Threats to soils and food security

There are a wide range of pollutants that have been added to soils over recent centuries and these can constitute a major problem for health and food security. Initial contamination came from various types of mining, such as for lead, coal and other minerals. These processes tend to accumulate large quantities of 'spoil'or waste in the countryside with high quantities of elements undesirable to humans and animals. In more recent years the Industrial Revolution has left behind a legacy of contaminated land. One of the consequent problems has been acid rain formed in the atmosphere as a result of factory chimneys passing into the atmosphere large amounts of sulphur and nitrous oxides. Acidified rainfall has acidified in turn many soils across northern Europe and North America. When soils become acidic, aluminium, a potential danger for human health, for example, can becomes more soluble in soils and can be leached into the waterways where it can cause serious damage to aquatic life.

In the last 50 years we have had further threats to our soils from two main directions. Firstly, in the years following World War II, farmers began to use much larger amounts of fertiliser, in fact up to 15 times the amount previously used. Usually less than 50 per cent of this was used by the crops, the remainder being washed, or leached, down through the soil into the water table and so to water courses where it has caused eutrophication, leading to death of fish and disruption to the aquatic ecosystem. The second example, again from farming, is the use of pesticides. These contain toxic compounds which can become resident in the soil causing a danger to soil organisms and the food chain. These compounds can also leach down to water courses where they lead to disruption of aquatic ecosystems, or even destruction. As science develops, these problems can be tackled, but the problems in the environment can be severe and represent a real challenge.The most worrying examples of pollution and contamination derive from the use of soils in landfill sites, for domestic and industrial waste. Organic based pollutants turning up in soils, such as PCBs (polychlorobiphenols), PAHs (polyaromatic hydrocarbons) and pathogens, are mainly associated with various industrial outputs and the chemicals used by the industries. There are many thousand synthetic chemicals used in industry and these can reach the soil by both direct and indirect means. Where such materials have been deposited, such chemicals represent a major threat to the use of soils. Their life cycle in soils is not well understood and their impact on future soil use is difficult to estimate. In the meantime a 'precautionary principle' should be adopted. While the more developed countries have begun to recognize the problem and to introduce measures to restrict its continuation, the same cannot be said of emergent economies such as those in Asia, where rapid population growth and industrial growth lead to great pressures and conflicts on the use of environment. Yet these are also countries where, due to the rapid population expansion, there will be a growing requirement upon soils to grow the food required.

Countries seek to be able to grow enough food to feed their population - termed 'food security'. However, all too often in the developing countries, the state of the soils is a concern with a gradual decline seen in the quality of soils as well a high rate of land degradation. Many farmers find themselves in a poverty trap, with insufficient funds to maintain the fertility of the land. As the fertility declines, so does the crop yield and hence the chance of food security. This issue must represent one of the greatest challenges for the future, with growing populations and food requirements, increasing land degradation, and the growing and very real threat of the effects of climate change. With falling soil fertility, the outlook for many peoples of the world in these areas is bleak. Although international organisations, such as the UN Food and Agriculture Organisation (FAO) are well aware of the problems, the scale is of such magnitude that there are major causes for concern in trying to halt the downward spiral towards ever increasing soil degradation, hunger and extreme poverty.