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Hydrolysis

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Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Does not correspond to hydrolysis but to oxidative degradation. Non GLP, non guideline study, but in-depth investigations which are relevant for risk assessment of environmental hazards and exposures.
Qualifier:
no guideline available
Principles of method if other than guideline:
Investigates oxidation in water as a function of pH, dissolved oxygen and metallic divalent ion (Cu2+) concentrations.
GLP compliance:
no
Remarks:
prior to GLP
Radiolabelling:
no
Analytical monitoring:
yes
Estimation method (if used):
The consumption of oxygen was measured by a dissolved oxygen monitor (Yellow Springs International model 53).
UV spectra were recorded on a Cary 14 spectrophotometer and HPLC analyses were performed on a Waters M6000A instrment with µC 18 Bondapack as the stationary phase and 99% (1% acetic acid in water) - 1% acetonitrile as the mobile phase.
GC measurements were conducted on a Hewlett Packard 5730A FID chromatograph
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#3

The kinetic reaction contains a copper ion-catalyzed as well as an uncatalyzed component: kobs = k1 + k2 * [Cu2+], with [CU2 +] in g/mol at a given pH:

- at pH 7.0: k1= 6.68 E-4 /min; k2 = 1.20 E+3 /(g/mol)/min

- at pH 9.2: k1= 6.94 E-3 /min; k2= 1.81 E+3 /(g/mol)/min

At null [Cu2 +] level, the overall rate constant is approximately 7 E-3 /min (extrapolated) or 5.64 E-3 /min (measured).

At [Cu2 +] up to 1E-6 g/mol, the overall rate is similar at neutral and alcaline pH (7.0 and 9.2).

At higher [Cu2 +] up to 1E-5 g/mol, the overall rate gets up to 3-fold higher in alcaline than neutral water.

No UV-absorbing degradation products were detected.

Chromotropic acid revealed formation of formaldehyde, at around 30% with little dependence on [MMH] or [Cu2+].

Also hydrazine is expected to be formed, see attached picture.

Validity criteria fulfilled:
not applicable
Remarks:
not a standard assay
Executive summary:

The rate (amount per min) of MMH aqueous degradation due to oxidation by dissolved oxygen increases with:

- increasing water Cu2+ levels (acts as a catalyst; major effect),

- increasing water pH (moderate effect).

It is unlikely that these materials will be present for longer than one or two days in non-acidic waters.

The degradation products are formaldehyde and hydrazine.

Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Does not correspond to hydrolysis but to oxidative degradation. Non GLP, non guideline study, but in-depth investigations which are relevant for risk assessment of environmental hazards and exposures.
Qualifier:
no guideline available
Principles of method if other than guideline:
Investigates oxidation in water as a function of pH, dissolved oxygen and metallic divalent ion (Cu2+) concentrations.
APHA, AWWA, and WPCF: Standard Methods for the Examination of Water and Wastewater. 12th ed. American Public Health Assn., Inc., New York, 1965.
GLP compliance:
no
Remarks:
pior to GLP
Radiolabelling:
no
Analytical monitoring:
yes
Estimation method (if used):
Various physical properties, phenolphthalein and total alkalinity, pH, specific conductance, water hardness, and dissolved oxygen were examined immediately following preparation of fresh solutions and at the same time each day for 4 days. More frequent measurements were made to assess the effects on the oxygen content of water and to some extent chemical stability in the test solution.
Details on test conditions:
Hard water:
- origin: supernate of raw ground water allowed to stand for one week for sedimentation
- characteristics: pH of 7.8 to 8.2, dissolved oxygen (DO) of 6.9 to 7.8 mg/L, hardness (EDTA) of 400 to 500 mg/l as CaCO3 , specific conductance of 700 to 870 µmho/cm, total alkalinity of 185 to 232 mg/l as CaCO3.
- composition: no detectable amount of chlorine, copper or iron (copper shown to cause appreciable degradation)

Soft water:
- origin: prepared just before use by making a 1:20 dilution of the hard water with distilled water containing no detectable Ca, Mg or Cu.
- characteristics: pH of 6.3 to 6.9, hardness of 20 to 25 mg/l, DO of 6.9 to 7.8 mg/l, specific conductance of 50 to 65 µmho/cm, alkalinity of 16 to 18 mg/L.

MMH was made into hard water (HW) and soft water (SW) solutions at final concentrations ranging from 100 to 0.1 mg/l, in 2L.
Two liters each of hard and soft water served as controls.
Duration:
4 d
Negative controls:
yes
Remarks:
see above
Details on results:
- Only MMH in hard water at a concentration at or above 1 mg/l showed some degree of turbidity.
- No noticeable change in temperature (> 0.5°C) of any of the chemical solutions.
- NB: Hydrazine was very stable in soft water but less so in hard water over 4 days.
- MMH did not affect phenolphthalein alkalinity, but at 100 mg/l caused a 7-fold increase in total alkalinity in soft water and little or no increase in hard water (in which binding with calcium and other ions occurs).
- MMH produced an appreciable increase in pH in both hard and soft water only at 100 mg/L; in soft water the values decreased a little along time. Minimally larger increase in pH in soft water than hard water (buffering action of hard water).
- MMH at 100 mg/l produced a significant increase in the specific conductance in soft water but a slight reduction in hard water.
- EDTA hardness: small decrease at the 100 mg/l level in hard water only (suggests appreciable coordination or binding to calcium ions)
- Dissolved oxygen: MMH at 100 mg/l caused a reduction in the DO level, greatest in soft than hard water (5.0 vs. 6.2 mg/l at 24 h) throughout the test period but mainly during first 24h.
Validity criteria fulfilled:
not applicable
Remarks:
not a standard assay
Executive summary:

MMH is more stable in soft water than hard water due to the various ions present. Low concentrations up to 1.0 mg/l had no significant effect on any of the parameters evaluated. The 100 mg/l concentration level produced a relatively greater effect on total alkalinity, pH and specific conductance in soft water than hard water, along with a small drop in EDTA hardness over time in hard water only, indicating that MMH coordinates with calcium and other ions present in hard water. A decrease in the oxygen content occured at 100 mg/l within the first 24 hours, especially in soft water.

