Despite the fact that Doñana National Park has the highest legal protection status, pesticides from nearby agricultural activities jeopardise the reproductive success of several bird species. This has been demonstrated by a study conducted by the Institute of Environmental Assessment and Water Research (IDAEA-CSIC) and the Doñana Biological Station (EBD-CSIC). Researchers have detected 26 pesticides in eggs of 7 species of birds in Doñana in the period from 1999 to 2021. The researchers observed a change in the trend in the use of these compounds in agricultural areas around the park and warn that the combined effect of these pesticides reduces the reproductive capacity of the booted eagle (Hieraaetus pennatus).

The study, published in the journal Environmental Pollution, shows that, despite the fact that organochlorine pesticides have not been used for several decades (the use of DDT in agricultural practices has been banned in Spain since 1977), 96% of the eggs analysed had high levels of DDE, the most persistent metabolite of DDT. On the other hand, this ban has led to an increase in the use of other insecticides groups, such as pyrethroids. Precisely, fenvalerate, one of the pyrethroid insecticides analysed, has increased its presence in the eggs of birds in the park since 2013. In addition, the herbicides oxadiazon and oxyfluorfen have been detected for the first time in the most recent samples (corresponding to the 2021 clutches).

"Although we observed that levels of organochlorine pesticides have been decreasing over the years, they are still present in birds several decades after they were banned. In addition, we detected new pesticides, the long-term effect of which we do not know. For example, oxadiazon has been included in the list of pesticides banned by the European Union from 2022, which will require stricter control and monitoring measures," says IDAEA-CSIC researcher Ethel Eljarrat, lead author of the study.

Impact of pesticides

To assess the impact of these pesticides on bird reproduction, the EBD-CSIC researchers related hatching success (probability of at least one chick hatching from a clutch) and reproductive success (probability of at least one chick leaving the nest at the end of the breeding period) to pesticide levels in the eggs of two species of birds of prey: the black kite (Milvus milvus) and the booted eagle.

"The most worrying results are those of the booted eagle, whose hatching and reproductive success decreased with the concentration of the insecticide DDE and the fungicide hexachlorobenzene, respectively, as well as with the cumulative impact of multiple pesticides," describes EBD-CSIC researcher and co-author Fabrizio Sergio.

In addition, eggs from aquatic species were found to have three times higher levels of organochlorine pesticides than those from terrestrial species. "Differences in the diet of each species can lead to different exposure. For example, the black-bellied sandpiper feeds on fish and other aquatic organisms, which increases its exposure to pesticides," explains Andrea Peris, researcher at IDAEA-CSIC and co-author of the study.

The results highlight the importance of assessing the impact of pesticides in areas that, despite their protection, such as Doñana, are surrounded by potential threats, as well as the importance of including a wide range of pesticides. "Even if pesticide levels are apparently harmless individually, synergistic interactions between pesticides can occur that affect reproduction and have a negative impact on bird populations in the medium to long term," concludes Eljarrat.

This study is part of the project "Impacto de las actividades agrícolas en la fauna de los parques nacionales (APAN)", funded by the Ministry of Agriculture and Fisheries, Food and Environment in the framework of the National Research Call for National Parks in Spain (Convocatoria de Ayudas a la Investigación en materias relacionadas con la Red de Parques Nacionales, year 2017).

A. Peris, R. Baos, A. Martínez, F. Sergio, F. Hiraldo, E. Eljarrat. Pesticide contamination of bird species from Doñana National park (southwestern Spain): Temporal trends (1999–2021) and reproductive impacts. Environmental Pollution, 2023, 121240. DOI: 10.1016/j.envpol.2023.121240

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