Quaternary ammonium compounds, coco alkyltrimethyl, chlorides

Sediment toxicity

Administrative data

Endpoint:

sediment toxicity: long-term

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Based on the results from the available studies, the test substance is concluded to be readily biodegradable.

Biodegradation in water:

readily biodegradable

Study 1: A study was conducted to determine the ready biodegradability of the test substance, TMAC C, according to OECD 301D and EEC Guidelines using a closed bottle test. The test substance at 3 mg/L was incubated with sludge from an activated sludge plant treating predominantly domestic waste and O2 consumption was determined for 28 d. The biodegradation was calculated as the ratio of the biochemical oxygen demand to the theoretical oxygen demand. The test substance reached a biodegradation of 75% on Day 28. As evident from the biodegradation of 59% at Day 5 and 74% at Day 17, the plateau for ready biodegradability of the test substance was reached within 14 d of the time point when 10% degradation occurred. Under the test conditions, the test substance is readily biodegradable (van Ginkel, 1989).

 

Study 2: A study was conducted to determine the biodegradability of the test substance, TMAC C (34% TMAC C in water), according to the OECD 310D by closed bottle test, in an aerobic activated sludge test system. The method was modified according to the recommendations of ECETOC (1985) or Blok et al. (1985). In the experiment, dark glass bottles of about 280 mL with glass stoppers were filled with a suspension of preconditioned activated sludge (3 mg s.s/L) in dilution water and a concentration of the test substance equivalent to about 6 mg ThOD/L (Theoretical Oxygen Demand). The test was carried out in triplicate and at every observation time measurements of oxygen and pH were carried out in a new series of three bottles. The percentage degradation calculated based on measured BOD/COD values at 2, 4 and 6 weeks, was found to be 90%, 97% and 97% respectively. Based on the results, it was concluded that the test substance passed the OECD criteria of 60% to classify the substance as readily biodegradable. Therefore, under the study conditions, the test substance was considered to be readily biodegradable (Balk, 1987).

 

 

Based on the above studies, the Biocides assessment report on TMAC C, published by the Italian authorities in April 2016, also concluded:“Coco alkyltrimethylammonium chloride is readily biodegradable. Further studies are not necessary because it is readily biodegradable applies.”(ECHA biocides assessment report, 2016).     

Further, the results obtained with the test substance are in agreement with what is reported in the literature for other quaternary ammonium substances, as summarized below inTable 4.4.

Table 4.4. Compilation of ready biodegradability test results obtained with quaternary ammonium salts (adapted van Ginkel, 2007)

Substance	Test	Results at Day 28 (%)
Cocotrimethylammonium (TMAC C)	Closed bottle	>60
Hexadecyltrimethylammonium Chloride (C16 TMAC)	Headspace Carbon Dioxide	75*
Octadecyltrimethylammonium Chloride (C18 TMAC)	Sturm test	>70
Octylbenzyldimethylammonium chloride (C18 ADBAC)	MITI	>80
Tetradecylbenzyldimethylammonium Chloride (C14 ADBAC)	MITI	>80
Decylbenzyldimethylammonium Chloride (C10 ADBAC)	Closed bottle	>60

*Mean from 10 laboratories; also cited in OECD TG 310 (adopted on 23 March 2006)

