Tetrahydrothiophene 1,1-dioxide

Endpoint summary

Description of key information

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.

Additional information

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 regulatory reviews.

 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.