Ecotoxicological hazard of metals, pesticides and pharmaceuticals in the Tagus river basin

Published On: May 9, 2019

A new study by the Ecotoxicology group

The occurrence and risks of organic and inorganic contaminants in the upper reach of the Tagus river basin is reported in the journal Science of the Total Environment. In this study, the Ecotoxicology group from IMDEA Water, in collaboration with the Water Quality analysis laboratory, evaluate prioritize individual contaminants and mixtures regarding their ecotoxicological risks, and assess the compliance of the measured contaminant concentrations with the Environmental Quality Standards (EQS) established as part of the European Water Framework Directive (WFD).

Pesticides and point source contaminants (primarily pharmaceuticals) were monitored in 16 sampling sites during spring, summer and autumn of 2016 using a grab sampling method. A qualitative screening analysis was performed using a library of 430 compounds, followed by a quantitative analysis based on LC-MS/MS for 52 organic compounds selected according to their toxicity, frequency of detection and potential use in the basin.

Additionally, several water quality parameters and metals were monitored. They used passive sampling devices (POCIS) to detect compound-specific exposure patterns and for comparisons with the conventional grab sampling method during the summer sampling campaign. Also, the study measured the variation of the different groups of chemicals as regards to land use and sampling season. The prioritization of organic and inorganic contaminants was based on the toxic unit (TU) approach, using toxicity data for algae, invertebrates and fish. Finally, the compliance with the Environmental EQS set as part of the WFD was evaluated for the quantified substances.

This study concludes that the land use characteristics had a large influence on the spatial distribution of the contaminants and other water quality parameters, while temporal trends were only significant for physico-chemical parameters, and marginally significant for insecticides. Acute toxicity is likely to occur for some metals (copper and zinc) in some sites. Low acute toxicity was determined for organic contaminants (individual compounds and mixtures) on the basis of grab samples. However, the assessment performed with POCIS samples identified diuron, chlorpyrifos and imidacloprid as potentially hazardous compounds.

Mixture toxicity

Several contaminant mixtures that may cause chronic toxicity were identified, which include insecticides and some pharmaceuticals (valsartan, paracetamol, naproxen). These mixtures are usually formed by a limited number of compounds (i.e, 5 or less), and their composition does not show a marked seasonal variation.


This study also shows that some metals and pesticides exceeded the water framework directive regulatory thresholds and that only 30% of the sampled sites had a good chemical status. These results indicate that further research is urgently needed to investigate chemical emission hot-spots and to reduce chemical contamination in the Tagus river basin.

The study has been published in two parts (Part 1 and Part 2) in the journal Science of the Total Environment.

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