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1 Introduction to Agriculture and Pollution
Industrial activity has always resulted in pollution. But agriculture, for most of its history, has been environmentally benign. Even when industrial technology began to have an impact in the eighteenth and nineteenth centuries, agriculture continued to rely on natural ecological processes. Crop residues were incorporated into the soil or fed to livestock, and the manure returned to the land in amounts that could be absorbed and utilized. The traditional mixed farm was a closed, stable and sustainable ecological system, generating few external impacts.
Since the Second World War this system has disintegrated. Farms in the industrialized countries have become larger and fewer in number, highly mechanized and reliant on synthetic fertilizers and pesticides. They are now more specialized, so that crop and livestock enterprises are separated geographically. Crop residues and livestock excreta, which were once recycled, have become wastes whose disposal presents a continuing problem for the farmer. Straw is burnt since this is the cheapest and quickest method of disposal. Livestock are mostly reared indoors on grain and silage on farms whose arable land is insufficient to take up the waste.
Coincident with these changes, growing urbanization and population densities, coupled with increased affluence, have intensified the conflicts over land use. Urban populations have become reliant on agricultural catchments for their drinking water, are demanding uncontaminated food, and are increasingly valuing the countryside for attributes other than food and fibre production. Amenity, recreation and nature conservation are now important products of the countryside in their own right. Hiking, horse-riding, angling and camping are pursuits followed by millions. Thus, not only has the potential for contamination increased, so have the consequences, because of the greater value we now place on our environment.
Similar changes are beginning to occur in many parts of the Third World. The advent of new high-yielding cereal varieties as part of the Green Revolution, together with intensification of export crop agriculture, have resulted in a dramatic growth of pesticide and fertilizer use. Pollution problems are already apparent and are likely to grow in importance in the next few years. Although the use of the countryside for leisure is confined, at present, to a very few urban dwellers, many Third World countries are developing strong conservation movements among whose concerns are the effects of agriculture on wildlife.
The nature of pollution
At its most inclusive, the term pollution encompasses all unwanted effects of human or natural activities. According to this definition an unsightly farm building would be classified as āaesthetic pollutionā. However, in this book we use the term as more commonly and narrowly defined whereby a pollutant is a substance (e.g. a chemical compound or waste material) or an energy (e.g. noise) which produces unwanted effects. It is usual to restrict the term pollutant to substances or energies created by human beings while recognizing that, under certain conditions, natural processes generate āpollutantsā, for example the sulphur dioxide given off during a volcanic eruption. It is also useful to make a distinction between a contaminant, which is any substance or energy introduced by human beings into the environment, and a pollutant, which is a contaminant that is causing, or liable to cause, damage or harm.1
The primary environmental contaminants produced by agriculture are agrochemicals, in particular pesticides and fertilizers. These are deliberately introduced into the environment by farmers to protect crops and livestock and improve yields. Contamination is also caused, though, by the various wastes produced by agricultural processes, in much the same way as occurs in industry. The wastes comprise straw, silage effluent and livestock slurry, and, in the Third World, the wastes from on-farm processing of agricultural products such as oil palm and sugar. From the immediate environment of the farm contamination spreads to food and drinking water, to the soil, to surface and groundwaters and to the atmosphere, in some instances reaching as high as the stratosphere (Table 1.1).
Table 1.1 The principal pollution problems caused by agriculture
| Contaminant or Pollutant | Consequences |
| Contamination of water |
| Pesticides | Contamination of rainfall, surface and groundwater, causing harm to wildlife and exceeding standards for drinking water |
| Nitrates | Methaemoglobinaemia in infants; possible cause of cancers |
| Nitrates, phosphates | Algal growth and eutrophication, causing taste problems, surface water obstruction, fish kills, coral reef destruction; and illness due to algal toxins |
| Organic livestock wastes | Algal growth, plus deoxygenation of water and fish kills |
| Silage effluents | Deoxygenation of water and fish kills; nuisance |
| Processing wastes from plantation crops (rubber, oil palm) | Deoxygenation of water and fish kills; nuisance |
| Contamination of food and fodder |
| Pesticides | Pesticide residues in foods |
| Nitrates | Increased nitrates in food; methaemoglobinaemia in livestock |
| Contamination of farm and natural environment |
| Pesticides | Harm to humans; harm to humans; nuisance |
| Nitrates | Harm to plant communities |
| Ammonia from livestock and paddy fields | Disruption of plant communities; possible role in tree deaths |
| Metals from livestock wastes | Raised metal content in soils |
| Pathogens from livestock wastes | Harm to human and livestock health |
| Contamination of atmosphere |
| Ammonia from livestock manures and paddy fields | Odour nuisance; plays role in acid rain production |
| Nitrous oxide from fertilizers | Plays role in ozone layer depletion and global climatic warming |
| Methane from livestock and paddy rice | Plays role in global climatic warming |
| Products of biomass burning (cereal straw, forests, savannas) | Enhances localized ozone pollution of troposphere; plays role in acid rain production, ozone layer depletion and global climatic warming; nuisance |
| Indoor contamination |
| Ammonia, hydrogen sulphide from livestock wastes | Harm to farm worker and animal health Odour nuisance |
| Nitrogen dioxide from silage in silos | Harm to farm worker health |
The assessment of pollution
Pollution assessment is a complicated process. Ideally it requires an understanding of the components and linkages of a chain that stretches from underlying causes, through effects, to perceptions and costs (Figure 1.1). Once this is fully understood, it is then possible to seek out and implement appropriate preventative or control measures. But ...
