tris (4-nonylphenol, branch) phosphorous acid ester

Endpoint summary

Additional information

Abiotic degradation

 

 TNPP can in theory be hydrolysed in contact with water to give nonylphenol and phosphorous acid.  In practice however this process is dependent on both water solubility and temperature.  The water solubility of TNPP is so low that the amount of material in solution is below the limit of detection (a figure of 0.05mg/l is used in the EU risk assessment documents) and although a theoretical half life of 13 hours has been calculated, evidence from biodegradation testing shows that there is no measurable degradationin  a 28 day Sturm test (OECD 301B), whereas nonylphenol in the same test protocol shows evidence of 68% degradation over a similar time frame.  The degree of abiotic degradation in water is therefore considered to be of no significance. 

 

In the atmosphere, TNPP may be degraded by reactions with photochemically generated hydroxyl radicals. This atmospheric photo-oxidation potential has been estimated using structure activity relationships models developed by the U.S. Environmental Protection Agency.  Using the global annual average concentration of OH radicals in the atmosphere (5x10⁵molec.cm^-3), kdeg_airis calculated to 2.19 d^-1and the half life for the reaction of hydroxyl radical with TNPP in the atmosphere is calculated as 0.32 days (7.6 hours).  With such a low half life, TNPP will be rapidly degraded in the air.

Biotic degradation

TNPP has not found to be readily biodegradable in two separate OECD 301 studies. In one study 4% of TNPP was found to degrade after 28 days and in another study 1% of TNPP degraded after 29 days.

Degradation rate in water:	TNPP is not readily biodegradable but showed some signs of degradation.
Degradation rate in sediment:	Sediment degradation is generally comparatively slow in comparison with water.  No sediment degradation has been carried out due to the analytical difficulties inherent in such a test.  Anaerobic degradation is generally lower than aerobic degradation and although degradation is likely to occur, the rates will be slow.
Degradation rate in soil:	Soil degradation is generally comparatively slow in comparison with water.  No soil degradation tests have been carried out due to the analytical difficulties inherent in such tests.  Soil degradation rates are generally lower than aerobic degradation in water and will be dependent on the degree of oxidation. Degradation is likely to occur although the rates will be slow.
Degradation rate in air:	Using the global annual average of OH radicals in the atmosphere (5x10^5molec.cm^-3), kdegairis calculated to 2.19 d^-1and the half life for the reaction of hydroxyl radical with TNPP in the atmosphere is calculated as 0.32 days (7.6 hours).

The environmental distribution of TNPP is governed by the physicochemical characteristics of the molecule. The substance is of very low water solubility, below that which can be readily measured by analysis and with an exceptionally high Log K_OW. These characteristics suggest that bioaccumulation is a possibility, however the values are so extreme, that the amount that is present in the water column is so small that the rate of absorption is comparatively slow and although the biodegradation rate is low, TNPP is inherently biodegradable.  Log KOW values >3 are generally considered to represent a potential bioaccumulation risk, however at values of Log KOW >8 there is no evidence of bioaccumulation potential as there is so little material present that rate of uptake is less than the rate of elimination.  In consequence the theoretical potential accumulation in soil and sediment is not considered to present a significant risk, a fact acknowledged in the EU Risk assessment model referred to in section 4.2.3 above.  Material that does enter the soil and sediment will ultimately degrade through in-situ bioremediation although because of the current lack of suitable analytical techniques this cannot be demonstrated experimentally.  TNPP entering the atmosphere will be low due to the low volatility of the substance, however photohydrolysis indicates a half life of 7.6 hours.  TNPP is not considered likely to accumulate in the environment.