Dodecyl(2-hydroxy-3-sulphonatopropyl)dimethylammonium

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

toxicity to microorganisms, other

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1995-05-19 to 1995-06-16

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Remarks:

The primary aim of this study was to assess the ready biodegradability of dodecyl(2-hydroxy-3-sulphonatopropyl)dimethylammonium (Betadet S-20). The study was technically compromised and the results cannot be evaluated reliably for that purpose and it therefore provides only supporting, qualitative information under Point 5.2.1. However, the study design included a toxicity control treatment that is not affected to the same extent by the deficiency that invalidated the biodegradability aspect and the results of the toxicity control provide a valid endpoint for microbial inhibition in the context of aerobic biological STP processes.

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)

Version / remarks:

The relevant data to address this data point are taken from the toxicity control treatment of the ready biodegradability test.

Deviations:

no

GLP compliance:

no

Specific details on test material used for the study:

Identity: Betadet S-20.
Description: Colourless liquid.
Batch/Lot number: Not reported.
Considered to be the batch (7244) received by the same laboratory on 1995-05-01 for acute toxicity testing with D. magna (Point 6.1.3, Wetton (1995)).
Purity: Not reported.

The Certificate of Analysis for batch 7244 (not included in the report) provides the following information:
Batch: 7244 (29/03/1995)
Appearance: Liquid, transparent, slightly yellowish, fluid
Dry matter: 44.5%
pH: 6.8
Sodium chloride: 6.4%

The principal constituent (included in the 44.5% 'dry matter') represented approximately 30% (w/w) of the tested batch.

Analytical monitoring:

no

Details on sampling:

Pairs of incubation bottles were sacrificed to make measurements of residual dissolved oxygen (DO) concentrations after 3, 6, 9, 12, 15, 21 and 28 days.

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Effluent from the secondary (activated sludge) treatment stage at Belper STP, Derbyshire, UK, which treats sewage of predominantly domestic origin. Test media were inoculated at the rate of one drop of effluent per litre.

Test type:

static

Water media type:

freshwater

Remarks:

Mineral salts medium as specified by OECD 301D.

Limit test:

yes

Total exposure duration:

28 d

Post exposure observation period:

Not relevant.

Hardness:

Not relevant.

Test temperature:

Not reported.

pH:

Not reported. The pH of the phosphate buffer solution added to the test medium was 7.4.

Dissolved oxygen:

The test medium was prepared with pre-aerated reverse-osmosis water and left to equilibrate for 24 h at room temperature (ca. 21 degrees C) before use. Initial (Day 0) dissolved oxygen (DO) concentrations were uniformly 8.90 mg/L. DO concentrations declined over the course of the incubation to 7.90, 3.25, 4.55 and 1.80 mg O2/L in the blank control, reference, Betadet S-20 and toxicity control treatments, respectively, on Day 28.

Salinity:

Not relevant.

Conductivity:

Not relevant.

Nominal and measured concentrations:

The toxicity cotrol treatment of the biodegradability test contained the test substance Betadet S-20 combined with the readily biodegradable reference compound sodium benzoate at nominal concentrations of 10 and 1.5 mg/L, respectively.

Details on test conditions:

The test design comprised the following four treatments:

1) blank control, consisting of inoculated test medium;
2) test substance Betadet S-20 dosed at 10 mg/L (nominally 4.3 mg ThOD/L) in inoculated test medium;
3) reference substance sodium benzoate dosed at 3 mg/L (nominally 5.0 mg ThOD/L) in inoculated test medium;
4) toxicity control comprising Betadet S-20 (10 mg/L) plus sodium benzoate (1.5 mg/L), giving a combined nominal ThOD of 6.8 mg O2/L, in inoculated test medium.

The various media were dispensed to sufficient test vessels at initiation to facilitate measurements of residual dissolved oxygen (DO) concentrations in pairs of vessels at each of the following timepoints: 3, 6, 9, 12, 15, 21 and 28 days.

Reference substance (positive control):

yes

Key result

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

10 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of heterotrophic respiration

Remarks:

(Na benzoate mineralisation)

Details on results:

See table and following text below.

Results with reference substance (positive control):

Sodium benzoate was biodegraded by 66% within 3 days and biodegradation at the end of the test on Day 28 was 93%.

Reported statistics and error estimates:

Not relevant.

Oxygen demand data calculated from measurements of residual DO concentrations in pairs of test vessels are presented in the table below.

