Hydrazine

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Data waiving:

study technically not feasible

Justification for data waiving:

other:

Description of key information

In the absence of any reliable data to describe the adsorption/ desorption behaviour of hydrazine, a new study would become necessary. But in accordance with Section 2 of REACh annex XI, a test on adsorption/ desorption cannot be conducted as it is technically not possible. Furhtermore, no reliable QSAR models exist to estimate the Koc values for ionizable inorganic compounds. 

Additional information

The adsorption/desorption behaviour of an ionisable substance can be determined by the means of the HPLC method (OECD Guideline No 121) as well as the batch equilibrium method (OECD Guideline No 106). The performance of the HPLC method (OECD Guideline No 121) is technical not feasible since hydrazine cannot be detected directly by common detectors. The detection requires the derivatisation of hydrazine causing a change in substance properties and thus its retention behaviour. Determined Koc values thus reflect the distribution behaviour of the derivatised hydrazine compound rather than the pure hydrazine itself. The distribution behaviour of a substance between an aqueous and a soil phase, as determined by the means of the batch equilibrium method (OECD Guideline No 106), is measured either indirectly based on the concentration in the aqueous phase (mass balance) or directly by the fraction bound on soil. Hydrazine is known to rapidly degrade in the aqueous phase especially in the presence of colloids, organic matter and metal ions hampering the distinction between the fraction (irreversibly) sorbed on soil and degraded, respectively. Results based solely on aqueous concentrations are not representative implying a high sorption potential of the substance although the majority might already be degraded. The fraction directly bound to the soil or sediment would be more representative, but there are no methods to reliably extract hydrazine from soil without introducing further uncertainty. Concluding, experimental determined Koc values following the OECD Guideline No 121 or No 106 would not adequately reflect the adsorption/desorption behaviour of hydrazine. Furthermore, calculated Koc values could be derived based on several available structure-activity relationships. As hydrazine is inorganic and ionisable dissociating at environmental relevant pH values, common models are not suitable to estimate the Koc value based on physico-chemical properties of the test item (for example logPow, water solubility).

Nevertheless, there are several studies available (Moliner & Street (1989b), Hayes et al. (1984) and Heck et al. (1963)) dealing with the behaviour of hydrazine in the presence of soil. Assessed individually, they all have several drawbacks hampering the determination of a partition coefficient as the documentation is insufficient. But summarizing the information, hydrazine might sorb or degrade when present in soil depending on the prevailing conditions. At low pH values, sorption mainly occurs, whereas at higher pHs, degradation is supported. Additionally, the soil composition might contribute to hydrazine degradation. No definite value for sorption on soil can be determined as a multitude of factors determine the behaviour of hydrazine in that environmental compartment.