Nonylphenol, branched, ethoxylated

Biodegradation in water: screening tests

Description of key information

Based on available evidence, NPEO can be considered as not persistent in the environment.

Additional information

A study was conducted to evaluate the ready biodegradability of NPE-1.5 (a commercial product, 100% purity) and NPE-9 (a commercial product, purity not indicated) using sludge from a municipal wastewater treatment plant as the microbial seed. The procedure followed OECD Guideline 301B, in compliance with GLP. The test substance with the standard nutrient medium inoculated with inoculum (30 mg suspended solids/L) was kept in bottles (in darkness) at 22± 2°C for 35 days. A blank control, reference material (sodium benzoate) and a toxicity control were run in parallel for validation purposes. Carbon dioxide traps were removed and analysed on Days 1, 2, 4, 6, 9, 13, 22, 28 and 35. Test substance and dissolved oxygen concentrations for each test medium were determined on Days 15 and 35. The reference material attained 95.4% degradation after 35 days. NPE-1.5 attained 45.3% degradation after 28 days and 58.7% after 35 days. NPE-1.5 therefore cannot be considered to be readily degradable under the conditions of OECD Guideline 301B but the but the high level of degradation obtained suggests that it would be inherently biodegradable. NPE-9 attained 74.8% degradation after 28 days and 79.5% after 35 days but failed the 10-day window (Gledhill WE, 1999) . It could be considered ‘readily biodegradable but failing the 10 d window’. Based on this data, Staples CA et al. (2001) calculated first order half-lives (primary degradation) of 18.9 days (NPE-1.5, lag time = 9 days) and 13.6 days (NPE-9, lag time = 1 day).

In another study, NP (95.6% p-NP, the rest o-NP) was tested for ready biodegradability according to OECD Guideline 301F, in compliance with GLP. NP and the mineral medium inoculated with activated sludge were kept in respirometer flasks at 22°C for 28 days. The consumption of oxygen was determined by measuring the quantity of oxygen produced electrolytically that is required to maintain constant gas volume in the respirometer flask. A blank control and a reference material (sodium benzoate) were run in parallel for validation purposes. The reference material attained 94% degradation after 28 days. NP reached 62% degradation within 28 days but did not meet the 10-day window and can therefore considered to be ‘readily biodegradable but failing the 10 d window’ (Staples CA et al., 1999).

There are numerous papers studying the degradation behavior of NPEOs in the environment. Most deal with the more common longer-chain ethoxylates (NPE-8 and 9) and often with linear ethoxylation chains. Overall, the evidence shows that NPEOs are not persistent, the degradation rate depending on the environmental conditions (ECB, 2002). Longer chain NP ethoxylates are rapidly converted to NPE-1 and NPE-2, then further to the corresponding carboxylates or NP (ECHA, 2013). The carboxylates and NP are broken down at a slower pace but may eventually be degraded completely to CO₂ and water. Degradation rate is affected by the degree of branching and is faster for linear versus branched isomers (Environment Canada, 2001).