Fate of Barbiturates and Non-steroidal Anti-inflammatory Drugs During Carcass Composting

With disease issues, the decline of the rendering industry, a ban on use of downer cows for food, and rules to halt horse slaughter, environmentally safe and sound practices for disposal of horses and other livestock mortalities are limited. Improper disposal of carcasses containing veterinary drugs has resulted in the death of domestic animals and wildlife. Composting of carcasses has been performed successfully to reduce pathogens, nutrient release, and biosecurity risks. However, there is concern that drugs used in the livestock industry, as feed additives and veterinary therapies do not degrade readily and will persist in compost or leachate, threatening environmental exposure to wildlife, domestic animals and humans. Two classes of drugs commonly used in the livestock and horse industries include barbiturates for euthanasia and non-steroidal anti-inflammatory drugs (NSAID) for relief of pain and inflammation. Sodium pentobarbital (a barbiturate) and phenylbutazone (an NSAID) concentrations in liver, compost, effluent and leachate were analyzed in two separate horse carcass compost piles in two separate years. Horse liver samples were also buried in 3 feet of loose soil in the first year and drug concentrations were assessed over time. In year one, phenylbutazone concentrations in the liver of the horse were undetectable (< 10 ppb) by 20 days of composting or burial in loose soil and were undetectable in effluent from the pile at the time of first sampling on day 6. Pentobarbital concentrations were undetectable (< 10 ppb) in liver samples retrieved from both the compost pile and loose soil by day 83. Rate of decay was faster in the soil, exponentially decreasing by 18% per day, with a half-life of 3 days, than in the compost pile where there was a 2% decrease per day and a half-life of 31 days, but occurred at the same rate of 1% and a half-life between 55 and 67 mesophilic degree days when calculated on the number of mesophilic degree days to which it was exposed. This suggests that breakdown of pentobarbital is not initiated by the heat of composting, but by the biological degradation that occurs in both soil and compost at mesophilic temperatures. Pentobarbital in the effluent decreased by 20% per day with a half-life of 3.1 days but was still detectable (0.1 ppm) at 223 days of composting. In year 2, phenylbutazone was not detected in any of the samples analyzed (compost and leachate) other than blood taken from the jugular vein of the horse immediately after euthanasia. Pentobarbital concentratoins in the compost were still detectable after 224 days of composting, but had decreased from 79.2 (initial) to 5.8 ppm. Pentobarbital in leachate was 2.2 ppm at day 56 of composting, after which no additional fluids leached into the leachate collection containers. Rate of decay in the leachate was 35.2% per day with a half-life of 1.6 days. When managed properly, composting will deter domestic and wild animals from scavenging on treated carcasses while they contain the highest drug concentrations providing an effective means of disposal of euthanized and/or NSAID treated livestock. The resulting compost contains either no or very low concentrations of both NSAIDs and barbiturates.