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Environmental fate & pathways

Biodegradation in soil

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Endpoint:
biodegradation in soil: simulation testing
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
Principles of method if other than guideline:
The biodegradation of cyanuric acid was studied in a variety of soils and muds
GLP compliance:
no
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
anaerobic
Soil classification:
not specified
Soil no.:
#1
Soil type:
other: Garden
Soil no.:
#2
Soil type:
other: Chemical plant area
Soil no.:
#3
Soil type:
other: Farm
Soil no.:
#4
Soil type:
other: Barnyard (a): air-dried in laboratory for > 6 months. 20 g of H2O was added per 100 g of air dried soil
Soil no.:
#5
Soil type:
other: Barnyard (b): air-dried in laboratory for > 6 months. 20 g of H2O was added per 100 g of air dried soil, experiment started one month after moistening
Soil no.:
#6
Soil type:
other: Barnyard (c): air-dried in laboratory for > 6 months. 90 g of H2O was added per 100 g of air dried soil
Details on soil characteristics:
Sampling sites:
Garden soil: Santa Clara, California, USA
Chemical plant area: S. Charleston, W. Va. USA
Farm: Princeton, N. J. USA
Barnyard: New Brunswick, N. J. USA
Soil No.:
#1
Duration:
23 d
Soil No.:
#2
Duration:
23 d
Soil No.:
#3
Duration:
23 d
Soil No.:
#4
Duration:
23 d
Soil No.:
#5
Duration:
23 d
Soil No.:
#6
Duration:
15 d
Parameter followed for biodegradation estimation:
CO2 evolution
Soil No.:
#1
% Degr.:
91
Parameter:
CO2 evolution
Sampling time:
23 d
Soil No.:
#2
% Degr.:
106
Parameter:
CO2 evolution
Sampling time:
23 d
Soil No.:
#3
% Degr.:
103
Parameter:
CO2 evolution
Sampling time:
23 d
Soil No.:
#4
% Degr.:
2
Parameter:
CO2 evolution
Sampling time:
23 d
Soil No.:
#5
% Degr.:
10
Parameter:
CO2 evolution
Sampling time:
23 d
Soil No.:
#6
% Degr.:
52
Parameter:
CO2 evolution
Sampling time:
15 d
Transformation products:
not specified

Table 1: 14CO2 evolution from 14C labelled cyanuric acid on soils

Medium

Days at room temp

14C added evolved as CO2 (%)

Soils:

Garden

23

91

Chemical plant area

23

106

Farm

23

103

Barnyarda

23

2

Barnyardb

23

10, 13

Barnyardc

15

52

a air-dried in laboratory for > 6 months.  20 g of H2O was added per 100 g of air dried soil.

b air-dried in laboratory for > 6 months.  20 g of H2O was added per 100 g of air dried soil, experiment started one month after moistening

c air-dried in laboratory for > 6 months.  90 g of H2O was added per 100 g of air dried soil.

Conclusions:
Cyanuric acid biodegrades readily in anaerobic soils
Endpoint:
biodegradation in soil: simulation testing
Type of information:
experimental study
Adequacy of study:
supporting study
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:
The relative degradation rate of cyanuric acid was studied in Greenfield sandy loam soil
GLP compliance:
no
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic/anaerobic
Soil classification:
not specified
Soil no.:
#1
Soil type:
sandy loam
% Clay:
6
% Silt:
29
% Sand:
65
% Org. C:
1.1
pH:
7.1
Details on soil characteristics:
SOIL COLLECTION AND STORAGE
- Soil preparation: The soil was collected from the field, air dried passed through a 2mm sieve and 500 g portions placed in 1-liter Erlenmyer flasks.

Soil No.:
#1
Duration:
375 d
Parameter followed for biodegradation estimation:
CO2 evolution
Details on experimental conditions:
Soil incubation:
The organic amendment was lima bean straw which contained 1.1% nitrogen and was applied at the rate of 0.5% on a dry weight basis. For aerobic incubation the soil was adjusted to 60% water-holding capcacity and for the saturated soil treatment 20% water in excess of capacity was added. 2.5 ppm of 14-C cyanuric acid was added to the soil in solution to give a concentration of 2.5 ppm on a dry soil basis. Treatments were made in duplicate.

CO2 free air was continuously passed over the soil surface in the flasks and the CO2 evolved was collected in 25 ml of 3N KOH.

Fungal incubation:
Stachybotrys chartarum and Hendersonula toruloidea were cultured. Fungal pads were harvested by filtration, washing and lyophilization. Humic-type polymers present in the culture solution of these fungi were concentrated at 65°C, dialyzed against frequent changes of distilled water and lyophilized.
Transformation products:
not specified

Table 1: Percent of 14C recovered as 14CO2 from 2.5 ppm cyanuric acid

Treatment

Time after treatment (days)

16

32

66

192

264

375

Aerobic soil

87

96

98

99

-

-

Aerobic soil plus bean straw

96

98

99

99

-

-

Saturated soil

N.S

57

83

97

98

99

Saturated soil plus bean straw

N.S

76

87

93

93

94

N.S - not sampled

The carbon of cyanuric acid was rapidly and almost completely evolved as CO2 with or without organic amendment additions. Even though saturated soil conditions retarded CO2 evolution, decomposition exceeded 83% in 66 days. The almost complete evolution of the cyanuric acid carbon to CO2 indicates that the soil population does not use the ring carbon of this compound for cell synthesis.

