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Ecotoxicological information

Toxicity to terrestrial plants

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Endpoint:
toxicity to terrestrial plants: short-term
Data waiving:
other justification
Justification for data waiving:
other:
Endpoint:
toxicity to terrestrial plants
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: Study is provided as supporting information for justification of non- submission of a guideline study for terrestrial plant toxicity on the substance of interest, cyanuric acid, for environmental effects.
Principles of method if other than guideline:
Seeds of barley (Hordeum vulgare L.), corn (Zea mays L.), rye (Secale cereale L.) and wheat (Triticum aestivum L.) were tested in 4 different soils to determine if urea, urea fertilisers or impurities in urea fertilisers (biuret and cyanuric acid) affected germination
Species:
other: Hordeum vulgare L, Zea mays L., Secale cereale L and Triticum aestivum L
Plant group:
Monocotyledonae (monocots)
Details on test organisms:
- Common name: Barley, corn, rye and wheat
Total exposure duration:
7 d
Test temperature:
20°C
Details on test conditions:
Soils were air dried and crushed to pass through a 2 mm sieve prior to use (see table 1 for properties of soils used).
Two 85 mm discs of germination paper or 40 g of soil were placed in a 15 mm x 100 mm Petri dish and moistened with 10 mL water (control) or 10 mL water containing the test material. Seeds (25 with corn, 100 with others) were placed between the discs of germination paper or on the soil. Each dish was covered with a lid and kept in the dark for 7 days in an incubator maintained at 20°C. The number of germinated seeds was then counted and calculated as a percentage of the number of seeds sown. The criteria for germination was the emergence of a radicle and a coleoptile that were longer than the seed
Nominal and measured concentrations:
0.5, 1.0, 1.5, 2.0 and 2.5 mg/g soil

Table 2: Germination of seeds

Amount added mg/g of soil

% germination of seeds in 7 days

Barley

Corn

Rye

Wheat

None (control)

94

86

95

92

0.5

95

86

96

95

1.0

93

85

92

93

1.5

92

87

93

91

2.0

93

83

95

94

2.5

97

86

94

92

Conclusions:
Cyanuric acid at test concentrations up to 2.5 mg/g soil (equivalent to 0.8 mg of N/g of soil) did not have an adverse effect on the germination of seeds under the conditions of the study.
Endpoint:
toxicity to terrestrial plants
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: Study is provided as supporting information for justification of non submission of a guideline study for terrestrial plant toxicity on the substance of interest, cyanuric acid, for environmental effects.
Principles of method if other than guideline:
The availability of nitrogen in urea and urea pyrolysis products for four crops of corn forage and for four clippings of Bermuda grass grown in greenhouse cultures were studied. Further field experiments with wheat were also performed.
Greenhouse studies:
Minimum temperature of 70°F maintained in the greenhouse, ranging as high as 90°F in daytime during spring and summer periods.
Adequate phosphorus and potassium were added as concentrated superphosphate and potassium sulphate.
Details on sampling:
Corn:
Sampling was performed at harvesting only.

Bermuda grass:
Sample clippings made on October 25th, November 22nd, January 23rd and April 9th (4 clippings made prior to test material application were discarded)

Wheat:
Clipping and dry forage yield determinations during February or early March 1962

Plant group:
Monocotyledonae (monocots)
Details on test organisms:
- Common name: Corn, Coastal Bermuda grass and wheat
Substrate type:
natural soil
Test temperature:
Minimum temperature of 70°F maintained in the greenhouse, ranging as high as 90°F in daytime during spring and summer periods.
Moisture:
Soil was kept moist between croppings.
Nominal and measured concentrations:
Corn: Test material applied in amounts sufficient to supply 100 mg, 400 mg or 800 mg nitrogen per culture. Equal to 33, 133, 267 mg/kg of dry soil.
Bermuda grass: Test material applied in amounts sufficient to supply 200 or 800 mg of nitrogen per flat. Equal to 13 or 53 mg/kg of dry soil.
Wheat: Test material applied in amounts sufficient to supply 100 pounds nitrogen per acre.

Corn:

Cyanuric acid was toxic to the first crop at all test concentrations. The toxic effects from 400 mg of nitrogen as cyanuric acid observed in the first crop were less obvious in later crops. The second crop leaves had an abnormal intense green colour, but dry weight and particularly nitrogen uptake increases were substantial. Some evidence of continued toxicity was found with the 800 mg of nitrogen application, as there was some increase in yield over no nitrogen but lower yields than from 400 mg.There was no evidence of toxicity  on 3rd or 4th crops from either rate and nitrogen yield from cyanuric acid was above that obtained from urea pyrolyzate. Total yields, however, were less than those from urea pyrolyzate

Bermuda grass

Apparent recovery per 100 mg applied nitrogen (total uptake less uptake with no nitrogen, divided by 8) was 41 for cyanuric acid

Cyanuric acid applied at 800 mg rate of nitrogen was apparently toxic for the first clipping of grass

Cyanuric acid was relatively more available for Bermuda grass than corn.

Wheat

Cyanuric acid was toxic in all three experiments as evidenced by lower yields than from no applied nitrogen

Conclusions:
Cyanuric acid is toxic if applied to plants at the time of planting at concentrations relating to ≥ 400 mg nitrogen under the conditions of the study. If applied two or more weeks prior to planting it would be considered as a good source of nitrogen.
Endpoint:
toxicity to terrestrial plants: long-term
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:

Description of key information

The chlorinated isocyanurates are unstable in the environment, because the free available chlorine is rapidly reduced.  CYA, or its salt, is the stable degradation product. Therefore, CYA, or its sodium salt, is the substance of interest for terrestrial plant studies.

Key value for chemical safety assessment

Additional information

Plants are already exposed to CYA from natural sources in soil. A study conducted in 1917 showed that CYA naturally occurs in soils at concentrations of 0.9 to 6.5 ppm (1). 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 (2). 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.

CYA in soil is rapidly degraded by microorganisms. Anaerobic studies performed on a variety of soil types showed that CYA is readily degraded to carbon dioxide by microorganisms, which multiply in anaerobic conditions and do not require acclimatisation to be active for CYA decomposition (3) The mineralization of CYA in soil has also been found to occur from investigation of the nitrification of triazine nitrogen.(4) Certain plant species are capable of metabolizing CYA. A study with corn showed that it is capable of metabolizing 80% of CYA (5).

The algae toxicity showed CYA has no toxic effects to algae with a 48 h EC50 >1000 mg/kg 6

Due to the natural occurrence of CYA in soils and the evidence of the rapid degradation by microorganisms an acute toxicity study on plants would yield no pertinent information and is therefore scientifically unjustified.

References:

1 Wise L E and Walters E H (1917) Isolation of Cyanuric Acid from Soil. Journal of Agricultural Research. 10(2) 85 - 91.

2. 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

Cook AM and Hutter R (1981) sTriazines as Nitrogen Sources for Bacteria J. Agr. Food. Chem 29:(6) 1135 -1143

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

3. Saldick (1974) Biodegradation of Cyanuric Acid, Applied Microbiology, 28 (6) 1004 – 1008

4,5. 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

6. Vryenhoef H, Hill, J W F (2007) Monosodium salt of cyanuric acid: Navicula pelliculosa; Algal inhibition test. SafePharm Laboratories Ltd., Project No. 2255/0001.