Dicyclopentyldimethoxysilane

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1997-05-12 to 1997-05-16

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

yes

Details on test solutions:

Test article amounts of 49, 26, 12, 6 and 3 mg were weighed and ejected into 1000-ml brown glass flasks, filled with 284 ml of deionised water and stirred. Stirring continued for 30 hours.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Activated sludge from a domestic wastewater treatment plant (ARA Ergolz II, Fullinsdorf/Switzerland).
Washed by centrifugation, supernatant decanted, solid material resuspended.
Dry weight of activated sludge 4 g/l.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Post exposure observation period:

Oxygen consumption measured over a period of up to ten minutes (Winkler flasks and oxygen electrode)

Test temperature:

22°C

Nominal and measured concentrations:

6, 12, 24, 50 and 100 mg/l nominal.

Reference substance (positive control):

yes

Remarks:

3, 5-Dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

In comparison to the inoculum controls the respiration rate of the activated sludge was not inhibited at nominal concentrations of 6, 12, 24, 50 and 100 mg/l. Based on the appearance of test substance in the deionised water by visual assessment after 30 minutes of stirring, but prior to addition of synthetic sewage feed and activated sludge, and obvious excess of test article was present in all test flasks bu the test article droplets were generally finely distributed. EC50 and EC20 values are clearly higher than the limit of water solubility of the substance under the present conditions, or >100 mg/l nominal.

Results with reference substance (positive control):

3hr EC50 19.6 mg/l

Table 2: Controls, reference substance (3, 5-dichlorophenol) and test substance: oxygen consumption and percentage inhibition of the respiration rate.

	Flask	Nominal concentration (mg/l)	Oxygen consumption (mg O2/l/min)	% Inhibition respiration rate
1	Inoculum control	0	0.935	-
12	Inoculum control	0	1.004	-
	Mean		0.970
7	Test substance	100	0.976	-0.7
8	Test substance	50	1.061	-9.4
9	Test substance	24	0.979	-1.0
10	Test substance	12	1.029	-6.1
11	Test substance	6	1.066	-10.0
2	Reference substance	100	0.094	90.3
3	Reference substance	32	0.198	79.6
4	Reference substance	10	0.778	19.8
5	Reference substance	3.2	0.975	-0.6

 

Validity criteria fulfilled:

yes

Conclusions:

An activated sludge respiration inhibition 3hr EC50 value of >100 mg/l (nominal) was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

yes

Remarks:

Minor deviations only. These did not affect the integrity or outcome of the study.

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

Owing to the limited water solubility of the substance the solutions for both the range-finder and definitive tests were prepared by direct addition of the substance to the vessels containing mixtures of reverse-osmosis water and synthetic sewage. These solutions were ultrasonicated for approximately 10 minutes in order to attempt to disperse the test substance as an emulsion prior to adding the inoculum.

For the range finding test the following four concentrations of DCPMS were tested (each tested in duplicate): 1.0, 10, 100 and 1,000 mg/l.

For the definitive test the following five concentrations of DCPMS were tested (each tested in duplicate): 1,000, 2,000, 5,000, 10,000 and 20,000 mg/l.

Observations during the definitive test indicated that the test substance tended to spread as an oily film over the surface of the solution during ultrasonication and that only partial emulsification was noted at the two highest concentrations tested of 10,000 and 20,000 mg/l.

3,5-Dichlorophenol was used as a reference inhibitor. A stock solution of this substance was prepared by dissolving 0.125 g in 250 ml of reverse-osmosis water before use. The reference inhibitor was tested at conentrations of 5, 15 and 45 mg/l (single replicates of each) in both the range finding test and the definitive test).

Two separate 1 litre batches of 100-fold OECD synthetic sewage concentrate were prepared. The first batch was used to feed the inoculum before and after the range finding test and to provide the substrate for the test mixtures in the range finding test. The second batch was used to feed the inoculum once in the period between the range finding test and the definitive test and also in the definitive test.

For the range finding test, the incubations were started sequentially at timed intervals by adding 200 ml inoculum to 300 ml of the aqeuous solutions containing the DCPMS and synthetic sewage (16 ml). The controls consisted of 200 ml inoculum added to 300 ml in reverse-osmosis water containing 16 ml synthetic sewage. The reference substance solutions were similarly prepared with the appropriate volumes of 3,5-dichlorophenol stock solution.

For the definitive test, the test solutions were prepared in the same way but, owing to the limited amount of test substance available, all volumes were halved (a final volume of 250 ml rather than 500 ml was used).

