IATP Hog Report - Institute for Agriculture and Trade Policy

Section 4
odorous and its emissions are low or negligible if farmers use enough
carbon-rich bedding to keep wet spots in the beds covered and maintain a
high carbon/nitrogen (C/N) ratio in the manure-bedding mixture. Carbon/
nitrogen ratios of 36 to one or greater permit carbon in the bedding to bind
ammonia nitrogen and prevent it from volatilizing. 9 Generally,
maintaining the top of the bedding pack in such a way as to provide a dry
and comfortable environment for the animals will be sufficient to maintain
a high C/N ratio and keep ammonia emissions negligible.
Odors associated with intensive hog production come from a mixture of
urine, fresh and decomposing feces, spilled feed, 10 and putrefying
carcasses. They are in the air ventilated from buildings where the animals
are intensively confined as well as in the air coming off liquid manure
storage structures and fields where liquid manure has been spread. This air
is distributed in the form of a plume that changes direction with the wind.
Endotoxins produced by bacteria found in the air inside the buildings also
may be present in the plume. 11
Most research on manure odors by land grant university agricultural
scientists has been directed toward developing and testing odor control
technologies for liquid manure handling systems. However, both scientific
evidence and human experience reveal that efforts to control odors are not
synonymous with addressing liquid manure's potential to create serious
public health problems.
Hydrogen sulfide is the most odorous of the manure gasses at low levels in
the atmosphere. At higher levels, hydrogen sulfide paralyzes the olfactory
senses but is still toxic. Manure gas accidents have demonstrated hydrogen
sulfide's ability to kill [see Part 2. Putting Lives in Peril, above].
Past thinking has been that if an exposure to hydrogen sulfide has not been
fatal, no bad effects linger. 12 Scientists now believe that even at low,
chronic concentrations, hydrogen sulfide is a potent neurotoxin and poses
a serious, irreversible threat to human health. According to one scientist,
"hydrogen sulfide poisons the brain and the poisoning is irreversible." 13
Hydrogen sulfide interferes with an enzyme necessary for cells to make
use of oxygen. 14 Neurological tests of residents living close to oil
refineries, another industry whose operations emit hydrogen sulfide, have
shown pronounced deficits in balance and reaction time, attention deficits,
and inability to process information quickly, "analogous to an outdated
computer program. It runs, but it is maddeningly slow and inefficient." 15
Dizziness, insomnia, and overpowering fatigue were reported by residents.
The dangers of hydrogen sulfide have been known for nearly three
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