CSIC assesses the impact of agricultural pollutants in the Ebro Delta to preserve its biodiversity

The Institute of Environmental Assessment and Water Research (IDAEA-CSIC) in Barcelona evaluates pesticide and contaminant levels in species such as bats, flamingos and gulls

IDAEA-CSIC investigates contaminant levels in animals such as birds. | Sílvia Lacorte

Rice, together with maize and wheat, is one of the pillars of global food supply. In Spain alone, 338,000 tonnes of rice were produced in 2023, according to the latest data from the Yearbook of Statistics of the Ministry of Agriculture, Fisheries and Food. This crop, which covers 55,000 hectares (equivalent to a quarter of the province of Gipuzkoa), is an essential part of the economy in regions such as Tarragona. However, this agricultural activity must strike a difficult balance with the environmental realities of the territories where it takes place.

The work of the Institute of Environmental Assessment and Water Research (IDAEA-CSIC), a centre of the Spanish National Research Council (CSIC), seeks to ensure sustainability in rice production and to prevent chemical compounds used in agriculture from threatening the survival of protected ecosystems. For example, the Albufera de València receives up to 1.5 tonnes of pesticides every year from surrounding rice fields, while 24 different compounds have been detected in sediments from the Delta del Ebro.

Data collected by IDAEA-CSIC researchers show a sustained environmental impact over time. In 2010, they found high levels of industrial contaminants and pesticides in the Ebro Delta. Later, in 2017, they detected up to 35 different pesticides in the area, 17 of which were already banned and most of which were linked to rice cultivation. Their findings highlight the need to develop strategies to make production of this strategic cereal more sustainable without compromising the health of our natural spaces.

Bats to assess the impact of pesticides

To analyse the current state of the Delta, ecotoxicologist Ana López Antia leads an IDAEA-CSIC group investigating the possible effects of pesticides used by rice growers on the entire ecosystem.

“When a pesticide product is authorised in the European Union, it is assessed to ensure it has no negative effects on certain taxa, such as birds and aquatic organisms. The problem is that its overall impact on the ecosystem is not evaluated, only on those specific species, without taking into account the interactions between them. Moreover, pesticides are not used in isolation but applied together with others, so animals are exposed not to a single substance but to a mixture of products whose combined effect is not assessed,” explains López Antia.

Thanks to the European project Syberac, the group aims to address these blind spots by comprehensively investigating the risks posed by chemical products that accumulate and mix once released into the ecosystem. The project seeks to understand the flow of contaminants between terrestrial and aquatic environments and their effects on the ecosystem, using bats from the Ebro Delta and their trophic network as a model, while also considering implications for birds and invertebrates.

Syberac aims to improve how pesticide effects are assessed and predicted, in order to prevent situations similar to that of neonicotinoids: a family of insecticides harmful to beneficial insects that feed on nectar and pollen, including honey-producing bees. In 2018, the European Union banned the outdoor use of three neonicotinoids due to their damage to pollinating insects.

“Neonicotinoids became the most widely used insecticides worldwide for ten years,” explains López Antia.

IDAEA-CSIC is also working closely with rice growers to find a balance between productivity and conservation.

Although the European Union has guidelines for assessing pesticide risks in various crops, rice falls outside this framework because “it is a very different crop, grown under flooded conditions,” the expert explains. There is a major knowledge gap in how to assess pesticide risks in rice fields, particularly for birds and mammals. The same applies to bats. “Until now, shrews have been used as a reference model to study impacts on bats at European level, but these animals are completely different,” she notes.

Among these key differences are bats’ ability to fly and their distinct energy demands. Most bat species have only one offspring per year and are thought to absorb high doses of toxic substances through their wings, whose skin is extremely thin and highly vascularised.

“We study rice and bats because there is clearly a knowledge gap, and the project can help assess risks,” López Antia adds.

Flamingos, gulls and contaminants in the Ebro

One of the waterbird species nesting in the Ebro Delta is the colourful flamingo. In their natural refuge, these birds are exposed to toxic residues from human activities: intensive agriculture, industry and tourism. Research led by Maria Dulsat Masvidal and Sílvia Lacorte, from IDAEA-CSIC, found that flamingo chicks’ blood in the Ebro contained high levels of per- and polyfluoroalkyl substances (PFAS), a family of synthetic chemicals used in industry and consumer products, often referred to as “forever chemicals” due to their persistence in the environment.

These residues accumulate in organisms and biomagnify along food chains. Birds may be exposed to PFAS through their diet and can transfer these compounds to their offspring via eggs during laying.

“In flamingos from the Ebro Delta, PFOA levels are similar to those found in individuals living near an industrial chemical plant of a multinational company where these substances are produced,” Lacorte explains.

Her team is analysing PFAS present in pesticides to clarify the origin of the substances detected in chicks’ blood, which, due to their high concentration, cannot be explained solely by maternal transfer but likely by diet.

They also detected polycyclic aromatic hydrocarbons (PAHs) in birds’ blood: organic pollutants resulting from incomplete combustion of organic matter, potentially originating from agricultural vehicles or biomass burning. Traces of banned organochlorine insecticides such as DDT were also found, indicating historical rather than current exposure. However, no currently used pesticides were detected in birds’ blood, which may mean either that they are not exposed or that they eliminate them rapidly. “It is much more likely that they metabolise them quickly, but that does not mean they have no effects,” says Ana López, a researcher not involved in the study.

Gulls are another species analysed by IDAEA, as they are good indicators of habitat contamination levels because they are resident birds that lay eggs in the same area. Silvia Lacorte’s team has conducted annual monitoring of persistent organic pollutants under the Stockholm Convention in gull eggs since 2009. They analyse two species: the yellow-legged gull (Larus michahellis), which feeds from diverse sources including landfills, and Audouin’s gull (Larus audouinii), which feeds exclusively on fish. Results showed that Audouin’s gull eggs contained higher contaminant levels than those of yellow-legged gulls. High PFAS concentrations again stood out.

To assess PFAS contamination sources in gulls, local fishers were contacted and sardines and anchovies from the area were analysed. A model was developed to evaluate PFAS accumulation and maternal transfer from adult blood to eggs. Diet-based estimates matched levels found in eggs.

“Yellow-legged gulls have lower contaminant concentrations than fish-eating species, as landfill feeding represents a much more varied diet compared to a strictly piscivorous one,” Lacorte explains.

The source of PFAS detected in birds from the Ebro Delta remains unknown. IDAEA teams are analysing water, soils and sediments to determine their origin – a significant knowledge gap in this economically important natural area, which scientists are striving to fill in order to shed light on the multiple causes behind the decline of birds in Europe.

Content produced by Fermín Grodira within the CSIC–BBVA Foundation Science Communication Grants Programme, 2024 Call.