1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, zinc salt

Endpoint summary

Description of key information

ZMB2 and MB2: WAIVER: In accordance with REACH Annex IX, Section 9.3.2, Column 2, bioaccumulation testing need not be conducted if:the substance has a low potential for bioaccumulation.  LANXESS (2018 - see Section 13.2 of IUCLID) clearly shows that 2H-Benzimidazole-2-thione, 1,3-dihydro-4(or 5)-methyl-, zinc salt (2:1) (ZMB2), i.e. the registered substance, exhibits its salt characteristic in aqueous solution, i.e., dissolving in water to 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione (MB2) and zinc ions in a matter of seconds.  Therefore, the measured log Pow value for ZMB2 is not considered relevant for bioaccumulation assessment as it will never exist in the aquatic environment.  Instead, the data presented for MB2 (log Pow = 0.3 - 0.4) is most relevant for bioaccumulation potential.  The low partitioning behaviour of MB2 is consistent with a conclusion of low bioaccumulation potential, and therefore bioaccumulation testing with the registered substance is not considered necessary.

Desthio-MB2: Bioconcentration factor (BCF) = 6.94 L/kg wet-wt., BCFBAF v3.01, Anderson, C (2019).

MB2-sulfonic acid: Bioconcentration factor (BCF) = 3.16 L/kg wet-wt., BCFBAF v3.01, Anderson, C (2019).

MB2-acetic acid: Bioconcentration factor (BCF) = 3.16 L/kg wet-wt., BCFBAF v3.01, Anderson, C (2019).

Hydroxy-MB2: Bioconcentration factor (BCF) = 10.5 L/kg wet-wt., BCFBAF v3.01, Anderson, C (2019).

Additional information

ZMB2 / MB2

WAIVER: In accordance with REACH Annex IX, Section 9.3.2, Column 2, bioaccumulation testing need not be conducted if:the substance has a low potential for bioaccumulation.  LANXESS (2018 - see Section 13.2 of IUCLID) clearly shows that 2H-Benzimidazole-2-thione, 1,3-dihydro-4(or 5)-methyl-, zinc salt (2:1) (ZMB2), i.e. the registered substance, exhibits its salt characteristic in aqueous solution, i.e., dissolving in water to 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione (MB2) and zinc ions in a matter of seconds.  Therefore, the measured log Pow value for ZMB2 is not considered relevant for bioaccumulation assessment as it will never exist in the aquatic environment.  Instead, the data presented for MB2 (log Pow = 0.3 - 0.4) is most relevant for bioaccumulation potential.  The low partitioning behaviour of MB2 is consistent with a conclusion of low bioaccumulation potential, and therefore bioaccumulation testing with the registered substance is not considered necessary.

Major transformation products identified in the OECD 309 water simulation study; desthio-MB2; MB2 -sulfonic acid; MB2 -acetic acid

in Silico profiling of four major transformation products observed in the OECD 309 simulation study (Gartner, C. 2019 - Section 5.2.2); desthio-MB2, MB2-sulfonic acid, MB2-acetic isomers and hydroxy-MB2 and structural analogues was conducted. A number of physical chemical and environmental fate properties based on (Q)SAR predictions and experimental data was compared and contrasted between the aforementioned target substances and their respective source substances. Endpoint data relating to the bioaccumulation potential of the substances was investigated thoroughly. For each substance, the log Kow, a key indicator endpoint for bioaccumulation potential, was predicted to be < 4.5. Further, BCF values for each of the major transformation products was predicted to be <2000 L/kg wet wt (actual: desthio MB2= 6.9 Lkg wet wt, MB2 -sulfonic acid, MB2 acetic acid = 3.2 L/kg wet wt and hydroxy-MB2 = 11 L/kg wet wt). It was concluded that desthio-MB2, MB2-sulfonic acid, MB2-acetic acid or hydroxy-MB2 did not meet the criteria for bioaccumulation (B).