| Environmental Impact of Livestock Farming in Europe : Summary
Modern animal production is increasingly regarded as a source of solid,
liquid and gaseous emissions which can be both a nuisance and environmentally harmful.
Solid and liquid manure and waste water contain nitrogen and phophorus which are the most
important plant nutrients, but are harmful when applied to agricultural land in excess amounts
thereby leading to pollution of ground water by nitrates, surface water with phosphorous
(causing eutrophication) and soil with heavy metals such as zinc and copper which are used
as growth promoters in the feed stuff. A third group of potentially hazardous effluents are
drug residues, such as antibiotics, which may be present in the excreta of farm animals after
medical treatment and which are passed to the environment during grazing or spreading of animal
manure where they may conceivably contribute to the formation of antibiotic resistance in certain
strains of bacteria. The same risk arises when sludge and waste water from sewage plants
containing residues of antibiotics and other drugs from human consumption are discharged as
fertiliser in the soil and water body.
The most important aerial pollutants are odours, gases, dust, micro-organisms and
endotoxins, also called bioaerosols, which are emitted by way of the exhaust air
into the environment from buildings and during manure storage, handling and disposal
as well as grazing. More than 130 different gaseous compounds have been identified in
the air of animal houses, which are a major source of these pollutants. Aerial pollutants
can give cause for concern for several reasons. Firstly, there is strong epidemiological
evidence that the health of farmers working in animal houses may be harmed by regular
occupational exposure to air pollutants. Secondly, an animal's respiratory health may
be compromised by these pollutants. In some herds, half of all slaughter pigs may show
signs of pneumonia, pleuritis or other respiratory disease. In broilers, about 30% of the
birds which are rejected at meat inspection show lung lesions. The third reason for concern
is that aerial pollutants from livestock contribute to soil acidification (ammonia, NH3) and
global warming (eg. methane, CH4, nitrous oxide, N2O). For example, animal production emits
about 750,000 t of NH3 per year in Germany. About 20% of global methane production originates
from ruminants. Animal production systems which use straw release distinct higher amounts of
nitrous oxide than those employing liquid manure systems. Fourthly, particulate emissions,
such as dust and microorganisms, from livestock buildings may be a source of complaint from
people living in the vicinity of livestock farms. The travel distance of viable bacteria from
animal houses via the air is presently estimated at 200 to 300 m downwind; Mycoplasma species
may travel about 400 m. From epidemiological modelling and studies, we know that the virus
causing Mouth and Foot Disease can be transmitted over more than 75 km while in an airborne
state. Very little is known about the distribution characteristics of bioaerosols, such as dust
particles, endotoxins, fungi and their spores, in the air surrounding animal houses. Dispersion
models for these pollutants are lacking.
Table 1 summarizes our present knowledge of the impact
of emissions from livestock farming on farm livestock and
man and the distance over which the emissions may have effects.
Odours are relevant closer to animal houses only. Ammonia can act
directly on needles and leaves of trees close to sources where high
amounts are released. It also causes damage in the far environment by
overfertilizing soils and water and contributes to the decay of forests
(via acid rain). Indoors, ammonia is an irritant for the respiratory tract
of man and animal. Hydrogen sulphide is noticed as a prominent odourous compound
outside animal houses. Occasionally indoors it can be fatal to animals and man at
very high concentrations after the release of high amounts, e.g. when old liquid manure
is agitated. Methane and nitrous oxide contribute to the greenhouse effect, but do not
cause significant problems indoors. Little is known about the fate of dust, microorganisms
and endotoxins outside livestock buildings, although there is some concern that these
compounds may cause a nuisance to the population living in the vicinity of animal
enterprises, particularly in areas with high animal densities. Nitrate and its
product nitrite can cause pollution of ground and drinking water. The effects are
local and the impact on human health is low. Together with phosphate both nutrients
can enhance eutrophication of surface waters. Zinc and copper, which are increasingly
used as growth promoters instead of antibiotics in animal feed, are accumulating eg. in
pig liver and locally in soils and plants that then cause health problems in grazing sheep.
Not much is known about the fate of veterinary drugs such as antibiotics in the environment
which are excreted with the faeces. There is some concern that they may contribute to the
development of drug resistance in bacteria.
Livestock farming causes significant emissions such as nitrate, phosphate,
heavy metals and possibly antibiotics in manure and liquid effluents as well
as odour, gases, dusts, microoganisms and endotoxins in the exhaust air from
animal houses, from manure storage facilities, during application of manure and during grazing.
These effluents can have distinct impacts on air, water, soil, biodiversity in
plants, forest decay and also on animal and man.
There are indoor health effects on man and livestock
(ammonia, hydrogen sulphide, bioaerosols) and impacts on the local,
regional and global environment.
Odour, bioaerosols, ammonia, nitrogen, phosphorous and heavy metals may
either have a local or a regional inpact. Gases such as methane and nitrous oxide
contribute to global warming.
There is equally a lack of knowledge on the airborne transmission of
infectious agents such as virus and microorganisms between farms.
Little is known on the role of drugs such as antibiotics in the environment.
There is concern that these residues may contribute to the development of bacterial resistance.
Local and regional environmental problems are enhanced by high animal
densities, insufficient distances between farms and to residential areas.
1. Adequate and efficient feeding regimes are required with minimal wastage
of nitrogen and phosphorous and limited use of growth promoters.
2. The development of low emission production systems should be encouraged
including mitigation techniques, eg. biofilters, bioscrubbers, covered manure
pits and shallow manure application.
3. The administration of drugs has to be restricted to the
treatment of diseases only. The fate of the drugs in the environment has to be investigated.
4. There is an urgent need to establish safe distances between farms and to
residential areas to prevent transmission of harmful substances. This should become
an essential part of local and regional planning.
5. Environmental standards for animal production should be established
and applied to all European countries.
6. An environmental risk analysis is required to compare different
production systems and different regions in the world.
7. For the realization of these aims the cooperation of farmers,
agricultural engineers, veterinarians and governmental agencies is necessary.
This conference was funded by Deutsche Bundesstiftung Umwelt.
Much of the work described was funded by the Commission of the European
Union under Project No PL900703.
Supplementary funding was also received
from the Ministry of Agriculture, Fisheries and Food of Lower Saxony, Germany.
Table 1: Environmental impact from livestock sources