4-[(2,5-dichlorophenyl)azo]-N-(2,3-dihydro-2-oxo-1H-benzimidazol-5-yl)-3-hydroxynaphthalene-2-carboxamide

Endpoint summary

Description of key information

According to the criteria set in Annex XI of REGULATION (EC) No 1907/2006 a ready biodegradation study is scientifically unnecessary based on the following arguments applied for naphtolone pigment. Since it is generally known that pigments are not or only marginally (bio)degradable, the persistent-criterion is accepted for PB25. As PB25 is of very poor water solubility, rather inherent than ready biodegradability was assessed in the Modified MITI Test (II) according to OECD 302 C.

The inherent biodegradability of the test item was determined in the Modified MITI Test (II) with non adapted activated sludge for a period of 28 days. The study was conducted according to OECD Guideline 302 C. The test item concentration selected as appropriate was 30 mg/L, corresponding to a ThOD of 42.0 mg O₂/L. The oxygen was depleted by respiration of bacteria and the degradation was followed by measuring the oxygen concentration. The biodegradation is therefore expressed as the percentage BOD depletion and was calculated for each study day. The mean oxygen depletion in the inoculum control was 53.6 mg O₂/L on day 28.

The 1^sttest item replicate reached the 10 % level (beginning of biodegradation) after 13 days and came to a maximum of 15 % after 20 days. The 2^ndand the 3^rdtest item replicates did not reach the 10 % level until day 28. The pass level > 70 % for evidence of inherent, ultimate biodegradability was not reached within 28 days. After 28 days the mean biodegradation rate was 4 %.