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Category name:
Category 2 - Rosin Esters (July 2017)

Justifications and discussions

Category definition:
The category of Rosin Esters consists of rosin which has been esterified with alcohols, typically methanol, ethylene glycol, diethylene glycol, triethylene glycol, glycerol and pentaerythritol. Resin acids are the predominant components of rosin (>85%). Resin acids are composed of three skeletal classes of tricyclic carboxylic acids which share similar structure, but vary in the position of the double bonds and methyl groups. Hydrogenated rosin is implicitly included in the definition of rosin as disproportionated rosin which is a combination of hydrogenated and dehydrogenated rosin naturally produced when rosin is heated. The category therefore also includes the hydrogenated rosin forms of these substances. Due to the reactivity of resin acids, dimers can be formed. These rosin dimers are also known as oligomers or by the trivial name of polymerised rosin.

As each member of this category is a UVCB, the resin acid components will vary in type and proportion.

The number of ester bonds that can be formed is driven by the alcohol. Methanol can form mono-esters, ethylene glycol, diethylene glycol and triethylene glycol can form mono- and di- esters, glycerol can form mono-, di- and tri-esters and pentaerythritol can form mono-, di-, tri- and tetra-esters. In each case, the esterification reaction results in a UVCB containing esters with varying numbers of ester bonds formed by the reaction of the various resin acids with the alcohol.

All substances in the category contain ester constituents with different levels of esterification and non-esterified resin acids. Properties of Category 2 substances change in a consistent manner depending on the level of esterification.
Category order description:
Not specific for a UVCB category
Category rationale:
Rosin is the resinous constituent of the oleo-resin exuded by various species of pine. The separation of the oleo-resin into the essential oil (spirit of turpentine) and common rosin is accomplished by distillation. The essential oil is taken leaving fluid rosin, which is run off and purified. The category of Rosin Esters, is comprised of rosins which have been esterified with alcohols, typically methanol, diethylene glycol, triethylene glycol, glycerol and pentaerythritol.

The chemistry of Rosin and its derivatives is highly complex. H4R has produced a reference document on analytical aspects. It also provides an insight into this chemistry. A copy is also given in the registration dossier.

The category falls into three sub-categories; Simple esters, Linear esters and Bulky esters. These sub-categories and composition ranges are detailed in the Category Justification Document.

Physico-Chemical
The molecular weight of the alcohol to form the ester varies, and so does the potential for esterification, therefore it would be expected that there would some differences in physico-chemical properties.

Environmental
Ready biodegradation studies have been conducted for the following members of the rosin esters category: Resin acids and rosin acids, Me esters; Resin acids and rosin acids, hydrogenated, Me esters; Resin acids and rosin acids, esters with diethylene glycol; Resin acids and rosin acids, esters with glycerol; Resin acids and rosin acids, hydrogenated esters with glycerol; Resin acids and rosin acids, esters with pentaerythritol; and Resin acids and rosin acids, hydrogenated, esters with pentaerythritol.

None of the rosin ester substances could be considered to be readily biodegradable on the basis of these results, with percentage biodegradation determined in the studies ranging from 0 – 50.7% after 28 days. However, rosin ester substances are made up of different constituents and the biodegradation potential varies between constituents, due, for example, to differences in the size of the molecule and differences in water solubility.

A screening assessment, using QSAR predictions using the BIOWIN models (part of EPISuite, US EPA 2000), has been carried out for the ester components of rosin ester substances. The QSAR results show that di-, tri- and tetra-esters are potentially persistent. However, some of the mono-esters are likely to biodegrade and therefore would not be persistent in the environment. Further biodegradation testing of the mono-ester fraction is currently ongoing to clarify the persistence assessment for these constituents. This testing was requested in Final Decision letters received from ECHA on 9 February 2017 for the category members resin acids and rosin acids, hydrogenated, esters with glycerol and resin acids and rosin acids, hydrogenated, esters with pentaerythritol.

No measured bioaccumulation data is available for rosin ester substances. Measured Kow values are available for rosin ester substances, however results are variable due to the difficulties with testing these substances, with log Kow values ranging from 2.44 - >6.5. BCF values are known to increase with increasing Kow, however at very high Kow values a decrease in BCF is observed, due to reduced uptake based on the size of the molecule. Due to the difficulties with measuring Kow for these substances and the fact that a single measured Kow is unlikely to be representative of the constituents in the UVCB, as well as the problems with assessing unbounded Kow values, bioaccumulation potential is assessed based on QSAR predictions for representative structures in the UVCB substances.

