Reaction mass of methyl dihydrogen phosphate and orthophosphoric acid and dimethyl hydrogen phosphate

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Mutagenic activity of the reaction mass of Methyl dihydrogen phosphate and Orthophosphoric acid and Dimethyl hydrogen phosphate was investigated in one bacterial reverse mutation assay (Ames test; test strains used: S. typhimurium TA 98, TA 100, TA 1535, TA 1537 and E. coli WP2 uvr A), in an in vitro gene mutation study in mammalian cells (Chinese Hamster V79 cells) and in two in vitro chromosome aberration study in Chinese Hamster V79 cells and in human lymphocytes. Negative results were obtained in the Ames test and the gene mutation test. In two mammalian cytogenicity studies (using Chinese Hamster V79 cells and in human lymphocytes) in which the genotoxic potential of reaction mass of Methyl dihydrogen phosphate and Orthophosphoric acid and Dimethyl hydrogen phosphate was examined in vitro for the detection of chromosomal aberrations, negative results were obtained in the absence of metabolic activation. A slight increase in chromosome aberrations in Chinese hamster V79 cells was observed in the presence of the S9 mix. However, of reaction mass of Methyl dihydrogen phosphate and Orthophosphoric acid and Dimethyl hydrogen phosphate did not induce chromosome aberrations up to 5000 µg/mL in the absence and presence of metabolic activation in an in vitro Chromosome Aberration test performed in human lymphocytes which is considered to be the most relevant cell system for it contains the whole human metabolic enzyme set (e.g. V79 are not p53 competent).

Link to relevant study records

Reference

Endpoint:

in vitro gene mutation study in mammalian cells

Remarks:

Type of genotoxicity: gene mutation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

15 March 2012 until 04 October 2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: according to OECD 476, GLP conform

Qualifier:

according to guideline

Guideline:

OECD Guideline 476 (In Vitro Mammalian Cell Gene Mutation Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method B.17 (Mutagenicity - In Vitro Mammalian Cell Gene Mutation Test)

Deviations:

no

Principles of method if other than guideline:

first experiment 4 hours treatment with and without metabolic activation
second experiment 24 hours treatment without metabolic activation, 4 hours treatment with metabolic activation

GLP compliance:

yes (incl. QA statement)

Type of assay:

mammalian cell gene mutation assay

Target gene:

HPRT

Species / strain / cell type:

Chinese hamster lung fibroblasts (V79)

Details on mammalian cell type (if applicable):

- Type and identity of media: MEM
- Periodically checked for Mycoplasma contamination: yes
- Periodically checked for karyotype stability: yes
- Periodically "cleansed" against high spontaneous background: yes

Metabolic activation:

with and without

Metabolic activation system:

Phenobarbital/Beta-Naphtoflavone induced Rat liver S9

Test concentrations with justification for top dose:

Experiment I:
without metabolic activation: 156.3; 312.5; 625.0; 1250; 2500; 5000 µg/mL
with metabolic activation: 156.3; 312.5; 625.0; 1250; 2500; 5000 µg/mL
Experiment II:
without metabolic activation: 156.3; 312.5; 625.0; 1250; 2500; 5000 µg/mL
with metabolic activation. 156.3; 312.5; 625.0; 1250; 2500; 5000 µg/mL
In both main experiments the cultures at the lowest concentration in the presence and absence of metabolic activation were not continued since a minimum of only four analys-able concentrations is required by the guidelines.

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: water
- Justification for choice of solvent/vehicle: solubility properties

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

ethylmethanesulphonate

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

7,12-dimethylbenzanthracene

Details on test system and experimental conditions:

METHOD OF APPLICATION: in medium


DURATION
- Exposure duration: Experiment I: 4 hours with and without metabolic activation, Experiment II: 24 hours without metabolic activation, 4 hours with metabolic activation
- Expression time (cells in growth medium): 72 hours
- Selection time (if incubation with a selection agent): 10 days

SELECTION AGENT (mutation assays): 6-Thioguanine


NUMBER OF REPLICATIONS: 2


NUMBER OF CELLS EVALUATED: >1,5x10exp. 6


DETERMINATION OF CYTOTOXICITY
- Method: cloning efficiency

Evaluation criteria:

A test item producing neither a concentration-related increase of the mutant frequency nor a reproducible positive response at any of the test points is considered to be non-mutagenic in this system.
A mutagenic response is described as follows:
The test item is classified as mutagenic if it induces reproducibly with one of the concen¬trations a mutation frequency that is three times higher than the spontaneous mutation fre¬quency in the experiment.
The test item is classified as mutagenic if there is a reproducible concentration-related increase of the mutation frequency. Such evaluation may be considered also in the case that a threefold increase of the mutant frequency is not observed.
In a case by case evaluation this decision depends on the level of the correspon¬ding solvent control data.