Biodegradation pathways of quaternary substances

Several literature data are available to clarify the metabolic basis of degradation by micro-organisms. Bacteria identified as Pseudomonas sp capable of degrading alkyltrimethylammonium salts were isolated from activated sludge (van Ginkelet al., 1992; Takenakaet al., 2007). Alkyltrimethylammonium salts with octadecyl, hexadecyl, tetradecyl, dodecyl, decyl, octyl, hexyl and coco alkyl chains supported growth of the isolates, showing the broad substrate specificity with respect to the alkyl chain length. Alkanals, and fatty acids can also serve as a carbon and energy source (van Ginkelet al., 1992; Takenakaet al., 2007). In simultaneous adaptation studies,1H nuclear magnetic resonance spectrometry (1H-NMR) and GC-MS showed that acetate, alkanals and alkanoates are the main intermediates of alkyltrimethylammmonium salt degradation, indicating that the long alkyl chain is utilized for microbial growth (van Ginkelet al., 1992; Nishiyama and Nishihara, 2002; Takenakaet al., 2007). Trimethylamine is stoichiometrically produced by pure cultures of microorganisms growing with the alkyl chain of alkyltrimethylammonium chloride as the sole source of carbon. The cleavage of the C-alkyl-N bond of alkyltrimethylammonium salts resulting in the formation of trimethylamine is initiated by a mono-oxygenase (van Ginkelet al., 1992). Additional evidence of the cleavage of the C-alkyl-N bond as the initial degradation step of alkyltrimethylammonium salts was presented by Nishiyamaet al. (1995) and Takenakaet al. (2007).

Dehydrogenase activity present in cell-free extract of hexadecyltrimethylammonium chloride-grown cells catalysed the oxidation of alkanal to fatty acids. The route of the fatty acid degradation is by β-oxidation. Trimethylamine, a naturally occurring compound is readily biodegradable (Pitter and Chudoba 1990). Complete degradation of trimethylamine is demonstrated through the assessment of the biodegradation pathway. Trimethylamine is degraded by methylotrophic bacteria through successive cleavage of the methyl groups (Large, 1971; Meiberg and Harder, 1978). Consortia of microorganisms degrading the alkyl chain of alkyltrimethylammonium salts and trimethylamine are therefore capable of complete (ultimate) degradation of alkyltrimethylammonium salts. Complete degradation of alkyltrimethylammonium salts using a mixed culture has been demonstrated by Nishiyamaet al. (1995). More recently, Nishiyama and Nishihara (2002) have isolated aPseudomonas spcapable of degrading both the alkyl chain and trimethylamine.  Both the pure and mixed culture studies showed that the degradation of the alkyl chain of alkyltrimethylammonium salts results in the formation of water, carbon dioxide and ammonium (seeFigure 2).

 

Figure 2: Biodegradation pathway of alkyltrimethylammonium salts (van Ginkel, 2004, 2007)

Further, according to the evidence presently available on the biodegradation rate, microorganisms readily oxidize the hydrophobic alkyl chains of the cationic surfactants, which is followed by a slower oxidation of the hydrophilic moiety (the corresponding amines) (van Ginkel, 2004). The above biodegradation process for the two moieties plays a key role in the differences in the results between the different cationic surfactants. However, based on the available experimental data and literature evidence, the alkyl chains and the trimethylamine of the test substance is readily biodegradable.

Overall, considering all the above information together, the test substance is considered to be readily biodegradable undergoing complete mineralization.

Cross-reference 2

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

The results of the read across study, supported with the estimated BCF value for the test substance together with its ionic nature indicates a low bioaccumulation and biomagnification potential. The higher experimental BCF value of 79 L/kg wt-wt from the read across study with C12 -16 ADBAC and the growth corrected kinetic biomagnification factor (BMFkg) value of 0.0463 based on read across to C18 TMAC, has been considered further for hazard/risk assessment.

BCF (aquatic species):

79 L/kg ww

BMF in fish (dimensionless):

