Determination of residue levels of alpha - chloralose in duck tissues

Alpha-chloralose (AC) is used to capture nuisance waterfowl so that they can be relocated. Concerns for food safety limit its use prior to or during the waterfowl hunting season. To determine its half-life in tissue, we administered AC to adult male (n = 7) and female (n = 5) mallard ducks (Anas platyrhynchos) via oral gavage. A gel capsule containing 100 μCi of radioactive AC (14C-AC) and sufficient nonlabeled AC to produce a dose of approximately 30 mg/kg was given to each duck.The ducks were euthanized at 2, 6, 10, and 18 hours postdosing (n = 3 per exposure period), and tissue samples were collected for radioactive analysis. Residues observed in edible tissues from ducks dosed with radioactive AC demonstrated a delayed uptake as the duck was under the anesthetic effects of the AC. Following the period when the ducks were unconscious, most of the AC was rapidly excreted from the body with mean half-life (t1⁄2) values of 9.0 hours, 9.8 hours, and 9.1 hours for breast muscle, liver, and skin, respectively. An approximation of total excretion (99%) was made by taking 7 times the t1⁄2, resulting in values of between 27 to 33 hours post-exposure. These results suggest that tissues from mallard ducks are safe for human consumption 48 hours after dosing, a period that is significantly shorter than the FDA-required 30-day withdrawal period. Key word: alpha-chloralose, disposition, ducks, human–wildlife conflicts, immobilizing agent, radio-labeled Removal or relocation of nuisance wildlife is a continuing problem that is being addressed by the U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Services Wildlife Services (WS). Humane removal or relocation of nuisance birds, such as Canada geese (Branta canadensis) and various species of ducks, continues to be a primary goal of WS. One tool available for the removal of these birds is an immobilizing drug known as alphachloralose (AC; Borg 1955, Belant et al. 1999). The drug is a chlorinated acetal derivative of glucose prepared by condensing chloral with pentose or hexose sugars in the presence of sulfuric acid. It has been in use as a human and veterinary anesthetic since the 1890s (Hanriot and Richet 1893). Although the specific mode of action of AC is not fully understood, it is assumed to cause depression of the cortical centers of the brain (Williams 1966, Lees 1972, Silverman and Muir 1993), but at low doses it also produces some hyperexcitability (Balis and Monroe 1964). In 1992, the U.S. Food and Drug Administration (FDA) granted WS permission to use AC under an Investigational New Animal Drug application to capture waterfowl (Anatidae spp.), pigeons (Columba livia), and American coots (Fulica americana). Sandhill cranes (Grus canadensis) and common ravens (Corvus corax) were allowed by the FDA at a later date (Woronecki et al. 1992, O’Hare et al. 2007). Widely used by the WS program to control pest populations of geese, such as Canada geese due to the absence of relevant excretion data, AC use is limited by a default moratorium for use 30 days before and during waterfowl hunting season. Birds captured within 30 days of or during open hunting season must either be euthanized or held in captivity for 30 days prior to release. An absorption, distribution, metabolism, and excretion (ADME) study conducted with radio-labeled AC is critical for generating data to determine a science-based use restriction period that protects food safety. If all AC derived residues are excreted prior to 30 days post dosing, it is likely that these data can be used to justify a reduction in the length of the pre-hunting season moratorium on AC 124 Human–Wildlife Interactions 8(1) use. Also, if AC residues never reach significant concentrations in edible tissues, it may be possible eliminate the moratorium. The objective of this study was to administer AC to mallard ducks (Anas platyrhynchos) and euthanize them at selected times post-dose and analyze edible tissues (breast muscle, liver, and skin) to determine residue levels. The data would be used to generate a half-life of elimination and to evaluate potential risk to humans from consumption of these tissues. Methods Test material The test material for this study was AC obtained from TCI Chemicals (CAS# 15879-933; Lot# AT01; Tokyo, Japan). The material was a mix of the alpha and beta isomers and had a certified purity of 89.7%. The radiolabeled AC contained only the alpha-isomer and was ubiquitously labeled on the glucose ring ([glucosyl-14C(U)]-alpha-chloralose; 283 mCi/ mmol; 99% radiochemical purity; Perkin Elmer, Waltham, Mass.). The beta isomer of chloralose does not have significant narcotic activity and does not contribute to the dose delivered to each duck.