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Environmental fate & pathways

Biodegradation in soil

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Description of key information

The substance has low volatility, so aerial deposition is unlikely, and the substance is not applied directly to soil and is not expected to enter sewage treatment works at significant concentrations which could lead to agricultural exposure via application of sewage sludge to land. Thus, terrestrial exposure of the substance is considered unlikely and as the terrestrial toxicity would not be environmentally relevant, these tests have not been conducted.

Key value for chemical safety assessment

Additional information

The soil simulation testing may be waived if it can be demonstrated that direct and indirect exposure of soil is unlikely to occur. ECHA (2012) states that “In the case of readily biodegradable substances which are not directly applied to soil, it is generally assumed that the substances will not enter the terrestrial environment and as such there is no need for testing of soil organisms”.

In most cases the reactions to form the grease thickener occur in situ during the grease manufacturing process and consequently these grease thickeners normally only exist in the base oil matrix. The matrix effect, as recognised by the OECD Lubricant Emission Scenario document (OECD 2004), needs to be taken into account as the process of manufacturing the thickener in an inert base oil is likely to influence factors such as availability of the thickeners. In the grease manufacturing process unique interactions, more appropriately defined as physical bonding effects, occur between the base oils and the thickeners. The interactions between the thickener and base oil do not strictly fall under the definitions of a reaction product nor do they act as a simple mixture of components. In realistic use scenarios, the thickeners will be contained in base oil, with the formulated greases specifically designed to minimise the leaching of the thickener. Therefore, during use, the concentrations of the substances which would be bioavailable are limited.

As the substance is only manufactured in situ in a generic inert carrier, typically base oil, and would not be bioavailable, the isolated thickener is unlikely to come in contact with the terrestrial environment and the derivation of terrestrial data on the isolated thickener is not considered to be relevant to the potential exposure of the substance in the environment.

Furthermore, in the environment, the substance will dissociate and degrade into inorganic aluminium species and fatty acids. The fatty acid component of the substance is readily biodegradable. At environmental pH (ca 7.0), aluminium will mainly be in the form of essentially insoluble hydrated oxide species which are likely to absorb onto sewage sludge. However, hydrated aluminium oxides occur naturally in the environment and are not considered hazardous.

 

The isolated form (i.e. outside base oil) of the substance is considered readily biodegradable based on proprietary data read across from aluminum, benzoate C16-18-fatty acids complexes (Harlan 2013). Aluminum, benzoate C16-18-fatty acids complexes is considered suitable for read-across as it contains a fatty acid moiety coordinated to an aluminium atom, although it also contains a coordinated benzoate ion. However, proprietary data are available (Harlan 2013) showing the substance at 50% w. w. pharmaceutical white oil (representative of the form in which it is marketed and used) only reached 31% degradation after 28 days and therefore cannot be considered readily biodegradable. The white oil, which constituted 50% by weight of the substance tested, is known not to be readily biodegradable (31% biodegradation after 28 days) (ECHA Dissemination Portal CAS 8042-47-5). It can therefore be concluded that the test results are significantly determined by the properties of the pharmaceutical white oil.

 

Although the substance itself in isolated form (i.e. extracted from base oil) can be considered readily biodegradable, the substance in the form in which it is marketed and used cannot be considered readily biodegradable. Therefore, further review of the terrestrial compartment was undertaken.

ECHA guidance document REACH Chapter R.10 – Dose [Concentration]-Response Regarding Environment (2008) states that chemicals can reach the soil via several routes: application of sewage sludge in agriculture, direct application of chemicals and deposition from the atmosphere.

The substance is used as thickeners in lubricants and greases in open and closed systems and thus there is no direct application to soil. The substance also has no identified uses in which it would enter the sewage treatment system in significant quantities which would lead to exposure to agriculture from the spreading of sewage sludge. The majority of greased parts are designed to keep the grease within the contact zone. A large proportion of light to medium duty grease-lubricated parts are sealed for life and the user will not interact with the grease during any time of the part’s use from purchase to disposal. Due to the nature of the grease as a semi-solid, even in catastrophic failure, it will remain within the part and not be released. Some applications require a grease to be used as a total loss lubricant, such as on rail tracks, heavy duty trucks, spindles on agricultural crop pickers and marine applications. In these applications, there are voluntary/compulsory schemes in place that limit the type of product used based on its toxicity, ecotoxicity and biodegradability (e.g. Nordic Swan, Ecolabel, Blaue Engel, VGP).

The vapour pressure of the substance as a 50% w. w. concentration in pharmaceutical white oil was determined to be 0.00015 Pa at 25°C (Harlan 2013). As the substance has very low volatility, it is not expected to enter the atmosphere. Thus, aerial deposition of the substance will be negligible and deposition is not expected to be a relevant route of exposure.

As the substance has low volatility, would not enter STPs in significant quantities which would lead to exposure to agriculture from the spreading of sewage sludge and is not applied directly to soil, it is generally assumed that it will not enter the terrestrial environment.