Z-85

Biodegradation in water: screening tests

Description of key information

Although the test material attained 78% biodegradation after 28 days, it did not achieve >60% within the 10-day window. As a UVCB, the test item may be considered rapidly biodegradable since the pass level of 70% degradation was achieved within 28 days. 
In an inherent biodegradation study, 31.5% degradation was measured in activated sludge within the 28 -day test period. This exceeded the % biodegradation pass level of 20%. 
The test substance is considered readily and inherently biodegradable 

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

There is one key study and two supporting studies in relation to the biodegradability of the test material.

The key ready biodegradation study (Clark N, 2007) was performed in accordance with OECD guideline 301B. A mixed population of activated sewage sludge microorganisms were used, collected at a predominantly domestic sewage plant. The control as well as standard material (sodium benzoate) and test material vessels were prepared each in duplicate. The test material plus standard material in inoculated culture medium acted as toxicity control (one vessel only). Each test vessel was inoculated with the prepared inoculum at a final concentration of 30 mg suspended solids (ss)/L. The study was carried out in a temperature controlled room at 21 °C, in darkness. The vessels were closed and CO2 -free air bubbled through the solution at a rate of approximately 40 mL/min with continuous stirring. CO2 as well as DOC (Dissolved Organic Carbon) analysis was performed during the study period. Sodium benzoate attained 65 % degradation after 14 days and 100% degradation after 28 days thereby confirming the suitability of the inoculum and test conditions.

The test material attained 78% degradation at day 28. Although the test material attained 78% biodegradation after 28 days, it did not achieve >60% within the 10-day window.

The toxicity control attained 74% degradation after the study period thereby confirming that the test material was not toxic to the sewage treatment micro-organisms used. The total CO2 evolution in the control vessels on day 28 was 27.82 mg/L.

The test material may be considered as readily biodegradable as evidence of >70% degradation was attained over 28 days.

The supporting ready biodegradation study (Zhang Y, 2007a) was performed to OECD Guideline 301B and the SEPA, P.R. China the Guidelines for the Testing of Chemical No. 301F (Adopted: May 2004) "Manometric Respirometry Test". The biodegradation test was conducted using activated sludge in an aerobic aqueous medium by measuring its biochemical oxygen demand (BOD). The test substance was added to the culture medium at a level of 99.00 and 93.78 mg ThOD/L, respectively.

The degradation of the reference substance, sodium benzoate, exceeded 60% on the second day and reached 85.6% by the 14th day. This met the validation requirements of the OECD Guideline. The biodegradation of the toxicity control was 51.7% within 14 days and the value exceeded 25% based on ThOD, which indicated that the test substance added to the inoculated mixture was not inhibitory. The test substance reached 46.2% biodegration following 28 days but failed to reach >60% within the 10 day window.

Based on these results and the grading criteria in the Guidelines for the Hazard Evaluation of New Chemcial Substances, State Environmental Protection Agency of P.R.C. (HJ/T 154-2004), the test substance did nto meet criteria for "ready biodegradability" under this test condition, but has a good potential for biodegradation.

In a supporting study (Zhang Y 2007b) the inherent biodegradation was assessed using OECD Guideline 302C and SEPA, PR China No 302C Inherent Biodegradability : Modified MITI Test II. The inherent biodegradability of the test substance was assessed by measuring its biochemical oxygen demand (BOD). The test substance was added to the culture medium at a concentration of 30.07 mg/L.

31.5% degradation was measured in activated sludge within the 28 -day test period. This exceeded the % biodegradation pass level of 20%. The reference substance also met the % degradation criteria as a 74.6% degradation was measured following 14 days.

The test substance is considered inherently biodegradable based on the study results and on the grading criteria in the test guidelines.