Teflubenzuron

Toxicity to soil macroorganisms except arthropods

Description of key information

The short-term LC50 of the test item for soil macroorganisms except arthropods is considered to be > 1000 mg/kg soil dry weight.

Key value for chemical safety assessment

Short-term EC50 or LC50 for soil macroorganisms:

1 000 mg/kg soil dw

Additional information

One valid acute toxicity test with the test item according to OECD 207 on earthworms is available. Supportive information from one long-term toxicity study with the metabolites are summarized below, but not documented in separate IUCLID endpoint study records.

All presented studies were peer-reviewed during the assessment of teflubenzuron according to Council Directive 91/414/EEC (2007).

 

Key information

Shell (1991): Teflubenzuron: The toxicity of NOMOLT to the earthworm, Eisenia foetida, in a 14 day artificial soil test. Unpublished report, rpeort No. SRC45491, according to Draft Assessment Report (2007) according to Council Directive 91/414/EEC, crossreference: MCA 8.4.1/01

To assess the short-term toxicity of the test item to earthworms (Eisenia foetida) a 14-days artificial soil test according to OECD TG 207 was carried out. Adult earthworms with clitellum (2 months old, weighing 300 - 600 mg) were exposed to one nominal test item concentrations of 1000 mg a.s./kg soil dry weight (5 replicates of 10 worms per concentration and control). In parallel a positive control with chloroacetamide was performed. For the artificial soil test the substrate was made up of industrial sand, kaolinite clay, and sphagnum peat in the weight ratio 7:2:1, with a pH adjusted to 6 and a water content of 31%. The test temperature was 19.9 ± 1 °C.

The test compound was applied as milled suspension in deionized water. For each group, the dose was thoroughly mixed with the soil. After cleaning and weighing, 10 individual worms were placed on the soil surface of each test container. After seven days, the contents of the dishes were examined and the condition of the worms was recorded. Any dead animals were discarded. The soil in each dish was reweighed. After further seven days, the contents of the dishes were examined again and the number of live worms in each dish was recorded. The test item proved to be non-toxic to the worms at doses up to 1000 mg/kg soil dry weight.

The NOEC of the test item was set at 1000 mg a.s./kg soil dry weight, the highest dose tested. The LC50 for the test item was concluded to be > 1000 mg a.s./kg soil dry weight. In this study the mortality in the controls did not exceed 10% at the end of the test (measured: 2%). The validity criterion was met and, consequently, this study is considered acceptable for use in the risk assessment. The 7 and 14 day LC50 values for chloracetamide (positive control) were 36 mg/kg and 35 mg/kg respectively, which is in the agreed range.

In the Draft Assessment Report for teflubezuron according to Council Directive 91/414/EEC (2007) the 14-d EC50 of > 1000 mg a.s./kg soil dry weight is indicated as key value for the short-term toxicity of the test item to soil macroorganisms except arthropods. 

 

Supporting Information

The long-term toxicity of the metabolites CL 902374 (CFPU, 3,5-dichloro-2,4-difluorophenyl­urea) and CL 907373 (CFA, 3,5-dichloro-2,4-difluoroaniline) to earthworms was investigated in 56-day artificial soil study on Eisenia andrei (ECT, 2003).

For the supporting information no separate IUCLID endpoint study records have been prepared. For details please refer to the original Draft Assessment Report (DAR) Volume 3 Ecotoxicology for teflubenzuron according to the Council Directive 91/414/EEC, Volume 3 – B.9 (AS) (2007).

 

ECT (2003): Mixture of 3,5-dichloro-2,4-difluorophenylurea & 3,5-dichloro-2,4-difluoroaniline (Teflubenzuron metabolites): Reproduction toxicity to the earthworm Eisenia andrei. Unpublished report, according to Draft Assessment Report prepared in compliance with Council Directive 91/414/EEC, crossreference MCA 8.4.2/01

A mixture of 62.5% 3,5-dichloro-2,4-difluorophenylurea (CFPU, CL 902374) and 37.5% 3,5-dichloro-2,4-difluoroaniline (CFA, CL 902373) was used as test item. A stock solution was prepared by dissolving both metabolites in deionised water using an ultrasonic bath. This stock solution was used to produce the various test item solutions. Therefore clitellate adults (age: 2-12 months, fresh weight: 300-600 mg) were exposed to the test item for 28 days at concentrations of 0.08, 0.253, 0.8, 2.53 and 8.0 mg test item/kg soil (dw) mixed into artificial soil (based on OECD Guideline No. 222). Four replicates per concentration and control containing 10 worms per replicate were tested. The lowest concentration was specified underlying the calculated PEC_soil for teflubenzuron (0.48 mg a.s./kg) following single application of 120 g a.s/ha, the maximum recovery rate of the two metabolites in soil and the molecular weight ratio of the two metabolites in the parent compound. The worms were acclimatised in artificial soil under test conditions for at least 24 hours before start of the test. The temperature was 20 ± 2 °C and the photoperiod was 16/8 hours light/dark with an intensity at the substrate surface of 400-800 lx. The water content of the test substrate was checked weekly and losses of water were compensated. The worms were fed weekly with finely ground cow manure (5 g per test vessel). The test parameters were mortality, biomass development and effects on the morphology and the behaviour of the adult worms (28 days after application) and the reproduction rate (number of juvenile worms 56 days after application). The NOEC based on the comparison of the number of juveniles in the control and the treated vessels was determined by using analysis of variance followed by a Dunnett’s test.

No effects on behaviour or morphology of the adult earthworms were observed. All validity criteria of the guideline and the study plan have been fulfilled. The temperature was 18 – 21°C (recommended 20 ± 2°C), the photoperiod was 16/8 hours light/dark and the light intensity was 546 lx (recommended 400–800 lx). No mortality was observed in the control and all concentrations of the test item tested. There was no statistically significant difference in biomass development of indi­vidual adults and in the number of juvenile worms over 28 days between the control and any of the test item concen­trations tested. Therefore, the NOEC derived from this study was regarded to be ≥ 8.0 mg test item/kg soil (dry weight).

 

Conclusion

In the acute artificial soil test with E. foetida according to OECD TG 207 the 14-day EC50 of the test item was determined to be > 1000 mg a.s./kg soil dry weight, the highest dose tested. Supporting information of the toxicity on earthworms is provided by the 56-days study with the metabolites of the test item CL 902374 (CFPU) and CL 907373 (CFA). Eisenia andrei were exposed to a mixture of 62.5% CFPU (3,5-dichloro-2,4-difluorophenylurea) and 37.5% CFA (3,5-dichloro-2,4-difluoroaniline) at concentrations of 0.08 to 8.0/kg soil (dw). Since no toxic effects were observed the NOEC was estimated to be ≥ 8.0 mg test item/kg soil (dw).

Based on the most reliable study on the active substance the 14-day EC50 of the test item was determined to be > 1000 mg a.s./ mg/kg soil dry weight. This value is fully in line with the conclusion drawn in the Draft Assessment Report for teflubenzuron prepared according to the Council Directive 91/414/EEC, Volume 3 – B.9 (AS), 2007.