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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
comparable to guideline study
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test)
Deviations:
yes
Remarks:
guideline not cited, no in depth reporting, results comparable to guideline test
Principles of method if other than guideline:
Surface water samples were incubated with 5 different guanidinium concentrations (added as 64% guanidinium chloride) and 1µCi carbon-14 guanidinium. Percentaged of guanidinium carbon converted to carbon dioxide were determined from levels of trapped radioactivity in each sample during up to 90 days.
GLP compliance:
not specified
Radiolabelling:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
natural water
Details on source and properties of surface water:
surface water samples obtained from two streams in the vicinity of a nitroguanidine pilot production facility (Hansen and Kill Creek) and several stream (Carroll Creek) and river (Monocacy) sites in the vicinity of Frederick, USA
Duration of test (contact time):
< 90 d
Initial conc.:
0.001 mg/L
Based on:
other: Guanidinium
Initial conc.:
0.01 mg/L
Based on:
other: Guanidinium
Initial conc.:
0.1 mg/L
Based on:
other: Guanidiniumø
Initial conc.:
1 mg/L
Based on:
other: Guanidiniumø
Initial conc.:
10 mg/L
Based on:
other: Guanidiniumø
Parameter followed for biodegradation estimation:
radiochem. meas.
Details on study design:
TEST CONDITIONS
- Volume of test solution/treatment: 250ml water
- Composition of medium: 0.2% potassium phosphate, pH7
- Additional substrate: 17mg/L arginine
- Test temperature: 25°C
- Aeration of dilution water: agitation
- Suspended solids concentration: 20mg/L guanidine nitrate
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: flask
- Method used to create aerobic conditions: agitation


CONTROL
- Abiotic sterile control: autoclaved water

Parent/product:
parent
Compartment:
water
Key result
% Degr.:
9.9
Parameter:
radiochem. meas.
Sampling time:
93 d
Remarks on result:
other: 0.0005 mg/l
Parent/product:
parent
Compartment:
water
Key result
% Degr.:
5.3
Parameter:
radiochem. meas.
Sampling time:
93 d
Remarks on result:
other: 0.01 mg/l
Parent/product:
parent
Compartment:
water
Key result
% Degr.:
77
Parameter:
radiochem. meas.
Sampling time:
93 d
Remarks on result:
other: 0.10 mg/l
Parent/product:
parent
Compartment:
water
Key result
% Degr.:
80
Parameter:
radiochem. meas.
Sampling time:
75 d
Remarks on result:
other: 1.0 mg/l
Parent/product:
parent
Compartment:
water
Key result
% Degr.:
85
Parameter:
radiochem. meas.
Sampling time:
75 d
Remarks on result:
other: 10 mg/l
Key result
Compartment:
water
DT50:
8 d
Remarks on result:
other: Winter Carroll Creek (west) after 52 d lag
Key result
Compartment:
water
DT50:
3 d
Remarks on result:
other: Winter Carroll Creek (central) after 28 d lag
Key result
Compartment:
water
DT50:
3 d
Remarks on result:
other: Winter Monocacy (north) after 22 d lag
Key result
Compartment:
water
DT50:
4 d
Remarks on result:
other: Winter Monocacy (south) after 20 d lag
Key result
Compartment:
water
DT50:
7.5 d
Remarks on result:
other: Summer Carroll Creek (central) after 50 d lag
Key result
Compartment:
water
DT50:
3 d
Remarks on result:
other: Summer Monocacy River (south) after 40 d lag
Key result
Compartment:
water
DT50:
4.5 d
Remarks on result:
other: Winter Hansen Creek after 11 d lag
Key result
Compartment:
water
DT50:
5 d
Remarks on result:
other: Winter Kill Creek after 16 d lag
Transformation products:
yes
No.:
#1
Evaporation of parent compound:
no
Validity criteria fulfilled:
not applicable
Conclusions:
Guanidine chloride is shown to be biodegraded in environmental water.
Executive summary:

Guanidine chloride is shown to be biodegraded in environmental water.

For Guanidine chloride, levels of carbon dioxide production after 1 and 10 days were less than 1 and 5% respectively for all of the concentrations tested and did not exceed their initial rates during that period. At the three highest concentrations (0.1 - 10 mg Guanidinium/l), inflections in carbon dioxide production occurred with continued incubation such that by the end of the experiment 85, 80, and 77% respectively of the guanidinium carbon was converted to carbon dioxide. Similar extensive mineralization did not occur at or below 0.01 mg/L and developed more slowly at 0.1 mg/L than at the two higher concentrations. Mineralization patterns for guanidinium carbon were reproducible in surface water from a second site (Carroll Creek), Thus, the development of the microbial populations capable of enhanced guanidinium mineralization is related to the concentration of the cation. At higher concentrations, a biodegrading population could well develop that would ultimately effect the persistence of the cation. However, both from direct observations in surface water samples (other experiments in the publication) and from the evaluation of an enriched laboratory population, the development of such a population as well as its degradation of guanidinium would likely be slow.

