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Classification & Labelling & PBT assessment

PBT assessment

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PBT assessment: overall result

PBT status:
the substance is not PBT / vPvB
Justification:

Assessment of PBT/vPvB Properties - Comparison with the Criteria of Annex XIII

Persistence Assessment

For all three members of the Montan waxes category reliable data on ready biodegradability (OECD 301) are available. In a Modified Sturm Test (OECD 301-B)Montan waxes, type Sproved to be not readily biodegradable within 28 days and from this test also no inherent biodegradability could be deduced (total degradation within 28 d: 8%). Ready biodegradability forMontan waxes, type OPwas addressed by a Closed Bottle Test (OECD 301-D). With a total biodegradation of 22% within 28 days it is also to be regarded as not readily biodegradable, but the limited biodegradation observed can be taken as indication for inherent, primary biodegradation (according to criteria in OECD, 2006).Montan waxes, type Ealso was tested for ready biodegradability by the Closed bottle test. Within 28 days biodegradation reached 54%, thereby being close to the pass level of 60%. Therefore, also Montan waxes, type E must be regarded as not readily biodegradable. However, according to guidance on data requirements and chemical safety assessment, part R.7B, chapter R.7.9.4.1, without further tests on inherent biodegradability a substance is regarded as inherently biodegradable, if the pass level criterion is almost fulfilled in ready biodegradability tests. As such, Montan waxes, type E could be regarded as inherently biodegradable.

Montan waxes, type S was the only substance tested in a Modified Sturm Test, whereas Montan waxes, type E and OP were tested with the Closed Bottle Test. This may explain the observed degradation with the latter two compared to the very poor degradation (8%) of Montan waxes, type S.

Altogether, the members of the Montan waxes category are not readily biodegradable. The available tests however point to the potential of some biodegradability of the group.

Despite these indications of a (limited) biodegradation, for the purpose of the PBT and vPvB Assessment the P criterion is considered to be fulfilled.

Bioaccumulation Assessment

Bioconcentration as the first step to bioaccumulation can be estimated from the log Kow-value of a substance. For all three substances of the Montan waxes category the log Kow was determined by reliable studies and values were 0.9 (Montan waxes, type E), 1.2 (Montan waxes, type S) and 2.0 (Montan waxes, type OP). As the screening criterion for bioconcentration is a log Kow > 4.5, from their log Kow the substances of the Montan waxes category are to be regarded as not bioaccumulative. However, as water solubility is in the 10 mg/L range and octanol solubility in the 100 mg/L range, experimental determination of the log Kow is associated with some uncertainty. Also, because standard methods for determination of the log Kow were not applicable due to technical reasons (analytical detectability), log Kow was calculated from the experimentally determined solubility in water and octanol. For multi-constituent substances such as the Montan waxes this increases the uncertainty associated with the values obtained.

However, also a second parameter argues against bioaccumulative behaviour of the members of the Montan waxes category: molecular size. According to ECHA’s Guidance on Data Requirements and Chemical Safety Assessment, Part R.11, Chapter R.11.1.3.2, a maximum molecular length of a substance exceeding 4.3 nm is assumed to be incompatible with the internal structure of cellular lipid bilayers and therefore renders molecules of this size highly unlikely to bioaccumulate. As the “Discussion paper for the TC NES subgroup on PBTs” (Comber et al., 2006) points out, according to Opperhuizen et al. (1987) and Hardy et al. (1974) uptake of long chain alkanes was disturbed for chain lengths above C27H56in codlings. This chain length is corresponding to a maximum molecular length of 4.3 nm. As the chain length of Montanic acids are in the range of C28-C32and even much larger in the esterified state (double length by esterification with diols), besides the low log Pow also molecular length argues against any bioaccumulative potential of the Montan waxes category.

A third argument against biaccumulative behaviour of the Montan waxes category is their toxicokinetic behaviour (at least) in mammals. Very long chain acids are either incorporated into phospholipids or undergo ß-oxidation. The alcohols originating from wax ester cleavage are oxidised to acids and metabolised in a similar way. As has been shown with certain human patients showing inherited deficiencies in fatty acids metabolism, fatty acids of structural homology to fatty acids of Montan waxes accumulate with the consequences of various serious toxic effects., whereas this is not the case with the broad majority of the general population that do not show these deficiencies.

Summing up, physicochemical characteristics (log Pow, molecular size) as well as toxicokinetic behaviour argue against a bioaccumulative potential of the members of the Montan waxes category. In conclusion, the members of the Montan waxes category are to be regarded as not bioaccumulative.

Toxicity Assessment

As no ecotoxicity at all and no chronic mammalian toxicity had been observed for the members of the Montan waxes category, in various short-term and long-term tests (see the respective chapters of this CSR) the T-criterion is not fulfilled. The members of the Montan wax category are not classified for human health endpoints.

Summary and overall Conclusions on PBT or vPvB Properties

As the criteria for ready biodegradation are not fulfilled (despite the indications for a - at least limited - biodegradability), the substances are considerer to fulfil the P (or vP) criterion. Neither biophysical (log Pow, molecular size) nor toxicokinetic criteria (potential for metabolism) are compatible with a potential for bioaccumulation and as the members of the Montan waxes category are neither toxic nor ecotoxic, they are regarded as

  • P or vP
  • Not B
  • Not T.

In conclusion, the members of the Montan waxes category show neither PBT nor vPvB characteristics.

Emission Characterisation

The submission substances are not PBT or vPvB. Therefore no emission characterisation is required.

References cited:

Comber, M., Robertson, S., and Sijm, D. (2006).Discussion paper for the TC NES subgroup on PBTs. ACHS/06/11A

Opperhuizen A, Damen H W J, Asyee G M and van der Steen J M D, 1987, Uptake and elimination by fish of polydimethylsiloxanes (Silicones) after dietary and aqueous exposure.Toxicological and Environmental Chemistry13, 265-285, cited in Comber et al., 2006

Hardy R, MacKie P R, Whittle K J and McIntyre A D, 1974, …,Nature252, 577-578, cited in Comber et al., 2006