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

The activated sludge sample was collected from a return sludge channel at a sewage treatment works treating predominantly domestic waste water. On arrival at the laboratory the sludge sample was continually aerated prior to use.

The inoculum was prepared by dilution of the activated sludge sample in tap water to give a total volume of 8 litres with a dry suspended solids concentration of around 4 g/l. The inoculum was not acclimatised or adapted to the test substance before use in the test.

Once prepared the inoculum was maintained by feeding overnight with 100-fold OECD synthetic sewage conceentrate at a rate of 50 ml/l prior to the rangefinding test. The inoculum was used in the range finding test on the day after collection and was kept continually aerated throughout this period.

The suspended solids concentration of the inoculum was re-determined immediately prior to the definitive test and a subsample was adjusted (diluted) with dechlorinated tap water to give a suspended solids contents of 4 g/l. The pH of the inoculum was determined to be 7.49 which is within the permitted range of the test and so the inoculum was used without further pH adjustment.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Hardness:

Reverse-osmosis water used.

Test temperature:

The temperature during the tests was in the range 20.2 to 21.7°C which is within the range of 20 +/- 2 °C required in the Test Guideline.

Nominal and measured concentrations:

The nominal concentrations of DCPMS were 1.0, 10, 100 and 1,000 mg/l in the range-finder test and 1,000, 2,000, 5,000, 10,000 and 20,000 mg/l in the definitive test.

Details on test conditions:

The test solutions were incubated for 3 hours with aeration. At the end of the incubation period, sub-samples of each solution were used for dissolved oxygen measurements. For this a portion of the test mixture was transfered to fill a 250 ml sampling bottle containing a magnetic stirrer bar. A dissolved oxygen probe was then inserted into the sample bottle, the bottle sealed and continually stirred, and the dissolved oxygen concetration continually recorded on a chart. The respiration rate was derived from the longest liner portion of the trace.

The reduction in respiration rate was determined as the difference between mean control and the test respiration rate expressed as a percentage of the mean control respiration rate.

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 20 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Details on results:

For the range-finder test no significant inhibition of respiration was observed with DCPMS at concentrations of 1.0 and 10 mg/l compared with the control solution. The percentage inhibitation relative to the controls seen at 100 mg/l and 1,000 mg/l was 15% and 29% respectively. Linear regression analysis (using log 10 concentration values) of these effects data gave the following estimated EC20 and EC50 (regression coefficient 0.9998).

EC20 = 233 mg/l
EC50 = 27,339 mg/l (note: extrapolated above the highest concentration tested).

For the definitive study, it was found the the mean respiration rate recorded for the controls was around 18% higher than recored in the corresponding samples in the range-finding study (see Tables below). The reason for this was not known but it was suggested in the test report that this may be related to adaptation of to the synthetic sewage substrate that was used to feed the inoculum during the interval between the range-finding and definintive study.

The percantagae inhibition compared with the control solution seen in the definitive test was between 17% and 24% at all concentrations tested and so it was not possible to determine an EC50 value.

The test report noted that there was a small descrepancy between the results of the range finding test (which found 29% inhibition at 1,000 mg/l and suggested and EC50 of around 27,000 mg/l) and the definitive test (which showed a maximum 24% inhibition at concentrations up to 20,000 mg/l). The report suggested that this discrepancy may result from inhibition of nitrification by DCPMS with no effect on carbonaeceous respiration. It was noted that carbonaceous respiration usually exceeds nitrogenous oxygen demand roughly in the proportion 70:30 and so the 29% inhibition seen in the range-finding test may suggest that nitrification was inhibited at 1,000 mg/l in this test. For the definitive test the highest inhibition was lower than in the range-finding test at 24%. The test report indicates that the reason for this was unknown but it was suggested that it was possible that the ratio of the carbonaceous respiration to nitrogenous oxygen demand may have shifted to approximately 75:25 by the time the sludge sample was used in the definitive test an again selective inhibition of nitrification would then explain the data seen. This is supported by the plateau observed in the definitive test where relatively little further inhibition occurred at concentrations above 1,000 mg/l. The test report indicates, however that further work with a method designed to assess chemicals for inhibition of nitrification would be required in order to resolve this matter conclusively.

It should be noted that the concentrations tested in the definitive study are all above the water solubility of the test substance.

Results with reference substance (positive control):

For the range-finding test, the following effect concentrations were determined for 3,5-dichlorophenol.

EC20 = 2 mg/l
EC50 = 6 mg/l
EC80 = 15 mg/l

In the definitive test, the following effect concentrations were determined for 3,5-dichlorophenol

EC20 = 6 mg/l
EC50 = 15 mg/l
EC80 = 38 mg/l

Reported statistics and error estimates:

The effect concentrations were estimated using linear regression analysis of the log 10 [concentration] against percentage inhibition of respiration rate.

