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EC number: 915-730-3
CAS number: -
Abiotic degradation: DT50 in water and air are > 1 year and < 2 days, respectively.
Ready biodegradability: The substance is readily biodegradable in a study performed according to OECD TG 301F.
Activated sludge simulation test: equivalent to OECD TG 303A: In effluent the substance transforms into polar metabolites for 96% (log Kow < 2.1) including CO2 formation and uptake in biomass;
Simulation test in river water, equivalent to OECD TG 314: DT50 is < 1 day at 20°C and < 1.9 days at 12°C;
Simulation test in river sediment, equivalent OECD TG 308: DT50 is 9.5 days at 22°C and 17.4 days at 12°C;
Simulation test in soil, equivalent OECD TG 307: DT50 is 6 days at 22°C and 11 days at 12°C.
Bioaccumulation: Log BCF in fish: 2.6 in an OECD TG 305 study.
Environmental fate and distribution: Log Koc: 4.1; Henry coefficient: 11.3 Pa.m3/m3 (25C)
- Abiotic degradation:
Air: Based on a study conducted by Aschmann et al. (2001), OTNE undergoes in air rapid degradation after reaction with hydroxyl radicals and NO3 radicals. The atmospheric DT50 value after reaction with hydroxyl radicals and NO3 radicals is 1 hour and 1.4 minutes respectively. The half-life time of the substance is < 2 days. The substance will not reach the stratosphere and is therefore not considered to be a long-range transported chemical in air (http: //www.unece.org/fileadmin/DAM/env/documents/2000/ece/eb/ece%20eb%20air.60.e.pdf).
The substance does not have an ozone depletion potential because it does not contain halogens and does not have the potential to reach the stratosphere (EU CLP (EC 1272/2008 and its amendments).
Water: It can be reliably predicted that it is hydrolytically stable. It does not contain hydrolysable groups in its chemical structure such as esters, carbamates, epoxides, halomethanes, acylhalides (see Hydrowin, EpiSuite for all hydrolysable groups). The half-life at 20°C is therefore expected to be > 1 year.
- Biotic degradation:
In the key screening study according to OECD TG 301F 96.3% biodegradation (based on O2-consumption) was found after 28 days. This study shows that the substance is readily biodegradable meeting the 10-day window under the conditions of this test.
Die-away studies were carried out with radio-labelled C14 -OTNE in river water, in sediment as well as in soils. All tests confirm that OTNE degrades rapidly and that metabolites are formed that are transformed to polar metabolites and to CO2.
In an activated sludge simulation test (similar to OECD TG 303A by Schaefer and Cartee at Wildlife sponsored by RIFM, 2009) it was found that during steady state 96% of the substance in the effluent was transformed into more polar products including CO2 and uptake in biomass. These polar products had log Kow <2.1 (excluding one metabolite with similar Log Kow >2.1<6.5). In the whole system 89.72% of the parent OTNE was removed due to metabolite conversion, mineralisation, volatile loss and loss due to sorption to solids.
The river water test mimics the conditions in the mixing zone after the STP and is equivalent to OECD TG 314 (Schaefer, at Wildlife sponsored by RIFM, 2006). After 28 days 10% mineralisation to CO2 was detected. The DT50 for primary degradation is < 1 days at 20 +/-3oC. The kinetic assessment showed an initial first-order loss rate of 1.83/h and a second first-order loss rate of 0.022/h. The converted DT50 at 12oC is < 1.9 days.
In a sediment study, equivalent to OECD TG 308 (Envirogen sponsored by IFF, 1999) circa 50% was recovered as CO2 after 8 weeks and < 1% remained of the parent material. The half-life of the parent substance was estimated to be 9.5 days at 22oC. The converted DT50 at 12oC is 17.4 days.
In agricultural soil study, equivalent to OECD TG 307 (Envirogen, sponsored by IFF, 1999), the substance is almost completely degraded after 6 weeks. After 6 weeks the mineralisation (CO2 evolution) is circa 50%. After a lag time of approx. 7 days the initial rate of CO2 production was 1.4 - 1.8% /day in the sludge amended soil and in the agricultural soil, respectively. The half-life of the parent substance was estimated to be 4.2 and 6 days in the sludge amended soil and in the agricultural soil, respectively, at 22oC. The converted DT50 for agricultural soil at 12oC is 11 days.
Overall Conclusion on simulation tests: OTNE is rapidly biodegraded in more polar compounds including CO2 under natural conditions in activated sludge, river water, in sediment as well as in soils, with half-life time of 1.9 day in water, 17.4 days in sediment and 7.7 days in soil when converted to 12°C.
- Environmental fate and distribution:
Adsorption/Desorption: The substance is a lipophilic substance with log Kow 5.65. The sorption to organic matter, log Koc, has been determined using measurements in samples of sludge and effluent in sewage treatment plants in southern and northern Europe and is 4.12. This indicates that the substance will have a moderate potential to adsorb to sediment/soil.
Volatility: To assess the volatilisation potential of the substance a Henry's law constant was calculated using EUSES, which gave a result of 23.6 Pa. m3/mol at 25°C and 11.3 Pa. m3/mol at environmental temperature (12°C). From the distribution modelling results it can be concluded that volatilisation is of some importance in the environmental behaviour of the substance.
Bioaccumulation: The BCF value for fish (lipid content 5%) was determined to be 391. It can be concluded that the substance has a relatively low bioaccumulation potential.
The BCF in earthworms was estimated to be 5361 l/kg ww with the equation from EUSES (Jager, 1998), indicating that the potential for bioaccumulation in terrestrial organisms will be moderate.
BCF for air-breathing organisms: Using the criteria in the PBT guidance on air breathing organisms (2017) OTNE fulfils these: log Kow (5.6: > 2) and log Koa (6.9: > 5). The concern for air-breathing organisms is relevant for non-metabolising substances, which are not excreted via kidneys and for which the ventilation rate between air and blood is lower than for fish. This type of bioaccumulation is not relevant for metabolizing substances as Gobas et al. explicitly mentions (2020, figure 6, D, assessing oxygen containing substances). OTNE is an oxygen (ketone) substance with a hydrocarbon unsaturated backbone with two-ring structures. The ketone is expected to be reduced to an alcohol because glucuronidation is the key excretion pathway and this acid can only conjugate with an alcohol bond (see toxico-kinetic section). This transformation is expected to occur in all (air-breathing) organisms. Glucuronic acid has a low log Kow (<-1) and also OTNE-glucuronidated will have the acidic group and therefore this log Kow < -1. This results in excretion via kidneys as can be seen in the repeated dose-toxicity studies. In addition, the half-life in fish in the BCF test is 1.2 days. In mammals (rat) the DT50 was 1.4 days after oral doses of 20 mg/kg bw showing absence of bioaccumulating in fish and in air-breathing organisms. This means that OTNE and its degradants or metabolites are not a concern for air-breathing organisms.
Based on Level III distribution modelling using EPISUITE (assuming equal and continuous releases to air, water and soil) using the CAS number 54464-57-2 and the measured physico-chemical parameters as input, it is estimated that the majority of the substance released to the environment will partition mainly into soil (89.1%) with smaller amounts to water (8.84%) and sediment (2.08%) and a negligible amount to air (0.02%).
The SimpleTreat model, which is incorporated in EUSES, simulated the distribution of the substance in a Sewage Treatment Plant based on vapour pressure, water solubility, log Koc and biodegradability. The model predicts that 46% of the substance will biodegrade, 7.5% of the substance will partition to water, 45% to sewage sludge and 1.7% to air at 12°C.
Experimental simulation data show that the removal from the STP ranges from >50% to far more than 90%.
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