EASON,C.T. EASON MILNE1, L. etMILNE, al.: POISONING M. POTTS, RISKS G. MORRISS, WITH BRODIFACOUM G.R.G. WRIGHT and O.R.W. SUTHERLAND 219 Landcare Research, P.O. Box 69, Lincoln 8152, New Zealand E-mail: [email protected] 1Author for correspondence SECONDARY AND TERTIARY POISONING RISKS ASSOCIATED WITH BRODIFACOUM __________________________________________________________________________________________________________________________________ Summary: The field use of brodifacoum baits (Talon® and Pestoff®) to control brushtail possums (Trichosurus vulpecula) has increased in recent years. This has raised concerns of secondary and tertiary poisoning, resulting from the transfer of this toxicant through the food chain. In New Zealand, feral pigs (Sus scrofa) are known to scavenge possum carcasses and may also gain access to bait stations containing possum baits. We have determined the concentrations of brodifacoum in muscle and liver tissue from captive pigs after primary and secondary poisoning. Highest concentrations were found in the liver. Pigs eating 500 to 1776 g of brodifacoum bait containing 20 mg kg-1 had muscle concentrations ranging from 0.02 to 0.07 mg kg-1 and liver concentrations ranging from 0.72 to 1.38 mg kg-1 . Both appeared to be independent of the amount of bait eaten. Possums fed 400 g of bait had similar liver concentrations (0.52–1.20 mg kg-1). Pigs that had eaten the soft tissue from eight poisoned possums had brodifacoum concentrations of 0.32 to 0.80 mg kg-1 present in the liver and the concentration increased in a dose-dependent manner. Brodifacoum was detected in muscle from only one of these animals. In a preliminary field survey, 11 of 21 wild pigs sampled from areas where possum control had been undertaken were contaminated with brodifacoum concentrations in the liver ranging from 0.007 to 1.7 mg kg-1. In view of the potential impact on pig hunters and dogs consuming wild pig meat and offal, some restrictions on the wide-scale field use of brodifacoum baits appears to be warranted. __________________________________________________________________________________________________________________________________ Keywords: Anticoagulant; baits; non-target species; pigs; possums. Introduction possums is 0.17 mg kg-1 (equivalent to 20 g of bait containing 20 mg kg-1 for a 2–3 kg possum) Brodifacoum (3- [3-(4' - bromobiphenyl-4-yl) -1, 2, (Godfrey, 1985). However, because of the slow 3,4- tetrahydro-1-naphthyl] -4- hydroxycoumarin), is onset of action of brodifacoum, some possums will a potent, second-generation, anticoagulant eat more than 1 kg of bait before dying, which can rodenticide developed in the mid-1970s, which make the use of brodifacoum expensive compared causes concern because of its extreme persistence in with 1080 (Eason et al., 1994; Henderson et al., target and non-target species (Eason, Wright and 1994). Nevertheless, this toxicant can be cost- Batcheler, 1996). It has been used with success in effective when used after 1080, cyanide, or trapping, recent rodent eradication programmes on New to maintain possum numbers at very low levels. Zealand’s offshore islands to protect populations of During the last 2 or 3 years there has been an endangered indigenous birds (Taylor and Thomas, increasing use of cereal bait containing 20 mg kg-1 1993; Buckle and Fenn, 1992; Robertson, Colbourne brodifacoum (Talon® and Pestoff®) for killing and Nieuwland, 1993; Towns, McFadden and possums. The difficulties with using 1080, including Lovegrove, 1993). In addition to its world-wide use the increasing public concerns and the legal consents to control and eradicate rats, brodifacoum has also process and notifications required before using 1080, been used to eradicate rabbits (Oryctolagus are probably contributing to this increased user- cuniculus L.) from offshore islands (Merton 1987; preference for brodifacoum bait. Towns et al., 1993). It is now commonly used in This wide-scale field use of brodifacoum in New Zealand to control brushtail possums New Zealand is in itself unusual: in the USA and (Trichosurus vulpecula Kerr) (Eason et al., 1993). UK, the toxicant is used only for commensal rodent Brodifacoum differs markedly in its mode of control (A. Buckle, pers. comm.). Even this action when compared to the fast-acting toxins, such comparatively restricted use, around farm buildings, as sodium monofluoroacetate (1080) or cyanide, causes concern in regard to secondary poisoning of since possums may take 3 or more weeks to die after birds and mustelids (Duckett, 1984; Hegdal and eating a lethal dose of brodifacoum bait (Eason et Colvin, 1988; Newton, Wyllie and Freestone, 1990; al., 1994). The reported LD50 for brodifacoum in Colvin, Jackson and Hegdal, 1991). New Zealand Journal of Ecology (1999) 23(2): 219-224 ©New Zealand Ecological Society 220 NEW ZEALAND JOURNAL OF ECOLOGY, VOL. 23, NO. 2, 1999 The toxicology