Tar acids, xylenol fraction

PBT assessment

PBT assessment: overall result

PBT status:

the substance is not PBT / vPvB

Justification:

The PBT Assessment for D-Glucopyranose, oligomeric, undecyl glycoside (CAS 98283-67-1) is based on the criteria set out in the “Guidance on information requirements and chemical safety assessment, Chapter R.11: PBT Assessment” (ECHA, 2012).

Persistence

No data on Tar acids, Xylenol fraction (CAS 84989-06-0) itself are available. However, the biodegradation potential was assessed based on numerous data available for the constituents of Tar acids, Xylenol fraction (CAS 84989-06-0).

Although there is evidence that constituents like cresols, ethylphenols or some xylenols are readily biodegradable Tar acids, Xylenol fraction (CAS 84989-06-0) is considered as inherently biodegradable since rapid degradation cannot be shown for all constituents of the UVCB.

Results on the biodegradation in sediment provide evidence that these constituents will be ultimately degraded under aerobic conditions with half-lives between 9.4 and 43 h for p-cresol in water and between 5.9 and 11 h in water/sediment systems. In so-called eco-cores, p-cresol degraded with half-lives between 3.0 and 16 h. In simulation studies with soil o-cresol degraded with half-live times of 1.6 d for sandy loam and 5.1 d for sandy silt loam. m-cresol degraded with half-live times of 0.6 d for sandy loam and 11.3 d for sandy silt loam. Therefore, the substance has a low potential for accumulation in soil and sediment.

Since rapid degradation cannot be shown for all constituents of Tar acids, Xylenol fraction (CAS 84989-06-0) the persistency criteria cannot finally be assessed and the substance needs to be considered as potentially P and vP.

Bioaccumulation

In accordance with ECHA Guidance R.11 (ECHA, 2017) Tar acids, xylenol fraction (CAS 84989-06-0) is not considered to meet the screening criterion for bioaccumulation in aquatic species. This is based on an analogue read-across approach. Available data for all main components of Tar acids, xylenol fraction (CAS 84989-06-0) demonstrate the log Kow to be below 3, i.e. xylenol-isomers: 2.09 to 2.42 (DEZA, 2010; EPA, 2010; Sangster, 1989); cresol-isomers: 1.94 to 1.98 (OECD SIDS, 2003; Sangster, 1989); ethyl-phenols: 2.09 to 2.58 (DEZA, 2010; Umeyama et al., 1971; Sangster, 1989), or trimethyl-phenols: 2.67 to 2.73 (Sangster, 1989). Thus, all available log Kow values for all main components of Tar acids, xylenol fraction (CAS 84989-06-0) are below the trigger value of 4.5.

However, according to ECHA Guidance R.11 (ECHA, 2017) there is indication that accumulation in air breathing organisms might occur based on log Koa values slightly above the trigger value of >5 (5.45 - 7.08) exemplarily calculated for some representative components, i.e. 2,4-xylenol (CAS 105-67-9), m-cresol (CAS 108-39-4) and 4-ethylphenol (CAS 123-07-9), in combination with the log Kow > 2.

These screening values (Kow and Koa) referred to in the ECHA Guidance R.11 are a function of the modelled organisms, food webs and environments used to obtain these values. To develop this partition coefficient combination it was clearly indicated in the guidance that biomagnification potential is only assumed for substances with high chemical absorption efficiency from the diet, no biotransformation after absorption and negligible active transport (in or out).

Since there are no studies available in which the toxicokinetic behavior of tar acid, xylenol fraction (CAS 84989-06-0) has been investigated in accordance with Annex VIII, Column 1, Section 8.8.1, of Regulation (EC) No 1907/2006 and with Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance (ECHA, 2017), an assessment of the toxicokinetic behavior of tar acid, xylenol fraction is conducted to the extent that can be derived from the relevant available information. This comprises a qualitative assessment of the available substance-specific data on physico-chemical and toxicological properties according to Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance (ECHA, 2017) and taking into account further available information on surrogate substances and constituents, respectively.

The evaluation of the toxicokinetic behavior indicates that Tar acid, xylenol fraction (CAS 84989-06-0) is expected to be well absorbed via the oral route. Mechanisms by which substances can be absorbed in the gastro-intestinal (GI) tract include the passage of small water-soluble molecules (molecular weight up to around 200) through aqueous pores or carriage of such molecules across membranes with the bulk passage of water. As the test substance and its constituents are soluble in water and have a relatively low molecular weight, this passive diffusion will be the predominant mechanism for absorption in the GI tract. In addition moderate octanol/water partition coefficient (log Kow) values (between -1 and 4) are favorable for absorption by passive diffusion, being applicable for the test substance and it constituents. Following the above it can be concluded that the test substance and its constituents will result in a high systemic exposure after oral administration. For hazard and risk assessment purposes oral absorption of the tar acid, xylenol fraction is set to 100%. The results of the toxicity studies with cresol isomers and xylenol isomers do not provide reasons to deviate from this proposed oral absorption.

As regards distribution, once absorbed the water soluble tar acid, xylenol fraction (CAS 84989-06-0) and its constituents are expected to widely distribute through the body. Its moderate lipophilic character indicates that they are likely to distribute into cells and the intracellular concentration may be higher than extracellular concentration. Wide distribution through the body is confirmed from the histopathologic findings in the repeated dose studies.

Considering metabolism, Tar acid, xylenol fraction (CAS 84989-06-0) and its constituents are expected to undergo Phase I reactions including aliphatic and aromatic hydroxylation and further oxidation. Phase II reactions, including glucuronidation and sulfation, will further increase water solubility.

Based on the high water solubility and the low molecular weight, tar acid, xylenol fraction (CAS 84989-06-0) and its conjugation products are expected to be mainly excreted in the urine.

Thus, with reference to the toxicokinetic behavior Tar acid, xylenol fraction (CAS 84989-06-0) is expected to be well absorbed via the oral, dermal and inhalation route. Absorption factors of 100% are proposed for all routes. The substance is anticipated to be widely distributed through the body, metabolized and excreted mainly in the urine. No bioaccumulation potential is expected.

In conclusion, the trigger values for biomagnification in air-breathing (terrestrial) organisms as stipulated in the ECHA Guidance R.11 are likely to overestimate the potential for biomagnification in the food chain. Even though absorption via oral exposure is likely the described metabolic and excretion pathways are expected to minimize biomagnification in the food chain. 

Thus, Tar acids, xylenol fraction (CAS 84989-06-0) exhibits a low potential for bioaccumulation and is not B and not vB.

Toxicity

Considering the environment the lowest availabe chronic value among all trophic levels, species and environmental compartments is a NOEC of 1 mg/L for the constituents p-cresol. Furthermore, according to Directive 67/548/EEC no classification applies for carcinogenicity (category 1 or 2), mutagenicity (category 1 or 2) or toxicity to reproduction (category 1, 2, or 3) and/or no classification applies according to the consolidated version of Regulation (EC) No 1272/2008 and further amendments (ATPs) for carcinogenicity (category 1A or 1B), germ cell mutagenicity (category 1A or 1B) or toxicity to reproduction (category 1A, 1B, or 2). Further, there is no evidence of chronic toxicity, as indentified by the classifications T, R48 or Xn, R48 according to Directive 67/548/EEC or specific target organ toxicity after repeated exposure (STOT RE category 1 or 2) according to Regulation EC No 1272/2008.

Therefore, Tar acids, xylenol fraction (CAS 84989-06-6) is not toxic and is considered not T.

In summary Tar acids, xylenol fraction (CAS 84989-06-0) is not PBT/vPvB.