Guanidinium chloride

Biodegradation in soil

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in soil, other

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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

Reason / purpose for cross-reference:

reference to other study

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

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

other: field soil samples

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: local soil samples: Duffield silt loam pH6.4-7.1 (soil no.: #1)
Hagerstown silt loam, pH7.1 (soil no. #2)
Collington loamy fine sand, pH6.3 (soil no. #3)
- Sampling depth (cm): 2.54-10.16cm (=1-4 inches)
- Soil preparation (e.g., 2 mm sieved; air dried etc.): maintained as described by Pramer and Bartha( 1972), pased through a 2mm screen prior to use

Soil No.:

#1

Initial conc.:

0.22 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#1

Initial conc.:

10 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#1

Initial conc.:

25 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#1

Initial conc.:

50 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#1

Initial conc.:

100 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#1

Initial conc.:

200 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#1

Initial conc.:

400 mg/kg soil d.w.

Based on:

test mat.

Key result

Soil No.:

#1

% Degr.:

> 40

Parameter:

radiochem. meas.

Sampling time:

1 d

Key result

Soil No.:

#1

% Degr.:

80

Parameter:

radiochem. meas.

Sampling time:

4 d

Key result

Soil No.:

#2

% Degr.:

> 40

Parameter:

radiochem. meas.

Sampling time:

1 d

Key result

Soil No.:

#2

% Degr.:

80

Parameter:

radiochem. meas.

Sampling time:

4 d

Key result

Soil No.:

#3

% Degr.:

> 50

Parameter:

radiochem. meas.

Sampling time:

8 d

Key result

Soil No.:

#4

DT50:

17 d

Type:

not specified

Remarks on result:

other: 400 mg Guanidinium/kg dw

Key result

Soil No.:

#5

DT50:

12 d

Type:

not specified

Remarks on result:

other: 200 mg Guanidinium/kg dw

Key result

Soil No.:

#6

DT50:

8 d

Type:

not specified

Remarks on result:

other: 100mg Guanidinium /kg dw

Key result

Soil No.:

#7

DT50:

6 d

Type:

not specified

Remarks on result:

other: 50 mg Guanidinium/kg dw

Key result

Soil No.:

#8

DT50:

5 d

Type:

not specified

Remarks on result:

other: 25 mg Guanidinium /kg dw

Key result

Soil No.:

#9

DT50:

2.5 d

Type:

not specified

Remarks on result:

other: 10 mg Guanidinium/kg dw

Transformation products:

yes

Mineralization of Guanidinium Carbon at several concentrations in Duffield Soil:

Guanidiniume concentration (mg/kg soil)	Half life (days)^1	final percentage of guanidinium carbon mineralized (%)
10	2.5	78
25	5	78
50	6	77
100	8	76
200	12	78
400	17	62

 ¹numbers graphically determined from figure in publication

Effects of Carbon and nitrogen compounds on the mineralization of Guanidiunium Carbon in Duffied Soil:

Sample	nM mineralized/24h (1s)	% control (1s)
control^1	634 (4)	100 (<1)
carbon added as:^2
Cellulose	776 (26)	122.4 (4)
Glucose	2481 (273)	391.4 (43)
Nitrogen added as:^2
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)

¹Triplicate flasks each contained 1microCi and 20.9 microM guanidinium at a concentration  

 of 100mg/kg soil

²Carbon and nitrogen compounds were 4% (w/w) and 20.9microM respectively

Conclusions:

14-C Guanidinium in aerated soil is biodegraded with a half live of 2.5 - 8 days for guanidine concentrations of 2.5 – 100 mg/kg dw. The degradation rate is dependent on the concentration of guanidinium with a lower degradation rate at high concentrations, on the type of soil used and on the availability of carbon sources (Glucose or Cellulose) which enhance mineralization rate. Nitrogen in form of Ammonium, Nitrate, Nitroguanidine only slightly inhibit guanidinium mineralization.

Executive summary:

The biotransformation of radiolabelled Guanidinium (as chloride) was studied in soil(s) Duffied silt loam (pH 6.4 to 7.1), from Maryland, USA in different experiments.

Experiment 1 incubation for 4 d under aerobic conditions at 20 ºC, and 60 % moisture. Guanidinium was applied at the rate of 0.22 mg a.i./kg soil.  Samples were analysed at 0, 1,2, 3 and 4 days of incubation. 
The concentration of the parent compound decreased from 100 % of the applied amount at day 0, to 20 % at the end of study period.  More than 40% of the guanidinium carbon was mineralized by the first day of incubation to soil, after which time mineralization continued at a decreasing rate until 80% of Guanidinium was converted to carbon dioxide after 4 days.  The major transformation products detected was carbon dioxide.

Experiment 2 incubation of 10 –400 mg 14-C-guanidinium /kg soil dw for up to 25 days.

The degradation rate is dependent on the concentration of guanidinium with a lower degradation rate at high concentrations, on the type of soil used and on the availability of carbon sources (Glucose or Cellulose) which enhance mineralization rate. Nitrogen in form of Ammonium, Nitrate, Nitroguanidine only slightly inhibit guanidinium mineralization.

Description of key information

Guanidine was rapidly and extensively mineralized in soil with a half-live of 2.5-8 days for guanidine concentrations of 2.5-100mg/kg soil.

Key value for chemical safety assessment

Half-life in soil:

8 d

at the temperature of:

25 °C

Additional information

14-C Guanidinium in aerated soil is biodegraded with a half live of 2.5 - 8 days for guanidine concentrations of 2.5 – 100 mg/kg dw. The degradation rate is dependent on the concentration of guanidinium with a lower degradation rate at high concentrations, on the type of soil used and on the availability of carbon sources (Glucose or Cellulose) which enhance mineralization rate. Nitrogen in form of Ammonium, Nitrate, Nitroguanidine only slightly inhibit guanidinium mineralization. Also other studies of Praveen-Kumar and Brumme (1999) and Williams et al (1989) supports the conclusion that Guanidine Nitrate was rapidly and extensively mineralized in soil although the values differ depending on the soil and method used and there are some different findings concerning the dependence of mineralization on availability of carbon source.

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. 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 nitrate for effects of guanidine dissociated from guanidine hydrochloride 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 for read-across is attached in IUCLID chapter 13.