Guanidinium nitrate

Toxicity to soil microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods

Qualifier:

equivalent or similar to guideline

Guideline:

other: No guideline reported.

Principles of method if other than guideline:

Degradation of C-14 guanidinium chloride in field soil samples was followed by trapping and counting of radioactivity (14-CO2). Test were made with sterile soil (no degradation), different concentrations of test substance, different additions carbon source (cellulose, glucose) and nitrogen.

GLP compliance:

not specified

Analytical monitoring:

no

Test organisms (inoculum):

soil

Total exposure duration:

24 h

Test temperature:

20 °C

Moisture:

60%

Reference substance (positive control):

yes

Remarks:

Guanidinium chloride

Key result

Duration:

24 h

Dose descriptor:

other: EC6

Effect conc.:

ca. 100 mg/kg soil ww

Conc. based on:

test mat.

Basis for effect:

other: Reduction of mineralization of Guanidinium Carbon

Shown in Table are the effects of two carbon sources and three major nitrogenous components in nitroguanidine wastestreams on guanidinium carbon mineralization. Both glucose and to a much lesser extent its natural polymer cellulose enhanced 24 hour mineralization rates: production of radiolabeled carbon dioxide was nearly four times the unamended control in the presence of glucose and was increased by twenty percent in the presence of cellulose.

The wastewater components nitroguanidine, ammonium, and nitrate showed only a slight tendency to inhibit guanidinium mineralization whether alone at equimolar concentrations to guanidinium or in concert. Previous results have demonstrated that environmental microorganisms in surface water can mineralize guanidinium carbon slowly as a sole substrate and more rapidly in the presence of metabolizable carbon (Mitchell, 1987). While the relative contribution of such populations to the mineralization of the cation in soil can not be assessed in the present study, results with the added carbon sources suggest that the latter process can also be stimulated in soil.

Table Effects of Carbon and Nitrogen Compounds on the Mineralization of Guanidinium Carbon in Duffield Soil

Sample                            nM Mineralized/24Hours (1xsigma)       %Control (1xsigma)

Control(i)                            634 (4)                                                        100 (<1)

Carbon added as(ii):

Cellulose                            776 (26)                                                        122.4 (4)

Glucose                            2481 (273)                                                      391.4 (43)

Nitrogen added as (ii):

Ammonium                         579 (47)                                                         91.3 (7)

Nitrate                                596 (8)                                                           94 (1.3)

Nitroguanidine                     542 (22)                                                        85.5 (3.5)

Composite                           578 (44)                                                        91.7 (7)

i. Triplicate flasks each contained 1 µCi and 20.9 µM guanidinium at a concentration of 100 mg/Kg soil.

ii. Carbon and nitrogen compounds were 4% (w/w) and 20.9 µM respectively.

Validity criteria fulfilled:

not applicable

Conclusions:

At a concentration of 96 mg nitrate /Kg soil ww (196 mg Guanidinium nitrate) / Kg soil ww, the mineralization rate of guanidinium carbon was 94% of the rate in absence of nitrate.
(596 nM mineralized/24hours compared to 634nM mineralized/24hours.) Nitrate showed only a slight tendency to inhibit guanidinium mineralization.

Executive summary:

The ability of soil microorganism to mineralize guanidine carbon was tested with radiolabelled guanidinium. At a concentration of 96 mg nitrate /Kg soil ww (196 mg Guanidinium nitrate / Kg soil ww), the mineralization rate of guanidinium carbon was 94% of the rate in absence of nitrate. (596 nM mineralized/24hours compared to 634nM mineralized/24hours.)

Nitrate showed only a slight tendency to inhibit guanidinium mineralization.

Reference 2

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

Supporting information for read-across, structural analogue approach.

Principles of method if other than guideline:

Degradation of C-14 guanidinium chloride in field soil samples was followed by trapping and counting of radioactivity (14-CO2). Test were made with sterile soil (no degradation), different concentrations of test substance, different additions carbon source (cellulose, glucose) and nitrogen.

GLP compliance:

not specified

Analytical monitoring:

yes

Details on sampling:

1 x per day

Test organisms (inoculum):

soil

Total exposure duration:

23 d

Test temperature:

20 °C

Moisture:

60% soil mosture holding capacity

Details on test conditions:

The mineralization of guanidinium carbon was measured in the incubation and trapping system described by Marrinucci and Bartha (1979). Triplicate test flasks received 1 microCi carbon-14 guanidine chloride (Amersham, 22 mCi/mMole), sufficient distilled water to achieve 60% soil moisture holding capacity, and the equivalent of 20 g dry weight soil. Chemical additions including unlabeled guanidine chloride and the inhibitors mercuric chloride and sodium azide were made in conjunction with the moisture ad- justment. The organic carbon sources, cellulose and glucose, were added as sterile dry solids (4% by weight) and were mixed to homogeneity with a sterile glass rod.

Reference substance (positive control):

yes

Remarks:

Guanidinium chloride

Duration:

23 d

Dose descriptor:

NOEC

Effect conc.:

400 mg/kg soil ww

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

Guanidinium ion

Basis for effect:

other: Reduction of mineralization of Guanidinium Carbon

Duration:

23 d

Dose descriptor:

NOEC

Effect conc.:

636

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

Guanidine chloride

Basis for effect:

other: Reduction of mineralization of Guanidinium Carbon

Details on results:

Mineralization rates showed no tendency to decrease at any concetnration ( tested: 10, 25, 50, 100, 200, 400 mg/kg) until most of the Guanidinium was degraded.