0.046

Study 1: A study was conducted to determine the aquatic bioaccumulation of the read across substance, C12-16 ADBAC (30.64% active; 98.9% radiolabeled purity) in Lepomis macrochirus (bluegill fish) under flow-through conditions, according to EPA OPP 165-4, in compliance with GLP. The blue gill fish were continuously exposed to a nominal concentration of 0.050 mg/L of the read across substance (equivalent to a measured concentration of 0.076 mg/L) in well water for 35 days, followed by transfer of 35 fish into flowing uncontaminated water for a 21-d depuration period. Sampling was carried out on Days 0, 1, 3, 7, 9, 10, 14, 21, 23, 28 and 35 for the exposure period and Days 1, 3, 7, 10, 14 and 21 for the depuration period. Water samples were collected on Day 8 of the exposure period and Day 16 of the depuration for analytic determination of the read across substance concentration. Radiometric analyses of the water and selected fish tissues revealed that the mean steady state bioconcentration factor (BCF) in the edible, non-edible and whole-body fish tissue during the 35 days of exposure to be 33, 160 and 79 L/kg. The half-life for non-edible tissue was attained between Days 14 and 21, while it could not be reached for the edible and whole-body fish tissues by the end of 21-d depuration period. By Day 21 of the depuration period, the 14C residues present on the last day of exposure in the edible, non-edible and whole-body fish tissues had been eliminated by 29, 60 and 44% respectively. Analysis of skin tissue after 35 d of exposure showed residue levels somewhat higher than those observed for edible tissue at the same sampling period, indicating that there is likely significant binding of 14C-ADBAC to the skins and scales of exposed bluegill, as expected behaviour of cationic surfactants. Under the conditions of the study, the whole body BCF of the read across substance was determined to be 79, indicating low potential to bioaccumulate (Fackler, 1989).

 

Study 2: A study was conducted to determine the tissue distribution of two cationic surfactants mixtures in Rainbow Trout (Oncorhynchus mykiss) following exposure via water for seven days and analysis of different fish tissues. The test chemicals were grouped into two mixtures of six containing 10 alkyl amines and 2 quaternary alkylammonium surfactants: C10 TMAB (as part of MIX 2) and C14 TMAC (as part of MIX 1). Studying chemical mixtures has the advantage that differences in behavior between chemicals are not obscured by biological variability or experimental variables. Bioconcentration studies with mixtures have been shown to provide similar results to studies with single chemicals. The experiments were conducted in 300 L fiberglass aquaria with a water renewal rate of 1.3 L min−1 (MIX 1) and 1.45 L min−1 (MIX 2). A solution of the test chemical mixture in methanol was infused continuously (3.5 and 3.8 μL min−1 for MIX 1 and MIX 2, respectively) into the water inflow using a syringe pump. The intended concentrations of C10 TMAB and C14 TMAC were 59 and 1.3 μg/L (measured). The water temperature was 10 °C and the pH 7.5. The water hardness was estimated to be 1.1 mM Ca2+. For each mixture, the syringe pump was started in an aquarium containing no fish. After 16 h, to allow the concentrations to stabilize, 12 rainbow trout were added. After 7 d of exposure, the fish in the exposure aquaria as well as several unexposed (control) fish were sacrificed followed by blood collection.The surface of the fish posterior of the gills was rinsed with 100% methanol to remove read across substance residues adsorbed to the outer surface of the skin and absorbed in the skin mucus.The fish were then dissected and the liver, the kidney, the gills, and the remaining contents of the abdominal cavity were taken and weighed. Skin and muscle samples were prepared from the upper dorsal region on semi-frozen fish after the methanol rinse had removed the mucus. For 6 fish from each aquarium and 3 control fish, samples of muscle, skin, liver, and gills were homogenized in a bullet blender (muscle and liver) or in a cryo-mill (skin and gill). A sub-sample of 0.5−1.2 g of the homogenate was extracted twice in methanol, employing centrifugation at 4000 rpm for phase separation. Isotope labeled standards of C10 TMAB and C14 TMAC were added to a portion of the extract corresponding to 12−75 mg of the sample. Whole blood was analyzed rather than plasma because of the small quantity of sample available and the anticipated low concentrations. The test chemical concentrations generally increased in the order muscle <blood < skin < gills < liver. Because the mass of extracted mucus was not determined, the concentrations in mucus were normalized to the estimated fish’s total surface area excluding the head, which was not rinsed. The concentration in mucus was on average 3.9 (range 0.9−11.6) times lower than the surface area-normalized concentration in gills. To calculate the quantity of the test chemical in the different tissues, the amount of each tissue in the fish was estimated and multiplied by the concentration in that tissue. The test chemical quantities in the different tissues were then summed to give the body burden in each fish. The apparent BCFs (BCFapp) values at the end of the 7-day exposure were calculated by dividing the surfactant body burden (blood, muscles, liver, gills, skin, mucus) by the fish mass, and dividing this by the average measured concentration in water samples taken during the exposure phase. Under the study conditions, the BCFapp for the two quaternary substances C10 TMAB and C14 TMAC was determined to be 0.1 and 31 L/kg wet weight, respectively. Mucus, skin, gills, liver, and muscle each contributed at least 10% of body burden for the majority of the test chemicals. In contrast to the analogue alkylamine bases, the permanently charged quaternary ammonium compounds accumulated mostly in the gills and was nearly absent in internal tissues, indicating that systemic uptake of the charged form of cationic surfactants is very slow (Kierkegaard, 2020). Based on the results of the read across study, a similar low bioaccumulation potential is expected for the test substance.

