Livestock drugs infiltrate dust: another hazard for farmers.

Recent research has investigated how human and veterinary drugs enter the environment at subtherapeutic concentrations and what the downstream effects of this contamination may be. Now German researchers led by Gerd Hamscher of the Hannover School of Veterinary Medicine have documented a new route of entry for veterinary drugs into the environment, and they cite a new potential risk for people who spend long periods inside enclosed animal buildings: inhaling residues of antibiotics in the dust in such buildings [EHP 111:1590-1594].

Antibiotics are given to livestock to preempt disease, treat outbreaks of illness, control the spread of infection from sick to healthy animals, and promote growth. Large-scale use of antibiotics in pig production is widespread within the European Union and the United States, although its use in the European Union is now restricted to treating and containing infection.

The researchers used tandem mass spectrometry to retrospectively analyze dust samples taken from a 350- to 420-head pig-fattening farm from 1981 to 2000. Dust was collected using a metal sampling flame placed 1.5 meters above the floor, the typical breathing height of humans. From the 10-15 samples collected inside the building each year, the researchers randomly selected 1 for analysis. The dust particles originated primarily from the animals' feed and dried feces and urine.

In 18 of the 20 samples analyzed, as many as 5 different antibiotics were detected at levels of 0.2-12.5 milligrams per kilogram (mg/kg) dust. Tylosin occurred in 16 samples, reaching a top concentration of 12.18 mg/kg. Sulfamethazine was present in 13 samples at levels up to 2.9 mg/kg. Several tetracyclines appeared in 12 samples at concentrations of 0.2-5.2 mg/kg. Both tylosin and sulfamethazine can cause allergic reactions in susceptible people, and the European Union banned tylosin as a feed additive in 1998. Chloramphenicol was detected in 3 samples at concentrations of 2.0-9.1 mg/kg. Chloramphenicol is capable of causing severe side effects in humans, including in rare cases aplastic anemia and gray baby syndrome (another name for chloramphenicol toxicity in new-borns, the often-fatal result of giving newborns the drug for bacterial infection). The compound was prohibited in farming in 1994, Hamscher says, because of its potential to damage DNA. Neither tylosin nor chloramphenicol were found in samples taken after their respective bans.

Pharmaceuticals have been detected in rivers and groundwater at parts-per-billion levels ranging up to several micrograms per liter. In contrast, says Hamscher, these dust samples yielded relatively high drug content for an environmental sample--in the parts-per-million range, representing concentrations approximately three orders of magnitude higher.

Other studies have shown that chronic exposure to subtherapeutic concentrations of antibiotics is optimal for the development of resistance. Furthermore, the same allergenicity risks posed by consumption or injection of antibiotics may also occur through inhalation. No acceptable daily intake has been established for drugs inhaled via dust.

Because of the potentially harmful effects of inhaling antibiotic-laden dust, the study authors conclude that the use of antibiotics in farm animals should be reduced when possible. They also say further investigation with more frequent sampling rates is needed of the dust in larger pig operations (this facility was relatively small) as well as hen houses, where the potential for dust production is even higher than in pig houses. Future research on the risks to farmers of breathing dust laden with microorganisms and allergens should also examine antibiotic residues and their impact. Such investigations should include monitoring farmers' environment health and determining their state of antibiotic resistance