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EC number: 204-783-1
CAS number: 126-33-0
The evidence from a weight of evidence review appended to Section 13 is
that under favourable aerobic conditions sulfolane will ultimately
degrade and therefore is not P or vP.
The available data from standard studies
suggest that sulfolane is not readily biodegradable. An OECD Guideline
301 C (Ready Biodegradability: Modified MITI Test (I) (CITI 1992)
reported 10.1 % of the substance degraded within 2 weeks and QSAR
predictions with Biowwin V4.1 do not predict the substance to be readily
biodegradable. An additional study of the aerobic degradation of
sulfolane in seawater (Hill 2006) also reported sulfolane not to degrade
rapidly.There is however evidence that sulfolane will biodegrade
in bioreactors in the presence of a population of sulfolane degrading
bacteria under aerobic conditions (Chou and Swatloski 1983; Ying et al.
1994) and in experiments with populations of sulfolane adapted bacteria
(Greene et al. 2000).
There are also several non-standard
published studies on sulfolane that demonstrate that while sulfolane may
not be readily biodegradable it is inherently degradable under
appropriate environmental conditions (Greene et al. 1998; Greene et al.
1999). These papers have been considered alongside previous regulatory
conclusions on sulfolane as part of a weight of evidence assessment on
persistence which is appended to the CSR in Section 13. The weight of
evidence assessment shows that sulfolane can be degraded within the PBT
criteria of 40 days for surface waters (Greene et al. 1998; Greene et
al. 1999) and 120 days for soils (Greene and Fedorak 2001; Saint Fort
2006) at environmentally relevant temperatures between 8-10°C. To
maximise biodegradation of sulfolane, aerobic, nutrient rich conditions
are required. An existing population of sulfolane degrading bacteria
(for example due to pre-exposure to the substance) will also accelerate
biodegradation by reducing the lag time for degradation. Under aerobic
conditions, sulfolane will degrade completely to carbon dioxide, water,
biomass and sulphate. Some intermediates of sulfolane degradation under
aerobic conditions have been identified but these are expected to
undergo rapid mineralisation (Greene et al. 2000). Temperature, test
concentration and nutrient content all contribute to the degradation
rates for sulfolane and, under certain conditions, the lag time before
degradation is such that the criteria for persistence will not be met
(Greene et al. 1998; Greene et al. 1999). The evidence from this review
suggests that if the conditions remain favourable sulfolane will
ultimately degrade and this conclusion is supported by previous
Sulfolane will be persistent under
anaerobic conditions (Kim et al. 2000; Greene et al. 1998). There is
some limited evidence for anaerobic degradation of sulfolane and one
potential metabolite, thiolane, may be toxic to microbes, limiting
degradation (Kim et al. 2000).
The overall conclusion for persistence
under aerobic conditions is not P or vP.
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