Statistics:

A linear regression (least squares) was performed to assess a possible dose dependent increase of mutant frequencies. The number of mutant colonies obtained for the groups treated with the test item were compared to the solvent control groups. A trend is judged as significant whenever the p-value (probability value) is below 0.05. However, both, biological and statistical significance were considered together.
experimental group: p-value:
experiment I, culture I without S9 mix 0.831
experiment I, culture II without S9 mix 0.564
experiment I, culture I with S9 mix 0.553
experiment I, culture II with S9 mix 0.308
experiment II, culture I without S9 mix 0.871
experiment II, culture II without S9 mix 0.773
experiment II, culture I with S9 mix 0.373
experiment II, culture II with S9 mix 0.789

Species / strain:

Chinese hamster lung fibroblasts (V79)

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Positive controls validity:

valid

Additional information on results:

TEST-SPECIFIC CONFOUNDING FACTORS
- Effects of pH:
In the pre-experiment the pH at concentrations of 156.3 µg/mL and above was adjusted to neutral with 2 N sodium hydroxide. In the main experiments the pH at concentrations of 312.5 µg/mL and above was adjusted as described above.

- Effects of osmolality: Not effected
- Evaporation from medium: Not examined
- Water solubility: Not indicated

- Precipitation:
The test medium was checked for precipitation or phase separation at the end of each treatment period prior to removal of the test item. No precipitation occurred up to the maximum concentration in the presence and absence of metabolic activation following 4 and 24 hours treatment.

- Other confounding effects: None

RANGE-FINDING/SCREENING STUDIES:
According to the current OECD Guideline for Cell Gene Mutation Tests at least four ana-lysable concentrations should be used in two parallel cultures. For freely-soluble and non-cytotoxic test items the maximum concentration should be 5 mg/mL, 5 µL/mL or 10 mM, whichever is the lowest. For cytotoxic test items the maximum concentration should result in approximately 10 to 20 % relative survival or cell density at subcultivation and the ana-lysed concentrations should cover a range from the maximum to little or no cytotoxicity. Relatively insoluble test items should be tested up to the highest concentration that can be formulated in an appropriate solvent as solution or homogenous suspension. These test items should be tested up or beyond their limit of solubility. Precipitation should be evalu-ated at the end of treatment by the unaided eye.

In the range finding pre-experiment test item concentrations between 39.1 and 5000 µg/mL according to OECD guideline were used to evaluate toxicity in the presence (4 hours treatment) and absence (4 hours and 24 hours treatment) of metabolic activation.
Relevant cytotoxic effects indicated by a relative suspension growth below 50% were noted at 2500 µg/mL and above without metabolic activation following 4 hours treatment.

The test medium was checked for precipitation or phase separation at the end of each treatment period prior to removal of the test item. No precipitation occurred up to the maximum concentration in the presence and absence of metabolic activation following 4 and 24 hours treatment.
In the pre-experiment the pH at concentrations of 156.3 µg/mL and above was adjusted to neutral with 2 N sodium hydroxide. In the main experiments the pH at concentrations of 312.5 µg/mL and above was adjusted as described above.
Based on the results of the pre-experiment, the maximum concentration of the main ex-periments was again 5000 µg/mL. The individual concentrations were spaced by a factor of 2.

In both main experiments the cultures at the lowest concentration in the presence and absence of metabolic activation were not continued since a minimum of only four analys-able concentrations is required by the guidelines.


COMPARISON WITH HISTORICAL CONTROL DATA: Complies


ADDITIONAL INFORMATION ON CYTOTOXICITY:
Main experiments:
No relevant cytotoxic effects occurred up to the maximum concentration with and without metabolic activation following 4 and 24 hours treatment.

Remarks on result:

other: all strains/cell types tested

Remarks:

Migrated from field 'Test system'.

