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Environmental fate & pathways

Biodegradation in soil

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Endpoint:
biodegradation in soil
Type of information:
experimental study
Adequacy of study:
other information
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Principles of method if other than guideline:
Nitrification of triazine nitrogen.
GLP compliance:
not specified
Test type:
laboratory
Oxygen conditions:
aerobic
Soil classification:
not specified
Soil no.:
#1
Soil type:
silty clay loam
pH:
8.2
Soil no.:
#2
Soil type:
sandy loam
pH:
5.2
Details on soil characteristics:
Two soils were used: Webster silty clay loam (Iowa) pH 8.2; and Hartsells fine sandy loam (Alabama) pH 5.2
Soil No.:
#1
Duration:
28 wk
Soil No.:
#2
Duration:
24 wk
Soil No.:
#1
Initial conc.:
2 000 mg/kg soil d.w.
Based on:
test mat.
Soil No.:
#1
Initial conc.:
230 mg/kg soil d.w.
Based on:
test mat.
Soil No.:
#2
Initial conc.:
230 mg/kg soil d.w.
Based on:
test mat.
Parameter followed for biodegradation estimation:
other: Nitrification
Soil No.:
#1
Temp.:
32 °C
Humidity:
60 %
Soil No.:
#2
Temp.:
32 °C
Humidity:
60 %
Details on experimental conditions:
Different experiments were performed. All materials were added as granules or prills screened to pass -8+12 mesh.
Incubation experiment: up to 28 wk, 32 °C.
Experiment 1: Duplicate samples of about 200 mg test material, mixed with 100 g soil No. #1;
Experiment 2: 7.0 mg of triazine (or urea) N were added as solid or in solution to 30 g soil #1, or same concentration was added as solid to soil #2.
Experiment 3: 3 rates of N (7, 14, 21 mg) as melamine were incubated in 30 g of soil No. #1 for 24 hours

Perfusion experiments were performed to study the nitrification of triazines and their effects on the oxidation of added ammonium.
Dilute solutions of triazines (10 mg N as melamine or cyanuric acid alone, or supplemented with with 10 mg N of NH4) were continuously circulated in a well aerated closed system, the triazine solution passing through 30 g of Krilium-treated soil No. #1 at 25 °C, for up to 165 d. Treatment consisted of mixing a 0.1 % aqueous solution of Krilium with soil to form a thick slurry, followed by drying and granulation. Samples of pot solution were taken at weekly intervals for nitrite and nitrate analysis.
Soil No.:
#1
% Degr.:
0.7
Parameter:
other: nitrification; % of organic N, found as NO3- N; granules.
Sampling time:
10 wk
Soil No.:
#1
% Degr.:
0
Parameter:
other: nitrification; granules.
Sampling time:
28 wk
Soil No.:
#1
% Degr.:
6.4
Parameter:
other: nitrification; solution
Sampling time:
6 wk
Soil No.:
#1
% Degr.:
9.1
Parameter:
other: nitrification; solution
Sampling time:
12 wk
Soil No.:
#1
% Degr.:
10.5
Parameter:
other: nitrification; solution
Sampling time:
18 wk
Soil No.:
#1
% Degr.:
13.7
Parameter:
other: nitrification; solution
Sampling time:
24 wk
Soil No.:
#1
% Degr.:
7.7
Parameter:
other: nitrification; powder
Sampling time:
6 wk
Soil No.:
#1
% Degr.:
9.1
Parameter:
other: nitrification; powder
Sampling time:
12 wk
Soil No.:
#1
% Degr.:
15.4
Parameter:
other: nitrification; powder
Sampling time:
18 wk
Soil No.:
#1
% Degr.:
17.9
Parameter:
other: nitrification; powder
Sampling time:
24 wk
Soil No.:
#2
% Degr.:
0
Parameter:
other: nitrification; powder
Sampling time:
6 wk
Soil No.:
#2
% Degr.:
0
Parameter:
other: nitrification; powder
Sampling time:
12 wk
Soil No.:
#2
% Degr.:
3.9
Parameter:
other: nitrification; powder
Sampling time:
18 wk
Soil No.:
#2
% Degr.:
8.9
Parameter:
other: nitrification; powder
Sampling time:
24 wk
DT50:
> 2 - < 3 yr
Type:
other: estimated by ECETOC.
Transformation products:
no
No.:
#1
No.:
#2
Evaporation of parent compound:
no
Volatile metabolites:
no
Details on results:
Experiment 1: The extent of nitrate formation from melamine was low (0.7 % of organic N found as NO3-N in week 10, and 0 % in week 28). The extent of nitrate formation increased from melamine to cyanuric acid, that is with decreasing amination of the triazine. Nitrification of cyanuric acid was 35 % at week 10 and 73 % at week 28.
Experiment 2: The extent of nitrate formation increased in both soils inversely with the degree of amination of cyanuric acid.
Powdered Melamine and cyanuric acid nitrified to a slightly greater degree than solutions of these materials.
Both powders and solutions of melamine (and cyanuric acid) nitrified to a much greater extent than the -8+12 mesh granules used in experiment 1 in the same soil and under similar conditions.
In experiment 3, three rates of nitrogen of melamine were incubated in 30 g soil #1 for 24 h. The % of the total N which was recovered as nitrate decreased with increasing rates of application, being 17.9, 7.0 and 4.2 % of the 7, 14, and 21 mg rates of nitrogen of melamine, respectively; and 92.2, 91.5 and 85.5 % of the same rates for cyanuric acid.
Further experiment on the inhibition of of nitrification of added ammonium by cyanuric acid: Cyanuric acidcan inhibit the nitrification under not clearly described circumstances.

