Agriculture Reference
In-Depth Information
crops. A variety of best management practices
(BMPs) are used by farmers to reduce nutrient
losses from their farms. Most states in the USA
provide significant cost-share funds or tax credit
programmes to support the implementation of
BMPs. Their implementation is seen as a key
component of strategies to reduce non-point-
source nutrient pollution. Common BMPs include
buffer strips, constructed wetlands and stream-
bank fencing.
One recent report suggests that with a
combination of BMPs implemented by a permit-
ted concentrated dairy farm, surface waters
downstream of the farm were no different from
upstream waters in terms of oestrogenic activity
(Shappell et al ., 2010). Maximum oestrogenic
activity in samples from farm tile drains
(£ 0.257 ng l −1 ) was twice as high as in the creek,
but were only 25% of the proposed 'no observa-
ble effect' concentration for E 2 . In many cases,
the effects of these BMPs on the fate of EDCs are
not known, but inferences can be drawn.
Constructed wetlands are marshes built to
treat sewage, stormwater, leachate and increas-
ingly, agricultural wastewater with the purpose of
removing BOD, nutrients, metals and toxic organic
compounds (Reddy and D'Angelo, 1997) and can
be a potential means of removing steroidal hor-
mones from agriculture wastewater. There are
hardly any studies evaluating the effect of con-
structed wetlands on steroidal hormone removal
but in a study with swine wastewater, oestrogenic
activity (measured with the in vitro E-screen assay)
was reduced by 83-93% with constructed wet-
lands and wetland outflow concentrations were
below 3 ng l −1 (Shappell et al ., 2007).
Buffer strips are narrow strips of a perma-
nent vegetative cover planted across a slope
along a waterway to reduce runoff of nutrients,
organic matter and pathogens from manure-
amended fields to water bodies. Few data are
available about hormone removal by buffer
strips, but (Nichols et al ., 1998) observed
reduced oestrogen mass loss from poultry-litter
amended pastures after using buffer strips;
reduction by 79%, 90% and 98% with buffer
strips of 6-, 12- and 18-m width.
Stream bank fencing is the most common
BMP to prevent the access of cattle to streams
and other waterways reducing direct deposition
of nutrients, pathogens and steroid hormones
in manure. This practice can have significant
negative economic impacts but researchers have
found that simply providing an alternative water
source will reduce the time cattle spend in
streams by up to 90%, even without fencing
(Sheffield et al ., 1997). While no data exist on the
effect of preventing or limiting access to water-
ways on steroidal hormone deposition in streams,
it is reasonable to expect a significant benefit.
One recent report suggests that with a
combination of BMPs implemented, oestro-
genic activity in surface waters downstream of
a large permitted dairy farm were no different
from in upstream waters (Shappell et al ., 2010).
Maximum oestrogenic activity in samples from
farm tile drains (£ 0.257 ng l −1 ) was twice as
high as in the creek, but were only 25% of the
proposed 'no observable effect' concentration
for E 2 . Because BMPs are so widely implemented
and represent a significant investment of public
funds, where effects on hormone fate are truly
unknown more research is merited.
Antibiotic Use in Livestock and the
Development of Antibiotic Resistance
Sub-therapeutic doses of antibiotics are fed to
livestock for growth promotion and disease pre-
vention and their use can reduce morbidity
and mortality (Wileman et al ., 2009). However,
the unintentional selection of bacteria that
are resistant to powerful antibiotics could have
important human health consequences, with
several studies noting identical resistance ele-
ments in both humans and food animals
(Boerlin et al ., 2001; van den Bogaard et al .,
2001; Lauderdale et al ., 2002; Ho et al ., 2010).
The use and environmental impact of antibiotic
use in food animals has been extensively reviewed
(Sarmah et al ., 2006). Some of the more com-
mon uses of antibiotics and their environmental
impact are summarized here with a focus on
sub-therapeutic and growth promotion uses.
The inclusion of oxytetracycline (a tetracy-
cline) and neomycin (an aminoglycoside) in milk
replacer for young calves is one of the most com-
mon uses of sub-therapeutic antibiotics in the
US and Canadian dairy industries. About 70%
of calves in the USA are fed milk replacer (USDA,
2007) and 80% of milk replacers used contained
antibiotics. Other tetracylines are used widely
for prevention of disease in poultry, swine and
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