The accumulation of pesticides (insecticides, pesticides, fungicides), used in agricultural crops in the Doñana environment, is reducing the reproductive capacity of the booted eagle, a medium-sized raptor with a wingspan of about 120 centimeters, characteristic of the park of this park. This has been verified by a CSIC study based on the analysis of the number of eggs that did not prosper and the monitoring of specimens that managed to fly, which were correlated with the levels of the polluting compounds found.
This study concludes that the reproductive success of this species and the hatching of the eggs have decreased due to the high presence in the food chain of organochlorine pesticides, whose high concentrations continue to occur despite the fact that they have been prohibited for decades.
Scientists have detected 26 different types of pesticides in 130 egg samples of 7 bird species tested, including the black kite and white stork, in the period from 1999 to 2021.
The pesticides used in agriculture reach the park through the water, are concentrated in the sediments and enter the aquatic food trophic chain, so that when a bird comes to feed, it ingests them, and then accumulates in its body. before transferring it to the egg.
Contaminants retained in sediments can take decades to break down.
Experts detect the presence of organochlorine pesticides, such as DDT - and to a much lesser extent, hexachlorobenzene or lindane, substances that were banned decades ago. DDT has been banned in Spain since 1977; but 96% of the eggs tested had high levels of DDE, the most persistent metabolite of DDT.
The study was made from the analysis of the eggs that failed to hatch (and which are collected in the nest review that biologists do every spring). On the other hand, live specimens are not analyzed, since as they are protected species, they are not sacrificed to be analyzed.
“What we have observed is that although levels of organochlorine pesticides have dropped in recent years, they are still present in birds decades after their ban; and they are, in any case, the compounds that present the highest levels of contamination of all pesticides”, says Ethel Eljarrat, a researcher at the Institute for Environmental Diagnosis and Water Studies (IDAEA) of the CSIC.
Likewise, they detected substitute insecticides for organochlorines (pyrethroids), which shows that these compounds also bioaccumulate (compared to what was thought); its levels have been increasing in the eggs of the park's birds since 2013 as they are used more and more, adds Ethel Eljarrat.
Finally, "new pesticides were found that until now had not been reported in bird samples and whose long-term effect we do not know", such as the herbicide oxadiazon, included in the list of pesticides prohibited by the EU as of 2022, "for that it will be necessary to implement stricter control and surveillance measures”.
For its part, the high presence of DDT derivatives could be related to the increase in fraudulent use of this product in 2007 and 2008 in the Doñana area, while the use of hexachlorobenzene and lindane has subsided.
The study on the impact of pesticides on bird reproduction focused on two species of raptors: the booted eagle and the black kite.
To do this, the EBD-CSIC researchers correlated hatching success (probability that at least one chick is born from a clutch) and reproductive success (probability that at least one chick leaves the nest at the end of the reproductive period) with pesticide levels in the eggs of these species of birds of prey.
Thus, it was seen that in the case of the booted eagle, hatching and reproduction success decreased either due to the presence of DDT or due to the presence in some cases of hexachlorobenzene and also when the cumulative effect of all the compounds is seen.
"The most worrying results are those of the booted eagle, whose hatching and reproduction 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 Fabrizio Sergio, the researcher at the Station. Biologica de Doñana (EBD), center of the Higher Council for Scientific Research.
In this case, 31 samples were analyzed, collected between 2010 and 2021. This correlation was not observed in the case of the black kite (46 samples).
Another conclusion is that birds that feed in the aquatic environment have higher levels of contamination than those that have a mixed diet of food obtained in the aquatic and terrestrial environment.
The eggs of aquatic species had levels of organochlorine pesticides three times higher than those of terrestrial species.
“Differences in the diet of each species can lead to a different exposure. For example, the black-billed moth feeds on fish and other aquatic organisms, which increases its exposure to pesticides”, explains Andrea Peris, IDAEA-CSIC researcher and co-author of the study.
The results highlight the importance of evaluating the impact of pesticides in areas that, despite their protection, such as Doñana, have been surrounded by potential threats, as well as the importance of including a wide range of pesticides.
"Even if the levels of pesticides are apparently innocuous individually, synergistic interactions between them can occur that affect reproduction and have a negative impact on bird populations in the medium and long term," concludes Eljarrat.
“The problem of organochlorine compounds has not been resolved due to their great persistence in the environment, but their levels are gradually decreasing. However, the new compounds that are being used are even more worrisome if possible; some are increasing and to this day we do not know what effects they may cause in the medium and long term in bird populations” says Eljarrat.
“In any case, we are paying the consequences for the lack of control over the substances that are put into the environment. If we continue to favor the entry of dangerous substances into the natural environment without control, if they are later shown to be toxic and you ban them later, we will have to wait again 30 or 40 years to solve the problem that you have created”, argues Eljarrat.
Even if the levels of pesticides are apparently innocuous on an individual basis, "synergistic interactions can occur between them that affect reproduction and have a negative impact on bird populations in the medium and long term," adds the researcher.
The damage on reproductive success has not only been seen for organochlorines, but also for the sum of all the different pesticides. For this reason, “even if the problem of organochlorines were solved, the rest of the current pesticides could also cause problems, even if it was not one in particular, but rather the sum of all of them. And that is where the emphasis must be placed on the pesticides that are currently being applied.
The study has observed the effect in the booted eagle, but there were not enough data available to know if it is in other species such as the white stork. The correlation between pesticide levels and reproductive success has only been possible for booted eagles and black kites. "For the rest of the birds studied, we did not have reproductive success data, but we have also observed the presence of different pesticides in their eggs."
Another important point is to highlight the drought problem suffered by Doñana, since "not only the quantity of water that reaches the park matters, but also its quality".
The study was carried out in the context of an investigation to evaluate agricultural activities in the fauna of Doñana and, specifically, to analyze the impact of the pesticides used in the environment of this area.
Specifically, the presence of those pesticides that can accumulate in living organisms was analyzed. There are some pesticides that are found in the water, have a short life span and then degrade: and there are other more persistent pesticides, which can also be retained in the sediments, and which can enter the trophic chain of living beings; the study has focused on these.
