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

Abstract

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.

Anticoagulant Rodenticide Toxicity to Non-target Wildlife Under Controlled Exposure Conditions

“…In highly detailed studies, Weir et al (2015) reported that brodifacoum administered orally (capsule) or applied dermally (neat material placed on dorsal surface and covered with an occlusive bandage) to Western fence lizards (Sceloporus occidentalis) did not evoke signs of intoxication at doses ranging up to 1750 mg/kg. Using similar methods, the acute oral median lethal dose for coumatetralyl exceeded 1750 mg/kg, for diphacinone the LD50 was ~1750 mg/kg, and for pindone the LD50 was estimated to be 550 mg/kg (Weir et al 2016). Thus, the LD50s for coumatetralyl, diphacinone, pindone and brodifacoum in Western fence lizards exceeded laboratory rodent values by one to two orders of magnitude.…”

“…6). The limited data for reptiles (Brooks et al 1998;Weir et al 2015Weir et al , 2016 does not permit a generalized sensitivity comparison to higher vertebrates.…”

Variability in the fundamental versus realized niches of North American mangroves

“…For each experiment, we used linear logistic regression to determine the 50% survival threshold in response to varying water and air temperature, with separate curves modelled for black and red mangroves from both BC and Florida. We chose a 50% threshold as it is widely used in the ecophysiology and toxicology fields to estimate population mortality rates after exposure to various abiotic stressors (Lagarto Parra et al, 2001;Randhawa, 2009;Weir et al, 2016).…”

The tissue distribution, metabolism and hepatotoxicity of benzoylurea pesticides in male Eremias argus after a single oral administration

“…The metabolic capacity of flufenoxuron in the tissues may be lower than that of diflubenzuron, which induced higher residua level at the end of exposure. Because of the lower metabolic rate of flufenoxuron, it may take longer for toxicity to occur in reptiles given the same dose (Weir et al, 2016). A previous study also suggested that the enhanced toxicity of flufenoxuron to Spodoptera littoralis compared with diflubenzuron may be attributed to its lower metabolism (Clarke and Jewess, 1990).…”