1,5,2,4-dioxadithiane 2,2,4,4-tetraoxide

Endpoint summary

Additional information

An analytical report for hydrolysis with MMDS is available which indicates that the substance undergoes rapid hydrolysis at pH 7, but there are no data presented on pH4 and pH9. Despite some restrictions, the test gives enough evidence to confirm that the test substance is hydrolytically unstable and that the substance is assumed to hydrolyse completely within less than two hours (average of 104 minutes). The hydrolysis products were determined to be methandisulphonic acid (MDSA) with EC# 207-966-4 and formaldehyde (EC# 200-001-8). Stability information was available for the hydrolysis product MDSA: the substance MDSA tested as 50% water solution was shown by IR to be stable during the dosing period of the 28 day repeated dose study in rats. This was confirmed in the aquatic toxicity studies (see section 6.1).

The carbon dioxide (CO₂) evolution test (modified Sturm test) was performed with MMDS. The test revealed 48 and 60% (mean of 54%) biodegradation of MMDS. As biodegradation of MMDS of at least 60% was not reached within a 10-day window, the criterion for ready biodegradability was not met. In the toxicity control, MMDS was found not to inhibit microbial activity.

Although the substance MMDS was tested in this study, one can assume that, based on the rapid hydrolisation, the biodegradation is actually the biodegradation of the hydrolysis products MDSA and formaldehyde.

QSAR calculations were applied for both hydrolysis products: formaldehyde showed ready biodegradability and for MDSA, no conclusion on biodegradability was possible as the various models used did not reveal the same results. However, from the biodegradation test of MMDS one can estimate the contribution of each of the hydrolysis products to the biodegradation. The biodegradation test on MMDS revealed 54% biodegradation based on CO2 evolution. Considering that additionally about 30-40% is incorporated into biomass (REACH Guidance Chapter R.7.9.4.1), this result of 54% indicates a nearly complete ultimate degradation of MMDS. Considering that MMDS hydrolyses into 2 molecules with equal carbon mass, this also implies that both hydrolysis products contribute significantly to the biodegradation.

For the CSA, the hydrolysis products will be considered instead of the substance MMDS. It is deemed acceptable to use the value of ready biodegradable for formaldehyde. For MDSA, although the above considerations imply that both hydrolysis products biodegrade significantly, the QSAR models did not lead to a definite conclusion. As no conclusion could be reached, it was decided to apply the worst case result and consider MDSA as not readily biodegradable.

The test substance MMDS is not likely to adsorb to sediment or soil particles as the substance is hydrolytically unstable.

The hydrolysis product MDSA is a substance with pKa values (Pallas) of -1.81 and -1.21. This means that in the whole environmental relevant pH range, the substance will be fully ionized. This substance is thus expected to have a very low potential for adsorption and will be present only in the water phase. As a pragmatic approach, a Koc value of 10 is chosen for chemical safety assessment purposes. Also the other hydrolysis product, formaldehyde, is not expected to have a high adsorption potential as the estimated Koc by the QSAR KOCWIN (V2.00) is 7.75 L/kg (logKoc 0.889).