A screening assessment has been carried out for the ester components of rosin ester substances. QSAR predictions have been run for representative structures of mono-, di-, tri- and tetra-esters in order to assess the bioaccumulation potential of the individual constituents. The bioaccumulation screening assessment shows that di-, tri- and tetra-ester constituents are predicted to have log Kow values >10. Based on this, these constituents are unlikely to be taken up due to the large molecular size of the constituents and are therefore considered not to be bioaccumulative or very bioaccumulative.

Mono-ester constituents have predicted log Kow values of between 4.66 and 6.42 and therefore bioaccumulation of these constituents cannot be ruled out based on log Kow alone. For those mono-ester constituents with predicted log Kow values between 4.66 and 5.3, the predicted BCF values are less than 2000 L/kg. On this basis, these substances are considered to be unlikely to bioaccumulate and these constituents are not considered to be bioaccumulative or very bioaccumulative. Mono-ester constituents with higher predicted log Kow values (between 5.67 and 6.42) have predicted BCF values greater than 2000 L/kg or 5000 L/kg. Based on these predicted BCF values, bioaccumulation of these constituents cannot be ruled out and they are considered to be potentially bioaccumulative or very bioaccumulative.

Acute ecotoxicity studies are available for the following members of the rosin esters category: Resin acids and rosin acids, hydrogenated, Me esters (fish, Daphnia and algae); Resin acids and rosin acids, esters with pentaerythritol (fish, Daphnia and algae); Resin acids and rosin acids, esters with glycerol (Daphnia); and Resin acids and rosin acids, esters with ethylene glycol (fish, Daphnia, algae).

A 48-hour EL50 of 27 mg/L was determined for resin acids and rosin acids, hydrogenated, Me esters and this was the most sensitive result for this substance. For all category members with higher molecular weights than the Me ester substances, the EL50 values in all studies were determined to be above the highest loading rate tested.

Environmental Hazard Assessment
Resin acids and Rosin acids, hydrogenated, Me esters (8050-15-5) and Resin acids and Rosin acids, Me esters (68186-14-1) are both classified as Aquatic Chronic 3.

For higher molecular weight esters (with molecular weights higher than for the Methyl esters), no effects were seen at the limit of solubility in acute ecotoxicity studies and therefore no environmental classification is assigned.

Conclusion for PBT/vPVB
The PBT assessment of rosin ester substances has been conducted by assessing the PBT potential of different constituents within the UVCB, as constituents will behave differently in the environment and have different potential for toxicity.

Some mono-ester constituents exceed the screening criterion for bioaccumulation based on QSAR predictions, and biodegradation predictions are borderline for persistence. As the QSAR results show some uncertainty, direct ready biodegradation testing of the mono-ester fraction is currently ongoing to clarify the persistence assessment for these constituents. This testing was requested in Final Decision letters received from ECHA on 9 February 2017 for the category members resin acids and rosin acids, hydrogenated, esters with glycerol and resin acids and rosin acids, hydrogenated, esters with pentaerythritol.

Based on the results of the QSAR screening assessment, di, tri and tetra esters are not considered to be bioaccumulative and are therefore not PBT / vPvB. Free resin acids within the UVCBs are not considered to be persistent or bioaccumulative based on measured data, and are therefore not PBT / vPvB.

Mammalian Toxicity
The available toxicity data demonstrate that there are no significant or classifiable toxicological effects identified across the whole of Category 2, with the exception of foetal effects at a sub-maternally toxic dose in an OECD 414 study with Resin acids and rosin acids, esters with ethylene glycol (CAS# 68512-65-2). No similar findings were observed in an OECD 414 study with another member of the linear esters sub-category, Resin acids and rosin acids, esters with triethylene glycol. Furthermore, five key guideline (OECD 414) pre-natal toxicity studies and two combined reproductive / developmental toxicity screening tests (OECD 421 and OECD 422) are available to evaluate the developmental toxicity potential of the Rosin Esters category.

The only Category 2 member in which classifiable effects were seen is Resin acids and rosin acids, esters with ethylene glycol. Consequently, the foetal findings in this OECD 414 study are not considered to be representative of the developmental toxicity of the UVCB substances in Category 2.

Additionally, there is only one registration of Resin acids and rosin acids, esters with ethylene glycol (CAS 68512-65-2) and the registrant had ceased production/sale of this substance in the EU in quarter 4 of 2016.