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Biodegradation in water: screening tests

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Description of key information

under test conditions no biodegradation observed

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

The ready biodegradation was not tested on the substance under registration (OB 5 -A).

The substance is predicted as non readily biodegradable. The estimation of biodegradation using the BioWin v. 4.10[1] tool was performed on the basis of both the acid and the bound [Na] forms (no difference occurs in the estimated results).

 

Non-linear model prediction (BIOWIN 2): 0.0000; does not biodegrade fast.

Ultimate biodegradation timeframe prediction (BIOWIN 3): 0.0521

Biowin5 (MITI linear model): -1.5845

MITI non-linear model prediction (BIOWIN 6): 0.0000; does not biodegrade fast

Such estimates may be used for preliminary identification of substances with a potential for persistency. The combined results of the three freely available estimation models BIOWIN 2, 6 and 3 in the EPI suite may be used as follows:

- Non-linear model prediction (BIOWIN 2): does not biodegrade fast (probability < 0.5) and ultimate biodegradation timeframe prediction (BIOWIN 3): ≥ months (value < 2.2), or

- MITI non-linear model prediction (BIOWIN 6): does not biodegrade fast (probability < 0.5) and ultimate biodegradation timeframe prediction (BIOWIN 3): ≥ months (value < 2.2).

All substances of the Stilbene Fluorescent Whitening Agents category are predicted as non readily biodegradable and for many members of the category readily and inherently biodegradability tests were performed, confirming the previsions (see the Category Justification Report attached to the section 13).

The most similar substance within the category is OB 3a-A(Na), the analogous dihydroxyethylamino derivative disulphonated sodium salt.

Both, the substance under registration and the analogous, are disulphonated sodium salts with a very similar chemical structure. Tanimoto similarity is > 0,85. The only difference is a carbamoyl teminal organic group in the OB 5 -A instead an hydroxyethyl group of OB 3a-A(Na); water solubility, thus the aquatic bioavailability, is also similar (57.4 g/l vs 48.2 g/l, respectively).

 

Biodegradation was tested for OB 3a-A(Na) according to the Zahn Wellens method (Novartis Services AG., 1997), where the substance is demonstrated to adsorb to the sludge from 67 % to 84 % in 24 h and no biodegradation is observed.

The studies performed on OB 3a-MSA, the analogue dihydroxyethylamino derivative tetrasulphonated, are here reported. Water solubility of OB 3a-MSA is much higher than OB 5 -A (650 g/l vs. 57.4 g/l, respectively), thus it can be considered as a conservative representative for biodegradation, since it is more bioavailable in the water compartment and it has less potentiality to adsorb to the sludge .

In a ready biodegradability, test according to OECD guideline 301A, a DOC removal of 1.2 % was observed (Ciba-Geigy Ltd., 1992); hence, OB 3a-MSA is considered not readily biodegradable. Additional information are given from two Zahn Wellens tests, performed according to the OECD 302B. One of them indicates a biodegradation of 24 % after 28 days (Ciba-Geigy Ltd., 1992): this value is obtained at about the fifth day, afterwards the degradation process seems to stop. The slope of the 28 days curve and the second test of inherent biodegradation (Novartis Services AG., 1997) reported suggest that the 24 % of DOC removal recorded in the first test can still be related to a slow adsorption process more than a biological degradation.

In conclusion, the substance can be considered as neither readily nor inherently biodegradable.

[1]Biowin v.4.10 is an application contained in the EpiSuite 4.1, the suite of physical/chemical property and environmental fate estimation programs developed by the EPA’s Office of Pollution Prevention Toxics and Syracuse Research Corporation (SRC).