79 (MCI method). Henry's Law Constant values were determined using the group and bond contribution methods. The constants of representative constituents were found to range from 7,143 to 103,352 Pa. m3/mole and from 1,956 to 98,184 Pa.m3/mole for the group and bond contribution methods, respectively.

 

The category members are not expected to persist in the environment because they have a low potential for adsorption to organic matter, have a low potential for bioaccumulation and most of them are predicted to degrade rapidly.