New Zealand Journal of Ecology (2016) 40(3): 342- 350

Acute toxicity and risk to lizards of rodenticides and herbicides commonly used in New Zealand

Research Article
Scott M. Weir 1,5*
Shuangying Yu 1,6
Ami Knox 2,7
Larry G. Talent 3
Joanne M. Monks 4
Christopher J. Salice 1,8
  1. The Institute of Environmental and Human Health, Department of Environmental Toxicology, Texas Tech University, 1207 S Gilbert Dr, Lubbock, TX 79416, USA
  2. University Studies, Texas Tech University, 2500 Broadway, Lubbock, TX 79409, USA
  3. Department of Natural Resources Ecology and Management, Oklahoma State University, Stillwater, OK 74074, USA
  4. Science and Policy Group, Department of Conservation, PO Box 5244, Moray Place, Dunedin 9058, New Zealand
  5. Present address: Department of Biology, Queens University of Charlotte, 1900 Selwyn Ave, Mail Stop 1264, Charlotte, NC 28207, USA
  6. Present address: Department of Environmental Science and Chemistry, Queens University of Charlotte, 1900 Selwyn Ave, Mail Stop 1264, Charlotte, NC 28207, USA
  7. Present address: Research Integrity Office, Texas Tech University Health Sciences Center, Texas Tech University, Lubbock, TX 79409, USA
  8. Present address: Environmental Science and Studies, Department of Biological Sciences, Towson University, Towson, Maryland 21252, USA
*  Corresponding author

Invasive species can have negative consequences on native reptile populations, especially on island systems. Chemical control can be a cost-effective way to control or eradicate invasive species. Chemical control is currently in use in New Zealand to limit impacts of non-native mammals and plants on a range of native biodiversity. However, it is important to consider the potential non-target risks of chemical control to native species that are likely already significantly reduced in number. We aimed to characterise the toxicity of several rodenticides and herbicides to reptiles and to provide a screening-level risk assessment of these chemicals applicable to native reptiles of New Zealand using the western fence lizard, Sceloporus occidentalis, as a surrogate organism. We used the Up-and-Down testing procedure to estimate oral toxicity for all compounds. We tested five rodenticides (brodifacoum, coumatetralyl, pindone, diphacinone and cholecalciferol). Only pindone was toxic to fence lizards at concentrations below 1750 μg g–1 (LD50 = 550 μg g–1). We tested five herbicides (glyphosate, clopyralid, triclopyr, metsulfuron-methyl and haloxyfop-methyl) and one common adjuvant in glyphosate formulations (polyethoxylated tallowamine or POEA). Only triclopyr was toxic to fence lizards below 1750 μg g–1 (LD50 = 550 μg g–1). Toxicity does not necessarily imply risk. Using the pindone concentrations in accepted bait formulations in New Zealand, a 10 g lizard would need to ingest 4.7 g of pindone bait in a single day in order to achieve toxic levels, which is extremely unlikely. We used the highest acceptable application rate for triclopyr to estimate risk for reptiles and found minimal risk of acute toxicity from triclopyr applications. Taken together, our data suggest little risk of reptile acute toxicity from the tested rodenticides or herbicides in New Zealand, but research into sub-lethal effects is also required in order to make informed decisions about the ecological impacts of chemically controlling invasive species.