Teflubenzuron

Toxicity to terrestrial plants

Description of key information

In the seedling emergence and growth test according to the OECD 209 the test item showed no significant effect on the emergence of the seedlings. Therefore the ER50 and the NOEC for all six plants were determined to be > 120 g teflubenzuron/ha, which corresponds to > 0.125 mg teflubenzuron/kg soil dw.

Key value for chemical safety assessment

Long-term EC10, LC10 or NOEC for terrestrial plants:

0.125 mg/kg soil dw

Additional information

A study of the toxicity of the test item on the seedling emergence and seedling growth test according to OECD TG 208 is available. The study was performed with a SC formulation containing 150 g/L test item. The presented study was peer-reviewed during the assessment of teflubenzuron according to Council Directive 91/414/EEC.

 

Key information

ECT (2003): Study on the Toxicity of BAS 309 00 l (Nomolt 150 SC Teflubenzuron): Sprayed onto the Soil Surface to Six Plant Species according to OECD Guideline 2008 A (July 2000), Terrestrial (Non-Target) Plant Test 2008 A: Seedling Emergence and Seedling Growth Test. Unpublished report, report No. G4PA, according to Draft Assessment Report (2007) according to Council Directive 91/414/EEC, crossreference: B.9.9.2/02

A 21-day seedling emergence and seedling growth test according to OECD TG 208 was carried out to assess the toxicity of the test item to several plant species. Nominal test item concentration of 120 g a.s./L were applied to the monocotyledons onion (Allium cepa L.) and oats (Avena sativa L.) as well as to the dicotyledons rapeseed (Brassica napus L.), cucumber (Cucumis sativus), soy bean (Glycine max) and tomato (Lycopersicon lycopersicum). The test item was dissolved in water to obtain a stock solution, which was further diluted to obtain a number of test solutions. The test item was applied pre-emergence (shortly after seeding) by spraying the test item solution on the soil surface using a laboratory spray cabin. The control replicates were treated in a similar way with deionized water. The seeds were planted in a standard loamy sand, LUFA Sp2.2. Immediately after sowing, the SC formulation containing 150 g/L Teflubenzuron was sprayed on the soil surface at one single concentration (limit test) corresponding to 120 g a.s./ha with water as the carrier (300 L/ha). Following application of the test item, the plants were allowed to emerge and to grow for 21 days following 50% emergence of the control plants under laboratory conditions. Soils were supplied with water or nutrient solution by glass fibre wicks. The test was performed in a growth chamber at a temperature of 22 ± 3°C and lighting of 13000 ± 2000 Ix (16 hours per day). At day 7 and 14 after 50% of the control seedling had emerged, a visual inspection was done. At day 21 the plants were counted, visually inspected and harvested to determine their shoot length and biomass (fresh weight). Steinberg nutrient solution was used instead of Hoagland solution as proposed by the draft guideline. The organic carbon content of the soil was higher than the recommended value and the number of plants per species and treatment level was reduced (30 - 32 instead of 40).

 

All calculations were based on nominal concentrations. Analytical verification of the stock solutions taken at the dates of application resulted in recoveries of 92.74 and 95.00%, respectively.

The test item had no significant effect on the emergence of the seedlings.

Brassica napus seeds did not emerge sufficiently. As a consequence, the emergence rate of 50% in the control vessels could not be reached. Therefore, a germination capacity test was performed with an older stock of seeds. The results showed an emergence rate of 91.1% after three days. Thus, the test with Brassica napus was repeated using the older stock of seeds.

Due to a miscalculation, the stock solution for the application on May 16, 2003 had a nominal concentration of 108.1 g a.s./ha instead of 120.0 g a.s./ha. Chemical analysis of the stock solution revealed a recovery of 92.74% of nominal, which corresponds to 100.3 g a.s./ha. Taking into account the mean spray application of 104.7% the actually applied amount of test item corresponds to 87.5% of the application rate of 120 g a.s./ha. Therefore, a repetition of the test concerning this application seemed to be not necessary.

At day 7, no effects on the six test species were observed. Some plants were obviously smaller than other ones or stopped growth at the cotyledon stadium. This occurred also in the control vessels. No effects could be observed after 14 and 21 days.

The shoot length and the biomass of all six species was not reduced in the test vessels treated with test substance compared to the control vessels. In the seedling emergence and growth test according to the OECD 209 the test item showed no significant effect on the emergence of the seedlings. Therefore the ER50 for all six plants were determined to be > 120 g teflubenzuron/ha, which corresponds to > 0.125 mg teflubenzuron/kg soil dw.

 

Conclusion

In the seedling emergence and growth test according to the OECD 209 the test item showed no significant effect on the emergence of the seedlings. Therefore the NOEC and the ER50 for all six plants were determined to be > 120 g teflubenzuron/ha, which corresponds to > 0.125 mg teflubenzuron/kg soil dw.