Pesticides in sediments of the Ebro River Delta cultivated area (NE Spain): Occurrence and risk assessment for aquatic organisms.

Intense agricultural activities are performed in the Ebro River Delta (NE Spain) with extensive use of pesticides. Medium to highly polar pesticides have not been studied intensively in sediments despite its larger use in the recent years. This work aimed at assessing the occurrence of 69 pesticides, including medium to highly polar compounds, in sediments collected from drainage and irrigation channels of the Ebro River Delta during the main rice growing season. In addition, an environmental risk assessment was performed to evaluate the potential adverse effects to sediment-dwelling organisms with the risk quotient approach. A total of 24 pesticides were detected in sediments with bentazone and cypermethrin exhibiting high detection frequencies (79%) as well as high mean concentration levels (61.9 and 81.8 ng g-1 dw, respectively). Overall, the Alfacs bay, in the South of the delta, presented higher pesticide contamination than the Fangar bay, in the North. A similar pesticide distribution profile was observed in both bays, with oxadiazoles, organochlorines, pyrethroids, benzothiazinones and organophosphates as major, predominant classes. The presence of oxadiazon, pendimethalin and thifensulfuron methyl in the sediments may pose a moderate risk to sediment-dwelling organisms while bentazone, chlorpyrifos, and cypermethrin exhibited a potential high risk. Thus, the importance of the inclusion of medium to highly polar pesticides in the analysis of sediments is emphasized since some polar pesticides such as bentazone, imidacloprid, and thifensulfuron-methyl have been detected at concentrations that may pose a risk to aquatic organisms. Moreover, the co-occurrence of pesticides may potentially pose a high risk to sediment-dwelling organisms in 13 out of the 14 investigated locations. Finally, it could be concluded that the risk derived from the presence of pesticides in sediments must be assessed since some pesticides not detected at concerning levels in water, may pose a moderate/high risk in the sediments.

Occurrence and risk assessment of pesticides in a Mediterranean Basin with strong agricultural pressure (Guadiana Basin: Southern of Portugal).

The study aimed to assess the occurrence and the environmental risk of a group of 51 selected pesticides in the Guadiana Basin (a biodiversity hotspot, in the Mediterranean). The most abundant pesticides were bentazone and 2,4-D, while terbuthylazine together with terbutryn constituted the most ubiquitous pesticides. Eighteen out of the 38 pesticides detected are no longer approved in Europe, and 5 of them are included in the list of priority substances. The risk assessment showed that azinphos ethyl, diflufenican, irganol, imidacloprid, and oxadiazon occurred occasionally, but always in concentrations above their respective ecotoxicological threshold value. Contrary, bentazone, terbuthylazine, and terbutryn presented a high risk in most of the sampled locations and periods. The site-specific risk assessment showed a spatial and temporal pattern, with a higher risk occurring mainly in intermittent streams, in the drought period. The presence of pesticides banned from the EU market since 2009 showed the importance of improving the monitoring process, to identify the main sources of pollution and the fate of these emerging compounds. The results showed the need of implementing actions to improve the sustainable use of pesticides in agricultural areas, working with farmers and management entities to reduce the contamination of aquatic ecosystems. Transboundary water governance is also required to solve potential transboundary contamination problems.