Degradation tests with 8 river water samples from different locations showed a mean degradation half life for guanidine of 5.25 d at 25°C after a mean lag phase of 30 d.

Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Read-across from a GLP guideline study with Reliability 1 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. A detailed justification is outlined in IUCLID chapter 13.2 "Justification for read-across".
Reason / purpose for cross-reference:
read-across source
GLP compliance:
not specified
Duration of test (contact time):
< 90 d
Key result
% Degr.:
9.9
Parameter:
radiochem. meas.
Sampling time:
93 d
Remarks on result:
other: 0.0005 mg/l
Key result
% Degr.:
5.3
Parameter:
radiochem. meas.
Sampling time:
93 d
Remarks on result:
other: 0.01 mg/l
Key result
% Degr.:
77
Parameter:
radiochem. meas.
Sampling time:
93 d
Remarks on result:
other: 0.10 mg/l
Key result
% Degr.:
80
Parameter:
radiochem. meas.
Sampling time:
75 d
Remarks on result:
other: 1.0 mg/l
Key result
% Degr.:
85
Parameter:
radiochem. meas.
Sampling time:
75 d
Remarks on result:
other: 10 mg/l
Key result
Compartment:
water
DT50:
8 d
Remarks on result:
other: Winter Carroll Creek (west) after 52 d lag
Key result
Compartment:
water
DT50:
3 d
Remarks on result:
other: Winter Carroll Cree (central) after 28 d lag
Key result
Compartment:
water
DT50:
3 d
Remarks on result:
other: Winter Monocacy (north) after 22 d lag
Key result
Compartment:
water
DT50:
4 d
Remarks on result:
other: Winter Monocacy (south) after 20 d lag
Key result
Compartment:
water
DT50:
7.5 d
Remarks on result:
other: Summer Carroll Creek (central) after 50 d lag
Key result
Compartment:
water
DT50:
3 d
Remarks on result:
other: Summer Monocacy River (south) after 40 d lag
Key result
Compartment:
water
DT50:
4.5 d
Remarks on result:
other: Winter Hansen Creek after 11 d lag
Key result
Compartment:
water
DT50:
5 d
Remarks on result:
other: Winter Kill Creek after 16 d lag
Transformation products:
yes
No.:
#1
Evaporation of parent compound:
no

no remark

Validity criteria fulfilled:
not applicable
Conclusions:
Guanidine nitrate is expected to be biodegraded in environmental water.
Executive summary:

Levels of carbon dioxide production after 1 and 10 days were less than 1 and 5% respectively for all of the concentrations tested and did not exceed their initial rates during that period. At the three highest concentrations (0.1 - 10 mg Guanidinium/l), inflections in carbon dioxide production occurred with continued incubation such that by the end of the experiment 85, 80, and 77% respectively of the guanidinium carbon was converted to carbon dioxide. Similar extensive mineralization did not occur at or below 0.01 mg/L and developed more slowly at 0.1 mg/L than at the two higher concentrations. Mineralization patterns for guanidinium carbon were reproducible in surface water from a second site (Carroll Creek), Thus, the development of the microbial populations capable of enhanced guanidinium mineralization is related to the concentration of the cation. At higher concentrations, a biodegrading population could well develop that would ultimately effect the persistence of the cation. However, both from direct observations in surface water samples (other experiments in the publication) and from the evaluation of an enriched laboratory population, the development of such a population as well as its degradation of guanidinium would likely be slow.

Degradation tests with 8 river water samples from different locations showed a mean degradation half life for guanidine of 5.25 d at 25°C after a mean lag phase of 30 d.

Description of key information

Guanidine nitrate is expected to be biodegraded in environmental water.

Key value for chemical safety assessment

Half-life in freshwater:
5.25 d
at the temperature of:
25 °C

Additional information

The development of the microbial populations capable of enhanced guanidinium mineralization is related to the concentration of the cation. At the three highest concentrations (0.1 - 10 mg/l), a biodegrading population developed that ultimately effected the persistence of the cation. Mineralization occurred also at 3 guanidinium concentrations tested from 0.0005 - 0.01 mg/l but not with a similar extensive mineralization rate as at 0.1 - 10 mg/ Guanidinium /L and mineralization rate developed more slowly as at 0.1 mg/L.

Both from direct observations in surface water samples (other experiments in the publication) and from the evaluation of an enriched laboratory population, the development of such a population as well as its degradation of guanidinium would likely be slow.

Degradation tests with 8 river water samples from different locations showed a mean degradation half life for guanidine of 5.25 d at 25°C after a mean lag phase of 30 d.

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.