Shown in Table are the effects of two carbon sources and three major nitrogenous components in nitroguanidine wastestreams on guanidinium carbon mineralization. Both glucose and to a much lesser extent its natural polymer cellulose enhanced 24 hour mineralization rates: production of radiolabeled carbon dioxide was nearly four times the unamended control in the presence of glucose and was increased by twenty percent in the presence of cellulose.

The wastewater components nitroguanidine, ammonium, and nitrate showed only a slight tendency to inhibit guanidinium mineralization whether alone at equimolar concentrations to guanidinium or in concert. Previous results have demonstrated that environmental microorganisms in surface water can mineralize guanidinium carbon slowly as a sole substrate and more rapidly in the presence of metabolizable carbon (Mitchell, 1987). While the relative contribution of such populations to the mineralization of the cation in soil can not be assessed in the present study, results with the added carbon sources suggest that the latter process can also be stimulated in soil.

Table Effects of Carbon and Nitrogen Compounds on the Mineralization of Guanidinium Carbon in Duffield Soil

Sample                            nM Mineralized/24Hours (1xsigma)       %Control (1xsigma)

Control(i)                            634 (4)                                                        100 (<1)

Carbon added as(ii):

Cellulose                            776 (26)                                                        122.4 (4)

Glucose                            2481 (273)                                                      391.4 (43)

Nitrogen added as (ii):

Ammonium                         579 (47)                                                         91.3 (7)

Nitrate                                596 (8)                                                           94 (1.3)

Nitroguanidine                     542 (22)                                                        85.5 (3.5)

Composite                           578 (44)                                                        91.7 (7)

i. Triplicate flasks each contained 1 µCi and 20.9 µM guanidinium at a concentration of 100 mg/Kg soil.

ii. Carbon and nitrogen compounds were 4% (w/w) and 20.9 µM respectively.

Validity criteria fulfilled:

not applicable

Conclusions:

For loading rates of 10 - 400 mg Guanidine /kg soil ww (15.9 - 636 mg Guanidine chloride /kg soil ww) mineralisation rates of Guanidine carbon to Carbon dioxide showed not tendency to decrease at any concentration.

Executive summary:

In a non guideline test with natural soil microorganism, degradation rates for mineralisation of 14C radiolabeled guanidine carbon were determined. Quantification was made by determination of trapped 14C labelled carbon dioxide. For loading rates of 10 - 400 mg Guanidine /kg soil ww (15.9 - 636 mg Guanidine chloride /kg soil ww) mineralisation rates of Guanidine carbon to Carbon dioxide showed not tendency to decrease at any concentration.

Description of key information

At a concentration of 96 mg nitrate /Kg soil ww (196 mg Guanidinium nitrate / Kg soil ww),

the mineralization rate of guanidinium carbon was 94% of the rate in absence of nitrate.

Key value for chemical safety assessment

Short-term EC50 for soil microorganisms:

826.68 mg/kg soil dw

Additional information

The ability of soil microorganism to mineralize guanidine carbon was tested with radiolabelled guanidinium. At a concentration of 96 mg nitrate /Kg soil ww (196 mg Guanidinium nitrate / Kg soil ww), the mineralization rate of guanidinium carbon was 94% of the rate in absence of nitrate. (596 nM mineralized/24hours compared to 634nM mineralized/24hours.)

Nitrate showed only a slight tendency to inhibit guanidinium mineralization.

In a non guideline test with natural soil microorganism, degradation rates for mineralisation of 14C radiolabeled guanidine carbon were determined. Quantification was made by determination of trapped 14C labelled carbon dioxide. For loading rates of 10 - 400 mg Guanidine /kg soil ww (15.9 - 636 mg Guanidine chloride /kg soil ww) mineralisation rates of Guanidine carbon to Carbon dioxide showed not tendency to decrease at any concentration.

Recalculated for guanidine nitrate the values are 20.67 - 826.68 mg Guanidine nitrate /kg soil ww

(Remark: key value for chemical safety assesment NOEC 826.68 mg/kg is wet weight; pick list doesn't allow to choose ww but dw)

Justification for read-across:

Guanidine hydrochloride and guanidine nitrate dissociate in aqueous media to yield the guanidine ion and the respective anion. Therefore it is reasonable to discuss the effects of the ions separately. The chloride ion is a naturally occurring essential ion in human beings with well-known metabolism and mechanisms of action as described in standard textbooks on pharmacology and physiology. As well it is found as salt in the Earth´s crust and is dissolved in seawater. The nitrate ion occures in waste waters and natural waters with other sources as guanidine nitrate (for example fertilisers). Nitrate is a nitrogen source for algae and microorganisms. It is metabilised and incorporated by organisms or reduced to nitrogen.

Effects of guanidine hydrochloride are expected to be based primarily on the guanidine ion. The physiological processing of the guanidine ion is expected to be independent of the individual source. Therefore read-across from guanidine hydrochloride for effects of guanidine dissociated from guanidine nitrate is considered valid. This strategy is supported by a quite similar toxicological profile of both substances, as shown in acute toxicity, irritation, sensitization and genotoxic studies.

A more detailed justification is attached and outlined in CSR chapter 1.1.2 as well.