Pesticides and nitrates in groundwater from oriziculture areas of the ‘Baixo Sado’ region (Portugal)

Abstract

The aim of this study was the groundwater evaluation to pesticide compounds and nitrates in oriziculture areas of the ‘Baixo Sado’ region (Portugal), based on their use, predictive approaches, and field and laboratory work. One or more of the pesticide compounds analysed (chlorfenvinphos, cycloxydim, 3,4-dichloroaniline, endosulphan, MCPA, molinate, oxadiazon, profoxydim, propanil) were detected in 62% of 171 water samples collected from 22 wells used for public supply, domestic supply, and irrigation, during 2002 and 2003. From the total samples, 6% presented maximum concentration levels of at least one of the compounds above 0.1 µg L−1. Mixtures of pesticide compounds were observed in 25% of the total groundwater samples, with up to five substances being detected in each one. The concentration sum of all was above 0.5 µg L−1 in four water samples. All the analysed compounds, with the exception of the insecticide chlorfenvinphos, occurred in groundwater. Molinate was the most frequently detected (55%), particularly with maximum concentration levels above 0.1 µg L−1. Detection frequencies were higher in water samples collected from irrigation wells (78%). Groundwater exposure to total pesticides and nitrates was analysed. Maximum concentration levels were 59.6 µg L−1 and 183 mg L−1 respectively. A seasonal variation pattern could be observed for both parameters in water samples collected from some wells. The results from this study show that sustainable use of pesticides and nitrogen fertilizers is required in order to achieve an overall contamination reduction from these compounds in the aquatic environment.