 

Study 3: A study was conducted to determine the biomagnification (BMF) potential of the read across substance, C18 TMAC (purity 95%), following the principles of OECD TG 305. For the main study rainbow trout (Oncorhynchus mykiss) with an average weight of 5.42 g were fed test diets enriched with read across substance (23.6 mg/kg read across the substance in feed. The resulting treatment and one control group (each 40 animals) were tested simultaneously. The uptake phase of 14 days was followed by a depuration phase lasting 14 days. All animals were fed the non-spiked feed during the depuration phase. The concentrations of the read across substance in fish samples were determined by chemical analysis and all tissue concentrations were calculated based on a wet weight basis. Chemical analysis of the read across substance was performed by liquid chromatography with coupled mass spectrometry (LC-MS/MS). In the main study five animals of each group were sampled randomized on Day 7 and Day 14 of the uptake phase and after 10 h, 24 h, 2 days, 3 days, 7 days and 14 days of depuration. Biomagnification factor (BMF) and distribution factor were calculated based on the tissue concentrations measured at the end of the uptake phase. No mortality or abnormal behaviour of the test animals was observed during the main study. The experimental diets were accepted by the test animals and showed a decent digestibility as confirmed by the texture and appearance of the feces. One fish was euthanized at Day 25 due to injuries. The specific growth rates of the animals ranged from 1.95 to 2.71 %/d over the entire experiment. During the study, the feed conversion ratio (FCR) was 0.69 to 0.95. Fish were measured and weighed at the beginning of the experiment as well as at respective sampling time points to monitor growth and associated growth-dilution effects during the feeding study. Growth rate constants were determined separately for the uptake and depuration phases, for the treatments and the control group, using the ln-transformed weights of the fish. A subsequent parallel line analysis (PLA, as suggested by the OECD Guideline) resulted in no statistical differences between the uptake and the depuration phase among the treated groups with the read across substance. No statistically significant difference was detected with regard to the growth of the treated groups. Hence it was deduced that neither adverse nor toxic effects were caused by the enriched diets. As steady state seemed to be reached after 14 days of exposure, steady state biomagnification factors (BMFss) could be calculated as 0.02709 g/g, which showed that read across substance did not biomagnify after dietary exposure. In general, the GIT and the liver showed the highest values for the BMFk and BMFkg. The kinetic BMF (BMFk) and growth-corrected biomagnification factor (BMFkg) were calculated for the read across substance to be 0.0404 and 0.0463, respectively. Overall, it was concluded from the screening that ionization lowers the tendency of a chemical to bioaccumulate, compared to non-ionized chemicals. Aside from the well-known lipophobicity of ionized groups, fast depuration seems to be a major reason for the observed low biomagnification of ionic compounds, in particular anions. Fast depuration may happen due to rapid metabolism or conjugation of charged compounds, and future studies should test this hypothesis. Under the study conditions, the read across substance BMFss, BMFk and BMFkg values on whole body wet weight basis in rainbow trout were determined to be 0.02709, 0.0404 and 0.0463 g/g, respectively, suggesting low biomagnification potential (Schlechtriem, 2021). Based on the results of the read across study, a similar low biomagnification potential is expected for the test substance.