Summary Table

			relative	relative	relative	mutant		relative	relative	relative	mutant
	conc.	S9	cloning	cell	cloning	colonies/	induction	cloning	cell	cloning	colonies/	induction
	µg/mL	mix	efficiency I	density	efficiency II	10^6cells	factor	efficiency I	density	efficiency II	10^6cells	factor
			%	%	%			%	%	%
Column	1	2	3	4	5	6	7	8	9	10	11	12
Experiment I / 4 h treatment			culture I					culture II
Solvent control with water		-	100.0	100.0	100.0	21.7	1.0	100.0	100.0	100.0	18.2	1.0
Positive control (EMS)	150.0	-	102.2	76.5	96.9	138.6	6.4	96.3	91.0	95.7	148.6	8.2
Test item	156.3	-	104.0	culture was not continued^#				101.6	culture was not continued^#
Test item	312.5	-	101.9	88.6	87.8	15.2	0.7	86.4	113.9	106.9	13.9	0.8
Test item	625.0	-	106.8	79.5	100.2	19.6	0.9	103.2	86.8	99.3	16.2	0.9
Test item	1250.0	-	103.5	69.9	97.5	12.0	0.6	101.8	86.4	100.0	13.1	0.7
Test item	2500.0	-	98.9	85.0	100.8	23.6	1.1	100.6	92.1	96.6	43.3	2.4
Test item	5000.0	-	97.3	81.4	91.2	18.4	0.8	103.5	79.8	99.8	18.3	1.0
Experiment I / 4 h treatment			culture I					culture II
Solvent control with water		+	100.0	100.0	100.0	12.3	1.0	100.0	100.0	100.0	20.3	1.0
Positive control (DMBA)	1.1	+	34.8	252.7	94.4	862.0	70.2	38.2	57.6	84.5	1147.2	56.4
Test item	156.3	+	101.9	culture was not continued^#				95.9	culture was not continued^#
Test item	312.5	+	100.8	86.4	108.9	18.5	1.5	92.2	154.9	111.3	26.4	1.3
Test item	625.0	+	102.3	127.7	123.2	18.6	1.5	97.3	79.3	124.2	12.8	0.6
Test item	1250.0	+	97.2	162.8	110.8	11.6	0.9	92.6	233.4	95.3	24.6	1.2
Test item	2500.0	+	99.8	86.5	108.5	44.0	3.6	93.9	109.5	102.3	30.3	1.5
Test item	5000.0	+	100.5	153.2	108.4	18.3	1.5	90.2	88.4	89.8	27.0	1.3
Experiment II / 24 h treatment			culture I					culture II
Solvent control with water		-	100.0	100.0	100.0	10.8	1.0	100.0	100.0	100.0	15.8	1.0
Positive control (EMS)	150.0	-	103.3	159.8	69.4	385.4	35.5	108.4	105.0	90.3	280.5	17.8
Test item	156.3	-	101.9	culture was not continued^#				98.5	culture was not continued^#
Test item	312.5	-	102.0	157.7	69.7	21.7	2.0	103.2	148.2	99.8	12.7	0.8
Test item	625.0	-	105.1	158.4	85.8	19.5	1.8	99.7	131.6	100.9	17.1	1.1
Test item	1250.0	-	105.3	171.1	84.9	24.1	2.2	96.8	102.0	92.3	16.1	1.0
Test item	2500.0	-	107.3	143.8	82.6	17.3	1.6	97.4	133.4	93.6	23.6	1.5
Test item	5000.0	-	105.9	134.9	72.6	16.2	1.5	74.0	90.5	86.2	14.5	0.9
Experiment II / 4 h treatment
Solvent control with water		+	100.0	100.0	100.0	17.0	1.0	100.0	100.0	100.0	16.6	1.0
Positive control (DMBA)	1.1	+	94.8	83.1	66.3	771.1	45.4	65.6	63.2	77.1	789.9	47.4
Test item	156.3	+	102.4	culture was not continued^#				101.4	culture was not continued^#
Test item	312.5	+	105.2	110.6	95.8	25.3	1.5	99.9	92.2	83.2	40.4	2.4
Test item	625.0	+	113.4	101.1	97.1	9.4	0.6	102.4	92.2	81.3	12.5	0.8
Test item	1250.0	+	113.1	92.8	75.9	24.2	1.4	101.1	85.9	100.9	19.7	1.2
Test item	2500.0	+	104.0	124.7	56.1	18.2	1.1	89.4	82.6	94.7	12.5	0.8
Test item	5000.0	+	113.1	105.6	66.5	26.6	1.6	97.5	81.4	90.7	21.9	1.3

^#   culture was not continued since a minimum of only four analysable concentrations is required

Conclusions:

Interpretation of results (migrated information):
negative with metabolic activation
negative without metabolic activation

In conclusion it can be stated that under the experimental conditions reported the test item did not induce gene mutations at the HPRT locus in V79 cells. Therefore, Hordaphos CC MS is considered to be non-mutagenic in this HPRT assay.

Executive summary:

The test item Hordaphos CC MS was assessed for its potential to induce gene mutations at the HPRT locus using V79 cells of the Chinese hamster.

The study was performed in two independent experiments, using identical experimental procedures. In the first experiment the treatment period was 4 hours with and without metabolic activation. The second experiment was performed with a treatment time of 4 hours with and 24 hours without metabolic activation.

