They are known as B-esterases, and are proteins that act as hydrolysis enzymes -they break larger molecules- and are present in sea turtle plasma.
Between 70,000 and 130,000 tons of microplastics (<5 mm fragments) and between 150,000 and 500,000 tons of macroplastics (the equivalent of 66,000 garbage trucks) end up in the Mediterranean and other European seas each year. Now, a new study by the Institut de Ciències del Mar (ICM-CSIC) in Barcelona and the Oceanogràfic Foundation in Valencia has found some proteins, B-esterases -that act as hydrolysis enzymes, i.e. to break down larger molecules - that are capable of estimating the exposure of sea turtles to plastic.
In 2019, the European Union, through the Marine Strategy Framework Directive, proposed the use of the loggerhead sea turtle (Caretta caretta) as a sentinel of environmental pollution in the Mediterranean. However, to date, the scientific community was unaware that these biomarkers, traditionally used to assess exposure to pesticides, could also inform on the exposure of these chelonians to chemical components of plastics.
"The results of our work, supported by fishermen and recovery centers, highlight the susceptibility of turtles to reflect exposure to certain plastic components and, in particular, to their chemical additives", explains Montserrat Solé, ICM-CSIC researcher and lead author of the study.
To carry out the work, recently published in the journal Science of the Total Environment, a total of 191 plasma samples of turtles from the ARCA del mar Recovery Center were analysed. They corresponded to wild individuals that were in the recovery phase after having been accidentally captured by fishermen.
"Collaboration between different institutions in the study of endangered wildlife not only makes it possible to restore these animals to health, but also offers a unique opportunity to carry out studies that can contribute significantly to the knowledge and conservation of the species," states Daniel García-Párraga, scientific director of the Oceanogràfic Foundation and director of the aquarium's Zoological Operations.
"An example of this," continues García-Párraga, "is this study between the ICM-CSIC and the Oceanogràfic of Valencia, which highlights the recovery centers' role in advancing knowledge of the marine environment and in preserving its biodiversity.
Finally, researchers found that the stress caused by the handling of turtles during capture does not alter the response of these biomarkers, which supports the use of these and other accidentally captured animals as sentinels of plastic pollution in the ocean. In fact, scientists have already started working with dolphins from the Oceanogràfic to apply the use of B-esterases as biomarkers in cetaceans.
Previous studies with turtles led by the ICM-CSIC in collaboration with the CRAM Foundation had already proposed the use of B-esterases as biomarkers of plastic exposure in loggerhead turtles. In this case, in vitro assays in the laboratory showed that these molecules are inhibited -that is, they stop working- by a wide variety of pollutants, including plastic additives such as flame retardants.
For future research, the team will complement, and support, the use of biomarkers with the plastic incidence in turtles’ excreta within the framework of the CAQUA project of the University of Montpellier. The final goal is to implement these measures to other marine species accidentally caught and export this low-cost methodology to other countries with fewer economic resources.