The synthetic pyrethroid bifenthrin is a third generation pyrethroid, which is used extensively for termite control in new housing estates in many other parts of the world. 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 today’s market. Bifenthrin can be dispersed from application via run off and dust and can contaminate local waterbodies where it may pose a threat to aquatic biota. For example, bifenthrin is one of the frequently detected contaminants present in stormwater wetlands across Greater Melbourne. This means that there is a high chance of bifenthrin being present in stormwater wetlands that support threatened growling grass frog (Litoria raniformis) populations.
This study aims to measure bifenthrin concentrations within a range of wetlands and creeks across Greater Melbourne known to support growling grass frogs (either currently or historically) and understand if these concentrations are likely to be toxic to growing grass frogs. Sediment samples were collected from a total of 17 sites in March and April 2021 and analysed for synthetic pyrethroids and metals. Results confirmed that 8 of these sites had bifenthrin present at levels that have the potential to be toxic to aquatic fauna including growling grass frogs.
In addition to the field study, water and sediment toxicity testing with bifenthrin was carried out with L. raniformis tadpoles. This presentation will discuss both the field concentrations on bifenthrin and the toxicity results of bifenthrin on L. raniformis tadpoles.