 

Study 4: The Bioconcentration factor (BCF) value of test substance, C12-16 TMAC was predicted using regression-based and Arnot-Gobas BAF-BCF models of BCFBAF v3.02 program (EPI Suite^TM v4.11). The Arnot-Gobas method, takes into account mitigating factors, like growth dilution and metabolic biotransformations, therefore the BCF value using this method is generally considered to be more realistic or accurate. However, ionic, pigments and dyes, perfluorinated substances are currently excluded from the applicability domain of this model. In the case of the test substance, considering that it is a UVCB consisting of a mix of ionic (e.g., the quaternary ammonium salts) and non-ionic constituents (e.g., amines), the BCF values were predicted using the regression-based method for the ionic constituents and the Arnot-Gobas BAF-BCF method for the non-ionic constituents, using SMILES codes as the input parameter. The BCF values for the constituents ranged from 3.16 to 447.5 L/kg ww (log BCF: 0.50 to 2.64), indicating a low bioaccumulation potential. On comparing with domain descriptors, all constituents were found to meet the MW, log Kow and/or maximum number of correction factor instances domain criteria as defined in the BCFBAF user guide of EPISuite. Further, given that the major constituents are structurally very similar and vary only in the carbon chain length, a weighted average value, which takes into account the percentage of the constituent in the substance, has been considered to dampen the errors in predictions (if any). Therefore, the weighted average BCF value was calculated as 67.21 L/Kg ww (Log BCF = 1.83). Overall, considering either the individual BCF predictions for the constituents or the weighted average values, the test substance is expected to have a low bioaccumulation potential. However, taking into consideration the model’s training set and validation set statistics and the fact that the training set only contains 61 ionic compounds, the BCF predictions for the individual constituents are considered to be reliable with moderate confidence.

 

This is further supported by the no bioaccumulation potential evidence observed in in the two toxicokinetic studies in mammals with the read across substance, C12 -16 ADBAC (Selim, 1987 and Appelqvist, 2006).

Also, the biocides assessment reports available from RMS Italy on TMAC C and C12-16 ADBAC, concluded the substances to show low potential for bioaccumulation, based on the results from the above study (Fackler, 1989) and an additional read across to DDAC for the TMAC C's assessment ((ECHA biocides assessment report, 2015, 2016). The report concluded the following in the TMAC C assessment report:“Coco alkyltrimethylammonium chloride is readily biodegradable, is rapidly excreted and does not accumulate in mammals, and it adsorbs onto the fish surface where its irritating action is expressed (therefore accumulation is more related to the concentration of the administered solution). Based on these properties’ bioaccumulation is not expected to be of concern for ATMAC/TMAC. An experimental BCFwhole body of 81 L/kg was determined in a flow-through test with Lepomis machrochirus and the read across substance DDAC (Lonza Cologne GmbH and Akzo Nobel Surface Chemistry AB, same study). A very similar result was obtained for the other quaternary ammonium compound benzyl-C12-16-alkyldimethyl ammonium chloride (C12-16-BKC/ADBAC) in a fish bioconcentration test, which gave a BCFwhole body = 79 L/kg (Akzo Nobel Surface Chemistry AB, access to Lonza Cologne GmbH study). Being both studies equally reliable, the BCFwhole body = 81 L/kg is chosen because related to the lead read across substance (DDAC) and it is slightly higher than the C12-16 BKC/ADBAC endpoint.”

 

Overall, the results of the read across studies, supported with the estimated BCF value for the test substance together with its ionic nature indicate a low bioaccumulation and biomagnification potential. The higher experimental BCF value of 79 L/kg wt-wt from the read across study with C12 -16 ADBAC and the growth corrected kinetic biomagnification factor (BMFkg) value of 0.0463 based on read across to C18 TMAC, has been considered further for hazard/risk assessment.

