2-nitrotoluene

Biodegradation in soil

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in soil, other

Type of information:

other: EU Risk Assessment

Adequacy of study:

other information

Reliability:

other: EU Risk Assessment

Rationale for reliability incl. deficiencies:

other: No reliability is given as this is a summary entry for the EU RAR.

Principles of method if other than guideline:

EU Risk Assessment

GLP compliance:

no

Specific details on test material used for the study:

- Analytical purity: not specified

EU Risk Assessment (2008):

 

If released to soil, 2-nitrotoluene may be resistant to oxidation and chemical hydrolysis. An earlier study (Alexander and Lustigman, 1966) worked with a procedure based on the loss of ultraviolet absorbance when the benzene ring is cleaved by mixed population of microorganisms derived from a soil inoculum under aerobic conditions in aqueous mineral salts media. 2-nitrotoluene was inoculated at an initial concentration of 10 µg/l of test compound as the sole carbon source. Another series identical to this was set up to determine if the chemical concentration was toxic to the microflora. The authors determined the rate of degradation of 2-nitrotoluene by a spectrophotometric technique. It relied upon the loss of ultraviolet absorbance when the benzene ring was cleaved by microorganisms derived from a soil inoculum. The solution contained the test compound as the sole carbon source to support microbial proliferation. The wavelength chosen was 263 nm, at which the light absorption was at, or near, the absorption maximum for the test substance, and so, considered to be sufficiently high for convenient use. Results indicate that 2-nitrotoluene was quite difficult to degrade, being the ultraviolet light retained for periods in excess of 2 months. The designation >64 indicates that significant ring cleavage was not detected even on the 64^th day, which would correspond to the most persistent compounds. This study is considered not assignable for this assessment but included, as additional information, regarding the possible incapability of soil microorganisms to degrade the 2-nitrotoluene, even after a period enough for the acclimation of soil microorganisms.

 

According to equilibrium partitioning equations, degradation half-life for (bulk) soil, partly based on Kpsoil is followed. Measured Kpsoil values are preferred, but as not available, a calculated Kpsoil = 4.19 l/kg for 2 -nitrotoluene (see section 3.1.3.2.1) will be used for estimations. And so, according to the Technical Guidance Document, the half-life for the soil compartment will be assumed to be 300 days.

 

Regarding the degradability on sediment compartment, and following the equilibrium partitioning method according to the Technical Guidance Document equations:

 

Kbiosed = Ln 2 · Faersed/ DT50 biosoil

 

DT50 biosoil   = half-life for biodegradation in bulk soil (days).

Kbiosed            = first order rate constant for degradation in bulk sediment (days-1).

Faersed            = fraction of the sediment compartment that is aerobic (0.10)

 

Kbiosed = Ln 2 · 0.1 / 300 = 2.3 · 10 -4 days-1

 

This implies that the total half-life for the sediment compartment will be a factor of ten higher than the half-life in soil. That means DT50biosed = 3,014 days (8.3 years).

 

Regarding the information, and in terms of the environmental modelling of the risk assessment, it is assumed the biodegradation rate in sediment and soil compartment given in the Technical Guidance Document, as can be seen in the following table:

 

Summary of calculated ultimate biodegradation rate constants in soil and sediment used in EUSES

Compartment	Reaction rate constant	Half-life	Reference
Soil (Kpsoil = 4.19)	2.3 × 10^-3d^-1	300 d	TGD
Sediment (Kpsoil = 4.19)	2.3 × 10^-4d^-1	3.014 d	TGD

Executive summary:

EU Risk Assessment (2008):

If released to soil, 2-nitrotoluene may be resistant to oxidation and chemical hydrolysis.

According to equilibrium partitioning equations, degradation half-life for (bulk) soil, partly based on Kpsoil is followed. Measured Kpsoil values are preferred, but as not available, a calculated Kpsoil = 4.19 l/kg for 2 -nitrotoluene will be used for estimations. And so, according to the Technical Guidance Document, the half-life for the soil compartment will be assumed to be 300 days.

Description of key information

For transported isolated intermediates according to REACh, Article 18, this endpoint is not a data requirement. However, data is available for this endpoint and is thus reported under the guidance of "all available data".

EU Risk Assessment (2008):

If released to soil, 2-nitrotoluene may be resistant to oxidation and chemical hydrolysis.

According to equilibrium partitioning equations, degradation half-life for (bulk) soil, partly based on Kpsoil is followed. Measured Kpsoil values are preferred, but as not available, a calculated Kpsoil = 4.19 l/kg for 2 -nitrotoluene will be used for estimations. And so, according to the Technical Guidance Document, the half-life for the soil compartment will be assumed to be 300 days.