Risk Assessment of the Insecticide/Acaricide Milbeknock with the Active Substance Milbemectin
Authors: Sverdrup Line Emilie , Bjørge Christine , Eklo Ole Martin , Grung Merete , Källqvist Torsten , Klingen Ingeborg , Låg Marit , Rivedal Edgar , Ropstad Erik , Øvrebø Steinar 
Published: June 2022

Milbeknock is a new insecticide/acaricide containing the new active substance milbemectin, which is a microbial fermentation product of Streptomyces. It is applied for control of mites and leafminers. The intended use is as a foliar spray in fruits (apples/pears), strawberries (only after harvest) and in ornamental plants growing in greenhouse and outdoors. The risk assessment was finalized at a meeting November 24, 2011, by VKM’s Scientific Panel on plant protection products (Panel 2). Panel 2 is in particular asked by the Norwegian Food Safety Authority to look at the following: 1) The human health risk for operators related to the properties of the active substance and the product. 2) The degree of oral absorption. 3) Acute toxicity. 4) The reproduction and developmental toxicity. 5) Establishment of reference values (ADI, AOEL and ARfD). 6) The fate and behaviour in the environment and environmental risk with regard to the  properties of Milbeknock and milbemectin. 7) Bioavailability of milbemectin. 8) The microcosm study. 

VKM Panel 2’s conclusion is as follows:  

Health: Panel 2 proposes to set the absorption to 50%, which is in agreement with the EU DAR report (propose 47%). For acute toxicicity, Panel 2 concludes that milbemectin probably has a LD50 for dogs between 100 and 200 mg/kg body weight (bw)/day. Dogs seem to be the most sensitive experimental species and should be considered for hazard classification purposes. With respect to reproduction and developmental toxicity, Panel 2 concludes that the documentation of the role of the P-glycoprotein transporter is not convincing, and that the CF1 mice study cannot be used to support the argumentation of no developmental toxicity put forward by the applicant. The following reference values have been estimated: ADI of 0.03 mg/kg bw/day; AOEL of 0.015 mg/kg bw/day and ARfD of 0.067 mg/kg bw/day for milbemectin. Provided that personal protection equipment is used, the AOEL for operators is not exceeded. 

Environment: With respect to environmental fate, the opinion of the Panel is that the relatively rapid degradation in soil indicates a significant bioavailability in both soil and water-sediment systems. Further it concludes that 0.058µg/L should be regarded as NOECpopulation for the microcosm study. Panel 2 concludes that there is a medium risk of toxic effects on aquatic organisms due to exposure of milbemectin sprayed in fruits with the proposed application regime, provided that a buffer zone of 30 meters to surface water is applied. There are minimal risks of toxic effects on aquatic organisms with sufficient buffer zones in other applied crops. Panel 2 further considers the risk for foliage dwelling non-target predators and parasitoids to be high, and the risk to earthworms to be medium. 

The strong sorption to soil suggests that the bioavailability in soil may be limited. However, the opinion of the Panel is that the relatively rapid degradation in soil indicates a significant bioavailability. Also, for a substance with such a high log Kow the reported water solubility is relatively high, which will contribute to the availability for biological uptake. The toxicity observed in the microcosm study indicates high bioavailability also in a water/sediment system.