N,N''-(isobutylidene)diurea

Endpoint summary

Additional information

IBDU is used as a slow releasing nitrogen fertilizer and by thereby an exposure of the terrestrial compartment takes place. There are several studies available on the effects of IBDU to terrestrial organisms, comprising three trophic levels. Acute toxicity to Eisenia fetida was tested in a study according to OECD guideline 207. The 14d- LC50 value was 648 mg/kg soil (BASF AG 2001). Ma et al. (1990) studied long-term effects (20 y) on nitrogenous fertilizers usage on lumbricid earthworms in soil. This study revealed that, IBDU (2 applications per year of 180 kg N/ha = 216 mg IBDU/kg soil) had effects on earthworm numbers and biomass. However, the effects were attributed to the lowering of pH observed in parallel with IBDU application in the absence of liming. However, the aim of this study was to investigate the effects of various fertilizers using typical application rates and therefore IBDU concentrations that are rather promotive than inhibiting. In addition, due to the lacking control in this study, this test may provide strong backround evidence for assessing the long term effects of IBDU on one side, but is likewise inappropriate for the derivation of PNEC_soil on the other side.

No guideline studies are available on the toxicity of IBDU to plants. However, in two field studies the effects of IBDU application to plant growth/ flowering were studied. Both studies significantly show that IBDU is rather promotive than inhibiting to plant growth and flowering. I.e. no toxic response was noted in bermudagrass (Cynodon sp.) after application of up to 1900 kg IBDU/ha every week, whereas off-color was observed in Lolium perenne after 1 month of application of approximately 700 kg IBDU/ha (Volk and Dudeck 1976, approx. 4 months duration). With IBDU, applied up to 323 kg per ha to Boronia megastigma, toxicity did not occur (Reddy and Menary 1989, approx. 10 months duration).

Vertraete et al. (1974) studied the influence of different slow-release fertilizers on some natural soil microbiological populations and compared the effect to those of urea. The influence of the fertilizers was evaluated by applying the compounds at a low and at a high dose, corresponding respectively with the application of 173 kg N/ha and 1215 kg N/ha (222 and 1550 mg IBDU/kg wet soil). Of the populations studied, none were significantly inhibited, but stimulations were noticed with Fungi, and with ammonifying- and nitrite-forming microorganisms.

There are no data available on the long term toxicity to birds. However, due to the fact that IBDU is readily biodegradable and exhibits a low log Pow, it is highly unlikely that a secondary poisoning risk will occur by this substance. Therefore and for reasons of animal wellfare, the assessment of secondary poisoning of this substance will be based on mammalian data.

The application rate of 323 kg IBDU / ha, as derived from a long term study to plants (Reddy and Menary 1989), was used a NOEC in order to calculate the PNEC_soil. For the derivation of PNEC_soil this study is considered to be most relevant, since IBDU is traditionally used as a fertilizer. Furthermore, we consider this study to be more relevant than the Equilibrium Partitioning method, in which only toxicity tests on aquatic organisms are taken into account. However, due to it´s use as fertilizer, the hazard assessment for the terrestrial compartment should preferably be based on tests, conducted with soil organisms.