10. Health Risks Associated with Pesticides in Soils

The world population is expected to grow 50% until 2050 to nine billion people which combined with sophisticated diet demands may double the world food demand until the mid of this century. Increasing food demand requires the intensification of agriculture, as there is very limited scope for expanding the global agricultural land area. Intensifying agriculture involves increase of soil fertility, the use of improved crop varieties as well as the more efficient use of plant nutrients and water. It also goes along with the more intensive use of pesticides that have significantly contributed to the increase of agricultural productivity and food supply. However, they are a source of concern because of human and environmental health side effects. Pesticides themselves do not directly contribute to better crop yields but help to control the potential losses caused by weeds, plant pathogens (fungi, viruses and bacteria) and animal pests (e.g. insects, mites, nematodes and rodents). On a world scale an estimated 35% of potential crop production is lost to pests, pathogens and weeds each year.

Pesticides are a broad group of biologically active chemical compounds used for pest management. The term “pesticide” is a composite term that comprises chemicals used to control or kill pests. In agriculture, this term includes herbicides (weeds), insecticides (insects), fungicides (fungi), nematicides (nematodes), and rodenticides (vertebrate poisons). It is estimated that there are roughly 2000 pesticides in commercial use worldwide. Assuming the trend of the past several decades will continue, pesticide production worldwide will be 2.7 times higher in 2050 compared to 2000.

The application of pesticides is often not very precise. Unintended exposures occur to non-target organisms in the general area where pesticides are applied. Part of the pesticides applied remain in the soil as so-called “bound residues” while other part is lost via vaporization, surface runoff or leaching to the groundwater following precipitation or irrigation. These losses may cause large-scale, long-term damage to the environment. Ecosystem impacts of pesticides include soil microorganism response, effects on natural enemies of pests and crop pollinators, domestic and wild animal response, and effects on human health. The dispersal of pesticides in the environment on the one hand depends on the chemical and physical properties of the compounds, such as molecular structure, water pressure, solubility in water, stability and adsorption properties. On the other hand, pesticide dispersal depends on conditions in the atmosphere (precipitation, wind, temperature, UV-radiation, moisture, particles), on soil (texture, structure, pH, adsorption capacity, biological activity, oxygen content, temperature, moisture, etc.) and water conditions (pH, biological activity, oxygen content, etc.).

Although the past decades have been characterized by efforts to reduce toxicity and to improve the effectiveness of pesticides through the use of new technologies and better information, this group of chemicals can severely affect animal and human health. Even low levels of exposure may have adverse health effects. Children are particularly vulnerable to the harmful effects of pesticides. Pesticide exposure can cause loss of coordination and memory, reduced speed of response to stimuli, reduced visual ability and altered mood. Some pesticides are known to disrupt hormones and reduce the ability to successful reproduction. Others have been associated with specific cancers or even death. The World Health Organization estimates that there are three million cases of pesticide poisoning each year and up to 220,000 deaths, primarily in developing countries.

A number of agronomic strategies and alternative control measures are available which in some cases can combat more than one weed, pest or disease. These measures can help reduce not only the current requirements for pesticides but also the buildup of resistance to pesticides. However, suitable decisions for the specific measures require deep knowledge of field conditions, crop rotations and pests.