The following regression coefficients were reported.

DCPMS - range-finding study = 0.9998.
DCPMS - definitive study = no regression analysis possible
3,5-dichlorophenol - range-finding study = 0.96077
3,5-dichlorophenol - definitive study = 0.99829

The results from the range-finding study are summarised in Table 1.

Table 1: Respiration rate and inhibition data from the range-finding study

Treatment	Replicate		Respiration rate (mg O2/l . h)		Percentage inhibition
			Individual values	Mean
Control	1 (start of series)		50.20	49.31	-
	2 (start of series)		49.50
	3 (end of series)		49.61
	4 (end of series)		47.91
1.0 mg/l DCMPS	1		49.40	48.23	2%
	2		47.06
10 mg/l DCMPS	1		49.70	49.23	0%
	2		48.75
100 mg/l DCMPS	1		42.13	41.91	15%
	2		41.68
1,000 mg/l DCMPS	1		35.71	34.89	29%
	2		34.06
5 mg/l 3,5-dichlorophenol	1		29.15		41%
15 mg/l 3,5-dichlorophenol	1		11.13		77%
45 mg/l 3,5 -dichlorophenol	1		5.39		89%

The results from the definitive study are summarised in Table 2.

Table 2: Respiration rate and inhibition data from the definitive study

Treatment	Replicate		Respiration rate (mg O2/l . h)		Percentage inhibition
			Individual values	Mean
Control	1 (start of series)		54.95	58.40	-
	2 (start of series)		57.46
	3 (end of series)		68.45^1
	4 (end of series)		62.79
1,000 mg/l DCMPS	1		49.40	48.23	2%
	2		47.06
10 mg/l DCMPS	1		49.70	49.23	0%
	2		48.75
100 mg/l DCMPS	1		42.13	41.91	15%
	2		41.68
1,000 mg/l DCMPS	1		35.71	34.89	29%
	2		34.06
5 mg/l 3,5-dichlorophenol	1		29.15		41%
15 mg/l 3,5-dichlorophenol	1		11.13		77%
45 mg/l 3,5 -dichlorophenol	1		5.39		89%

Validity criteria fulfilled:

yes

Conclusions:

The EC50 for DCPMS on respiration of activated sludge was found to be in excess of 20,000 mg/L in a study conducted according to a relevant test method and in compliance with GLP. The result is considered to be reliable.

Reference 3

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: Huls Method (oxygen consumption test)

Principles of method if other than guideline:

Determination of the toxicity to bacteria in an oxygen consumption test.

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

yes

Details on test solutions:

Test solutions were made up using an emulsifier (nonylphenol ethoxylate (10 EO)/propoxylate (5 PO). The following concentrations of DCPMS were tested: 0.97, 9,7, 97 and 970 mg/l based on active substance.

Sterile control solutions were prepared using HgCl2 at a concentration of 3 mg/l.

The test medium was mineral salts medium containing glucose.

Test organisms (species):

Pseudomonas putida

Details on inoculum:

The test species was Pseudomonas putida Migula. The inoculum concentration used was ca. 100,000 cells/ml.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

5 h

Remarks on exposure duration:

The actual exposure duration was 4.92 hours.

Test temperature:

The tests were carried out at a temperature of 24.9 to 25.9 °C (mean 25.3 °C).

Reference substance (positive control):

no

Duration:

5 h

Dose descriptor:

EC10

Effect conc.:

> 970 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: oxygen consumption

Duration:

5 h

Dose descriptor:

EC50

Effect conc.:

> 970 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: oxygen consumption

Details on results:

No significant effect on oxygen consumption was seen in the test solutions with DCPMS when compared with controls at any concentration tested.

The results are summarised in Table 1.

Table 1: Oxygen consumption and inhibition test

Treatment	Mean dissloved oxygen concentration (mg O2/l)		Oxygen consumption (mg O2/l)	Percentage inhibition
	Start of test	End of test
Controls (four replicates)	8.71	4.05	4.66
0.97 mg/l DCPMS (2 replicates)	8.83	4.13	4.70	-0.9%
9.7 mg/l DCPMS (2 replicates)	8.83	4.19	4.65	0.3%
97 mg/l DCPMS (2 replicates)	8.67	4.23	4.44	4.8%
970 mg/l DCPMS (2 replicates)	8.84	4.07	4.77	-2.3%

Validity criteria fulfilled:

yes

Conclusions:

The EC10 and EC50 for DCPMS was found to be in excess of 970 mg/l.

