Seasonal-spatial survey of pesticides in the most significant estuary of the Iberian Peninsula – the Tagus River estuary

Abstract

Estuarine environments are being constantly pressured by new sources of pollution (e.g. new pesticides) derived from the activities of industry and intensive agriculture. The present study aim at quantify pesticides of three different categories (fungicides, herbicides and insecticides) in the Tagus River basin. Seasonal transition water samples were collected during 2010 and 2011, from seven sites distributed on both margins (north and south) of this estuary. Pesticides were subjected to solid phase extraction and then analyzed using gas chromatography coupled to tandem mass spectroscopy. Data showed that 95% of the analyzed pesticides were measurable in all samples, some being above the 2013/39/EU Directive levels (total loads ranged from 1.4 μg/L, in winter, up to 5.5 μg/L, in spring). Additionally, a panel of selected physicochemical parameters—linked with water quality standards, such as total phosphorous and total nitrogen—revealed high amounts close to the Trancão River mouth. Centered on the concentration addition and independent action models, a two-tiered approach was used to assess the risk of the pesticide mixture, at the maximum concentration found. This reflected the potential risk, mainly to fish. From the results, we conclude that legal quality standards are not being followed in this emblematic ecosystem and so there are risks to the biota. Hence, refined studies are required to identify both sources and impacts of the pesticides, and also to monitor preventive and depollution measures.