Increasing incidence of barbiturate intoxication in avian scavengers and mammals in Spain

    Barbiturate exposure poses an increasing risk of secondary intoxication for scavengers, which points out the need of a correct carcass disposal after euthanasia.


    Currently, pharmaceuticals are considered emerging contaminants with a constated impact in wildlife. Among them, euthanasia agents are commonly used in veterinary medicine, and specially barbiturates.

    Scientists from the Research Group in Wildlife Toxicology of the Instituto de Investigación en Recursos Cinegéticos (IREC – CSIC, UCLM, JCCM), in collaboration with the Environmental Research Institute of the University of the Highlands and Islands (United Kingdom), have studied the occurrence of barbiturate intoxications in wildlife and domestic animals from 2004 to 2020 in Spain corresponding to 3210 suspected intoxicated animals analysed.

    From the total intoxicated animals diagnosed, barbiturate exposure was observed in 3.4% (45/1334). The incidence of intoxication of this group of chemicals has increased in the last years in Spain, which suggests that barbiturates used in euthanasia can pose an increasing risk for scavengers if the carcasses of these animals are abandoned in the field or in dumps.

    The Eurasian griffon vulture was the avian scavenger most affected by barbiturate intoxications in Spain.

    Pentobarbital was the most frequently detected barbiturate (42/45, 93.3%), but we also detected phenobarbital, barbital and thiopental (2.2% each). Avian scavengers were the group of species most affected by barbiturate intoxication (n = 36), especially the Eurasian griffon vulture (Gyps fulvus) (n=28). This compound was also detected in other avian scavengers including the Egyptian vulture (Neophron percnopterus), the cinereous vulture (Aegypius monachus) or the red kite (Milvus milvus). In addition, pentobarbital was detected in vomit from a Spanish imperial eagle (Aquila adalberti) which recovered after a long-time treatment in the “El Chaparrillo” Wildlife Rehabilitation Centre (Ciudad Real).

    At least two big intoxication events affecting griffon vultures were linked to consumption of previously euthanized livestock. One of these events affected 8 griffon vultures, which were found dead showing pentobarbital residues in gastric content and liver, in addition, the tissues the euthanized foal also presented pentobarbital residues. Most of the intoxication cases in griffon vulture were detected in Navarra (67.9%). This suggests that a greater effort is needed in Navarra and other regions to control the disposal of carcasses containing residues of this pharmaceutical in order to prevent potential secondary intoxications.

    Sample distribution in the present study and barbiturate prevalence by regions. Numbers correspond to animal species of intoxication cases. 1: Griffon vulture, 2: Egyptian vulture, 3: Cinereous vulture, 4: Eurasian buzzard, 5: Red kite, 6: Spanish imperial eagle, 7: Red fox, 8: Stone marten, 9: European badger, 10: Red squirrel, 11: Wild boar, 12: Domestic dog.

    This study points out the need of the reinforcement of barbiturate use regulation to avoid secondary intoxications in wildlife, especially regarding the carcass disposal after euthanasia.

    The scientific publication of this research is available at: