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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

QSAR_BCFBAF v3.01_Bioconcentration factor (BCF) in fish_Regression based estimate (most relevant): 15.7 L/kg, Arnot-Gobas Method: 688.2 L/kg

Key value for chemical safety assessment

BCF (aquatic species):
15.7 L/kg ww

Additional information

1,3,4-Thiadiazolidine-2,5-ditione, reaction products with hydrogen peroxide and tert-nonanethiol (CAS 91648-65-6) possesses a partition coefficient (logPow) of > 8 (logPow > 9.4, Fox, 2012), thus strong bioaccumulation in aquatic biota is not expected. Only limited bioaccumulation is assumed for compounds with a logPow < 4.5 or > 6 (based on ECHA REACH Guidance R.11 PBT Assessment). Concerning logPow exceeding 6, a gradual decrease of the Bioconcentration Factor (BCF) is observed practically. Examples are discussed in a literature study of the German Federal Environment Agency (Umweltbundesamt (Ed.): Comparative analysis of estimated and measured BCF data (OECD 305). Report No. (UBA-FB) 001435/E, ISSN: 1862-404, Dessau, March 2011).

Furthermore, it has been hypothesized by different authors in publications that a high logPow is more an effect of solubility than lipophilicity of the substance. In conclusion, according to REACH, Annex IX, Section 9.3.2 (column 2), this endpoint can be waived.

For confirmation, the bioconcentration factor (BCF) of 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-nonanethiol was determined by the computer program BCFBAF v3.01 (EPIWIN software) by US-EPA (Chemservice S.A., 2013). In general, the bioconcentration factor describes the accumulation potential of a substance dissolved in water. BCFBAF v3.01 calculates also the BAF (Bioaccumulation factor) of the chemical, which is defined as the steady-state (equilibrium) ratio of the substance concentration in an organism to the concentration in the surrounding medium. However, this value is not taken into account for the risk assessment and is not relevant for a registration under REACH Regulation (EC) 1907/2006.

Using the regression-based estimate (traditional method) a Bioconcentration Factor (BCF) of 15.7 L/kg wet-wt was calculated for the substance 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-nonanethiol. Using the Arnot-Gobas method, which is based on mechanistic first principles, an aquatic BCF of 688.2 L/kg wet-wt is the result.

The whole body primary biotransformation rate estimate for fish results in a half-life of 16.7 days, whereby the bio half-life is normalized to 10 g fish at 15 °C. The rate constant (kM) for 10 g fish is 0.04/day. This is taken into account to predict the apparent metabolism half-life in fish of the substance. With the Arnot-Gobas method it is possible to differentiate between three trophic levels. For the lower trophic level the BCF results in 46.77 L/kg wet-wt, for a mid trophic level the result is 42.45 L/kg wet-wt and for the higher trophic level 30.96 L/kg wet-wt.