Hydrazine, a possible degradation product of MMH, was shown to be quite stable over 4 days in preliminary assays.

Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Non-GLP, non-guideline study. Water DT50: relevant for BPT assessment and seem reliable although some data are missing. Soil data: not reliable based on minimal or aberrant recoveries.
Qualifier:
no guideline followed
Principles of method if other than guideline:
Decomposition rates of MMH in aqueous environments (distilled, seawater, and freshwater) were determined.
Soil percolation and decomposition studies.
GLP compliance:
no
Remarks:
prior to GLP
Radiolabelling:
no
Analytical monitoring:
yes
Details on test conditions:
Water:
Natural waters used in these studies were obtained from a freshwater pond on Tyndall AFB, FL and from the Gulf of Mexico. Filtered through Whatman filter paper for each study.
Cleaned to remove organic material, rinsed with deionized, distilled water, soaked in a 50-percent solution of nitric acid, and again rinsed with deionized, distilled water. Without cleaning, randomly accelerated legradation rates were observed, possibly the result of trace metals which catalyze the breakdown.
MMH test concentrations: 0.1% and 0.05%., studied at room temperature.

Soil:
Four soils (sand, clay = acid soil, organic, Vandenberg Air Force Base soil).
Transformation products:
not specified
DT50:
>= 13 - <= 18 d
St. dev.:
2
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: total degradation (not only hydrolysis), pond water
DT50:
>= 13 - <= 24 d
St. dev.:
9
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: total degradation (not only hydrolysis), seawater

Soil: in sand, 0% adsorbed and/or decomposed, 3% extractable by HCl, all the rest was not recovered. In all other soil types, about half of the amount was adsorbed and/or decomposed. Data were unclear with some totals >>100% and some other with minimal recovery.

Validity criteria fulfilled:
not applicable
Remarks:
missing data, non standard assay
Executive summary:

Water DT50 (pseudo-first order):

At room temperature, unknown pH (most likely neutral, based on water sources and neutral pKa of MMH): MMH's DT50 range of means was 13 -24 days in pond water and sea water.

Soil (non reliable data):

There was no single dominating process; both chemical decomposition and physical adsorption were important in fuel-soil interactions.

Description of key information

Relevant data were available to fulfil that endpoint, even if they do not strictly correspond to hydrolysis (reaction with water), but to oxidation (dissolved oxygen). In water, oxidation is catalyzed by dissolved divalent metals, and leads to quick degradation. Furthermore, pseudo-first order DT50 was experimentally determined in water and the range of means was 13-24 days, for pond water and sea water combined. These data are much more relevant for risk assessment (incl. persistence assessment) than simple hydrolysis as a function of pH (a test in which dissolved oxygen and metals do not have to be detailed). Hydrolysis testing as a function of pH would not give any useful data for classification either.

Key value for chemical safety assessment

Additional information

The studies on degradation in water are summarised in the following table:

Method

Results

Remarks

Reference

Decomposition rates of MMH in aqueous environments (distilled, seawater, and freshwater) were determined.

also: Soil percolation and decomposition studies.

Half-life (DT50):

t1/2: >= 13 to <= 18 d; Type: (pseudo-)first order (= DT50) (total degradation not only hydrolysis, pond water)

t1/2: >= 13 to <= 24 d; Type: (pseudo-)first order (= DT50) (total degradation not only hydrolysis, seawater)

Soil data: not reliable, ignored

2 (reliable with restrictions)

key study

experimental result

Test material (EC name): methylhydrazine

Braun BA, Zirrolli JA (1983)

Investigates oxidation kinetics in water as a function of pH, dissolved oxygen and metallic divalent ion (Cu2+) concentrations.

The consumption of oxygen was measured by a dissolved oxygen monitor (Yellow Springs International model 53).

UV spectra and GC measurements were conducted

The rate (amount per min) of MMH aqueous degradation due to oxidation by dissolved oxygen increases with:

- increasing water Cu2+ levels (acts as a catalyst; major effect),

- increasing water pH (moderate effect).

MMH not expected to stay for longer than one or two days in non-acidic waters.

Degradation products are formaldehyde (around 30% of original MMH amount) and hydrazine.

2 (reliable with restrictions)

Supporting study

experimental result

Test material (Common name): Monomethylhydrazine hydrochloride

Sikka HC, Banerjee S, Appleton HT (1979)

Investigates consequences of MMH introduction on water characteristics, and MMH stability.

APHA, AWWA, and WPCF: Standard Methods for the Examination of Water and Wastewater. 12th ed. American Public Health Assn., Inc.,, 1965.

Various physical properties, incl. water hardness, and dissolved oxygen were examined for 4 days after MMH introduction.

MMH more stable in soft water than hard water due to the ions present.

In hard water MMH reduces EDTA hardness, indicating coordination with calcium and other ions.

In soft water MMH consumes oxygen, indicating MMH oxidation.

 

2 (reliable with restrictions)

Supporting study

experimental result

Test material (EC name): methylhydrazine

Slonim (1975)