Fumigation of rabbit warrens with chloropicrin produces poor welfare outcomes - a review

Abstract

Chloropicrin (CLPN) is used in Australia and New Zealand as a warren fumigant for the control of exotic European rabbits (Oryctolagus cuniculus) but is no longer registered for this purpose in the United States or the European Union. This review summarises the mammalian toxicology and clinical records from 56 accounts where signs, symptoms and pathology have been related to a range of CLPN concentrations. The approach follows a general principle where an assessment of the humaneness of vertebrate pest control techniques should be firstly based upon a thorough synopsis of published behavioural, physiological and pathological impacts. Chloropicrin produces intense irritation by stimulation of trigeminal nerves and brief exposures to concentrations of ≤1 ppm can severely irritate the eyes and cause lacrimation in mammals. Beyond 8 ppm, exposures are reported to be painful and incapacitating in humans. Mammals experience an array of common signs and symptoms including: headache, nausea, diarrhoea, laboured breathing, decrease in spontaneous motor activity, salivation, rhinorrhea, blood stains around the nose and mouth, painful irritation of mucous membranes, profuse lacrimation, audible obstruction of respiration and distress vocalisation. Acute pathological changes from CLPN exposure can cause death in mammals from pulmonary oedema, bronchopneumonia, emphysema or general destructive changes and necrosis of the small and medium bronchi. Overall, the signs, symptoms and pathology arising from CLPN exposure at any airborne concentration beyond 0.3 ppm indicate that it must be assumed to cause suffering in all mammals. Exposure to CLPN that is not acutely lethal may debilitate rabbits and other species and cause a protracted death over hours or days. To produce a humane death a fumigant must be non-irritating, have an initial depressive action on the central nervous system and/or produce a rapid death without protracted distress while having little ability to cause debilitation or chronic injury. Given that CLPN has none of these characteristics, it cannot be considered to be acceptably humane.