Melamine (and cyanuric acid) perfusing with added ammonium slightly delayed the nitrification of ammonium by ca. 2 days.
Melamine and cyanuric acid perfusing without added ammonium degraded at a slow but constant rate for about 4 wk, after which time nitrate assimilation in the perfusion system occurred faster than nitrate production. After 46 d, a maximum of 14 and 9.8 % of N apparently originating from Melamine and cyanuric acid, respectively, was found as nitrate.
Melamine solutions (ca. 490 mg melamine/ kg soil) perfusing through soil slightly delayed the rate of nitrate formation from added ammonium, and caused a marked but temporary accumulation of nitrite.
The biochemical degradation of melamine proceeds at a very slow rate in soils.
Conclusions:
Nitrification of melamine occurrs in soil at a low rate.
Melamine solutions (ca. 490 mg melamine/ kg soil) perfusing through soil slightly delayed the rate of nitrate formation from added ammonium, and caused a marked but temporary accumulation of nitrite.
Executive summary:

Nitrification of N released from cyanuric acid, ammelide, ammeline, or melamine varied inversely with the number of amino groups on the triazine ring. Nitrification of melamine and cyanuric acid from powders was slightly greater than from solutions and considerably greater than from granules of these materials. Melamine solutions perfusing through soil slightly inhibited the rate of nitrate formation from added ammonium, and caused a marked temporary accumulation of nitrite.

More nitrate was produced from triazine incubated in soil bottle cultures than from triazine perfusing through soil.

Endpoint:
biodegradation in soil
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
other information
Justification for type of information:
Please refer to the analogue justification attached to section 13
Reason / purpose:
read-across source
Principles of method if other than guideline:
Nitrification of triazine nitrogen.
Soil No.:
#1
% Degr.:
0.7
Parameter:
other: nitrification; % of organic N, found as NO3- N; granules.
Sampling time:
10 wk
Soil No.:
#1
% Degr.:
0
Parameter:
other: nitrification; granules.
Sampling time:
28 wk
Soil No.:
#1
% Degr.:
6.4
Parameter:
other: nitrification; solution
Sampling time:
6 wk
Soil No.:
#1
% Degr.:
9.1
Parameter:
other: nitrification; solution
Sampling time:
12 wk
Soil No.:
#1
% Degr.:
10.5
Parameter:
other: nitrification; solution
Sampling time:
18 wk
Soil No.:
#1
% Degr.:
13.7
Parameter:
other: nitrification; solution
Sampling time:
24 wk
Soil No.:
#1
% Degr.:
7.7
Parameter:
other: nitrification; powder
Sampling time:
6 wk
Soil No.:
#1
% Degr.:
9.1
Parameter:
other: nitrification; powder
Sampling time:
12 wk
Soil No.:
#1
% Degr.:
15.4
Parameter:
other: nitrification; powder
Sampling time:
18 wk
Soil No.:
#1
% Degr.:
17.9
Parameter:
other: nitrification; powder
Sampling time:
24 wk
Soil No.:
#2
% Degr.:
0
Parameter:
other: nitrification; powder
Sampling time:
6 wk
Soil No.:
#2
% Degr.:
0
Parameter:
other: nitrification; powder
Sampling time:
12 wk
Soil No.:
#2
% Degr.:
3.9
Parameter:
other: nitrification; powder
Sampling time:
18 wk
Soil No.:
#2
% Degr.:
8.9
Parameter:
other: nitrification; powder
Sampling time:
24 wk
DT50:
> 2 - < 3 yr
Type:
other: estimated by ECETOC.
Transformation products:
no

Description of key information

Key value for chemical safety assessment

Additional information

Experimental studies investigating biodegradation of diphosphoric acid, compound with 1,3,5-triamine (1:2) in soil are not available. The substance will dissociate in aqueous environments under environmentally relevant conditions forming melamine and pyrophosphate ions. Pyrophosphate is an inorganic substance and thus biodegradation is no relevant pathway for the substance. The assessment of biodegradation is therefore based on read across data available for the substance compound melamine (CAS 108-78-1). The read across approach is in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5. Further justification is given in the analogue justification in IUCLID section 13.

A study investigating the nitrification of melamine in two different soil types is available. The substance was added in solution or as a solid to silty clay loam and Hartsells fine sandy loam respectively. The soils were incubated at 32°C for 24 – 28 weeks. A low nitrification rate of melamine in soils was determined. A slow degradation of melamine in soil with a half-life of 2-3 years is expected.