Kontaminationsrisiken durch Bewässerung

Summary

This study provides an overview of the contamination risks in agriculture arising from the use of irrigation water. Various water sources are used for irrigation: surface water, groundwater, drinking water, collected rainwater, desalinated seawater and treated or untreated wastewater. Common contaminants in water are pathogens from human or animal origin, heavy metals and a wide range of organic contaminants such as pharmaceuticals, cosmetics, detergents and pesticides.
Wasterwater is usually the cheapest and sometimes the only source of water that can be used for irrigation. Its use for irrigation is attractive, because it contains many plant nutrients. However, the elevated levels of organic contaminants, salts, heavy metals and pathogens also pose risks. Moreover, surface waters often contain a certain proportion of treated or untreated wastewater. Thus, wastewater may be used unconsciously for irrigation purposes.
The transfer of contaminants from irrigation water to agricultural products has been demonstrated in some cases. The risk of pathogen contamination is greatest for crops where the edible parts grow close to the surface (e.g. herbs, lettuce). Heavy metals have been shown to accumulate in soils and in crops. According to the World Health Organization, boron and cadmium are a particular threat. The accumulation of organic contaminants varies greatly from one substance to another, but depends also on soil quality and transpiration rate of the crop. Generally speaking, leafy vegetables have higher absorption potential than root vegetables, followed by cereals, fodder plants and fruit vegetables.
Most current guidelines for reducing risks associated with irrigation water address risks from pathogens. The most important measures include the reduction of contamination of water bodies, disinfection or purification of irrigation water, storage of water in ponds and adapted irrigation technology. Finally, the harvested products can be washed, peeled or cooked to reduce pathogen contamination. These measures can be expected to have a partial effect against other contaminants too, but there is need for further research. From a food safety point of view, pathogens pose the greatest risk. For many other contaminants (in particular cosmetics and pharmaceuticals), the primary exposition via direct application by far exceeds the potential levels resulting from contaminated crops. Nevertheless, their presence in food does not match consumer expectance, particularly for organic food, and such contaminants should also be monitored and minimised. As water demand in agriculture will continue to increase in the future, the risks posed by irrigation water must be monitored and further investigated.