Cross-reference 3

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Based on the most recent and radiolabelled aerobic biodegradation study in soil with the read across substance, C12-16 ADBAC, the transformation of the substance was considered to be rapid with DT50 values ranging from 2.2-28.7 days with the SFO model and 1.6 – 23.3 days with the FOMC model at 20°C.​ Further, in the biocides dossier, a weighted estimate of the DT50 value at 12°C was extrapolated for C12-16 ADBAC by assuming the highest allowable concentrations for the major chains. These calculations resulted in the estimated FOMC DT50 of 17.1 days at 12°C and SOF DT50 of 19.2 days at 12°C. The DT50 of 17.1 days at 12°C based on the biphasic model (FOMC) showing better visual fit and lower error (x2)compared to the SFO model was used further for risk assessment. 

Half-life in soil:

17.1 d

at the temperature of:

12 °C

Study 1: A study was conducted to determine the aerobic transformation/dissipation in the soil of the read across substance, C12 -16 ADBAC (radiochemical purity: 98.5%), according to the OECD Guideline 307, in compliance with GLP. Four different standard soils (LUFA 2.2, 2.3, 2.4 and 5M, field fresh sampled), varying in their organic carbon content, pH, clay content, cation exchange capacity and microbial biomass, were treated with [ring-U-14C] Benzalkonium chloride. Soil samples were incubated in the dark under aerobic conditions for up to 128 days under controlled laboratory conditions. After appropriate time intervals, soil samples were extracted, and the extracts were analysed for read across substance and transformation products to calculate DT50 and DT90 values. The mineralization was determined by trapping and analysis of the evolved 14CO2. Non-extractable residues (NER) were determined after combustion of the extracted soil samples. The total radioactivity of the soil extracts, the extracted soil (NER) and evolved 14CO2 was determined by LSC. Read across substance and transformation products in the soil extracts were analysed by LC-FSA (radio-HPLC). Evaluation of the transformation pathway was done by LC-HRMS. Transformation of the C12 chain of the read across substance [ring-U-14C]Benzalkonium chloride was rapid in all four soils. The transformation of the C14 chain started after a short adaptation phase but was thereafter rapid as well. Within 7 - 21 days the concentration of the C12 chain decreased from initially 67.2 – 69.6% of applied radioactivity (AR) to < 20 % of AR. The concentration of the C14 chain decreased from initially 23.8 – 24.6 % of AR to < 10 % of AR within 10 – 36 days. Formation of NER started directly after application of the read across substance. Further formation of NER increased in parallel to the start of increased mineralisation, indicating that a major amount of NER is comprised by radioactivity incorporated in microbial biomass. At the test end, the biomass concentration was in the range of 1.46 – 2.62 % of soil organic carbon content in all four soils, indicating that viable microbial biomass was present throughout the incubation time. The mass balance was in the range 99.9 – 103.0 % at test start and 90.4 – 94.0 % at test end.The predominant initial degradation step was the oxidative removal of the alkyl chain. Dimethylbenzylamine was determined as the major metabolite, the highest concentrations of dimethylbenzylamine were determined until Day 22, thereafter the concentrations deceased continuously until test end. Methylbenzylamine was transient and only present in traces. Benzylamine, a suspected metabolite, was not detected. Further metabolites containing partly degraded alkyl chains were all transient and were not detected or only <0.2 % of AR (soil 2.3) at the test end. With regard to the kinetics, the transformation showed a slight bi-phasic pattern, therefore the ‘Single First Order Model’ (SFO) and the ‘First-Order Multi-Compartment Model’ (FOMC) were compared. Based on the visual fit and x2 error, the transformation of [ring-U-14C]Benzalkonium chloride met the requirements for both models well for all four soils. The calculated DT50 values with the Single-First-Order Model (SFO) for the dissipation of [ring-U-14C]Benzalkonium chloride were 2.2 – 8.7 days (C12 chain) and 6.1 – 28.7 days (C14 chain), the DT90 values were 7.2 – 28.8 (C12 chain) days and 20.2 – 95.4 days (C14 chain). The calculated DT50 values with the FOMC model for the dissipation of [ring-U-14C]Benzalkonium chloride were 1.6 – 7.2 days (C12 chain) and 5.5 – 23.3 days (C14 chain), the DT90 values were 15.0 – 48.8 days (C12 chain) and 35.8 – 164.3 days (C14 chain).

