Kendra Kimbirauskas
Sierra Club
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Portland, OR 97214
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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].
(Embedded image moved to file:
pic19169.jpg)
Snout route. Research shows that
veterinary pharmaceuticals can enter
the environment through barn dust,
putting livestock farmers at risk for
inadvertently inhaling these drugs.
image credit: Corbis
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 frame 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
newborns,
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'
health and determining their state of antibiotic resistance.
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