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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Reference
Endpoint:
biodegradation in water and sediment: simulation testing, other
Remarks:
degradation in freshwater/sediment systems
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
This read-across is based on the hypothesis that source and target substances have similar toxicological properties because
• they are manufactured from similar or identical precursors under similar conditions
• they share structural similarities with common functional groups: quaternary ammonium and saturated or unsaturated alkyl chains with comparable length (corresponding to scenario 2 of the read-across assessment framework)

The read-across hypothesis is based on structural similarity of target and source substances. Based on available experimental data, including key physicochemical properties and data from acute toxicity, irritation, sensitization (human) and genotoxicity studies, the read-across strategy is supported by a quite similar toxicological profile of all substances.

Therefore, read-across from the existing ecotoxicity, environmental fate and toxicity studies conducted with the source substances is considered as an appropriate adaptation to the standard information requirements of the REACH Regulation for the target substance, in accordance with the provisions of Annex XI, 1.5 of the REACH Regulation.

A justification for read-across is attached to IUCLID section 13.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
See justification for read-across attached to IUCLID section 13.

3. ANALOGUE APPROACH JUSTIFICATION
See justification for read-across attached to IUCLID section 13.

4. DATA MATRIX
See justification for read-across attached to IUCLID section 13.
Reason / purpose:
read-across source
Reason / purpose:
read-across: supporting information
% Degr.:
8
Parameter:
radiochem. meas.
Remarks:
14CO2
Sampling time:
28 d
Remarks on result:
other: of 0.05 mg/L in river water alone
% Degr.:
19
Parameter:
radiochem. meas.
Remarks:
14CO2
Sampling time:
28 d
Remarks on result:
other: of 0.5 mg/L in river water alone
% Degr.:
11
Parameter:
radiochem. meas.
Remarks:
14CO2
Sampling time:
63 d
Remarks on result:
other: of 0.05 mg/L in river water alone
% Degr.:
22
Parameter:
radiochem. meas.
Remarks:
14CO2
Sampling time:
63 d
Remarks on result:
other: of 0.5 mg/L in river water alone
% Degr.:
43
Parameter:
radiochem. meas.
Remarks:
14CO2
Sampling time:
28 d
Remarks on result:
other: of 0.05 mg/L in river water + 5g/L adapted sediment
% Degr.:
65
Parameter:
radiochem. meas.
Sampling time:
63 d
Remarks on result:
other: of 0.05 mg/L in river water + 5g/L adapted sediment
Transformation products:
not measured
Executive summary:

The ultimate biodegradation of Di-C12-18 alkyldimethyl ammonium chloride is predicted to be low based on results obtained with the structurally related substance DSDMAC.

In river water alone (50 mg/l suspended solids, < 25 mg/l sediment), degradation was low (8% of 0.05 mg/l and 19% of 0.5 mg/l in 28 days). After 63 days the degradation results are not much higher (11% and 22% respectively), and the degradation curve ends in a plateau, suggesting that degradation will not continue. However, in the presence of sediments (5g/L), degradation was significantly higher (43% of 0.05 mg/l after 28 days and 65% after 63 days).

Description of key information

river water: 8% degradation of 0.05 mg/L in 28 days, 22% in 63 days

river water in the presence of sediments (5 g/L): 43% degradation of 0.05 mg/L after 28 days and 65% after 63 days

Key value for chemical safety assessment

Half-life in freshwater:
80 d
at the temperature of:
12 °C
Half-life in freshwater sediment:
500 d
at the temperature of:
12 °C

Additional information

The ultimate biodegradation of Di-C12-18 alkyldimethyl ammonium chloride is predicted to be low based on results obtained with the structurally related substance DODMAC.

In river water alone (50 mg/l suspended solids, < 25 mg/l sediment), degradation was low (8% of 0.05 mg/L and 19% of 0.5 mg/L in 28 days). After 63 days the degradation results are not much higher (11% and 22% respectively), and the degradation curve ends in a plateau, suggesting that degradation will not continue. However, in the presence of sediments (5g/L), degradation was significantly higher (43% of 0.05 mg/L after 28 days and 65% after 63 days).

Degradation in surface water

"It is shown in several tests that DODMAC/DHTDMAC are not readily biodegradable and there is no standard guideline test from which inherent biodegradability could be concluded. Adaptation seems to be necessary for significant degradation but even then mineralisation is very slow. In river water tests with adapted inocula degradation is occurring with a half-life in the range of several weeks. In two cases degradation discontinued after 63 days reaching approx. 10% at a lower and 20% at a higher DODMAC concentration. In another study a degradation half-life of approx. 80 days could be derived. Based on these results a degradation constant kbiowater = 0.0047 d-1 can be extrapolated for surface water, which would correspond to inherently biodegradable substances (DT50 = 150 days). With this value it is taken into account that the lower DODMAC concentrations in surface waters are degraded slower than in the cited tests probably. DT50-values of <80 days from river water tests with added adapted sediment reveal situations where the concentration of biodegrading microorganisms is increased over the normal level. Therefore these results can not be used for the derivation of the degradation rate constant in surface waters." (EU RAR, 2002)

Degradation in sediment

"For degradation in sediments simulation tests are lacking. Two tests on degradation in river water spiked with sediment (Larson, 1983; Larson & Vashon; cited above) suggest degradation half-lifes in sediment of 80 days or lower. Some experimental details did presumably not represent regular environmental conditions, e.g. sediments were possibly pre-adapted and the concentration of biodegrading microorganisms is regarded to be increased above the normal level.

The available monitoring data reveal that biodegradation in environmental sediments is lower. In Section 3.1.6, it is elaborated that a rapid degradation is not compatible with measured

concentrations in sediments. Hellmann (1995; cited in Section 3.1.2.1) found an increase of the DHTDMAC concentration at high river flows. As the causes whirling of sediments and rinsing

of agricultural soil during strong rainfalls are stated. These results indicate that DHTDMAC adsorbed onto sediments is not or very slowly degraded. A degradation rate cannot be derived

from the monitoring data. Therefore, analogously to the degradation in soil, a half-life of 500 d (k = 1.4 . 10-3 d-1) for the aerobic sediment layer is used in the exposure assessment.

There is no hint that DODMAC/DHTDMAC can be degraded under anaerobic conditions.

According to the TGD biodegradation in total sediments is assumed to be a factor of 10 lower than in soil: kbiosed = 1.4 . 10-4 d-1." (EU RAR, 2002)

[Type of water: freshwater]