Many consumers are aware of the potential perils associated with eating products from animals treated with antibiotics and steroids. Concerns include the increase in antibiotic-resistant strains of bacteria, as well as unwanted human exposure to antibiotics and steroids in food products. Consumption of treated cow milk has been one controversial topic, along with the use of hormones in animal farming. Countries have regulations governing the use of veterinary medical products, along with other safeguards.
One veterinary medicine that has not been under scrutiny – until now – is antiparasitics. Benzimidazole medicines, such as flubendazole and fenbendazole, are used to treat intestinal parasites such as roundworms, tapeworms, and pinworms. Veterinary use includes in aquarium and fishery fishes, horses, cattle, pigs, sheep, poultry, dogs, cats, and other animals.
One criticism of flubendazole is that, while it kills parasites, its use may allow bacterial and fungal infections to escalate. It is poorly absorbed in treated animals (and humans), so that the intact compound is rapidly excreted in feces. Tests have been conducted to set limits on amount and duration of doses. Additionally, hens given flubendazole excrete this compound in their eggs for days after being treated; residues are also found in meat from treated animals. Fenbendazole may be carcinogenic at higher doses in rats, as well as having a few other physiological effects. It has been detected in cow’s milk, and use is limited by species-specific criteria.
As these antiparasitics pass fairly intact through the digestive system, the present study looked at pig manure and soil samples – both drugs were present after 102 days. In contrast, sulfonamide antibiotics rapidly broke down and could not be be extracted from samples.
Flubendazole was completely unchanged, while fenbendazole was slightly more degraded. Laboratory studies of these compounds found that it took about six months to break down half the amount of flubendazole, but only two months for a similar amount of fenbendazole. The application of this finding is long-term manure storage, where manure is kept in low-oxygen conditions. Clearly, storage of manure needs to exceed six months to ensure environmental exposure to these anthelmintics. Increased microbial activity – introduced with additional manure – speeds up the degradation process.
On the positive side, although these compounds are slow to break down, tests showed that they did not leach out of the clay soil tested, implying that they are not potential sources of groundwater contamination – at least in this type of soil.
