Agriculture Reference
In-Depth Information
are no provisions within the Safe Drinking
Water act to monitor or regulate antibiotics.
With respect to impacts on soil microorganisms,
sulfonamides were found to reduce enzymatic
activity and have a prolonged effect on micro-
bial community structure and diversity (Schmitt
et al
., 2005; Thiele-Bruhn and Beck, 2005;
Hammesfahr
et al
., 2008; Gutiérrez
et al
.,
2010; Toth
et al
., 2011). In contrast, chlorotet-
racycline was shown to have no effect on soil
respiration and bacterial community struc-
ture, which can be attributed to sorption of the
antibiotic to the soil matrix (Zielezny
et al
.,
2006). However, effects of sulfonamides were
only observed when soils were amended with
a C source (e.g. manure, glucose), which was
responsible for stimulating bacterial growth
and activity. This is an important implication,
as use of manure as a fertilizer source may not
only enhance the horizontal transfer of antibi-
otic resistance genes, but exacerbate the effect
of antibiotics on the soil microbial community.
As a result, there is great interest in under-
standing the effect of sustained applications of
antibiotic-containing manures on the long-
term health and function of agronomic soils.
Of additional concern is the ability of some
plant species to absorb antibiotics into their tis-
sues, creating another route for exposure of
humans to antibiotics (Kumar
et al
., 2005).
composting and anaerobic digestion (Sobsey
et al
., 2006; Martens and Böhm, 2009).
Windrow composting was shown to eliminate
Salmonella
in pig manure when temperatures
were maintained between 64° and 67°C for up
to 3 weeks (Tiquia
et al
., 1998). In a bench-
scale study,
E. coli
O157:H7 and
Salmonella
enteritidis
were not detected after 72 h of com-
posting at 45°C (Lung
et al
., 2001). In another
laboratory study, Grewal
et al
. (2006) reported
that
E. coli, Salmonella
and
Listeria
were not
detectable after 3 days in dairy manure mixed
with straw or sawdust and incubated at 55°C.
When cattle slurry was fed into a mesophilic
anaerobic digester for 24 days at an operating
temperature of 28°C, only moderate reductions
in
Salmonella typhimurium, Yersinia enteroco-
litica, L. monocytogenes
and
Campylobacter
jejuni
were reported (Kearney
et al
., 1993).
Pathogenic reductions, however, are generally
greater at higher temperatures used in thermo-
philic digesters (Lund
et al
., 1996; Burtscher
et al
., 1998). As an added benefit, anaerobic
digestion and composting have also been
found effective in significantly reducing the
level of VAs in livestock manures (Arikan, 2008;
Ramaswamy
et al
., 2010; Wu
et al
., 2011).
Summary
The sustainability of modern manure manage-
ment is far from certain, with many demonstrat-
ing significant limitations from the standpoint
of efficient use of manure resources and pro-
tection of environmental quality and human
health. As demonstrated in this chapter, for
manure management to be sustainable, a broad
array of issues must be considered and add-
ressed, all in the context of highly competitive
modern livestock production systems that
largely seek to minimize costs to the consumer.
In the past decade, there have been major inno-
vations in the areas of land application, manure
treatment and processing and in the science of
understanding the impact of manure manage-
ment. As a result, major opportunities exist to
improve the components of manure manage-
ment. To be sustainable, these optimized compo-
nents must work within the constraints of the
broader livestock production system.
Effect of manure treatment
technologies on pathogens
To reduce risk factors associated with the
land application of manures, various physical,
chemical and biological treatment technolo-
gies could be used to reduce or eliminate the
presence of pathogens (Heinonen-Tanski
et al
.,
2006). While there are advantages and dis-
advantages with these methods, some can
provide additional benefits, such as the produc-
tion of compost that can be used to enhance the
properties of agricultural soils (Tester, 1990) or
biogas for energy generation (Holm-Nielsen
et al
., 2009). As mentioned previously in this
chapter, there is a wide variety of technologies
available to treat livestock manures; however,
the only processes with a documented record
of cost-effective pathogen reduction are
