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Environmental fate & pathways

Hydrolysis

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Endpoint:
hydrolysis
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
Remarks:
specially designed to characterise the degradation behaviour of the substance in natural surface water.
Principles of method if other than guideline:
Surface water from a natural pond and the river Rhine were collected and immedatialy spiked with Hydrazine in the laboratory. The test vessels were stirred under aerobic conditions and a light regime. Hydrazine was measured photometrically at different time periods. Photometry, determination of Hydrazine according to DIN 38413-P1.
GLP compliance:
no
Remarks:
The experiment was specially designed to characterise the degradation behaviour of the substance in natural surface water.
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
Two sampling sites close to Leverkusen City (Germany) were selected to take the surface water samples needed for this study: a wet gravel pit, east of Leverkusen, immediately adjacent to the Autobahn A3, and the eastern bank of the Rhine river at Leverkusen-Hitdorf (north of Leverkusen City). Samples were taken from the river bank, or gravel pit bank, using a water sampler, and were subsequently transported to the laboratory without delay.

Buffers:
no buffers were used
Details on test conditions:
Culturing apparatus : Light chamber in which a temperature in the range 21°C to 24°C was maintained at +/- 2°C, and continuous uniform illumination was provided in the spectral range 400 to 700 nm. Temperature was measured and recorded daily in a water filled flask which was incubated under the same conditions as the test flasks.
Light intensity : At the average of the test solutions, a light intensity in the range 60 to 120 μE. x m-2 x s-1, or an equivalent range of 4000 to 8000 lx, was used.
Test item concentration : 39 μg/L hydrazine hydrate, equalling to 25 μg/L hydrazine
Method of administration : direct weighing
Duration of exposure : 48 hours
Duration:
48 h
pH:
7
Temp.:
20 °C
Initial conc. measured:
>= 24 - <= 27 µg/L
Statistical methods:
Calculation of the half lives and the rate constants using the equations for first order kinetics.
Transformation products:
not measured
pH:
8.2
Temp.:
20 °C
Hydrolysis rate constant:
0
DT50:
2.67 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Wet grevel pit (natural pond water)
pH:
8.1
Temp.:
20 °C
Hydrolysis rate constant:
0
DT50:
24 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: natural Rhine water

Degradation of Hydrazine

 time (h)  Hydrazine in Gravel pit (mg/L)  Hydrazine in Rhine water (mg/L
 0 0.024  0.027
 1.5  0.015  0.022
 3  0.01  0.0185
 6  <0.01  0.0155
 24  <0.01  0.012
 48  <0.01 <0.01 
Executive summary:

A study was performed to assess the stability, or dissipation respectively, of hydrazine hydrate administered to two different surface water samples, over a 48h exposure period under defined laboratory conditions. With initial concentrations of hydrazine hydrate adjusted to 0.0375 mg/L (wet gravel pit sample), or 0.0422 mg/L (Rhine river sample), the test item concentrations dropped below the limit of quantification (photometry: LOQ = 0.0156 mg/L) within 6 to 24 hours. Half life times of 2.67 to 24 hours at 20°C could be calculated.

Endpoint:
hydrolysis
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:

Description of key information

A guideline test was waived as the substance is marketed as aqueous dilution with varying concentrations of hydrazine, a hydrolytical reaction can be excluded. The disappearance of hydrazine is rather caused by the presence of various water constituents (for example organic matter, oxygen, carbonate, metal ions) than by the presence of water molecules itself. This has been shown by a study where natural surface water (pond water, river water) was spiked with hydrazine. The substance declined rapidly with half lives of 2.6 hours (pond water) and 24 hours (river water) (Sapers 2010). Another study (Slonim 1076) supports these finding, as half-lives for hydrazine in natural surface waters were a few hours, whereas clean tap waters showed higher stability to hydrazine.
Supporting evidence is given by a synopsis of the available literature (Canada hydrazine assessment 2011) where a melange of data is given assessing biodegradation and abiotic degradation.

Key value for chemical safety assessment

Half-life for hydrolysis:
24 h
at the temperature of:
20 °C

Additional information