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Category name:
Category 4 - Rosin Adduct Esters (July 2017)

Justifications and discussions

Category definition:
Rosin Adduct Esters are UVCB substances produced by the reaction of rosin, rosin acids, and resin acids with fumaric acid or maleic anhydride followed by esterification with glycerol and/or pentaerythritol. They comprise a group of close structural analogues and are expected to have similar intrinsic toxicological and environmental properties.
Category order description:
Not specific for a UVCB category
Category rationale:
Rosin Adduct Esters are formed when rosin is reacted with maleic anhydride (or maleic acid) or fumaric acid yielding a maleated rosin adduct or a fumarated rosin adduct, respectively, followed by esterification with a combination of glycerol and pentaerythritol or pentaerythritol alone. The adducts are formed via a Diels-Alder reaction in which the single carboxylic acid rosin is converted to a rosin derivative with three carboxylic acid groups following reaction with fumaric acid or maleic anhydride/acid.

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.

Physico-chemical
All the substances in this category are solids at ambient temperature, with similar densities and low vapour pressures. Melting points are in a similar range (72.4 – 145°C) and all substances decompose before boiling. Solubility and partition coefficient values are likely to be similar for individual constituents within the UVCB substances, however, as the proportion of different constituents varies between category members measured results for the whole substances are variable.

Environmental
Ready biodegradation studies have been conducted for the following members of the rosin adduct esters category: Rosin, fumarated, reaction products with glycerol and pentaerythritol and Resin acids and rosin acids, fumarated esters with pentaerythritol. Members of this category have not been shown to be readily biodegradable in biodegradation screening tests.

QSAR predictions conducted with Episuite’s BIOWIN model show that di- and tri- adduct ester constituents screen as potentially persistent (BIOWIN 3 value <2.2 and BIOWIN 6 or BIOWIN 2 <0.5). Tetra-ester constituents are also considered to be potentially P, but these constituents could not be run through the model due to issues processing the SMILES notation. In addition, the tetra-ester constituents are outside the model domain.

Mono-ester constituents do not screen as persistent based on BIOWIN results. Resin acids are the main components of rosin (>85%) and based on measured ready biodegradation studies with rosin these constituents are considered to be readily biodegradable and not persistent.

No measured bioaccumulation data is available for rosin adduct ester substances. Measured Kow values are available for all members of this category, however, results are variable due to the difficulties with testing these substances, with log Kow values ranging from 2.44 - >6.5. The wide range of measured Kow values are considered to reflect the differences in partitioning behaviour between constituents.

Based on QSAR predictions using Episuite’s KOWWIN and BCFBAF models (regression based estimates), di- and tri- ester constituents are not considered to be bioaccumulative as their large molecular size and very high predicted log Kow values (9.82 – 16.51) mean that these constituents are unlikely to be taken up by organisms. Predicted BCF values are therefore low (3.16 L/kg ww, log BCF 0.5, regression based estimate). Structures for tetra-ester constituents could not be run through the model, but as these constituents have an even larger molecular size than the di-esters they are also unlikely to bioaccumulate.
Mono-ester constituents are considered to be potentially bioaccumulative based on predicted log Kow values (log Kow 3.75 – 4.23), although predicted BCF values for these constituents are still low (3.16 L/kg ww, log BCF 0.5, regression based estimate). Resin acid constituents are also present in rosin adduct esters and these are not bioaccumulative based on measured data for fish, with BCF values between <25 and 130 (Niimi and Lee 1992) and for mussels, with BCF values between 110 and 330 L/kg (Burggraaf et al. 1996).

Measured toxicity data are available for Daphnia magna for all category members (Laus 2013a, Laus 2013b, Harlan Laboratories 2010a, Harlan Laboratories 2010b, Water Quality Institute 1993) for algae for resin acids and rosin acids, fumarated esters with glycerol and resin acids and rosin acids, maleated esters with pentaerythritol (Laus 2013a, Laus 2013b, Water Quality Institute 1993) and for fish for resin acids and rosin acids, maleated, esters with pentaerythritol (Water Quality Institute 1993). In all studies, the EL50 value was determined to be above the highest concentration tested.

Environmental Hazard Assessment
No effects were observed at the highest loading rate tested in any of the acute toxicity studies for fish, Daphnia magna or algae. Substances in this category would not therefore be classified for acute environmental hazards. However, as these substances are of low solubility, are not readily biodegradable and have log Kow values of >4 a "safety net" classification of Chronic Category 4 is assigned to substances in this category.

Conclusion for PBT/vPVB
Members of the category rosin adduct esters are not considered to be PBT or vPvB.
Whole substance screening level data are available for the assessment of biodegradation and bioaccumulation for rosin adduct esters. However, assessing the substances as a whole is not considered to be the most appropriate method for assessing the PBT potential of complex UVCB substances such as these, as different constituents will have different environmental fate properties.

Assessing rosin adduct esters based on constituents within the UVCBs using QSAR predictions:
• Mono adduct esters are considered to be not P but potentially B and therefore not PBT or vPvB.
• Di-, tri- and tetra- adduct ester constituents are potentially P but not B and therefore not PBT or vPvB.
• Free resin acids are not P or B.

Based on whole substance data none of the substances in the category are T. Therefore, none of the constituents in rosin adduct ester substances are PBT or vPvB.

Mammalian Toxicity
Based on similarity in structure and molecular weight (>500), these substances are expected to be poorly absorbed and relatively non-hazardous with regulatory classifications limited to eye irritation and dermal sensitisation potential. This assumption is supported by results from toxicological testing which demonstrated that Rosin Adduct Esters are not acutely toxicity via ingestion and demonstrate negligible uptake from the gastrointestinal tract following oral administration to rats. They are not irritating to the skin and produce moderate reversible eye irritation. Results of in vitro genotoxicity testing revealed no mutagenic activity in microbial or mammalian cells, both in the absence and presence of exogenous metabolic activation. Results of 90- and 28-day repeated dose studies, developmental toxicity studies and screening reproductive toxicity studies provided no data to trigger reproductive, developmental or specific target organ toxicity classifications.