of brodifacoum and the species discussed alongside some preliminary data from at risk from primary and secondary poisoning in samples taken from feral pigs. New Zealand have been reviewed elsewhere (Eason et al., 1993; Eason and Spurr, 1995). The acute toxicity of brodifacoum in birds varies from an LD50 Method of <1 mg kg-1 in pukeko (Porphyrio p. melanotus Temminck) to >20 mg kg-1 in paradise shelduck Standard Pestoff® possum bait containing 20 mg kg-1 (Tadorna variegata Gmelin). In several species of brodifacoum and a fortified bait containing 100 mg mammals, including rodents, pigs and possums, the kg-1 brodifacoum were obtained from Animal Control -1 LD50 is < 0.4 mg kg . Because of its toxicity, all Products, Wanganui. Possums were captured from the vertebrates that eat baits or poisoned prey containing wild, housed singly in cages and fed cereal pellets brodifacoum residues are at risk, including humans. and vegetables with water available ad libitum. There are numerous documented cases of deliberate Domestic pigs (weighing between 17 and 28 kg) were or inadvertent poisoning of humans (Barlow, Gay obtained from a local breeder and penned in groups of and Park, 1982; Jones, Groew and Naiman, 1984; four on a concrete floor covered with straw. Pigs Lipton and Klass, 1984; Chong, Chan and Ho, 1986; were fed twice daily with weaner pig pellets Hoffman, Smilkstein and Goldfrank, 1988; Weitzel (Archers, Rangiora) and greens, and offered water et al., 1990; Wallace et al., 1990; Kruse and Carlson, ad libitum. This investigation was carried out with the 1992; Tasheva, 1995). For example, in one fatal approval of the Landcare Research Animal Ethics incident villagers in South Sumatra, Indonesia, used Committee. a 50 ppm brodifacoum rice grain bait as a food source. They attempted to remove the rodenticide by Primary poisoning of pigs repeated washing, rinsing, and cooking before eating the rice. Because of the delay in the appearance of Sixteen pigs held in captivity were divided into four symptoms, it appeared to the villagers that they had groups of four each. Group 1 received non-toxic been successful, thus encouraging others to eat the pellets; Group 2 were fed 500 g (± 31.2 g), Group 3 rice, resulting in several deaths (Tasheva, 1995). were fed 937 g (± 34.2 g), and Group 4 were fed To date there are no recorded incidents of 1776 g (± 81.4 g) of brodifacoum bait, respectively. humans being poisoned after eating contaminated All groups were fed the pellets over a 2-day period. meat. However, a risk exists which is compounded Pigs in the medium and high dose groups received by the unusual persistence of this toxicant and other between 5 and 200 g of fortified (i.e., 100 mg kg-1) second generation anticoagulants in vertebrate brodifacoum on the second day to elevate total species compared with first generation intake to the required levels and minimise the anticoagulants (Parmar et al., 1987), or most other within-group variation in the amount of brodifacoum xenobiotics which are usually excreted in a matter of ingested. The rationale for the dosages used is as hours or days (Eason, Bonner and Parke, 1990), follows. The published LD50 values for brodifacoum rather than weeks or months. For example, in pigs vary from 0.1 mg kg-1 (Godfrey, 1985) to brodifacoum has been shown to persist in the liver 0.5–2.0 mg kg-1 (Dublock and Kaukeinen, 1978). of sheep (Ovis aries L.) for 16 weeks (Laas, Forss Since possum baits contain 20 ppm (or 20 mg kg-1), and Godfrey, 1985) and possums for 9 months a 20-kg pig would need to eat 1 kg of bait to ingest 1 (Eason, et al., 1996), respectively. However, little mg kg-1 of brodifacoum, which would be consideration has been given to the potential dangers approximately equivalent to an LD50 dose. Half this to humans arising from brodifacoum residues in would be approximately an LD25 dose, and double possum carcasses, or to other wildlife, including this would be approximately equivalent to an LD90. game species. Pigs are one of a number of species Furthermore, these amounts could approximate the that may scavenge possum carcasses, and possums quantity of bait wild pigs might readily obtain if they dying up to 1 year after being exposed to sublethal fed directly from possum bait stations. Some of amounts of brodifacoum will contain residues, these would be expected to survive, and even those particularly in the liver, which could be transferred eating lethal amounts of bait could be hunted and through the food chain (Eason, et al., 1996). eaten prior to the toxicant taking effect. In this paper we report our findings on the All the pigs were humanely killed 5 days after concentration of brodifacoum in pig serum and they had started eating toxic bait, prior to the onset tissue (liver and muscle) after the primary poisoning of major clinical signs associated with anticoagulant and secondary poisoning of captive pigs.