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Environmental fate & pathways

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In accordance with REACH Annex XI, the "Hydrolysis as a function of pH" does not need to be conducted as the test is scientifically unjustified respective technically not feasable. The guanidine ion is expected to have such a long hydrolysis half-life at environmentally relevant pH that the measurement is not feasable. This is concluded from abiotic biodegradation control with river water (Mitchel, Chemosphere, 1987).



Due to the low vapour pressure the substance under investigation will not be present in the gas phase in the atmosphere in appreciable amounts and therefore the elimination path photodegradation in air will be only of minor importance.


Guanidine chloride is inherently biodegradable. This was shown in a non guideline, read-across study with Guanidine nitrate (Mitchell 1987). Test conditions especially test substance concentration and bacteria concentration are comparable to guideline OECD301, inoculum is expected to be adapted.

Guanidine chloride is also biodegradable under less favourable conditions as was demonstrated in degradation tests with 14-C Guanidine in river water and aerated soil (Mitchell, Chemosphere (1987), Mitchel, Bull. Environ. Contam. Toxicol. (1987)).

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.

The river water die away test showed that 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 14-C guanidinium 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.

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

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.



In accordance with column 2 of REACH Annex IX, the study on bioaccumulation (required in section 9.3.2) does not need to be conducted as the substance has a low potential for bioaccumulation (measured log Kow < -1.7).

Transport and distribution:

In accordance with REACH Annex IX, the study on "Further information on adsorption/desorption" (required in section 9.3.3) does not need to be conducted as the substance has a low potential for bioaccumulation (measured log Kow < -1.7).

Additional information