Oxygen uptake recorded for Betadet S‑20 in a 28‑day Closed Bottle Test (OECD 301D). 

Treatment		Oxygen consumption (mg O2/L)
		D3	D6	D9	D12	D15	D21	D28
Inoculated medium control	mean:	0.150	0.400	0.575	0.850	0.975	1.000	0.975
Reference substance: Sodium benzoate (3 mg/L)	rep 1:	3.250	3.900	4.225	4.200	4.725	4.700	4.675
	rep 2:	3.350	4.000	4.275	4.150	4.525	4.600	4.675
	mean:	3.300	3.950	4.250	4.175	4.625	4.650	4.675
Test substance: Betadet S‑20 (10 mg/L)	rep 1:	0.050	0.200	0.425	1.850	2.525	3.050	3.325
	rep 2:	0.050	0.300	0.725	2.050	2.725	2.950	3.375
	mean:	0.050	0.250	0.575	1.950	2.625	3.000	3.350
Toxicity control: Betadet S‑20 (10 mg/L) + sodium benzoate(1.5 mg/L)	rep 1:	1.550	2.100	2.525	2.350	5.875	5.900	6.125
	rep 2:	1.750	1.950	2.225	2.500	5.925	5.900	6.125
	mean:	1.650	2.025	2.375	2.425	5.900	5.900	6.125
	mean ×2	3.300	4.050	4.750	4.850	9.250	11.80	12.25

 

The bottom row of the table (not reported) doubles the BOD recorded in the toxicity control. The resulting values at Days 3 & 6 (corresponding to the times when BOD may be attributed solely to Na benzoate oxidation, before a significant contribution from the degradation of the Betadet S-20 component) – match the contemporary BOD values recorded in the reference treatment that contained Na benzoate only, at a 2× higher concentration. This shows that the presence of 10 mg Betadet S-20/L caused no suppression of Na benzoate mineralisation in the toxicity control.

The reported % biodegradation values for the test substance Betadet S-20 were calculated with a COD value ca 5x lower than the ThOD that may be estimated from the structural formula of the test substance (see summary of the biodegradation test under Point 5.2.1). The reliability of the % biodegradation values reported for Betadet S-20 is therefore uncertain and it cannot be ruled out that the values may be over-estimated by as much as x5. It is therefore not possible to make a reliable quantitative assessment of the ready biodegradability of Betadet S-20 from the information presented in the test report. Nevertheless, from a qualitative point of view it is evident that at least partial biodegradation did occur: the degradation of Betadet S-20 followed a sigmoid curve, with a phase of rapid oxidation that commenced after approximately Day 8 and continued to around Day 15.

The test design included a reference treatment dosed with 3 mg sodium benzoate/L. Na benzoate performed as expected for a readily biodegradable substance: rapid mineralisation started immediately and recorded BOD exceeded 60% of ThOD within the first three days of incubation.

The toxicity control vessels contained half the concentration of sodium benzoate (1.5 mg/L) as was present in the reference medium where Na benzoate was dosed alone (3 mg/L), and the same concentration of Betadet S-20 (10 mg/L) as was present in the test substance treatment. Because of the unreliability of the COD value of the Betadet S-20 component it is not possible to evaluate the performance of the toxicity control mixture reliably with respect to the trigger value of 25% degradation that conventionally marks the threshold of significant toxicity. However, the degradation curve of the toxicity control is distinctly biphasic and it is possible to match its second phase to the delayed onset of degradation of the Betadet S-20 component as it coincides with the timing of the rapid degradation phase observed in the vessels dosed with the test substance alone. The initial phase of the toxicity control degradation curve up to and including Day 6 - the timescale in which suppression of microbial activity would be most relevant to aerobic STP processes - is due to Na benzoate oxidation. When corrected for the two-fold difference in applied concentrations, the BOD recorded in the toxicity control on Days 3 and 6 corresponds very closely to that recorded at the same times in the reference vessels containing Na benzoate alone. It may therefore be concluded that the presence of 10 mg Betadet S-20 in the toxicity control caused no inhibition of the microbial degradation of Na benzoate and a microbial NOEC of 10 mg/L may be derived from the results of this study.

Validity criteria fulfilled:

yes

Remarks:

(in the context of the test as a study of ready biodegradability).

