Agricultural Use of Pesticides in Galicia (NW Spain) During the 20th Century: Inventory of Active Substances and Their Geographic Distribution

Production of agricultural pesticides underwent an exponential increase during the 20th century. Many of these pesticides have since been prohibited because they are toxic and because they are bioaccumulated and persist in the environment. Detailed knowledge about any substance that is applied to land is essential to enable evaluation of potential contamination effects and the risk of latent exposure to these types of substances. However, accurate determination of the type and amounts of pesticides used throughout the history of agriculture in Spain is greatly complicated by the absence of historical records, scarce control of use and the lack of effective legislation until well into the 21st century. The aims of this study were: 1) to elaborate an inventory of the active substances of the agricultural pesticides (phytosanitary products) used in Galicia throughout the 20th century, 2) to develop a model of their geographic distribution by using a geographic information system (GIS), and 3) to contrast the geographical model obtained for selected persistent pesticides with the presence of these compounds in raw water. We consulted a large variety of sources of information and carried out a geographic analysis for the most commonly used pesticides in different crops. We inventoried a total of 176 active substances belonging to more than 50 different classes of chemicals and observed a clear geographic zoning according to the chemical class and mode of action of the substances. The presence of pesticide residues at drinking water extraction points is consistent with the geographic delimitation established in the study.