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PBT assessment

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PBT assessment: overall result

PBT status:
the substance is not PBT / vPvB


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

MBT being released into the waste water and the atmosphere undergo different degradation reactions. The known reaction pathways and relevant metabolites of MBT are already described in the appendix A of the EU-Risk Assessment for CBS from 2008.These described metabolites are MBTS (CAS: 120-78-5), BT (CAS: 95-16-9), BTon (CAS: 934-34-9), MeSBT (CAS: 615-22-5).All these compounds are detected in waste water and environmental compartments; therefore they are included into the MBT risk assessment and PBT/vPvB assessment.

The assessment of PBT and vPvB is performed by comparison of the relevant intrinsic properties of MBT and its described metabolites with the criteria of the REACH regulation (Annex XIII) as shown inTable 52:

Table52PBT and vPvB criteria and the corresponding properties ofMBT and its described metabolites

 Criterion  PBT criteria  vPvB criteria  MBT and its described metabolites  Criterion fulfilled?
 P Half-life in marine water > 60 d, or half-life in fresh- or estuarine water > 40 d, or half-life in marine sediment > 180 d, or half-life in fresh- or estuarine water sediment > 120 d, or half-life in soil > 120 d Half-life in marine, fresh or esturarine water > 60 d, or half-life in marine, fresh or esturarine sediment > 180 d, or half-life in soil > 180 d Not readily biodegradable (MITI, 1992) Fast photolysis (CMA, 1989a) The main hydrolysis products BT and BTon are persistent (EU-RAR, 2008) yes 
 B   BCF > 2000  BCF > 5000 BCF of MBT<2000 (MITI, 1992)BCF of the described metabolites of MBT<2000 (EU-RAR, 2008) no
T   Long-term NOEC for marine or freshwater organisms    89d-NOEC (fish) = 0.041 mg/L (CMA, 1989f) no 
T CMR  n.a.  Not classified as CMR no
T Other evidence of chronic toxicity, as identified by the classifications: T, R48, or Xn, R48 according to Directive 67/548/EEC  n.a.  Not classified as T, R48, or Xn, R48 according to Directive 67/548/EEC no

Persistence Assessment

MBT is not readily biodegradable (MITI, 1992), but it photolyzed in water fast with a half-life of ca. 30 min (CMA, 1989a). The main photolysis products of MBT are BT and BTon (Brownlee, 1992). They are also not readily biodegradable and already reported as persistent under environmental conditions in EU-Risk Assessment for CBS from 2008. As the described metabolites of MBT, MBTS is also not readily biodegradable but can be hydrolyzed or photolyzed to BT and BTon. MeSBT is also reported in EU-Risk Assessment of CBS from 2008 as resistant both to biodegradation and abiotic degradation.

Accordingly MBT is not persistent due to fast hydrolysis but its photolysis products BT and BTon are persistent and the described metabolite MeSBT is also persistent.

Bioaccumulation Assessment

The BCFs of MBT and all of its described metabolites are smaller than 2000, either from experiment or from estimation. Therefore MBT together with its described metabolites does not fulfil the B criterion.

Toxicity Assessment

The chronic effects of MBT are tested for three trophic species and the most sensitive result is from fish (89d-NOEC of 0.041 mg/L) (CMA, 1989f) above the criterion of 0.01 mg/L and hence MBT does not fulfil the T criterion. The metabolites of MBT are all less toxic to aquatic organisms than MBT itself and hence they do not fulfil the toxic criterion as well.

MBT and its described metabolites are all not classified as carcinogenic, mutagenic or toxic for reproduction.

Summary and overall Conclusions on PBT or vPvB Properties

Due to the B and T criteria are not fulfilled; MBT is neither PBT nor a vPvB substance.