The read across substance is predominantly C12-ADBAC and C14-ADBAC, with low to negligible amounts of C16-ADBAC. The chain length distribution is defined as follows:C12 (35-80%), C14 (20-55%), C16 (0-15%). C16-ADBAC was not included in this study because it is present in very low amounts; there are technical difficulties with having sufficient radioactivity for substances present in small amounts relative to other constituents. C16-ADBAC would be expected to degrade by the same route but at a slower rate than its C12 and C14 counterparts, as degradation rate tends to decrease with increasing chain lengths.Under the study conditions, transformations of both C12 and C14 carbon chains of the read across substance were determined to be rapid in all four soils and the DT50 values were determined to be 2.2 – 8.7 days [C12 chain] and 6.1 – 28.7 days [C14 chain] with the SFO model and 1.6 – 7.2 days [C12 chain] and 5.5 – 23.3 days [C14 chain] with the FOMC modelat 20°C (Fiebig, 2019).

 

Further, in the biocides dossier, to account for the potential contribution of C16 ADBAC to the overall DT50 of ADBAC, a geometric mean of SFO and FOMC DT50s for C12 and C14 ADBAC in the four soils (as recommended in BPR Vol IV Part B and C) was calculated and converted to 12° using the following equation (DT50 (12°) = DT50 (20°) * e(0.08*(20-12)). This was followed by linear extrapolation of the geometric mean DT50s for C12 and C14 ADBAC, to estimate the DT50 for C16 ADBAC. See table below:

	Soil 2.2	Soil 2.3	Soil 2.4	Soil 5M	Geo. Mean	Adj. to 12° C
SFO DT50s
C12 ADBAC	2.2	3.3	6.2	8.7	4.4	8.4
C14 ADBAC	6.1	8.9	12.9	28.7	11.9	22.6
C16 ADBAC	--	--	--	--	--	36.7
FOMC DT50s
C12 ADBAC	1.6	3.2	5.8	7.2	3.8	7.3
C14 ADBAC	5.5	8.3	12.1	23.3	10.7	20.2
C16 ADBAC	--	--	--	--	--	33.1

A weighted estimate of the DT50 of ADBAC (C12-C16) at 12°C was calculated by assuming the highest allowable concentrations of C14- and C16- ADBAC and the balance of C12-ADBAC (i.e., 12% C16, 52% C14 and 36% C12), which resulted in the following estimated DT50s:

SFO DT50 = 19.2d at 12°C; FOMC DT50 = 17.1d at 12°C

However, due to the relatively low levels of C16-ADBAC, the overall estimated DT50s were considered rather insensitive to the assumed DT50 for C16-ADBAC.The DT50 of 17.1 days at 12°C based on the biphasic model (FOMC) showing better visual fit and lower errorwas used further for risk assessment.

Based on the results of the read across study, similar degradation potential and half-life is considered for the test substance.

 

Study 2:A study was conducted to determine the aerobic biodegradation of the read across substance, C12-16 ADBAC (50% active in water) in loamy soil, according to the US FDA Environmental Assessment Handbook, Technical Assistance Document 3.12 (1987). The study comprised two treatments: test and chemical blank control group, each with three replicates. The read across substance was added into biometers at a concentration of 10 mg carbon per 50 g soil using appropriate amount of deionised water required for bringing the soils to 50-70% of the moisture capacity. Loam was added to the biometers after the test solutions to facilitate uniform moistening of the soils by capillary action. The test was then incubated at 22 ± 3°C and run for approximately 90 d. The side tube of the biometer contained 20 mL 0.2 M KOH for absorbing carbon dioxide produced by the microorganisms. The theoretical CO2 production of the read across substance was calculated from its carbon content. The amounts of carbon dioxide were calculated by subtracting the mean carbon dioxide production in the test systems containing the read across substance and the mean carbon dioxide production level in the control blank. Biodegradation was calculated as the ratio of experimental carbon dioxide production to theoretical carbon dioxide production [ThCO2P]. Under the study conditions, there was 64% degradation of the read across substance after 70 days. This percentage of the theoretical carbon dioxide production presumes complete mineralization. The DT50 was estimated to be 40 days (Ginkel, 1994). Based on the results of the read across study, similar degradation potential and half-life is considered for the test substance.  ​

