Risk Assessment of the Growth Inhibitor Bonzi with the Active Substance Paclobutrazol

Bonzi is a new plant growth regulator containing the active ingredient paclobutrazol of the triazole chemical class. Bonzi is for use on ornamental plants, such as Chrysanthemum, Perennial Plants, Bedding Plants, Foliage Plants, Geraniums, Hibiscus and Azaleas, in nurseries and greenhouses. VKM was requested by the Norwegian Food Safety Authority to consider the potential of Bonzi and paclobutrazol to induce reproductive effects in humans; in particular the relative sensitivity and relation between maternal effects and the effects on the offspring; and to what extent cleft palate observed in developmental studies in rat can be regarded as a specific teratogenic effect of relevance for humans. The risk assessment was finalized in a meeting in VKM’s Scientific Panel on Plant Protection Products on May 24. 2013. VKM’s conclusions are as follows: No adverse effect on fertility or reproductive performance was seen in rats. VKM concluded that the incidences of twisted snout observed in the F1 and F2 offspring of paclobutrazol treated rats are not likely to represent a developmental alteration, but rather an unspecific toxic effect. Marked maternal toxicity was seen in rats above 250 mg/kg bw/day, while partially ossified 7th cervical transverse processes and supernumerary 14th ribs were found in the offspring at 10 - 40 mg/kg/day. VKM concluded that the latter should be regarded as a direct teratogenic effect of paclobutrazol. Furthermore, VKM concluded that the data from the developmental toxicity studies are inconclusive regarding the effect on cleft palate development in rat foetuses. VKM proposes a NOAEL of 2.5 mg/kg bw/day for paclobutrazol based on a developmental toxicity study in rats.