Phenylhydrazine

Endpoint summary

Additional information

Degradation

In a modified OECD ready biodegradability screening test (OECD 301E), phenylhydrazine was “readily biodegradable”; elimination was 77 % after 10 days and 97 % after 28 days using non-adapted inoculum. Elimination through abiotic processes in controls was 11 % after both 10 and 28 days (BASF, 1993). In the Zahn-Wellens test for inherent biodegradability (OECD 302B), 20–30 % elimination occurred over 3 h (sorption), with 80 % chemical oxygen demand achieved over 15 days using non-acclimatized industrial activated sludge. Using acclimatized activated sludge, 85 % elimination was seen after 10 days (Hoechst, 1980, 1992). A similar value of 85 % elimination in 9–13 days was reported in the same test by Wellens (1990).

Environmental distribution

Most emissions of phenylhydrazine into the environment are into the hydrosphere. At acidic pH, phenylhydrazine occurs as the salt (BUA, 1995). In the atmosphere, phenylhydrazine would exist solely in the vapour phase (HSDB, 1998). Calculated half-lives of 3.1 h (BUA, 1995) and 9 h (Meylan & Howard, 1993) were reported for phenylhydrazine following reaction with hydroxyl radicals in the atmosphere. Phenylhydrazine strongly absorbs ultraviolet light in the environmentally significant range, suggesting that it may photolyse in sunlight (HSDB, 1998); slow photodecomposition in diffuse daylight in the absence of oxygen is deduced in BUA (1995). In the presence of oxygen, phenylhydrazine is subject to autoxidation, the reaction being accelerated by light and heat; the substance becomes reddish brown on exposure to air as a result of this autoxidation (Ullmann, 1977).

Bioaccumulation

No hydrolysis of phenylhydrazine is expected to occur (BUA, 1995). The Henry’s law constant for phenylhydrazine was calculated at 9.69E-03 Pa m3/mol (BUA, 1995). This is equivalent to a dimensionless Henry’s law constant (air/water partition coefficient) of 3.92E-06.These values indicate that phenylhydrazine is essentially non-volatile from water surfaces. Reported log octanol/water partition coefficients (log Kow) range from 1.25 to 1.90 (BUA, 1995); an estimated bioconcentration factor of 5 was based on the lower value (HSDB, 1998), indicating a low capacity for bioaccumulation. However, sorption based on chemical binding is possible, which could lead to some bioaccumulation (BUA, 1995). The sorption coefficient (Koc) was calculated to range between 7.3 (Organisation for Economic Co-operation and Development [OECD] Technical Guidance Manual) and 11 (Karickhoff et al., 1979), indicating little sorption to particulates and a capacity for mobility in soil. However, the regression equations on which these estimates are based derive from hydrophobic compounds and may not adequately reflect the likely sorption of the hydrophilic phenylhydrazine.

Secondary poisoning

Based on the low bioconcentration factor obtained for phenylhydrazine (BCF = 5) there is practically no hazard from secondary poisoning.