At the termination of the experiments the soil waas dried and the amount of 14C remaining in the soil was determined. In both the aerobic and saturated soil incubations the amount recovered as 14CO2 plus the activity remaining in the soil accounted for 91 to 103% of the initial activity added to the soil.

Table 2: Influence of cyanuric acid on the growth and CO2 evolution by Stachybotrys chartarum and Hendersonula toruloidea*

Growth and CO2evolution

H. toruloidea

S. chartarum

Dry weight of pads

mg per 100 ml of medium

687

319

CO2evolution

mg C as CO2per100 ml of medium

950

599

* Eight week incubation. Cyanuric acid added at the rate of 166.7 ppm

Cyanuric acid increased CO2 evolution by an amount greater than could be accounted for by the additional carbon added to the medium as cyanuric acid (166.7 ppm). This effect probably represents a shift in the metabolism of the organisms.

Table 3: Distribution of 14C activity in CO2, fungal cells and fungal products after 8 week incubation of Hendersonula toruloidea and Stachybotrys chartarum with 166.7 ppm cyanuric acid

Percent activity recovered as

H. toruloidea

14CO2

Cell material

Humic type polymer

15.1

6.3

53.8

S. chartarum

99.4

0.0

3.6

Cyanuric acid was rapidly and completely oxidized to CO2 by the fungus S. chartarum with essentially all of the added activity recovered as 14CO2 after 28 days of incubation. No activity could be found in the cell material and < 4% was recovered in the humic type polymer. The fungus H. toruloidea exhibited a different pattern of cyanuric acid oxidation. For the first 28 days of incubation < 1% of the activity was recovered as 14CO2. In the last 28 days of the 8 week incubation, 15% of the activity was recovered as 14CO2. THus all of the oxidation of cyanuric acid by this fungus occurred during the stationary and death phase of growth.

Conclusions:
After 16 days 87% of the labeled cyanuric acid had evolved as 14CO2 and after 32 days the percentage had increased to 96% indicating that after ring cleavage the cyanuric acid C is not used for cell synthesis by the soil organisms. Evolution of 14CO2 was retarded under saturated soil conditions. Losses were 83% for cyanuric acid in 66 days. Pure culture studies with two soil fungi, Stachybotrys chartarum and Hendersonula toruloidea could degrade cyanuric acid to CO2.
Endpoint:
biodegradation in soil: simulation testing
Data waiving:
other justification
Justification for data waiving:
other:
Justification for type of information:
JUSTIFICATION FOR DATA WAIVING
Cyanuric acid biodegrades readily in anaerobic soils [1]. CYA naturally occurs in soils at concentrations of 0.9 to 6.5 ppm[2]. The presence and identification of the levels of CYA found in the study predate the large scale commercial manufacture and use of products which breakdown to CYA thus providing evidence that the substance occurs due to other sources. CYA is also present in soil as a result of plant protection products such as the S-triazines, atrazine and simazine which have been commercially used for over 40 years. [3] The s-triazine herbicides undergo enzyme catalysed degradation yielding CYA as an intermediate, which is then hydrolytically processed to ammonia and carbon dioxide. Urea and other urea based compounds used as fertilizers can also form CYA as an intermediate. References: 1.Saldick, J. (1974) Biodegradation of cyanuric acid. Applied Microbiology 28 (6) 1004 – 1008. 2.Wise L E and Walters E H (1917) Isolation of Cyanuric Acid from Soil. Journal of Agricultural Research. 10(2) 85 - 91. 3.Müllar PW and Payot PH (1966) Fate of 14C-labelled Triazine herbicides in plants Isotopes and Weed Research Proceedings of the IACA Symposium, Vienna, Austria, 1966 p61-70, 4. Cook AM and Hutter R (1981) sTriazines as Nitrogen Sources fro Bacteria J. Agr. Food. Chem 29:(6), Eaton RW and Karns JS (1991) Cloning and Analysis of s-Triazine catabolic genes from Pseudomonas spp. strain NRRLB-12227, Journal of Bacteriology p.1215-1222, Vol. 173, No. 3

Description of key information

CYA biodegrades readily in soils.

Key value for chemical safety assessment

Additional information

In a series of studies performed in different anaerobic soils (Saldick J 1974) it was observed that CYA biodegrades readily in anaerobic soils. Over a 23 day period degradation was highest when there is a large water to solid ratio and a potentially large anaerobic microorganism population, for example 100% degradation in farm soil in 23 days.

In a further study (Wolf & Martin 1975) the relative degradation rate of cyanuric acid was studied in Greenfield sandy loam soil. After 16 days 87% of the labelled cyanuric acid had evolved as 14CO2 and after 32 days the percentage had increased to 96% indicating that after ring cleavage the cyanuric acid C is not used for cell synthesis by the soil organisms. Evolution of 14CO2 was retarded under saturated soil conditions. Losses were 83% for cyanuric acid in 66 days. Pure culture studies with two soil fungi, Stachybotrys chartarum and Hendersonula toruloidea could degrade cyanuric acid to CO2.