Based on the most recent and radiolabelled aerobic biodegradation study in soil with the read across substance, C12-16 ADBAC, the transformation of the C12 and C14 carbon chains of the substance was considered to be rapid with DT50 values ranging from 2.2-28.7 days with the SFO model and 1.6 – 23.3 days with the FOMC model at 20°C.​ Further, in the biocides dossier, a weighted estimate of the DT50 value at 12°C was extrapolated for C12-16 ADBAC by assuming the highest allowable concentrations for the major chains. These calculations resulted in the estimated FOMC DT50 of 17.1 days at 12°C and SOF DT50 of 19.2 days at 12°C. The DT50 of 17.1 days at 12°C based on the biphasic model (FOMC) showing better visual fit and lower error (x2)compared to the SFO model was used further for risk assessment. Therefore, in line with the biocides dossier, the DT50 of 17.1 days at 12°C derived for the read across substance based on the biphasic model (FOMC) also has been considered further for hazard/risk assessment of the test substance.  

Cross-reference 4

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Based on the results of the read across study, a similar complete removal of the test substance from the domestic wastewater treatment plants can be expected.  Further, based on the results of the soil biodegradation study with the read across substance, the DT50 value for degradation in the sediment compartment can be considered to be approximately 171 days at 12 °C.

Half-life in freshwater sediment:

171 d

at the temperature of:

12 °C

Surface water simulation testing: 

The study does not need to be conducted because the substance is readily biodegradable. 

Sewage treatment simulation testing 

A continuous activated sludge (CAS) study was conducted to determine the biodegradation of the read across substance, C12-16 ADBAC (49.2% active in water), in domestic wastewater according to OECD Guideline 303A, in compliance with GLP. In this study, the domestic waste microorganisms were exposed to the read across substance, by spiking at a nominal influent concentration of 49 mg/L (36 mg/L carbon) for a period of 58 days. An additional unit fed only with the domestic wastewater was maintained as the control group. All samples were analysed for NPOC. A strong increase in the concentration of NPOC was noted on Day 2 in the test units. This was probably caused by toxicity of the read across substance. The activated sludge acclimatised to the read across substance within a few days, resulting in a decrease of the NPOC concentrations. After 3 weeks, very high carbon removal percentages were achieved. The mean removal percentage in the test unit assessed using a HLPC-MS/MS was determined to be 99.998%, indicating ultimate biodegradation. Removal of the read across substance from the influent through adsorption onto sludge was only 0.023% on Day 58, showing that the main mechanism of elimination was biodegradation. Based on the results of the study, the read across substance was removed from wastewater at a very high percentage (approximately 99.998%) in the continuous activated sludge test. Removal of the read across substance from the influent through adsorption onto sludge was only 0.016 to 0.023% at two sampling times, demonstrating that the read across substance was removed almost completely and biodegraded. This suggests that the read across substance biodegrades almost completely in conventional biological wastewater treatment plants (Ginkel, 2007). Based on the results of the read across study, a similar complete removal of the test substance from the domestic wastewater treatment plants can be expected.  

Sediment simulation testing 

The study does not need to be conducted because the substance is readily biodegradable. Nevertheless, as per the ECHA E.16 guidance, the half-life in the sediment compartment will be a factor 10 higher than the half-life in soil. Therefore, the sediment half-life value of 171 days has been considered further for risk assessment.