Reference 4

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Details on test solutions:

The following five concentrations of DCPMS were tested: 20, 40.4, 60.4 78.4 and 100 mg/l.

The test solutions were prepared by adding 200 ml inoculum to 300 ml of the aqueous solutions containing the test substance and synthetic sewage (16 ml). The controls consisted of 200 ml inoculum added to 300 ml water containing 16 ml synthetic sewage. The reference substance solutions were similarly prepared with the appropriate amounts of 3,5-dichlorophenol.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

The activated sludge sample was collected from a municipal waste water treatment plant. The sludge was diluted in drinking water to give a suspended solids conentration of 2 g/l.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

The test temperature was in the range 20.5 to 22.0°C.

pH:

The pH of the solutions was in the range 8.1 to 8.4.

Nominal and measured concentrations:

The nominal concentrations of DCPMS were 20, 40.4, 60.4, 78.4 and 100 mg/l.

Details on test conditions:

The test solutions were incubated for 3 hours. The dissolved oxygen concentration was determined at the start and end of the incubation period and the respiration rate determined.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Details on results:

The test substance was found to have little or no effect on the respiration rate compared with the controls at any concentration test. The highest reduction in respiration rate compared with the controls was 5.4% at a DCPMS concentration of 40.4 mg/l.

Results with reference substance (positive control):

The EC50 for the reference substance (3,5-dichlorophenol) was estimated to be 5.4 mg/l.

The results from the study are summarised in Table 1.

Table 1: Respiration rate and inhibition data

Treatment	Respiration rate (mg O2/l . h)	Percentage inhibition
5 mg/l 3,5-dichlorophenol	9.35	47.4%
7 mg/l 3,5-dichlorophenol	7.30	58.9%
10 mg/l 3,5-dichlorophenol	4.89	72.5%
100 mg/l DCPMS	16.95	4.6%
78.4 mg/l DCPMS	18.00	-1.3%
60.4 mg/l DCPMS	17.70	0.4%
40.4 mg/l DCPMS	16.80	5.4%
20 mg/l DCPMS	17.04	4.1%
Control - replicate 1	17.27
Control - replicate 2	18.26

Validity criteria fulfilled:

yes

Conclusions:

The EC10 for DCPMS on respiration of activated sludge was found to be in excess of 100 mg/L in a study conducted according to a relevant test method and in compliance with GLP. The result is considered to be reliable.

Description of key information

Parent substance: Activated sludge respiration inhibition EC₅₀ >1000 mg/L, based on weight of evidence from three respiration inhibition tests.

Hydrolysis product: Activated sludge respiration inhibition EC₅₀ >100 mg/L (nominal), based on read-across from a structurally-related substance.

Key value for chemical safety assessment

EC50 for microorganisms:

1 000 mg/L

Additional information

The effect of dicyclopentyl(dimethoxy)silane (CAS 126990-35-0) on the respiration rate of activated sludge has been investigated in two studies using standard guidelines and conducted according to GLP. In both studies no effects were seen at the highest concentration tested (20000 mg/L and 100 mg/L respectively). The effect on the respiration rate of Pseudomonas putida has also been investigated, in a standard study conducted according to GLP. No effects were seen at the highest concentration tested (970 mg/L).

These studies were conducted at concentrations far higher than the water solubility of the parent substance. Where the experimentally derived EC₅₀ is higher than the aqueous solubility, it can still be used as valid information to derive a PNEC_stp as untreated waste water may well contain undissolved material above the limit of solubility. However, 20000 mg/L is considered to represent an unrealistic release rate, and therefore the value is capped at 1000 mg/L.

No data are available for the hydrolysis product of dicyclopentyl(dimethoxy)silane, dicyclopentylsilanediol. An EC₅₀ of >100 mg/L (nominal) has been determined for the structurally-related substance dichloro(dicyclopentyl)silane (CAS 139147-73-2), which has the same hydrolysis product as dicyclopentyl(dimethoxy)silane.

Dichloro(dicyclopentyl)silane hydrolyses very rapidly, and the activated sludge would have been exposed to the hydrolysis product, dicyclopentylsilanediol. The other hydrolysis product of dichloro(dicyclopentyl)silane is HCl. Effects of hydrochloric acid on microorganisms are limited to those that result from changes to pH in unbuffered media. The other hydrolysis product of dicyclopentyl(dimethoxy)silane is methanol. Methanol is non-toxic to the environment.

This read-across, indicating no evidence of toxicity to microorganisms, is supported by an overall review of the toxicity to microorganisms of the organosilane substances category as a whole.