The synthetic pyrethroid bifenthrin is a type I, third generation pyrethroid, which is being extensively used for termite control in new housing estates in Melbourne. Bifenthrin has a very low solubility in water with a half-life of 7 days to 8 months. It has one of the longest residual termicide actions registered in the market today. Bifenthrin can be dispersed from these housing estates via dust and contaminate local waterbodies where it may pose a threat to aquatic biota.
This research investigates how bifenthrin is affecting the urban aquatic fauna including the threatened growling grass frog (GGF; Litoria raniformis) and dwarf galaxias (Galaxiella pusilla). Specifically, the study aims to identify the current bifenthrin concentrations within a range of wetlands and rivers across Greater Melbourne and understand if these concentrations are likely to be toxic to the aquatic fauna. A total of 17 wetlands/rivers were sampled for GGFs and 14 for dwarf galaxias in March/April 2021 and sediment samples were analysed for synthetic pyrethroids and metals. Results confirmed that 8 growling grass frog habitats and 6 dwarf galaxias habitats have bifenthrin and/or permethrin present in the sediments.
Toxicity testing with bifenthrin will be carried out with a related common frog species, the brown tree frog (Litoria ewingii), with the assumption that this species will react similarly to pyrethroids. This presentation will discuss the current concentrations of bifenthrin in growling grass frog and dwarf galaxias habitats and present initial toxicity results on the brown tree frog.