Agriculture Reference
In-Depth Information
sheep, though their use is banned in the EU and
Australia. The macrolide tylosin is used in
swine, beef cattle and poultry.
Ionophores (e.g. monensin, lasalocid) are
antibiotics commonly fed to beef and dairy cattle
to increase weight gain and feed efficiency, and
to various species of poultry for control of coc-
cidiosis (Table 17.5). They have been used in
growing dairy and beef cattle since 1977, and in
lactating dairy cows in Canada since 1997 and
the USA since 2004. They are used in virtually
all beef feedlots in the USA and fed to 58% of
dairy heifers (USDA, 2007). Their use is not
allowed in the EU and Australia.
Most antibiotics are poorly absorbed from
the gastrointestinal tract so are largely excreted
via faeces (Sarmah
et al
., 2006). Chlortetra-
cycline and tetracycline were detected in ppm
(mg l
−1
) concentrations in swine manure leaving
the flush barn and in the holding pond (Zilles
et al
., 2005).
concentrations in soil for macrolides and
fluoroquinolones to nearly ppm (mg kg
−1
) for
tetracyclines (Kemper, 2008). While antibiotics
bound to soil are not prone to leaching and their
runoff can be controlled if erosion is controlled,
soil does act as a reservoir of pollutant that may
migrate to the aqueous phase over time. For
antibiotics that sorb tightly to soil, BMPs such as
buffer strips and sedimentation traps may be
especially effective in controlling loss (Smith
et al
., 1994; Chu
et al
., 2010).
Less tightly sorbed to soils are the iono-
phores, especially monensin (Lee
et al
., 2007).
Sulfonamides stand out for their relatively
low sorption potential (Sarmah
et al
., 2006),
and their soil concentrations are relatively low
(in the low ppb in soil). These are considered
relatively mobile in soil.
Degradation of antibiotics in manure and
soil is largely microbial (Sarmah
et al
., 2006)
and is influenced by temperature, rainfall and
soil properties. As with steroidal hormones,
degradation is faster under aerobic conditions
than anaerobic (Lee
et al
., 2007). The half-lives
of tetracyclines are in the order of weeks, while
monensin has a half-life of
Potential for runoff of antibiotics
following land application of manure
2 months in anaer-
obically stored manure. Once land applied,
however, monensin is rapidly degraded with a
half-life of 2-3 days (Lee
et al
., 2007). Tylosin is
rapidly degraded with a half-life in manure and
manure soil mixtures of days to weeks (Zilles
et al
., 2005; Sarmah
et al
., 2006).
Rainfall simulation studies with antibio-
tics directly sprayed on soil suggest that the
transport of different antibiotics in soil and to
runoff varies significantly (Kim
et al
., 2010).
Monensin was susceptible to runoff in the
aqueous phase, while tylosin and erythromycin
were most susceptible to runoff bound to sedi-
ment. (This report is not contradictory to the
common observation that tylosin is rapidly
degraded in manure, because the runoff was
collected following direct application of anti-
biotic to plots.) No sediment-bound sulfathia-
zole was found in runoff, and tetracycline and
chlortetracycline were found only in low con-
centrations in sediment-bound samples taken
at 5, 10 and 15 min into the rainfall event.
Instead, these three compounds were more
likely to be transported to subsurface soil.
Varying behaviour of different antibiotics in
soil will require different control practices to
prevent environmental contamination.
∼
The potential environmental impact of various
excreted antibiotics is affected by their relative
degradability and ability to sorb to manure and
soil particles (Sarmah
et al
., 2006). Many land-
applied antibiotics are polar compounds but not
highly soluble in water, so they become highly
sorbed to soil. For instance, tetracycline, oxytet-
racycline and tylosin bind tightly to soil and
are relatively stable if land-applied (Kemper,
2008). Soil concentrations are, therefore, usually
higher than in water, ranging from ppb (mg kg
−1
)
Table 17.5.
Approved ionophores for use in the
USA. Adapted from McGuffey
et al
. (2001).
Ionophore
Species approved
Laidlomycin
Cattle
Lasalocid
Poultry, cattle, rabbits,
sheep
Monensin
Poultry, cattle, goats,
lactating dairy cows
Maduramicin
Poultry
Narasin
Poultry
Salinomycin
Poultry
Semduramicin
Poultry