Conclusions:

An assessment of the ready biodegradability of Betadet S-20 was performed with the test substance applied at a concentration of 10 mg/L in the Closed Bottle Test (OECD TG 301D). The test was inoculated with a low density of activated sludge microorganisms obtained from the secondary effluent of a STP that received sewage of predominantly domestic origin. The test design included a toxicity control that comprised a mixture of Betadet S-20 (10 mg/L) and the readily biodegradable reference compound sodium benzoate. The toxicity control response showed no evidence of suppression of the microbial utilisation of Na benzoate by the presence of Betadet S-20, when compared to the parallel performance of the reference treatment dosed with Na benzoate alone. These findings support a microbial NOEC of 10 mg Betadet S-20/L. The NOEC is equivalent to 3.0 mg principal constituent/L after correction for the 30% (w/w) p.c. content of the tested batch of Betadet S-20.

Executive summary:

A study of the ready biodegradability of Betadet S-20 was performed according to the closed Bottle Test (OECD TG 301D).  The study was dosed with Betadet S-20 at a concentration of 10 mg/L, based on a chemical oxygen demand (COD) value of 0.43 mg O2/mg determined by a bench-top digestion kit system, and the same COD value was used as the comparator for calculating percentage biodegradation from measurements of biochemical oxygen demand (BOD) recorded at intervals during the 28-day incubation.  However, the COD value obtained for Betadet S-20 is ca. 5x lower than would be anticipated based on structural considerations, which suggests the COD determination may have achieved only partial oxidation.  This would in turn mean that the biodegradation percentages calculated for Betadet S-20 are over-estimated by a similar margin.  Betadet S-20 was reported to have achieved 78% biodegradation in 28 days and to have fulfilled the criteria for classification as readily biodegradable, however these findings must be considered to be unreliable in view of the uncertainty over the COD value. The test data do provide qualitative evidence of Betadet S-20 mineralisation under stringent Closed Bottle Test conditions.

The test design included a reference treatment dosed with 3 mg sodium benzoate/L. Na benzoate performed as expected for a readily biodegradable substance: rapid mineralisation started immediately and recorded BOD exceeded 60% of ThOD within the first three days of incubation.

The toxicity control vessels contained half the concentration of sodium benzoate (1.5 mg/L) as was present in the reference medium where Na benzoate was dosed alone (3 mg/L), and the same concentration of Betadet S-20 (10 mg/L) as was present in the test substance treatment. Because of the unreliability of the COD value of the Betadet S-20 component it is not possible to evaluate the performance of the toxicity control mixture reliably with respect to the trigger value of 25% degradation that conventionally marks the threshold of significant toxicity. However, the degradation curve of the toxicity control is distinctly biphasic and it is possible to match its second phase to the delayed onset of degradation of the Betadet S-20 component as it coincides with the timing of the rapid degradation phase observed in the vessels dosed with the test substance alone. The initial phase of the toxicity control degradation curve up to and including Day 6 - the timescale in which suppression of microbial activity would be most relevant to aerobic STP processes - is due to Na benzoate oxidation. When corrected for the two-fold difference in applied concentrations, the BOD recorded in the toxicity control on Days 3 and 6 corresponds almost exactly to that recorded at the same times in the reference vessels containing Na benzoate alone. It may therefore be concluded that the presence of 10 mg Betadet S-20 in the toxicity control caused no inhibition of the microbial degradation of Na benzoate and a microbial NOEC of 10 mg/L may be derived from the results of this study. The NOEC is equivalent to 3.0 mg principal constituent/L, based on the 30% p.c. content of the tested batch of Betadet S-20.

Unreliability of the biodegradability outcome notwithstanding, the results obtained in this study with the reference substance sodium benzoate and the assessment of the microbial toxicity of Betadet S-20 that may be inferred from the toxicity control that contained sodium benzoate and Betadet S-20 in combination are considered to be valid.   

Description of key information

An assessment of the ready biodegradability of Betadet S-20 was performed with the test substance applied at a concentration of 10 mg/L in the Closed Bottle Test (OECD TG 301D).  The test was inoculated with a low density of activated sludge microorganisms obtained from the secondary effluent of a STP that received sewage of predominantly domestic origin.  The test design included a toxicity control that comprised a mixture of Betadet S-20 (10 mg/L) and the readily biodegradable reference compound sodium benzoate.  The toxicity control response showed no evidence of suppression of the microbial utilisation of Na benzoate by the presence of Betadet S-20, when compared to the parallel performance of the reference treatment dosed with Na benzoate alone.  These findings support a microbial NOEC of 10 mg Betadet S-20/L.  

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

10 mg/L