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Biodegradation in water: screening tests

Description of key information

Phosphonium, tetrakis(hydroxymethyl)-, sulfate (2:1) (salt), polymer with urea (Reaction mass THPS-urea monomer) is considered as not readily biodegradable and not inherently biodegradable based on the results of a chlorure salt analogue.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

Five studies on the chloride salt analogue [Tetrakis(hydroxymethyl)phosphonium chloride, oligomeric reaction products with urea] of the registered substance are available and have been used in a read-across strategy to fulfill the endpoint on biodegradation in water. Indeed, the constituents of the source and the target substances are similar including the impurities and the main difference is the anion of the THP+ salt, that being inorganic is not assess to contribute to the biodegradation potential of the substances.

Two key studies and one supporting study were performed to assess readily biodegradability when one key study and one supporting study were performed to assess inherent biodegradability as summarised below.

Method	Duration	Inoculum	Test conditions	Parameter	Result	Reference	Flag Key study   Key study Supporting study Key study Supporting study
OECD 302C	28 d	AS (domestic, industrial) 100 mg ss/L	30 mg/L Aerobic, Dark 25°C	O2 consumption DOC ThOD (test material) = 15.99 mg O2/L	%Degr.=0% (O2 and DOC)	Mead, 1996a
OECD 301B	28 d	AS(domestic) 30 mg ss/L	24.6 mg/L (equivalent to 5 mg C/L) Aerobic, Dark 21°C	CO2 production	%Degr.=8% (on Day 28)	Mead, 1996b
OECD 302B	14 d	AS 300 mg ss/L	121 mg/L (equivalent to 21 mg DOC/L) 293 mg/L (equivalent to 50 mg DOC/L)	DOC Removal	%Degr.=29% toxicity observed	Gottfried E, 2010
OECD 301D	28 d	AS (domestic)	20 mg/L Aerobic, Dark	O2 consumption	%Degr.=11%	Handley & Sewell, 1992
5day- BOD	5 d	Sludge from a sewage treatment plant	1:19 dilution of 500 mg/L	BOD COD	BOD5= 10.10 mgO2/L COD= 115 mgO2/L	Handley & Mead, 1992

AS: Activated Sludge

Ready biodegradation studies

The test item has been found in three tests to be toxic to the inoculum at concentration equal and above 20 mg/L. The highest biodegradation rate 11% based on oxygen depletion was obtained in a close bottle test (OECD 301) .

 

Inherent Biodegradation study

The full OECD302C study shows a biodegradation of the test material of 0% after 28 days. It cannot excluded that the test item was toxic to the inoculum since the degradation in the toxicity control was slightly delayed in time

The screening test showed a significant toxicity of the test material to the microorganisms at concentrations of 121 and 293 mg/L. Due to the toxicity of the test material on the microorganisms, a full OECD 302B test was considered irrelevant.

 

Conclusion

Under the conditions of the different studies and by analogy with Tetrakis(hydroxymethyl)phosphonium sulfate, oligomeric reaction products with urea, the registered substance is considered as not readily biodegradable and not inherently biodegradable.

However, it should be noted that the limited potential for biodegradation is expected to result from the inhibitory effect of the test substances on the inoculum.