At the request of the Minister for the Environment, the NSW Chief Scientist & Engineer commissioned an independent Human Health Risk Assessment (HHRA) for the Lord Howe Island’s proposed Rodent Eradication Program.
The HHRA looked at a number of potential exposure pathways – human interaction with the bait, including exposure through soil, air (dust), sediment, surface water, tank water as well as food sources such as seafood and locally grown fruits and vegetables.
Potential risks from these pathways were then considered for those most sensitive, which included toddlers, school children, pregnant women and adults spending large amounts of time outside.
According to the recent Visitors Survey (2016) the World Heritage values of Lord Howe Island are the 2nd highest motivation (behind escape to a remote island) visitors give for visiting; with beautiful scenery and natural environment the top ranking associations visitors have with the Island.
Tourism is the largest industry on Lord Howe Island, with the dramatic scenery and natural environment, along with its world heritage status, playing an important part in visitors experience and linking the maintenance of those world heritage values inextricably to future tourism.
Base on this association, the LHIB undertook an Economic Evaluation (Gillespie Economics) comparing proceeding with the REP to continuing with the current rodent control.
The potential impacts to non target species and the environment arising from the REP were extensively assessed through the various environmental approval documents and processes.
- Pollution of soil, air or water
- Mortality of non-target species due to primary poisoning from consumption of bait pellets
- Mortality of non-target species due to secondary poisoning from consumption of poisoned rodents, fish or invertebrates
- Bird strikes and collisions from helicopter activity
- Disturbance from helicopter activity
- Potential impacts as a result of handling and captive management during the captive management program
- Long term changes to ecological relationships affecting threatened species following the eradication of rats, mice and owls.
Based on evidence from similar eradications around the world, studies done on LHI, the physical and chemical properties of the bait and toxin and the relatively small quantity used in a one-off eradication, the risk to the environment and most species from the REP was shown to be very low.
Potential impacts to the marine environment were extensively considered as part of the approval process for the project. All marine impacts by the LHI REP were deemed minimal with appropriate controls in place. A key control was that no bait were to be intentionally applied to the marine environment.
For successful eradication, all terrestrial habitats which may harbour rodents must receive bait, including smaller islands, ocean cliffs and islets. When brodifacoum pellets are applied aerially to these areas in attempts to eradicate rodents it is often the case that a small quantity of bait may enter the marine environment near the shore. Studies on other island eradications have shown that the small amounts of bait that enter the water disintegrate quickly, particularly in areas with high wave action. The low-moderate application rate of brodifacoum (0.4 g/ ha) for the LHI REP, low solubility, high dilution factor in the marine environment and one off eradication mean that any sea water contamination would be of a sufficiently low magnitude as to not present a significant risk to marine life or humans through any activity (including swimming or snorkelling).