The cell cultures were evaluated at the following concentrations:

exposure period	S9 mix	concentrations in µg/mL
		Experiment I
4 hours	-	312.5	625.0	1250	2500	5000
4 hours	+	312.5	625.0	1250	2500	5000
		Experiment II
24 hours	-	312.5	625.0	1250	2500	5000
4 hours	+	312.5	625.0	1250	2500	5000

 

No relevant cytotoxic effects occurred up to the maximum concentration with and without metabolic activation following 4 and 24 hours treatment.

No relevant and reproducible increase in mutant colony numbers/10⁶cells was observed in the main experiments up to the maximum concentration.

In the first culture of experiment I the induction factor exceeded the threshold of three times the mutation frequency of the corresponding solvent control at 2500 µg/mL in the presence of metabolic activation. The historical range of solvent controls was also exceeded at this experimental point (44.0 versus 36.6 mutant colonies per 10⁶cells, see Historical Data, Annex II). However, the effect was not reproduced in the parallel culture under identical experimental conditions, and was therefore, judged as biologically irrelevant.

In the second culture of the second experiment the historical range of solvent controls was also exceeded at 312.5 µg/mL with metabolic activation (40.4 versus 36.6 mutant colonies per 10⁶cells).The increase was not dose dependent and was again not reproduced in the parallel culture under indentical experimental conditions and was therefore, judged as biologically irrelevant.

A linear regression analysis (least squares) was performed to assess a possible dose dependent increase of mutant frequencies.No significant dose dependent trend of the mutation frequency indicated by a probability value of <0.05 was determined in any of the experimental groups.

In both experiments of this study (with and without S9 mix) the range of the solvent controls was from 10.8 up to 21.7 mutants per 10⁶cells; the range of the groups treated with the test item was from 9.4 up to 44.0 mutant colonies per 10⁶cells.

EMS(150 µg/mL) and DMBA (1.1 µg/mL) were used as positive controls and showed a distinct increase in induced mutant colonies.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

Additional information from genetic toxicity in vitro:

The reaction mass of Methyl dihydrogen phosphate and Orthophosphoric acid and Dimethyl hydrogen phosphateshowed negative results in the study for the induction of gene mutations (bacterial reverse mutation assay) by frameshift or base-pair substitutions with and without metabolic activation. The study was performed with the test strainsS. typhimuriumTA 98, TA 100, TA 1535, TA 1537 andE. coliWP2 uvr A. Test concentrations up to the limit concentration of 5000 µg/plate were tested in the experiment. The test compound proved to be not mutagenic to the bacterial strains.

The reaction mass of Methyl dihydrogen phosphate and Orthophosphoric acid and Dimethyl hydrogen phosphatealso yielded negative results in anin vitrogene mutation study in mammalian cells in concentration up to 5000 µg/ml.

The reaction mass of Methyl dihydrogen phosphate and Orthophosphoric acid and Dimethyl hydrogen phosphatewas assessed for its potential to induce chromosome aberrations in Chinese hamster cells (V79) and human lymphocytesin vitro.Negative results were obtained in the absence of metabolic activation. A slight increase in chromosome aberrations in Chinese hamster V79 cells was observed in the presence of the S9 mix. However, of reaction mass of Methyl dihydrogen phosphate and Orthophosphoric acid and Dimethyl hydrogen phosphatedid not induce chromosome aberrations up to 5000 µg/mL in the absence and presence of metabolic activation in anin vitroChromosome Aberration test performed in human lymphocytes which is considered to be the most relevant cell system for it contains the relevant human metabolic enzyme set (e.g. V79 are not p53 competent).

Justification for selection of genetic toxicity endpoint
This study is selected as key study representing the toxicological endpoint "Genetic toxicity" since it was performed using mammalian cells and examines the most sensitive genotoxic mechanism. The study was performed according to the current OECD Guideline 476 and GLP.

Justification for classification or non-classification

In conclusion, the reaction mass of Methyl dihydrogen phosphate and Orthophosphoric acid and Dimethyl hydrogen phosphate is not mutagenic in the bacterial reverse mutation assay, the in vitro gene mutation study in Chinese V79 cells and the in vitro chromosome aberration in human lymphocytes in the presence and absence of metabolic activation up to the tested concentrations.

The reaction mass of Methyl dihydrogen phosphate and Orthophosphoric acid and Dimethyl hydrogen phosphate does not have to be not classified for mutagenicity since this substance did not reveal any mutagenic effect in the bacterial reverse mutation assay in the presence or absence of metabolic activation in concentrations up to 5000 µg/plate, in the in vitro gene mutation assay (up to 5000 µg/mL) or in the in vitro chromosome aberration study in human lymphocytes in concentrations up to 5000 µg/mL.