The risk of herbicides in groundwater

Chemical control in agricultural practice has a recent history, but it has increased greatly in the last few decades. At the end of the last century in Europe, copper sulphate was already being used to control broadleaved weeds in grass crops, but it is only since the 1950s that selective herbicides have been introduced onto the market. The enormous success of these products was an incentive for research and development and this led to a number of new herbicides belonging to different chemical classes being marketed. This was followed by a big expansion of the use of chemical products for weed control worldwide. In developed countries, herbicides are used on 85% to 100% of all main crops. In the 1994 Annual Index of Weed Abstracts, 333 active ingredients are listed, and about 200 of these are widely distributed and used all over the world.

Although the environmental risk from pesticides was recognised relatively early on, the occurrence of pesticides in groundwater was not detected until much later and the major concern was directed towards DDT and other persistent organochlorine compounds. This was due mainly to lack of knowledge about the important features of chemicals movement through the soil, and gave rise to the general misconception that less persistent pesticides could not leach into the groundwater under normal conditions. One of the first references to the discovery of pesticides other than chlorinated hydrocarbons in groundwater was by Richard et al. (1975). In the late 1970s, however, the number of detections increased rapidly, along with concern from public authorities about chemical contamination of groundwater.